Cholinergic and GABAergic fibers in the stria medullaris of the rabbit

Abstract

After placing uni- and bilateral electrolytic lesions in the habenula (Hb), stria medullaris (SM), septum (Sep) and lateral preoptic area (LPA), activities of choline acetyltransferase (ChAc), acetylcholinesterase (AChE) and L-glutamic acid decarboxylase (GAD), which are the synthesizing and degradating enzymes of acetylcholine and the synthesizing enzyme of γ-aminobutyric acid (GABA) respectively, were analysed in the interpeduncular nucleus (Ipd) and Hb. Confirming earlier results in the rat [5,9,15,16], ChAc activity in the Ipd was markedly reduced after destruction of the Hb and to lesser extent after placing lesions in the Sep or LPA. When lesions were made in the SM, Sep, or LPA, ChAc activity in the Hb was decreased to 25–40% of the control values one week after the operation. Activity of GAD values, on the other hand, was practically not altered in the structures studied, except that the activity decreased in the Hb after placing lesions in the SM. On the basis of these findings, it is suggested that the SM contains Cholinergic afferent fibers to the Hb, that these fibers possibly arise in the forebrain structures including the Sep and LPA, and that some of the Cholinergic fibers in the SM course through the Hb toward the Ipd. The SM might also contain GABAergic afferent fibers to the Hb.