PREPRODYNORPHIN MESSENGER-RNA-EXPRESSING NEURONS IN THE RAT PARABRACHIAL NUCLEUS - SUBNUCLEAR LOCALIZATION, HYPOTHALAMIC PROJECTIONS AND COLOCALIZATION WITH NOXIOUS-EVOKED FOS-LIKE IMMUNOREACTIVITY

The dorsal lateral subnucleus of the rat pontine parabrachial nucleus is a major target for ascending nociceptive information from the spina l cord. With in situ hybridization histochemistry, using a radiolabell ed cRNA probe, we demonstrate that neurones in and near the dorsal lat eral subnucleus express preprodynorphin mRNA. The cRNA probe was const ructed from a PCR product amplified from rat genomic DNA. Sequencing o f the PCR product revealed that it corresponded to the sequence 466-11 01 of the rat preprodynorphin gene exon 4. Tract tracing experiments, using injection of cholera toxin subunit B into the hypothalamic media n preoptic nucleus, showed a retrograde labelling pattern of neurones in the parabrachial nucleus that was almost identical to that of the p reprodynorphin mRNA expressing neurones, Double-labelling, combining i mmunohistochemical detection of tracer and in situ hybridization, reve aled that the retrogradely labelled neurones expressed preprodynorphin mRNA. A similar double-labelling, combining in situ hybridization wit h immunohistochemical detection of noxious-evoked fos following formal in injection into one hindpaw of awake animals, showed that almost all fos-immunoreactive neurones in the dorsal lateral parabrachial subnuc leus also expressed preprodynorphin mRNA. Quantitative analysis sugges ted that the evoked fos immunoreactivity was accompanied by an increas ed preprodynorphin mRNA expression. The findings provide evidence that neurones in the dorsal lateral subnucleus produce dynorphin and proje ct to the median preoptic nucleus, and that noxious stimulation in awa ke animals synaptically activates the dynorphinergic neurones in this subnucleus. These observations are consistent with the idea of a funct ional and chemical heterogeneity among different parabrachial subnucle i that serves to produce specific homeostatic responses to stimuli tha t changes the physiological status of the organism, including tissue d amage.