The effect of electrolytic thalamic lesions on the NADPH-diaphorase activity of neurons of the laterodorsal tegmental and pedunculopontine nuclei in rats

Cholinergic neurons of the mesopontine complex have extensive ascending pro jections to the forebrain: the laterodorsal tegmental nucleus extensively i nnervates the anterior thalamus, the anteroventral nucleus in particular, w hereas the pedunculopontine nucleus has widespread projections to both the thalamus and extrapyramidal structures. Most of their neurons express nitri c oxide synthase (NOS) activity. Following electrolytic lesions of the ante roventral thalamic nucleus, nicotinamide adenine dinucleotide phosphate-dia phorase (NADPHd) activity in neurons of the laterodorsal tegmental nucleus changed drastically. The intensity of NADPH-diaphorase staining increased i n laterodorsal tegmental neurons ipsilateral to the lesion side, but decrea sed contralaterally. The intensity of the NADPH-diaphorase staining of neur ons of the pedunculopontine nucleus, however, remained unchanged bilaterall y. After partial lesions of the anteroventral thalamic nucleus a similar ef fect was noted. In contrast, large electrolytic lesions involving other tha lamic nuclei or extrapyramidal structures did not change the number of NADP H-diaphorase neurons or their intensity of staining in the laterodorsal teg mental nuclei. These data show that electrolytic lesions of target areas ca n lead to an upregulation of NOS expression in the parent cell bodies, prov ided that there is no wide collateralization as found for the pedunculopont ine nucleus. (C) 2000 Elsevier Science B.V. All rights reserved.