Colocalization

NAAG is sometimes found in neurons that are also cholinergic, nor-adrenergic, serotonergic, or GABAergic. Motoneurons have long been known to be cholinergic, and yet they, their axons, and terminals all contain NAAG (see above). Intense double staining for NAAG and ChAT is seen in both spinal and medullary motoneurons, including those of the facial, ambiguus, and trigeminal nuclei.40 In addition, a subset of cholinergc neurons in the basal forebrain and medial septum contain NAAG.40

Many nor-adrenergic neurons contain NAAG. All cells of the locus coeruleus contain both NAAG and dopamine p-hydroxylase, the synthesizing enzyme for noradrenaline.40 Except for the A2 cell group, which contains little or no NAAG, most of the other noradrenergic and adrenergic cell groups in the medulla label for NAAG in addition to dopamine p-hydroxylase.

NAAG co-localizes with serotonin in some cells. A few serotonergic neurons in the dorsal raphe stain for NAAG. Co-labeling is more apparent in the median raphe, although most cells are singly labeled.40

Some, but by no means all, GABAergic neurons contain NAAG. In cat, a few ama-crine and retinal ganglion cells contain both NAAG and GABA.43 , 44 Similarly, in rat, a few cells of the inner nuclear layer (presumably amacrine cells) contain both NAAG and GAD67, but most are singly labeled for NAAG.9 In rat cerebral cortex, NAAG labeling is strongest in cells with the morphology of interneurons, suggesting likely co-localization with GAD.23, 31 Cells of the thalamic reticular nucleus are known to be GABAergic45 and to contain somatostatin46 and aspartate or glutamate;47 they also label heavily for NAAG.9, 23 Indeed, cells of the rat's thalamic reticular nucleus and those of the cat's perigeniculate nucleus, the visual part of the thalamic reticular nucleus, contain both NAAG and GAD.9, 29 In contrast, in LGN, GAD is found in interneurons, whereas NAAG is found in relay cells.9, 29 In cerebellar pathways, NAAG and GAD distributions are largely complementary,37 although since some37 or most30 Purkinje cells are labeled for NAAG, these should be double-labeled.

Cellular labeling for NAAG is seen in the substantia nigra,24 whose cells are largely dopaminergic.48 The role of this NAAG may be to modulate the release of dopamine in

the striatum.49, 50

0 0

Post a comment