Structure and function of the vomeronasal system: an update

The limbic system of the brain regulates a number of behaviors that are essential for the survival of all vertebrate species including humans. The limbic system predominantly controls appropriate responses to stimuli with social, emotional or motivational salience, which includes innate behaviors such as mating, aggression and defense. Activation of circuits regulating these innate behaviors begins in the periphery with sensory stimulation (primarily via the olfactory system in rodents), and is then processed in the brain by a set of delineated structures that primarily includes the amygdala and hypothalamus. While the basic neuroanatomy of these connections is well established, much remains unknown about how information is processed within innate circuits and how genetic hierarchies regulate development and function of these circuits. Utilizing innovative technologies including channel rhodopsin-based circuit manipulation and genetic manipulation in rodents, recent studies have begun to answer these central questions. In this article we review the current understanding of how limbic circuits regulate sexually dimorphism and how these circuits are established and shaped during pre- and post-natal development. We also discuss how understanding developmental processes of innate circuit formation may inform behavioral alterations observed in neurodevelopmental disorders, such as autism spectrum disorders, which are characterized by limbic system dysfunction.

/pdf/wired-for-behaviors-from-development-to-function-of-innate-47pte9iilq.pdf

Wired for behaviors: from development to function of innate limbic system circuitry.

Near-term fetuses of different mammalian species, including humans, exhibit functional sensory and learning capabilities The neurobiological literature indicates that the unborn organism processes sensory stimuli present in the amniotic fluid, retains this information for considerable amounts of time, and is also capable of associating such stimuli with biologically relevant events This research has stimulated studies aimed at the analysis of fetal and neonatal learning about ethanol, a topic that constitutes the core of the present review Ethanol has characteristic sensory (olfactory, taste, and trigeminal) attributes and can exert pharmacologic reinforcing effects The studies under examination support the hypothesis that low to moderate levels of maternal ethanol intoxication during late pregnancy set the opportunity for fetal learning about ethanol These levels of prenatal ethanol exposure do not generate evident morphologic or neurobehavioral alterations in the offspring, but they exert a significant impact upon later ethanol-seeking and intake behaviors Supported by preclinical and clinical findings, this review contributes to strengthening the case for the ability of prenatal ethanol exposure to have effects on the postnatal organism

/pdf/fetal-learning-about-ethanol-and-later-ethanol-5fojf288p9.pdf

Fetal Learning About Ethanol and Later Ethanol Responsiveness: Evidence Against "Safe" Amounts of Prenatal Exposure

Resume Les reponses initiales d'orientation et leur developpement precoce sont analysees chez des nouveau-nes exposes simultanement a l'odeur de leur liquide amniotique (AF) et a l'odeur des secretions lactees (L) maternelles. L'orientation relative entre ces deux odeurs est etudiee en fonction de l'âge postnatal (1–5 j) et de l'experience de tetee (0–32 tetees). Avant le troisieme jour, les nouveau-nes ne differencient pas AF de L. Cette reponse indifferenciee est interpretee en termes d'equivalence sensorielle et/ou hedonique d'AF et de L. Apres 3 j et de 7 a 12 tetees, une preference en faveur de L est exprimee, refletant a la fois l'exposition repetee a l'odeur L et un changement qualitatif du lait maternel lors de l'installation de la lactogenese. Cette sequence developpementale revele que: i) les reponses du nouveau-ne humain au colostrum pourraient etre influencees par l'exposition a des qualites chimiosensorielles similaires in utero, et ii) que ces reponses sont ajustees au changement progressif des proprietes chimiosensorielles du lait lors de la lactogenese.

Orientation responses to biological odours in the human newborn. Initial pattern and postnatal plasticity

Explanations for the chemosensory abilities of newborn mammals focus primarily on food (milk) acquisition and communication (e.g., maternal–infant bonding). However, the relative importance of the main and accessory (vomeronasal) olfactory systems is hypothesized to differ at birth between altricial and precocial mammals. Strepsirrhines (lemurs and lorises) possess main and accessory olfactory systems, and vary in life-history traits related to infant dependency and maturation. Accordingly, this study examines the size and maturational characteristics of vomeronasal (VNNE) and olfactory (OE) neuroepithelia in strepsirrhines. Serially sectioned heads of 18 infant cadavers were examined microscopically for neuroepithelial distribution. Measurements were taken on the length of the nasal fossa on one side that was occupied by VNNE and OE. The data were corrected for body size using the cranial length or body mass, and were then examined for correlation with several life-history variables, as well as activity pattern. In addition, immunohistochemistry was used to identify cells in the VNNE and OE that express olfactory marker protein (OMP), a marker of mature olfactory neurons. Relative OE extent was not significantly correlated with any of the life-history variables. Relative VNNE length was negatively correlated with relative gestation length and relative neonatal mass (P<0.05). However, when we corrected for phylogenetic relationships, we found no significant correlations between either of the neuroepithelial measurements and life-history variables. Immunohistochemical findings suggest that OE has more OMP-reactive cells than VNNE in all species. OMP-reactive cells appear to be less numerous in diurnal species compared to most nocturnal species. These results indicate that the VNNE may be relatively longer at birth in altricial species. However, it remains uncertain how phylogeny and/or ontogeny may explain these findings. Am. J. Primatol. 69:74–85, 2007. © 2006 Wiley-Liss, Inc.

Perinatal size and maturation of the olfactory and vomeronasal neuroepithelia in lorisoids and lemuroids

Recent evidence suggests that the accessory olfactory system (AOS) may mediate chemoreception before birth. Such a capability may allow the fetus to begin to sample chemical stimuli from the outside world, a possibility that has important developmental and evolutionary implications. Herein we describe the development in the mouse of the duct that connects the vomeronasal organ (VNO), containing the primary receptor neurons of the AOS, with the nasal cavity and thus with external stimuli. Twenty-four mice, four at each of six different ages from the last day of gestation through 25 days of age, were fixed and embedded in glycol methacrylate. Serial sections were examined under the light microscope so that the VNO duct could be reconstructed in three dimensions. Results confirm an earlier study which demonstrated that the VNO duct is not patent before birth. The duct becomes patent sometime after the first day of life but remains in an immature condition throughout the normal prepubertal period. During this period the duct is characterized by an internal surface that is rapidly desquamating such that the lumen of the duct contains sloughed tissue. These results suggest that the VNO is unlikely to function in the prenatal period, since the route for external stimuli to reach its receptor surface is blocked. The protracted period of VNO duct development reported here is consistent with the great bulk of data on the AOS of mammals which firmly establishes its role in the detection of pheromones which coordinate reproduction.

The vomeronasal duct has a protracted postnatal development in the mouse.

Olfaction in utero: Behavioral studies of the mouse fetus.

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The vomeronasal duct has a protracted postnatal development in the mouse.

Olfaction in utero: Behavioral studies of the mouse fetus.