[Show abstract][Hide abstract] ABSTRACT: 5-HT1A receptors are widely expressed in the brain and play a critical role in feedback inhibition of serotonin (5-HT) neurons through multiple mechanisms. Yet, it remains poorly understood how these feedback mechanisms, particularly those involving long-range projections, adapt in mood disorders. Here, we examined several aspects of 5-HT1A receptor function in the 5-HT transporter knockout mouse (SERT-KO), a model of vulnerability to stress and mood disorders. We found that in comparison to wild-type (WT) mice, SERT-KO mice had more passive coping in response to acute swim stress and this was accompanied by hypo-activation of medial prefrontal cortex (mPFC) Fos expression. Both of these effects were reversed by systemically blocking 5-HT1A receptors. Ex-vivo electrophysiological experiments showed that 5-HT exerted greater 5-HT1A-mediated inhibitory effects in the mPFC of SERT-KO mice compared to WT. Since 5-HT1A receptors in the mPFC provide a key feedback regulation of the dorsal raphe nucleus (DRN), we used a disinhibition strategy to examined endogenous feedback control of 5-HT neurons. Blocking 5-HT1A receptors disinhibited several fold more 5-HT neurons in the DRN of SERT-KO than in WT mice, revealing the presence of enhanced feedback inhibition of 5-HT neurons in the SERT-KO. Taken together our results indicate that increased stress sensitivity in the SERT-KO is associated with the enhanced capacity of 5-HT1A receptors to inhibit neurons in the mPFC as well as to exert feedback inhibition of DRN 5-HT neurons.
[Show abstract][Hide abstract] ABSTRACT: Early-life serotonin [5-hydroxytryptamine (5-HT)] signaling modulates brain development, which impacts adult behavior, but 5-HT-sensitive periods, neural substrates, and behavioral consequences remain poorly understood. Here we identify the period ranging from postnatal day 2 (P2) to P11 as 5-HT sensitive, with 5-HT transporter (5-HTT) blockade increasing anxiety- and depression-like behavior, and impairing fear extinction learning and memory in adult mice. Concomitantly, P2-P11 5-HTT blockade causes dendritic hypotrophy and reduced excitability of infralimbic (IL) cortex pyramidal neurons that normally promote fear extinction. By contrast, the neighboring prelimbic (PL) pyramidal neurons, which normally inhibit fear extinction, become more excitable. Excitotoxic IL but not PL lesions in adult control mice reproduce the anxiety-related phenotypes. These findings suggest that increased 5-HT signaling during P2-P11 alters adult mPFC function to increase anxiety and impair fear extinction, and imply a differential role for IL and PL neurons in regulating affective behaviors. Together, our results support a developmental mechanism for the etiology and pathophysiology of affective disorders and fear-related behaviors.
Journal of Neuroscience 09/2014; 34(37):12379-93. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cholinergic stimulation of the cerebral cortex is essential for tasks requiring attention; however, there is still some debate over which cortical regions are required for such tasks. There is extensive cholinergic innervation of both primary and associative cortices, and transient release of acetylcholine (ACh) is detected in deep layers of the relevant primary and/or associative cortex, depending on the nature of the attention task. Here, we investigated the electrophysiological effects of ACh in layer VI, the deepest layer, of the primary somatosensory cortex, the primary motor cortex, and the associative medial prefrontal cortex. Layer VI pyramidal neurons are a major source of top-down modulation of attention, and we found that the strength and homogeneity of their direct cholinergic excitation was region-specific. On average, neurons in the primary cortical regions showed weaker responses to ACh, mediated by a balance of contributions from both nicotinic and muscarinic ACh receptors. Conversely, neurons in the associative medial prefrontal cortex showed significantly stronger excitation by ACh, mediated predominantly by nicotinic receptors. The greatest diversity of responses to ACh was found in the primary somatosensory cortex, with only a subset of neurons showing nicotinic excitation. In a mouse model with attention deficits only under demanding conditions, cholinergic excitation was preserved in primary cortical regions but not in the associative medial prefrontal cortex. These findings demonstrate that the effect of ACh is not uniform throughout the cortex, and suggest that its ability to enhance attention performance may involve different cellular mechanisms across cortical regions.
European Journal of Neuroscience 05/2014; · 3.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The activity of the prefrontal cortex is essential for normal emotional processing and is strongly modulated by serotonin (5-HT). Yet, little is known about the regulatory mechanisms that control the activity of the prefrontal 5-HT receptors. Here, we found and characterized a deregulation of prefrontal 5-HT receptor electrophysiological signaling in mouse models of disrupted serotonin transporter (5-HTT) function, a risk factor for emotional and cognitive disturbances. We identified a novel tyrosine kinase-dependent mechanism that regulates 5-HT-mediated inhibition of prefrontal pyramidal neurons. We report that mice with compromised 5-HTT, resulting from either genetic deletion or brief treatment with selective serotonin reuptake inhibitors during development, have amplified 5-HT1A receptor-mediated currents in adulthood. These greater inhibitory effects of 5-HT are accompanied by enhanced downstream coupling to Kir3 channels. Notably, in normal wild-type mice, we found that these larger 5-HT1A responses can be mimicked through inhibition of Src family tyrosine kinases. By comparison, in our 5-HTT mouse models, the larger 5-HT1A responses were rapidly reduced through inhibition of tyrosine phosphatases. Our findings implicate tyrosine phosphorylation in regulating the electrophysiological effects of prefrontal 5-HT1A receptors with implications for neuropsychiatric diseases associated with emotional dysfunction, such as anxiety and depressive disorders.
Journal of Neuroscience 04/2014; 34(17):6107-11. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The experience of early stress contributes to the etiology of several psychiatric disorders and can lead to lasting deficits in working memory and attention. These executive functions require activation of the prefrontal cortex (PFC) by muscarinic M1 acetylcholine (ACh) receptors. Such Gαq-protein coupled receptors trigger the release of calcium (Ca(2+)) from internal stores and elicit prolonged neuronal excitation.
In brain slices of rat PFC, we employed multiphoton imaging simultaneously with whole-cell electrophysiological recordings to examine potential interactions between ACh-induced Ca(2+) release and excitatory currents in adulthood, across postnatal development, and following the early stress of repeated maternal separation, a rodent model for depression. We also investigated developmental changes in related genes in these groups.
Acetylcholine-induced Ca(2+) release potentiates ACh-elicited excitatory currents. In the healthy PFC, this potentiation of muscarinic excitation emerges in young adulthood, when executive function typically reaches maturity. However, the developmental consolidation of muscarinic ACh signaling is abolished in adults with a history of early stress, where ACh responses retain an adolescent phenotype. In prefrontal cortex, these rats show a disruption in the expression of multiple developmentally regulated genes associated with Gαq and Ca(2+) signaling. Pharmacologic and ionic manipulations reveal that the enhancement of muscarinic excitation in the healthy adult PFC arises via the electrogenic process of sodium/Ca(2+) exchange.
This work illustrates a long-lasting disruption in ACh-mediated cortical excitation following early stress and raises the possibility that such cellular mechanisms may disrupt the maturation of executive function.
[Show abstract][Hide abstract] ABSTRACT: Cholinergic modulation of prefrontal cortex is essential for attention. In essence, it focuses the mind on relevant, transient stimuli in support of goal-directed behavior. The excitation of prefrontal layer VI neurons through nicotinic acetylcholine receptors optimizes local and top-down control of attention. Layer VI of prefrontal cortex is the origin of a dense feedback projection to the thalamus and is one of only a handful of brain regions that express the α5 nicotinic receptor subunit, encoded by the gene chrna5. This accessory nicotinic receptor subunit alters the properties of high-affinity nicotinic receptors in layer VI pyramidal neurons in both development and adulthood. Studies investigating the consequences of genetic deletion of α5, as well as other disruptions to nicotinic receptors, find attention deficits together with altered cholinergic excitation of layer VI neurons and aberrant neuronal morphology. Nicotinic receptors in prefrontal layer VI neurons play an essential role in focusing attention under challenging circumstances. In this regard, they do not act in isolation, but rather in concert with cholinergic receptors in other parts of prefrontal circuitry. This review urges an intensification of focus on the cellular mechanisms and plasticity of prefrontal attention circuitry. Disruptions in attention are one of the greatest contributing factors to disease burden in psychiatric and neurological disorders, and enhancing attention may require different approaches in the normal and disordered prefrontal cortex.
Cellular and Molecular Life Sciences CMLS 10/2013; · 5.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Maternal smoking during pregnancy repeatedly exposes the developing fetus to nicotine and is linked with attention deficits in offspring. Corticothalamic neurons within layer VI of the medial prefrontal cortex are potential targets in the disruption of attention circuitry by nicotine, a process termed teratogenesis. These prefrontal layer VI neurons would be likely targets because they are developmentally excited and morphologically sculpted by a population of nicotinic acetylcholine receptors (nAChRs) that are sensitive to activation and/or desensitization by nicotine. The maturational effects of these α4β2* nAChRs and their susceptibility to desensitization are both profoundly altered by the incorporation of an α5 subunit, encoded by the chrna5 gene. Here, we investigate nicotine teratogenesis in layer VI neurons of wildtype and α5(-/-) mice. In vivo chronic nicotine exposure during development significantly modified apical dendrite morphology and nAChR currents, compared with vehicle control. The direction of the changes was dependent on chrna5 genotype. Surprisingly, neurons from wildtype mice treated with in vivo nicotine resembled those from α5(-/-) mice treated with vehicle, maintaining into adulthood a morphological phenotype characteristic of immature mice together with reduced nAChR currents. In α5(-/-) mice, however, developmental in vivo nicotine tended to normalize both adult morphology and nAChR currents. These findings suggest that chrna5 genotype can determine the effect of developmental in vivo nicotine on the prefrontal cortex. In wildtype mice, the lasting alterations to the morphology and nAChR activation of prefrontal layer VI neurons are teratogenic changes consistent with the attention deficits observed following developmental nicotine exposure.
[Show abstract][Hide abstract] ABSTRACT: The 5-HT(5A) receptor is the least understood serotonin (5-HT) receptor. Here, we electrophysiologically identify and characterize a native 5-HT(5A) receptor current in acute ex vivo brain slices of adult rodent prefrontal cortex. In the presence of antagonists for the previously characterized 5-HT(1A) and 5-HT₂ receptors, a proportion of layer V pyramidal neurons continue to show 5-HT-elicited outward currents in both rats and mice. These 5-HT currents are suppressed by the selective 5-HT(5A) antagonist, SB-699551, and are not observed in 5-HT(5A) receptor knock-out mice. Further characterization reveals that the 5-HT(5A) current is activated by submicromolar concentrations of 5-HT, is inwardly rectifying with a reversal potential near the equilibrium potential for K+ ions, and is suppressed by blockers of Kir3 channels. Finally, we observe that genetic deletion of the inhibitory 5-HT(5A) receptor results in an unexpected, large increase in the inhibitory 5-HT(1A) receptor currents. The presence of functional prefrontal 5-HT(5A) receptors in normal rodents along with compensatory plasticity in 5-HT(5A) receptor knock-out mice testifies to the significance of this receptor in the healthy prefrontal cortex.
Journal of Neuroscience 04/2012; 32(17):5804-9. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nicotinic signaling in prefrontal layer VI pyramidal neurons is important to the function of mature attention systems. The normal incorporation of α5 subunits into α4β2* nicotinic acetylcholine receptors augments nicotinic signaling in these neurons and is required for normal attention performance in adult mice. However, the role of α5 subunits in the development of the prefrontal cortex is not known.
We sought to answer this question by examining nicotinic currents and neuronal morphology in layer VI neurons of medial prefrontal cortex of wild-type and α5 subunit knockout (α5(-/-)) mice during postnatal development and in adulthood.
In wild-type but not in α5(-/-) mice, there is a developmental peak in nicotinic acetylcholine currents in the third postnatal week. At this juvenile time period, the majority of neurons in all mice have long apical dendrites extending into cortical layer I. Yet, by early adulthood, wild-type but not α5(-/-) mice show a pronounced shift toward shorter apical dendrites. This cellular difference occurs in the absence of genotype differences in overall cortical morphology.
Normal developmental changes in nicotinic signaling and dendritic morphology in prefrontal cortex depend on α5-comprising nicotinic acetylcholine receptors. It appears that these receptors mediate a specific developmental retraction of apical dendrites in layer VI neurons. This finding provides novel insight into the cellular mechanisms underlying the known attention deficits in α5(-/-) mice and potentially also into the pathophysiology of developmental neuropsychiatric disorders such as attention-deficit disorder and autism.
[Show abstract][Hide abstract] ABSTRACT: Attention depends on cholinergic stimulation of nicotinic and muscarinic acetylcholine receptors in the medial prefrontal cortex. Pyramidal neurons in layer VI of this region express cholinergic receptors of both families and play an important role in attention through their feedback projections to the thalamus. Here, we investigate how nicotinic and muscarinic cholinergic receptors affect the excitability of these neurons using whole-cell recordings in acute brain slices of prefrontal cortex. Since attention deficits have been documented in both rodents and humans having genetic abnormalities in nicotinic receptors, we focus in particular on how the cholinergic excitation of layer VI neurons is altered by genetic deletion of either of two key nicotinic receptor subunits, the accessory α5 subunit or the ligand-binding β2 subunit. We find that the cholinergic excitation of layer VI neurons is dominated by nicotinic receptors in wild-type mice and that the reduction or loss of this nicotinic stimulation is accompanied by a surprising degree of plasticity in excitatory muscarinic receptors. These findings suggest that disrupting nicotinic receptors fundamentally alters the mechanisms and timing of excitation in prefrontal attentional circuitry.
Journal of Neuroscience 11/2011; 31(45):16458-63. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Serotonin and its receptors (HTRs) play critical roles in brain development and in the regulation of cognition, mood, and anxiety. HTRs are highly expressed in human prefrontal cortex and exert control over prefrontal excitability. The serotonin system is a key treatment target for several psychiatric disorders; however, the effectiveness of these drugs varies according to age. Despite strong evidence for developmental changes in prefrontal Htrs of rodents, the developmental regulation of HTR expression in human prefrontal cortex has not been examined. Using postmortem human prefrontal brain tissue from across postnatal life, we investigated the expression of key serotonin receptors with distinct inhibitory (HTR1A, HTR5A) and excitatory (HTR2A, HTR2C, HTR4, HTR6) effects on cortical neurons, including two receptors which appear to be expressed to a greater degree in inhibitory interneurons of cerebral cortex (HTR2C, HTR6). We found distinct developmental patterns of expression for each of these six HTRs, with profound changes in expression occurring early in postnatal development and also into adulthood. However, a collective look at these HTRs in terms of their likely neurophysiological effects and major cellular localization leads to a model that suggests developmental changes in expression of these individual HTRs may not perturb an overall balance between inhibitory and excitatory effects. Examining and understanding the healthy balance is critical to appreciate how abnormal expression of an individual HTR may create a window of vulnerability for the emergence of psychiatric illness.
PLoS ONE 07/2011; 6(7):e22799. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hypofunction of the N-methyl D-aspartate subtype of glutamate receptor (NMDAR) is hypothesized to be a mechanism underlying cognitive dysfunction in individuals with schizophrenia. For the schizophrenia-linked genes NRG1 and ERBB4, NMDAR hypofunction is thus considered a key detrimental consequence of the excessive NRG1-ErbB4 signaling found in people with schizophrenia. However, we show here that neuregulin 1β-ErbB4 (NRG1β-ErbB4) signaling does not cause general hypofunction of NMDARs. Rather, we find that, in the hippocampus and prefrontal cortex, NRG1β-ErbB4 signaling suppresses the enhancement of synaptic NMDAR currents by the nonreceptor tyrosine kinase Src. NRG1β-ErbB4 signaling prevented induction of long-term potentiation at hippocampal Schaffer collateral-CA1 synapses and suppressed Src-dependent enhancement of NMDAR responses during theta-burst stimulation. Moreover, NRG1β-ErbB4 signaling prevented theta burst-induced phosphorylation of GluN2B by inhibiting Src kinase activity. We propose that NRG1-ErbB4 signaling participates in cognitive dysfunction in schizophrenia by aberrantly suppressing Src-mediated enhancement of synaptic NMDAR function.
Nature medicine 03/2011; 17(4):470-8. · 28.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Prefrontal serotonin 5-HT(2) receptors have been linked to the pathogenesis and treatment of affective disorders, yet their function in psychiatric vulnerability is not known. Here, we examine the effects of 5-HT(2) receptors in a rat model of psychiatric vulnerability using electrophysiology, gene expression, and behavior. Following the early stress of chronic maternal separation, we found that serotonin has atypical 5-HT(2) receptor-mediated excitatory effects in the adult prefrontal cortex that were blocked by the 5-HT(2A) receptor antagonist MDL 100907. In the absence of a serotonergic agonist, the intrinsic excitability of the prefrontal cortex was not enhanced relative to controls. Yet, in response to stimulation of 5-HT(2) receptors, adult animals with a history of early stress exhibit heightened prefrontal network activity in vitro, enhanced immediate early gene expression in vivo, and potentiated head shake behavior. These changes arise in the absence of any major alteration of prefrontal 5-HT(2A/C) mRNA expression or 5-HT(2) receptor binding. Our microarray results and quantitative PCR validation provide insight into the molecular changes that accompany such enhanced 5-HT(2) receptor function in adult animals following early stress. We observed persistent prefrontal transcriptome changes, with significant enrichment of genes involved in cellular developmental processes, regulation of signal transduction, and G-protein signaling. Specific genes regulated by early stress were validated in an independent cohort, and several altered genes were normalized by chronic blockade of 5-HT(2) receptors in adulthood. Together, our results demonstrate enhanced prefrontal 5-HT(2) receptor function and persistent alterations in prefrontal gene expression in a rat model of psychiatric vulnerability.
Journal of Neuroscience 09/2010; 30(36):12138-50. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Stimulation of the prefrontal cortex by acetylcholine is critical for attention; however, the cellular mechanisms underlying its influence on attention pathways within the brain are not well understood. Pyramidal neurons in layer VI of the prefrontal cortex are believed to play an important role in this process because they are excited by acetylcholine and provide a major source of feedback projections to the thalamus. Here, we show using whole-cell electrophysiology that the relatively rare alpha5 subunit of the nicotinic acetylcholine receptor powerfully enhances nicotinic currents in layer VI pyramidal neurons in prefrontal cortical brain slices from adult mice. In addition, behavioral experiments using the five-choice serial reaction time test show that the presence of the nicotinic receptor alpha5 subunit also increases the accuracy of adult mice on this visual attention task under highly demanding conditions. Together, these findings demonstrate a novel and important role for the nicotinic receptor alpha5 subunit in adult brain circuitry required for attentional performance.
Journal of Neuroscience 07/2010; 30(27):9241-52. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by the hemizygous deletion of 28 genes on chromosome 7, including the general transcription factor GTF2IRD1. Mice either hemizygously (Gtf2ird1(+/-)) or homozygously (Gtf2ird1(-/-)) deleted for this transcription factor exhibit low innate anxiety, low aggression and increased social interaction, a phenotype that shares similarities to the high sociability and disinhibition seen in individuals with WBS. Here, we investigated the inhibitory effects of serotonin (5-HT) on the major output neurons of the prefrontal cortex in Gtf2ird1(-/-) mice and their wildtype (WT) siblings. Prefrontal 5-HT receptors are known to modulate anxiety-like behaviors, and the Gtf2ird1(-/-) mice have altered 5-HT metabolism in prefrontal cortex. Using whole cell recording from layer V neurons in acute brain slices of prefrontal cortex, we found that 5-HT elicited significantly larger inhibitory, outward currents in Gtf2ird1(-/-) mice than in WT controls. In both genotypes, these currents were resistant to action potential blockade with TTX and were suppressed by the selective 5-HT(1A) receptor antagonist WAY-100635, suggesting that they are mediated directly by 5-HT(1A) receptors on the recorded neurons. Control experiments suggest a degree of layer and receptor specificity in this enhancement since 5-HT(1A) receptor-mediated responses in layer II/III pyramidal neurons were unchanged as were responses mediated by two other inhibitory receptors in layer V pyramidal neurons. Furthermore, we demonstrate GTF2IRD1 protein expression by neurons in layer V of the prefrontal cortex. Our finding that 5-HT(1A)-mediated responses are selectively enhanced in layer V pyramidal neurons of Gtf2ird1(-/-) mice gives insight into the cellular mechanisms that underlie reduced innate anxiety and increased sociability in these mice, and may be relevant to the low social anxiety and disinhibition in patients with WBS and their sensitivity to serotonergic medicines. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11689-010-9044-5) contains supplementary material, which is available to authorized users.
Journal of Neurodevelopmental Disorders 06/2010; 2(2):99-108. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is a large sex difference in the prevalence of attention deficit disorder; yet, relatively little is known about sex differences in the development of prefrontal attention circuitry. In male rats, nicotinic acetylcholine receptors excite corticothalamic neurons in layer VI, which are thought to play an important role in attention by gating the sensitivity of thalamic neurons to incoming stimuli. These nicotinic currents in male rats are significantly larger during the first postnatal month when prefrontal circuitry is maturing. The present study was undertaken to investigate whether there are sex differences in the nicotinic currents in prefrontal layer VI neurons during development.
Using whole cell recording in prefrontal brain slice, we examined the inward currents elicited by nicotinic stimulation in male and female rats and two strains of mice. We found a prominent sex difference in the currents during the first postnatal month when males had significantly greater nicotinic currents in layer VI neurons compared to females. These differences were apparent with three agonists: acetylcholine, carbachol, and nicotine. Furthermore, the developmental sex difference in nicotinic currents occurred despite male and female rodents displaying a similar pattern and proportion of layer VI neurons possessing a key nicotinic receptor subunit.
This is the first illustration at a cellular level that prefrontal attention circuitry is differently affected by nicotinic receptor stimulation in males and females during development. This transient sex difference may help to define the cellular and circuit mechanisms that underlie vulnerability to attention deficit disorder.
PLoS ONE 02/2010; 5(2):e9261. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The modulation of the prefrontal cortex by the neurotransmitter serotonin (5-HT) is thought to play a key role in determining adult anxiety levels. Layer II/III of the prefrontal cortex, which mediates communication across cortical regions, displays a high level of 5-HT(1A) receptor binding in normal individuals and a significantly lower level in patients with mood and anxiety disorders. Here, we examine how serotonin modulates pyramidal neurons in layer II/III of the rat prefrontal cortex throughout postnatal development and in adulthood. Using whole cell recordings in brain slices of the rat medial prefrontal cortex, we observed that serotonin directly inhibits layer II/III pyramidal neurons through 5-HT(1A) receptors across postnatal development (postnatal days 6-96). In adulthood, a sex difference in these currents emerges, consistent with human imaging studies of 5-HT(1A) receptor binding. We examined the effects of early life stress on the 5-HT(1A) receptor currents in layer II/III. Surprisingly, animals subjected to early life stress displayed significantly larger 5-HT(1A)-mediated outward currents throughout the third and fourth postnatal weeks after elevated 5-HT(1A) expression during the second postnatal week. Subsequent exposure to social isolation in adulthood resulted in the almost-complete elimination of 5-HT(1A) currents in layer II/III neurons suggesting an interaction between early life events and adult experiences. These data represent the first examination of functional 5-HT(1A) receptors in layer II/III of the prefrontal cortex during normal development as well as after stress.
Journal of Neuroscience 09/2009; 29(32):10094-103. · 6.75 Impact Factor