Evidence for a functional and anatomical relationship between the lateral septum and the hypothalamus in the control of flank marking behavior in Golden hamsters

Reciprocal connections of lateral septal neurons and neurons in the lateral hypothalamus in the rat: a combined phaseolus vulgaris-leucoagglutinin and Fluoro-Gold immunocytochemical study

Reciprocal connections between lateral septal neurons and neurons in the lateral hypothalamus/lateral preoptic area were studied in the rat. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde tracer Fluoro-Gold (FG) were simultaneously injected into the lateral septum. After double-immunocytochemistry, PHA-L-labeled terminals were found in synaptic contact with dendrites of retrogradely FG-labeled neurons in the lateral hypothalamic/lateral preoptic area.

Differential lateral septal vasopressin innervation in aggressive and nonaggressive male mice

The vasopressinergic (VP) projection from the bed nucleus of the stria terminalis (BNST) to the lateral septum (LS) is sexually dimorphic and dependent of androgens at adult and neonatal age. We studied the relation between testosterone (T) and VP in male mice, which were genetically selected for their differences in aggression level. Aggressive males, characterized by a short attack latency (SAL), have a higher production capacity of T at adult age compared to males with a long attack latency (LAL). Neonatally, however, a higher T production occurs in the nonaggressive LAL males than in SAL males. In the present study we showed a more dense VP-immunoreactive (VP-ir) innervation in the LS and a higher VP-ir neuron density in the BNST of LAL males as compared to SAL males. The described differences may be the consequence of a differential neonatal androgen effect on the organization of the forebrain vasopressinergic network.

Vasopressin innervation of sexually dimorphic structures of the gerbil forebrain under various hormonal conditions

The distribution of vasopressin-immunoreactive fibers in the forebrain of male and female gerbils was studied, focusing on the lateral septum and the sexually dimorphic area (SDA) found at the border between the medial preoptic area and the anterior hypothalamus. To study hormonal influences on the densities of these fibers, some animals of each sex were gonadectomized or gonadectomized and given testosterone. Others were given sham operations. High densities of vasopressin-immunoreactive fibers were found in the lateral septum. In the SDA, the densities of these fibers varied considerably. Many were found in the medial half of the medial SDA, but few in the lateral SDA. Vasopressin-immunoreactive fibers were also sparse in the lateral half of the medial SDA, except for a dense cluster in the SDA pars compacta of males. Similar but smaller clusters were seen in the same location in females although the SDA pars compacta could not be detected in Nissl-stained sections from the female brains. Fiber densities in two areas, the lateral septum and the lateral SDA, were sensitive to gonadal steroids. In both cases, castration reduced fiber density and testosterone enhanced it. In addition, fiber densities in two areas, the lateral septum and the medial SDA, were sexually dimorphic. In each case, fiber density was greater in males. There was no hormonal effect, however, on the fiber densities in the medial SDA. The fact that the fiber plexuses in the lateral septum and the medial SDA respond differently to gonadal steroids suggests that they arise from different cells and possibly from different areas of the brain. The vasopressin-immunoreactive fibers in the lateral septum probably come from steroid-sensitive vasopressin neurons in the bed nucleus of the stria terminalis. Those in the medial SDA may originate in the dorsal aspect of the suprachiasmatic nucleus where vasopressin-immunoreactive cell bodies were seen.

Microinjection of arginine-vasopressin into the periaqueductal gray stimulates flank marking in Syrian hamsters (Mesocricetus auratus)

Syrian hamsters can communicate using a distinctive form of scent marking called flank marking. Vasopressin-sensitive neurons within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) play a critical role in the control of this form of olfactory communication. Extrahypothalamic regions may also mediate hamster flank marking. Since the MPOA-AH and the periaqueductal gray (PAG) are reciprocally connected, the present study investigated whether PAG neurons are involved in the control of flank marking. The first study found that microinjection of vasopressin, but not oxytocin or saline, into the PAG induced high levels of flank marking in male (n = 8) and female (n = 5) hamsters (P less than 0.01). The second study demonstrated that microinjection of vasopressin into the PAG stimulated flank marking in a dose-dependent manner in both male (n = 7) and female (n = 11) hamsters (P less than 0.01). These data suggest that vasopressin-responsive neurons within the periaqueductal gray participate in the control of hamster flank marking.

The efferent connections of the lateral septal nucleus in the guinea pig: intrinsic connectivity of the septum and projections to other telencephalic areas

The distribution of efferent fibers originating in the lateral septal nucleus was investigated in guinea pigs by means of anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Special emphasis was placed on the intraseptal fiber systems. The fibers originating from the different subnuclei of the lateral septal nucleus formed massive horizontal connections in the rostrocaudal axis. Projections to the contralateral, congruent subnuclei were also detected. In the medial septum/diagonal band of Broca complex the largest number of PHA-L-stained fibers was found after application of the tracer into the dorsal subnucleus of the lateral septal nucleus; the density of the efferent fibers decreased progressively after injection into the intermediate or ventral subnuclei. In all cases the diagonal band contained a much higher number of efferent fibers from the lateral septal nucleus than from the medial septal nucleus. In the medial septal nucleus, terminal labeling was generally sparse. Other telencephalic areas (organum vasculosum of the lamina terminalis, nucleus accumbens, bed nucleus of the stria terminalis, amygdala, hippocampal complex, and other cortical areas) contained varying numbers of labeled projections. In double-labeling experiments, a close spatial relationship between PHA-L-stained fibers and vasoactive intestinal polypeptide-immunoreactive perikarya was observed in several of these target areas.

The efferent connections of the lateral septal nucleus in the guinea pig: projections to the diencephalon and brainstem

The anterograde Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing technique was used to determine the distribution of efferent fibers originating in the lateral septal nucleus of the guinea pig. For complementary detection of the chemical identity of the target neurons, double-labeling immunocytochemistry was performed with antibodies to PHA-L and to vasopressin, oxytocin, vasoactive intestinal polypeptide, serotonin or dopamine beta-hydroxylase, respectively. The hypothalamus received the majority of the PHA-L-stained septofugal fibers. Here, a specific topography was observed. (1) The medial and lateral preoptic area, (2) the anterior, lateral, dorsal, posterior hypothalamic and retrochiasmatic area, (3) the supraoptic, paraventricular, suprachiasmatic, dorsomedial, caudal ventromedial and arcuate nuclei, and (4) the tuberomammillary, medial and lateral supramammillary, dorsal and ventral premammillary nuclei always contained PHA-L-labeled fibers. The rostral portion of the ventromedial nucleus and the medial and lateral mammillary nucleus only occasionally showed weak terminal labeling. In other diencephalic areas, termination of PHA-L-labeled fibers was observed in the epithalamus and the nuclei of the midline region of the thalamus. In the mesencephalon, terminal varicosities occurred in the ventral tegmental area, interfascicular and interpeduncular nucleus, and periaqueductal gray. In addition, the dorsal and medial raphe nuclei of the metencephalon, together with the locus coeruleus and the dorsal tegmental nucleus, received lateral septal efferents.

Vasopressin in the septal area of the golden hamster controls scent marking and grooming

Microinjection of arginine vasopressin into the lateral septum and bed nucleus of the stria terminalis of male hamsters stimulates intense flank marking and flank gland grooming, while microinjections of vasopressin in sites immediately adjacent to these areas or in the lateral ventricle are ineffective. Microinjections of oxytocin, angiotensin II and the behaviorally active C-terminal fragment of vasopressin, metabolite neuropeptide, by comparison, do not stimulate flank marking. Effective sites for vasopressin injection are clearly superimposable upon autoradiographically defined sites of high V1-receptor density. Furthermore, vasopressin-sensitive neurons in the lateral septum and bed nucleus of the stria terminalis are necessary for the expression of naturally elicited flank marking since the microinjection of a V1-receptor antagonist into these sites was able to temporarily block flank marking triggered by odors from conspecifics.