Regional Distribution Of Receptors Research Articles

Pharmacotherapy of Insomnia: Focus on Zolpidem Extended Release

The imidazopyridine drug zolpidem ( N,N,6-trimethyl-2[4-methyl-phenyl]imidazo[1,2-a]pyridine-3-acetamide) is a sedative/hypnotic with relative selectivity for α1 subunits of the GABAA receptor/chloride channel complex. Because of this selectivity and regional receptor distribution, zolpidem is less generalized in its CNS depressive actions than benzodiazepines and largely devoid of their major, undesired side- and after-effects, at recommended doses. Zolpidem is rapidly taken up and distributed, binds extensively to plasma proteins, and is readily inactivated by hepatic cytochrome P450 monooxygenases, especially CYP3A4. Zolpidem is thus a rapidly acting agent which provides effective facilitation of sleep onset. However, plasma levels of the immediate release (IR) formulation frequently decline too quickly for effective sleep maintenance. To address this problem zolpidem extended release (ER) has been developed. At age-specific dosages, it increases, in middle-aged and elderly patients, total sleep time and reduces the number of nocturnal awakenings. Both zolpidem IR and ER have favorable toxicological profiles. Adverse effects are moderate, frequently in the incidence range of placebos, and certainly less frequent and severe than those of benzodiazepines. Zolpidem IR and ER are practically devoid of next-day hangover effects and only infrequently cause rebound insomnia of usually short duration. Both variants of zolpidem have a limited potential for dependence and abuse.

Electron microscopic studies of receptor localization.

The localization and density of G-protein-coupled receptors (GPCRs) on the cell surface is a critical factor for specifying signaling within and between neurons. GPCRs and their associated signaling components are localized to specific neuronal compartments that give rise to a variety of functional implications. Therefore, information regarding the precise localization of GPCRs is a prerequisite for studies designed to elucidate their contribution to neuronal function, and can be achieved only by immunoelectron microscopy. Three main techniques for immunoelectron microscopy exist: the preembedding immunoperoxidase, the preembedding immunogold, and the postembedding immunogold techniques. The preembedding immunogold method is reliable for the localization of receptors at extrasynaptic and perisynaptic sites. The preembedding immunoperoxidase method provides valuable information on regional distribution of receptors. Finally, to localize any receptor at synaptic sites the only reliable method is the postembedding immunogold technique. Therefore, the three immunocytochemical methods provide complementary information about the cellular, subcellular, and subsynaptic location of any receptor.

Improved method for autoradiographic localization of beta-adrenoceptors using photoaffinity labelling.

Contact autoradiography of tissue sections, using emulsion coated coverslips or X-ray films, is widely used to provide information about the regional distribution of receptors. This easy to perform, standard technique has the disadvantage of an image spread due to the gap between the radioactive source and the film. The present study describes a new technique which combines photoaffinity labeling of beta-adrenoceptors with "dipping" autoradiography and a modified trichrome stain. Incubation of 16 microns cryosections of rat lung tissue with the iodinated, photoaffinity labeling, non-selective, beta-adrenergic agonist [125I]-cyanopindololazide II ([125I]-CYPA II) (100 pmol/l) in the absence or presence of 1 mumol (+/-)-propranolol revealed strong, specific beta-adrenoceptor binding to alveolar parenchyma and bronchial epithelium of large and small bronchioles, lesser binding to smooth muscle bundles of large airways and only sparse binding to the smooth muscle of small bronchioles or peripheral branches of pulmonary artery. With standard autoradiographic techniques, a similar distribution of the label was obtained, although resolution and sensitivity were inferior. Staining of tissue sections through the photoemulsion by means of a modified Mallory's trichrome dye facilitated the discrimination between alveolar and bronchial epithelium, muscular and collagenous tissues. In conclusion, the photoaffinity labeling of beta-adrenoceptors with [125I]-CYPA II allows the use of "dipping" autoradiography. This technique, in combination with trichrome staining through the photoemulsion, results in an improved autoradiographic image together with a better association of the label with distinct histological structures and the higher sensitivity of the method.

Utility of [16 alpha-125I] iodoestradiol for autoradiography for the study of cellular and regional distribution of receptors.

We demonstrate the utility of [16 alpha-125I]iodoestradiol for thaw-mount autoradiography with 2 micron and 4 micron thick sections of rat and mouse uterus, pituitary, and brain after in vivo administration. Under the conditions of the experiments, short-term autoradiography with exposure times between 3 and 14 days provides optimal cellular resolution, whereas long-term autoradiography with 1-2 months of exposure may be used to obtain topographic-regional surveys of distribution.

3H]muscimol binding of GABA receptors in the visual cortex of normal and monocularly deprived cats

In vitro receptor binding techniques were used to compare the total number, affinity and regional distribution of GABA receptors in visual cortex, as revealed by [ 3H]muscimol binding, in 5 normal and 5 monocularly deprived (MD) cats. Analysis of saturation kinetics and pharmacological specificity indicated that binding was to a single site having the characteristics of the GABA A receptor. No differences were found between normal and MD cats in either number or affinity of receptors. Within visual cortex, there were laminar differences in the density of binding, but no evidence for a lateral (columnar) organization. Label was densest in the superficial layers (I–IV), lowest in layer V and intermediate in layer VI. This pattern of label varied with incubation parameters with layer IV showing the densest label when high concentrations of [ 3H]muscimol and short rinse times were used. There were no differences between normal and MD cats in regional distribution of receptors under any incubation condition.

The isolated human epicardial coronary artery

Ring segments from coronary arteries from recipient hearts of patients receiving cardiac transplants were prepared and mounted in an organ bath. Spontaneous contractile activity, factors that affect basal tone, agonist-induced contractile responses, regional receptor distribution, activity of cardioactive drugs, and species differences were studied. Agents that mediate contraction include histamine, acetylcholine, norepinephrine, potassium and some prostaglandins. Calcium-entry blockers, nitrates and beta-adrenergic agonists caused relaxation. Major species differences exist in coronary vascular pharmacology. Ring segments from human epicardial coronary arteries are suitable for pharmacologic studies, and because of species differences, they offer an ideal model for investigating the pharmacology of the human coronary circulation.

Localization of125I-labeled FSH in the Testes of Hypophysectomized Rats by Autoradiography at the Light and Electron Microscope Levels12

Previous evidence has indicated that the testicular receptors for FSH reside on plasma membranes in seminiferous tubules, and that the Sertoli cell is a primary target of the hormone. Since the Sertoli cell is large and elaborately structured, it is important to know whether there is a regional distribution of receptors over its extensive surface. In the present study, the specific binding of 25I-labeled hFSH to seminiferous tubules of hypophysectomized rats was examined, utilizing autoradiography at both the light and electron microscope levels. Purified hFSH (LER-1575C) was iodinated to an average specific activity of 29 μCi/μg, and approximately 1 μg was administered intratesticularly in 40 day old rats which had been hypophysectomized 10 days earlier. In some cases, testosterone was administered after hypophysectomy in order to maintain spermatogenesis. Controls were of two types: 40 day old intact littermates in which endogenous FSH presumably occupied most of the receptors, and hypophysectomized rat...