INVOLVEMENT OF THE SPINOPARABRACHIAL PATHWAY IN INFLAMMATORY NOCICEPTIVE PROCESSES - A C-FOS PROTEIN STUDY IN THE AWAKE RAT

The effect of graded inflammatory stimuli (intraplantar-carrageenan, 0 .2, 1, and 6 mg/150 mu l) on paw edema and c-Fos protein expression at two levels of the spinoparabrachial pathway the spinal cord and parab rachial area (PB), were studied. The present study, in awake rats, is an extension of previous study (Bester et al. [1997] J. Comp. Neurol. 383:339-458) which evaluated, in anesthetized rats, the effect of grad ed cutaneous heat stimulation on c-Fos-expression at the same levels. At the spinal level, the c-Fos-protein-like-immunoreactive (c-Fos-LI) neurons were located primarily in superficial laminae ipsilateral to i ntraplantar carrageenan. The number of c-Fos-LI neurons increased dose dependently (r = 0.973, n = 24) for carrageenan, from a number close to zero for the saline injection. At the PB level, c-Fos was predomina ntly expressed contralateral to intraplantar carrageenan, c-Fos-LI neu rons were located primarily around the pontomesencephalic junction in (i) a restricted pontine area, centered in the lateral crescent, and i ncluding an adjacent part of the outer portion of the external lateral subnucleus, and (ii) the mesencephalic superior lateral subnuclei. Th e number of c-Fos-LI neurons in the PB area was correlated with that i n the superficial laminae (r = 0.935, n = 24) and with the paw edema ( r = 0.931, n = 24). No significant changes in c-Fos expression were ob served in the nucleus of the solitary tract and ventrolateral medulla. The close correlation between c-Fos expression at both the spinal and PB levels and inflammatory edema provides further evidence for the in volvement of spinoparabrachial pathway in inflammatory nociceptive pro cesses. The present results are congruent with the existence of electr ophysiologically demonstrated spinoparabrachio-amygdaloid and -hypotha lamic nociceptive pathways. (C) 1998 Wiley-Liss, Inc.