The effect of baclofen and somatostatin on neuronal activity in the rat ventromedial hypothalamic nucleus in vitro.
The electrical properties of neurones within the ventromedial hypothalamic nucleus of the rat were studied in an in vitro slice preparation, using conventional intracellular recording techniques. A detailed analysis of 36 intracellular recordings appeared to suggest 3 cell types, based on membrane capacitance and resistance characteristics, confirming previous reports of a diversity of cell types within this nucleus. The responsiveness of each cell type to exogenously-applied baclofen and somatostatin was also investigated. The inhibitory responses to both of these drugs were concentration-related (over the range 100 nM to 1 microM), tetrodotoxin-resistant and consisted of a membrane hyperpolarization (mean +/- SEM = 6.7 +/- 1 and 10.7 +/- 1 mV for 1 microM somatostatin and baclofen, respectively) and an associated reduction in the firing frequency of spontaneously active cells. These agonist-evoked responses probably represented direct postsynaptic actions but they were not restricted to any single type of cell. Evidence for an additional presynaptic effect of baclofen was also obtained. Responses to baclofen were extremely robust and readily quantifiable, whereas those to somatostatin showed pronounced long-lasting desensitization, which was particularly marked a larger concentrations. These data support previous contentions, based on in vivo studies, that somatostatin and GABA are likely to participate in the control of complex functions by the ventromedial hypothalamic nucleus.
Merck Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Harlow, Essex, U.K.
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Priestley
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001418:Baclofen / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity / Q000187:drug effects; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology*; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology*
D013004:Somatostatin; D001418:Baclofen