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Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording In Vivo
Published on: March 29, 2014
Endogenously released 5-hydroxytryptamine depresses the spinal monosynaptic reflex via 5-HT1D receptors
Motoko Honda1, Keiko Imaida, Mitsuo Tanabe
1Laboratory of CNS Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan. honda@phar.nagoya-cu.ac.jp
Abstract:
In the spinal cord, various 5-hydroxytryptamine (5-HT) receptor subtypes are involved in the modulation of motor output. Previously, we have shown that 5-HT1B receptors mediate the monosynaptic reflex depression induced by exogenously applied 5-HT that was formed from the precursor L-5-hydroxytryptophan in spinalized rats. In this study, we determined the effects of endogenous 5-HT, which was released from serotonergic terminals by DL-p-chloroamphetamine, on spinal reflexes. DL-p-chloroamphetamine depressed the monosynaptic reflex and increased the polysynaptic reflex. The depletion of 5-HT abolished the monosynaptic reflex depression, but the increase in polysynaptic reflexes was maintained, suggesting that endogenous 5-HT released by DL-p-chloroamphetamine mediates depression of the monosynaptic reflex in the spinal cord. The depression of the monosynaptic reflex was antagonized by GR127935 (N-[methoxy-3-(4-methyl-l-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide; 5-HT1B/1D receptor antagonist) and BRL15572 (3-[4-(4-chlorophenyl)piperazin-1-yl]-1,1-diphenyl-2-propanol; 5-HT1D receptor antagonist) but not by isamoltane (5-HT(1B) receptor antagonist). These results suggest that 5-HT released from serotonergic terminals depresses monosynaptic reflex transmission via 5-HT1D receptors.
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Somatic Spinal Reflexes
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...
