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Recurrent Hypoglycemia Increases Anxiety and Amygdala Norepinephrine Release During Subsequent Hypoglycemia

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Recurrent hypoglycemia (RH) is a common and debilitating side effect of therapy in patients with both type 1 and, increasingly, type 2 diabetes. Previous studies in rats have shown marked effects of RH on subsequent hippocampal behavioral, metabolic, and synaptic processes. In addition to impaired memory, patients experiencing RH report alterations in cognitive processes that include mood and anxiety, suggesting that RH may also affect amygdala function. We tested the impact of RH on amygdala function using an elevated plus-maze test of anxiety together with in vivo amygdala microdialysis for norepinephrine (NEp), a widely used marker of basolateral amygdala cognitive processes. In contrast to findings in the hippocampus and prefrontal cortex, neither RH nor acute hypoglycemia alone significantly affected plus-maze performance or NEp release. However, animals tested when hypoglycemic who had previously experienced RH had elevated amygdala NEp during plus-maze testing, accompanied by increased anxiety (i.e., less time spent in the open arms of the plus-maze). The results show that RH has widespread effects on subsequent brain function, which vary by neural system.
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ORIGINAL RESEARCH
published: 20 November 2015
doi: 10.3389/fendo.2015.00175
Edited by:
Subbiah Pugazhenthi,
Denver VA Medical Center, USA
Reviewed by:
Craig Beall,
University of Exeter, UK
Sampath Rangasamy,
TGen, USA
*Correspondence:
Ewan McNay
emcnay@albany.edu
Specialty section:
This article was submitted to
Diabetes, a section of the
journal Frontiers in Endocrinology
Received: 14 August 2015
Accepted: 02 November 2015
Published: 20 November 2015
Citation:
McNay E (2015) Recurrent
Hypoglycemia Increases Anxiety and
Amygdala Norepinephrine Release
During Subsequent Hypoglycemia.
Front. Endocrinol. 6:175.
doi: 10.3389/fendo.2015.00175
Recurrent Hypoglycemia Increases
Anxiety and Amygdala
Norepinephrine Release During
Subsequent Hypoglycemia
Ewan McNay
*
Behavioral Neuroscience, University at Albany (SUNY), Albany, NY, USA
Recurrent hypoglycemia (RH) is a common and debilitating side effect of therapy in
patients with both type 1 and, increasingly, type 2 diabetes. Previous studies in rats have
shown marked effects of RH on subsequent hippocampal behavioral, metabolic, and
synaptic processes. In addition to impaired memory, patients experiencing RH report
alterations in cognitive processes that include mood and anxiety, suggesting that RH
may also affect amygdala function. We tested the impact of RH on amygdala function
using an elevated plus-maze test of anxiety together with in vivo amygdala microdialysis
for norepinephrine (NEp), a widely used marker of basolateral amygdala cognitive pro-
cesses. In contrast to findings in the hippocampus and prefrontal cortex, neither RH nor
acute hypoglycemia alone significantly affected plus-maze performance or NEp release.
However, animals tested when hypoglycemic who had previously experienced RH had
elevated amygdala NEp during plus-maze testing, accompanied by increased anxiety
(i.e., less time spent in the open arms of the plus-maze). The results show that RH has
widespread effects on subsequent brain function, which vary by neural system.
Keywords: hypoglycemia, insulin, amygdala, anxiety, diabetes, norepinephrine, recurrent hypoglycemia
INTRODUCTION
The opening paragraph of a recent commentary (1) describes the significance of recurrent hypo-
glycemia (RH) vividly: “[RH] is the limiting factor in the glycemic management of diabetes. It causes
recurrent morbidity in most people with type 1 diabetes and many with advanced type 2 diabetes and
is sometimes fatal. It impairs defenses against subsequent hypoglycemia and, thus, causes a vicious
cycle of recurrent hypoglycemia. The barrier of hypoglycemia generally precludes maintenance of
euglycemia over a lifetime of diabetes.
Hypoglycemia is a common side effect of insulin therapy in both type 1 and type 2 diabetes
mellitus (T1 and T2DM). RH, and specifically the impact of RH on the brain (both in actuality
and in patients’ worry about such impact), is the biggest obstacle to optimal, intensive insulin
therapy aimed at tightly preventing hyperglycemia and restoring normal blood glucose (24). The
majority of work studying RH and the brain has been in the context of RH-induced hypoglycemia-
associated autonomic failure (HAAF): unawareness of and inability to respond to hypoglycemia that
can in extremes lead to coma and death, focusing on detection of glucose levels in the ventromedial
hypothalamus (VMH) (58). However, RH is also clinically associated with marked cognitive
and behavioral impairments such as mood swings, impaired judgment and mental flexibility,
Frontiers in Endocrinology | www.frontiersin.org November 2015 | Volume 6 | Article 1751
McNay Recurrent Hypoglycemia and Amygdala Function
memory loss, and debilitating anxiety (917), many of which are
likely to be associated with alterations in amygdala function. Cog-
nitive impairment is especially prevalent during subsequent hypo-
glycemia, which can have profound consequences: for instance,
car accidents are a leading cause of death among diabetic patients,
linked to impaired judgment during hypoglycemia (1013, 18).
Despite this, the neural and cognitive impact of RH has been
relatively little studied outside the VMH. Our recent review (19)
concluded that there is strong evidence that RH can alter cognitive
and neural function, but studies of RH in human beings have often
had difficulty in controlling for confounding disease states and/or
variable prior history of hypoglycemia (6, 15, 17, 20, 21). In three
previous reports that examined RH in rats, we have characterized
the impact of RH on subsequent hippocampal function including
spatial memory (22, 23) and on mental flexibility, mediated by
the prefrontal cortex (24). The rat model of RH used in those
studies accurately simulates the effects of RH and HAAF in human
beings (2228), and we have continued to use this model in the
present work. Here, we examined the impact of RH on amygdala
function. The amygdala plays a key role in anxiety and mood,
which are reported to be dysregulated after RH in human beings,
and previous studies have shown that similarly to the hippocam-
pus, cognitive processing in the amygdala is limited by glucose
metabolism (29, 30), suggesting that RH may alter subsequent
amygdala function.
A key finding from the studies of RH and hippocampal
function is that the impact of RH varies with acute glycemic
state: although hippocampal function is preserved and perhaps
enhanced when tested at euglycemia, marked impairment is seen
during a subsequent hypoglycemic episode (22, 23), matching
symptoms seen in humans. In contrast, mental flexibility and PFC
glucose metabolism were impaired after RH even when measured
at euglycemia, suggesting that the impact of RH may vary by brain
region. That hypothesis is supported by the findings reported here:
we show using an elevated plus-maze task that after RH, rats show
no change in anxiety or amygdala norepinephrine (NEp) release
when measured at euglycemia, but are significantly more anxious
during subsequent hypoglycemia, accompanied by elevated amyg-
dala NEp release. NEp release in the basolateral amygdala (BLA)
has been widely shown to be a marker for amygdala cognitive
modulation (3133).
MATERIALS AND METHODS
Experimental Timeline
All procedures were approved by the Institutional Animal Care
and Use Committee at the University at Albany. 36 male Sprague-
Dawley rats (Charles River, Wilmington, MA, USA) were pair
housed in enriched conditions (toys, plastic tubing, paper cups,
etc.) From 11 weeks of age, rats are handled daily for a minimum
of 10 min; this reduces stress hormone release at the time of testing
to baseline levels (22). At 13–14 weeks, animals underwent stereo-
tactic implantation of a microdialysis guide cannula (CMA12,
CMA/Microdialysis) into the left BLA, then 1 week of single-
housed recovery with close monitoring and continued handling.
At 14–15 weeks, animals were treated with either i.p. insulin or
i.p. saline once daily for 3 days, then tested on the fourth day,
humanely killed, and samples taken for analysis. At the start of
treatment, animals were randomly assigned to either control or
RH conditions; on the day of testing, animals were randomly
assigned to either hypoglycemic or euglycemic conditions. This
created four groups with between 8 and 10 animals in each group
in a 2 × 2 factorial design.
Surgical Procedures
Rats were anesthetized with 5% isoflurane. Standard sterile stereo-
taxic surgical procedures were used as described previously (34
36) to implant the microdialysis guide cannula, secured in place
with acrylic cement and two screws, and a dummy stylet was
inserted. Rats recovered in a heated chamber and returned to their
home cages once they had regained consciousness and full motor
control. Animal recovery was monitored for 3 days. Rimadyl once
daily was used for post-surgical analgesia. Correct cannula place-
ment was confirmed visually in all animals at the time of tissue
extraction by locating the tract path created by the cannula which
terminated in the BLA: all animals had correctly placed cannulae.
Microdialysis
As published (22, 30, 3740): a fresh probe was inserted, and
animals were acclimated for 2 h prior to testing. The dialysis
membrane was 1 mm. Rats moved freely, avoiding any confound
from restraint stress. Probes were perfused with an artificial
extracellular fluid [aECF; composition in millimolar: 153.5 Na,
4.3 K, 0.41 Mg, 0.71 Ca, 139.4 Cl, 1.25 glucose, buffered at pH 7.4
(40)] at 1.5 μL/min. Microdialysis samples were frozen for later
NEp analysis.
Hypoglycemia
Hypoglycemia was induced with 10 U/kg insulin (Humulin, Eli
Lilly) given i.p. to animals made hypoglycemic for the first time,
or either 8 or 6 U/kg (because of reduced counter-regulation) to
RH animals (22, 23, 41); control animals receive volume-matched
sterile saline.
RH Model
The model used here (3 h of moderate hypoglycemia on each of
three consecutive days, followed by testing on the fourth day)
has been validated as accurately recreating adaptation seen in
human patients with RH. Animals received i.p. insulin (Humulin,
Eli Lilly) at 10, 8, and 6 U/kg over the 3 days, with reduction in
doses compensating for reduced counterregulation due to HAAF.
This reliably produced 2–3 h between 40 and 50 mg/dL plasma
glucose; any animal not spontaneously recovering after 3 h was
returned to normoglycemia using i.p. glucose. Results from this
model closely track those obtained in a 16-month study using
once-weekly 3-h hypoglycemia (23), matching the experience of
human patients receiving insulin therapy (4245). In our previous
studies, data from T1DM and non-diabetic animals did not differ
(22), supporting RH studies in non-diabetic animals to avoid
confound from disease-state variables; these data were consistent
not only for behavior but also for hippocampal metabolism (22)
and synaptic electrophysiology (23). During hypoglycemia, ani-
mals were randomly sampled via thigh prick to confirm target
hypoglycemia.
Frontiers in Endocrinology | www.frontiersin.org November 2015 | Volume 6 | Article 1752
McNay Recurrent Hypoglycemia and Amygdala Function
Performance Variable Controls
In studies to date, RH in our model has not impaired or reduced
motor activity, visual acuity, or, e.g., motivation: for example, RH
animals make the same number of maze-arm choices (22, 23),
have the same latency to seek reward (24), and perceive both
visual and textural stimuli as well as or better than control animals
(24). We confirmed that RH had no measureable effects on motor
performance, motivation, or sensory acuity using small separate
cohorts of animals, treated identically to those reported here and
tested on a simple Y-maze alternation task.
Elevated Plus-Maze Testing
With microdialysis throughout, animals were placed into the
center of a four-arm plus-maze constructed from opaque black
plexiglas and allowed to explore freely for 10 min, then returned
to home cages. Two, opposing, arms of the four-arm maze had no
walls; the other two arms had 20 cm-high walls. Animals spend
the majority of time in a closed arm with periodic forays to
explore the open arms and/or cross the maze center. Increased
time spent in the open arms is taken as a measure of decreased
anxiety. Microdialysis is performed in the BLA, where this task is
mediated (4649).
Sample Analysis
Microdialysis samples were measured for NEp using HPLC on an
ESA Coulochem III.
Data Analysis
Data were analyzed in GraphPad Prism using a two-way ANOVA
design with RH (or control) and acute glycemic state as the two
factors. Where significant main effects were seen, post hoc group
comparisons using Tukey’s multiple comparisons test identified
specific inter-group differences.
RESULTS
Plus-Maze Performance
Both RH treatment and acute glycemic state had significant effects
on anxiety, as measured by time spent in the open arms during
plus-maze testing (both p < 0.001). As shown in Figure 1, post hoc
comparisons showed that animals in the RH-hypo group spent
significantly less time in the open arms than animals in all other
groups, indicating increased anxiety (all p < 0.001). No other
inter-group comparisons showed significant differences. Impor-
tantly, no effect of RH was seen on number of center-crossings,
supporting the conclusion from our performance control experi-
ments that this difference in open-arm time was not the result of
altered motor function or motivation in the RH-hypo group.
Amygdala Norepinephrine Release
Mean microdialysis sample NEp concentration during the plus-
maze testing is shown in Figure 2, reported as a percentage
of baseline NEp concentration (with baseline defined as the
mean of the three samples immediately prior to placement on
the plus-maze; absolute baseline NEp levels did not vary across
groups). Consistent with the behavioral data, significant effects
FIGURE 1 | Animals in the RH-hypo group spent significantly less time
in the open arms of the plus-maze, on average, than did animals in
other groups. * indicates significant difference vs all other groups, p < 0.001.
This is interpreted as increased anxiety in the RH-hypo animals. N = 8 for
control and hypo groups, and N = 10 for RH and RH-hypo groups.
FIGURE 2 | Animals in the RH-hypo group had significantly higher
levels of NEp in microdialysis samples from the basolateral amygdala
during elevated plus-maze testing, on average, than did animals in
other groups. * indicates significant difference vs all other groups, p < 0.05.
This is interpreted as increased anxiogenic processing in the amygdala of
animals in the RH-hypo group. N = 8 for control and hypo groups, and
N = 10 for RH and RH-hypo groups.
of both treatment and glycemic state were seen (both p < 0.05) in
which post hoc comparisons revealed to be due to a significantly
increased NEp concentration in samples from RH-hypo animals
compared to those in all other groups (all p < 0.05, no other
significant inter-group differences).
DISCUSSION
Our data are both consistent with, and extend, previous studies
that have examined the impact of RH on subsequent cognitive
and neural function: when tested during a hypoglycemic episode,
animals with prior RH treatment showed both heightened anx-
iety and increased amygdala activity, assessed by NEp levels in
the BLA.
Frontiers in Endocrinology | www.frontiersin.org November 2015 | Volume 6 | Article 1753
McNay Recurrent Hypoglycemia and Amygdala Function
Our previous work (2224, 50) suggested that neural adapta-
tions seen following RH might be maladaptive during subsequent
hypoglycemia. This is consistent with the clinical experience of
patients, where RH is associated with, e.g., increased risk of death
while driving. Patients also report symptoms, including alterations
in mood and anxiety, that are suggestive of altered emotional pro-
cessing subsequent to RH: the present data support these reports
and suggest that amygdala responsiveness to an aversive stimulus
such as exposure on an elevated, open platform may be increased
when hypoglycemic after RH. Because amygdala cognitive pro-
cessing causes increased local glucose metabolism (29), meeting
the metabolic requirements of such increased amygdala activation
might further diminish the brains ability to function optimally at
times of reduced glucose availability.
On the other hand, it is possible to speculate (based on the small
amount of data presented here) that increased anxiety, fear, or
similar emotional arousal might be at least somewhat adaptive in
that it could serve as a signal for danger at times of hypoglycemia,
alerting the patient to an acute need for fuel. One common effect of
RH is diminished release of stress hormones during hypoglycemia
[known as HAAF; (5, 51, 52)]: increased amygdala responsiveness
caused by RH could, perhaps, be a beneficial adaptation that
would oppose and attenuate reduced awareness of hypoglycemia.
Stress hormones including epinephrine and glucocorticoids are
key modulators of cognitive function, and especially of improved
performance at times of moderate stress (31, 5355), effects that
are transduced via the amygdala; it is hence possible that an
increase in amygdala responsiveness may be adaptive in acting
to positively modulate other brain regions [in particular, the
hippocampus; (5557)] even when systemic hormone release is
attenuated. Importantly, though, one study that examined amyg-
dala metabolism in humans, during hypoglycemia, found that in
contrast to the present findings fluorodeoxyglucose uptake was
better maintained in the amygdala of aware vs unaware patients
(58); this is in contrast to our data that suggest increased amygdala
activity in the RH animals which would be expected to correspond
to hypoglycemia-unaware patients. Although there are significant
methodological differences as well as a species difference between
the studies, this finding does constrain the ability to generalize
from the small dataset presented here. It is also true that stress-
related hormones, particularly epinephrine, are released when
hypoglycemic but such release diminishes after RH: thus, the
enhanced anxiety in the RH-hypo group observed here is some-
what paradoxical and the amygdalas response to stress hormones
under such conditions may repay further study.
The role of hypoglycemia-associated hormone release in alter-
ation of cognitive processes subsequent to RH merits further
attention. One of the best supported molecular causes of HAAF,
in the VMH, is hypoglycemia-associated GC release, and sev-
eral studies show that prevention of GC signaling in the VMH
during RH prevents HAAF (7, 5961). Similar causality may be
involved in the cognitive impact of RH: glucocorticoid receptors
(GRs) are expressed at high levels in the hippocampus (62, 63),
and GCs have been extensively shown to mediate hippocam-
pal damage from metabolic stressors (such as hypoglycemia):
specifically, GCs exacerbate damage from inadequate glucose sup-
ply (6466) and are linked to excitotoxic cell death following
severe hypoglycemia. Conversely, when fuel supply is adequate,
GCs enhance hippocampal memory and glutamate release (54,
55, 67): this pattern closely matches the impact of RH on hip-
pocampal function seen in our previous work (22, 23). We did
not measure GC levels either systemically or centrally during
these studies, but future work should consider including such
measurements.
Taken together with our previous studies, the findings here
indicate that RH affects multiple neural systems and brain struc-
tures, with the impact of RH varying by region and system. For
instance, during subsequent euglycemia, RH enhances hippocam-
pal memory (22, 23), impairs mental flexibility processes in the
prefrontal cortex (24), but does not affect performance in an
elevated plus-maze test of anxiety (present data). The ability of a
rodent model of RH to accurately mimic many of the cognitive
effects seen in human patients after RH suggests that this is an
appropriate system for further studies aimed at identifying the
molecular mechanisms transducing the cognitive, neural, and
metabolic impact of RH, with a goal of identifying appropriate
therapeutic approaches to prevention and intervention.
FUNDING
This work was supported by funding from the American Diabetes
Association (Award 7-12-BS-126).
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Conflict of Interest Statement: The author declares that the research was con-
ducted in the absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.
Copyright © 2015 McNay. This is an open-access article distributed under the terms
of the Creative Commons Attribution License (CC BY). The use, distribution or
reproduction in other forums is permitted, provided the original author(s) or licensor
are credited and that the original publication in this journal is cited, in accordance with
accepted academic practice. No use, distribution or reproduction is permitted which
does not comply with these terms.
Frontiers in Endocrinology | www.frontiersin.org November 2015 | Volume 6 | Article 1756
... Its administration in hyperglycemic mice reversed the depletion of dopamine and 5-HT levels in the hippocampus, frontal cortex, and striatum, and also diminished depressive behavior (Huang et al., 2016). The amygdala is associated with emotion, fear, motivation, and reward (Janak & Tye, 2015) and is implicated in diabetes-associated cognitive and mood disturbances (McNay, 2015). The amygdala of diabetic mice exhibited disturbed dopaminergic transmission and lesser expression of dopamine receptors . ...
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Evidence supports a strong bidirectional association between depression and Type 2 diabetes mellitus (T2DM). The harmful impact of oxidative stress and chronic inflammation on the development of both disorders is widely accepted. Nuclear factor erythroid 2-related factor 2 (NRF2) is a pertinent target in disease management owing to its reputation as the master regulator of antioxidant responses. NRF2 influences the expression of various cytoprotective phase 2 antioxidant genes, which is hampered in both depression and T2DM. Through interaction and crosstalk with several signaling pathways, NRF2 endeavors to contain the widespread oxidative damage and persistent inflammation involved in the pathophysiology of depression and T2DM. NRF2 promotes the neuroprotective and insulin-sensitizing properties of its upstream and downstream targets, thereby interrupting and preventing disease advancement. Standard antidepressant and antidiabetic drugs may be powerful against these disorders, but unfortunately, they come bearing distressing side effects. Therefore, exploiting the therapeutic potential of NRF2 activators presents an exciting opportunity to manage such bidirectional and comorbid conditions.
... Such episodes often lead to enhanced oxidative stress and neuronal death largely in brain regions associated with memory formation and storage, especially the hippocampus, amygdala [9], and sensory cortex [10] besides white matter [1] despite glucose normalization [11]. During hypoglycemic insults, the activation of hypothalamic-pituitary-adrenal (HPA) axis and sympathetic adrenomedullary pathway, both of which are involved in glucose counter-regulatory mechanisms [12], results in stress-related anxiety [13], intensifying the decline in executive functions like decision-making and working memory consolidation [14]. ...
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Neuronal regeneration is crucial for maintaining intact neural interactions for perpetuation of cognitive and emotional functioning. The NRG1-ErbB receptor signaling is a key pathway for regeneration in adult brain and also associated with learning and mood stabilization by modulating synaptic transmission. Extreme glycemic stress is known to affect NRG1-ErbB-mediated regeneration in brain; yet, it remains unclear how the ErbB receptor subtypes are differentially affected due to such metabolic variations. Here, we assessed the alterations in NRG1, ErbB receptor subtypes to study the regenerative potential, both in rodents as well as in neuronal and glial cell models of hyperglycemia and hypoglycemic insults during hyperglycemia. The pro-oxidant and anti-oxidant status leading to degenerative changes in brain regions were determined. The spatial memory and anxiogenic behaviour of experimental rodents were tested using ‘T’ maze and Elevated Plus Maze. Our data revealed that the extreme glycemic discrepancies during diabetes and recurrent hypoglycemia lead to altered expression of NRG1, ErbB receptor subtypes, Syntaxin1 and Olig1 that shows association with impaired regeneration, synaptic dysfunction, demyelination, cognitive deficits and anxiety.
... Its administration in hyperglycemic mice reversed the depletion of dopamine and 5-HT levels in the hippocampus, frontal cortex, and striatum, and also diminished depressive behavior (Huang et al., 2016). The amygdala is associated with emotion, fear, motivation, and reward (Janak & Tye, 2015) and is implicated in diabetes-associated cognitive and mood disturbances (McNay, 2015). The amygdala of diabetic mice exhibited disturbed dopaminergic transmission and lesser expression of dopamine receptors . ...
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Diabetes increases the likelihood of developing depression and vice versa. Research on this bidirectional association has somewhat managed to delineate the interplay among implicated physiological processes. Still, further exploration is required in this context. This review addresses the comorbidity by investigating suspected common pathophysiological mechanisms. One such factor is psychological stress which disturbs the hypothalamic-pituitary-adrenal axis causing hormonal imbalance. This includes elevated cortisol levels, a common biomarker of both depression and diabetes. Disrupted insulin signaling drives the hampered neurotransmission of serotonin, dopamine, and norepinephrine. Also, adipokine hormones such as adiponectin, leptin, and resistin, and the orexigenic hormone, ghrelin, are involved in both depression and T2DM. This disarray further interferes with physiological processes encompassing sleep, the gut-brain axis, metabolism, and mood stability. Behavioral coping mechanisms, such as unhealthy eating, mediate disturbed glucose homeostasis, and neuroinflammation. This is intricately linked to oxidative stress, redox imbalance, and mitochondrial dysfunction. However, interventions such as psychotherapy, physical exercise, fecal microbiota transplantation, and insulin-sensitizing agents can help to manage the distressing condition. The possibility of Glucagon-like peptide 1 possessing a therapeutic role has also been discussed. Nonetheless, there stands an urgent need for unraveling new correlating targets and biological markers for efficient treatment.
... Its administration in hyperglycemic mice reversed the depletion of dopamine and 5-HT levels in the hippocampus, frontal cortex, and striatum, and also diminished depressive behavior (Huang et al., 2016). The amygdala is associated with emotion, fear, motivation, and reward (Janak & Tye, 2015) and is implicated in diabetes-associated cognitive and mood disturbances (McNay, 2015). The amygdala of diabetic mice exhibited disturbed dopaminergic transmission and lesser expression of dopamine receptors . ...
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Diabetes increases the likelihood of developing depression and vice versa. Research on this bidirectional association has somewhat managed to delineate the interplay among implicated physiological processes. Still, further exploration is required in this context. This review addresses the comorbidity by investigating suspected common pathophysiological mechanisms. One such factor is psychological stress which disturbs the hypothalamic-pituitary-adrenal axis causing hormonal imbalance. This includes elevated cortisol levels, a common biomarker of both depression and diabetes. Disrupted insulin signaling drives the hampered neurotransmission of serotonin, dopamine, and norepinephrine. Also, adipokine hormones such as adiponectin, leptin, and resistin, and the orexigenic hormone, ghrelin, are involved in both depression and T2DM. This disarray further interferes with physiological processes encompassing sleep, the gut-brain axis, metabolism, and mood stability. Behavioral coping mechanisms, such as unhealthy eating, mediate disturbed glucose homeostasis, and neuroinflammation. This is intricately linked to oxidative stress, redox imbalance, and mitochondrial dysfunction. However, interventions such as psychotherapy, physical exercise, fecal microbiota transplantation, and insulin-sensitizing agents can help to manage the distressing condition. The possibility of Glucagon-like peptide 1 possessing a therapeutic role has also been discussed. Nonetheless, there stands an urgent need for unraveling new correlating targets and biological markers for efficient treatment.
... In fact, RH might lead to decline in intelligence quotient and persistent cognitive impairment in patients with diabetes (Sheen and Sheu, 2016). An animal study demonstrated that RH impaired spatial working memory during subsequent hypoglycemia and decreased mental flexibility in rats when euglycemic (McNay, 2015). Neurons are considered agents of cognitive function. ...
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The present study aimed to determine the relationship between astrocytes and recurrent non-severe hypoglycemia (RH)¹ -associated cognitive decline in diabetes. RH induced cognitive impairment and neuronal cell death in the cerebral cortex of diabetic mice, accompanied by excessive activation of astrocytes. Levels of the neurotrophins BDNF and GDNF, together with BDNF and GDNF- related signaling, were downregulated by RH. In vitro, recurrent low glucose (RLG)² impaired cell viability and induced apoptosis of high-glucose cultured astrocytes. Accumulating mitochondrial ROS and dysregulated mitochondrial functions, including abnormal morphology, decreased membrane potential, downregulated ATP levels, and disrupted bioenergetic status, were observed in these cells. SS-31 mediated protection of mitochondrial functions reversed RLG-induced cell viability defects and neurotrophin production. These findings demonstrate that RH induced astrocyte overactivation and mitochondrial dysfunction, leading to astrocyte-derived neurotrophin disturbance, which might contribute to diabetic cognitive decline. Targeting astrocyte mitochondria might represent a neuroprotective therapy for hypoglycemia-associated neurodegeneration in diabetes.
... 16,17 Reports also demonstrate increased anxiety in previously RH-exposed rats during acute hypoglycemia and decreased mental flexibility when euglycemic. 18 Furthermore, the hippocampal synaptic function was found to be markedly impaired in RH-exposed rats during further hypoglycemic conditions. 17 Human studies are controversial; difficulties in controlling for diabetic history and related disease processes have produced mixed results. ...
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Aims: Exposure to recurrent hypoglycemia (RH) is common in diabetic patients receiving glucose-lowering therapies and is implicated in causing cognitive impairments. Despite the significant effect of RH on hippocampal function, the underlying mechanisms are currently unknown. Our goal was to determine the effect of RH exposure on hippocampal metabolism in treated streptozotocin-diabetic rats. Methods: Hyperglycemia was corrected by insulin pellet implantation. Insulin-treated diabetic (ITD) rats were exposed to mild/moderate RH once a day for 5 consecutive days. Results: The effect of RH on hippocampal metabolism revealed 65 significantly altered metabolites in the RH group compared with controls. Several significant differences in metabolite levels belonging to major pathways (eg, Krebs cycle, gluconeogenesis, and amino acid metabolism) were discovered in RH-exposed ITD rats when compared to a control group. Key glycolytic enzymes including hexokinase, phosphofructokinase, and pyruvate kinase were affected by RH exposure. Conclusion: Our results demonstrate that the exposure to RH leads to metabolomics alterations in the hippocampus of insulin-treated streptozotocin-diabetic rats. Understanding how RH affects hippocampal metabolism may help attenuate the adverse effects of RH on hippocampal functions.
... The second scheme involved the measurement of BDNF and serotonin concentrations as the crucial factors in neural mechanisms [43]. T2DM has been reported to cause the functional impairment and reduced concentrations of these parameters [10,11], as well as amygdala damage [44]. One of the proposed mechanisms is that gut microbial dysbiosis can lead to such disorders [15]. ...
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Type 2 diabetes mellitus (T2DM) can lead to major complications such as psychiatric disorders which includes depressive and anxiety-like behaviors. The association of the gut–brain axis in the development of such disorders, especially in T2DM has been elucidated; however, gut dysbiosis is also reported in patients with T2DM. Hence, the regulation of the gut–brain axis, in particular, the gut–amygdala, as a vital region for the regulation of behavior is essential. Thirty-five male Wistar rats were divided into six groups. To induce T2DM, treatment groups received HF diet and 35 mg/kg STZ. Then, supplements of Lactobacillus Plantarum, inulin or their combination were administered to each group for 8 weeks. Finally, the rats were sacrificed for measurement of blood and tissue parameters after behavioral testing. The findings demonstrated the favorable effects of the psychobiotics (L. plantarum, inulin or their combination) on oxidative markers of the blood and amygdala (SOD, GPx, MDA and TAC), as well as on concentrations of amygdala serotonin and brain-derived neurotrophic factor (BDNF) in the diabetic rats. In addition, beneficial effects were observed on the elevated plus maze (EPM) and forced swimming tests (FST) with no change in locomotor activity of the rats. There was a strong correlation between the blood and amygdala oxidative markers, insulin and FBS with depressive and anxiety-like behaviors. Our results identified L. plantarum ATCC 8014 and inulin or their combination as novel psychobiotics that could have improving the systemic and nervous antioxidant status and improving amygdala performance and beneficial psychotropic effects.
... injection of Novolog (insulin aspart, Novo Nordisk, AIS, Denmark) [24]. Duration, frequency, and total number of hypoglycemia episodes were decided based on earlier studies [45,68,70,103]. Glucose levels were measured at baseline and every hour during hypoglycemia. Additional insulin or 50% dextrose solution was administered by s.c. ...
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Diabetes significantly increases the risk of stroke and post-stroke mortality. Recurrent hypoglycemia (RH) is common among diabetes patients owing to glucose-lowering therapies. Earlier, we showed that RH in a rat model of insulin-dependent diabetes exacerbates cerebral ischemic damage. Impaired mitochondrial function has been implicated as a central player in the development of cerebral ischemic damage. Hypoglycemia is also known to affect mitochondrial functioning. The present study tested the hypothesis that prior exposure of insulin-treated diabetic (ITD) rats to RH exacerbates brain damage via enhanced post-ischemic mitochondrial dysfunction. In a rat model of streptozotocin-induced diabetes, we evaluated post-ischemic mitochondrial function in RH-exposed ITD rats. Rats were exposed to five episodes of moderate hypoglycemia prior to the induction of cerebral ischemia. We also evaluated the impact of RH, both alone and in combination with cerebral ischemia, on cognitive function using the Barnes circular platform maze test. We observed that RH exposure to ITD rats leads to increased cerebral ischemic damage and decreased mitochondrial complex I activity. Exposure of ITD rats to RH impaired spatial learning and memory. Our results demonstrate that RH exposure to ITD rats potentially increases post-ischemic damage via enhanced post-ischemic mitochondrial dysfunction.
... The amygdala, as a seat of emotion processing and information relay, is a likely candidate for dysfunction in T2DM-associated CNS complications. Increasing evidence indicates the role of the amygdala in the CNS pathology of diabetes [15][16][17] . Additionally, dopamine (DA) is of high importance because it extensively innervates the brain, the sequel to which is a wide array of behavioral parameters like cognition, emotion, perception, motivation, reward, sleep, and so on (reviewed in [18] ). ...
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Objective: Diabetic neuropathy is a chronic and often disabling condition that affects a significant number of individuals with diabetes mellitus (DM). It is now established that DM causes various CNS complications like Alzheimer's, dementia, anxiety, depression, neurodegeneration, mood disorders, cognitive dysfunctioning, and so on. Since amygdala and dopaminergic circuitry are critical in controlling several aspects of social behavior, even social recognition memory (SRM), we aimed to study the expression analysis of dopaminergic circuitry in amygdala using real-time polymerase chain reaction. Material and methods: Animals were divided into 2 age- and weight-matched groups: group I-control group and group II-diabetic group. Diabetes was induced by injecting 50 mg/kg streptozotocin (STZ; in 0.1 mL ice cold citrate buffer, pH 4.5) i.p. for 5 consecutive days. Behavioral tests were performed 8 weeks after diabetes was introduced. On day 60, animals were sacrificed, amygdala was dissected, and the total RNA was isolated. Expression analysis was carried out using real time PCR. Results: No significant changes were observed in social interaction and social isolation aspects of diabetic mice, but SRM was significantly dysregulated. Additionally, we found that dopaminergic neurotransmission (dopaminergic receptor expression and expression of enzymes controlling dopamine turnover) was significantly downregulated in the amygdala of STZ mice as compared to controls. Conclusion: We hypothesize that the altered SRM could be due to the dysregulated dopaminergic circuitry in amygdala, although a detailed investigation is required to establish a causal relationship.
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Psychological trauma and obesity co-occur frequently and have been identified as major risk factors for psychiatric disorders. Surprisingly, preclinical studies examining how obesity disrupts the ability of the brain to cope with psychological trauma are lacking. The objective of this study was to determine whether an obesogenic Western-like high-fat diet (WD) predisposes rats to post-traumatic stress responsivity. Adolescent Lewis rats (postnatal day 28) were fed ad libitum for 8 weeks with either the experimental WD diet (41.4% kcal from fat) or the control diet (16.5% kcal from fat). We modeled psychological trauma by exposing young adult rats to a cat odor threat. The elevated plus maze and the open field test revealed increased psychological trauma-induced anxiety-like behaviors in the rats that consumed the WD when compared with control animals 1 week after undergoing traumatic stress (p < 0.05). Magnetic resonance imaging showed significant hippocampal atrophy (20% reduction) and lateral ventricular enlargement (50% increase) in the animals fed the WD when compared with controls. These volumetric abnormalities were associated with behavioral indices of anxiety, increased leptin and FK506-binding protein 51 (FKBP51) levels, and reduced hippocampal blood vessel density. We found asymmetric structural vulnerabilities to the WD, particularly the ventral and left hippocampus and lateral ventricle. This study highlights how WD consumption during adolescence impacts key substrates implicated in post-traumatic stress disorder. Understanding how consumption of a WD affects the developmental trajectories of the stress neurocircuitry is critical, as stress susceptibility imposes a marked vulnerability to neuropsychiatric disorders.
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Serotonin (5-HT) can either increase or decrease anxiety-like behaviour in animals, actions that depend upon neuroanatomical site of action and 5-HT receptor subtype. Although systemic studies with 5-HT(2) receptor agonists and antagonists suggest a facilitatory role for this receptor subtype in anxiety, somewhat inconsistent results have been obtained when such compounds have been directly applied to limbic targets such as the hippocampus and amygdala. The present study investigated the effects of the 5-HT(2B/2C) receptor agonist mCPP bilaterally microinjected into the dorsal hippocampus (DH: 0, 0.3, 1.0 or 3.0nmol/0.2microl), the ventral hippocampus (VH: 0, 0.3, 1.0 or 3.0nmol/0.2microl) or the amygdaloid complex (0, 0.15, 0.5, 1.0 or 3.0nmol/0.1microl) in mice exposed to the elevated plus-maze (EPM). Test sessions were videotaped and subsequently scored for conventional indices of anxiety (percentage of open arm entries and percentage of open arm time) and locomotor activity (closed arm entries). Results showed that mCPP microinfusions into the DH or VH failed to affect any behavioural measure in the EPM. However, when injected into the amygdaloid complex, the dose of 1.0nmol of this 5HT(2B/2C) receptor agonist increased behavioural indices of anxiety without significantly altering general activity levels. This anxiogenic-like effect of mCPP was selectively and completely blocked by local injection of a behaviourally-inactive dose of SDZ SER-082 (10nmol/0.1microl), a preferential 5-HT(2C) receptor antagonist. These data suggest that 5HT(2C) receptors located within the amygdaloid complex (but not the dorsal or ventral hippocampus) play a facilitatory role in plus-maze anxiety in mice.
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Serotonin (5-HT) can either increase or decrease anxiety-like behaviour in animals, actions that depend upon neuroanatomical site of action and 5-HT receptor subtype. Although systemic studies with 5-HT 2 receptor agonists and antagonists suggest a facilitatory role for this receptor subtype in anxiety, somewhat inconsistent results have been obtained when such compounds have been directly applied to limbic targets such as the hippocampus and amygdala. The present study investigated the effects of the 5-HT 2B/2C receptor agonist mCPP bilaterally microinjected into the dorsal hippocampus (DH: 0, 0.3, 1.0 or 3.0 nmol/0.2 l), the ventral hippocampus (VH: 0, 0.3, 1.0 or 3.0 nmol/0.2 l) or the amygdaloid complex (0, 0.15, 0.5, 1.0 or 3.0 nmol/0.1 l) in mice exposed to the elevated plus-maze (EPM). Test sessions were videotaped and subsequently scored for conventional indices of anxiety (percentage of open arm entries and percentage of open arm time) and locomotor activity (closed arm entries). Results showed that mCPP microinfusions into the DH or VH failed to affect any behavioural measure in the EPM. However, when injected into the amygdaloid complex, the dose of 1.0 nmol of this 5HT 2B/2C receptor agonist increased behavioural indices of anxiety without significantly altering general activity levels. This anxiogenic-like effect of mCPP was selectively and completely blocked by local injection of a behaviourally-inactive dose of SDZ SER-082 (10 nmol/0.1 l), a preferential 5-HT 2C receptor antagonist. These data suggest that 5HT 2C receptors located within the amygdaloid complex (but not the dorsal or ventral hippocampus) play a facilitatory role in plus-maze anxiety in mice.
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Hypoglycemia is the limiting factor in the glycemic management of diabetes. The concept of hypoglycemia-associated autonomic failure (HAAF) in diabetes posits that recent antecedent iatrogenic hypoglycemia causes both defective glucose counterregulation (by reducing the epinephrine response to falling glucose levels in the setting of an absent glucagon response) and hypoglycemia unawareness (by reducing the autonomic and the resulting neurogenic symptom responses) and thus a vicious cycle of recurrent hypoglycemia. Perhaps the most compelling support for HAAF is the finding that as little as 2-3 wk of scrupulous avoidance of hypoglycemia reverses hypoglycemia unawareness and improves the reduced epinephrine component of defective glucose counterregulation in most affected individuals. Insight into this pathophysiology has led to a broader view of the clinical risk factors for hypoglycemia to include indexes of compromised glucose counterregulation and provided a framework for the study of the mechanisms of iatrogenic hypoglycemia and, ultimately, its elimination from the lives of people with diabetes.
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Purpose: The present study describes the epidemiology of severe hypoglycemia and identifies patient characteristics or behaviors associated with severe hypoglycemia in patients with insulin-dependent diabetes mellitus (IDDM) participating in the Diabetes Control and Complications Trial (DCCT). Patients and methods: The DCCT is a multicenter randomized clinical trial designed to compare the benefits and risks of intensive therapy with those of conventional management of IDDM. The DCCT's feasibility phase demonstrated that intensive therapy, with the aim of achieving glucose levels as close to the non-diabetic range as possible, was accompanied by a threefold increase in severe hypoglycemia compared with conventional therapy. This report is based on the first 817 subjects who entered the DCCT, with a mean follow-up of 21 months. Results: Two hundred sixteen subjects reported 714 episodes of severe hypoglycemia; 549 (77%) occurred in intensively treated subjects. The incidence of severe hypoglycemia in the intensive treatment group ranged from two to six times that observed with conventional treatment. Severe hypoglycemia occurred more often during sleep (55%); 43% of all episodes occurred between midnight and 8 AM. Of episodes that occurred while subjects were awake, 36% were not accompanied by warning symptoms. In intensively treated subjects, predictors of severe hypoglycemia included history of severe hypoglycemia, longer duration of IDDM, higher baseline glycosylated hemoglobin (HbA1c) levels, and a lower recent HbA1c. Multivariate analyses failed to yield predictive models with high sensitivity. Conclusions: In the DCCT, intensive treatment of IDDM increased the frequency of severe hypoglycemia relative to conventional therapy. Intensive treatment may cause even more frequent severe hypoglycemia when applied to less selected and less motivated populations in the clinical practice setting. These findings underscore the importance of determining the benefit-risk ratio of intensive and standard therapy of IDDM.
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Context Laboratory studies have shown impairments in driving performance among subjects with type 1 diabetes mellitus when their blood glucose (BG) level is between 2.6 and 3.6 mmol/L (47-65 mg/dL). However, to our knowledge, no data exist examining subjects' decisions to drive at various BG levels during their daily routine.Objective To examine type 1 diabetic subjects' decisions to drive during their daily routine based on perception of BG levels compared with actual measured BG levels.Design and Setting Two separate groups of patients were recruited 2 years apart from 4 academic medical centers.Participants All subjects were adults with type 1 diabetes who were drivers and who performed at least 2 BG tests per day. Group 1 (initial) subjects (n=65) had a mean (SD) age of 38.6 (8.9) years with a mean (SD) diabetes duration of 20.5 (10.6) years, were taking 38.8 (16.8) U/d of insulin, and had a mean (SD) glycosylated hemoglobin (HbA1) level of 10.0% (1.9%). Group 2 (replication) subjects (n=93) were 35.8 (8.0) years old with a mean diabetes duration of 17.0 (10.6) years, were taking 40.0 (15.5) U/d of insulin, and had a mean (SD) HbA1 level of 8.5% (1.6%). Each subject used a handheld computer to record data on symptoms, cognitive function, insulin dosage, food, activity, estimated and actual BG levels, and whether he/she would drive. Data were entered 3 to 6 times per day for a total of 50 to 70 collections per subject during a 3- to 4-week period.Main Outcome Measures Decisions to drive when subjects estimated their BG level to be less than 2.2 mmol/L (40 mg/dL), 2.2 to 2.8 mmol/L (40-50 mg/dL), 2.8 to 3.3 mmol/L (50-60 mg/dL), 3.3 to 3.9 mmol/L (60-70 mg/dL), 3.9 to 10 mmol/L (70-180 mg/dL), and more than 10 mmol/L (>180 mg/dL), and driving decisions when actual BG levels were in these ranges.Results Subjects stated they would drive 43% to 44% of the time when they estimated their BG level to be 3.3 to 3.9 mmol/L (60-70 mg/dL), and 38% to 47% of the time when their actual BG level was less than 2.2 mmol/L (40 mg/dL). Logistic regression analysis demonstrated that number of autonomic symptoms, degree of impairment on cognitive function tests, and BG level estimate predicted 76% to 80% of decisions to drive (P<.01 for all). Approximately 50% of subjects in each group decided to drive at least 50% of the time when their BG level was less than 3.9 mmol/L (70 mg/dL).Conclusions Our data suggest that persons with type 1 diabetes may not judge correctly when their BG level is too low to permit safe driving and may consider driving with a low BG level even when they are aware of the low level. Health care professionals should counsel their patients about the risk of driving with hypoglycemia and the importance of measuring BG level before driving.
Article
The Diabetes Control and Complications Trial has demonstrated that intensive diabetes treatment delays the onset and slows the progression of diabetic complications in subjects with insulin-dependent diabetes mellitus from 13 to 39 years of age. We examined whether the effects of such treatment also occurred in the subset of young diabetic subjects (13 to 17 years of age at entry) in the Diabetes Control and Complications Trial. One hundred twenty-five adolescent subjects with insulin-dependent diabetes mellitus but with no retinopathy at baseline (primary prevention cohort) and 70 adolescent subjects with mild retinopathy (secondary intervention cohort) were randomly assigned to receive either (1) intensive therapy with an external insulin pump or at least three daily insulin injections, together with frequent daily blood-glucose monitoring, or (2) conventional therapy with one or two daily insulin injections and once-daily monitoring. Subjects were followed for a mean of 7.4 years (4 to 9 years). In the primary prevention cohort, intensive therapy decreased the risk of having retinopathy by 53% (95% confidence interval: 1% to 78%; p = 0.048) in comparison with conventional therapy. In the secondary intervention cohort, intensive therapy decreased the risk of retinopathy progression by 70% (95% confidence interval: 25% to 88%; p = 0.010) and the occurrence of microalbuminuria by 55% (95% confidence interval: 3% to 79%; p = 0.042). Motor and sensory nerve conduction velocities were faster in intensively treated subjects. The major adverse event with intensive therapy was a nearly threefold increase of severe hypoglycemia. We conclude that intensive therapy effectively delays the onset and slows the progression of diabetic retinopathy and nephropathy when initiated in adolescent subjects; the benefits outweigh the increased risk of hypoglycemia that accompanies such treatment. (J PEDIATR 1994;125:177-88)
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