Evidence for excitatory 5-HT2-receptors on rat brainstem neurones.
1. The technique of microiontophoresis was used to investigate the identity of the receptor mediating the excitatory effects of 5-hydroxytryptamine (5-HT) upon neurones in the midline of the medullary brainstem of the rat in vivo. 2. The 5-HT1-like receptor agonists 5-carboxamidotryptamine (5-CT) and 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) failed to excite the majority of neurones excited by 5-HT. The mobilities of 5-CT and 8-OH-DPAT when tested in vitro were found not to differ significantly from that of 5-HT, suggesting that the lack of effect of these agonists was not due to a lower rate of release from the microelectrodes. 3. The excitatory responses to 5-HT were attenuated by the 5-HT 2-receptor antagonists ketanserin and methysergide when applied microiontophoretically or administered intravenously (0.3 and 1 mg kg-1 respectively). Excitatory responses to glutamate and noradrenaline were not reduced. 4. The 5-HT3-receptor antagonist MDL 72222 failed to attenuate selectively the excitatory response to 5-HT when applied either by microiontophoresis or administered intravenously (1 mg kg-1). 5. Microiontophoretic application of the alpha 1-adrenoceptor antagonist prazosin did not attenuate excitatory responses to either 5-HT or noradrenaline. Intravenously administered prazosin (0.8 mg kg-1) also failed to attenuate excitatory responses to 5-HT, but did block excitatory responses to noradrenaline. 6. These results suggest that 5-HT2-receptors, but not 5-HT1-like receptors, 5-HT3-receptors or alpha 1-adrenoceptors, are involved in the excitatory response of midline medullary neurones to 5-HT.
Davie
M
M
Department of Physiology, University College Cardiff.
Wilkinson
L S
LS
Roberts
M H
MH
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001933:Brain Stem / Q000032:analysis* / Q000502:physiology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000032:analysis / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011985:Receptors, Serotonin / Q000032:analysis* / Q000502:physiology; D012701:Serotonin / Q000502:physiology
D011985:Receptors, Serotonin; D012701:Serotonin; D007650:Ketanserin; D009638:Norepinephrine; D011224:Prazosin