Ventral midbrain stimulation, blood pressure responses and their relation to the dopaminergic nigro-striatal pathways.

In 40 cats systematic, electrical stimulation of ventral midbrain structures was performed. In the lightly anaesthetised animals, fixed in a stereotaxic frame, ECoG and arterial blood pressure were registrated. As a result stimulation-induced phasic blood pressure increases have been found within a distinct area including substantia nigra and ventral tegmentum. From the same region nonspecific responses in the ECoG (spindling, recruiting and desynchronisation by low and middle frequent stimulation) could be obtained. The blood pressure responses were enhanced after hemisection at the level of the posterior hypothalamus ipsilateral to the stimulation side. Drugs (Haloperidol, alpha-methyltyrosin and 6-hydroxydopamine), affecting the dopamine metabolism in different ways, abolished the stimulation-induced blood pressure responses. In agreement with previous findings it is concluded that motor and autonomic activation, elicited in ventral midbrain structures are mediated by catecholaminergic transmission.