Journal of Neural Transmission

Substituted amphetamines are known to selectively destroy serotonin (5-HT) nerve endings in distant projection fields of the dorsal raphe nuclei and the systemic administration of these drugs is widely used in investigations of the role of the central 5-HT system and of the mechanisms involved in their toxicity. Until now Sprague-Dawley rats were almost exclusively used for this purpose and the findings were thought to apply to other strains as well. We compared the long-term effects of the administration of different doses of para-chloroamphetamine (PCA) on three specific markers of the density of 5-HT presynapses, [3H]-paroxetine binding to 5-HT-transporters, tryptophan hydroxylase apoenzyme contents, and 5-HT levels in the frontal cortex of Sprague-Dawley and Wistar rats. PCA-treatment caused a dose dependent decline of all three parameters which was much more pronounced in Sprague-Dawley compared to Wistar rats. An i.p. dose of 4mg PCA/kg body weight, which caused a severe, about 90% reduction of all three parameters of 5-HT innervation in Sprague-Dawley rats was almost ineffective in Wistar rats. The dose of 8mg/kg which was required to eliminate about 80% of cortical 5-HT presynapses in Wistar rats was already lethal to Sprague-Dawley rats. The reasons of this different susceptibility of the 5-HT system in the two rat strains are unknown. Their elucidation will contribute to a better understanding of inherited differences in individual vulnerability to the neurotoxic effects of substituted amphetamines. The combined measurements of transporter density, of tryptophan hydroxylase apoenzyme contents, and of 5-HT levels is a powerful tool for the assessment of experimentally induced changes in the density of 5-HT innervation in distant projection fields of the raphe nuclei.

Molecular dynamics simulations and energy calculations based on the AMBER force field were used to examine the molecular movements and low-energy conformations of acetylcholine in vacuum and in aqueous solution. Electronic structures of acetylcholine were calculated byab initio quantum mechanical calculations. Three conformations obtained from crystal structures and two from previous calculations were used as starting geometries in the simulations. Thetrans, gauche conformer had lowest energy both in vacuum and in aqueous solution. Bothtrans, gauche andtrans, trans conformers were observed during molecular dynamics in water, which indicates that both conformations are relatively stable. The acetyl methyl group rotated more rapidly than those at the nitrogen atom during molecular dynamics simulations in water. Correlation times of both types of methyl groups were in good agreement with NMR data, which demonstrates that such simulations provide valid information about molecular movements of the neurotransmitter.

Levetiracetam (LEV) has been shown to suppress myoclonus of various origins. Corticobasal degeneration (CBD), a progressive neurodegenerative disorder with Parkinsonian syndrome, is frequently accompanied by myoclonus. We investigated the effect of LEV on myoclonus in two CBD patients. LEV remarkably decreased the myoclonic activity in both patients already at 1,500 mg/day dose. This is the first report on LEV alleviating myoclonus in CBD. Our data indicate that it might be worthwhile to assess this effect in an appropriately designed study.

Prepulse inhibition (PPI) is the attenuation of the startle response towards an instantaneous and intense stimulus when preceded by a weaker non-startling stimulus. Deficits in this sensorimotor gating process have been associated with the pathophysiology of schizophrenia and other psychiatric disorders. Among the neurotransmitters involved in PPI modulation, serotonin (5-HT) has so far received comparably little attention. While a recent pharmacological study suggests an important role of different 5-HT receptor (5-HTR) subtypes in PPI modulation, the mechanisms by which 5-HTR impact on PPI remain to be further elucidated. Therefore, we employed a molecular genetic approach in order to examine whether PPI is associated with two functional 5-HTR gene polymorphisms, 5-HTR1A C−1019G and 5-HTR2A T102C. In a sample of 81 healthy volunteers, we found no significant main effects of the polymorphisms, but a significant interaction effect on PPI at short (50 ms) and mid-long (150 ms) pulse–prepulse intervals. The presence of the 5-HTR2A T allele (reported to result in higher 5-HTR2A expression) led to attenuated PPI only in the absence of the 5-HTR1A G allele (reported to result in reduced 5-HTR1A autoreceptor expression). Our results may indicate that a higher 5-HTR2A expression together with a reduced 5-HTR1A autoreceptor expression and consequently, elevated firing rates of serotonergic neurons results in elevated 5-HTR2A activation by serotonin which could potently attenuate PPI. While further research into the molecular mechanisms underlying this interaction is needed, our results underscore the role of 5-HTR in PPI modulation and further implicate the 5-HTR1A G−1019C and the 5-HTR2A T102C polymorphisms in the pathophysiology of schizophrenia.