A subpopulation of rat dorsal root ganglion neurones is catecholaminergic

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Abstract
The neurotransmitters used by the sensory neurones of the dorsal root ganglia (DRG) are unknown. A proportion of these cells contain physiologically active peptides; for example, sub-populations of small-diameter neurones contain substance P or somatostatin1,2. Although these peptides probably have some influence on synaptic transmission in the dorsal horn of the spinal cord, their status as neurotransmitters is uncertain and it is possible that they coexist with conventional neurotransmitters. In addition, the neurones containing identified peptides account for only a fraction of the DRG sensory neurones2,3. There is evidence that the DRG contain catecholamines within fibres thought to be autonomie, but these substances have not been found within the sensory cell bodies themselves4,5. Moreover, the apparently inappropriate, inhibitory physiological effect of catecholamines in the dorsal horn6,7 has argued against their being primary sensory neurotransmitter molecules. We have used here antisera against tyrosine hydroxylase (TH; EC 1.14.16.2) and dopamine-β-hydroxylase (DBH; EC 1.14.17.1), two enzymes specific to catecholaminergic cells8–10, to show that a subpopulation of rat DRG neurones is catecholaminergic and that the neurotransmitter they make is probably dopamine. We believe this to be the first report of catecholaminergic sensory neurones.