[The function of sigma receptors--electrophysiological approach]

The Sigma1 Protein as a Target for the Non-genomic Effects of Neuro(active)steroids: Molecular, Physiological, and Behavioral Aspects

Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.

Is a nitrogen atom an important pharmacophoric element in sigma ligand binding?

A lingering question in sigma receptor ligand development is whether a nitrogen atom serves as an important pharmacophoric element in binding affinity. To address this question, we have synthesized several phenylalkylpiperidines and phenylalkylpiperazines and demonstrated that removal of the N atom from a typical phenylalkylpiperidine led to little or no binding to sigma receptors. In addition, where two N atoms occur in a compound, such as with phenylalkylpiperazines, the N atom on the longer alkyl chain appears to be more important. Thus, based on this study, the N atom is an important pharmacophoric element in the binding of phenylalkylpiperidines and phenylalkylpiperazines to sigma receptors.