Intracranial self-stimulation induces fos expression in gabaergic neurons in the rat mesopontine tegmentum

The cholinergic neurons which originate in the mesopontine tegmentum and in nervate the midbrain ventral tegmental area have been proposed to play a ke y role in intracranial self-stimulation reward. This mesopontine area also contains GABA neurons, Detailed information is still lacking, however, abou t the relationship of cholinergic and GABAergic neurons in this region to s elf-stimulation reward. Therefore, using double immunostaining for Fos as a marker of neuronal activity and choline acetyltransferase as a marker of c holinergic neurons, or for Fos and GABA, we investigated whether self-stimu lation of the medial forebrain bundle induces Fos expression within choline rgic and GABAergic neurons in two regions of the mesopontine tegmentum, i.e ., pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus. S elf-stimulation of the medial forebrain bundle for 1 h induced a large incr ease in the number of cells expressing Fos in both the pedunculopontine teg mental nucleus and laterodorsal tegmental nucleus. when compared to control brains, However. the self-stimulation-induced expression of Fos was restri cted mostly to GABA, but not choline acetyltransferase-. immunostained cell s. We also examined, using microdialysis, whether self-stimulation increase s acetylcholine efflux in the ventral tegmental area, a terminal region of the mesopontine tegmentum cholinergic pathway. One hour of self-stimulation significantly increased acetylcholine efflux from this terminal area. These results indicate that intracranial self-stimulation of the medial for ebrain bundle may increase acetylcholine release without affecting expressi on of Fos in cholinergic neurons, while the same stimulation may induce Fos expression in GABAergic neurons of the mesopontine tegmentum, GABAergic as well as cholinergic neurons in this area appear to be activated by self-st imulation reward in the medial forebrain bundle. (C) 2001 IBRO. Published b y Elsevier Science Ltd. All rights reserved.