Amino acid neurotransmitters are single amino acid residues that are released from presynaptic nerve terminals in response to an action potential, cross the synaptic cleft, and bind to specific receptor proteins on the postsynaptic membrane to elicit a postsynaptic response.
In summary, the discovery of neuroactive steroids has led to a new appreciation of endocrine-nervous system interactions. The modulation of GABAA receptors by steroid hormone metabolites has far-reaching physiological and pharmacological implications, including relevance to human psychiatric and neurological problems (Fig. 7): I. MECHANISM OF GENERAL ANESTHESIA (Alphaxalone) II. GABA TONE IN SOME REGIONS (e.g., caudate) III. ANTI-ANXIETY ACTIVITY: (Post-partum depression, premenstrual syndrome?) (New drugs?) IV. CHILDBIRTH V. ANTIEPILEPTIC ACTIVITY (New drugs?) VI. REGIONAL HETEROGENEITY (Receptor subtypes) VII. PARTIAL AGONISTS (Better clinical profile?) FIG. 7. Implications of GABAA receptor as a nongenomic CNS target of steroids.
This is the first reported controlled trial of a partial benzodiazepine agonist, abecarnil, utilized in the treatment of generalized anxiety disorder (GAD). It was a sequential dose-finding study comparing 15-30 mg/day, 7.5-15 mg/day, and 3-9 mg/day to placebo for 3 weeks of treatment followed by abrupt discontinuation through placebo substitution. Although the two higher dose groups had high incidence of central nervous system (CNS) sedative adverse effects, the 3-9 mg/day group tolerated the medication well with no dropouts. The 3-9 mg/day group, in comparison to the two higher doses and placebo, demonstrated efficacy in global improvement ratings and Hamilton Anxiety Scale (HAM-A) scores. At Week 3, 61 percent of the abecarnil 3-9 mg/day group was rated as at least 50 percent improved on the HAM-A, compared to 30 percent of the placebo group. With abrupt discontinuation there were mild to moderate withdrawal symptoms and loss of efficacy in the two higher dose groups. However, in the 3-9 mg/day abecarnil group, there were few withdrawal symptoms and almost no loss of efficacy following discontinuation.
