Pontine cholinergic neurons simultaneously innervate two thalamic targets

Cholinergic neurons located in the lateral dorsal tegmental (LDT) and pedunculopontine tegmental (PPT) nuclei have been shown to principally innervate the thalamus. In order to determine whether some of these neurons might simultaneously project to two thalamic targets we made microinjections of rhodamine-conjugated microbeads into the central-lateral nucleus of the thalamus and fluorescein isothiocyanate (FITC)-conjugated microbeads into the dorso-lateral geniculate nucleus. We then determined whether both tracers were found in immunohistochemically identified cholinergic somata in the LDT and PPT nuclei. Results showed that some cholinergic and non-cholinergic neurons in the LDT and PPT nuclei projected to both thalamic sites. This finding extends our understanding of the projections of the LDT-PPT cholinergic neurons and further supports the role of these neurons in complex behaviors.