Immunochemical studies of substance P and cholecystokinin octapeptide recovery in dorsal horn following unilateral lumbosacral ganglionectomy.

Deafferentation of the cat lumbosacral dorsal horn following unilateral ganglionectomy (L2-S3) produced an ipsilateral depletion of substance P (sP) and cholecystokinin octapeptide (CCK) immunoreactivity (IR). The loss of sP IR and CCK IR was most marked at 11 days postlesion, and partial recovery of sP IR and CCK IR was noted in the upper laminae of the dorsal horn ipsilateral to the lesion 14 days after deafferentation. The dorsal horn sP IR and CCK IR distribution and density of staining on the deafferented side were indistinguishable from those on the control side 1 month after ganglionectomy. The pattern and density of methionine-enkephalin (M-ENK) IR was not disrupted by deafferentation, demonstrating that the sP IR and CCK IR depletions were due to the deafferentation and not to nonselective vascular damage. The recovery of sP IR and CCK IR was not affected by midline myelotomy or thoracic cord transections, implying a local origin for the recovered sP IR and CCK IR. Moreover, capsaicin, a primary afferent neurotoxin, depleted sP IR and CCK IR only from the intact side. Thus, these studies indicate that the recovery of two immunochemically identified primary afferent transmitters in the dorsal horn does not involve intraspinal sprouting of primary afferents. Radioimmunoassay (RIA) analysis of the ganglionectomies followed by recovery periods ranging from 7 to 28 days confirmed the depletion and recovery of sP IR, but the RIA indicated a temporal shift in depletion and recovery. Maximal depletion was measured at 21 days and recovery was observed at 28 days after unilateral deafferentation.