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Modified coeruleo‐cortical noradrenergic neurotransmission after serotonin depletion by PCPA: Electrophysiological studies in the rat
Author(s) -
Ferron André
Publication year - 1988
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.890020509
Subject(s) - locus coeruleus , serotonin , stimulation , clonidine , autoreceptor , neurotransmission , electrophysiology , chemistry , medicine , endocrinology , neuroscience , premovement neuronal activity , neuron , neurotransmitter , dorsal raphe nucleus , serotonergic , psychology , central nervous system , receptor
To detect eventual modifications in the efficacy of the noradrenergic (NA) coeruleo‐cortical system after serotonin (5‐HT) depletion by parachlorophenylalanine (PCPA), three electrophysiological parameters were investigated in urethane‐anesthetized rats which were treated for 2 days with daily injections of this inhibitor of 5‐HT synthesis. (1) The spontaneous activity of locus coeruleus (LC) noradrenergic neurons showed a significant increase in PCPA‐treated compared to control rats (4.3 vs. 2.6 Hz). (2) The sensitivity of NA autoreceptors was measued in the LC by the effect of intravenous administrations of clonidine or microiontophoretic applications of NA on spontaneous neuronal firing. In treated rats, clonidine and NA induced a lesser reduction of LC neuron firing than in the controls (27 vs. 75% decreases and 1,367 vs. 280 nC, respectively). (3) The responsiveness of cortical neurons to electrical stimulation of the LC was assessed by peristimulus time histograms in the dorsal fronto‐parietal cortex. Following stimulation at 2 or 4 Hz, a majority of spontaneously firing cortical units was inhibited by electrical stimulation of the LC, but the percentage of such units was reduced and showed a decreased responsiveness after PCPA treatment. These findings suggest that following 5‐HT depletion by PCPA, cortical NA neurotransmission is makedly reduced in its efficacy in spite of some increase in the spontaneous activity of coeruleo‐cortical NA neurons.