N-Methyl-D-aspartate (NMDA, 200 pzM) evokes the release of [3H]norepinephrine ([3H]NE) from preloaded hippocampal slices. This effect is potentiated by dehydroepiandrosterone sulfate (DHEA S), whereas it is inhibited by pregnenolone sulfate (PREG S) and the highaffinity r inverse agonist 1,3-di(2-tolyl)guanidine, at concentrations of .100 nM. Neither 3a-hydroxy-5a-pregnan-20-one nor its sulfate ester modified NMDA-evoked [3H] NE overflow. Eighty-four female Sprague-Dawley rats (180-225 g), purchased from Iffa Credo, were kept at 21°C on a 12 hr:12 hr light/dark cycle with free access to water and Purina chow. At least 4 weeks prior to the release experiments, rats were anesthetized under ether and bilateral ovariectomy was carried out by lateral access. In a subgroup of 16 rats, anesthetized with chloral hydrate (400 mg/kg, i.p.) 3-11 days prior to the experiments, PTX (1 ,g/2 ,ul of physiological saline) was injected (using a 10-uAl Hamilton syringe) bilaterally into the dorsal hippocampus at A: 4.5, L: 4, and D: 4, according to the atlas of Paxinos and Watson (25) as described (3). Twelve control rats received an equal volume of the vehicle. When appropriate, the rats were killed by decapitation and their brains were rapidly dissected. Coronal slices (0.4-mm thick) of the hippocampus were prepared with a McIlwain tissue chopper. The slices were incubated in Krebs' solution containing[3H]NE (0.1 ,uM) and bubbled with a mixture of 95% 02/5% CO2 at 37°C for 30 min. The composition of the Krebs' solution (in mM) was NaCl 118, KCl 4.7, CaCl2 1.3, MgCl2 1.2, NaH2PO4 1, NaHCO3 25, glucose 11.1, Na2EDTA 0.04, and ascorbic acid 0.06. At the end of the incubation period, each glass chamber received two slices that were superfused continuously at a rate of 0.5 ml/min with oxygenated Mg2+-free Krebs' solution at 37°C for 68 min. As indicated in Results, one steroid and/or one of the cr ligands DTG, haloperidol, BD-1063, or spiperone were added in Mg2+-free Krebs' solution throughout the superfusion period. The prototypic a-ligand DTG was chosen since it acts on both a-i and o'2 receptors (3, 26). The universal o-antagonist haloperidol also binds to dopaminergic, serotoninergic, adrenergic, and cholinergic sites Abbreviations: 3a,5a-THP, 3a-hydroxy-Sa-pregnan-20-one; CNS, central nervous system; DHEA, dehydroepiandrosterone; DTG, 1,3-di(2-tolyl)guanidine; Gi/o protein, guanine nucleotide-binding pro-

No abstract

Most physiological effects of 1 receptor ligands are sensitive to pertussis toxin, suggesting a coupling with cell membrane-bound G proteins. However, the cloning of the 1 receptor has allowed the identification of an intracellular protein anchored on the endoplasmic reticulum. Here, we show, using the isolated adult guinea pig brainstem preparation, that activation of the 1 receptor results in its translocation from the cytosol to the vicinity of the cell membrane and induces a robust and rapid decrease in hypoglossal activity, which is mediated by phospholipase C. The subsequent activation of protein kinase C ␤ 1 and ␤ 2 isoforms and the phosphorylation of a protein of the same molecular weight as the cloned 1 receptor lead to a desensitization of the 1 motor response. Our results indicate that the intracellular 1 receptor regulates several components implicated in plasma membrane-bound signal transduction. This might be an example of a mechanism by which an intracellular receptor modulates metabotropic responses.

Abstract. 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 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the γ-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 (σ) receptors. Recent studies particularly demonstrated that the σ 1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the σ 1 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 σ 1 -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 σ 1 drugs.