Receptors In Different Regions Research Articles

Effect of ovarian steroids on the concentration of μ opiate receptors in different regions of the brain of the female rat

Effect of ovarian steroids on the concentration of μ opiate receptors in different regions of the brain of the female rat

Distribution of kappa opioid receptors in the brain of young and old male rats

The experiments to be described have been designed in order to: (a) provide new information on the concentrations of opioid kappa receptors in different regions of the brain of the male rats; and (b) to analyze whether the density of brain kappa receptors might be modified by the process of aging. The concentration of kappa receptors was investigated in the hypothalamus, amygdala, mesencephalon, corpus striatum, hippocampus, thalamus, frontal poles, anterior and posterior cortex collected from male rats of 2 and 19 months of age. 3H-bremazocine (BRZ) was used as the ligand of kappa receptors, after protection of mu and delta receptors respectively with dihydromorphine and d-ala-d-leu-enkephalin. The results obtained show that: (1) in young male rats, the number of kappa opioid receptors is different in the various brain areas examined: the hypothalamus and the striatum have a concentration of kappa binding sites which is significantly higher that that found in the mesencephalon and in the amygdala; much lower concentrations of kappa binding sites have been found in the thalamus, the frontal poles, the hippocampus, the anterior and posterior cerebral cortex. (2) Aging exerts little influence on the number of kappa receptors in the majority of the brain structures considered. However in the amygdala and in the thalamus the number of kappa receptors was increased in old animals. To the authors' knowledge, the data here presented are the first ones which suggest that age may increase rather than decrease the number of neurotransmitter receptors in the brain.

Differences in nuclear triiodothyronine binding in rat brain cells suggest phylogenetic specialization of neuronal functions.

The central nervous system depends on thyroid hormones (TH) in regard to its development, maturation, and maintenance of normal functions. As there is much evidence to suggest that the effects of TH are mainly mediated through specific nuclear binding sites, we have studied the anatomical distribution of T3 nuclear receptors in different regions of adult rat brain, and the localization of receptors in the fractionated neuronal and glial nuclei of neocortex, paleocortex, and cerebellum. Purified nuclei from the various brain regions were prepared by ultracentrifugation in 2.2 M sucrose. Purified neuronal and glial fractions were obtained by discontinuous sucrose gradient centrifugation in 2.2 and 2.4 M sucrose. The washed nuclear fractions were used for T3 binding assay at 37 C for 30 min and the data analyzed by least squares nonlinear regression analysis. Nonfractionated nuclei from all regions studied were found to have similar dissociation constant (Kd) values (1.04-1.38 nM) and Eadie-Hofstee plots indicated the presence of an apparently ubiquitous single class of high affinity, low capacity binding sites. The increase in binding from cerebellum (54 +/- 24 fmol/mg DNA; mean +/- SE) to neocortex (666 +/- 89 fmol/mg DNA) showed a caudo-cranial pattern. In fractionated neuronal nuclei, the same trend was observed, only to a greater degree (1628 +/- 266, 994 +/- 76 and 212 +/- 29 fmol/mg DNA in neocortex, paleocortex, and cerebellum, respectively); the difference between corresponding values for glial nuclei of neocortex and paleocortex (357 +/- 139 and 250 +/- 92 fmol/mg DNA, respectively) was not statistically significant, and no specific T3 binding was found in cerebellar glial nuclei. These data suggest that TH may have an important role in neurons from phylogenetically newer regions, concerned with higher mental functions. The caudo-rostral distribution pattern may also indicate a gradient of TH actions in central nervous system regions.

A search for endogenous modulators of the GABA receptor in different regions of the rat CNS

The possible existence of endogenous substances other than γ-aminobutyric acid (GABA), that can also bind to rat brain GABA receptors, has been investigated in synaptic membranes derived from whole rat brain, or from cerebral cortex; as well as in isolated synaptic vesicles obtained from cerebral cortex, striatum, hypothalamus, cerebellum and spinal cord and in the superfusion fluid of electrically stimulated brain cortex slices, where a GABA-like substance is released by a calcium-dependent process. The detector used to study the presence of such presumed non-GABA endogenous ligands, were frozen and thawed rat brain synaptic membranes, that had been treated with 0.05% Triton X-100 and thoroughly washed. With this highly sensitive preparation, at least 5 pmol of GABA/ml could be detected. The extracts of the different preparations where these hypothetical ligands were looked for, were analyzed by means of gel filtration on Sephadez G-10, paper chromatography and high voltage electrophoresis. In a very great number of experiments performed, the only endogenous ligand detected was GABA itself. The possible influence of a number of peptides on binding of GABA to its receptor, was also looked for. No significant effect was found for substance P, neurotensin, cholecystokinin octapeptide sulfated, somatostatin, thyrotropin releasing hormone, luteinizing hormone releasing hormone, methionine enkephalin (all 10 −5 M), angiotensin II (10 −4 M), ACTH (3 × 10 −7 M), poly- l-lysine (30 μg/ml) or poly- l-glutamate (30 μg/ml).

Age-related and sex-related alterations in β-adrenergic receptors in different regions of rat brain

The binding of (−)[ 3H]dihydroalprenolol, an antagonist of norepinephrine, to β-adrenergic receptors in different regions of the brain of male and female rats of various ages was measured. The binding to the synaptosomal fraction of corpus striatum, hypothalamus, cerebral cortex, cerebellum and the brainstems shows a significant decrease in the binding in old rats of both sexes. Only in the female corpus striatal region, the binding in the adult and the old is the same. In the case of females, the highest binding is seen in the young. In the male, an increase in binding occurs up to adulthood, after which it declines, suggesting a definite sex-related difference in the β-adrenergic receptor.

Recent developments in opiate and opioid peptide research and their relation to tolerance and dependence

In 1680, the English physician Thomas Sydenham wrote, Among the remedies which it has pleased Almightly God to give man to relieve his suffering, none is so universal and so efficacious as opium. Over the intervening centuries, the admiration of the medical community for the pain relieving effects of opium and its derivatives has been tempered by an increasing awareness of their toxicity and addictiveness. This, together with the lack of any other known class of drugs that exert the powerful analgesic action of opiates, has stimulated an intensive search for synthetic opiates with the desirable properties of morphine, but without the undesirable sideeffects. More recently, natural morphine-like substances have been found in the brain. These substances promise to open new avenues to an understanding of precisely where in the body opiates act, how they do so and why they are addictive. The general aim of this conference is to discuss drug-related problems and drug dependence. The basic scientist approaches this important field of study by attempting to understand precisely how these drugs affect the organism, and, in the case of opiates, how they interact with the central nervous system (CNS). My intention isto describe some recent advances in opiate research, including some of our own work, and to give an overview of how these affect the problems of dependence. Drugs, hormones and neurotransmitters all produce their effects at very low concentration. It is usually assumed they act at specific receptor sites located on the external surface of cells in the target organs. The notion that some tissues might possess such receptors for opiates is supported by the facts that (1) opiate agonists have similar chemical structure, (2) they are stereospecific in that only the laevo isomers are active, and (3) opiate antagonists can be formed by very slight molecular modifications of agonists. For these reasons, pharmacologists assumed that specific opiate receptors must exist in the brain and possibly in other tissues. In the early 1970s, receptors for opiates were identifed by binding radioactively labelled opiates to fragments of membrane from homogenized brain cells. Not only was this binding shown to be stereospecific, but perhaps more importantly, the affinity or tightness with which a range of agonists bound to the receptor closely paralleled their pharmacological activity. With these techniques it was soon demonstrated that the distribution and density of the opiate receptor in different regions of the CNS corresponded to those regions and pathways believed associated with the sensory and emotional aspects of pain. What are these receptors for opiates doing there? The findings suggested the presence of a natural morphine-like substance in the brain, possibly a neurotransmiffer, that acts at these receptors. The speculafion ended when, in 1975, a remarkable discovery was made w two pentapeptides were isolated from the brain which behaved like opiates in a number of pharmacological tests using peripheral tissues, such as the mouse vas deferens and guinea pig ileum. These actions were stereospecific and were antagonized by naloxone, indicating an action on the opiate receptor. 12 These pentapeptides, with the amino acid sequences of TYR-GLY-GLY-PHE-MET and TYR-GLY-GLY-PHE-LEU, were given the names Methionine- and Leucine-Enkephalin respectively. This sequence was soon recognized by some chemists to be present within the pituitary homone betalipotropin. The enkephalin sequence occurs at positions 61-65 in the 91 amino acid beta-lipotropin molecule, and the C-terminal fragment (amino acids 61-91) was found to be a potent opiate peptide. The term endorphins has been applied to the family of larger peptides, the prototype beta-Upotropin 61-91 being called beta-endorphine (for review, see Snyder,

Resolution of dopamine and serotonin receptor components of [3H]spiperone binding to rat brain regions.

A procedure was developed to identify receptors for dopamine and serotonin separately and selectively by means of [3H]spiperone and to measure the density of each receptor in different regions of the rat brain. In the striatum, the binding of [3H]spiperone to dopamine receptors was inhibited by sulpiride but not by quinazolinedone R43448 (R43448); in the frontal cortex, however, the binding of [3H]spiperone to serotonin receptors was inhibited by R43448 but not by sulpiride. Thus, the density of dopamine receptors (D2 sites) was measured by [3H]spiperone binding in the presence of 0.1 microM R43448 (to preclude the attachment of the 3H-labeled ligand to serotonin sites), while the density of serotonin receptors (S2 sites) was measured by [3H]spiperone binding in the presence of 10 microM sulpiride (to preclude the attachment of the 3H-labeled ligand to dopamine sites). The density of D2 sites was highest in the striatum, followed by the olfactory tubercle, hypothalamus, substantia nigra, and the lower pons--medulla region. All five regions had similar dissociation constants (Kd values) of 0.05--0.15 nM. The density of S2 sites was highest in the frontal cortex, followed by the posterior cortex, olfactory tubercle, striatum, hypothalamus, and thalamus, and all regions had Kd values in the range 0.6--2.3 nM. Thus, because the Kd values were similar for all regions, and because Scatchard analyses revealed a single set of sites for either D2 or S2 (where detected), the main criteria for resolving the dopamine and serotonin components of [3H]spiperone binding were considered fulfilled.

The character of the muscarinic receptors in different regions of the rat brain.

The binding characteristics of muscarinic receptors have been critically examined in six regions of the rat brain. The binding curves of antagonists are similar for all six areas but the binding curves of agonists show large differences. It is shown that in all regions there are three classes of receptors with similar binding characteristics but that these are present in different proportions. The binding constants to the three receptor types of a range of agonists were examined and evidence was produced in support of the theory that the subclasses of brain receptors are due to a single receptor subunit subject to different conformational constraints.

Regional and subcellular distribution of β- and α-adrenergic receptors in the myocardium of different species

1. 1. [ 3H]Dihydroalprenolol ([ 3H]DHA) was employed to detect β-adrenergic receptors in different regions of the myocardium of various commonly used laboratory animals (rat, rabbit, guinea pig and dog). 2. 2. In general, the β-receptor densities (in terms of pmole/g tissue) of all regions of canine myocardium were greater than the corresponding regions of other species examined; the rank order was dog > guinea pig > rabbit > rat. 3. 3. Among the subcellular fractions, the highest specific binding activity of [ 3H]DHA was found in the microsomal fraction whereas 40–60% of the total binding activity of homogenate was found in the low gravitational fraction that contained substantial amounts of sarcolemmal membranes. 4. 4. [ 3H]Dihydroergocryptine ([ 3H]DHEC) was used to detect α-adrenergic receptors in different regions of the myocardium of rat, rabbit, guinea pig and dog. 5. 5. With the assay used, α-receptor sites were reliably detected in the case of rat but not in other species examined. In the case of rat, ventricular α-adrenergic receptor density (in terms of pmole/g tissue) was greater than the atrial region. 6. 6. Amongst the subcellular fractions derived from rat ventricles, a considerable amount of DHEC binding was associated with the fractions enriched in plasma membrane and microsomal membranes.