Cerebral cortical afferent terminations on identified spiny basilar pontine neurons, a combined Golgi-EM degeneration study.

Observations contained in this study suggest that in general, the population of spiny basilar pontine (BP) projection neurons receives synaptic contacts from both small dark and large filamentous degenerating cortical axon terminals. In some instances a single spiny BP neuron was contacted by both types of cortical boutons. Long-Evans hooded rats received unilateral thermocautery lesions involving a large expanse of sensorimotor and visual cortices. Following survival periods ranging from 4-8 days, brains were perfused and processed routinely for rapid-Golgi staining. Selected tissue blocks containing spiny basilar pontine projection neurons isolated within known termination zones of the ablated ipsilateral cortex were removed from the brainstem and the cells drawn in their entirety, gold toned, de-impregnated and processed for electron microscopy. Processes of these neurons identified by their content of electron dense gold particles were then localized in sequences of ultrathin sections taken through the tissue block. All degenerating boutons contacting gold-containing profiles of the identified neuron were categorized as dark or filamentous and their location approximated on the surface of the cell. If the two different varieties of degenerating corticopontine boutons reflects a difference in functional properties, the implications of the present findings are that (1) the population of spiny-type BP projection neurons receive convergent inputs from both corticopontine systems and (2) that some individual spiny BP neurons integrate both types of input.