Amygdalohippocampal Area Research Articles

Multiple Stressors Induce Amygdalohippocampal Volume Reduction in Adult Male Rats as Detected by Longitudinal Structural Magnetic Resonance Imaging

BackgroundTraumatic events can cause long-lasting and uncontrollable fear and anxiety. Posttraumatic stress disorder is an intractable mental disorder, and neurobiological mechanisms using animal models are expected to help development of posttraumatic stress disorder treatment. In this study, we combined multiple stress (MS) and longitudinal in vivo magnetic resonance imaging to reveal the effects of long-lasting anxiety-like behaviors on adult male rat brains. MethodsTwelve male Wistar rats (8 weeks old) were exposed to the MS of 1-mA footshocks and forced swimming, while 12 control rats were placed in a plastic cage. Contextual fear conditioning with 0.1-mA footshocks in a context different from the MS was conducted 15 days after the MS for both groups. Three retention tests were administered after 24 hours and 9 and 16 days. Two magnetic resonance imaging scans were conducted, one on the day before MS induction and one the day after the third retention test, with a 32-day interval. ResultsThe MS group showed greater freezing responses than the control group in all retention tests. Whole-brain voxel-based morphometry analyses revealed reduced gray matter volume in the anterior amygdalohippocampal area in MS group rats compared with control rats. These volume changes were negatively associated with freezing time in the third retention test in the MS group. ConclusionsThese results suggest that individual variability in the amygdalohippocampal area may be related to long-lasting fear responses after severe stress.

First Optimization of Novel, Potent, Selective PDE11A4 Inhibitors for Age-Related Cognitive Decline.

Phosphodiesterase 11A4 (PDE11A4) is a dual-acting cyclic nucleotide hydrolase expressed in neurons in the CA1, subiculum, amygdalostriatal transition area and amygdalohippocampal area of the extended hippocampal formation. PDE11A4 is the only PDE enzyme to emanate solely from hippocampal formation, a key brain region for the formation of long-term memory. PDE11A4 expression increases in the hippocampal formation of both humans and rodents as they age. Interestingly, PDE11A knockout mice do not show age-related deficits in associative memory and show no gross histopathology. This suggests that inhibition of PDE11A4 might serve as a therapeutic option for age-related cognitive decline. A novel, yeast-based high throughput screen previously identified moderately potent, selective PDE11A4 inhibitors, and this work describes initial efforts that improved potency more than 10-fold and improved some pharmaceutical properties of one of these scaffolds, leading to selective, cell-penetrant PDE11A4 inhibitors, one of which is 10-fold more potent compared to tadalafil in cell-based activity.

Sex differences in distribution and identity of aromatase gene expressing cells in the young adult rat brain

BackgroundAromatase catalyzes the synthesis of estrogens from androgens. Knowledge on its regional expression in the brain is of relevance to the behavioral implications of these hormones that might be linked to sex differences in mental health. The present study investigated the distribution of cells expressing the aromatase coding gene (Cyp19a1) in limbic regions of young adult rats of both sexes, and characterized the cell types expressing this gene.MethodsCyp19a1 mRNA was mapped using fluorescent in situ hybridization (FISH). Co-expression with specific cell markers was assessed with double FISH; glutamatergic, gamma-aminobutyric acid (GABA)-ergic, glial, monoaminergic, as well as interneuron markers were tested. Automated quantification of the cells expressing the different genes was performed using CellProfiler. Sex differences in the number of cells expressing Cyp19a1 was tested non-parametrically, with the effect size indicated by the rank-biserial correlation. FDR correction for multiple testing was applied.ResultsIn the male brain, the highest percentage of Cyp19a1+ cells was found in the medial amygdaloid nucleus and the bed nucleus of stria terminalis, followed by the medial preoptic area, the CA2/3 fields of the hippocampus, the cortical amygdaloid nucleus and the amygdalo-hippocampal area. A lower percentage was detected in the caudate putamen, the nucleus accumbens, and the ventromedial hypothalamus. In females, the distribution of Cyp19a1+ cells was similar but at a lower percentage. In most regions, the majority of Cyp19a1+ cells were GABAergic, except for in the cortical-like regions of the amygdala where most were glutamatergic. A smaller fraction of cells co-expressed Slc1a3, suggesting expression of Cyp19a1 in astrocytes; monoaminergic markers were not co-expressed. Moreover, sex differences were detected regarding the identity of Cyp19a1+ cells.ConclusionsFemales show overall a lower number of cells expressing Cyp19a1 in the limbic brain. In both sexes, aromatase is expressed in a region-specific manner in GABAergic and glutamatergic neurons. These findings call for investigations of the relevance of sex-specific and region-dependent expression of Cyp19a1 in the limbic brain to sex differences in behavior and mental health.

The brain of the tree pangolin (Manis tricuspis). VII. The amygdaloid body.

Here, we describe the cytoarchitecture and chemoarchitecture of the amygdaloid body of the tree pangolin. Our definition of the amygdaloid body includes the pallial portions of the amygdala, and the centromedial group that is a derivative of the subpallium and part of the extended amygdala. The remainder of the extended amygdala is not described herein. Within the amygdaloid body of the tree pangolin, we identified the basolateral group (composed of the lateral, basal, and accessory basal amygdaloid nuclei), the superficial, or cortical nuclei (the anterior and posterior cortical nuclei, the periamygdaloid cortex, and nuclei of the olfactory tract), the centromedial group (the central amygdaloid nucleus and the medial nuclear cluster), and other amygdaloid nuclei (the anterior amygdaloid area, the amygdalohippocampal area, the intramedullary group, and intercalated islands). The location within and relative to each other within the amygdaloid body and the internal subdivisions of these groups were very similar to that reported in other mammalian species, with no clearly derived features specific to the tree pangolin. The only variation was the lack of an insular appearance of the intercalated islands, which in the tree pangolin were observed as a continuous band of neurons located dorsomedial to the basolateral group similar in appearance to and almost continuous with the intramedullary group. In carnivores, the closest relatives of the pangolins, and laboratory rats, a similar appearance of portions of the intercalated islands has been noted.

Identification of two distinct neuronal subpopulations encoding parenting and aggressive behaviors toward pups in the population of amygdalohippocampal area neurons projecting to the medial preoptic area using projection-specific and activity-dependent labelling

Identification of two distinct neuronal subpopulations encoding parenting and aggressive behaviors toward pups in the population of amygdalohippocampal area neurons projecting to the medial preoptic area using projection-specific and activity-dependent labelling

Estrogen signaling modulates behavioral selection toward pups and amygdalohippocampal area in the rhomboid nucleus of the bed nucleus of the stria terminalis circuit

Gonadal steroid hormone influences behavioral choice of adult animals toward pups, parental or aggressive. We previously reported that long-term administration of 17β-estradiol (E2) to male mice during sexual maturation induces aggressive behavior toward conspecific pups, which is called “infanticide,” and significantly enhanced excitatory synaptic transmission in the rhomboid nucleus of bed nucleus of the stria terminalis (BSTrh), which is an important brain region for infanticide. However, it is unclear how estrogen receptor–dependent signaling after sexual maturity regulates neural circuits including the BSTrh. Here we revealed that E2 administration to gonadectomized mice in adulthood elicited infanticidal behavior and enhanced excitatory synaptic transmission in the BSTrh by increasing the probability of glutamate release from the presynaptic terminalis. Next, we performed whole-brain mapping of E2-sensitive brain regions projecting to the BSTrh and found that amygdalohippocampal area (AHi) neurons that project to the BSTrh densely express estrogen receptor 1 (Esr1). Moreover, E2 treatment enhanced synaptic connectivity in the AHi-BSTrh pathway. Together, these results suggest that reinforcement of excitatory inputs from AHi neurons into the BSTrh by estrogen receptor–dependent signaling may contribute to the expression of infanticide.

The amygdalohippocampal area that projects to the medial preoptic area mediates aggression toward the infant

The amygdalohippocampal area that projects to the medial preoptic area mediates aggression toward the infant

Distribution and morphology of calbindin neurons in the Amygdaloid Complex of the marmoset monkey (callithrix jacchus)

The location and distribution of the calcium-binding protein calbindin-D28k (CB) has been considered to be of great value as a neuronal marker for identifying distinct brain regions and discrete neuronal populations. In the amygdaloid complex (AC), the balance of excitatory and inhibitory inputs is controlled by CB immunoreactive interneurons. Alterations of inhibitory mechanisms in the AC may play a role in the emotional symptomatology of neurological diseases like Alzheimer's and psychiatric disorders like posttraumatic stress disorder. The present investigation examined the distribution and morphology of CB-containing neurons, neuropils and fibers in marmoset monkey ACs by using immunohistochemical and morphometrical methods. We recognized four types of CB cells in the AC: type 1 (multipolar), type 2 (spherical or bipolar), type 3 (pyramidal) and type 4 (halo cells), a cell type specific to the marmoset located in the basal and central nuclei. We detected CB cells in all nuclei and areas of the AC, where most of the cells were present in the deep nuclei (lateral, basal, accessory basal and paralaminar). In the superficial nuclei (the nucleus of the lateral olfactory tract, medial nucleus, periamygdaloid cortex and cortical nuclei), the CB cells were abundant in layers 2 and 3. The intercalated nuclei contained small densely packed cells. The CB neuropils were particularly dense in layer 1 of the superficial nuclei, in the deep nuclei and in the amygdalohippocampal area. Large CB immunoreactive neurons in the white matter and fibers with varicosities were found in the myelin tracts that surrounded the AC. These findings are the first step in determining whether some of these cells are specifically disrupted in pathological states.

Experience-dependent plasticity in an innate social behavior is mediated by hypothalamic LTP

All animals can perform certain survival behaviors without prior experience, suggesting a "hard wiring" of underlying neural circuits. Experience, however, can alter the expression of innate behaviors. Where in the brain and how such plasticity occurs remains largely unknown. Previous studies have established the phenomenon of "aggression training," in which the repeated experience of winning successive aggressive encounters across multiple days leads to increased aggressiveness. Here, we show that this procedure also leads to long-term potentiation (LTP) at an excitatory synapse, derived from the posteromedial part of the amygdalohippocampal area (AHiPM), onto estrogen receptor 1-expressing (Esr1+) neurons in the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl). We demonstrate further that the optogenetic induction of such LTP in vivo facilitates, while optogenetic long-term depression (LTD) diminishes, the behavioral effect of aggression training, implying a causal role for potentiation at AHiPM→VMHvlEsr1 synapses in mediating the effect of this training. Interestingly, ∼25% of inbred C57BL/6 mice fail to respond to aggression training. We show that these individual differences are correlated both with lower levels of testosterone, relative to mice that respond to such training, and with a failure to exhibit LTP after aggression training. Administration of exogenous testosterone to such nonaggressive mice restores both behavioral and physiological plasticity. Together, these findings reveal that LTP at a hypothalamic circuit node mediates a form of experience-dependent plasticity in an innate social behavior, and a potential hormone-dependent basis for individual differences in such plasticity among genetically identical mice.

SUN-253 PROKR2 Neurons of the Amygdalohippocampal Area in Reproductive Function

Kallmann Syndrome (KS) is characterized by infertility and anosmia due to deficiency in gonadotropin releasing hormone (GnRH) neuronal migration and olfactory bulb dysgenesis. Genetic studies have revealed that KS is caused by loss-of-function mutations in several genes including the prokineticin receptor 2 (PROKR2) gene (Abreu et al., 2008, Hardelin & Dode 2008). Mice with global deletion of Prokr2 replicate the phenotype of KS patients (Ng et al., 2005, Matsumoto et al., 2006). Whereas the role of PROKR2 during development is defined, little is known about PROKR2 neurons in adult reproduction. PROKR2 mRNA are highly expressed in reproductive control sites of the adult mouse brain (Cheng et al., 2006). Previous studies in our lab found PROKR2 mRNA and Prokr2-Cre GFP+ cells highly expressed in the amygdalohippocampal area (AHi, also called posterior nucleus of the amygdala) in a sexually-dimorphic pattern. Male mice have higher PROKR2 expression in the AHi compared to female mice (Mohsen et al., 2017). The amygdala is an important site of socio-sexual inputs and reproductive neuroendocrine responses in rodents and primates, including humans. We hypothesize Prokr2-Cre neurons in the AHi have a role in both male and female reproductive function. Using genetic tracing techniques, we mapped AHi Prokr2-Cre neuronal projections in both male and female mice and found dense innervation to reproductive control sites such as the medial preoptic area and the ventral premammillary nucleus in a sexually dimorphic pattern. A soiled bedding exposure test in sexually experienced male mice showed that an estimated 45% of cFos + cells in the AHi express Prokr2-Cre GFP. Dense sex steroid receptors expression was observed in AHi Prokr2-Cre GFP neurons of both male and female mice. Our preliminary data suggests AHi Prokr2-Cre neurons have a reproductive function in male and potentially also in female mice. Future studies will focus on selective activation and inhibition of these neurons using chemogenetic technology to determine putative inputs to brain sites that control the hypothalamo-pituitary-gonadal axis. We expect our studies will contribute to the understanding of the role of PROKR2 neurons in adult reproduction and reproductive deficits associated with PROKR2 mutations.

Amygdalohippocampal Area Neurons That Project to the Preoptic Area Mediate Infant-Directed Attack in Male Mice.

Male animals may show alternative behaviors toward infants: attack or parenting. These behaviors are triggered by pup stimuli under the influence of the internal state, including the hormonal environment and/or social experiences. Converging data suggest that the medial preoptic area (MPOA) contributes to the behavioral selection toward the pup. However, the neural mechanisms underlying how integrated stimuli affect the MPOA-dependent behavioral selection remain unclear. Here we focus on the amygdalohippocampal area (AHi) that projects to MPOA and expresses oxytocin receptor, a hormone receptor mediating social behavior toward pups. We describe the activation of MPOA-projection AHi neurons in male mice by social contact with pups. Input mapping using the TRIO method reveals that MPOA-projection AHi neurons receive prominent inputs from several regions, including the thalamus, hypothalamus, and olfactory cortex. Electrophysiological and histologic analysis demonstrates that oxytocin modulates inhibitory synaptic responses on MPOA-projection AHi neurons. In addition, AHi forms the excitatory monosynapse to MPOA, and pharmacological activation of MPOA-projection AHi neurons enhances only aggressive behavior, but not parental behavior. Interestingly, this promoted behavior was related to social experience in male mice. Collectively, our results identified a presynaptic partner of MPOA that can integrate sensory input and hormonal state, and trigger pup-directed aggression.SIGNIFICANCE STATEMENT The medial preoptic area (MPOA) plays critical roles in parental behavior, such as motor control, motivation, and social interaction. The MPOA projects to multiple brain regions, and these projections contribute to several neural controls in parental behavior. In contrast, how inputs to MPOA are regulated by social and environmental information is poorly understood. In this study, we focus on the amygdalohippocampal area (AHi) that connects to MPOA and expresses oxytocin receptor. We demonstrate the disruption of the expression of parental behavior triggered by the activation of MPOA-projection AHi neurons. This behavior may be regulated not only by oxytocin but also by neural input from several regions.

Intrinsic functional connectivity of the central extended amygdala.

The central extended amygdala (EAc)-including the bed nucleus of the stria terminalis (BST) and central nucleus of the amygdala (Ce)-plays a critical role in triggering fear and anxiety and is implicated in the development of a range of debilitating neuropsychiatric disorders. Although it is widely believed that these disorders reflect the coordinated activity of distributed neural circuits, the functional architecture of the EAc network and the degree to which the BST and the Ce show distinct patterns of functional connectivity is unclear. Here, we used a novel combination of imaging approaches to trace the connectivity of the BST and the Ce in 130 healthy, racially diverse, community-dwelling adults. Multiband imaging, high-precision registration techniques, and spatially unsmoothed data maximized anatomical specificity. Using newly developed seed regions, whole-brain regression analyses revealed robust functional connectivity between the BST and Ce via the sublenticular extended amygdala, the ribbon of subcortical gray matter encompassing the ventral amygdalofugal pathway. Both regions displayed coupling with the ventromedial prefrontal cortex (vmPFC), midcingulate cortex (MCC), insula, and anterior hippocampus. The BST showed stronger connectivity with the thalamus, striatum, periaqueductal gray, and several prefrontal territories. The only regions showing stronger functional connectivity with the Ce were neighboring regions of the dorsal amygdala, amygdalohippocampal area, and anterior hippocampus. These observations provide a baseline against which to compare a range of special populations, inform our understanding of the role of the EAc in normal and pathological fear and anxiety, and showcase image registration techniques that are likely to be useful for researchers working with "deidentified" neuroimaging data.

Nuclear organization of the African elephant (Loxodonta africana) amygdaloid complex: an unusual mammalian amygdala.

Here we describe the nuclear organization of the African elephant amygdaloid complex using Nissl, myelin, and a range of immunohistochemical stains. The African elephant is thought to exhibit many affect-laden and social-empathic behaviours; however, to date the amygdaloid complex, which is the generator of emotional states of the brain is yet to be fully explored in the elephants. For the most part, the amygdaloid complex of the African elephant is similar to that observed in other mammals in terms of the presence of nuclei and their topological relationships; however, we did observe several specific differences in amygdaloid organization. The elephant amygdala has undergone rotation in both the coronal and sagittal planes, seemingly associated with the expansion of the temporal lobe. Numerous scalloped cell clusters, termed glomeruli, forming the intermediate nuclei of the basal, accessory basal and central nuclear groups, were occupied by structures immunopositive to doublecortin. The nuclei typically associated with the accessory olfactory system (posterior cortical nucleus and medial nuclear complex) were absent from the elephant amygdala. The anterior cortical nucleus is very large and appears to be comprised of two subdivisions. The lateral nuclear complex is expanded and has two novel subdivisions. The amygdalohippocampal area appears relatively enlarged. The numerous shared and derived characters make the elephant amygdaloid complex very unusual and unique amongst mammals, but the derived characters appear to relate to observed elephant affect-laden behaviours.

Sexually dimorphic distribution of Prokr2 neurons revealed by the Prokr2-Cre mouse model.

Prokineticin receptor 2 (PROKR2) is predominantly expressed in the mammalian central nervous system. Loss-of-function mutations of PROKR2 in humans are associated with Kallmann syndrome due to the disruption of gonadotropin releasing hormone neuronal migration and deficient olfactory bulb morphogenesis. PROKR2 has been also implicated in the neuroendocrine control of GnRH neurons post-migration and other physiological systems. However, the brain circuitry and mechanisms associated with these actions have been difficult to investigate mainly due to the widespread distribution of Prokr2-expressing cells, and the lack of animal models and molecular tools. Here, we describe the generation, validation and characterization of a new mouse model that expresses Cre recombinase driven by the Prokr2 promoter, using CRISPR-Cas9 technology. Cre expression was visualized using reporter genes, tdTomato and GFP, in males and females. Expression of Cre-induced reporter genes was found in brain sites previously described to express Prokr2, e.g., the paraventricular and the suprachiasmatic nuclei, and the area postrema. The Prokr2-Cre mouse model was further validated by colocalization of Cre-induced GFP and Prokr2 mRNA. No disruption of Prokr2 expression, GnRH neuronal migration or fertility was observed. Comparative analysis of Prokr2-Cre expression in male and female brains revealed a sexually dimorphic distribution confirmed by in situ hybridization. In females, higher Cre activity was found in the medial preoptic area, ventromedial nucleus of the hypothalamus, arcuate nucleus, medial amygdala and lateral parabrachial nucleus. In males, Cre was higher in the amygdalo-hippocampal area. The sexually dimorphic pattern of Prokr2 expression indicates differential roles in reproductive function and, potentially, in other physiological systems.

A Role for Phosphodiesterase 11A (PDE11A) in the Formation of Social Memories and the Stabilization of Mood.

The most recently discovered 3',5'-cyclic nucleotide phosphodiesterase family is the Phosphodiesterase 11 (PDE11) family, which is encoded by a single gene PDE11A. PDE11A is a dual-specific PDE, breaking down both cAMP and cGMP. There are four PDE11A splice variants (PDE11A1-4) with distinct tissue expression profiles and unique N-terminal regulatory regions, suggesting that each isoform could be individually targeted with a small molecule or biologic. PDE11A4 is the PDE11A isoform expressed in brain and is found in the hippocampal formation of humans and rodents. Studies in rodents show that PDE11A4 mRNA expression in brain is, in fact, restricted to the hippocampal formation (CA1, possibly CA2, subiculum, and the adjacently connected amygdalohippocampal area). Within the hippocampal formation of rodents, PDE11A4 protein is expressed in neurons but not astrocytes, with a distribution across nuclear, cytoplasmic, and membrane compartments. This subcellular localization of PDE11A4 is altered in response to social experience in mouse, and in vitro studies show the compartmentalization of PDE11A4 is controlled, at least in part, by homodimerization and N-terminal phosphorylation. PDE11A4 expression dramatically increases in the hippocampus with age in the rodent hippocampus, from early postnatal life to late aging, suggesting PDE11A4 function may evolve across the lifespan. Interestingly, PDE11A4 protein shows a three to tenfold enrichment in the rodent ventral hippocampal formation (VHIPP; a.k.a. anterior in primates) versus dorsal hippocampal formation (DHIPP). Consistent with this enrichment in VHIPP, studies in knockout mice show that PDE11A regulates the formation of social memories and the stabilization of mood and is a critical mechanism by which social experience feeds back to modify the brain and subsequent social behaviors. PDE11A4 likely controls behavior by regulating hippocampal glutamatergic, oxytocin, and cytokine signaling, as well as protein translation. Given its unique tissue distribution and relatively selective effects on behavior, PDE11A may represent a novel therapeutic target for neuropsychiatric, neurodevelopmental, or age-related disorders. Therapeutically targeting PDE11A4 may be a way to selectively restore aberrant cyclic nucleotide signaling in the hippocampal formation while leaving the rest of the brain and periphery untouched, thus, relieving deficits while avoiding unwanted side effects.

Brain-wide map of projections from mice ventral subiculum

The hippocampal formation plays a critical role in episodic memory formation and spatial navigation. Within the hippocampus, the subiculum is considered to be a hub connecting the hippocampal formation to the remainder of the brain. There are functional differences between the dorsal and ventral part of subiculum, while the ventral subiculum (vSub) plays a role in anxiety, stress and emotion. In the present study, we examined the projection of the ventral subiculum to the whole brain in mice by using a modified herpes simplex virus 1 strain H129 with an inserted fluorescent protein gene. In our experiments, the modified H129 transits the primary-order, second-order, and third-order neuronal projections at 36–44, 52–60 and 68–76h after inoculation in mice, respectively. Our data revealed that vSub directly projects to the medial entorhinal cortex, amygdalohippocampal area, anterodorsal thalamic nucleus, medial hypothalamus, supramammillary nucleus, medial septal nucleus and adjacent diagonal band, the connections between median raphe nucleus and interpeduncular nucleus in brain stem, while ventral prefrontal cortex, laterodorsal tegmental nucleus and locus coeruleus receives second-order projections from vSub. Our data would help further understanding the functional connections of vSub with other brain regions.

Afferent projections to the different medial amygdala subdivisions: a retrograde tracing study in the mouse.

The medial amygdaloid nucleus (Me) is a key node in the socio-sexual brain, composed of anterior (MeA), posteroventral (MePV) and posterodorsal (MePD) subdivisions. These subdivisions have been suggested to play a different role in reproductive and defensive behaviours. In the present work we analyse the afferents of the three Me subdivisions using restricted injections of fluorogold in female outbred CD1 mice. The results reveal that the MeA, MePV and MePD share a common pattern of afferents, with some differences in the density of retrograde labelling in several nuclei. Common afferents to Me subdivisions include: the accessory olfactory bulbs, piriform cortex and endopiriform nucleus, chemosensory amygdala (receiving direct inputs from the olfactory bulbs), posterior part of the medial bed nucleus of the stria terminalis (BSTM), CA1 in the ventral hippocampus and posterior intralaminar thalamus. Minor projections originate from the basolateral amygdala and amygdalo-hippocampal area, septum, ventral striatum, several allocortical and periallocortical areas, claustrum, several hypothalamic structures, raphe and parabrachial complex. MeA and MePV share minor inputs from the frontal cortex (medial orbital, prelimbic, infralimbic and dorsal peduncular cortices), but differ in the lack of main olfactory projections to the MePV. By contrast, the MePD receives preferential projections from the rostral accessory olfactory bulb, the posteromedial BSTM and the ventral premammillary nucleus. In summary, the common pattern of afferents to the Me subdivisions and their interconnections suggest that they play cooperative instead of differential roles in the various behaviours (e.g., sociosexual, defensive) in which the Me has been shown to be involved.

Sex-specific expression of estrogen receptors α and β and Kiss1 in the postnatal rat amygdala.

The rodent amygdaloid complex is composed of numerous subnuclei important for the sex-specific regulation of sociosexual behavior. Although estrogen receptors (ERs) are critical for organizing functional and cytoarchitectural sex differences in these subnuclei, a detailed developmental profile of ER expression in the amygdaloid complex is not available. Moreover, the kisspeptin gene (Kiss1) was recently identified in the adult amygdala, but it remains unknown if it is expressed during development. To fill these data gaps, rat brains (5-7/group) were assessed on postnatal days (PNDs) 0, 2, 4, 7, and 19 for ER alpha (ERα; Esr1), beta (ERβ; Esr2), and Kiss1 expression using in situ hybridization. Expression was quantified in the posterodorsal portion of the medial amygdala posterodorsal (MePD), lateral (PLCo), and medial (PMCo) components of the posterior cortical nucleus, and the amygdalohippocampal area (AHi). ERα expression was high throughout the amygdala at birth, but sexually dimorphic only in the AHi. ERα expression in the MePD and the PLCo showed a U-shaped expression pattern over time. In the PMCo, ERα expression decreased from PND 2 and remained low through PND 19. Sexually dimorphic expression of ERβ in the MePD was observed on PND 0, with higher levels in females, but reversed by PND 4 due to declining levels in females. No Kiss1 signal was observed in the postnatal amygdala, suggesting that expression arises after puberty. These data reveal that ER expression is region-specific within the neonatal amygdala. These differences likely contribute to sex differences in sociosexual behavior across the lifespan.

Revisiting the hippocampal–amygdala pathway in primates: Association with immature-appearing neurons

Elucidation of the ‘fear circuit’ has opened exciting avenues for understanding and treating human anxiety disorders. However, the translation of rodent to human studies, and vice versa, depends on understanding the homology in relevant circuits across species. Although abundant evidence indicates that the hippocampal–amygdala circuit mediates contextual fear learning, previous studies indicate that this pathway is more restricted in primates than in rodents. Moreover, cellular components of the amygdala differ across species. The paralaminar nucleus (PL) of the amygdala, a structure that is closely associated with the basal nucleus, is one example, having no clear homologue in rodents. In both human and nonhuman primates, the PL contains a subpopulation of immature-appearing neurons, which merge into the corticoamygdaloid transition area (CTA). To understand whether immature-appearing neurons are positioned to participate in fear circuitry, we first mapped the hippocampal–amygdala projection in the monkey. We then determined whether immature-appearing neurons were targets of this path. Retrograde results show that the hippocampal inputs to the amygdala originate in uncal region (CA1′) and the rostral prosubiculum, consistent with earlier studies. The amygdalohippocampal area, ventral basal nucleus, the medial paralaminar nucleus, and its confluence with the CTA are the main targets of this projection. Immature neurons are prominent in the PL and CTA, and are overlapped by anterogradely labeled fibers from CA1′, particularly in the medial PL and CTA. Hippocampal inputs to the amygdala are more focused in higher primates compared to rodents, supporting previous anatomic studies and recent data from human functional imaging studies of contextual fear. At the cellular level, a hippocampal interaction with immature neurons in the amygdala suggests a novel substrate for cellular plasticity, with implications for mechanisms underlying contextual learning and emotional memory processes.

Activation of PDE10 and PDE11 Phosphodiesterases

The most recently identified cyclic nucleotide phosphodiesterases, PDE10 and PDE11, contain a tandem of so-called GAF domains in their N-terminal regulatory regions. In PDE2 and PDE5, the GAF domains mediate cGMP stimulation; however, their function in PDE10 and PDE11 remains controversial. Although the GAF domains of PDE10 mediate cAMP-induced stimulation of chimeric adenylyl cyclases, cAMP binding did not stimulate the PDE10 holoenzyme. Comparable data about cGMP and the PDE11 GAF domains exist. Here, we identified synthetic ligands for the GAF domains of PDE10 and PDE11 to reduce interference of the GAF ligand with the catalytic reaction of PDE. With these ligands, GAF-mediated stimulation of the PDE10 and PDE11 holoenzymes is demonstrated for the first time. Furthermore, PDE10 is shown to be activated by cAMP, which paradoxically results in potent competitive inhibition of cGMP turnover by cAMP. PDE11, albeit susceptible to GAF-dependent stimulation, is not activated by the native cyclic nucleotides cAMP and cGMP. In summary, PDE11 can be stimulated by GAF domain ligands, but its native ligand remains to be identified, and PDE10 is the only PDE activated by cAMP.