A PHARMACOLOGICAL STUDY OF THE ADRENERGIC MECHANISMS INVOLVED IN THE STRETCH REFLEX OF THE DECEREBRATE RAT

Abstract

1 The effects of catecholamine precursors, enzyme inhibitors, and monoamine depletors have been studied on the stretch reflex in the decerebrate rat. 2 l-DOPA alone had a biphasic effect, facilitation followed by inhibition and recovery of the reflex. 3 About 10% of the preparations did not develop decerebrate rigidity. These preparations did not have a stretch reflex. Within 1 to 5 min of the injection of l-DOPA in these inactive preparations, a stretch reflex could be elicited. 4 Control experiments indicate that l-DOPA was acting centrally after decarboxylation. 5 dl-dihydroxyphenylserine had an inhibitory effect, without a preceding facilitation. 6 When l-DOPA was preceded by diethyldithiocarbamate (i.v.) or FLA-63 (i.p.), the predominant response was a sustained facilitation, without an accompanying inhibition. 7 It is concluded that in the decerebrate rat, increased stretch reflex activity is associated with increased central levels of dopamine, and decreased stretch reflex activity with increased central levels of noradrenaline. The results are discussed with reference to the possibility that dopamine acts by liberating 5-hydroxytryptamine.