[Effects of mesocortical dopaminergic lesions on stress-induced changes in monoamine metabolism in the discrete brain regions of rats].

This study assessed the possible influence of the mesocortical dopamine (DA) system on the reactivity of subcortical monoamine systems to stress. Rats were either sham-operated or subjected to DA-depleting lesions of the medial prefrontal cortex (mPFC) with 6-hydroxydopamine. Fourteen days after surgery, the rats were exposed to 30 or 60 min immobilization stress, and levels of noradrenaline, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG). DA, 3-4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin, and 5-hydroxyindoleacetic acid were measured in nine brain regions. The stress caused a significant increase in the levels of DA metabolites, DOPAC or HVA, in the mPFC of sham-operated, but not of lesioned animals. HVA concentrations in the nucleus accumbens, olfactory tubercle, and ventral tegmental area were significantly increased in both sham-operated and lesioned rats, but the effect of stress on the subcortical DA systems was unaffected by the lesion. The stress also significantly elevated MHPG levels in the amygdala and hypothalamus of both groups of animals, and these results were similar in the amygdala of rats with or without lesions. In the hypothalamus, however, 60 min stress caused a more marked increase in MHPG concentrations in lesioned rats than in sham-operated rats (lesion-group, 143%; sham-group, 122%), while 30 min stress produced a similar elevation in both groups of animals (lesion-group, 149%; sham-group, 142%). These results suggest that the mesocortical DA system may modulate the sensitivity of the noradrenergic system in the hypothalamus to stress.