Michel Dib

Affinity of cyamemazine, an anxiolytic antipsychotic drug, for human recombinant dopamine vs. serotonin receptor subtypes

Animal studies indicate that the anxiolytic properties of the antipsychotic agent cyamemazine may result from blockade of serotonin 5-HT(2C) receptors and to a lesser extent from blockade of serotonin 5-HT(3) receptors. Here, we used human recombinant receptors to determine the relative affinity of cyamemazine for serotonin and dopamine receptor subtypes. In addition, cyamemazine was tested in other brain receptor types and subtypes which are considered to mediate central nervous systems effects of drugs. Hence, cyamemazine affinity was determined in human recombinant receptors expressed in CHO cells (hD(2), hD(3), and hD(4.4) receptors, h5-HT(1A), h5-HT(2A), h5-HT(2C), and h5-HT(7), and hM(1), hM(2), hM(3), hM(4), and hM(5) receptors), L-cells (hD(1) receptor), and HEK-293 cells (h5-HT(3) receptors) or natively present in N1E-115 cells (5-HT(3) receptors) or in rat cerebral cortex (non-specific alpha(1)- and alpha(2)-adrenoceptors, GABA(A) and GABA(B) receptors, H(3) histamine receptors), and guinea-pig cerebellum (H(1) central and H(2) histamine receptors) membranes. Similarly to atypical antipsychotics, cyamemazine exhibited high affinity for: (i) h5-HT(2A) receptors (K(i)=1.5+/-0.7 nM, mean+/-SEM, N=3) and this was four times higher than for hD(2) receptors (K(i)=5.8+/-0.8 nM), (ii) h5-HT(2C) receptors (K(i)=11.8+/-2.2nM), and (iii) 5-HT(7) receptors (K(i)=22 nM). Conversely, cyamemazine exhibited very low affinity for h5-HT(3) receptors (K(i)=2.9+/-0.4 microM). In conclusion, similarly to atypical antipsychotic agents, cyamemazine, possesses high affinity for h5-HT(2A), h5-HT(2C), and h5-HT(7) receptors, a feature which can explain its low propensity to cause extrapyramidal adverse reactions in clinical practice. The high affinity for h5-HT(2C) receptors, but not for h5-HT(3) receptors, can account for the anxiolytic activity of cyamemazine in human subjects.

Neuroprotective effect of riluzole in acute noise-induced hearing loss

Riluzole has been reported to protect against the deleterious effect of cerebral ischemia by blocking glutamatergic neurotransmission. Here, we investigated whether acoustic trauma-induced cochlear excitotoxicity could be attenuated by riluzole. Cumulative intracochlear perfusion of riluzole completely abolished single-nerve fiber activity in the guinea pig cochlea and the compound action potential of the auditory nerve. Guinea pigs treated with riluzole (100 μM) showed significantly less hearing threshold shift than untreated guinea pigs, and presented no sign of dendritic damage in the cochlea observable by electron microscopy. When coapplied with glutamate, riluzole did not prevent glutamate-induced swelling of auditory nerve dendrites, suggesting that the protective effect of riluzole was mediated principally by inhibition of glutamate release from sensory inner hair cells.

Double-blind, comparative study of cyamemazine vs. bromazepam in the benzodiazepine withdrawal syndrome.

Cyamemazine is an anxiolytic antipsychotic, which reduces ethanol withdrawal symptoms. Here, we investigated if cyamemazine can be also effective as substitute drug to facilitate benzodiazepine withdrawal. A total of 168 patients treated with benzodiazepines for at least 3 months and with a <18 score in the Hamilton Anxiety Rating Scale (HARS) were included in the study. Previous benzodiazepine treatment was withdrawn, and patients were randomized to a 4-week treatment with cyamemazine (25-50 mg q.d.) or bromazepam (3-6 mg q.d.), followed by 2 weeks of placebo. The primary efficacy variable was the maximal anxiety rebound as measured with the HARS during the 42 days of treatment. No statistically significant differences between treatment groups were found for the extent or incidence of rebound anxiety. Considering all dropout patients as withdrawal failures, after 6 months of follow-up, 56/84 patients in the cyamemazine group (66.7%) and 55/84 patients in the bromazepam group (65.5%) were successfully withdrawn. 28 patients in the cyamemazine group and 18 in the bromazepam group had an adverse event, including anxiety, insomnia, dry mouth and somnolence. No extra-pyramidal symptoms were reported. In conclusion, cyamemazine was comparable to bromazepam in ensuring successful benzodiazepine withdrawal and in controlling the acute benzodiazepine withdrawal syndrome. Cyamemazine may be useful to facilitate benzodiazepine withdrawal in those patients where bromazepam substitution is not appropriate.

5-HT2A receptor antagonist properties of cyamemazine in rat and guinea pig smooth muscle

5-HT(2A) receptor antagonism seems to explain the low incidence of extrapyramidal side effects with atypical neuroleptics. Whether the neuroleptic cyamemazine, which at low doses is also devoid of extrapyramidal side effects, possesses 5-HT(2A) receptor antagonist properties is unknown. Cyamemazine was tested for its ability to antagonize 5-HT(2A)-mediated responses in isolated rat aorta and guinea pig trachea and to displace [3H]ketanserin specifically bound to rat brain membranes. In isolated rat aorta, cyamemazine potently and competitively antagonized serotonin-dependent contractions (pA(2)=8.82+/-0.26, n=7; Schilds slope=1.02+/-0.29). In this test, cyamemazine was of similar potency as ketanserin (pA(2)=8.23). In isolated guinea pig trachea, cyamemazine reduced maximum contractile responses to serotonin with pIC(50)=7.92+/-0.35, (n=4), whereas ketanserin exhibited a pIC(50)=8.79. Finally, cyamemazine displaced [3H]ketanserin specifically bound to rat brain membranes with pK(i)=8.76+/-0.53 (n=3). In conclusion, cyamemazine behaves as a potent antagonist at 5-HT(2A) receptors, which compares well with the reference compound, ketanserin. Whether this 5-HT(2A) receptor antagonist action of cyamemazine can explain its low incidence of extrapyramidal side effects deserves further investigation.