The effects of paraventricular hypothalamic lesions on maternal behavior in rats

The present study was undertaken to determine whether the disruptive effects of knife cuts which sever the lateral connections of the medial preoptic area (MPOA) on maternal behavior are mediated by interfering with the output of the paraventricular hypothalamic nucleus (PVN). Postpartum rats received one of the following: Knife cuts severing the lateral connections of the MPOA; knife cuts severing the lateral connections of the PVN; radiofrequency lesions of the PVN; sham lesions or knife cuts. Only females that received knife cuts severing the lateral connections of the MPOA showed severe deficits in maternal behavior. These results indicate that the influence of the MPOA on maternal behavior is not mediated by the output of the PVN. Since the PVN is the major source of oxytocin input to other brain regions, these results also suggest that oxytocinergic neural pathways are not critical for postpartum maternal behavior. Another important finding was that females with MPOA knife cuts that did not retrieve their young were capable of hoarding candy, suggesting that the retrieval deficit was not the result of a general oral motor deficit.     

Medial hypothalamic involvement in maternal aggression of rats

Extensive electrolytic lesions of the medial hypothalamus, or more restricted ones in its ventral division, decreased maternal aggression in rats operated upon on postpartum Days 2 and 3 and tested with female intruders 4 days later. Maternal aggression was attenuated also in mothers receiving intrahypothalamic infusions with ibotenic acid or parasagittal knife cuts along the lateral border of the ventromedial hypothalamic nucleus; in addition, the females with ibotenate lesions or knife cuts showed impaired lordosis behavior. None of the hypothalamic interventions were associated with deficits in pup retrieval. Lactation was impaired in groups with hypothalamic electrocoagulations but not in mothers with ibotenate lesions or knife cuts. The results suggest that the ventromedial hypothalamus and its lateral connections participate in control of maternal aggression.     

Intracerebral implantation of progesterone: re-examination of the brain sites responsible for facilitation of sexual receptivity in estrogen-primed ovariectomized rats.

Ovariectomized female rats were tested for sexual receptivity following SC priming with threshold doses of estradiol benzoate and intracerebral 27 ga implants of either progesterone or cholesterol. All females were repeatedly tested under both intracerebral hormone implant conditions. Cholesterol implants failed to activate receptivity, while progesterone implants in the interpeduncular-ventral tegmental area produced near maximal levels of receptivity within 30 min after implantation. Progesterone implants in the medial hypothalamus, anterior hypothalamus, preoptic area, pons, mesencephalic reticular formation and lateral mesencephalon failed to activate sexual receptivity.     

Localization of hypothalamic sites for the estrogen-priming of sexual receptivity in female hamsters

Ovariectomized female hamsters received small unilateral implants of estradiol at a variety of anterior-posterior levels of the medial preoptic area and hypothalamus. The results of an initial experiment using 27-ga. implants showed that females with estradiol implants in the ventromedial hypothalamus (VMN) or nearby anterior hypothalamus consistently showed higher levels of sexual receptivity than did females with implants farther rostral, in the preoptic area, or farther caudal, in the posterior hypothalamus. A second experiment used smaller, 28-ga. implants to compare directly the two areas at which implants were effective in the first experiment. The results confirm the findings of other recent studies of hamsters and rats by identifying the VMN as the most effective hypothalamic site for the estrogen priming of sexual receptivity.     

The connections of the medial preoptic region and maternal behavior in the rat

Female rats which are hysterectomized and ovariectomized on Day 16 of pregnancy and injected with estrogen show a short latency to onset of maternal behavior when presented with test pups 48 hrs later. In the present experiment, female rats were treated similarly except that on Day 16 of pregnancy they received knife cuts which severed either the lateral, anterior, dorsal, or posterior connections of the medial preoptic area (MPOA), or sham knife cuts. Severing the lateral connections of the MPOA severely disrupted materal behavior, while severing the dorsal or posterior connections of the MPOA produced either minor deficits or no deficits. Severing the anterior connections of the MPOA did produce large deficits in maternal behavior, but this was associated with hypoactivity and loss of body weight. Therefore, the maternal behavior deficits observed in the anterior cut group may have been a secondary effect of the knife cut. The results emphasize the importance of the lateral connections of the MPOA for maternal behavior.     

Sexual receptivity: Brain sites of estrogen action in female hamsters

In order to investigate the brain sites of estrogen action, ovariectomized hamsters were stereotaxically implanted with unilateral 27 gauge cannulae containing estradiol. Groups of females received implants into either the lateral septum, bed nucleus of the stria terminalis, preoptic area, anterior hypothalamus, ventromedial hypothalamus, arcuate nucleus, corticomedial amygdala or mesencephalic central gray. Another set of animals received implants containing cholesterol. One week later the animals were injected with progesterone and 4–5 hours later tested for sexual receptivity. The most receptivity and the most consistent response was seen in females with estradiol implants in the ventromedial hypothalamus. Only a few scattered animals in the other anatomical groups showed any receptivity. Only in animals with implants in the anterior hypothalamus was there any evidence of leakage of estrogen into peripheral circulation as measured by uterine weight. There was no response in females with cholesterol implants. Our results suggest that the ventromedial hypothalamus is the most sensitive brain area for the estrogenic induction of female sexual receptivity in hamsters.     

Maternal behavior in rats: evidence for the involvement of preoptic projections to the ventral tegmental area

This study provides evidence that a neural system extending from the preoptic region to the ventral tegmental area (VTA) of the midbrain is important for the normal expression of maternal behavior in lactating rats. In the first experiment, bilateral electrolytic lesions of the VTA severely disrupted the maternal behavior of postpartum rats. In the second experiment, lactating rats that received a unilateral knife cut severing the lateral connections of the medial preoptic area (MPOA) paired with a contralateral lesion of the VTA showed more severe maternal behavior deficits than females that received one of the following treatments: (a) a unilateral knife cut severing the lateral connections of the MPOA paired with an ipsilateral VTA lesion; (b) a unilateral knife cut severing the lateral connections of the MPOA paired with a contralateral lesion of the medial hypothalamus posterior to the MPOA; (c) a unilateral knife cut severing the lateral connections of the lateral preoptic area paired with a contralateral VTA lesion. The oral components of maternal behavior (retrieving and nest building) were particularly affected as a result of bilateral damage to the system extending from the preoptic area to the VTA.     

Sagittal knife cuts in the near and far lateral preoptic area-hypothalamus disrupt maternal behaviour in female hamsters

Parasagittal knife cuts with a varied mediolateral position were placed along the medial preoptic-medial anterior hypothalamic continuum (MPOA-MAH) in female hamsters. Near lateral (NL) knife cuts severed mediolateral connections between the MPOA-MAH and the medial forebrain bundle (MFB) while far lateral cuts (FL) were placed more laterally, sparing MPOA-MAH connections with the MFB. Across the knife cut condition, hamsters were either allowed to construct and maintain a food hoard or allowed to feed ad lib but not permitted to hoard. Animals were then tested for maternal behaviours. Both NL and FL cuts disrupted pup-directed behaviours in virgin maternal tests. NL, but not FL cuts severely disrupted nest building. These same animals were then mated and tested for maternal behaviour with their own young. There were no differences among the experimental groups in various maternal behaviours during these tests. Throughout lactation, however, the majority of NL and FL hamsters not permitted to hoard progressively cannibalized their entire litters. NL and FL counterparts with the hoarding opportunity, on the other hand, cannibalized fewer pups and reared healthy, moderate-sized litters that were smaller than those of surgical controls. That FL cuts were just as effective as NL cuts in disrupting pup-directed behaviour suggests that the mediolateral connections of the MPOA-MAH, other than with the MFB, are important for these behaviours.     

Effects of unilateral hypothalamic manipulations on the sexual behaviors of rats.

Four experiments that assessed the contributions of each side of the hypothalamus to the control of sexual behavior found the following. (a) Exposing the left, but not the right, ventromedial nucleus to estrogen neonatally defeminized sexual behavior in female rats. This asymmetry did not reverse as sexual differentiation progressed. (b) Unilateral cuts lateral to the medial preoptic area disrupted mounting in females that had mounted regularly before surgery, when given testosterone. The deficits were greater when the cuts were on the left side, but a third of the females with unilateral cuts showed severe deficits regardless of the side. (c) Comparable cuts did not impair masculine sexual behavior in gonadally intact males. In fact, left-side cuts seemed to accelerate copulation in males. (d) Unilateral lesions of the ventromedial nucleus disrupted lordosis in female rats in an essentially all-or-none fashion. This effect did not vary with side.     

The magnocellular medial preoptic nucleus I. Sources of afferent input

The magnocellular medial preoptic nucleus plays a crucial role in the regulation of male sexual behavior in Syrian hamsters. Histological and behavioral studies suggest that the magnocellular medial preoptic nucleus regulates male mating behavior by integrating chemosensory and hormonal signals. The present study is the first to systematically identify the afferent connections of the magnocellular medial preoptic nucleus by tracing the uptake of cholera toxin B from deposits in the magnocellular medial preoptic nucleus of adult male Syrian hamsters. Our findings indicate that the magnocellular medial preoptic nucleus receives 1) chemosensory input from areas in the main and accessory olfactory pathways including the posterior medial bed nucleus of the stria terminalis, anterior medial, anterior cortical and posterior cortical nuclei of the amygdala; 2) input from steroid responsive structures such as the posterior medial nucleus of the amygdala, bed nucleus of the stria terminalis, lateral septum, anteroventral periventricular nucleus, medial preoptic nucleus, ventromedial nucleus of the hypothalamus and arcuate nucleus; 3) input from structures in the brainstem such as the subparafascicular thalamic nucleus, peripeduncular nucleus and the premamillary nucleus in the hypothalamus that carry sensory information from the genitalia. The major afferent input to the magnocellular medial preoptic nucleus was confirmed by injecting anterograde tracer biotinylated dextran amine into the anterior medical nucleus of the amygdala, the posterodorsal part of the medial nucleus of the amygdala, the posteromedial part of the bed nucleus of the stria terminalis and the posterointermediate part of the bed nucleus of the stria terminalis. Our results support the hypothesis that the magnocellular medial preoptic nucleus is part of the chemosensory pathway that receives chemosensory and hormonal input to regulate mating behavior and suggest that the magnocellular medial preoptic nucleus may utilize information from the genitalia to regulate male mating behavior.     

Postparturitional reestablishment of pup cannibalism in female gerbils

Nonbreeding female Mongolian gerbils readily cannibalize all accessible pups. Among breeding females this behavior ceases a few days prior to parturition. If the litter remains with the female, cannibalism of newborn test pups returns between 11 and 20 days postpartum. If the litter is removed a few hours after parturition, however, 40% of the females will cannibalize on Days 1–5 and 72% will cannibalize on Days 6–10 postpartum. Thus, the presence of a litter appears to suppress pup cannibalism. The evidence suggests that the replacement of a litter 6–10 days old with newborn pups can prolong the suppression of pup cannibalism.     

LHRH pathways in rat brain: 'deafferentation' spares a sub-chiasmatic LHRH projection to the median eminence

Localization of luteotrophic hormone-releasing hormone (LHRH) was examined by immunocytochemistry in untreated male rats and rats that received an anterior hypothalamic deafferentation. Gonadotrophic function was assessed by examining testicular weight and morphology. All of the antisera used in this study were able to reveal LHRH cell bodies and fibers. Cells from the medial preoptic area, (particularly the preoptic periventricular or median preoptic nuclei) and lateral anterior hypothalamus sent axons to the median eminence. The fiber tracts were loosely organized into (1) a tract that coursed through the organum vasculum of the lamina terminalis between the optic nerves and along the ventral surface of the optic chiasm; (2) a tract that coursed to the organum vasculum from the preoptic area and then traversed along the floor of the third ventricle; (3) a tract that coursed from the medial preoptic area to the median eminence along the lateral walls of the third ventricle; and (4) a tract that arose from the more caudal portions of the LHRH cell field in the lateral preoptic and lateral anterior hypothalamus, coursed along with the fibers of the medial forebrain bundle and turned medially at the caudal hypothalamus to enter the median eminence. An anterior cut which served most of the connections between the medial preoptic area and hypothalamus but did not penetrate through the optic chiasm served tract 3 and most of tracts 2 and 4, but spared the subchiasmatic projection (tract 1). The fibers that remained in the median eminence were sufficient to retain gonadotrophic function. This study provides an explanation for the variable effects of deafferentation and lesions of the anterior hypothalamus and preoptic area on gonadotrophic function.     

Sagittal knife cuts in the near and far lateral preoptic area-hypothalamus reduce ultrasonic vocalizations in female hamsters

Although it has been reported that lesions of the medial preoptic area reduce ultrasonic vocalizations in female hamsters, the neural connections of this area important for ultrasound production have not been investigated. We, therefore, tested vocalizations in female hamsters following sagittal cuts along the medial preoptic area-medial anterior hypothalamic continuum (MPOA-MAH) at either the medial (Near Lateral or NL cuts) or lateral (Far Lateral or FL cuts) border of the medial forebrain bundle (MFB). Bilateral NL and FL cuts did not affect spontaneously occurring vocalizations or vocalizations occurring during contact with males, but were equally effective in substantially blocking increases in vocalizations following exposure to males. Another group of animals with a unilateral NL cut and a contralateral FL cut showed a vocalization deficit comparable to that in NL and FL groups, suggesting that NL and FL cuts severed a common pathway important for ultrasonic calling. These results indicate that the lateral connections of the MPOA-MAH are critical for ultrasonic vocalizations. Alternatively, a ventral pathway from the medial amygdala to the bed nucleus of the stria terminalis, one which crosses the plane of both NL and FL cuts, is discussed in relation to the deficits observed.     

Preoptic-brainstem connections and maternal behavior in rats.

This study presents evidence supporting the view that preoptic area (POA) projections through the ventral tegmental area (VTA) to lower brainstem regions are important for maternal behavior in postpartum rats. Experiment 1 demonstrated that bilateral coronal knife cuts posterior to the VTA disrupted maternal behavior, and Experiment 2 demonstrated a similar disruption when a unilateral knife cut that severed the lateral connections of the medial POA was paired with a contralateral knife cut posterior to the VTA. In a final anatomical experiment using horseradish peroxidase histochemistry, it was shown that knife cuts posterior to the VTA do sever POA efferents. However, such cuts severed other ascending and descending pathways as well, and these may also be involved in maternal behavior control.     

Brain transections differentially alter lordosis and ear wiggling of 6-day-old rats

Six-day-old male and female rats display lordosis and ear wiggling in response to tactile stimulation of the flanks and rump, without priming by exogenous estrogen. The involvement of various brain regions in these behaviors, which resemble components of adult female sexual behavior, was examined by making acute transections along the neuraxis from the olfactory tract to the medulla in 6-day-old rats. Four to 5 hr after the transection procedure, pups were tested for lordosis and ear wiggling. Lordosis was severely reduced or eliminated in pups with cuts through the hindbrain or diencephalon (above the level of the mammillary bodies) but was relatively unaffected by cuts through the posterior hypothalamus and rostral tegmentum and by cuts rostral to the anterior hypothalamus. Ear wiggling was disrupted by transections throughout the hindbrain and was facilitated only in females by transections throughout the forebrain (anterior to the mammillary bodies). These data suggest that facilitation from the hypothalamus is required for lordosis in the infant rat and the forebrain inhibitory systems for ear wiggling are functional in female infants by 6 days of age. Similarities and differences between the neural control of lordosis and ear wiggling in infant and adult rats suggest that the infant sex-like behaviors may be precursors of adult female sexual behavior.     

Experience with pups sustains maternal responding in postpartum rats

In these studies, we investigated the sustaining of postpartum maternal responsiveness through pup experience. In the first study, females were tested for maternal behavior at various times after pregnancy termination by Caesarean section (CS) at term. The females remained rapidly responsive to young for 7 days after pregnancy termination, but were no more responsive than virgins after 10 days. In the second study, females were allowed varying times of complete access to pups, beginning 24 hours after CS, and were tested for maternal behavior 10 days later. Females who retrieved and cared for pups for 30 minutes during exposure, remained rapidly maternal 10 days after CS; those who were allowed only 15 minutes of caring for pups did not. In the third study, females received 24 hours of exposure to distal sensory stimuli from pups, beginning 24 hours after CS. The proportion of females who became maternal within 24 hours of the beginning of maternal testing, 10 days after CS, was greater than that among females who received no exposure to pups.     

Distribution of cholinergic neurons and fibers in the hypothalamus of the rat using choline acetyltransferase as a marker

The distribution of choline-acetyltransferase-like immunoreactive structures in the rat hypothalamus and preoptic area was examined by using avidin-biotin immunocytochemistry. We found that the hypothalamus is richly innervated by the cholinergic neuron system. Sites containing cholinergic neurons of varying density were: medial and lateral preoptic areas, septohypothalamic nucleus, median preoptic area, lateral hypothalamus including the perifornical area, anterior hypothalamic nucleus, arcuate nucleus, dorsomedial hypothalamic nucleus, posterior hypothalamic nucleus, dorsal and ventral premammilary nuclei, neuropil mediodorsal to the anterior hypothalamic nucleus, neuropil ventral to the anterior hypothalamic nucleus and ventromedial hypothalamic nucleus, neuropil between lateral hypothalamus and ventromedial hypothalamus, and neuropil between dorsal premammilary nucleus and posterior hypothalamic nucleus. There were also many varicose and non-varicose fibers in the preoptic area and hypothalamus. Two kinds of varicose fibers, one with strong immunoreactivity and the other with weak immunoreactivity, were seen. Non-varicose fibers were also detected in the optic chiasma and habenulo-interpeduncular tract. These fibers were passing fibers.     

The bed nucleus of the stria terminalis in the Syrian hamster: subnuclei and connections of the posterior division

The bed nucleus of the stria terminalis is a key part of a ring of cells extending between the centromedial amygdala and bed nucleus of the stria terminalis referred to as the extended amygdala. The present study describes the architecture of the bed nucleus of the stria terminalis and the connections of subnuclei in posterior bed nucleus of the stria terminalis. The hamster bed nucleus of the stria terminalis is readily allotted to anterior and posterior divisions separated by the fibers of the body of the anterior commissure. The anterior division has four subnuclei: anteromedial, anterointermediate, anterolateral, and anteroventral. Within the posterior division, there are three distinct regions: posteromedial, posterointermediate, and posterolateral. In hamsters, the posterior bed nucleus of the stria terminalis contributes to male sexual behavior, particularly chemoinvestigation. Moreover, the posterior bed nucleus of the stria terminalis is part of a neural circuit essential for mating, including the medial amygdaloid nucleus and medial preoptic area. The connections of bed nucleus of the stria terminalis, posteromedial part, bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posterolateral part were visualized by co-injection of anterograde (Phaseolus vulgaris leucoagglutinin) and retrograde (cholera toxin B) tract tracers. The bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part have dense bidirectional connections with medial amygdaloid nucleus and cortical amygdala via the stria terminalis and ventral amygdalofugal pathway. These subnuclei also maintain bidirectional connections with steroid-concentrating areas including lateral septum, medial preoptic area, hypothalamus, and periaqueductal gray. The bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part receive projections from the subiculum and send projections to deep mesencephalic nuclei. By contrast, the bed nucleus of the stria terminalis, posterolateral part is connected with the central amygdala, lateral hypothalamus, subthalamic nucleus, nucleus accumbens, substantia innominata, substantia nigra and thalamus. Thus, the bed nucleus of the stria terminalis, posterointermediate part and bed nucleus of the stria terminalis, posteromedial part have similar connections with areas involved in social behaviors. The bed nucleus of the stria terminalis, posterolateral part maintains connections with areas involved in motivational circuits. This supports the concept of distinct circuits within the extended amygdala which differentially link the centromedial amygdala and bed nucleus of the stria terminalis.     

The medial preoptic area is necessary for motivated choice of pup- over cocaine-associated environments by early postpartum rats

Converging evidence suggests that the motivation to seek cocaine during the postpartum period is significantly impacted by the competing incentives of offspring, a stimulus unique to this life stage. In the present study, the functional role of the medial preoptic area (mPOA), a critical site involved in maternal responsiveness, on processing incentive value of pup-associated cues and influencing response allocation for pup- over cocaine-associated environments was investigated using a concurrent pup/cocaine choice conditioned place preference (CPP) paradigm. Early postpartum females with bilateral guide cannulae aimed into the mPOA or into anatomical control sites were conditioned, from postpartum days (PPD) 4 to 7, to associate different uniquely featured environments with pups or cocaine. CPP was tested on PPD8 following intra-mPOA infusions of either 2% bupivacaine or saline vehicle. In two additional experiments, the effects of intra-mPOA infusions of bupivacaine on expression of conditioned responding induced by environments associated with either pups or cocaine were examined separately. Transient inactivation of the mPOA selectively blocked the conditioned preferences for pup-associated environments, significantly contrasting the robust pup-CPP found in non-surgical and intra-mPOA vehicle-treated females. In contrast, mPOA inactivation failed to alter cocaine-CPP in postpartum females. When given a choice between environments associated with pups or cocaine, transient functional inactivation of the mPOA altered choice behavior, biasing the preference of females toward cocaine-associated environments, such that almost all preferred cocaine- and none the pup-associated option. The anatomical specificity was revealed when inactivation of adjacent regions to the mPOA did not affect CPP responses for pups. The findings support a critical role for the mPOA in mediating pup-seeking behavior, and further suggest that the competing properties of pups over alternative incentives, including drugs of abuse, rely on mPOA integrity to provide relevant pup-related information to the circuitry underlying the choice behavior between pups and alternative stimuli.