Vomeronasal and olfactory system modulation of maternal behavior in the rat

Variation in maternal care and individual differences in play, exploration, and grooming of juvenile Norway rat offspring

Individual differences in two different forms of maternal licking, time in nest and nursing, were measured during the first 2 weeks after birth. Two treatments were imposed to reduce maternal anogenital licking (AGL): peripheral zinc sulfate to interfere with reception of pup chemosignals, and dietary saline to reduce appetite for pup urine. Both treatments reduced AGL but did not affect other maternal licking. Zinc sulfate was more effective than saline during the first week, but was somewhat less selective as it also increased time in nest. Selected behavioral patterns were measured in male and female juveniles and related by multiple regression to the behavior of their mothers. Independent of the method of manipulation, maternal AGL was a significant predictor of play and open-field defecation males and of some forms of activity in the open field in both sexes. The relationships between other maternal variables and juvenile behavior were more modest. These data demonstrate that intervening in the sensory regulation of maternal behavior can produce predictable changes in stimulation provided by the dam, thereby providing a useful means for investigating the effects of protracted differences in early stimulation in otherwise normal developmental contexts.

Bilateral lesions of the bed nucleus of the accessory olfactory tract facilitate maternal behavior in virgin female rats

In this study the effects of electrolytic lesions of the bed nucleus of the accessory olfactory tract (BAOT) on the induction of maternal behavior in virgin female Wistar rats was investigated. Results demonstrate a functional role of the BOAT in the neural control of maternal behavior in virgin female rats since bilaterally BOAT lesioned (BL) animals showed significantly shorter sensitization latencies (BL = 6 days) than sham lesioned (SH = 12 days) and intact control (C = 12 days) female rats. At the same time, statistically significant differences were observed in retrieval latency between BL (5.5 days) and C (10 days) groups, but not in the SH group (8 days). In physical contact frequency, the BL group reached higher scores than SH or C group. However, bilateral BAOT lesions failed to affect other maternal patterns such as nest building quality. Thus these results indicate that the BOAT, a vomeronasal system structure, is involved in the control of maternal behavior and that BL electrolytic lesions facilitate the onset of this behavior in virgin female Wistar rats.

Sexual dimorphism in the bed nucleus of the accessory olfactory tract in the rat

This work investigates the existence of sex differences in the volume and number of neurons and glial cells in the bed nucleus of the accessory olfactory tract (BAOT). Males showed larger volume and number of cells than female rats. Early postnatal (day 1 after birth) orchidectomy in males, and androgenization in females, reversed these differences. No sex differences were found in BAOT glial cells. The sexual dimorphism found in the neuron/glial cell ratio reflects sex differences in neuron number. The existence of sexual dimorphism in the BAOT supports our earlier hypothesis which states that the vomeronasal system (VNS) is sexually dimorphic.

Morphine treatment and reproductive condition alter olfactory preferences for pup and adult male odors in female rats

Administration of morphine sulfate (MS) to pregnancy-terminated and postpartum lactating female rats disrupts both maternal behavior and postpartum aggression. Since the display of these behaviors may be heavily dependent on olfactory cues provided by the stimulus animals (rat pups and adult male rats, respectively), we examined whether MS was affecting the perception of the olfactory stimuli, and whether olfactory perception was modified by reproductive condition. In Experiment 1, lactating rats had their pups removed and were injected with MS (5.0 mg/kg, sc.) or saline. 60 min later they were placed into a two-choice apparatus, one side of which contained bedding soiled by neonates and the other clean bedding. Time spent on each side was recorded for a total of 5 min (300 s; chance = 150 s). Saline-treated mothers spent significantly more time on the pup-odor side, whereas MS-treated females spent significantly less. In Experiment 2, lactating females were treated with MS or saline and exposed to male odors (soiled bedding). MS significantly increased time spent on the side with male odors; when treated with saline, time spent was significantly reduced. Thus, in lactating rats. MS creates an aversion for pup odors while reducing the female's normal aversion toward male odors. In Experiment 3, ovariectomized (ovx) virgin females expressed neither an aversion nor a preference for the odor of pups following saline administration. After MS treatment, however, the virgins showed a distinct preference for pup odors. When exposed to male odors in Experiment 4 ovx virgins showed a marked preference for male odors after MS treatment, and neither a preference nor an aversion after saline. Experiment 5 examined pup odor preferences in intact virgins, early (Day 7), middle (Day 14), late-pregnant (Day 21), and prepartum (Day 22) rats. The pup odor preferences of virgin, Day 7, Day 14, and Day 21 pregnant rats were not different and generally were at chance levels. Day 22 pregnant females exhibited a marked preference for pup odors compared to chance levels, as well as compared to the other four groups. These findings suggest that opiates and endogenous opioids may regulate olfactory preferences and that alterations in this system may underlie normal behavioral changes toward conspecifics prepartum as well as during lactation.

Pheromonal emission by pregnant rats protects against infanticide by nulliparous conspecifics

The present studies of experiments focuses on infanticide in the nulliparous rat and asks two questions. First, what do infanticidal nulliparae gain from killing unrelated young? And second, does the recently parturient female have an effective strategy to counter female infanticide? With regard to the first question, we show two benefits from killing unrelated young, namely, that the killer utilizes the young as a food resource and that she occupies the nest site of the mother whose young she has destroyed. With regard to the second question, we show that an extended period of cohabitation with a pregnant female reduces the incidence of infanticidal behavior in nulliparae. Additionally, we demonstrate that the mother emits a pheromone during pregnancy which in itself reduces the incidence of infanticide and, in fact, often makes potentially infanticidal females maternal. The possible endocrine basis of this induced maternal behavior is discussed.

Intracranial dialysis measurement of oxytocin, monoamine and uric acid release from the olfactory bulb and substantia nigra of sheep during parturition, suckling, separation from lambs and eating

Intracranial dialysis was used to measure the release of oxytocin (OXY), monoamines and their metabolites and uric acid (UA) from the substantia nigra (SN) and olfactory bulb (OB) of sheep during parturition, suckling, separation from lambs and eating. Results showed that OXY concentrations increased significantly during parturition, suckling and eating in the SN and during parturition and suckling in the OB. Concentrations of dopamine (DA) increased significantly in the SN during suckling and eating and in the OB during parturition and suckling. The dopamine metabolite, homovanillic acid, also increased significantly in the SN during parturition. Concentrations of the noradrenaline metabolite, 4-hydroxy-3-methoxyphenylethan-1,2-diol (MHPG) and the purine metabolite, UA, were significantly raised during parturition, suckling and separation from the lambs in the SN and increased UA levels were also found during eating. In a separate experiment it was confirmed that OXY was detectable in homogenates of both the SN and the OB. These results show that, in the sheep, OXY and DA release in the SN is associated with maternal and ingestive behaviour whereas similar release in the OB may only be related to maternal behaviour. Release of MHPG in the SN may be associated with maternal behaviour and/or stress.

Infanticide in the male rat: the role of the vomeronasal organ

The present study constitutes the first demonstration that vomeronasal chemoreception plays a role in the response of the virgin male rat to conspecific newborn. Specifically, it shows that virgin males, after removal of the vomeronasal organ, exhibit a decrease in the incidence of infanticidal behavior. This finding is discussed in terms of how responsiveness to young can be affected by changes in the accessory olfactory system.

Infanticide in rats: male strategy and female counter-strategy

The present series of experiments addresses the question of whether mating governs infanticide in the male rat and, in addition, asks whether the female rat has available an effective counter-strategy to male infanticide. With regard to the first question, we found that mating provides a safeguard against the killing of own young. That is, mating induces a general inhibition of infanticide coincident with the birth of the male's young and a recrudescence of infanticide synchronized with their weaning. The particular gain realized in killing alien young depends on the age of young and consequently on whether the mother had reached postpartum estrus. We also found that the pregnant female has an effective strategy to counter male infanticide which she employs before the young are born. The data show that this counter-strategy involves the synthesis of a chemosignal of low volatility emitted during pregnancy. The possible role of the male's vomeronasal system in the reception of this chemosignal is discussed.

Preoptic area opioids and opiate receptors increase during pregnancy and decrease during lactation

Opiate receptor and endogenous opioid content were determined in pregnant, lactating, ovariectomized, and ovariectomized and subsequently estradiol- and progesterone-treated adult female rats. Levels of estradiol and progesterone produced by Silastic capsules implanted in animals of the ovariectomized, hormone-treated group were similar to natural levels of those hormones induced during pregnancy. Quantitative receptor autoradiography and radioimmunoassay were used to determine [3H]naloxone binding density and immunoreactive beta-endorphin content, respectively, in the preoptic area of the hypothalamus. Both opiate receptor binding density and beta-endorphin content in the preoptic area varied in the same direction in all experimental groups. The highest levels of both were observed during pregnancy and the lowest levels during lactation. Ovariectomy without subsequent hormone treatment produced intermediate levels of both opiate receptor and beta-endorphin. Ovariectomy with experimentally-induced estradiol and progesterone levels similar to those of pregnancy produced opiate receptor density and beta-endorphin content similar to those observed in pregnant animals. These data suggest that gonadal steroids are capable of altering function of the endogenous opiate system in the preoptic area. Moreover, preoptic area levels of opioids and opiate receptors are normally elevated during pregnancy and reduced during lactation. Since opiates are known to disrupt ongoing maternal behavior, a reduction of preoptic opiate function during lactation may be required to promote normal maternal behavior. The specific preoptic region involved in opiate regulation of maternal behavior may be illustrated by the zone of opiate receptor alteration observed herein.

Adenosine deaminase-containing neurons in the olfactory system of the rat during development

The development, distribution and olfactory bulb projections of neurons immunoreactive for the enzyme adenosine deaminase (ADA) were studied in olfactory systems of embryonic, early postnatal and young adult rats. On embryonic day (E) 12, ADA-immunoreactivity first appeared in the placode of the olfactory epithelium. On E15, ADA-immunoreactive olfactory receptor and precursor cells gave rise to immunostained axons projecting to the olfactory bulb. Numerous immunostained glomeruli were observed on postnatal day (P) 1. After P25, immunoreactivity within receptor cells and glomeruli decreased. In prenatal and early postnatal animals, ADA-immunoreactive neurons were observed in the anterior olfactory nucleus (AON), dorsal transition area, ventral taenia tecta, primary olfactory cortex (POC), entorhinal cortex and ventral agranular insular cortex. After P25 to P30, these neurons lost their immunoreactivity, except those in the medial AON where light immunostaining persisted. In contrast, ADA-immunostaining of neurons in the horizontal limb of the diagonal band (HDB) and olfactory tubercle increased throughout development. About 70 to 75% of the ADA-immunoreactive neurons in the AON, a small number of those in the POC and about 75% of the ADA-immunoreactive non-cholinergic neurons in the HDB were found to project to the olfactory bulb. The functions of ADA in the olfactory system may be related to the precocious development of, and/or purinergic neurotransmission within, this system.

Affect and nurturance: mechanisms mediating maternal behavior in two female mammals

This review will discuss hormonal and psychological factors involved in the initiation and maintenance of maternal behavior during the postpartum period in rat and human mothers. Research on primiparous rats suggests that among the ways hormones act to promote maternal responsiveness are by increasing the mother's attraction to odors of young pups, decreasing her natural neophobia and fearfulness, and increasing the ease with which experiences obtained during initial mother-young contacts are retained. Long-term maintenance of elevated maternal responsiveness in the rat is not directly under hormonal control but instead depends on a minimal period of direct interaction with young during the early postpartum. In human first-time mothers, the onset of maternal responsiveness is also directly affected by their mood state as well as their attraction to infants; these factors are, in turn, influenced by the amount of prior experience women have had caring for young. While the role of hormones in mediating maternal behavior in women is still unclear, initial results indicate they may facilitate responsiveness during the puerperium.

Electrophysiological mapping of the accessory olfactory bulb of the rabbit (Oryctolagus cuniculus)

Field potentials elicited by electrical stimulation of the vomeronasal nerve were measured in the accessory olfactory bulb of the rabbit. Maps were made of the distribution of surface field potentials and of the corresponding depth profiles. The surface maps followed closely the contours of the accessory olfactory bulb: at the frontal border the field potential tended to zero and at the center of the structure the field potential attained a maximum. Depth profiles of the field potentials through the accessory olfactory bulb presented a surface-negative wave and, in depth, a positive wave. The polarity reversal occurred at the deep part of the granule cell layer. The zero equipotential line followed closely the curvature of the granule cell layer. Current source density analysis of the depth profiles revealed a main sink at the external plexiform and granule cell layers. This indicates that the main activity in the accessory olfactory bulb is generated by the synapses between the mitral cells and the granule cells as is found in the main olfactory bulb.

The organization of neural inputs to the medial preoptic nucleus of the rat

There is general agreement that the medial preoptic nucleus (MPN) receives projections from widespread regions of the brain, although there are significant discrepancies in the literature with regard to certain specific inputs. Therefore, we have reexamined the inputs to this nucleus with both retrograde and anterograde axonal transport techniques. First, injections of the retrograde tracers true blue, SITS, or wheat germ agglutinin were made into the region of the MPN and the distribution of retrogradely labeled cells was charted. Then, autoradiographic material was used to confirm the results of the retrograde studies, to identify the route taken by fibers projecting to the MPN, and to describe the distribution of projections with respect to the three cytoarchitectonic subdivisions of the nucleus. The results indicate that the MPN receives inputs from widely distributed areas in both the forebrain and brainstem, and that these inputs appear to be distributed topographically within the three cytoarchitectonic subdivisions of the nucleus. Direct inputs to the MPN arise from all major areas of the hypothalamus (except for the median and magnocellular preoptic nuclei, the supraoptic and suprachiasmatic nuclei, and the medial and lateral mammillary nuclei). Projections from nuclei within the periventricular zone of the hypothalamus end primarily in the medial part of the MPN, while inputs from the lateral zone are mainly confined to the lateral part of the nucleus, as are projections from the nuclei within the medial zone, except for those from the anterior and ventromedial nuclei, which appear to be more widespread. The MPN receives major inputs from limbic regions including the amygdala, ventral subiculum, and ventral lateral septal nucleus, all of which end preferentially in the lateral part of the MPN. In contrast, the projection from the encapsulated part of the bed nucleus of the stria terminalis appears to end preferentially in the central part of the MPN and in immediately adjacent regions of the medial subdivision. In addition, the MPN may receive relatively sparse inputs from infralimbic and insular cortical areas, the nucleus accumbens, and the substantia innominata. Finally, ascending serotoninergic projections from the raphe nuclei appear to terminate principally in the lateral part of the MPN, whereas inputs from regions containing noradrenergic cell groups are chiefly distributed to the central and medial parts of the nucleus. Other brainstem regions that appear to provide modest inputs include the ventral tegmental area, central tegmental field, periaqueductal gray, pedunculopontine nucleus, and the peripeduncular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of sex steroids on the development of the accessory olfactory bulb mitral cells in the rat

The effects of postnatal (on day 1 after birth) male castration and female androgenization on accessory olfactory bulb (AOB) mitral cells population were studied. Control males showed a greater number of AOB mitral cells than females. Postnatal treatments abolished and inverted these differences. It is suggested that the population of AOB mitral cells is influenced by sex steroids during at least a postnatal period.

Sexual behavior in the female rat following removal of the vomeronasal organ

We used female Wistar rats from which the vomeronasal organ (VNO) has been removed. The first question addressed was whether such females would show deficits in sexual behavior. The data left no doubt that removal of the VNO severely depressed lordosis as well as such proceptive behaviors as "darting" and "hopping." We then injected estrogen and progesterone and, in still another experiment, estrogen and luteinizing hormone-releasing hormone (LHRH). Estrogen and progesterone significantly enhanced lordosis, but only estrogen and LHRH raised the lordosis quotient of VNO-ablated females to that of the control females. We discuss the results in terms of a theoretical model involving the complementary action of estrogen and LHRH in inducing lordosis in the intact female.

Mouse vomeronasal organ: effects on chemosignal production and maternal behavior

Adult male mice excrete a urinary chemosignal that accelerates puberty in females, whereas group-housed female mice excrete a urinary chemosignal that delays puberty in young females. We found that: (1) the excretion of the puberty-acceleration chemosignal by males persisted in the absence of the vomeronasal organs and (2) the puberty-delay chemosignal was not present in the urine of group-housed females whose vomeronasal organs had been surgically removed (VNX), but was present in the urine of group-housed females subjected to sham surgery (SHAM). These results suggest that in males, vomeronasal chemoreception does not affect the excretion of the puberty-acceleration chemosignal, but that in females, the vomeronasal organ receives chemosignals that influence the excretion of the puberty-delay chemosignal. Additionally, we found no difference between SHAM and VNX females in rates of conception, litter size, pup growth, pup recognition, or maternal behavior, indicating that normal maternal processes are expressed in the absence of an intact accessory olfactory system.

Impaired maternal behaviour and altered central serotonergic activity in the adult offspring of chronically ethanol treated dams

Female rats were given 16% ethanol solution as the sole liquid during the entire period of gestation. At birth the offspring was removed and reared by foster dams consuming normal tap water. At adult age the female offspring showed deficiencies in their maternal behaviour; they built nests of poor quality and they displayed prolonged times for retrieving pups placed outside the nest. In the whole brains of the prenatally ethanol-exposed females a decreased serotonin synthesis was observed. The offspring of the prenatally ethanol exposed mothers did not show any signs of disturbances in physical or behavioural development.

Vomeronasal organs and nerves of Jacobson in the human fetus

The vomeronasal organs and nerves of Jacobson were found on both sides of the nasal septum in a 28-week human fetus. The vomeronasal organ in the human is a tubular structure with an opening into the nasal cavity anteriorly and closed posterior end. The vomeronasal nerve is distributed equally to the medial and lateral aspects of the organ, courses along the nasal septum and goes through the cartilaginous cribriform plate with the olfactory nerve. The cellular configuration of the vomeronasal organ is similar to the olfactory neuroepithelium. No areas of receptor-free epithelium were found in the vomeronasal organs. Intraepithelial blood vessels and mitotic figures were not observed in the epithelium of the vomeronasal organs at 28 weeks. The lack of intraepithelial blood vessels and mitoses may suggest that the vomeronasal organs are undergoing degeneration at 28 weeks of gestation.

Effects of sex steroids on the development of the accessory olfactory bulb in the rat: a volumetric study

The effects of postnatal (on day 1 after birth) male castration and female androgenization on accessory olfactory bulb (AOB) volume were studied. Control males showed greater values than females in AOB volume. Postnatal treatments abolished and inverted these differences. It is suggested that the AOB development is influenced by sex steroids during at least a postnatal period.

Male hamster copulatory responses to a high molecular weight fraction of vaginal discharge: effects of vomeronasal organ removal

The importance of the vomeronasal (accessory olfactory) system for the copulatory responses of male hamsters to a high molecular weight fraction (HMF) of vaginal discharge was assessed in animals that had their vomeronasal organs (VNO) removed. These organs were extirpated bilaterally using an oral approach through the palate so as to eliminate the peripheral afferents to the accessory olfactory bulb (AOB) with minimal or no damage to the main olfactory system. The selective peripheral deafferentation procedure was verified by applying horseradish peroxidase intranasally following intraperitoneal injections of epinephrine to facilitate the vomeronasal pumping mechanism that draws fluids into the VNO. Heavy, bilateral anterograde labeling was evident in the olfactory nerve afferents within the main olfactory bulb of males that had their VNO removed and of animals that received sham surgery. Sham-operated males also had heavy, bilateral labeling in the vomeronasal nerve afferents within the AOB, whereas no such labeling occurred among animals with bilateral removal of the VNO. In sham-operated animals, both the HMF and the unfractionated discharge significantly increased the incidence of intromission attempts toward anesthetized males (surrogate females) whose hindquarters were scented with these stimuli. The unfractionated discharge also produced a significant elevation of overt copulatory behavior in males with selective peripheral deafferentation of the vomeronasal system, whereas the HMF did not facilitate copulatory behavior in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal contributions to the development of masculine sexual behavior in laboratory rats

Maternal licking was manipulated by lining the nasal passages of rat dams with polyethylene tubing to interfere with their olfactory competence. Olfactory cues from pups elicit maternal licking and handling, particularly of anogenital regions, and dams with olfactory deficits were observed to lick their pups less. Mature male and female offspring of these dams and their controls were gonadectomized, treated with testosterone propionate, and tested for masculine sexual behavior. The male offspring of dams that provided less maternal licking had longer ejaculatory latencies, longer post-ejaculatory intromission latencies, and longer inter-intromission intervals than controls. Female offspring of the intubed dams performed fewer mounts and intromissions, had longer intromission latencies, and longer inter-intromission intervals. It was concluded that stimulation from maternal licking contributes toward the development of a mechanism that underlies the timing of copulatory rate.

Effects of postpuberal gonadectomy on the neurosensorial epithelium of the vomeronasal organ in the rat

In the present report the effects of postpuberal gonadectomy on vomeronasal organ (VO) morphology were studied. Postpuberal gonadectomy induced in both male and female rats a decrement in the height of the epithelium and in the nuclear size of the bipolar neurons. These results show that the maintenance of neurosensorial normal morphology depend upon the activational effects of sex steroids.

The role of the accessory and main olfactory systems in maternal behavior of the primiparous rat

The objective of this study was to analyze the respective roles of the main and accessory olfactory systems in the development of maternal behavior in the primiparous Wistar rat. Females underwent one of the following treatments: vomeronasal nerve section (VN), irrigation of nasal cavities with 5% ZnSO4 solution (ZN), surgical control, saline irrigation control, and normal control. Surgical or first irrigation were done before mating occurred. Irrigations were done every 7 days thereafter. The dams and their litters were observed from the day the litter was born (Day 1) through Day 16. Pup weights and temperatures were recorded daily. Home cages were checked daily for changes in nest location and number of times pups were found out of the nest. Retrieving tests were conducted on Days 4, 7, 10, and 13. The following behavioral items were observed: number of pup retrievals , number of times mother nosed or licked pups, percentage of litter returned to nest by end of test, dam self-grooming, dam climbing or rising, and dam digging or burrowing in shavings. The VN dams and their litters were not significantly different from the control dams and their litters on any of the measures taken. The ZN dams and their litters were not significantly different from their controls on all measures except for pup body temperature which was slightly lower from Day 13 through day 16 and pup body weight which was slightly lower from Day 12 through Day 16. Since these differences are very small, they do not seem to indicate a serious deficiency in maternal behavior. The results indicate that adequate maternal behavior develops with either of the two systems intact.

Olfactory and vomeronasal system mediation of maternal recognition in the developing rat

Olfactory-mediated arousal and maternal recognition were evaluated in neonatal rat pups. Non-nutritionally deprived pups which underwent bilateral olfactory bulbectomies on day 5, failed to distinguish between the ventral and dorsal surfaces of a nursing rat and a heating pad. They showed virtually no arousal response to any of these surfaces. In contrast, pups with unilateral bulbectomies, and sham controls, graded their arousal response, and were maximally aroused by the mother's ventral surface. Following 24 h of maternal deprivation, bilaterally bulbectomized pups displayed a modest arousal response, directed primarily towards the dorsal surface. Pups with complete vomeronasal nerve sections displayed maximal arousal responses toward the dorsal surface. However, they were far more aroused than the bilaterally bulbectomized pups. Rat pups with incomplete vomeronasal lesions graded their response like controls, with maximal responsiveness directed toward the ventral surface. Shaving the dorsal surface markedly diminished the arousal response of bilaterally bulbectomized pups, but had only modest effects on sham and unilaterally bulbectomized controls. Thus, lesions that destroyed both the main and accessory's olfactory bulb systems severely impaired the pups' ability to effectively recognize a lactating female and markedly diminished maternally-induced arousal. Selective damage to the vomeronasal-accessory olfactory system appeared to disrupt discriminative capacity, but had little effect on the magnitude of the arousal response.

Evidence for olfactory function in utero

Pregnant rats received 2-[14C]deoxy-D-glucose (2DG) intravenously on the last day of gestation, and their fetuses were delivered 1 hour later by cesarean section. Fetal brains showed high 2DG uptake spread throughout the accessory olfactory bulb and little or no differential uptake in the main olfactory bulb. These findings demonstrate that functional activity occurs in the accessory olfactory bulb in utero and suggest that the accessory olfactory system may be the pathway by which fetal rats detect the odor quality of their intrauterine milieu.

Effects of neonatal thyroidectomy on the development of the vomeronasal organ in the rat

The effects of postnatal thyroidectomy (on day 8 after birth) and 131I treatment (on day 10) on the development of the vomeronasal organ (VO) has been studied In the rat. Thyroidectomized rats showed decrements in the overall VO volume, volume of the neurosensorial epithelium, neuronal population and nuclear size of neurons. These results in VO paralleled those reported in the central nervous system after thyroidectomy.

Effects of sex steroids on the development of the vomeronasal organ in the rat

In the present report the effects of postnatal (on day 1 after birth) male castration and female androgenization on vomeronasal organ (VO) development were studied. Control males showed greater values than females in VO volume and neurosensorial epithelium, while the opposite was true with respect to nuclear size. Postnatal treatments abolished these differences. It is suggested that the VO development is influenced by sexual hormones during at least a postnatal period as it occurs for several structures of the central nervous system connected with the VO.

Adjacent laminar terminations of two centrifugal afferent pathways to the accessory olfactory bulb in the mouse

Anterograde and retrograde axonal tracing methods have been combined with transection of the stria terminalis to investigate the centrifugal afferent connections of the accessory olfactory bulb in the mouse. Injection of tritiated proline into the postero-medial cortical amygdaloid nucleus (C3) gives rise to anterograde autoradiographic labelling of a pathway terminating in the internal granular layer of the accessory olfactory bulb (AOB). Transection of the ipsilateral stria terminalis completely abolishes labelling of this pathway. Injections further rostral, in the bed nucleus of the accessory olfactory tract (bnAOT) and medial amygdaloid nucleus (M), give rise to labelling of a second ipsilateral afferent pathway to the AOB which terminates in the internal plexiform layer (IPL) and is unaffected by strial transection. Injections of wheat germ lectin-HRP conjugate into the AOB confirm that it receives afferents from the ipsilateral bnAOT, M and C3, and from a few cells in the contralateral C3. Transection of the ipsilateral stria terminalis prevents retrograde labelling of any cells in the ipsilateral C3, but does not affect labelling of cells in M or bnAOT (or contralateral C3). The conjugate is also transported anterogradely in this system, labelling the efferent projections of the AOB to bnAOT, M and C3. It is concluded that the AOB receives at least two sets of ipsilateral afferents: one set from C3, via the stria terminalis, terminating in the internal granular layer, and a second set from M and/or bnAOT terminating in the IPL and probably running in the accessory olfactory tract.

Vomeronasal and olfactory pathways to the amygdala controlling male hamster sexual behavior: autoradiographic and behavioral analyses

Previous studies suggest that the rostral corticomedial amygdala (CMA), particularly the medial nucleus, is an important site where vomeronasal and olfactory stimuli critical to male hamster copulatory behavior are processed. To test the possibility that mating deficits seen after lesions of the rostrally-placed medial nucleus may be due to the interruption of chemosensory afferents to more caudal areas, we injected tritiated amino acids into the accessory and main olfactory bulbs of male hamsters in which we had first produced bilateral electrolytic lesions or sham lesions in either the rostral CMA or basolateral amygdala, and then observed mating behavior. Autoradiographic analysis of "vomeronasal' projections from the accessory olfactory bulb and "olfactory' projections from the main bulb, revealed that rostral CMA lesions which damaged the medial nucleus and extended to the ventral surface of the brain (ventral lesions) interrupted vomeronasal input to the more caudally-placed posteromedial cortical nucleus, but spared olfactory inputs to adjacent caudal areas of the amygdala and piriform lobe. In contrast, lesions which damaged a major portion of the medial nucleus but left its ventral surface intact (dorsal lesions) spared both vomeronasal and olfactory inputs to more caudal areas. Animals with both dorsal and ventral lesions failed to mate postoperatively, whereas animals bearing sham lesions of basolateral amygdaloid lesions, which, like dorsal lesions, spared caudally-directed chemosensory afferents, continued to mate normally. We conclude that mating deficits seen after rostral CMA lesions are due primarily to destruction of the medial nucleus.

Connections of the corticomedial amygdala in the golden hamster. I. Efferents of the "vomeronasal amygdala"

The medial (M) an posteromedial cortical (C3) amygdaloid nuclei and the nucleus of the accessory olfactory tract (NAOT) are designated the "vomeronasal amygdala" because they are the only components of the amygdala to receive a direct projection from the accessory olfactory bulb (AOB). The efferents of M and C3 were traced after injections of 3H-proline into the amygdala in male golden hamsters. Frozen sections of the brains were processed for autoradiography. The efferents of the "vomeronasal amygdala" are largely to areas which are primary and secondary terminal areas along the vomeronasal pathway, although the efferents from C3 and M terminate in different layers in these areas than do the projections from the vomeronasal nerve or the AOB. Specifically, C3 projects ipsilaterally to the internal granule cell layer of the AOB, the cellular layer of NAOT, and layer Ib of M. Additional fibers from C3 terminate in a retrocommissural component of the bed nucleus of the strain terminalis (BNST) bilaterally, and in the cellular layers of the contralateral C3. The medial nucleus projects to the cellular layer of the ipsilateral NAOT, layer Ib of C3, and bilaterally to the medial component of BNST. Projections from M to non-vomeronasal areas terminate in the medial preoptic area-anterior hypothalamic junction, ventromedial nucleus of the hypothalamus, ventral premammillary nucleus and possibly in the ventral subiculum. These results demonstrate reciprocal connections between primary and secondary vomeronasal areas between the secondary areas themselves. They suggest that M, but not C3, projects to areas outside this vomeronasal network. The medial amygdaloid nucleus is therefore an important link between the vomeronasal organ and areas of the brain not receiving direct vomeronasal input.

Intraepithelial blood vessels in the vomeronasal neuroepithelium of the rat. A light and electron microscopic study

Epithelial-vascular relationships are established during the development of the vomeronasal neuroepithelium of the rat. Special attention is given to the fine structure of the endothelial wall of intra-epithelial vessels, to ultrastructural aspects of the neuronal-vascular relationships, and to the appearance of inclusion bodies in the neuronal cells adjacent to these vessels. The neuronal perikarya surrounding the blood vessels are filled with highly developed smooth endoplasmic reticulum. Possible functional implications of the vascularization of the neuroepithelium of the vomeronasal organ in mediating olfacto-endocrine relationship are discussed. It is suggested that the intra-epithelial blood vessels are at least supportive and nutritive in nature, while their implication in an olfacto-endocrine connection remains obscure.

Scanning electron microscopic studies of the surface morphology of the vomeronasal epithelium and olfactory epithelium of garter snakes

Fixed vomeronasal and olfactory epithelia from normal adult garter snakes were microdissected, fractured, and examined with a scanning electron microscope. The method permits a detailed comparative study of the structural organization and morphological characteristics of the constituent cells of the vomeronasal and olfactory epithelia. Despite similarities in the nomenclature of the constituent cells in both epithelia, significant differences exist in their surface morphology. A unique columnar structure composed of non-neuronal elements is present in the vomeronasal epithelium. These columns house the bioplar neurons and undifferentiated cells. Such a columnar organization is absent in the olfactory epithelium. In vomeronasal epithelium the bipolar neurons possess microvillous terminals at their dendritic tips, while the dendritic tips of the bipolar neurons of the olfactory epithelium possess cilia. Vomeronasal supporting cells are covered with microvilli, while olfactory supporting cells are covered with cytoplasmic protuberances in addition to the microvilli. In the vomeronasal epithelium the pear-shaped neurons have a grossly smooth surface and are organized into clusters, while in the olfactory epithelium the elliptical bipolar neurons are spinous, aligned side-by-side and interdigitate. The basal (undifferentiated) cell layer in the vomeronasal epithelium has a high packing density and is composed of several layers of irregularly shaped cells. In the olfactory epithelium the basal cell layer is loosely organized and composed of a single layer of oval cells. This information on the three-dimensional cell structure of both epithelia provides a basis for experimental observations on changes in morphology of the bipolar neurons during genesis, development, maturation, degeneration, and regeneration in postnatal, adult animals.