Differences in the NADPH-diaphorase positivity of the cholinergic brain stem neurons following damage of their thalamic termination field.

Following electrolesions of the anteroventral thalamic nucleus (the target structure for the NADPH-diaphorase positive axons of the cholinergic mesopontine cells, e.g. laterodorsal, pedunculopontine and lateral parabrachial nucleus) the intensity of NADPH-diaphorase staining changed drastically, but unlikely in each nucleus: it increased in the cells of the laterodorsal nucleus on the side of the lesion and decreased on the contralateral nucleus, whereas the staining intensity of the pedunculopontine and parabrachial cells remained unchanged bilaterally. In cases with small (partial) lesions of the anteroventral thalamic nucleus only lower number of heavily stained cells were observed in the laterodorsal nucleus ipsilateral to the thalamic lesion, whereas the number of slightly stained cells in the contralateral laterodorsal nucleus decreased. In contrast, not even large lesions of other thalamic nuclei, anterior or tuberal hypothalamus, zona incerta, pallidum internum, striatum or corpus callosum changed the symmetric intensity of the NADPH-diaphorase staining of the laterodorsal, pedunculopontine or lateral parabrachial nuclei. Increased intensity of the NADPH-diaphorase staining in the cells of the mamillary body was found two weeks after the electrolesions of the ipsilateral mamillo-thalamic tract or anteromedial thalamic nucleus. No degenerative changes or decrease of number of neurons in the laterodorsal tegmental nucleus in Nissl staining were detected after the electrolesions. Our data show that electrolytic lesions of target areas can lead to an upregulation of NOS expression in the parent cell bodies, provided that there is no wide collateralization as found for the pedunculopontine or parabrachial nuclei.