The pedunculopontine and laterodorsal tegmental nuclei in the kainate model of epilepsy

Prior studies showed that epilepsy can be associated with reorganization of the septohippocampal cholinergic fiber system. Using the kainate model of epilepsy, we wished to further examine the structural integrity of the mesopontine tegmental nuclei (pedunculopontine, PPN, and laterodorsal, LDT), which provide the cholinergic input to the thalamus. It was found that the total numbers of the PPN and LDT cells immunoreactive to the vesicular acetylcholine transporter did not differ between control and epileptic rats. However, the cholinergic cells had enlarged perikarya in epileptic rats. We further examined the effects of epilepsy on the distribution pattern of cholinergic fiber varicosities in the parafascicular nucleus, one of the principal thalamic targets of PPN projections. The density of cholinergic varicosities, represented by two distinct populations, was increased in epileptic rats. These data provide the first morphological evidence for structural alterations in mesopontine cholinergic neurons in experimental epilepsy. They suggest dysfunctional cholinergic transmission in the brainstem-thalamic pathway, which may partly account for various epilepsy-related neurological disturbances.