Abstract
The localization of GABA A receptors in cat and rat spinal cord was analyzed using two monoclonal antibodies specific for an epitope shared by the β 2 and β 3 subunits of the receptor. β 2 /β 3 -subunit immunoreactivity was the most intense in inner lamina II, lamina III, and lamina X, and it was the least intense in lamina IX. In laminae I–III, generally, the staining had a rather diffuse appearance, but the surfaces of small cell bodies in these laminae were outlined clearly by discrete labeling, as were many cell bodies and dendrites in deeper laminae. Rhizotomy experiments and ultrastructural observations indicated that β 2 /β 3 -subunit immunoreactivity in the dorsal horn was largely localized in intrinsic neuropil elements rather than in the terminals of primary afferent fibers, even though labeling overlapped with the terminal fields of different types of primary afferents and was also detected on the membranes of dorsal root ganglion neurons. With few exceptions (most notably, a highly immunoreactive group of dorsolaterally located cells in the cat lumbar ventral horn), motoneurons expressed low levels of β 2 /β 3 -subunit immunoreactivity.
Labeling of neuronal membranes was fairly continuous, but focal accumulations of β 2 /β 3 -subunit immunoreactivity were also detected using immunofluorescence. Focal “hot spots” correlated ultrastructurally with the presence of synaptic junctions. Dual-color immunofluorescence revealed that focal accumulations of β 2 /β 3 -subunit immunoreactivity were frequently apposed by glutamic acid decarboxylase (GAD)-immunoreactive terminals. However, the density of continuous-membrane β 2 /β 3 immunolabeling and GAD terminal density were not correlated in many individual neurons. The results suggest the existence of “classical” (synaptic) and “nonclassical” (paracrine) actions mediated via spinal cord GABA A receptors. The study also revealed the relative paucity of β 2 /β 3 -subunit immunoreactivity postsynaptic to certain GABAergic terminals, particularly those presynaptic to motoneurons or primary afferent terminals. © 1996 Wiley-Liss, Inc.
Original language | American English |
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Journal | The Journal of Comparative Neurology |
Volume | 365 |
DOIs | |
State | Published - Feb 12 1996 |
Keywords
- primary afferent fibers
- motoneurons
- inhibitory control
- glutamic acid decarboxylase
- GABA
Disciplines
- Medical Cell Biology
- Medical Neurobiology
- Medical Physiology
- Medical Sciences
- Medicine and Health Sciences
- Neurosciences
- Physiological Processes