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A Tempel

Publications and source records attributed to A Tempel.

At least 19 recordsLinked to original sources
PubMed1993

Morphine-induced reciprocal alterations in G alpha s and opioid peptide mRNA levels in discrete brain regions.

The mechanisms involved in the development of morphine tolerance and dependence are still unknown. Recently much attention has been directed toward the changes in post receptor events. Opiate receptors, like other hormone and neurotransmitter receptors, have been shown to mediate their effects through guanine nucleotide binding proteins (G-proteins). This, in turn, may cause alterations in intracellular events, one of which is transcription of specific genes. We investigated the changes in the levels of mRNA of proenkephalin (PPE) and prodynorphin (DYN) and the stimulatory G protein alpha subunit (G alpha s) in adult morphine tolerant rats. Chronic morphine treatment induced reciprocal alterations in the levels of opioid peptide mRNA and G alpha s mRNA in discrete brain regions. In striatum, PPE mRNA decreased by 49% (P < .01) and in hypothalamus, DYN mRNA showed a decrease of 21% (P < .01). In contrast, G alpha s mRNA increased 20% (P < .01) in striatum and 97% (P < .01), in hypothalamus. In hippocampus the changes were reversed: PPE mRNA increased (55%, P < .05) and G alpha s mRNA decreased (33%, P < .01). Frontal cortex exhibited a small decrease in PPE (11.5%, P < .05) without any change on G alpha s or DYN mRNA levels. These reciprocal alterations suggest an opposing mode of regulation of G alpha s and PPE/DYN gene expression in morphine tolerant animals.

Analysis of Variance↗
PubMed1992

Chronic prenatal morphine treatment decreases G alpha s mRNA levels in neonatal frontal cortex.

G alpha s mRNA levels were measured in brain regions of newborn pups following prenatal morphine treatment. A significant decrease (24%) in G alpha s mRNA levels was observed in the frontal cortex. No changes were observed in other regions. This report demonstrates the first in vivo study of opiate effects on G-protein gene expression in neonates. The development of tolerance in vivo may involve complex interactions between several neurotransmitter systems having opposing actions on the G-protein system.

Animals↗
PubMed1991

Visualization of mu opiate receptor downregulation following morphine treatment in neonatal rat brain.

In order to visualize neuroanatomical alterations in specific brain regions, light microscopy autoradiography was carried out on neonatal brain sections from controls and neonates chronically treated with morphine. In the case of brains exposed to morphine from postnatal day (PD) 1-4, mu receptor density on PD 5 was non-existent in the patches of the striatum. There were also decreases in mu opiate receptor density in the surrounding matrix area, and in the nucleus accumbens and amygdala. Longer durations of morphine treatment (PD 1-8) did not show these alterations in mu opiate receptor density. These data demonstrate the unique plasticity seen in the immature opioid system. It is suggested that the differences observed in neonatal vs adult central nervous system may be due to interactions with and the differential development of the G-protein/cyclic adenosine 3',5'-monophosphate (cAMP) system.

Animals↗
PubMed1990

Chronic naltrexone treatment increases expression of preproenkephalin and preprotachykinin mRNA in discrete brain regions.

Long-term blockade of brain opioid receptors by the opiate antagonist naltrexone increases methionine-enkephalin content in the striatum and nucleus accumbens (Tempel et al., 1984). To determine whether these changes in peptide levels reflect increased peptide synthesis, we examined preproenkephalin mRNA content in discrete brain regions of control (placebo-treated) and chronic naltrexone-treated animals by Northern analysis. Chronic naltrexone treatment (8 d) led to an approximately 12-fold increase in the striatal content of preproenkephalin mRNA relative to that of control animals. In contrast, no statistically significant change was observed in striatal mRNA for cyclophilin (1B15) or actin. Small increases in preproenkephalin mRNA content occurred in the hippocampus (+40%) and hypothalamus (+19%). No significant changes occurred in the frontal cortex. Increases in levels of the mRNA were seen as early as 24 hr after antagonist treatment. In contrast, changes in opioid receptor density required 3-4 d to reach half-maximal up-regulation after chronic antagonist treatment. Recent evidence has suggested that substance P is regulated by opioid peptides. To determine whether substance P synthesis is altered by chronic antagonist treatment, the mRNA corresponding to the precursor for substance P was examined using a probe for exon-7 of the preprotachykinin gene. Preprotachykinin mRNA content in the striatum was increased 6-fold after chronic antagonist treatment relative to that of control animals. Substance P content was increased 3-fold after chronic antagonist treatment. These data suggest that chronic blockade of brain opioid receptors leads to the increased synthesis of both enkephalin and substance P in the striatum and that these changes are relatively specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Characterization of opioid receptors in rat nucleus accumbens following mesolimbic dopaminergic lesions.

The present study investigated the cellular localization of mu, delta and kappa opioid receptors in the rat nucleus accumbens in relation to dopaminergic neurons. Dopaminergic terminals were destroyed by intra-accumbens injections of the neurotoxin 6-hydroxydopamine (6-OHDA). Fourteen days after dopaminergic denervation, receptor binding assays and quantitative in vitro autoradiography with highly selective radioligands demonstrated that the density of mu opioid receptors in the nucleus accumbens was decreased by 30 +/- 6%. There was no change in delta or kappa receptors in the accumbens, a finding which indicates that the loss of mu opioid receptors was specific. A time course study demonstrated that the loss of mu receptors lagged behind the depletion of dopamine by about 5 days. Destruction of intrinsic neuronal cell bodies and dendrites by injection of ibotenic acid into the accumbens resulted in a loss of 36 +/- 3% of mu opioid receptors. Co-injection of 6-OHDA and ibotenic acid decreased mu receptors by 41 +/- 4%, only slightly more than the loss caused by ibotenic acid alone. These results suggest that only a small number of mu opioid receptors in the nucleus accumbens are located on dopaminergic terminals and are consistent with the possibility that the loss of opioid receptors following denervation of dopaminergic fibers in the accumbens is the result of transsynaptic degeneration.

Animals↗
PubMed1988

Age-related changes of muscimol binding in the substantia nigra.

Receptor binding studies of the substantia nigra (SN) and cerebellum revealed two affinity sites for muscimol binding in the SN and cerebellum of adult and 16-day-old rats. Scatchard analysis revealed a paucity of high-affinity muscimol receptors in the SN of 16-day-old rat pups. These results suggest that the lack of anticonvulsant action of muscimol in the SN of 16-day-old rat pups may be due to the paucity of high-affinity muscimol receptors as compared to adult rats.

Aging↗
PubMed1988

Morphine-induced downregulation of mu-opioid receptors in neonatal rat brain.

Chronic administration of morphine to pre- and postnatal rats produced a marked decrease in brain mu-opioid receptor density with-out change in receptor affinity. No significant changes in delta- or kappa-receptors were observed. This downregulation was accompanied by tolerance to the analgesic actions of morphine. In neonates exposed to morphine from postnatal day one, mu-receptor number was significantly depressed until postnatal day 8, then increased gradually to control levels by day 14 of treatment. Longer treatment produced no further change in opioid receptors. These data represent the first demonstration of in vivo downregulation of brain mu-opioid receptors following morphine administration and provide evidence for a unique plasticity of the immature opioid receptor system.

Aging↗
PubMed1988

Characterization and visualization of rat and guinea pig brain kappa opioid receptors: evidence for kappa 1 and kappa 2 opioid receptors.

kappa opioid receptors (kappa receptors) have been characterized in homogenates of guinea pig and rat brain under in vitro binding conditions. kappa receptors were labeled by using the tritiated prototypic kappa opioid ethylketocyclazocine under conditions in which mu and delta opioid binding was suppressed. In the case of guinea pig brain membranes, a single population of high-affinity kappa opioid receptor sites (kappa sites; Kd = 0.66 nM, Bmax = 80 fmol/mg of protein) was observed. In contrast, in the case of rat brain, two populations of kappa sites were observed--high-affinity sites at low density (Kd = 1.0 nM, Bmax = 16 fmol/mg of protein) and low-affinity sites at high density (Kd = 13 nM, Bmax = 111 fmol/mg of protein). To test the hypothesis that the high- and low-affinity kappa sites represent two distinct kappa receptor subtypes, a series of opioids were tested for their abilities to compete for binding to the two sites. U-69,593 and Cambridge 20 selectively displaced the high-affinity kappa site in both guinea pig and rat tissue, but were inactive at the rat-brain low-affinity site. Other kappa opioid drugs, including U-50,488, ethylketocyclazocine, bremazocine, cyclazocine, and dynormphin (1-17), competed for binding to both sites, but with different rank orders of potency. Quantitative light microscopy in vitro autoradiography was used to visualize the neuroanatomical pattern of kappa receptors in rat and guinea pig brain. The distribution patterns of the two kappa receptor subtypes of rat brain were clearly different. The pattern of rat high-affinity kappa sites paralleled that of guinea pig in the caudate-putamen, mid-brain, central gray substance of cerebrum, and substantia nigra; interspecies differences were apparent throughout most of the rest of the brain. Collectively, these data provide direct evidence for the presence of two kappa receptor subtypes; the U-69,593-sensitive, high-affinity kappa 1 site predominates in guinea pig brain, and the U-69,593-insensitive, low-affinity kappa 2 site predominates in rat brain.

Animals↗
PubMed1987

Neuroanatomical patterns of the mu, delta, and kappa opioid receptors of rat brain as determined by quantitative in vitro autoradiography.

Highly specific radioligands and quantitative autoradiography reveal strikingly different neuroanatomical patterns for the mu, delta, and kappa opioid receptors of rat brain. The mu receptors are most densely localized in patches in the striatum, layers I and III of the cortex, the pyramidal cell layer of the hippocampal formation, specific nuclei of the thalamus, the pars reticulata of the substantia nigra, the interpeduncular nucleus, and the locus coeruleus. In contrast, delta receptors are highly confined, exhibiting selective localization in layers I, II, and VIa of the neocortex, a diffuse pattern in the striatum, and moderate concentration in the pars reticulata of the substantia nigra and in the interpeduncular nucleus. delta receptors are absent in most other brain structures. This distribution is unexpected in that the enkephalins, the putative endogenous ligands of the delta receptor, occur essentially throughout the brain. The kappa receptors of rat brain exhibit a third pattern distinct from that of the mu and delta receptors. kappa receptors occur at low density in patches in the striatum and at particularly high density in the nucleus accumbens, along the pyramidal and molecular layers of the hippocampus, in the granular cell layer of the dentate gyrus, specific midline nuclei of the thalamus, and hindbrain regions. kappa receptors appear to be uniformly distributed across regions in the neocortex with the exception of layer III, which revealed only trace levels of binding. An important conclusion of the present study is that delta receptors occur at high density only in the forebrain and in two midbrain structures, whereas mu and kappa receptors exhibit discrete patterns in most major brain regions.

Animals↗
PubMed1986

Antagonist-induced opiate receptor upregulation in cultures of fetal mouse spinal cord-ganglion explants.

Chronic exposure of fetal mouse spinal cord-ganglion explants to the opioid antagonist naloxone (10 microM, 7 days) produced a pronounced upregulation of mu opioid receptors. The antagonist action was stereospecific, as it was produced by (-)-, but not by (+)-naloxone, and was dose-dependent. Half-maximal naloxone-induced receptor upregulation occurred after two days; receptor density was maximal at 5 days. Exposure of the explant cultures to naloxone (10 microM) in the presence of the protein synthesis inhibitor, cycloheximide (1 microM; a concentration which blocks greater than 90% protein synthesis) resulted in receptor density changes that were similar to those observed in cultures exposed to naloxone alone. This finding suggests that antagonist-induced opiate receptor upregulation does not require the synthesis of new receptor molecules.

Animals↗
PubMed1986

Interaction of [3H](-)-SKF-10,047 with brain sigma receptors: characterization and autoradiographic visualization.

The sigma opiates differ from other opiates in their stimulatory and psychotomimetic actions. The sigma opiate [3H](-)-SKF-10,047 has been used to characterize sigma receptors in rat nervous tissue. Binding of [3H](-)-SKF-10,047 to rat brain membranes was of high affinity, saturable, and reversible. Scatchard analysis revealed the apparent interaction of this drug with two distinct binding sites characterized by affinities of 0.03 and 75 nM (5 mM Tris-HCl buffer, pH 7.4, at 4 degrees C). Competition analyses involving rank order determinations for a series of opiates and other drugs indicate that the high-affinity binding site is the mu opiate receptor. The lower-affinity site (revealed after suppression of mu and delta receptor binding) has been identified as the sigma opiate/phencyclidine receptor. In vitro autoradiography has been used to visualize neuroanatomical patterns of receptors labeled using [3H](-)-SKF-10,047 in the presence of normorphine and [D-Ala2,D-Leu5]enkephalin to block mu and delta interactions, respectively. Labeling patterns differ markedly from those for mu, delta, or kappa receptors. The highest densities (determined by quantitative autoradiography) are found in the medial portion of the nucleus accumbens, amygdaloid nucleus, hippocampal formation, central gray, locus coeruleus, and the parabrachial nuclei. Receptors in these structures could account for the stimulatory, mood-altering, and analgesic properties of the sigma opiates. Although not the most selective sigma opiate ligand, [3H](-)-SKF-10,047 binds to sigma opiate receptors in brain, and this interaction can be readily distinguished from its interactions with other classes of brain opiate receptors.

Animals↗
PubMed1985

Neurochemical and functional correlates of naltrexone-induced opiate receptor up-regulation.

The neurochemical and functional correlates of opioid receptor up-regulation after chronic antagonist administration in vivo and of down-regulation after withdrawal of antagonist were examined. Total brain opioid receptors increased 1.9-fold by day 8 of naltrexone administration, after which no further increase was observed; the newly synthesized or unmasked receptors exhibited an enhanced sensitivity to guanyl nucleotide modulation. Withdrawal from chronic naltrexone treatment resulted in a return to nearly control levels of receptor density and guanyl nucleotide sensitivity in a period of 6 days. These results suggest that up-regulation is accompanied by an increased coupling of the receptors to the inhibitory guanyl nucleotide binding protein (Ni) and that down-regulation involves the dissociation of the receptor/Ni complex. In experiments designed to target opiate receptor subtypes, long-term treatment with naltrexone was found to produce a coordinated up-regulation of brain mu and delta receptors, but did not cause a significant change in the density or affinity of kappa or sigma receptors. These findings indicate that the kappa and sigma opiate receptor classes may be subject to independent control mechanisms. Chronic naltrexone treatment also resulted in an enhanced morphine-induced analgesia. This result indicates that a functional supersensitivity occurs as a result of the selective up-regulation of mu and delta receptors. After withdrawal from naltrexone, supersensitivity to morphine-induced analgesia decreased monotonically and, in parallel to opioid receptor density, to prenaltrexone treatment levels within 6 days. Together, these results suggest a functional significance for antagonist-induced mu and delta opiate receptor up-regulation.

Animals↗
PubMed1984

Visualization of opiate receptor upregulation by light microscopy autoradiography.

Light microscopy autoradiography has been used to visualize neuroanatomical patterns of brain opiate receptor upregulation in response to chronic naltrexone administration. Slide-mounted brain sections of frozen rat brain were labeled in vitro with dihydro[3H]morphine, a relatively selective mu opioid ligand. The greatest relative increases in opiate receptor density were observed in the nucleus accumbens, the amygdala, striatal patches, nuclei of the thalamus and hypothalamus, layers I and III of neocortex, substantia nigra compacta, midbrain periaqueductal gray regions, and the parabrachial nuclei of the brainstem. The substantia nigra reticulata, surrounding areas of striatal patches, and the locus ceruleus, were not affected by this drug treatment. These findings demonstrate that chronically administered naltrexone differentially regulates opiate receptors throughout the brain. In particular, three brain systems appear to be target areas of receptor upregulation : (i) the dopamine A9/A10 systems, (ii) the limbic system, and (iii) structures that receive input from afferent sensory pathways. Two possible mechanisms to account for this finding are (i) that the drug does not have uniform effects throughout the brain or (ii) that the receptors themselves may be associated with different functional systems. Receptor density changes are paralleled by increases in methionine-enkephalin content in the striatum, nucleus accumbens, periaqueductal gray, and hypothalamic areas of chronic naltrexone-treated rats relative to control rats. Thus opiate receptors and opioid peptides appear to be subject to regulatory mechanisms similar to those that modulate other neurotransmitters and their receptors. These results document in a visual manner brain patterns of opiate receptor upregulation .

Animals↗