Iontophoresis of norepinephrine onto neurons of the pigeon's lateral geniculate nucleus: characterization of an inhibitory response.
A group of neurons in the pigeon's lateral geniculate equivalent nucleus (LGNe) shows associative enhancement of their response to light during visually conditioned heart rate change. The source of the relevant unconditioned stimulus input to LGNe for this enhancement has been identified as the locus coeruleus (LC). Thus, we have begun to examine neurotransmitters synthesized in LC for possible involvement in associative modification of neuronal discharge in LGNe. As a first step, we have examined the responses of LGNe neurons to iontophoretic application of norepinephrine (NE) and identified the receptor mediating one response class. The majority of neurons in LGNe show inhibition of maintained activity in response to iontophoretic application of NE or its agonists. The potency of the NE agonists is alpha-methyl NE greater than epinephrine greater than NE greater than phenylephrine greater than isoproterenol. This profile is characteristic of an alpha 2-adrenoceptor. The alpha 2-agonist clonidine also induces inhibition of maintained activity. The alpha 2-antagonists WB-4101 and yohimbine block the NE-inhibition while the alpha 1-antagonist prazosin and beta-antagonist sotalol do not. It is thus suggested that the receptor mediating the NE-inhibition of maintained activity has the characteristics of an alpha 2-adrenoceptor.
Elmslie
K S
KS
Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794.
Cohen
D H
DH
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D010856:Columbidae / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005829:Geniculate Bodies / Q000187:drug effects / Q000502:physiology*; D007478:Iontophoresis; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*
D011942:Receptors, Adrenergic, alpha; D003000:Clonidine; D009638:Norepinephrine