Effects of morphine and methotrimeprazine (levomepromazine) on the caudate-induced inhibition of the thalamic somatosensory evoked potential

[My research life: from synaptic transmission to behavior]

I have studied signal transmission at synapses and the effects of drugs on it at the molecular and cellular levels. Specific areas of research interest are outlined here. 1) Electrophysiological experiments in cats and rabbits suggested that a new type of analgesic, the phenothiazine derivative levomepromazine, exerts analgesic effects by depressing emotional responses accompanying the sensation of pain. 2) It was hypothesized that motoneurons had long-term effects on muscle cell membrane properties, in addition to controlling moment-to-moment activities. The substance to recover the post-denervation changes in muscle properties in culture was partially purified from mouse nerve extract, which suggested that trophic influences were exerted by substances released from motoneurons. 3) Muscles innervated by adrenergic fibers had sites responsive to acetylcholine as well as to adrenaline in early life in chicks, but only the adrenaline-responsive sites remained during development. Acetylcholine receptor clusters on Xenopus muscles were concentrated at the cholinergic neuromuscular junctions by the movement of receptors from outside the junctions during development. The passive diffusion-trap mechanism explained the accumulation of synaptic receptors at synapses. 4) We found two endocytic pathways and pools of synaptic vesicles contributing to low- and high-frequency synaptic transmission at Drosophila nerve terminals. We then identified two Ca2+ channels designated for the low- and high-frequency endocytosis of synaptic vesicles, straightjacket Ca2+ channels in the active zone and La3+-sensitive Ca2+ channels in the inactive zone at the terminals, respectively. Recently, Drosophila melanogaster has been used as a model for studying the social brain, and the heat avoidance response of the flies was found to be socially enhanced. Future studies are expected to reveal mechanisms underlying social brain functions at the gene level.

Evidence of a central component in the analgesic effect of indoprofene

1. The central nervous system effects of the analgesic antiinflammatory drug, indoprofene were studied. 2. CNS effects were found using EEG in rats and cats. 3. Evoked cortical potentials were studied in cats, and evoked activity in ventroposterolateral thalamic nucleus and laminae V of spinal cord were studied in rats. 4. Indoprofene induced a modification of all the parameters studied. 5. Evoked activity of thalamic nuclei and laminae V were significantly depressed. 6. Central effects were not antagonized by naloxone. 7. It is postulated that indoprofene has a central component in its effect, which would contribute to its strong and rapid analgesic effect.

Acute effects of morphine on regional brain levels of acetylcholine in mice and rats

Morphine increased levels of acetylcholine in mouse striatum in a dose-dependent manner, the increase occurring at the lowest dose previously found to produce analgesia and coinciding with the time of peak analgesic effect. Naloxone blocked this increase. After repeated injections of high doses of morphine, no effect was seen. The hippocampus was the only other brain region showing an effect, and this after a high dose. In the rat, morphine (30 and 90 mg/kg) increased striatal acetylcholine levels. At these and lower doses (2.5 mg/kg and 10 mg/kg) the ratios in the striatum of levels of acetylcholine to levels of dopamine were significantly increased. Only at the highest dose did morphine increase the levels of dopamine in the striatum and of acetylcholine in the hippocampus. Morphine did not change the levels of dopamine in the striatum and of acetylcholine in the hippocampus. Morphine did not change the levels of norepinephrine in either the hypothalamus or cortex of the rat.

Inhibition of thalamic and hypothalamic somatosensory evoked potentials by stimulation of substantia nigra and its modification by morphine and methotrimeprazine (levomepromazine)

A brief electrical stimulation of the substantia nigra induced a marked and long lasting inhibition of the somatosensory evoked potentials recorded from the centrum medianum of the thalamus (CM) and posterior hypothalamic area (PHA) following sciatic stimulation in unanesthetized rabbits. The nigral inhibitory effect on CM was prolonged by the administration of morphine (4 mg/kg i.v.) but not influenced by that of methotrimeprazine (2-4 mg/kg i.v.). In contrast, the nigral inhibitory effect on PHA was enhanced by the injection of methotrimeprazine (2 mg/kg i.v.), but not changed by that of morphine (4 mg/kg i.v.). These results indicate that the inhibitory system originating from the substantia nigra operates on the somatosensory transmissions from the peripheral nerve to the thalamus and hypothalamus, and that morphine or methotrimeprazine in small doses induced a selective potentiation of the nigral inhibitory influence on the thalamus or hypothalamus, respectively.