Elsevier

Neuroscience

Volume 29, Issue 3, 1989, Pages 675-683
Neuroscience

Vasopressin immunoreactivity in the anterior hypothalamus is altered during the establishment of dominant/subordinate relationships between hamsters

https://doi.org/10.1016/0306-4522(89)90140-1Get rights and content

Abstract

When paired for 15-min periods for 5–8 consecutive days, castrated, testosterone-treated hamsters consistently assumed the dominant status, based on a higher aggression index (18 ± 3) and frequency of flank marking (15 ±3) as compared to their castrated, untreated subordinate partners (−1.3 ± 1 and 2.4 ± 1, respectively). In addition to these hamsters with established dominant/subordinate relationships, control hamsters with no social interactions were killed, and in all animals the vasopressin level in the anterior hypothalamus-medial preoptic area was assessed by counting vasopressin immuno-reactive perikarya following immunocytochemistry, or by radioimmunoassay of vasopressin from tissue punches. In the socialized pairs the subordinate hamsters had a significantly (P < 0.01) lower number of vasopressin staining perikarya in the anterior hypothalamus, specifically the area of the nucleus circularis, than their dominant partners (n = 6 pairs). There was also a significantly (P < 0.001) lower level of vasopressin immunoreactivity in punches taken from the area of the nucleus circularis in subordinate hamsters as compared to their dominant partners (n = 14 pairs). However, there were no significant differences in the number of perikarya or the concentration of immunoreactive vasopressin between subordinate and dominant hamsters in the supraoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus or bed nucleus of the stria terminalis. The number of perikarya (n = 5 pairs) and concentration of vasopressin (n = 8 pairs) for all vasopressin immunoreactive sites, including the nucleus circularis, were similar for testosterone-treated and untreated hamsters that remained isolated and not subjected to daily aggressive encounters. The values in both groups of unsocialized hamsters were also similar to those seen in the testosterone-treated dominant hamsters.

In summary, the only difference in the vasopressin level between dominant and subordinate hamsters was observed in the area of the nucleus circularis. Furthermore, the only group of hamsters that differed in both the number of vasopressin immunoreactive perikarya and concentration of vasopressin were castrated controls, i.e. subordinates, that were tested daily with highly aggressive testosterone-treated dominant hamsters. These data provide evidence showing (1) that the diminution in vasopressin immunoreactivity in subordinate hamsters occurs in response to repeated social encounters with aggressive dominant hamsters, (2) that a behavioral manipulation may contribute to changes in the neuroanatomy and/or chemistry of the central nervous system, and (3) that the vasopressinergic neurons of nucleus circularis may be involved in the control of vasopressin-dependent flank marking. The lower level of flank marking behavior in subordinate hamsters may reflect, in part, the level of vasopressin synthesis and release from this population of neurons.

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