Neurotransmitter Receptor Sites in the Spinal Cord
Since the studies discussed in this chapter concern the distribution of receptors for neurotransmitters, it is important to specify that the term “receptor” implies a physiologically functional unit. Binding of a transmitter molecule to its binding site on the neuronal membrane surface initiates a physical change in the receptor unit that results in a physiological change, i.e., a change in membrane ion permeability (nicotinic cholinergic receptor) or activation of an enzyme resulting in a change in the level of a biochemical intermediate within the cell (β-adrenergic receptors and many peptide hormone receptors). Binding studies and autoradiograms, however, reflect just the binding site portion of the receptor unit, and such data must be described in terms of binding sites. However, the radiolabeled ligands used to prepare the autoradiograms are pharmacologically active compounds whose physiological effects on the system may be well characterized. Therefore, in this discussion of the biological significance of binding sites, I refer to them as receptors.
KeywordsSpinal Cord Dorsal Root Ganglion Dorsal Horn Primary Afferent Neuron Central Canal
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