Nov 1, 1982

Intra-raphe muscimol induced hyperactivity depends on ascending serotonin projections

Pharmacology, Biochemistry, and Behavior
S M Sainati, S A Lorens


Acute microinjections of the GABA agonist, muscimol (100 ng), into either the dorsal (DR) or the median (MR) raphe nucleus of etherized rats induced post-anesthesia hyperactivity as measured in photocell chambers. The increased activity counts seen after MR injections, furthermore, were 4 times greater than those following DR injections. In animals implanted with chronically indwelling cannulae, a muscimol (25-400 ng) dose-response analysis confirmed the greater sensitivity of the MR site. Subsequent experiments thus employed only MR cannulae. The benzodiazepine, chlordiazepoxide, in a subataxic dose (3.8 mg/kg, IP) by itself did not affect activity level, but enhanced the locomotor response to low doses (25-50 ng) of muscimol. Conversely, a sub-convulsant dose of the GABA antagonist, bicuculline (1.1 mg/kg, IP), completely blocked the hyperactivity produced by muscimol (50-100 ng). Bilateral electrolytic destruction of the ventral tegmental nuclei of Gudden produced hyperactivity, but failed to alter the effect of muscimol. Forebrain 5-hydroxytryptamine (5-HT, serotonin) depletion following administration of 5,7-dihydroxytryptamine did not affect baseline activity level, but markedly attenuated the locomotor response produced ...Continue Reading

Mentioned in this Paper

Projections and Predictions
Serotonin Measurement
Hormone Receptors, Cell Surface
August Rats
GABA Antagonists
Receptors, Tryptamine
Entire Midbrain
Benzodiazepine [EPC]

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