Motherhood-induced gene expression in the mouse medial amygdala: Changes induced by pregnancy and lactation but not by pup stimuli.

During lactation, adult female mice display aggressive responses toward male intruders, triggered by male-derived chemosensory signals. This aggressive behavior is not shown by pup-sensitized virgin females sharing pup care with dams. The genetic mechanisms underlying the switch from attraction to aggression are unknown. In this work, we investigate the differential gene expression in lactating females expressing maternal aggression compared to pup-sensitized virgin females in the medial amygdala (Me), a key neural structure integrating chemosensory and hormonal information. The results showed 197 genes upregulated in dams, including genes encoding hormones such as prolactin, growth hormone, or follicle-stimulating hormone, neuropeptides such as galanin, oxytocin, and pro-opiomelanocortin, and genes related to catecholaminergic and cholinergic neurotransmission. In contrast, 99 genes were downregulated in dams, among which we find those encoding for inhibins and transcription factors of the Fos and early growth response families. The gene set analysis revealed numerous Gene Ontology functional groups with higher expression in dams than in pup-sensitized virgin females, including those related with the regulation of the Jak/Stat cascade. Of note, a number of olfactory and vomeronasal receptor genes was expressed in the Me, although without differences between dams and virgins. For prolactin and growth hormone, a qPCR experiment comparing dams, pup-sensitized, and pup-naïve virgin females showed that dams expressed higher levels of both hormones than pup-naïve virgins, with pup-sensitized virgins showing intermediate levels. Altogether, the results show important gene expression changes in the Me, which may underlie some of the behavioral responses characterizing maternal behavior.

Toward a unified analysis of cerebellum maturation and aging across the entire lifespan: A MRI analysis.

Previous literature about the structural characterization of the human cerebellum is related to the context of a specific pathology or focused in a restricted age range. In fact, studies about the cerebellum maturation across the lifespan are scarce and most of them considered the cerebellum as a whole without investigating each lobule. This lack of study can be explained by the lack of both accurate segmentation methods and data availability. Fortunately, during the last years, several cerebellum segmentation methods have been developed and many databases comprising subjects of different ages have been made publically available. This fact opens an opportunity window to obtain a more extensive analysis of the cerebellum maturation and aging. In this study, we have used a recent state-of-the-art cerebellum segmentation method called CERES and a large data set (N = 2,831 images) from healthy controls covering the entire lifespan to provide a model for 12 cerebellum structures (i.e., lobules I-II, III, IV, VI, Crus I, Crus II, VIIB, VIIIA, VIIIB, IX, and X). We found that lobules have generally an evolution that follows a trajectory composed by a fast growth and a slow degeneration having sometimes a plateau for absolute volumes, and a decreasing tendency (faster in early ages) for normalized volumes. Special consideration is dedicated to Crus II, where slow degeneration appears to stabilize in elder ages for absolute volumes, and to lobule X, which does not present any fast growth during childhood in absolute volumes and shows a slow growth for normalized volumes.

Maternal Motivation: Exploring the Roles of Prolactin and Pup Stimuli.

Motherhood entails increased motivation for pups, which become strong reinforcers and guide maternal behaviours. This depends on steroids and lactogens acting on the brain of females during pregnancy and postpartum. Since virgin female mice exposed to pups are nearly spontaneously maternal, the specific roles of endocrine and pup-derived signals in the induction of maternal motivation remain unclear. This work investigates maternal motivation in dams and virgin female mice, using a novel variant of the pup retrieval paradigm, the motivated pup retrieval test. We also analyse the role of prolactin (PRL) and of stimuli derived from a litter of pups and its mother, in the acquisition of maternal motivation. Experimental design included female mice in 3 conditions: lactating dams, comothers (virgins housed and sharing pup care with dams) and pup-naïve virgins. Females underwent 3 motivated-pup-retrieval trials, with pups displaced behind a 10-cm-high wire-mesh barrier. Dams retrieved with significantly lower latencies than comothers or virgins, indicating that full maternal motivation appears only after pregnancy. Although initially comothers and virgins showed no retrieval, comothers significantly improved throughout the experiment, suggesting an induced sensitization process. Lengthening exposure of comothers to the dyad pups-dam (from 2 to 5 days at the beginning of testing) had no strong effects on maternal sensitization. PRL responsiveness was analysed in these animals using immunohistochemical detection of phosphorylated signal transducer and activator of transcription 5 (pSTAT5, PRL-derived signalling marker). As expected, dams showed significantly higher pSTAT5 expression in most of the analysed nuclei. Moreover, comothers displayed significantly higher PRL responsiveness than pup-naïve virgins in the medial preoptic nucleus, even if they display similar circulating PRL levels, which are significantly lower than those of dams. Given the instrumental role of this nucleus in the relay and integration of pup-derived stimuli to facilitate proactive maternal responses, this increase in PRL responsiveness likely reflects the mechanism underlying the maternal sensitization process reported in this work. Since the analyses of maternal motivation and PRL signalling in the brain were performed in the same animals, we were able to explore correlation between both set of data. The results shed light on the neuroendocrine mechanisms underlying maternal motivation and other aspects of maternal behaviour.

Towards a unified analysis of brain maturation and aging across the entire lifespan: A MRI analysis.

There is no consensus in literature about lifespan brain maturation and senescence, mainly because previous lifespan studies have been performed on restricted age periods and/or with a limited number of scans, making results instable and their comparison very difficult. Moreover, the use of nonharmonized tools and different volumetric measurements lead to a great discrepancy in reported results. Thanks to the new paradigm of BigData sharing in neuroimaging and the last advances in image processing enabling to process baby as well as elderly scans with the same tool, new insights on brain maturation and aging can be obtained. This study presents brain volume trajectory over the entire lifespan using the largest age range to date (from few months of life to elderly) and one of the largest number of subjects (N = 2,944). First, we found that white matter trajectory based on absolute and normalized volumes follows an inverted U-shape with a maturation peak around middle life. Second, we found that from 1 to 8-10 y there is an absolute gray matter (GM) increase related to body growth followed by a GM decrease. However, when normalized volumes were considered, GM continuously decreases all along the life. Finally, we found that this observation holds for almost all the considered subcortical structures except for amygdala which is rather stable and hippocampus which exhibits an inverted U-shape with a longer maturation period. By revealing the entire brain trajectory picture, a consensus can be drawn since most of the previously discussed discrepancies can be explained. Hum Brain Mapp 38:5501-5518, 2017. © 2017 Wiley Periodicals, Inc.

From sexual attraction to maternal aggression: when pheromones change their behavioural significance.

This article is part of a Special Issue "Chemosignals and Reproduction". This paper reviews the role of chemosignals in the socio-sexual interactions of female mice, and reports two experiments testing the role of pup-derived chemosignals and the male sexual pheromone darcin in inducing and promoting maternal aggression. Female mice are attracted to urine-borne male pheromones. Volatile and non-volatile urine fractions have been proposed to contain olfactory and vomeronasal pheromones. In particular, the male-specific major urinary protein (MUP) MUP20, darcin, has been shown to be rewarding and attractive to females. Non-urinary male chemosignals, such as the lacrimal protein ESP1, promote lordosis in female mice, but its attractive properties are still to be tested. There is evidence indicating that ESP1 and MUPs are detected by vomeronasal type 2 receptors (V2R). When a female mouse becomes pregnant, she undergoes dramatic changes in her physiology and behaviour. She builds a nest for her pups and takes care of them. Dams also defend the nest against conspecific intruders, attacking especially gonadally intact males. Maternal behaviour is dependent on a functional olfactory system, thus suggesting a role of chemosignals in the development of maternal behaviour. Our first experiment demonstrates, however, that pup chemosignals are not sufficient to induce maternal aggression in virgin females. In addition, it is known that vomeronasal stimuli are needed for maternal aggression. Since MUPs (and other molecules) are able to promote intermale aggression, in our second experiment we test if the attractive MUP darcin also promotes attacks on castrated male intruders by lactating dams. Our findings demonstrate that the same chemosignal, darcin, promotes attraction or aggression according to female reproductive state.

The vomeronasal cortex - afferent and efferent projections of the posteromedial cortical nucleus of the amygdala in mice.

Most mammals possess a vomeronasal system that detects predominantly chemical signals of biological relevance. Vomeronasal information is relayed to the accessory olfactory bulb (AOB), whose unique cortical target is the posteromedial cortical nucleus of the amygdala. This cortical structure should therefore be considered the primary vomeronasal cortex. In the present work, we describe the afferent and efferent connections of the posteromedial cortical nucleus of the amygdala in female mice, using anterograde (biotinylated dextranamines) and retrograde (Fluorogold) tracers, and zinc selenite as a tracer specific for zinc-enriched (putative glutamatergic) projections. The results show that the posteromedial cortical nucleus of the amygdala is strongly interconnected not only with the rest of the vomeronasal system (AOB and its target structures in the amygdala), but also with the olfactory system (piriform cortex, olfactory-recipient nuclei of the amygdala and entorhinal cortex). Therefore, the posteromedial cortical nucleus of the amygdala probably integrates olfactory and vomeronasal information. In addition, the posteromedial cortical nucleus of the amygdala shows moderate interconnections with the associative (basomedial) amygdala and with the ventral hippocampus, which may be involved in emotional and spatial learning (respectively) induced by chemical signals. Finally, the posteromedial cortical nucleus of the amygdala gives rise to zinc-enriched projections to the ventrolateral septum and the ventromedial striatum (including the medial islands of Calleja). This pattern of intracortical connections (with the olfactory cortex and hippocampus, mainly) and cortico-striatal excitatory projections (with the olfactory tubercle and septum) is consistent with its proposed nature as the primary vomeronasal cortex.

Inhibition of the medial amygdala disrupts escalated aggression in lactating female mice after repeated exposure to male intruders.

Virgin female laboratory mice readily express pup care when co-housed with dams and pups. However, pup-sensitized virgins fail to express intruder-directed aggression on a single session of testing. To study whether repeated testing would affect the onset and dynamics of maternal or intruder-directed aggression, we tested dams and their accompanying virgins from postpartum day 4 to 6. Repeated testing led to escalated aggression towards male intruders in dams, but virgins never developed aggression. In dams, inhibition of the medial amygdala using DREADD (designer receptors exclusively activated by designer drugs) vectors carrying the hM4Di receptor blocked the expected increase in maternal aggression on the second testing day. Our data support that the onset of maternal aggression is linked to physiological changes occurring during motherhood, and that medial amygdala, a key centre integrating vomeronasal, olfactory and hormonal information, enables the expression of escalated aggression induced by repeated testing. Future studies selectively targeting specific neuronal populations of the medial amygdala are needed to allow a deeper understanding of the control of experience-dependent aggression increase, a phenomenon leading to the high aggression levels found in violent behaviours.

Structural progression of Alzheimer's disease over decades: the MRI staging scheme.

The chronological progression of brain atrophy over decades, from pre-symptomatic to dementia stages, has never been formally depicted in Alzheimer's disease. This is mainly due to the lack of cohorts with long enough MRI follow-ups in cognitively unimpaired young participants at baseline. To describe a spatiotemporal atrophy staging of Alzheimer's disease at the whole-brain level, we built extrapolated lifetime volumetric models of healthy and Alzheimer's disease brain structures by combining multiple large-scale databases (n = 3512 quality controlled MRI from 9 cohorts of subjects covering the entire lifespan, including 415 MRI from ADNI1, ADNI2 and AIBL for Alzheimer's disease patients). Then, we validated dynamic models based on cross-sectional data using external longitudinal data. Finally, we assessed the sequential divergence between normal aging and Alzheimer's disease volumetric trajectories and described the following staging of brain atrophy progression in Alzheimer's disease: (i) hippocampus and amygdala; (ii) middle temporal gyrus; (iii) entorhinal cortex, parahippocampal cortex and other temporal areas; (iv) striatum and thalamus and (v) middle frontal, cingular, parietal, insular cortices and pallidum. We concluded that this MRI scheme of atrophy progression in Alzheimer's disease was close but did not entirely overlap with Braak staging of tauopathy, with a 'reverse chronology' between limbic and entorhinal stages. Alzheimer's disease structural progression may be associated with local tau accumulation but may also be related to axonal degeneration in remote sites and other limbic-predominant associated proteinopathies.

Early life stress exacerbates behavioural and neuronal alterations in adolescent male mice lacking methyl-CpG binding protein 2 (Mecp2).

The methyl-CpG binding protein 2 gene (MECP2) encodes an epigenetic transcriptional regulator implicated in neuronal plasticity. Loss-of-function mutations in this gene are the primary cause of Rett syndrome and, to a lesser degree, of other neurodevelopmental disorders. Recently, we demonstrated that both Mecp2 haploinsuficiency and mild early life stress decrease anxiety-like behaviours and neuronal activation in brain areas controlling these responses in adolescent female mice. Here, we extend this work to males by using Mecp2-null and wild type adolescent mice subjected to maternal separation and their non-stressed controls. We assessed their behavioural responses in a battery of anxiety-provoking tests. Upon exposure to an elevated plus maze in aversive conditions, we evaluated changes in c-FOS expression in stress- and anxiety-related brain regions. In addition, we assessed the impact of maternal separation in neuronal maturation using doublecortin and reelin as surrogate markers. Mutant males showed reduced motor abilities, increased activation of the olfactory bulbs, probably due to breathing abnormalities, and decreased activation of the paraventricular thalamic nucleus, when compared to wild type mice. In addition, maternal separation increased the number of immature doublecortin-like neurons found in Mecp2-null animals. Moreover, this work shows for the first time that reelin is decreased in the mutant animals at the olfactory tubercle, piriform cortex and hippocampal dentate gyrus, an effect also associated to maternal separation. Taken together, our results suggest that maternal separation exacerbates some phenotypical alterations associated with lack of MeCP2 in adolescent males.

Becoming a mother shifts the activity of the social and motivation brain networks in mice.

During pregnancy hormones increase motivated pup-directed behaviors. We here analyze hormone-induced changes in brain activity, by comparing cFos-immunoreactivity in the sociosexual (SBN) and motivation brain networks (including medial preoptic area, MPO) of virgin versus late-pregnant pup-naïve female mice exposed to pups or buttons (control). Pups activate more the SBN than buttons in both late-pregnant and virgin females. By contrast, pregnancy increases pup-elicited activity in the motivation circuitry (e.g. accumbens core) but reduces button-induced activity and, consequently, button investigation. Principal components analysis supports the identity of the social and motivation brain circuits, placing the periaqueductal gray between both systems. Linear discriminant analysis of cFos-immunoreactivity in the socio-motivational brain network predicts the kind of female and stimulus better than the activity of the MPO alone; this suggests that the neuroendocrinological basis of social (e.g. maternal) behaviors conforms to a neural network model, rather than to distinct hierarchical linear pathways for different behaviors.

Neural activity patterns in the chemosensory network encoding vomeronasal and olfactory information in mice.

Rodents detect chemical information mainly through the olfactory and vomeronasal systems, which play complementary roles to orchestrate appropriate behavioral responses. To characterize the integration of chemosensory information, we have performed electrophysiological and c-Fos studies of the bulbo-amygdalar network in freely behaving female mice exploring neutral or conspecific stimuli. We hypothesize that processing conspecifics stimuli requires both chemosensory systems, and thus our results will show shared patterns of activity in olfactory and vomeronasal structures. Were the hypothesis not true, the activity of the vomeronasal structures would be independent of that of the main olfactory system. In the c-Fos analysis, we assessed the activation elicited by neutral olfactory or male stimuli in a broader network. Male urine induced a significantly higher activity in the vomeronasal system compared to that induced by a neutral odorant. Concerning the olfactory system, only the cortex-amygdala transition area showed significant activation. No differential c-Fos expression was found in the reward system and the basolateral amygdala. These functional patterns in the chemosensory circuitry reveal a strong top-down control of the amygdala over both olfactory bulbs, suggesting an active role of the amygdala in the integration of chemosensory information directing the activity of the bulbs during environmental exploration.

Corrigendum: Wired for motherhood: induction of maternal care but not maternal aggression in virgin female CD1 mice.

[This corrects the article DOI: 10.3389/fnbeh.2015.00197.].

Integrating pheromonal and spatial information in the amygdalo-hippocampal network.

Vomeronasal information is critical in mice for territorial behavior. Consequently, learning the territorial spatial structure should incorporate the vomeronasal signals indicating individual identity into the hippocampal cognitive map. In this work we show in mice that navigating a virtual environment induces synchronic activity, with causality in both directionalities, between the vomeronasal amygdala and the dorsal CA1 of the hippocampus in the theta frequency range. The detection of urine stimuli induces synaptic plasticity in the vomeronasal pathway and the dorsal hippocampus, even in animals with experimentally induced anosmia. In the dorsal hippocampus, this plasticity is associated with the overexpression of pAKT and pGSK3ß. An amygdalo-entorhino-hippocampal circuit likely underlies this effect of pheromonal information on hippocampal learning. This circuit likely constitutes the neural substrate of territorial behavior in mice, and it allows the integration of social and spatial information.

pBrain: A novel pipeline for Parkinson related brain structure segmentation.

Parkinson is a very prevalent neurodegenerative disease impacting the life of millions of people worldwide. Although its cause remains unknown, its functional and structural analysis is fundamental to advance in the search of a cure or symptomatic treatment. The automatic segmentation of deep brain structures related to Parkinson`s disease could be beneficial for the follow up and treatment planning. Unfortunately, there is not broadly available segmentation software to automatically measure Parkinson related structures. In this paper, we present a novel pipeline to segment three deep brain structures related to Parkinson's disease (substantia nigra, subthalamic nucleus and red nucleus). The proposed method is based on the multi-atlas label fusion technology that works on standard and high-resolution T2-weighted images. The proposed method also includes as post-processing a new neural network-based error correction step to minimize systematic segmentation errors. The proposed method has been compared to other state-of-the-art methods showing competitive results in terms of accuracy and execution time.

Pregnancy Changes the Response of the Vomeronasal and Olfactory Systems to Pups in Mice.

Motherhood entails changes in behavior with increased motivation for pups, induced in part by pregnancy hormones acting upon the brain. This work explores whether this alters sensory processing of pup-derived chemosignals. To do so, we analyse the expression of immediate early genes (IEGs) in the vomeronasal organ (VNO; Egr1) and centers of the olfactory and vomeronasal brain pathways (cFos) in virgin and late-pregnant females exposed to pups, as compared to buttons (socially neutral control). In pup-exposed females, we quantified diverse behaviors including pup retrieval, sniffing, pup-directed attack, nest building and time in nest or on nest, as well as time off nest. Pups induce Egr1 expression in the VNO of females, irrespective of their physiological condition, thus suggesting the existence of VNO-detected pup chemosignals. A similar situation is found in the accessory olfactory bulb (AOB) and posteromedial part of the medial bed nucleus of the stria terminalis (BSTMPM). By contrast, in the medial amygdala and posteromedial cortical amygdala (PMCo), responses to pups-vs-buttons are different in virgin and late-pregnant females, thus suggesting altered sensory processing during late pregnancy. The olfactory system also shows changes in sensory processing with pregnancy. In the main olfactory bulbs, as well as the anterior and posterior piriform cortex, buttons activate cFos expression in virgins more than in pregnant females. By contrast, in the anterior and especially posterior piriform cortex, pregnant females show more activation by pups than buttons. Correlation between IEGs expression and behavior suggests the existence of two vomeronasal subsystems: one associated to pup care (with PMCo as its main center) and another related to pup-directed aggression observed in some pregnant females (with the BSTMPM as the main nucleus). Our data also suggest a coactivation of the olfactory and vomeronasal systems during interaction with pups in pregnant females.

Male-specific features are reduced in Mecp2-null mice: analyses of vasopressinergic innervation, pheromone production and social behaviour.

Deficits in arginine vasopressin (AVP) and oxytocin (OT), two neuropeptides closely implicated in the modulation of social behaviours, have been reported in some early developmental disorders and autism spectrum disorders. Mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene are associated to Rett syndrome and other neuropsychiatric conditions. Thus, we first analysed AVP and OT expression in the brain of Mecp2-mutant mice by immunohistochemistry. Our results revealed no significant differences in these systems in young adult Mecp2-heterozygous females, as compared to WT littermates. By contrast, we found a significant reduction in the sexually dimorphic, testosterone-dependent, vasopressinergic innervation in several nuclei of the social brain network and oxytocinergic innervation in the lateral habenula of Mecp2-null males, as compared to WT littermates. Analysis of urinary production of pheromones shows that Mecp2-null males lack the testosterone-dependent pheromone darcin, strongly suggesting low levels of androgens in these males. In addition, resident-intruder tests revealed lack of aggressive behaviour in Mecp2-null males and decreased chemoinvestigation of the intruder. By contrast, Mecp2-null males exhibited enhanced social approach, as compared to WT animals, in a 3-chamber social interaction test. In summary, Mecp2-null males, which display internal testicles, display a significant reduction of some male-specific features, such as vasopressinergic innervation within the social brain network, male pheromone production and aggressive behaviour. Thus, atypical social behaviours in Mecp2-null males may be caused, at least in part, by the effect of lack of MeCP2 over sexual differentiation.

Lifespan Changes of the Human Brain In Alzheimer's Disease.

Brain imaging studies have shown that slow and progressive cerebral atrophy characterized the development of Alzheimer's Disease (AD). Despite a large number of studies dedicated to AD, key questions about the lifespan evolution of AD biomarkers remain open. When does the AD model diverge from the normal aging model? What is the lifespan trajectory of imaging biomarkers for AD? How do the trajectories of biomarkers in AD differ from normal aging? To answer these questions, we proposed an innovative way by inferring brain structure model across the entire lifespan using a massive number of MRI (N = 4329). We compared the normal model based on 2944 control subjects with the pathological model based on 3262 patients (AD + Mild cognitive Impaired subjects) older than 55 years and controls younger than 55 years. Our study provides evidences of early divergence of the AD models from the normal aging trajectory before 40 years for the hippocampus, followed by the lateral ventricles and the amygdala around 40 years. Moreover, our lifespan model reveals the evolution of these biomarkers and suggests close abnormality evolution for the hippocampus and the amygdala, whereas trajectory of ventricular enlargement appears to follow an inverted U-shape. Finally, our models indicate that medial temporal lobe atrophy and ventricular enlargement are two mid-life physiopathological events characterizing AD brain.

Lack of MeCP2 leads to region-specific increase of doublecortin in the olfactory system.

The protein doublecortin is mainly expressed in migrating neuroblasts and immature neurons. The X-linked gene MECP2, associated to several neurodevelopmental disorders such as Rett syndrome, encodes the protein methyl-CpG-binding protein 2 (MeCP2), a regulatory protein that has been implicated in neuronal maturation and refinement of olfactory circuits. Here, we explored doublecortin immunoreactivity in the brain of young adult female Mecp2-heterozygous and male Mecp2-null mice and their wild-type littermates. The distribution of doublecortin-immunoreactive somata in neurogenic brain regions was consistent with previous reports in rodents, and no qualitative differences were found between genotypes or sexes. Quantitatively, we found a significant increase in doublecortin cell density in the piriform cortex of Mecp2-null males as compared to WT littermates. A similar increase was seen in a newly identified population of doublecortin cells in the olfactory tubercle. In these olfactory structures, however, the percentage of doublecortin immature neurons that also expressed NeuN was not different between genotypes. By contrast, we found no significant differences between genotypes in doublecortin immunoreactivity in the olfactory bulbs. Nonetheless, in the periglomerular layer of Mecp2-null males, we observed a specific decrease of immature neurons co-expressing doublecortin and NeuN. Overall, no differences were evident between Mecp2-heterozygous and WT females. In addition, no differences could be detected between genotypes in the density of doublecortin-immunoreactive cells in the hippocampus or striatum of either males or females. Our results suggest that MeCP2 is involved in neuronal maturation in a region-dependent manner.

Sex versus sweet: opposite effects of opioid drugs on the reward of sucrose and sexual pheromones.

Endogenous opioids mediate some reward processes involving both natural (food, sweet taste) and artificial (morphine, heroin) rewards. In contrast, sexual behavior (which is also reinforcing) is generally inhibited by opioids. To establish the role of endogenous opioids for a newly described natural reinforcer, namely male sexual pheromones for female mice, we checked the effects of systemic injections of the general opioid antagonist naloxone (1-10 mg/kg) and the agonist fentanyl (0.1- 0.5 mg/kg) in a number of behavioral tests. Naloxone affected neither the innate preference for male-soiled bedding (vs. female-soiled bedding) in 2-choice tests nor the induction of place conditioning using male pheromones as rewarding stimuli, although it effectively blocked the preference for consuming a sucrose solution. In contrast, fentanyl inhibited the preference for male chemosignals without altering sucrose preference. These results suggest that, in macrosmatic animals such as rodents, opioidergic inhibition of sexual behavior might be due, at least partially, to an impaired processing of pheromonal cues and that the hedonic value of sweet-tasting solutions and sexual pheromones are under different opioid modulation.

Two interconnected functional systems in the amygdala of amniote vertebrates.

The amygdala shows ventropallial and lateropallial derivatives that can be compared among vertebrates according to their topological position, either superficial (cortical amygdala) or deep (basolateral amygdala and amygdalo-hippocampal area), connections and histochemical features. On the other hand, the subpallial amygdala, also called extended amygdala, is composed of medial and central divisions. In mammals, both divisions consist of an intra-amygdaloid portion and a part of the bed nucleus of the stria terminalis. In non-mammals, the intratelencephalic trajectory of the stria terminalis is short and both poles of the extended amygdala are close together. Like its mammalian counterpart, the medial extended amygdala of non-mammals receives an olfactory input (reduced in birds), projects to the medial hypothalamus and shows a sexually dimorphic vasotocinergic (vasopressinergic) cell group. Thus, the medial extended amygdala is part of the forebrain circuitry for the expression of defensive and reproductive behaviours. In turn, the central extended amygdala of amniotes shows a prominent CGRP innervation and a medially located CRF/neurotensin-expressing cell group, and projects to the lateral hypothalamus and to the midbrain and brainstem centres involved in fear/anxiety expression. The projections from the pallial amygdala to the central and medial extended amygdala are similarly organized in the mammals and non-mammals. These circuits, which have not changed substantially in birds despite the disappearance of the vomeronasal system, delineate two functional divisions within the amygdala that, together, orchestrate the expression of species-specific behaviours with a strong emotional component.