Maternal defense is modulated by beta adrenergic receptors in lateral septum in mice

Vasopressin regulates social play behavior in sex-specific ways through glutamate modulation in the lateral septum

Social play is a highly rewarding behavior that is essential for the development of social skills. Social play is impaired in children diagnosed with autism, a disorder with a strong sex bias in prevalence. We recently showed that the arginine vasopressin (AVP) system in the lateral septum (LS) regulates social play behavior sex-specifically in juvenile rats: Administration of a AVP 1a receptor (V1aR) antagonist increased social play behavior in males and decreased it in females. Here, we demonstrate that glutamate, but not GABA, is involved in the sex-specific regulation of social play by the LS-AVP system. First, males show higher extracellular glutamate concentrations in the LS than females while they show similar extracellular GABA concentrations. This resulted in a baseline sex difference in excitatory/inhibitory balance, which was eliminated by V1aR antagonist administration into the LS: V1aR antagonist increased extracellular glutamate release in females but not in males. Second, administration of the glutamate receptor agonist L-glutamic acid into the LS prevented the V1aR antagonist-induced increase in social play behavior in males while mimicking the V1aR antagonist-induced decrease in social play behavior in females. Third, administration of the glutamate receptor antagonists AP-5 and CNQX into the LS prevented the V1aR antagonist-induced decrease in social play behavior in females. Last, both sexes showed increases in extracellular LS-GABA release upon V1aR antagonist administration into the LS and decreases in social play behavior upon administration of the GABA-A receptor agonist muscimol into the LS, suggesting that GABA is not involved in the sex-specific regulation of social play by the LS-AVP system. Finally, to start identifying the cellular mechanism mediating the sex-specific effects of the LS-AVP system on LS-glutamate, we determined the presence of potential sex differences in the type of LS cells expressing V1aR. However, no sex differences were found in the percentage of Avpr1a+ LS cells expressing markers for either GABAergic neurons, somatostatin-expressing neurons, calbindin 1-expressing neurons, or astrocytes. In conclusion, these findings demonstrate that the LS-AVP system regulates social play sex-specifically via differential local glutamatergic neurotransmission in male and female juvenile rats. Further research is required to uncover the underlying cellular mechanism.

Lateral Septum Somatostatin Neurons are Activated by Diverse Stressors

The lateral septum (LS) is a forebrain structure that has been implicated in a wide range of behavioral and physiological responses to stress. However, the specific populations of neurons in the LS that mediate stress responses remain incompletely understood. Here, we show that neurons in the dorsal lateral septum (LSd) that express the somatostatin gene (hereafter, LSd^Sst neurons) are activated by diverse stressors. Retrograde tracing from LSd^Sst neurons revealed that these neurons are directly innervated by neurons in the locus coeruleus (LC), the primary source of norepinephrine well-known to mediate diverse stress-related functions in the brain. Consistently, we found that norepinephrine increased excitatory synaptic transmission onto LSd^Sst neurons, suggesting the functional connectivity between LSd^Sst neurons and LC noradrenergic neurons. However, optogenetic stimulation of LSd^Sst neurons did not affect stress-related behaviors or autonomic functions, likely owing to the functional heterogeneity within this population. Together, our findings show that LSd^Sst neurons are activated by diverse stressors and suggest that norepinephrine released from the LC may modulate the activity of LSd^Sst neurons under stressful circumstances.

Evolutionary endocrinology and the problem of Darwin's tangled bank

Like Darwin's tangled bank of biodiversity, the endocrine mechanisms that give rise to phenotypic diversity also exhibit nearly endless forms. This tangled bank of mechanistic diversity can prove problematic as we seek general principles on the role of endocrine mechanisms in phenotypic evolution. A key unresolved question is therefore: to what degree are specific endocrine mechanisms re-used to bring about replicated phenotypic evolution? Related areas of inquiry are booming in molecular ecology, but behavioral traits are underrepresented in this literature. Here, I leverage the rich comparative tradition in evolutionary endocrinology to evaluate whether and how certain mechanisms may be repeated hotspots of behavioral evolutionary change. At one extreme, mechanisms may be parallel, such that evolution repeatedly uses the same gene or pathway to arrive at multiple independent (or, convergent) origins of a particular behavioral trait. At the other extreme, the building blocks of behavior may be unique, such that outwardly similar phenotypes are generated via lineage-specific mechanisms. This review synthesizes existing case studies, phylogenetic analyses, and experimental evolutionary research on mechanistic parallelism in animal behavior. These examples show that the endocrine building blocks of behavior have some elements of parallelism across replicated evolutionary events. However, support for parallelism is variable among studies, at least some of which relates to the level of complexity at which we consider sameness (i.e. pathway vs. gene level). Moving forward, we need continued experimentation and better testing of neutral models to understand whether, how - and critically, why - mechanism A is used in one lineage and mechanism B is used in another. We also need continued growth of large-scale comparative analyses, especially those that can evaluate which endocrine parameters are more or less likely to undergo parallel evolution alongside specific behavioral traits. These efforts will ultimately deepen understanding of how and why hormone-mediated behaviors are constructed the way that they are.

Neurobiology of the lateral septum: regulation of social behavior

Social interactions are essential for mammalian life and are regulated by evolutionary conserved neuronal mechanisms. An individual's internal state, experiences, and the nature of the social stimulus are critical for determining apt responses to social situations. The lateral septum (LS) - a structure of the basal forebrain - integrates abundant cortical and subcortical inputs, and projects to multiple downstream regions to generate appropriate behavioral responses. Although incoming cognitive information is indispensable for contextualizing a social stimulus, neuromodulatory information related to the internal state of the organism significantly influences the behavioral outcome as well. This review article provides an overview of the neuroanatomical properties of the LS, and examines its neurochemical (neuropeptidergic and hormonal) signaling, which provide the neuromodulatory information essential for fine-tuning social behavior across the lifespan.

TMEM16B Calcium-Activated Chloride Channels Regulate Action Potential Firing in Lateral Septum and Aggression in Male Mice

The lateral septum (LS) plays an important role in regulating aggression. It is well recognized that LS lesions lead to a dramatic increase in aggressive behaviors. A better understanding of LS neurophysiology and its functional output is therefore important to assess LS involvement in regulating aggression. The LS is a heterogeneous structure that maintains inputs and outputs with multiple brain regions, and is also divided into subregions that innervate one another. Thus, it is challenging to identify the exact cell type and projections for characterization. In this study, we determined the expression pattern of the calcium-activated chloride channel, TMEM16B, in the LS of both male and female mice. We then investigated the physiological contribution of the calcium-activated chloride channel to LS neuronal signaling. By performing whole-cell patch-clamp recording, we showed that TMEM16B alters neurotransmitter release at the hippocampal-LS synapse, and regulates spike frequency and spike frequency adaptation in subpopulations of LS neurons. We further demonstrated that loss of TMEM16B function promotes lengthened displays of aggressive behaviors by male mice during the resident intruder paradigm. In conclusion, our findings suggest that TMEM16B function contributes to neuronal excitability in subpopulations of LS neurons and the regulation of aggression in male mice.SIGNIFICANCE STATEMENT Aggression is a behavior that arose evolutionarily from the necessity to compete for limited resources and survival. One particular brain region involved in aggression is the lateral septum (LS). In this study, we characterized the expression of the TMEM16B calcium-activated chloride channel in the LS and showed that TMEM16B regulates the action potential firing frequency of LS neurons. We discovered that loss of TMEM16B function lengthens the displays of aggressive behaviors in male mice. These findings suggest that TMEM16B plays an important role in regulating LS neuronal excitability and behaviors associated with LS function, thereby contributing to our understanding of how the LS may regulate aggression.

Serotonin and motherhood: From molecules to mood

Emerging research points to a valuable role of the monoamine neurotransmitter, serotonin, in the display of maternal behaviors and reproduction-associated plasticity in the maternal brain. Serotonin is also implicated in the pathophysiology of numerous affective disorders and likely plays an important role in the pathophysiology of maternal mental illness. Therefore, the main goals of this review are to detail: (1) how the serotonin system of the female brain changes across pregnancy and postpartum; (2) the role of the central serotonergic system in maternal caregiving and maternal aggression; and (3) how the serotonin system and selective serotonin reuptake inhibitor medications (SSRIs) are involved in the treatment of maternal mental illness. Although there is much work to be done, studying the central serotonin system's multifaceted role in the maternal brain is vital to our understanding of the processes governing matrescence and the maintenance of motherhood.

Involvement of dopamine, but not norepinephrine, in the sex-specific regulation of juvenile socially rewarding behavior by vasopressin

Social play is a highly rewarding behavior displayed mostly during the juvenile period. We recently showed that vasopressin V1a receptor (V1aR) blockade in the lateral septum (LS) enhances social play in male juvenile rats, but reduces it in females. Here, we determined whether the LS-AVP system modulates dopamine (DA) and/or norepinephrine (NE) neurotransmission in the LS to regulate social play behavior in sex-specific ways. Using microdialysis combined with retrodialysis, we demonstrated that both LS-AVP administration and social play exposure increased extracellular LS-DA release in females, but not in males. Pharmacological blockade of LS-DA receptors reduced social play in both sexes, but required a higher dose in females. This suggests that baseline LS-DA release is sufficient for social play in males, while increased LS-DA release is necessary for social play in females. Administration of a V1aR antagonist into the LS inhibited the social play-induced increase in extracellular LS-DA release in females. Furthermore, co-administration of the DA agonist apomorphine prevented the LS-V1aR blockade-induced decrease in social play in females. This suggests that LS-V1aR blockade reduces social play in females by dampening the rise in LS-DA release. Extracellular LS-NE release was enhanced in response to pharmacological manipulations of the LS-AVP system and to social play in males and/or females, but pharmacological blockade or stimulation of LS-NE receptors did not alter social play in either sex. Overall, we define a mechanism by which the LS-AVP system alters LS-DA neurotransmission differently in males than females resulting in the sex-specific regulation of juvenile social play behavior.

Down-regulation of fatty acid binding protein 7 (Fabp7) is a hallmark of the postpartum brain

Fatty acid binding protein 7 (Fabp7) is a versatile protein that is linked to glial differentiation and proliferation, neurogenesis, and multiple mental health disorders. Recent microarray studies identified a robust decrease in Fabp7 expression in key brain regions of the postpartum rodents. Given its diverse functions, Fabp7 could play a critical role in sculpting the maternal brain and promoting the maternal phenotype. The present study aimed at investigating the expression profile of Fabp7 across the postpartum CNS. Quantitative real-time PCR (qPCR) analysis showed that Fabp7 mRNA was consistently down-regulated across the postpartum brain. Of the 9 maternal care-related regions tested, seven exhibited significant decreases in Fabp7 in postpartum (relative to virgin) females, including medial prefrontal cortex (mPFC), nucleus accumbens (NA), lateral septum (LS), bed nucleus of stria terminalis dorsal (BnSTd), paraventricular nucleus (PVN), lateral hypothalamus (LH), and basolateral and central amygdala (BLA/CeA). For both ventral tegmental area (VTA) and medial preoptic area (MPOA) levels of Fabp7 were lower in mothers, but levels of changes did not reach significance. Confocal microscopy revealed that protein expression of Fabp7 in the LS paralleled mRNA findings. Specifically, the caudal LS exhibited a significant reduction in Fabp7 immunoreactivity, while decreases in medial LS were just above significance. Double fluorescent immunolabeling confirmed the astrocytic phenotype of Fabp7-expressing cells. Collectively, this research demonstrates a broad and marked reduction in Fabp7 expression in the postpartum brain, suggesting that down-regulation of Fabp7 may serve as a hallmark of the postpartum brain and contribute to the maternal phenotype.

Insights from extracellular matrix studies in the hypothalamus: structural variations of perineuronal nets and discovering a new perifornical area of the anterior hypothalamus

The hypothalamus controls metabolism, stress responses, and instinctive behaviors for individual survival and species preservation. Recent studies suggest that hypothalamic neurons retain plasticity throughout adulthood, which enables these neurons to respond to various kinds of changes in environment, nutrients, and fluctuating hormones. One of the mechanisms underlying the regulation of neural plasticity is the formation of a stable extracellular matrix (ECM) structure called perineuronal nets (PNNs). PNNs are large aggregates of heterogeneous ECM molecules such as chondroitin sulfate proteoglycans (CSPGs), hyaluronan, their link proteins, and tenascin-R. PNNs surround the cell body and proximal dendrites of a subset of neurons and limit adult neural plasticity. This review describes the CSPG-based ECM, including the PNNs, with a special focus on the hypothalamus of mice. We first provide an overview of PNNs in terms of their structure, molecular components, and functions, most of which have been demonstrated by extrahypothalamic studies. Second, we show the presence or absence of PNNs within individual hypothalamic regions and then describe non-PNN-formed ECM containing CSPGs that can be observed in particular hypothalamic regions. Finally, we will introduce a newly identified mouse hypothalamic area that we named the perifornical area of the anterior hypothalamus (PeFAH), which contains a cluster of PNN-positive neurons. PeFAH neurons express enkephalin and have bidirectional connections with the lateral septum. The anterior hypothalamus and lateral septum are thought to regulate defensive behaviors; therefore, the PeFAH neurons and PNNs around them could be involved in the regulation of defensive behaviors.

MicroRNA expression is altered in lateral septum across reproductive stages

MicroRNAs (miRNAs) inhibit RNA targets and may contribute to postpartum central nervous system (CNS) gene expression changes, although this has never been tested. In the present study, we directly evaluated miRNA levels using RNA sequencing during reproduction in female mice in the lateral septum (LS). We found the reliable and robust changes of miRNAs away from the virgin stage at the three other stages, namely pregnant, day 1 postpartum, and day 8 postpartum. For a given miRNA that was significantly different from the virgin condition in more than one group, the direction of change was always the same. Overall, we identified 32 upregulated miRNAs and 25 downregulated miRNAs that were consistently different from the virgin state. 'Arm switching' occurs for miR-433-3 and miR-7b. Unexpectedly, a third of upregulated miRNAs (relative to virgin) were highly localized within the 12qF1 region of chromosome 12 that includes the Dlk1-Dio3 gene cluster implicated in stem cell and neuronal differentiation. Over 1500 genes were targeted by multiple upregulated miRNAs with about 100 genes targeted by five or more miRNAs. Over 1000 genes were targeted by multiple downregulated miRNAs with about 50 genes targeted by five or more miRNAs. Half of the target genes were regulated by up and downregulated miRNAs, indicating homeostatic regulation. Transcriptional regulation was the most enriched pathway for genes linked to up or down regulated miRNAs. Other enriched pathways included protein kinase activity (e.g., MAP kinase), CNS development, axon guidance, neurotrophin signaling, neuron development/differentiation, and neurogenesis. Previously published postpartum LS gene expression changes were enrichment for LS miRNA targets, as expected. Surprisingly, postpartum gene expression changes from other regions were also enriched against LS miRNA targets, suggesting a core group of miRNAs may act across the CNS during reproduction. Together, we directly examine miRNAs and find significant alterations in the postpartum brain.

Immediate post-defeat infusions of the noradrenergic receptor antagonist propranolol impair the consolidation of conditioned defeat in male Syrian hamsters

Social defeat occurs when an animal is attacked and subjugated by an aggressive conspecific. Following social defeat, male Syrian hamsters fail to display species-typical territorial aggression and instead exhibit submissive or defensive behaviors even when in the presence of a non-aggressive intruder. We have termed this phenomenon conditioned defeat (CD). The mechanisms underlying CD are not fully understood, but data from our lab suggest that at least some of the mechanisms are similar to those that mediate classical fear conditioning. The goal of the present experiment was to test the hypothesis that noradrenergic signaling promotes the consolidation of CD, as in classical fear conditioning, by determining whether CD is disrupted by post-training blockade of noradrenergic activity. In Experiment 1, we determined whether systemic infusions of the noradrenergic receptor antagonist propranolol (0, 1.0, 10, or 20mg/kg) given immediately after a 15 min defeat by a resident aggressor would impair CD tested 48 h later. Hamsters that were given immediate post-training infusions of propranolol (1.0, but not 10 or 20mg/kg) showed significantly less submissive behavior than did those given vehicle infusions supporting the hypothesis that there is noradrenergic modulation of the consolidation of a social defeat experience. In Experiment 2, we demonstrated that propranolol (1.0mg/kg) given immediately, but not 4 or 24h, after defeat impaired CD tested 48 h after defeat indicating that the window within which the memory for social defeat is susceptible to beta-adrenergic modulation is temporary. In Experiment 3, we examined whether central blockade of noradrenergic receptors could recapitulate the effect of systemic injections by giving an intracerebroventricular infusion of propranolol immediately after defeat and examining the effect on CD 24h later. Centrally administered propranolol (20 μg/3 μl but not 2 μg/3 μl) was also effective in dose-dependently reducing consolidation of CD. Collectively, the present results indicate that noradrenergic activity promotes the consolidation of CD and suggest that CD is a valuable model to study the processes by which emotion and stress modulate memory in an ethologically relevant context. These data also suggest that the popular conception in the clinical literature that the anxiolytic effect of propranolol is primarily due to the drug's peripheral effects may need to be reconsidered.

Dynamic changes in extracellular release of GABA and glutamate in the lateral septum during social play behavior in juvenile rats: Implications for sex-specific regulation of social play behavior

Social play is a motivated and rewarding behavior that is displayed by nearly all mammals and peaks in the juvenile period. Moreover, social play is essential for the development of social skills and is impaired in social disorders like autism. We recently showed that the lateral septum (LS) is involved in the regulation of social play behavior in juvenile male and female rats. The LS is largely modulated by GABA and glutamate neurotransmission, but their role in social play behavior is unknown. Here, we determined whether social play behavior is associated with changes in the extracellular release of GABA and glutamate in the LS and to what extent such changes modulate social play behavior in male and female juvenile rats. Using intracerebral microdialysis in freely behaving rats, we found no sex difference in extracellular GABA concentrations, but extracellular glutamate concentrations are higher in males than in females under baseline conditions and during social play. This resulted in a higher glutamate/GABA concentration ratio in males vs. females and thus, an excitatory predominance in the LS of males. Furthermore, social play behavior in both sexes is associated with significant increases in extracellular release of GABA and glutamate in the LS. Pharmacological blockade of GABA-A receptors in the LS with bicuculline (100 ng/0.5 μl, 250 ng/0.5 μl) dose-dependently decreased the duration of social play behavior in both sexes. In contrast, pharmacological blockade of ionotropic glutamate receptors (NMDA and AMPA/kainate receptors) in the LS with AP-5+CNQX (2mM+0.4mM/0.5 μl, 30 mM+3mM/0.5 μl) dose-dependently decreased the duration of social play behavior in females, but did not alter social play behavior in males. Together, these data suggest a role for GABA neurotransmission in the LS in the regulation of juvenile social play behavior in both sexes, while glutamate neurotransmission in the LS is involved in the sex-specific regulation of juvenile social play behavior.

Medial prefrontal cortex: genes linked to bipolar disorder and schizophrenia have altered expression in the highly social maternal phenotype

The transition to motherhood involves CNS changes that modify sociability and affective state. However, these changes also put females at risk for post-partum depression and psychosis, which impairs parenting abilities and adversely affects children. Thus, changes in expression and interactions in a core subset of genes may be critical for emergence of a healthy maternal phenotype, but inappropriate changes of the same genes could put women at risk for post-partum disorders. This study evaluated microarray gene expression changes in medial prefrontal cortex (mPFC), a region implicated in both maternal behavior and psychiatric disorders. Post-partum mice were compared to virgin controls housed with females and isolated for identical durations. Using the Modular Single-set Enrichment Test (MSET), we found that the genetic landscape of maternal mPFC bears statistical similarity to gene databases associated with schizophrenia (5 of 5 sets) and bipolar disorder (BPD, 3 of 3 sets). In contrast to previous studies of maternal lateral septum (LS) and medial preoptic area (MPOA), enrichment of autism and depression-linked genes was not significant (2 of 9 sets, 0 of 4 sets). Among genes linked to multiple disorders were fatty acid binding protein 7 (Fabp7), glutamate metabotropic receptor 3 (Grm3), platelet derived growth factor, beta polypeptide (Pdgfrb), and nuclear receptor subfamily 1, group D, member 1 (Nr1d1). RT-qPCR confirmed these gene changes as well as FMS-like tyrosine kinase 1 (Flt1) and proenkephalin (Penk). Systems-level methods revealed involvement of developmental gene networks in establishing the maternal phenotype and indirectly suggested a role for numerous microRNAs and transcription factors in mediating expression changes. Together, this study suggests that a subset of genes involved in shaping the healthy maternal brain may also be dysregulated in mental health disorders and put females at risk for post-partum psychosis with aspects of schizophrenia and BPD.

Endogenous CNS expression of neurotensin and neurotensin receptors is altered during the postpartum period in outbred mice

Neurotensin (NT) is a neuropeptide identical in mice and humans that is produced and released in many CNS regions associated with maternal behavior. NT has been linked to aspects of maternal care and previous studies have indirectly suggested that endogenous NT signaling is altered in the postpartum period. In the present study, we directly examine whether NT and its receptors exhibit altered gene expression in maternal relative to virgin outbred mice using real time quantitative PCR (qPCR) across multiple brain regions. We also examine NT protein levels using anti-NT antibodies and immunohistochemistry in specific brain regions. In the medial preoptic area (MPOA), which is critical for maternal behaviors, mRNA of NT and NT receptor 3 (Sort1) were significantly up-regulated in postpartum mice compared to virgins. NT mRNA was also elevated in postpartum females in the bed nucleus of the stria terminalis dorsal. However, in the lateral septum, NT mRNA was down-regulated in postpartum females. In the paraventricular nucleus of the hypothalamus (PVN), Ntsr1 expression was down-regulated in postpartum females. Neurotensin receptor 2 (Ntsr2) expression was not altered in any brain region tested. In terms of protein expression, NT immunohistochemistry results indicated that NT labeling was elevated in the postpartum brain in the MPOA, lateral hypothalamus, and two subregions of PVN. Together, these findings indicate that endogenous changes occur in NT and its receptors across multiple brain regions, and these likely support the emergence of some maternal behaviors.

Patterns of phosphorylated tyrosine hydroxylase vary with song production in female starlings

Vocal signal production in male songbirds is well studied, but the neural correlates of female song production are poorly understood. In European starlings, females sing to defend nesting resources, and song can be considered agonistically motivated. Across vertebrates catecholamines strongly influence motivated, agonistic social behaviors. The present study was designed to provide insight into a possible role for catecholamine activity in territorial song in female starlings. We presented females that were defending nest-cavities with an unfamiliar female and assessed song production. We then measured immunolabeling for phosphorylated tyrosine hydroxylase (pTH-ir), the rate-limiting enzyme for catecholamine synthesis, in brain regions in which catecholamines stimulate agonistic behavior. Females that sang had higher pTH-ir in the caudomedial ventral tegmental area and the lateral septum than females that did not sing. Furthermore, the number of songs produced correlated positively with pTH-ir in the medial preoptic nucleus. Phosphorylation of TH is thought to occur after catecholamine release, so these results link increased catecholamine activity in several brain regions governing agonistic behavior to territorial song production in females.

Effects of noradrenergic alpha-2 receptor antagonism or noradrenergic lesions in the ventral bed nucleus of the stria terminalis and medial preoptic area on maternal care in female rats

RATIONALE

Maternal behavior in laboratory rats requires a network of brain structures including the ventral bed nucleus of the stria terminalis (BSTv) and medial preoptic area (mPOA). Neurotransmitter systems in the BSTv and mPOA influencing maternal behaviors are not well understood, although norepinephrine is an excellent candidate because the BSTv contains the densest noradrenergic fiber plexus in the forebrain and norepinephrine in the mPOA is known to influence other female reproductive functions.

OBJECTIVES

We hypothesized that downregulated noradrenergic activity in the BSTv and mPOA is necessary for mothering.

METHODS

Postpartum mother-litter interactions were observed after BSTv infusion of yohimbine (an α2 autoreceptor antagonist that increases norepinephrine release), and after BSTv or mPOA infusion of the more selective α2 autoreceptor antagonist idazoxan. Lastly, noradrenergic input to the BSTv/mPOA was selectively lesioned in nulliparous rats with anti-DBH-saporin to determine if this would facilitate mothering.

RESULTS

BSTv yohimbine almost abolished retrieval of pups but did not significantly affect dams' ability to initiate contact, lick, or nurse them. BSTv idazoxan disrupted retrieval somewhat less than yohimbine, but significantly reduced nursing. mPOA idazoxan impaired retrieval more severely than that found after BSTv infusion. Anti-DBH-saporin almost eliminated noradrenergic terminals in the BSTv and reduced them by over 60% in the mPOA, but did not promote maternal responding. It also did not affect females' anxiety-related behavior.

CONCLUSIONS

Downregulated noradrenergic activity in the BSTv and mPOA is necessary for postpartum maternal behavior in rats, but eliminating this system alone is insufficient to promote maternal behaviors in nulliparous females.

Glutamic acid decarboxylase 65 and 67 expression in the lateral septum is up-regulated in association with the postpartum period in mice

The postpartum period in mammals undergoes a variety of physiological adaptations, including metabolic, behavioral and neuroendocrine alterations. GABA signaling has been strongly linked to various emotional states, stress responses and offspring protection. However, whether GABA signaling may change in the lateral septum (LS), a core brain region for regulating behavioral, emotional and stress responses in postpartum mice has not previously been examined. In this study, we tested whether the expression of two isoforms of glutamic acid decarboxylase (GAD), GAD65 (GAD2) and GAD67 (GAD1), the rate-limiting enzyme for GABA synthesis, exhibits altered expression in postpartum mice relative to nonmaternal, virgin mice. Using microdissected septal tissue from virgin and age-matched postpartum females, quantitative real-time PCR and Western blotting were carried out to assess GAD mRNA and protein expression, respectively. We found both protein and mRNA expression of GAD67 in the whole septum was up-regulated in postpartum mice. By contrast, no significant difference in the whole septum was observed in GAD65 expression. We then conducted a finer level of analysis using smaller microdissections and found GAD67 to be significantly increased in rostral LS, but not in caudal LS or medial septum (MS). Further, GAD65 mRNA expression in rostral LS, but not in caudal LS or MS was also significantly elevated in postpartum mice. These findings suggest that an increased GABA production in rostral LS of the postpartum mice via elevated GAD65 and GAD67 expression may contribute to multiple alterations in behavioral and emotional states, and responses to stress that occur during the postpartum period. Given that rostral LS contains GABA neurons that are projection neurons or local interneurons, it still needs to be determined whether the function of elevated GABA is for local or distant action or both.