DISSOCIATION OF BEHAVIORAL-CHANGES IN RATS RESULTING FROM LESIONS OF THE HABENULA VERSUS FASCICULUS RETROFLEXUS AND THEIR POSSIBLE ANATOMICAL SUBSTRATES

Lesions in either the habenula or its primary efferent pathway, the fa sciculus retroflexus (FR), impaired avoidance responding. However, les ions of only the FR provided a persistent elevation of locomotor activ ity. Immunocytochemical study of the interpeduncular nucleus (IPN) thr ough injection of retrograde tracers into the IPN and the overlying ve ntral tegmental area indicated that habenular lesions spared both rost ral habenula and forebrain projections to the caudal midbrain, but the se projections were axotomized by FR lesions. Rostral sparing of the h abenula resulted in normal peptidergic staining in the IPN, and normal cholinergic innervation was absent. Performance of individual rats in behavioral tests was consistent with variations in anatomical sparing . Such considerations may account for previous discrepancies in functi onal effects of habenular lesions.