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The projection from ventromedial hypothalamus (VMH) to periaqueductal gray (PAG) has been implicated in various physiological processes in the rat, but the neurotransmitter mediating the excitatory response in PAG has not been identified. This pathway has been studied using a combination of anatomical and electrophysiological techniques. The retrograde labelling by D-[3H]aspartate in VMH, following injections into PAG, was particularly dense, suggesting that an excitatory amino acid may be the transmitter. This postulate is strengthened since VMH-evoked synaptic responses in PAG were reduced by microelectrophoretically administered antagonists of excitatory amino acids. Receptors of the N-methyl-D-aspartate and non-N-methyl-D-aspartate types appear to have a functional role in this projection. |
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