Further evidence of teratogenic effects apparently produced by neurotransmitters during brain differentiation.

1. Adult male rats treated neonatally with the monoamine oxidase inhibitor pargyline showed significantly increased nuclear volumes of the nerve cells in the medial and central amygdaloid nuclei and significantly decreased concentrations of noradrenaline and dopamine in the hypothalamus as compared to control males. 2. Adult male rats treated neonatally with the monoamine depletor reserpine also displayed increased nuclear volumes of the nerve cells in the medial and central amygdaloid nuclei in comparison to the control males but significantly decreased nuclear volumes in comparison to the pargylinized males. Furthermore, the number of synapses in the stratum radiatum (CA 1-region) of the hippocampus was significantly decreased in the reserpinized males in comparison to the control males. 3. Adult male rats treated neonatally with the acetylcholine esterase inhibitor pyridostigmine showed a slight decrease of the noradrenaline concentration in the hypothalamus. These findings suggest that changes of neurotransmitter concentrations and/or turnover rates apparently produced by psychotrophic drugs during brain differentiation are able to exert teratogenic effects.