Cardiac sympathetic afferent input onto neurons in nucleus ventralis posterolateralis in cat thalamus.

Neurons receiving cardiac sympathetic afferent input were studied in the nucleus ventralis posterolateralis (VPL) of the cat thalamus. Animals were anesthetized with urethan-chloralose. Units in the VPL were classified into 3 classes; low-threshold mechanoreceptive (LTM), nociceptive specific (NS) and wide dynamic range (WDR) units. Units driven by electrical stimulation of the left inferior cardiac nerve (ICN) were not included in the population of LTM units, but 43.5% of NS units and 68.8% of WDR units were excited by this stimulation. Units exclusively responsive to cardiac sympathetic afferents were not found. Both NS and WDR units were located in the shell region of the caudal VPL. NS units responsive to cardiac sympathetic afferents had a circumscribed cutaneous receptive field in the area corresponding to tactile dermatomes C5-T13. WDR units receiving cardiac sympathetic afferent input had at least a part of their receptive fields in the same area. These results suggest that the shell region of the caudal VPL constitutes a thalamic link in a cardiac pain pathway, and that cardiac and cutaneous pain systems share a common projection locus in the VPL.