Spinal cord injury-specific depression of monosynaptic spinal reflex transmission by l-5-hydroxytryptophan results from loss of the 5-HT uptake system and not 5-HT receptor supersensitivity.
We studied changes in the spinal segmental reflex and serotonergic (5-HT) responses in rats after spinal cord injury (SCI) produced by the weight-dropping method at the T8 level. The spinal monosynaptic reflex amplitude (MSR) was recorded from the L5 ventral root following stimulation of the ipsilateral L5 dorsal root. The 5-HT precursor l-5-hydroxytryptophan (L-5-HTP) depressed MSR in the spinal cord injured rats but not in normal rats. We investigated whether the SCI-specific depression of MSR by L-5-HTP was attributable to postsynaptic supersensitivity of 5-HT receptors or presynaptic loss of the 5-HT uptake system. Sumatriptan, a selective 5-HT(1B/1D) receptor agonist that is not taken up by 5-HT transporters, depressed the MSR similarly in both SCI and normal rats, suggesting that SCI resulted in the loss of 5-HT terminals and not postsynaptic supersensitivity of 5-HT receptors.
Honda
Motoko
M
Laboratory of CNS Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan.
Tanabe
Mitsuo
M
Ono
Hideki
H
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology*; D004195:Disease Models, Animal; D005260:Female; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000502:physiology; D012023:Reflex, Monosynaptic / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000502:physiology*; D018490:Serotonin Agents / Q000494:pharmacology; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013997:Time Factors
D018687:Antidepressive Agents, Second-Generation; D011985:Receptors, Serotonin; D018490:Serotonin Agents; D012701:Serotonin; D006916:5-Hydroxytryptophan