In Vivo Electrophysiological Characterization of 5-HT Receptors in the Guinea Pig Head of Caudate Nucleus and Orbitofrontal Cortex
Section snippets
Treatments
Male guinea pigs (250–300 g) were anesthetized with halothane and implanted with an osmotic minipump subcutaneously (Alza, Palo Alto, CA, U.S.A.) that delivered the 5-HT2 receptor antagonists metergoline or ritanserin (2 mg/kg/day) or 0.9% NaCl in the controls.
Single unit recording and microiontophoresis
Guinea pigs were anesthetized with chloral hydrate (200 mg/kg, i.p. followed by subsequent 50 mg/kg doses approximately every 30 min to achieve complete anesthesia) and placed in a stereotaxic frame. Body temperature was maintained at
RESULTS
Most caudate neurons were either quiescent or fired at extremely slow rate and were, therefore, activated by microiontophoretic application of QUIS. Since the average basal firing rate of spontaneously active caudate cells has been estimated at 4–6 spikes/sec (El Mansari et al., 1994), the ejection current of QUIS was set to activate quiescent cells to about this rate generally with currents of 80–100 nA. The average basal firing rate of spontaneously active orbitofrontal neurons was estimated
DISCUSSION
The present study was aimed at characterizing the 5-HT receptor subtypes mediating the effect of microiontophoretic ejection of 5-HT in the guinea pig head of caudate nucleus and orbitofrontal cortex. The inhibitory effect of 5-HT and of the 5-HT2 receptor agonists DOI and mCPP was not antagonized by acute intravenous administration of the 5-HT2 receptor antagonists metergoline and ritanserin, in the head of caudate nucleus. However, after a 4 day treatment with metergoline and ritanserin, the
Acknowledgements
This study was supported by the Medical Research Council of Canada grant MA-11014 and a Scientist awarded to P.B. and the Fonds de la Recherche en Santé du Québec (FRSQ). M.E. was in receipt of postdoctoral fellowship from the FRSQ.
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