An investigation was made of monoamine-related agents on the Straub tail reaction (STR) due to central excitatory effect of morphine (10 mg/kg). Apomorphine (10 mg/kg) showed a tendency to enhance the STR, and L-dopa (150 mg/kg) and methamphetamine (5 and 10 mg/kg) produced a significant increase in the STR. Phenoxybenzamine and propranolol induced the inhibition of the STR to a large extent. Diethyldithiocarbamatc (250 mg/kg) and disulfiram (200 and 400 mg/kg) had no influence on the STR. α-Methyl-p-tyrosine (100 and 400 mg/kg) reduced the STR. L-5-Hydroxytryptophan [L-5-HTP] (100 mg/kg) inhibited the STR significantly. Isocarboxazid (50 mg/kg), nialamide (50 and 100 mg/kg) and tranylcypromine (10 and 25 mg/kg) did not influence the STR. On the contrary, biochemical investigations showed that morphine (10 and 20 mg/kg) decreased the 5-hydroxytryptamine (5-HT) content of the lumbosacral cord significantly, although no alteration of 5-HT content occurred in various sites of the brain, compared to a vehicle-treated group. Morphine (10 and 20 mg/kg) did not act on the dopamine or norepinephrine content of various sites of the brain and spinal cord. Our results suggest that the STR is, at least to some extent, the result of an increase in catecholarninergic activity and/or a decrease in tryptaminergic activity in the central nervous system of mice.
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