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In seven female alpha-chloralose-anesthetized cats, 52 lateral thalamic neurons were tested with noxious distension of the urinary bladder, the distal colon and the lower esophagus. In addition, the neurons were characterized with innocuous and noxious mechanical stimulation of the skin and deep structures. Of the 52 neurons tested, 32 (62%) were visceroceptive. Of these visceroceptive neurons, 20 (63%) were located in the periphery of the ventral posterolateral nucleus (VPLp), 10 (31%) in the adjacent posterior complex (PO), and two (6%) in the ventrolateral nucleus (VL). No differences were found with respect to location between neurons responsive or unresponsive to visceral stimulation. Ten neurons (31%) received input from more than one viscus and, therefore, showed viscerovisceral convergence. Excitatory or "inhibitory" responses were elicited by stimulation of the esophagus in 21 neurons, of the colon in 13, and of the urinary bladder in 11 neurons. No indications were found for a segregation of neurons responsive to a certain viscus and their location in VPLp or PO. Of 51 neurons, for which a somatic receptive field was determined, 44 (86%) exhibited low threshold type (LT), and seven (14%) wide dynamic range type (WDR) responses. The data indicate that there might exist a somatovisceral coregistration, because many neurons (69%) had homosegmental receptive fields, and bladder stimulation was the most successful stimulus. It is concluded that VPLp and the adjacent PO in the cat play a role in the perception and localization of painful events originating from thoracic and pelvic organs.

The representation of the kidney in the lateral somatosensory thalamus was mapped using electrical stimulation of the renal nerve in pentobarbitone-anesthetized cats. Ninety-five of 197 thalamic neurons studied responded to renal nerve stimulation. The responsive neurons were located in the periphery of the ventral posterolateral nucleus (42%; VPLp) and the neighboring dorsal and lateral aspects of the posterior complex (58%; POd and POl). No visceroceptive neurons were found within VPL proper. The mean response latency of the thalamic neurons to electrical nerve stimulation was 9.5 +/- 2.6 ms (mean +/- S.D.), suggesting an involvement of A delta, and possibly A beta fibers in the primary afferent pathway. The visceroceptive neurons were further characterized with innocuous mechanical stimulation of the body surface, and for 94 of the 95 neurons a somatic receptive field could be determined. Of these, 35% were located on the lower back and belly, i.e., the dermatomes of the lower thoracic and upper lumbar spinal projection areas of the renal nerve. 52% of the somatic receptive fields were located on the contralateral foot, thigh, tail, or hind leg (lower lumbar, sacral and coccygeal dermatomes) and 13% covered the arm and upper body (upper thoracic and lower cervical dermatomes). Comparison between the thalamic representations of the renal and pelvic nerves showed that both covered comparable areas adjacent and around, but not within VPL proper. It is concluded that VPLp, POd and POl play a role in processing visceral, possibly including nociceptive, information from the kidney of the cat.

(1) The relationships between capsaicin sensitivity, cell size and the expression of voltage-dependent high-threshold (L- and N-type) and low-threshold (T-type) Ca-currents were investigated in cultured adult rat dorsal root ganglion neurons using the whole-cell patch-clamp technique. (2) The capsaicin (10 microM) evoked inward current was used to identify the capsaicin-sensitive population. To identify the voltage-dependent Ca-currents, the activation threshold and the inactivation kinetic were used. (3) In cultured dorsal root ganglion cells the capsaicin sensitivity is not restricted to the small cell population. About 28% of cells with large cross sectional areas (greater than or equal to 1001 microns 2) responded with about the same amplitude per micron2 cross sectional area as small cells. (4) The amplitude of the capsaicin evoked inward current depended on the length of time the cells were maintained in culture. (5) All cells exhibited the high-threshold Ca-currents. About 45% of the capsaicin-insensitive cells also had low-threshold Ca-currents. None of the capsaicin-sensitive cells had the low-threshold type. (6) Most of the cells which expressed the low-threshold type were in the upper size range.