Etude Histopathologique et Neurochimique Suite a des Lesions Unilaterales du Locus Coeruleus Chez le Rat et de la Region Postlocus Chez le Chat (Part 2)

Effect of anterior-posterior lesion location on the asymmetrical behavioral and biochemical response to cortical suction ablations in the rat

Small cortical suction ablations were produced at one of several stereotaxically located sites along the anterior-posterior axis of the right or left hemisphere in the rat. Analysis of variance showed a highly significant effect of lesion location in the right hemisphere on locomotor activity. The most anterior lesions produced both the most hyperactivity and also the greatest reductions in the concentrations of norepinephrine in the ipsilateral and contralateral cortex and locus coeruleus. These results suggest that the effect of cortical lesions on spontaneous activity may be graded across the right hemisphere and that the anatomy of certain neurotransmitter pathways in the cortex may help to explain both the biochemical and behavioral findings.

Suction lesions of the frontal cerebral cortex in the rat induce asymmetrical behavioral and catecholaminergic responses

Suction lesions of the right frontal cerebral cortex in rats induce a period of spontaneous hyperactivity. The hyperactivity, as measured by an increase in running wheel activity begins about one week post-operatively and continues throughout the remainder of a 30-day observation period. The increased activity is accompanied by a bilateral decrease in norepinephrine concentrations in both the ipsilateral and contralateral cortex and locus coeruleus. Identical lesions of the left frontal cerebral cortex produce neither the hyperactivity nor a decrease in norepinephrine concentrations. These experiments have reproduced many of the behavioral and biochemical asymmetries seen after middle cerebral artery ligation; however, suction lesions are both simpler to produce and histologically less variable in their effects.

Intracortical 6-hydroxydopamine induced an asymmetrical behavioral response in the rat

Doses of 6-hydroxydopamine (6-OHDA) from 1 to 6 microgram injected into the right frontal cortex of rats led to spontaneous hyperactivity beginning 1 week after injection and lasting throughout the 30-day postoperative period. Identical left hemispheric injections did not elicit hyperactivity until a dose of 6 microgram was reached. Biochemical assays revealed that 6-OHDA injected into either hemisphere caused approximately the same amount of depletion of norepinephrine. These results suggest that the neural asymmetry which leads to hyperactivity may be post-synaptic to the cortical noradrenergic terminals.