[Show abstract][Hide abstract] ABSTRACT: Functionally heterogeneous populations of serotonergic neurons, located within the dorsal raphe nucleus (DR), play a role in stress-related behaviors and neuropsychiatric illnesses such as anxiety and depression. Abnormal development of these neurons may permanently alter their structure and connections, making the organism more susceptible to anxiety-related disorders. A factor that critically regulates the development of serotonergic neurons is fibroblast growth factor 8 (Fgf8). In this study, we used acute restraint stress followed by behavioral testing to examine whether Fgf8 signaling during development is important for establishing functional stress- and anxiety-related DR neurocircuits in adulthood. Wild-type and heterozygous male mice globally hypomorphic for Fgf8 were exposed to acute restraint stress and then tested for anxiety-like behavior on the elevated plus-maze. Further, we measured c-Fos immunostaining as a marker of serotonergic neuronal activation and tissue 5-hydroxyindoleacetic acid concentrations as a marker of serotonin functional output. Results showed that Fgf8 hypomorphs exhibited 1) an exaggerated response of DR anxiety-promoting circuits and 2) a blunted response of a DR panic-inhibiting circuit to stress, effects that together were associated with increased baseline anxiety-like behavior. Overall, our results provide a neural substrate upon which Fgf8 deficiency could affect stress response and support the hypothesis that developmental disruptions of serotonergic neurons affect their postnatal functional integrity.
[Show abstract][Hide abstract] ABSTRACT: Serotonergic neurons in the dorsal raphe nucleus (DR) are organized in anatomically distinct subregions that form connections with specific brain structures to modulate diverse behaviors, including anxiety-like behavior. It is unclear if the functional heterogeneity of these neurons is coupled to their developmental heterogeneity, and if abnormal development of specific DR serotonergic subregions can permanently impact anxiety circuits and behavior. The goal of this study was to examine if deficiencies in different components of fibroblast growth factor (Fgf) signaling could preferentially impact the development of specific populations of DR serotonergic neurons to alter anxiety-like behavior in adulthood. Wild-type and heterozygous male mice globally hypomorphic for Fgf8, Fgfr1, or both (Fgfr1/Fgf8) were tested in an anxiety-related behavioral battery. Both Fgf8- and Fgfr1/Fgf8-deficient mice display increased anxiety-like behavior as measured in the elevated plus-maze and the open-field tests. Immunohistochemical staining of a serotonergic marker, tryptophan hydroxylase (Tph), revealed reductions in specific populations of serotonergic neurons in the ventral, interfascicular, and ventrolateral/ventrolateral periaqueductal gray subregions of the DR in all Fgf-deficient mice, suggesting a neuroanatomical basis for increased anxiety-like behavior. Overall, this study suggests Fgf signaling selectively modulates the development of different serotonergic neuron subpopulations. Further, it suggests anxiety-like behavior may stem from developmental disruption of these neurons, and individuals with inactivating mutations in Fgf signaling genes may be predisposed to anxiety disorders.
Full-text · Article · Feb 2014 · Behavioural brain research
[Show abstract][Hide abstract] ABSTRACT: In order to further understand the genetic basis for variation in inherent (untrained) exercise capacity, we examined the brains of 32 male rats selectively bred for high or low running capacity (HCR and LCR, respectively). The aim was to characterize the activation patterns of brain regions potentially involved in differences in inherent running capacity between HCR and LCR. Using quantitative in situ hybridization techniques, we measured messenger ribonuclease (mRNA) levels of c-Fos, a marker of neuronal activation, in the brains of HCR and LCR rats after a single bout of acute treadmill running (7.5-15 minutes, 15° slope, 10 m/min) or after treadmill running to exhaustion (15-51 minutes, 15° slope, initial velocity 10 m/min). During verification of trait differences, HCR rats ran six times farther and three times longer prior to exhaustion than LCR rats. Running to exhaustion significantly increased c-Fos mRNA activation of several brain areas in HCR, but LCR failed to show significant elevations of c-Fos mRNA at exhaustion in the majority of areas examined compared to acutely run controls. Results from these studies suggest that there are differences in central c-Fos mRNA expression, and potential brain activation patterns, between HCR and LCR rats during treadmill running to exhaustion and these differences could be involved in the variation in inherent running capacity between lines.
[Show abstract][Hide abstract] ABSTRACT: Background
Fibroblast growth factors (FGFs) and their receptors (FGFRs) are necessary for the proper development of gonadotropin-releasing hormone (GnRH) neurons, which are key activators of the hypothalamo-pituitary-gonadal axis. Transgenic mice that have the targeted expression of a dominant negative FGFR (dnFGFR) in GnRH neurons (dnFGFR mice) have a 30% decrease of GnRH neurons. Additionally, only 30–40% of the pups born to the transgenic dams survive to weaning age. These data raised the possibility that FGFR defects in GnRH neurons could adversely affect maternal behavior via novel mechanisms.
We first determined if defective maternal behavior in dnFGFR mothers may contribute to poor pup survival by measuring pup retrieval and a battery of maternal behaviors in primiparous control (n = 10–12) and dnFGFR (n = 13–14) mothers. Other endocrine correlates of maternal behaviors, including plasma estradiol levels and hypothalamic pro-oxyphysin and GnRH transcript levels were also determined using enzyme-linked immunoassay and quantitative reverse transcription polymerase chain reaction, respectively.
Maternal behaviors (% time crouching with pups, time off pups but not feeding, time feeding, and total number of nesting bouts) were not significantly different in dnFGFR mice. However, dnFGFR dams were more likely to leave their pups scattered and took significantly longer to retrieve each pup compared to control dams. Further, dnFGFR mothers had significantly lower GnRH transcripts and circulating E2, but normal pro-oxyphysin transcript levels.
Overall, this study suggests a complex scenario in which a GnRH system compromised by reduced FGF signaling leads to not only suboptimal reproductive physiology, but also suboptimal maternal behavior.
[Show abstract][Hide abstract] ABSTRACT: Fibroblast growth factor (FGF) signaling is essential for the development of the gonadotropin-releasing hormone (GnRH) system. Mice harboring deficiencies in Fgf8 or Fgf receptor 1 (Fgfr1) suffer a significant loss of GnRH neurons, but their reproductive phenotypes have not been examined. This study examined if female mice hypomorphic for Fgf8, Fgfr1, or both (compound hypomorphs) exhibited altered parameters of pubertal onset, estrous cyclicity, and fertility. Further, we examined the number of kisspeptin (KP)-immunoreactive (ir) neurons in the anteroventral periventricular/periventricular nuclei (AVPV/PeV) of these mice to assess if changes in the KP system, which stimulates the GnRH system, could contribute to the reproductive phenotypes. Single hypomorphs (Fgfr1(+/-) or Fgf8(+/-)) had normal timing for vaginal opening (VO) but delayed first estrus. However, after achieving the first estrus, they underwent normal expression of estrous cycles. In contrast, the compound hypomorphs underwent early VO and normal first estrus, but had disorganized estrous cycles that subsequently reduced their fertility. KP immunohistochemistry on Postnatal Day 15, 30, and 60 transgenic female mice revealed that female compound hypomorphs had significantly more KP-ir neurons in the AVPV/PeV compared to their wild-type littermates, suggesting increased KP-ir neurons may drive early VO but could not maintain the cyclic changes in GnRH neuronal activity required for female fertility. Overall, these data suggest that Fgf signaling deficiencies differentially alter the parameters of female pubertal onset and cyclicity. Further, these deficiencies led to changes in the AVPV/PeV KP-ir neurons that may have contributed to the accelerated VO in the compound hypomorphs.
Full-text · Article · Jan 2012 · Biology of Reproduction
[Show abstract][Hide abstract] ABSTRACT: Fibroblast growth factor (FGF) signaling is pivotal to the formation of numerous central regions. Increasing evidence suggests FGF signaling also directs the development of the neuroendocrine hypothalamus, a collection of neuroendocrine neurons originating primarily within the nose and the ventricular zone of the diencephalon. This review outlines evidence for a role of FGF signaling in the prenatal and postnatal development of several hypothalamic neuroendocrine systems. The emphasis is placed on the nasally derived gonadotropin-releasing hormone neurons, which depend on neurotrophic cues from FGF signaling throughout the neurons' lifetime. Although less is known about neuroendocrine neurons derived from the diencephalon, recent studies suggest they also exhibit variable levels of dependence on FGF signaling. Overall, FGF signaling provides a broad spectrum of cues that ranges from genesis, cell survival/death, migration, morphological changes, to hormone synthesis in the neuroendocrine hypothalamus. Abnormal FGF signaling will deleteriously impact multiple hypothalamic neuroendocrine systems, resulting in the disruption of diverse physiological functions.
Full-text · Article · Jan 2011 · Frontiers in Neuroendocrinology
[Show abstract][Hide abstract] ABSTRACT: Oxytocin (OT) is a nonapeptide essential for maternal care. The development of the OT neuroendocrine system is a multi-step process dependent on the action of many transcription factors, but upstream signaling molecules regulating this process are still poorly understood. In this study, we examined if fibroblast growth factor 8 (FGF8), a signaling molecule critical for forebrain development, is essential for the proper formation of the OT system. Using immunohistochemistry, we showed a significant reduction in the number of neurons immunoreactive for the mature OT peptide in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) in the hypothalamus of homozygous (HOMO) FGF8 hypomorphic mice compared to wild-type mice. The number of neurons positive for oxyphysin prohormone in the SON but not the PVN was also significantly reduced in FGF8 HOMO hypomorphs. However, steady-state mRNA levels of the oxyphysin prohormone were not significantly different between FGF8 hypomorphs and WT mice. These data suggest that a global reduction in FGF8 signaling leads to an overall reduction of mature OT and oxyphysin prohormone levels that may have resulted from defects in multiple stages of the hormone-synthesis pathway. Since proper hormone synthesis is a hallmark of mature OT neurons, this study suggests that FGF8 signaling may contribute to the phenotypic maturation of a neuroendocrine system that originates within the diencephalon.
[Show abstract][Hide abstract] ABSTRACT: Although selective 5-HT reuptake inhibitors (SSRIs) can reduce anxiety after chronic treatment, acute SSRI administration is associated with an increase in anxiety consistent with an acute increase in 5-HT neurotransmission. Exercise is anxiolytic in humans, and wheel running prevents anxiety-like behavioral consequences of uncontrollable stress in rats, but the effects of exercise on acute fluoxetine-induced anxiety-like behaviors are unknown.
The current studies tested the hypothesis that acute administration of the SSRI fluoxetine would produce behaviors in rats resembling those produced by uncontrollable stress and that these behaviors would be blocked by prior wheel running.
Adult, male Fisher 344 rats administered moderate (10 mg/kg) or high (20 mg/kg) doses of fluoxetine demonstrated exaggerated shock-elicited freezing and an interference with shuttle box escape compared to rats given either saline or low-dose fluoxetine (2.5 mg/kg). Fluoxetine-induced behaviors were similar to, but smaller in magnitude than, those produced by uncontrollable stress and were blocked by pretreatment with the 5-HT(2C) receptor antagonist SB 242084 (1 mg/kg). Rats allowed access to running wheels for 6 weeks were protected against the anxiety-like behaviors produced by a single injection of fluoxetine (10 mg/kg).
Behavioral effects of acute fluoxetine administration resemble those produced by uncontrollable stress. Results are consistent with the idea that exercise can produce resistance against the anxiogenic effects of acute increases in 5-HT and suggest that acute behavioral effects of antidepressants can depend on history of physical activity.
No preview · Article · Sep 2008 · Psychopharmacology
[Show abstract][Hide abstract] ABSTRACT: Altered serotonergic (5-HT) neurotransmission is implicated in the antidepressant and anxiolytic properties of physical activity. In the current study, we investigated whether physical activity alters factors involved in the regulation of central 5-HT neural activity.
In situ hybridization was used to quantify levels of 5-HT transporter (5-HTT), 5-HT(1A), 5-HT(1B), and alpha(1b)-adrenergic receptor (alpha(1b) ADR) messenger ribonucleic acids (mRNAs) in the dorsal (DRN) and median raphe (MR) nuclei of male Fischer rats after either sedentary housing or 3 days, 3 weeks, or 6 weeks of wheel running.
Wheel running produced a rapid and lasting reduction of 5-HT(1B) mRNA in the ventral DRN. Three weeks of wheel running decreased 5-HTT mRNA in the DRN and MR and increased alpha(1b) ADR mRNA in the DRN. After 6 weeks of wheel running, 5-HTT mRNA remained reduced, but alpha(1b) ADR mRNA returned to sedentary levels. Serotonin(1A) mRNA was increased in the MR and certain DRN subregions after 6 weeks only.
Data suggest that the central 5-HT system is sensitive to wheel running in a time-dependent manner. The observed changes in mRNA regulation in a subset of raphe nuclei might contribute to the stress resistance produced by wheel running and the antidepressant and anxiolytic effects of physical activity.