Influence of baclofen on temperature-sensitive neurons in chick hypothalamus.

Department of Pharmacology, Faculty of Medicine, Medical University, Sofia, Bulgaria.
Methods and Findings in Experimental and Clinical Pharmacology (Impact Factor: 0.77). 01/2005; 27(6):401-4. DOI: 10.1358/mf.2005.27.6.914775
Source: PubMed

ABSTRACT The effects of the GABA(B)-receptor agonist baclofen on neuronal tonic activity (firing rate) and temperature sensitivity (temperature coefficient, TC) of neurons in the preoptic area/anterior hypothalamus (PO/AH) have been examined in chick brain slices, using extracellular recordings. The tonic activity of both warm-sensitive and cold-sensitive neurons, as well as temperature-insensitive neurons, was significantly inhibited by superfusion with baclofen (1 microM). It is clearly evident from the present study that there was an increasing trend in warm-sensitive neurons and a significant (p<0.05) increase in TC of cold-sensitive neurons. Relatively high percentage (31.5%) of chick PO/AH neurons was determined as cold sensitive by present investigation. Particularly, GABA(B) mechanisms modify temperature sensitivity of the PO/AH neurons and thus modulation of temperature sensitivity in PO/AH is involved in the control of body temperature.

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    ABSTRACT: The goal of the study is to investigate the GABAergic action on firing rate (FR) and temperature coefficient (TC) on hypothalamic neurons in the juvenile chicken. Extracellular recordings were obtained from 37 warm-sensitive, 32 cold-sensitive and 56 temperature-insensitive neurons in brain slices to determine the effect of GABA(A)-receptor agonist muscimol, GABA(A)-receptor antagonist bicuculline, GABA(B)-receptor agonist baclofen and GABA(B)-receptor antagonist CGP 35348. Muscimol and baclofen in equimolar concentrations (1 microM) significantly inhibited FR of the neurons, regardless of their type of thermosensitivity. In contrast, bicuculline, as well as CGP 35348 (10 microM) increased FR of the majority of the neurons. The TC of most chick hypothalamic neurons could not be estimated during muscimol application because FR was completely inhibited. GABA(B)-receptor agonist specifically increased TC. This effect was restricted to cold-sensitive neurons, which were determined in a high number. The TC was significantly increased (p<0.05) by baclofen and significantly decreased (p<0.05) by CGP 35348. The effects of muscimol and baclofen on FR and TC were prevented by co-perfusion of the appropriate antagonists bicuculline and CGP 35348. The results suggest that the fundamental mechanisms of GABAergic influence on temperature sensitive and insensitive neurons in the chicken PO/AH are conserved during evolution of amniotes.
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