Noxious-evoked c-fos expression in brainstem neurons immunoreactive for GABAB, u-opioid and NK1 receptors (original) (raw)

2003, European Journal of Neuroscience

Modulation of nociceptive transmission at the brainstem involves several neurochemical systems. The precise location and speci®c characteristics of nociceptive neurons activated in each system was never reported. In this study, the presence of GABA B , m-opioid, and neurokinin-1 (NK-1) receptors in brainstem nociceptive neurons was investigated by double-immunocytochemical detection of each receptor and noxious-evoked induction of the c-fos proto-oncogene. Noxious cutaneous mechanical stimulation signi®cantly increased the proportions of neurons double-labelled for Fos and GABA B receptors in several brainstem regions, namely, the reticular formation of the caudal ventrolateral medulla (VLMlat and VLMrf), lateral reticular nucleus, spinal trigeminal nucleus, pars caudalis (Sp 5 C), nucleus of the solitary tract, dorsal reticular nucleus, ventral reticular nucleus, raphe obscurus nucleus and dorsal parabrachial nucleus (DPB). For m-opioid receptors, the proportions of double-labelled neurons in noxious-stimulated animals were higher than in controls only in the VLMlat, VLMrf, Sp 5 C, DPB and A 5 noradrenergic cell group. As for the NK-1 receptor, no signi®cant differences were found between control and stimulated animals. According to these results, neurons expressing GABA B , m-opioid and NK-1 receptors at several pain control centres of the brainstem are differentially involved in processing nociceptive mechanical input. The data provide the de®nition of new supraspinal targets for selective modulation of nociceptive neurons in order to de®ne better strategies of pain control.