Sarah Schilling Winans

OLFACTORY AND VOMERONASAL DEAFFERENTATION OF MALE HAMSTERS: HISTOLOGICAL AND BEHAVIORAL ANALYSES

Deafferentation of the vomeronasal system by cutting the vomeronasal nerves severely impaired mating behavior in 44% of male hamsters over a 1--2 month period of postoperative testing, but the remaining males mated normally after the surgery. Damage to the main olfactory bulbs, concomitant to vomeronasal nerve cuts, did not account for this behavioral difference. Subsequent deafferentation of olfactory system by intranasal infusion of zinc sulfate solution (5 g ZnSO4--7H2O in 95 ml 0.5% NaCl) had no effect on intromission or ejaculation latencies of sham vomeronasal cut males but eliminated mating behavior 2 days after treatment in males with bilateral vomeronasal nerve cuts. Some of these males recovered the behavior in 1--3 weeks of post zinc sulfate testing. Histological analyses of the olfactory mucosa in 7 males on day 2 after zinc sulfate showed that 89--97% of the mucosa had been destroyed in 6 out of 7 of the males and 78% in the seventh. We conclude that destruction of the vomeronasal system irreparably reduces arousal necessary for mating in some hamsters but in other males sufficient arousal for this behavior to occur is mediated through the olfactory system, presumably in conjunction with other sensory inputs. Subsequent removal of the olfactory input in these animals eliminates the behavior.

Efferent connections of dorsal and ventral agranular insular cortex in the hamster, Mesocricetus auratus.

The anterior portion of rodent agranular insular cortex consists of a ventral periallocortical region (AIv) and a dorsal proisocortical region (AId). Each of these two cortical areas has distinct efferent connections, but in certain brain areas their projection fields are partially or wholly overlapping. Bilateral projections to layers I, III and VI of medial frontal cortex originate in the dorsal agranular insular cortex and terminate in the prelimbic, anterior cingulate and medial precentral areas; those originating in ventral agranular insular cortex terminate in the medial orbital, infralimbic and prelimbic areas. The dorsal and ventral regions of the agranular insular cortex project topographically to the ipsilateral cortex bordering the rhinal fissure, which includes the posterior primary olfactory, posterior agranular insular, perirhinal and lateral entorhinal areas. Fibers to these lateral cortical areas were found to travel in a cell-free zone, between cortical layer VI and the claustrum, which corresponds to the extreme capsule. The dorsal and ventral regions send commissural projections to layer I, lamina dissecans and outer layer V, and layer VI of the contralateral homotopical cortex, via the corpus callosum. Projections from the ventral and dorsal regions of the agranular insular cortex to the caudatoputamen are topographically arranged and terminate in finger-like patches. The ventral, but not the dorsal region, projects to the ventral striatum and ventral pallidum. The thalamic projections of the ventral and dorsal regions are largely overlapping, with projections from both to the ipsilateral reticular nucleus and bilaterally to the rhomboid, mediodorsal, gelatinosus and ventromedial nuclei. The heaviest projection is that to the full anteroposterior extent of the medial segment of the mediodorsal nucleus. Brainstem areas receiving projections from the ventral and dorsal regions include the lateral hypothalamus, substantia nigra pars compacta, ventral tegmental area and dorsal raphe nucleus. In addition, the ventral region projects to the periaqueductal gray and the dorsal region projects to the parabrachial and ventral pontine nuclei. These efferent connections largely reciprocate the afferent connections of the ventral and dorsal agranular insular cortex, and provide further support for the concept that these regions are portions of an outer ring of limbic cortex which plays a critical role in the expression of motivated, species-typical behaviors.

Sexual behavior in peripherally anosmic male hamsters.

Abstract Sexually experienced and inexperienced male hamsters mated normally after they had been rendered temporarily anosmic by intranasal zinc sulfate treatment (Experiment 1), in contrast to the complete absence of sexual behavior following removal of the olfactory bulbs. The efficacy of our zinc sulfate technique was demonstrated by use of an olfactory discrimination training procedure. Hamsters lost the ability to smell both amyl acetate (Experiment 2) and the female hamster post-estrus vaginal discharge (Experiment 3) following zinc sulfate induced anosmia but at the same time retained normal sexual behavior.

Stria terminalis lesions alter the temporal pattern of copulatory behavior in the male golden hamster

The mating behavior of a group of male golden hamsters was observed before and after bilateral electrolytic lesions or knife cuts interrupting the stria terminalis (ST). Whereas males with bilateral lesions of the medial nucleus of the amygdala had previously been observed to stop mating, a majority of hamsters with bilateral ST destruction, whether by electrolytic lesions or knife cuts, continued to display mounts, intromissions, and ejaculations during tests over a two month postoperative period. ST-lesioned males did, however, display a distinctly altered pattern of copulation over the course of postoperative testing, consisting of an increase in mount latency during the first week, an increase in the inter-intromission interval during the second week, and an increase in the number of intromissions preceding ejaculation during the third and subsequent weekly tests. Males with bilateral lesions of the caudal amygdala, which damaged the amygdaloid exit of the ST, displayed alterations in copulatory behavior similar to those seen after bilateral ST destruction at a more rostral level.

Neonatal and two-stage olfactory bulbectomy: Effects on male hamster sexual behavior

The copulatory behavior of sexually mature male hamsters was investigated following removal of the olfactory bulbs in ways which might be expected to minimize postoperative behavioral effects. Neither two-stage bulbectomy in adults nor a one-stage operation in neonates prevented the total abolition of sexual behavior consequent to bilateral olfactory bulb removal in most of the animals. However, two bulbectomized hamsters (one, one-stage; one, two-stage) displayed an atypical persistence of mating postoperatively. Their lesions, which included total bilateral destruction of the main and accessory bulbs and damage to adjacent olfactory tissue, were histologically comparable to the lesions in two other bulbectomized hamsters (from different studies) which also copulated postoperatively. The behavior of these atypical animals supports the hypothesis that male hamsters can display normal sexual behavior in the absence of olfactory stimulation.

Evidence for a ventral non-strial pathway from the amygdala to the bed nucleus of the stria terminalis in the male golden hamster

Male hamsters in which the stria terminalis (ST) had been interrupted either by electrolytic lesions or knife cuts, or normal control males, received iontophoretic injections of horseradish peroxidase in either the bed nucleus of the stria terminalis (BNST) or the medial preoptic-anterior hypothalamic area (MPOAH). Comparison of intact and ST-lesioned brains revealed the existence of a ventral non-strial pathway, from cells in the medial amygdaloid nucleus (M) to the preoptic portion of the BNST but not to the MPOAH. Since bilateral lesions of M completely eliminate male hamster mating behavior, but ST lesions do not, we suggest that the ventral pathway to the BNST may be an important route by which M influences male copulatory behavior.

The photoneuroendocrine control of seasonal breeding in the ewe

Abstract The major environmental parameter controlling seasonal breeding in ewes is photoperiod. Short days stimulate, and long days inhibit breeding activity. One of the more intriguing enigmas of neuroendocrinology is the endocrine mechanism whereby a mere change in daylength initiates or prevents estrous cycles. Recent experiments have begun to solve this problem by demonstrating that in ewes, photoperiod governs response of the hypothalamo-pituitary axis to the negative feedback action of estradiol. In long days, estradiol is a potent inhibitor of gonadotropin secretion, whereas in short days it is relatively ineffective in this regard. These photoperiod-induced changes in estradiol feedback are proposed to permit or prevent estrous cycles by controlling the occurrence of a crucial step in the sequence of events leading to ovulation, namely a sustained, preovulatory rise in LH. Thus, estrous cycles cease in long days because an increase in estradiol negative feedback prevents the sustained rise in LH. In short days, estrous cycles resume because a decrease in estradiol feedback permits the sustained rise in LH required for ovulation. Even more puzzling, at present, than the mechanism of transduction of photoperiodic information into an endocrine event controlling seasonal breeding is the problem of transmission of photoperiodic information from the environment to the hypothalamo-pituitary axis. In sheep, early investigations of the transmission pathway have elicited provocative results, only some of which are similar to those obtained in other species. Among the questions which remain to be answered are: what is the location of the photoreceptors, and what, if any, are the roles of the suprachiasmatic nuclei and the pineal in photoperiodic control of seasonal breeding? These issues promise to provide a tantalizing challenge for future investigations into the photoneuroendocrine control of seasonal breeding.