Abstract
Intraspinal microinjection into the lumbar spinal segment (L5 was attempted to evaluate the direct effects of drugs or transmitters on the spinal reflexes. The micropipettes (tip diameter 40-50 μm) filled with drug solution were inserted into the ventral or dorsal horn, and the volume of 0.1-0.2 μl was injected. Control solution of high pH, low pH or high osmolarity had no effect on the monosynaptic reflex (MSR) or polysynaptic reflex (PSR). L-Glutamic acid microinjected into the ventral horn depolarized the resting ventral root potential, and GABA microinjected into the dorsal horn depolarized the resting dorsal root potential. Using this method, we investigated the role of serotonin in the spinal cord. Serotonin (2nM) microinjected into the ventral horn had no influence on MSR, but facilitated PSR. This effect was suppressed by methysergide (s.c.) and LSD (i.v.). Serotonin microinjected into the dorsal horn had no influence on MSR, but suppressed PSR. This effect was reduced by methysergide, but not influenced by LSD. It was thus suggested that serotonin had no direct effect on motoneurons and that there are at least two different serotonergic mechanisms in the interneurons of the rat spinal cord.
Published Version
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