ABSENCE OF CO-LOCALIZED GLUTAMIC-ACID DECARBOXYLASE AND NEUROPEPTIDESIN NORADRENERGIC AXONS OF THE RAT SPINAL-CORD

Patterns of co-localization of immunoreactivity for dopamine beta-hydr oxylase (the synthetic enzyme for noradrenaline) and glutamic acid dec arboxylase (the synthetic enzyme for GABA) or each one of six neuropep tides (neuropeptide Y, substance P, met-enkephalin, galanin, dynorphin A and somatostatin) were investigated with dual-colour confocal laser scanning microscopy in axons of cervical, thoracic and lumbar spinal segments of six adult rats. Four regions of the grey matter were studi ed (laminae I-II, V, IX and X) and, in thoracic segments, the intermed iolateral cell column was also examined. The extent of co-localization was estimated by direct assessment of merged pairs of optical section s and by automated image analysis. Significant co-localization was fou nd for neuropeptide Y in axons of the intermediolateral cell column of thoracic segments and in lamina X of cervical and thoracic segments. None of the other peptides or glutamic acid decarboxylase were found t o coexist at significant levels with dopamine beta-hydroxylase and hen ce it is Likely that this group of neuropeptides and GABA are not co-t ransmitters of bulbospinal noradrenergic axons in the rat.