Implication of central neurohypophyseal hormone receptor-mediated action in timing of reproductive events: evidence from novel observations on the effect of a vasotocin analogue on singing behaviour of the canary.

A highly discrete distribution of neurohypophyseal hormone receptors was discovered in the mammalian and avian brain. These receptors are heterogeneous. In rat brain oxytocin (OT) and V1a receptors can be distinguished which bind OT with an order of magnitude difference in affinity and which are located in discrete sites of the limbic-midbrain circuitry. In the brain of the canary low and high affinity vasotocin (VT) sites were identified; the latter putative VT receptors were found exclusively localized in the area encapsulating the nucleus robustus archistriatalis (RA). We show with recordings of singing behaviour that a VT analogue promotes the chain of seasonal events in this behaviour.

Localization of interleukin 6 mRNA and interleukin 6 receptor mRNA in rat brain.

The cytokine interleukin 6 (IL6) has several effects on the central nervous system in addition to the well established regulation of the acute phase inflammatory response. Therefore, the distribution of IL6- and IL6 receptor mRNA in the rat brain has been investigated by in situ hybridization using [35S]-labeled oligonucleotides. The messages of both genes were found in the CA1-CA4 regions as well as in the dentate gyrus of the hippocampus, in the habenulae, the dorsomedial and the ventromedial hypothalamus, in the internal capsule, the optic tract and in the piriform cortex. These data indicate both neuronal and glial localization of IL6 and IL6 receptor and their involvement in an autocrine or paracrine action of the cytokine in centrally regulated functions including neuroendocrine control.

Estradiol modulates density of putative 'oxytocin receptors' in discrete rat brain regions.

Previous studies have provided evidence for a discrete localization of two types of vasopressin (AVP)-labeled binding sites in the rat brain, i.e., regions labeled preferentially with AVP (putative AVP receptors) and regions labeled with AVP as well as oxytocin (OT). The latter binding sites are considered here as putative OT receptors. In the present study the effect of estradiol on the number of these putative receptor sites for OT and AVP was investigated in rat brain after daily subcutaneous administration of the steroid (10 micrograms/100 g body weight) to ovariectomized rats. Specific binding of [3H]-OT and [3H]-AVP was determined after in vitro incubation of frozen brain sections, autoradiography and quantitation of the images with computer-assisted densitometry. Estradiol increased the number of OT receptors at least 4-fold in the ventromedial nucleus of the hypothalamus, regions of the olfactory tubercle, the nucleus accumbens and occasionally in the organum vasculosum laminae terminalis. A smaller increase (two-fold) was noted in the central amygdala, while a tendency to a decrease in OT receptor number was noted in the olfactory nucleus and the ventral subiculum. Estradiol treatment permitted an estimation of binding constants of [3H]-OT-binding to a membrane fraction of microdissected ventromedial hypothalamic region (Kd: 1.3 nM, Bmax: 19.9 fmol/mg protein). The number of putative AVP receptors in the lateral septum and in the nucleus tractus solitarii was not affected by estradiol. In conclusion, the OT receptor system is subject to modulation by estradiol in some discrete brain regions, but not in others.(ABSTRACT TRUNCATED AT 250 WORDS)