Research on the manifestation mechanism of Parkinsonian tremor : On the role of serotonergic neuron of raphe nucleus.

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PURPOSE: The main lesion of Parkinson's disease is the selective neuronal death of the nucleus niger (clopaminergic neuron) and locus ceruleus of the midbrain (noradrenergic neuron). However, we cannot necessarily explain all the manifestations and mechanism of resting tremor by these sites of damage alone. The ventromedial tegmentum (VMT) is known as the region that includes Parkins-onian tremor in the monkey. We have reported that great numbers of cells in the nucleus niger and dorsal raphe nucleus were labeled by the local injection of horseraclish peroxidase into VMT in both of monkeys and cats . It is the purpose of this research to clarify that damages or not only the nucleus niger but also raphe nucleus serotonergic neurons are involved in the manifestation of tremor. METHOD : Fifteen mature cats were divided into two groups : one is a coagulation group of the dorsal raphe nucleus, and the other is a non-coagulation group. In the coagulation group, damage of the nucleus niger do … More pamine system is induded by MPTP, after the destruction of the dorsal raphe nucleus using a stereotactic coagulation technique. In both groups, MPTP (3 mg/kg/day) was injected intramuscularly every other day 8〜14 times in total. The reactions after injection were then recorded and analyzed in video and electromyogram. The coagulated lesions were confirmed in the serial-section samples of the brain. RESULT : Though there was a difference of severity, rigidity was observed in both groups after MPTP administration. In the three cats in which the dorsal raphe nucleus was accurately included in the coagulated lesion, the tremor was observed after the seventh or eighth repetitive administration of MPTP. The tremor occurred in the resting position and lightly bending position of the limbs, and its cycle was similar to Parkinsonian tremor of 4〜6 Hz. In two cats, the tremor appeared throughout the 15〜40 minutes after MPTP administration, and gradually dissappeared. In one other cat, a similar tremor was observed after the eighth administration of MPTP, even on the clay when MPTP was not administered. In the cats of which the dorsal raphe nucleus was not destroyed accuratehr by coagulation, the tremor did not develop. CONCLUSION : Even in the cat, it was possible to create a resting tremor that is similar to Parkinsonian tremor. From the facts described above, we may conclude that damages both of the raphe nucleus serotonin system and the nucleus niger dopamine system may be involvecl in the mechanism for Parkinsonian tremor . Less