Intracellular staining study of the feline cuneate nucleus. II. Thalamic projecting neurons

Morphological and physiological features of thalamic projecting neurons in the middle region of the cuneate nucleus of cats (from obex to 4 mm below it) have been studied, using intracellular recording and iontophoresis of horseradish peroxidase. All cuneothalamic neurons in the present sample) responded to movement of hairs on wrist, paw, or digits. However, approximately 50% of the neurons could be activated by other types of stimulation (e.g., light or maintained pressure on the skin, movement of claws, etc.). No clear differences were apparent in the physiological responses correlated with the varied dendritic pattern of stained neurons. Dendritic arborizations of most cuneothalamic neurons were more extensive than assumed previously, from Golgi impregnated material. As a consequence, only a few neurons have dendrites ramifying within a restricted region--i.e., corresponding to a typical cluster of the middle cuneate nucleus. Dendrites extending in various directions and spanning a distance up to 500 microns provide cuneothalamic neurons with the ability to receive input from relatively widespread areas. Collateral branches of axons of cuneothalamic neurons were observed in 50% of the stained neurons. Most of these collaterals terminated ventrally within the cuneate nucleus. Extensive collateral arborizations were observed in the dorsal as well as the ventral cuneate. These results, together with those reported in the previous paper, suggest complex interactions of afferent inputs on cuneothalamic neurons. In particular, such neurons are likely to be influenced by convergent input from different receptor classes and, because of their axonal collaterals, probably affect the excitability of other neurons, projecting or intrinsic, in their immediate vicinity or in other nuclear regions.