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D W Gallager

Publications and source records attributed to D W Gallager.

At least 37 records · Page 2Linked to original sources
PubMed1989

Regional differences in the distribution of muscarinic cholinergic receptors in the macaque cerebral cortex.

The in vitro autoradiographic technique was used to characterize the density and laminar distribution of muscarinic cholinergic receptors in 12 cytoarchitectonic areas in the frontal, parietal, and occipital lobes of the rhesus monkey. The entire population of muscarinic receptors was labeled with [3H]quinuclidinyl-benzilate; the M1 receptor subtype was labeled with [3H]pirenzepine; and the density of the M2 receptor subtype was estimated by subtracting the density of M1 receptors from the total population. The overall density of M1 and M2 receptor subtypes was similar throughout the cerebral cortex. However, their laminar distribution varied regionally. In cortical regions of the parietal and occipital lobes and in the primary motor cortex of the frontal lobe, both M1 and M2 receptor subtypes were concentrated in the supragranular layers. By contrast, in prefrontal cortical areas, the combined population of M1 and M2 receptors was evenly distributed across the cortical layers, though M1 receptors were most dense and M2 receptors least dense in layer IV. The difference in the distribution of cholinergic receptors in the prefrontal cortex compared to other neocortical areas reveals a degree of chemoarchitectural specificity of this region with respect to cholinergic markers that has escaped immunohistochemical and other anatomical and functional techniques.

Animals↗
PubMed1989

Relationship of agonist efficacy to changes in GABA sensitivity and anticonvulsant tolerance following chronic benzodiazepine ligand exposure.

Benzodiazepine ligands of differing efficacy including the agonist, diazepam, the partial agonist, Ro 16-6028 and the antagonist, Ro 15-1788, were administered in vivo to rats continuously for 3 weeks. The magnitude of change in various measures of GABA sensitivity could be correlated directly with increasing agonist efficacy: maximal changes were seen following chronic treatment with diazepam, intermediate changes were seen following the partial agonist Ro 16-6028 and no changes were observed following chronic Ro 15-1788 administration. The magnitude of change could also be correlated with increasing potential for tolerance development to anticonvulsant efficacy following chronic exposure to these benzodiazepine ligands.

Animals↗
PubMed1989

Electrophysiological and biochemical characterization of the development of alpha 1-adrenergic and 5-HT1 receptors associated with dorsal raphe neurons.

Electrophysiological and quantitative autoradiographic receptor binding approaches were used to characterize the postnatal development of alpha 1-adrenergic and serotonergic receptors in the midbrain dorsal raphe nucleus (DRN) in rats. Dose-response data were obtained from extracellular records of the firing of DRN neurons recorded in midbrain slices perfused with artificial cerebral spinal fluid containing varying concentrations of the drugs investigated. These data indicated that DRN neurons, at all postnatal ages, are equally sensitive to the excitatory effects of phenylephrine (an alpha 1-norepinephrine agonist) and the inhibitory effects of serotonin (5-HT). In contrast, LSD (a 5-HT agonist) was considerably more potent in neonates as compared to adults. With one exception, the autoradiographic binding data was found to be in agreement with the electrophysiological findings. There were no observed changes in the number of alpha 1-adrenergic ([3H]prazosin) binding sites at different ages suggesting that cells in this region exhibit functionally mature alpha 1-adrenergic responses at birth. Similarly, the number of [3H]LSD binding sites was found to increase in older animals consistent with the increased potency of LSD in older animals. Paradoxically, the number of [3H]5-HT sites was observed to increase with age, a finding inconsistent with the functional data obtained using 5-HT in the slice. Hypotheses for the observed discrepancy are examined.

Action Potentials↗
PubMed1989

Quantitative autoradiographic mapping of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in the neocortex of the rhesus monkey.

The in vitro autoradiographic technique was used to characterize the distribution of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in 11 cortical areas of frontal, parietal, and occipital lobes in the rhesus monkey; 5-HT1 receptors were labeled with [3H]5-HT; 5-HT2 receptors were labeled with [3H]ketanserin; and 5-HT uptake sites were labeled with [3H]citalopram. Five-HT1 and 5-HT2 receptors and 5-HT uptake sites were found in every cortical area examined with the absolute concentration of 5-HT1 receptors higher than that of 5-HT2 receptors in all areas. In eight regions of prefrontal and parietal as well as in prestriate cortex, 5-HT1 and 5-HT2 receptors had complementary distribution profiles: 5-HT1 receptors were concentrated in layers I and II and the upper strata of layer III, while 5-HT2 receptors had their highest concentration throughout layers III and IV. Only the primary motor and visual cortex had receptor distributions different from that described above. Thus, in the primary visual cortex, both 5-HT1 and 5-HT2 receptors were found in high concentration in sublayer IVc beta, though the density of 5-HT1 receptor was also high in other subdivisions of layer IV and in layers III, V, and VI. In the primary motor cortex, both receptor subtypes were concentrated in layers I and II and the upper strata of layer III. The pattern of distribution of serotonin uptake sites did not match the patterns of distribution of either 5-HT1 or 5-HT2 receptors alone; rather it approximated the combined patterns of distribution of both receptor subtypes. The complementary patterns of distribution of 5-HT1 and 5-HT2 receptors in most areas of the monkey cerebral cortex suggest that these two receptor subtypes may make differential contributions to cortical functions.

Animals↗
PubMed1989

Chronic diazepam treatment produces regionally specific changes in GABA-stimulated chloride influx.

GABA-stimulated 36Cl- influx was used to investigate regional differences in response to chronic diazepam treatment by comparing cortical and cerebellar tissue from rats chronically treated with diazepam for 3 weeks. Using a treatment protocol which has previously been shown to produce behavioral tolerance and physical dependence, cortical membrane preparations from chronic diazepam-treated rats were found to exhibit a decreased responsiveness to the stimulation of 36Cl- influx by GABA and a corresponding decrease in the ability of flunitrazepam to enhance GABA-stimulated 36Cl-influx. This decrease in sensitivity to flunitrazepam, however, appears to reflect the underlying decrease in sensitivity to GABA. In contrast, in membrane vesicles prepared from cerebella of chronic diazepam-treated rats, there was no measurable effect on GABA-stimulated 36Cl--influx or on the enhancement of GABA-stimulated 36Cl- influx by flunitrazepam. These results support the suggestion that there is a regionally specific reduction in GABA/benzodiazepine receptor function following chronic benzodiazepine treatment.

Animals↗
PubMed1989

Distribution of major neurotransmitter receptors in the motor and somatosensory cortex of the rhesus monkey.

The in vitro quantitative autoradiographic technique was used to characterize the distributions of alpha 1, alpha 2, beta 1 and beta 2 adrenergic, D1 and D2 dopaminergic, 5-HT1 and 5-HT2 serotonergic, M1 and M2 cholinergic, GABAA and benzodiazepine receptors in the motor (Brodmann's area 4) and somatosensory (Brodmann's areas 3, 1 and 2) cortex of the adult rhesus monkey. All receptor subtypes studied were present throughout all layers of both areas. In the somatosensory cortex, each receptor had its own laminar distribution. Some subtypes of the same receptor (5-HT1 and 5-HT2; alpha 1 and alpha 2) had complementary distributions while others (beta 1 and beta 2; D1 and D2; M1 and M2) had largely overlapping distributions. In contrast, different receptors had remarkably coincidental distributions in the motor cortex. In this area, they all tended to concentrate in layers I, II and the upper part of layer III. However, such coextensive distribution of many types of neurotransmitter receptors is not observed in motor cortex of rats and humans and therefore may be a distinctive feature of motor cortex in the rhesus monkey. The findings described in this paper indicate that somatosensory and motor areas are distinct in their receptor architecture and that receptor autoradiography provides a useful complement to classical histological techniques in elucidating areal differences in the cortex.

Animals↗
PubMed1989

Responses of substantia nigra pars reticulata neurons to benzodiazepine ligands after acute and prolonged diazepam exposure. I. Modulation of gamma-aminobutyric acid sensitivity.

We have examined the ability of the benzodiazepine inverse agonist, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), and the antagonist, Ro15-1788, to modulate gamma-amino-butyric acid (GABA) sensitivity of reticulata neurons after chronic (3 week) and acute (1 hr) diazepam exposure. Sensitivity to GABA was analyzed by monitoring single unit responses to microiontophoretically applied GABA. The inverse agonist DMCM decreased GABA sensitivity of reticulata neurons to similar levels in control, chronic diazepam and acute diazepam-treated groups. Ro15-1788 administration reversed the effects of DMCM on GABA sensitivity and also resulted in comparable levels of GABA sensitivity in all treatment groups. Thus, the ability of the inverse agonist DMCM and the antagonist Ro15-1788 to alter GABA sensitivity of reticulata neurons was not altered by diazepam treatment. However, reticulata GABA sensitivity in the absence of additional benzodiazepine ligands was enhanced in both acute and chronic diazepam groups when compared to control values. The similarity in reticulata responses after both chronic (3 week) and acute (1 hr) diazepam treatments suggests that the enhanced sensitivity to GABA merely reflects the presence of diazepam. Thus, the ability of diazepam to potentiate reticulata GABA responses does not show time-dependent changes with prolonged benzodiazepine exposure.

Animals↗
PubMed1989

Responses of substantia nigra pars reticulata neurons to benzodiazepine ligands after acute and prolonged diazepam exposure. II. Modulation of firing rate.

We have examined the effects of chronic (3 week) and acute (1 hr) exposure to diazepam on firing rate responses of reticulata neurons to the inverse agonist methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and the benzodiazepine antagonist Ro15-1788. The ability of DMCM and Ro15-1788 to alter firing rate were tested in control, chronic diazepam and acute diazepam-treated rats. In controls, DMCM increased firing rate of reticulata neurons. This effect was reversed by Ro15-1788, which had no effect on firing rate when administered alone. In acute and chronic diazepam-treated groups, low doses of DMCM were less effective in increasing firing than in controls. However, the administration of high doses of DMCM to diazepam-treated animals increased firing rates above the rates observed in control animals after the same compounds. Administration of Ro15-1788 also increased reticulata firing rates above control levels in both acute and chronic diazepam-treated groups. The similarity in reticulata responses after chronic (3 week) and acute (1 hr) diazepam treatments suggests that the altered properties of the benzodiazepine ligands observed after chronic exposure could reflect the presence of diazepam. This may indicate that reticulata neurons themselves do not show changes in sensitivity to benzodiazepine ligands after chronic benzodiazepine exposure. We propose that the altered responses to DMCM and Ro15-1788 in diazepam-treated rats reflect a compensatory change which occurs by 1 hr and maintains reticulata activity at a constant level throughout the period of prolonged exposure to the agonist.

Animals↗
PubMed1988

GABAergic subsensitivity of dorsal raphe neurons in vitro after chronic benzodiazepine treatment in vivo.

Previous studies have shown that chronic benzodiazepine treatment reduces the in vivo sensitivity of dorsal raphe neurons (DRN) to microiontophoretically applied gamma-aminobutyric acid (GABA). We have examined sensitivity of DRN in vitro using a modified midbrain slice technique which allows side-by-side analysis of slices from control and chronic diazepam-treated rats. GABA sensitivity of raphe neurons was reduced in slices from rats treated for 3 weeks with diazepam, compared to control sensitivity. Thus, GABA subsensitivity following chronic diazepam treatment appears to be dependent on changes intrinsic to the midbrain area.

Action Potentials↗
PubMed1988

Differential quenching and limits of resolution in autoradiograms of brain tissue labeled with 3H-, 125I- and 14C-compounds.

Problems in interpretation of autoradiograms generated by ligand binding in brain tissue may be caused by two types of technical limitations: the differential absorption of 3H-generated emissions within the tissue (differential quenching) and the reduced resolution when 125I and 14C are used as isotopes. In the course of our ongoing receptor binding studies in primate brain, we have examined these methodological problems using neocortex of adult rhesus monkey as an example of a complex multilayered brain structure. We have compared: (1) film images produced by brain sections mounted on 3H- and 14C-labeled plastic; (2) autoradiograms of sections labeled with pairs of similar compounds containing 3H, 125I or 14C; and (3) autoradiograms of normal and defatted brain sections. The results indicate that differential absorption of 3H-generated emissions presents a genuine problem for film autoradiography of neocortex of adult monkey when 3H-compounds are used. Particularly significant attenuations of 3H-generated emissions are associated with sublayer IVb of primary visual cortex (Brodmann's are 17) and layers III (deep strata), V and VI of primary motor cortex (Brodmann's area 4). This study provides the necessary corrections for autoradiographic measurements. We also found a loss of resolution associated with use of 125I and 14C, a result that poses a significant problem for analysis of fine laminar patterns of the neocortex in adult monkeys. The use of isotopes with high energy emissions tends to decrease the variations in optical densities within the autoradiograms of cortical sections. Thus, the variations in optical density of autoradiograms of cortices labeled with 125I- and 14C-compounds may not represent the true distribution of these compounds.

Animals↗
PubMed1988

Continuous slow release of low levels of diazepam produces tolerance to its depressant and anxiolytic effects on the startle reflex.

Development of tolerance to the depressant effects of diazepam on the acoustic startle reflex and to the blockade of fear-potentiated startle, a measure of fear or anxiety in rodents, was evaluated after chronic administration via continuous release from implanted diazepam-filled silastic capsules or daily intraperitoneal (i.p.) injections. After continuous exposure to diazepam via capsule implants, complete tolerance occurred to the depressant effects of diazepam on startle and partial tolerance occurred to the antifear effects. In contrast, no tolerance was observed after daily i.p. injection with comparable amounts of diazepam (5 mg/kg) although tolerance could be produced by daily i.p. injections of a much higher dose of diazepam (20 mg/kg). These data suggest that tolerance to at least some behavioral effects may be much easier to produce with continuous rather than intermittent occupation of benzodiazepine receptors.

Animals↗
PubMed1988

Altered gamma-aminobutyric acid/benzodiazepine interaction after chronic diazepam exposure.

Binding to components of the GABA/benzodiazepine receptor complex was examined in cortical membranes from rats treated for 3 weeks with continuously releasing diazepam pellet implants. Chronic diazepam treatment resulted in a decrease in the ability of GABA to inhibit benzodiazepine inverse agonist binding. The amount of binding of benzodiazepine agonist, antagonist, and inverse agonist to benzodiazepine recognition sites was unaltered by the chronic treatment, as were the potencies of these benzodiazepine ligands in inhibiting agonist (3H-flunitrazepam) binding. Chloride channel binding (35S-TBPS) was also unchanged by chronic diazepam treatment. A change in GABA/benzodiazepine coupling and/or a decreased effectiveness of GABA may be responsible for the desensitization of GABA/benzodiazepine interaction.

Animals↗
PubMed1988

Phosphorylation of the GABAa/benzodiazepine receptor alpha subunit by a receptor-associated protein kinase.

Partially purified preparations of GABAa/benzodiazepine receptor from rat brain were found to contain high levels of a protein kinase activity that phosphorylated a small number of proteins in the receptor preparations, including a 50-kilodalton (kD) phosphoprotein that comigrated on two-dimensional electrophoresis with purified, immunolabeled, and photolabeled receptor alpha subunit. Further evidence that the comigrating 50-kD phosphoprotein was, in fact, the receptor alpha subunit was obtained by peptide mapping analysis: the 50-kD phosphoprotein yielded one-dimensional peptide maps identical to those obtained from iodinated, purified alpha subunit. Phosphoamino acid analysis revealed that the receptor alpha subunit is phosphorylated on serine residues by the protein kinase activity present in receptor preparations. Preliminary characterization of the receptor-associated protein kinase activity suggested that it may be a second messenger-independent protein kinase. Protein kinase activity was unaltered by cyclic AMP, cyclic GMP, calcium plus calmodulin, calcium plus phosphatidylserine, and various inhibitors of these protein kinases. Examination of the substrate specificity of the receptor-associated protein kinase indicated that the enzyme preferred basic proteins as substrates. Endogenous phosphorylation experiments indicated that the receptor alpha subunit may also be phosphorylated in crude membranes by a protein kinase activity present in those membranes. As with phosphorylation of the receptor in purified preparations, its phosphorylation in crude membranes also appeared to be unaffected by activators and inhibitors of second messenger-dependent protein kinases. These findings raise the possibility that the phosphorylation of the alpha subunit of the GABAa/benzodiazepine receptor by a receptor-associated protein kinase plays a role in modulating the physiological activity of the receptor in vivo.

Animals↗
PubMed1988

Persistent reversal of tolerance to anticonvulsant effects and GABAergic subsensitivity by a single exposure to benzodiazepine antagonist during chronic benzodiazepine administration.

The persistence of benzodiazepine antagonists in reversing neuronal and behavioral tolerance during chronic diazepam exposure was examined in rodents by investigating the time course for antagonist-induced alterations in iontophoretic sensitivity to gamma-aminobutyric acid on dorsal raphe neurons and the re-emergence of anticonvulsant efficacy to bicuculline-induced seizures. In these studies, exposure to Ro15-1788 resulted in the persistent reversal of GABAergic subsensitivity and restoration of anticonvulsant actions of diazepam despite the continued presence of diazepam in the rats. Reversal of tolerance appears to persist for up to 7 days after a single exposure to benzodiazepine antagonists.

Animals↗
PubMed1987

Effects of chronic diazepam exposure on GABA sensitivity and on benzodiazepine potentiation of GABA-mediated responses of substantia nigra pars reticulata neurons of rats.

This study examined the effects of chronic diazepam treatment on GABA sensitivity of substantia nigra pars reticulata neurons and on the ability of benzodiazepines to enhance GABAergic responses of these neurons in rats. Chronic diazepam exposure failed to significantly alter the sensitivity of reticulata neurons to microiontophoretically applied GABA. However, following chronic diazepam treatment for 1 day, or 1, 3 or 7-11 weeks, reticulata neurons showed tolerance to additional systemically or iontophoretically applied benzodiazepines and displayed an increased firing rate following injection of Ro 15-1788. These changes were not apparent 24 h after cessation of chronic treatment. Thus, tolerance to the effects of benzodiazepines on reticulata neurons appeared to develop after a single day of diazepam exposure and to dissipate by 24 h after cessation of treatment. When compared to our previous studies on dorsal raphe neurons, these results demonstrate regional differences in neuronal responses to chronic diazepam exposure, which may help elucidate neural systems which are involved in tolerance to the various functional aspects of benzodiazepines.

Animals↗
PubMed1987

Time course for development of anticonvulsant tolerance and GABAergic subsensitivity after chronic diazepam.

The time courses for development of neuronal and behavioral tolerance to diazepam (DZ) were estimated in rats continuously exposed to low levels of DZ for 3, 7, 14 or 21 days. Microiontophoretic sensitivity of dorsal raphe neurons to gamma-aminobutyric acid (GABA) was initially facilitated after short-term exposure to DZ released from implanted capsules for up to 3 days but returned to control levels by 7 days postimplantation and continued to decrease thereafter. GABAergic sensitivity remained depressed for a minimum of 5 days following removal of DZ capsules. To obtain a behavioral measure of tolerance, the anticonvulsant activity of DZ against bicuculline-induced seizures was also assessed. Rats studied 3 days after capsule implantation showed a significant elevation in seizure threshold. Seizure liability returned to control levels ca. 7 days after chronic treatment was initiated. These results indicate that tolerance to anticonvulsant efficacy against bicuculline seizures are temporally related to the onset of reduced GABA sensitivity on dorsal raphe neurons during prolonged exposure to DZ.

Animals↗
PubMed1986

Periodic benzodiazepine antagonist administration prevents benzodiazepine withdrawal symptoms in primates.

Daily administration of diazepam (1.5 or 6 mg/kg) in Rhesus monkeys results in the progressive development of physical dependence, as evidenced by Ro15-1788 (5 mg/kg i.m.) precipitated withdrawal symptoms including retching, vomiting, face and limb tremors. Every third day administration of the benzodiazepine antagonist, Ro15-1788, during a similar period of continuous diazepam exposure, significantly decreases withdrawal behaviors. During the course of diazepam exposure (with or without periodic Ro15-1788 administration) effects of chronic diazepam on spontaneously elicited sedative and active behaviors were not altered. It is postulated that physical dependence reverts to a drug naive state after each exposure to the benzodiazepine antagonist. This treatment may represent a possible therapeutic approach for preventing the (time dependent) development of physical dependence and the accompanying severe withdrawal symptoms.

Animals↗