Changes in brain catecholamines and spontaneous locomotor activity in response to thyrotropin releasing hormone.

Repeated exposure of rats to thyrotropin releasing hormone produced a dose- and time-dependent increase in spontaneous locomotor activity accompanied by an increase in brain stem tyrosine hydroxylase. Dopamine levels in cerebral cortex were increased maximally by 34% in animals receiving thyrotropin releasing hormone at a dosage of 2 mg/kg for 10 days. The concentrations of brain stem tyrosine and cerebral cortex norepinephrine remained unaltered in response to thyrotropin releasing hormone treatment. Our data suggest that administration of thyrotropin releasing hormone increases the synthesis and perhaps the turnover of brain catecholamines and that this may constitute an underlying mechanism for the anti-depressant action of this synthetic hormone.