G.J. de Vries

The origin of the vasopressinergic and oxytocinergic innervation of the rat brain with special reference to the lateral septum

The origin of the vasopressin-containing fibers in the rat lateral septum was studied by means of lesioning specific areas, in which vasopressin-containing cells are found, or by surgically separating the septum from the underlying structures. Following these procedures sections of the brain were stained immunocytochemically for the presence of vasopressin. In addition, retrograde labeling tracers were injected in the lateral septum. Lesioning of the paraventricular nucleus did not result in the disappearance of vasopressin fibers from the lateral septum, nor from the various other areas studied. It did, however, cause the disappearance of fibers from the nucleus of the solitary tract and the nucleus ambiguus. By contrast, after the same lesion practically the whole oxytocinergic innervation of the brain disappeared. Injection of tracers into the lateral septum revealed retrograde labeled cells, e.g. in the bed nucleus of the stria terminalis, but not in the paraventricular and supraoptic nucleus. Horizontal cuts under the lateral septum, intersecting the diagonal band of Broca, resulted in a dramatic decrease of the vasopressin fibers in the lateral septum, suggesting that the fibers enter the septum via this structure. Moreover, since the vasopressin fiber density was found to decrease drastically in the lateral septum after lesioning the bed nucleus of the stria terminalis, the vasopressin cells found in this area are probably the source of these fibers. Other areas where fibers were seen to decrease after lesions of the bed nucleus are the diagonal band of Broca, the area of the anterior amygdala, the lateral habenular nucleus, the periventricular gray, and the locus coeruleus.

SEXUAL DIFFERENTIATION OF CENTRAL VASOPRESSIN AND VASOTOCIN SYSTEMS IN VERTEBRATES: DIFFERENT MECHANISMS, SIMILAR ENDPOINTS

Vasopressin neurons in the bed nucleus of the stria terminalis and amygdala and vasotocin neurons in homologous areas in non-mammalian vertebrates show some of the most consistently found neural sex differences, with males having more cells and denser projections than females. These projections have been implicated in social and reproductive behaviors but also in autonomic functions. The sex differences in these projections may cause as well as prevent sex differences in these functions. This paper discusses the anatomy, steroid dependency, and sexual differentiation of these neurons. Although the final steps in sexual differentiation of vasopressin/vasotocin expression may be similar across vertebrate species, what triggers differentiation may vary dramatically. For example, during development, estrogen masculinizes vasopressin expression in rats but feminizes its counterpart in Japanese quail. Apparently, nature consistently finds a way of maintaining sex differences in vasopressin and vasotocin pathways, suggesting that the function of these differences is important enough that it was conserved during evolution.

Vasopressin cells in the bed nucleus of the stria terminalis of the rat: sex differences and the influence of androgens

A sex difference in the number of vasopressin-immunoreactive cells was found in the bed nucleus of the stria terminalis of the rat. The number of cells found in males exceeded the female corresponding value. A sharp decrease in the number of vasopressin-immunoreactive cells was noted 21 weeks after the castration of adult male rats. This decline could be reversed completely by a 5-week testosterone substitution therapy.

Gonadal hormone actions on the morphology of the vasopressinergic innervation of the adult rat brain

Castration of adult male rats resulted in a gradual decrease in vasopressin fiber density over a period of 15 weeks to a point where hardly any fibers were found in those areas where the fibers probably are derived from the bed nucleus of the stria terminalis. The original fiber density could be restored by testosterone replacement therapy within 5 weeks. No effects of hormonal manipulations were found in the vasopressin projections of the paraventricular and the suprachiasmatic nucleus. Ovariectomy of female rats resulted in the same changes in the vasopressin fiber pathways, as did castration in males.

Effects of androgens and estrogens on the vasopressin and oxytocin innervation of the adult rat brain

Recently we reported that castration of rats eliminates vasopressin immunoreactivity in the lateral septum and other areas that appear to receive vasopressin innervation from the bed nucleus of the stria terminalis. Testosterone treatment counteracts this effect of castration. In the present study, we investigated whether this action of testosterone depends on its androgenic or estrogenic metabolites by treating long-term castrated rats with estradiol (E) and/or 5 alpha-dihydrotestosterone (DHT) or testosterone. The brains were then processed for immunocytochemistry or radioimmunoassay. DHT did not increase vasopressin staining in the lateral septum, although it fully restored the size of the seminal vesicles. E did restore the original fiber density, but individual fibers stained more weakly than in sham-operated males. Only treatment with both E and DHT fully restored the vasopressin innervation. This pattern was also reflected in the radioimmunoassay data. The vasopressin content of the lateral septum decreased about 90% after castration but was fully restored by either testosterone or E + DHT treatment. E alone, however, was only half as effective as E + DHT. The treatments had no effect on the oxytocin content of the septum, or on the vasopressin or oxytocin content of the dorsal vagal complex. The results suggest that E mediates most of the effects of testosterone on the vasopressin innervation of the lateral septum. DHT enhances the response to E but has little effect on its own.

Sex differences in the parental behaviour of adult virgin prairie voles: Independence from gonadal hormones and vasopressin

Sexually and parentally experienced prairie voles display robust biparental care of pups that is similar between the sexes. Little is known, however, about possible sex differences in the parental behaviours of sexually inexperienced prairie voles. Parental behaviour of adult virgin male and female prairie voles was examined in sham‐operated and gonadectomized subjects treated with vehicle or oestradiol. Since arginine‐vasopressin (AVP) has been suggested to stimulate parental behaviour in sexually inexperienced males, neural AVP immunoreactivity (AVP IR) was quantified. Most sham‐operated and castrated males displayed high levels of parental behaviour (9/9 controls, 6/9 castrates) during a 15‐min exposure to pups 4 weeks after surgery, and few behavioural differences were seen between groups. Conversely, almost all gonadally intact (8/9) and gonadectomized (8/9) females attacked pups. Implantation of a 0.1‐mg pellet of oestradiol immediately after gonadectomy had little effect on males (9/9 parental), whereas most (5/9) oestradiol‐treated females acted maternally. AVP‐immunoreactive (AVP‐ir) fibre density in the lateral septum (LS) and lateral habenula (LHb), expressed by the number of pixels that covered AVP‐ir fibres during computerized optical density analysis, was greater in males than females, was non‐significantly reduced in castrated males, and doubled in the LS of oestradiol‐treated females. In a second experiment, males tested 8 weeks after similar manipulations remained highly parental though castrated males had almost no AVP‐ir fibres in the LS and LHb. Levels of AVP IR in males treated with oestradiol were similar to those observed in intact males. A dramatic sex difference therefore exists in the parental behaviour of adult sexually naive prairie voles which cannot be explained by sex differences in gonadal hormones. Because both castrated and intact males were highly parental, even though castrates had virtually no AVP‐ir in the LS or LHb, AVP does not appear to be crucial for their responsiveness toward pups.

Seasonal variation in vasopressin innervation in the brain of the European hamster (Cricetus cricetus)

Using immunocytochemistry, vasopressin innervation was determined in the brain of the European hamster (Cricetus cricetus) during different seasons. It was found that the spring period coincides with a dense vasopressin innervation in many brain regions in the male hamster, and lower vasopressin fibre density in some brain regions in the female hamster. In autumn just before hibernation an almost complete disapperance of vasopressin innervation is noted in those brain regions that are sexually dimorphically innervated in spring. These results suggest that vasopressin activity in certain areas of the brain might be required for some-seasonal functions to find expression.

Changes with aging in the vasopressin and oxytocin innervation of the rat brain

The effect of aging on the vasopressin (AVP) and oxytocin (OXT) innervation of the brain was studied by means of immunocytochemistry, comparing the major innervated areas in 5-month-old and 34-month-old male Brown-Norway rats. A marked decrease of AVP fiber density was found in the old rats as compared with the young animals in the vertical limb of the diagonal band, the basal nucleus of Meynert, the lateral habenular nucleus, the medial amygdaloid nucleus, the substantia nigra, the ventral hippocampus, the central gray, the locus coeruleus and in the ambiguus nucleus. The AVP innervation of the lateral septum and the dorsomedial hypothalamic nucleus was moderately, although not significantly reduced. No age difference in AVP innervation was found in the paraventricular thalamic nucleus or in the nucleus of the solitary tract. OXT fiber density did not differ between young and old animals in the locus coeruleus, the nucleus of the solitary tract and the ambiguus nucleus. Thus, the aging process appears to affect AVP cells in a differential, rather than in a general way. Changes were found to be more pronounced in those areas where the AVP innervation is dependent upon circulating androgens.

MATERNAL BEHAVIOUR IN LACTATING RATS STIMULATES c-fos IN GLUTAMATE DECARBOXYLASE-SYNTHESIZING NEURONS OF THE MEDIAL PREOPTIC AREA, VENTRAL BED NUCLEUS OF THE STRIA TERMINALIS, AND VENTROCAUDAL PERIAQUEDUCTAL GRAY

Increased activity of the immediate-early gene c-fos can be observed in many areas of the lactating rat brain after dams physically interact with pups and display maternal behaviour. These sites include the medial preoptic area, ventral bed nucleus of the stria terminalis, and the ventrolateral caudal periaqueductal gray, each of which is critical for the normal performance of particular maternal behaviours. The phenotype of cells in these areas that show increased c-fos activity after maternal behaviour, however, is unknown. Via double-label immunocytochemistry, we determined if the population of cells in these sites that express c-fos after maternal behaviour in lactating rats overlaps with the population that expresses the 67,000 mol. wt isoform of glutamate decarboxlyase, the synthesizing enzyme for the inhibitory neurotransmitter GABA. Lactating rats were separated from pups beginning on day 5 postpartum, and 48h later half were allowed to interact with a litter of pups for 60min whereas the other half were not. Dams re-exposed to pups were highly maternal, retrieving and licking them as well as displaying prolonged nursing behaviour that included milk letdown. Both groups of dams had a similar number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells in each site, although the number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells per microscopic field was significantly greater in the caudal ventrolateral periaqueductal gray than in the ventral bed nucleus of the stria terminalis, which in turn was greater than the medial preoptic area. In pup-stimulated dams, two to fourfold more Fos-immunoreactive cells were found in these three sites compared with non-stimulated controls. Labeling for Fos immunoreactivity and 67,000 mol. wt glutamate decarboxylase immunoreactivity was heterogeneous within each site. In the medial preoptic area, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells (either single or dual-labeled) were found dorsally than ventrally. In the ventral bed nucleus of the stria terminalis, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells were found medially than laterally. Within the caudal ventrolateral periaqueductal gray, 67,000 mol. wt glutamate decarboxylase-immunoreactive labeling was greatest ventromedially, while high numbers of Fos-immunoreactive nuclei were found both ventromedially and ventrolaterally. In pup-stimulated dams, more than half (53% in the medial preoptic area, 59% in the ventral bed nucleus of the stria terminalis, and 61% in the caudal ventrolateral periaqueductal gray) of the total population of Fos-immunoreactive cells also expressed 67,000 mol. wt glutamate decarboxylase. These results suggest that many of the neurons in these sites that show elevated c-fos activity after maternal behaviour are either local inhibitory interneurons or provide inhibitory input to other neural sites. These inhibitory mechanisms may be critical for the display of postpartum nurturance, possibly facilitating maternal behaviour by removing tonic inhibition on sites necessary for maternal responding or by restricting activity in neural sites that inhibit it.

Coexistence of vasopressin, neurophysin and noradrenaline immunoreactivity in medium-sized cells of the locus coeruleus and subcoeruleus in the rat

Vasopressin-and neurophysin-immunoreactive cells have recently been demonstrated in the rat locus coeruleus (A6) and subcoeruleus (A7). Using consecutive 5 microns thick frozen sections, medium-sized cells throughout the locus coeruleus area, but predominantly in the posterior parts of the A6 displayed coexistence for vasopressin and noradrenaline or neurophysin and noradrenaline immunoreactivity. The putative projection areas of putative fibers from vasopressin-containing cells in the locus coeruleus still remain to be elucidated.