Biomedical subjects

Cliff H Summers

Publications and source records attributed to Cliff H Summers.

20 records · Page 2Linked to original sources

PubMed2002

GABAergic drugs alter hypothalamic serotonin release and lordosis in estrogen-primed rats.

The effects of muscimol, a GABA(A) agonist, and phaclofen, a GABA(B) antagonist, on serotonin (5HT) release in the mediobasal hypothalamus and lordosis behavior were studied in freely moving rats using in vivo microdialysis. Two days after implantation of bilateral guide cannulae directed towards the ventromedial nucleus of the hypothalamus (VMH), ovariectomized rats were primed with estradiol (E(2)). The rats were implanted with microdialysis probes 24 h later. Following a pretest for lordosis, perfusate 5HT was measured at 20-min intervals until the baseline was stable. The rats were treated with 10, 30 or 100 microM muscimol or 30 and 100 microM phaclofen in artificial CSF delivered via reverse dialysis for 40 min. Control animals were continuously perfused with artificial CSF. Behavior was tested 20, 60 and 180 min after introduction of the drug. Decreased hypothalamic 5HT (40-60% of baseline) and marked facilitation of lordosis were present 20 min after administration of either drug. The effects of 10 and 30 microM muscimol and 30 microM phaclofen on both 5HT and lordosis were reversed after 180 min. Reversal of the behavioral and neurochemical effects were not evident in either the 100 microM muscimol or 100 microM phaclofen groups at the time-points tested. Proceptive responses were observed in phaclofen-treated rats but not in rats treated with muscimol. Levels of hypothalamic 5HT and lordosis quotients in control rats did not significantly differ from initial values. These results suggest that GABAergic effects on lordosis may be mediated through an interaction with 5HT in the mediobasal hypothalamus.

Animals↗

PubMed2002

Manipulation of visual sympathetic sign stimulus modifies social status and plasma catecholamines.

Darkening of postorbital skin (eyespots) in Anolis carolinensis occurs during stressful situations via adrenal catecholaminergic activation of beta(2)-adrenergic receptors. The eyespots form more rapidly in dominant males during social interaction. It was hypothesized that eyespot darkening from green to black is a social signal that communicates disposition, resulting from sympathetic activation and determines social hierarchy. To assess the value of the eyespot as a signal influencing social dominance, males were paired according to size and weight, and painted postorbitally; one with green and the other with black paint. Painted pairs interacted with aggressive displays, approaches, and bites. Dominant status was determined by continued displacement of an opponent, superior perching position, and lighter color. Males with eyespots darkened by black paint were dominant in 100% of interactions and more aggressive. Males viewing an opponent with eyespots painted black exhibited higher plasma epinephrine (Epi), norepinephrine (NE), and dopamine (DA) levels than males with eyespots hidden with green paint and isolated controls. Results for behavior were similar, but those for plasma catecholamines contrast with those from recent experiments in which interactions occurred vs. a mirrored reflection. The eyespot is a potent stimulus, acting as a social signal that confers dominant status to its bearer, and activates the sympathetic nervous system in opponents that observe it during aggressive interactions.

Animals↗