The mouse glutamate vesicular transporter VGLUT2 has recently been characterized. The rat homolog of VGLUT2, differentiation-associated Na(+)/P(i) cotransporter (DNPI), was examined using a digoxigenin-labeled DNPI/VGLUT2 cRNA probe in the present study to determine which, if any, of the various groups of pontine or medullary monoaminergic neurons express DNPI/VGLUT2 mRNA and, thus, are potentially glutamatergic. DNPI/VGLUT2 mRNA was widely distributed within the brainstem and seemed exclusively neuronal. By using a double in situ hybridization method, the presence of the mRNA for DNPI/VGLUT2 and glutamic acid decarboxylase (GAD)-67 was mutually exclusive. By combining DNPI/VGLUT2 mRNA detection and conventional immunohistochemistry, DNPI/VGLUT2 mRNA was undetectable in lower brainstem cholinergic and serotonergic cells, but it was present in several tyrosine hydroxylase-immunoreactive (TH-ir) cell groups. DNPI/VGLUT2 mRNA was detected in most of the adrenergic neurons of the C1, C2, and C3 groups (75-80% of TH-ir neurons), in the A2 noradrenergic group (80%), and in vast numbers of area postrema cells. Within the A1 region, many fewer TH-ir cells contained DNPI/VGLUT2 (16%). Finally, DNPI/VGLUT2 mRNA was undetectable in the pontine noradrenergic cell groups (A5 and A6/locus coeruleus). In conclusion, the general pattern of DNPI/VGLUT2 expression and its exclusion from GABAergic, cholinergic, and serotonergic neurons supports the notion that DNPI/VGLUT2 mRNA identifies a subset of glutamatergic neurons in the lower brainstem. Within this region several catecholaminergic cell groups appear to be glutamatergic, including but not limited to the adrenergic cell groups C1-C3. Based on the present evidence, the noradrenergic cell groups of the pons (A5 and A6) do not contain either known vesicular glutamate transporter and are most likely not glutamatergic.
Copyright 2002 Wiley-Liss, Inc.