Benzodiazepine binding sites: localization and characterization in the limbic system of the rat brain

Diazepam suppresses the stress-induced dopaminergic release in the amygdala of methamphetamine-sensitized rat

Although the benzodiazepine class of drugs has proven useful in treating anxiety symptoms, recent studies yield no consistent empirical support for their use in treating psychiatric disorders. However, animal studies using a fear conditioning paradigm have suggested that benzodiazepines facilitate fear memory extinction, dependent on treatment timing and subject conditions. However, we have no data on the effect of subject conditions. The purpose of this study was to investigate whether the effect of benzodiazepines depends on hypersensitivity to fear-memory processing. We examined the effect of diazepam, a benzodiazepine, on the extracellular dopamine level in the left amygdala of methamphetamine-sensitized, fear-conditioned model rats, using microdialysis and high-performance liquid chromatography. In this model, the dopamine level in the amygdala excessively increases in response to a fear-conditioned stimulus; the phenomenon has been proposed as a biological marker for hypersensitivity to fear-memory processing. Diazepam inhibited this excessive increase. The extent of the inhibitory effect was greater in the sensitized condition. Diazepam alone increased amygdalar dopamine levels under physiological conditions but not under sensitized conditions. Diazepam did not shorten freezing time in any group. These results suggest that diazepam modulates amygdala dopamine with state dependence and that amygdalar dopamine fine-tuning accounts for part of the therapeutic effect of benzodiazepines on fear memory processing. Further investigation is required to identify patients suitable for treatment with benzodiazepines. This is the first report on the pharmacodynamic effects of benzodiazepine on the amygdalar dopamine basal level and on fear memory processing.

A neurophysiological study of the detrimental effects of alprazolam on human action monitoring

In order to adapt their behavior to different unexpected situations, humans need to be able to monitor their performance and detect and correct errors. Benzodiazepines have long been shown to impair performance in humans, but the performance-related neurophysiological processes targeted by these drugs remain largely unknown. In the present article, we assessed the impact of alprazolam administration on relevant aspects of action monitoring, i.e., the monitoring of response conflict and the detection and correction of errors by means of neurophysiological measures. Multichannel event-related brain potentials (ERPs) were recorded to assess the impact of the benzodiazepine alprazolam (0.25 mg and 1.00 mg) on action monitoring and motor preparation in a group of twelve healthy male volunteers who participated in a double-blind cross-over placebo-controlled clinical trial involving a letter flanker task. Error detection was evaluated using the error-related negativity (ERN); response conflict on correct trials was measured by means of the N2 amplitude difference between congruent and incongruent trials; motor preparation was assessed by means of the lateralized readiness potentials (LRPs); and post-error adjustments were assessed by measuring post-error slowing in reaction time. Alprazolam significantly reduced the amplitude of the ERN and the number of corrective responses and increased reaction time and LRP latencies. The drug had no effect on amplitude differences in the N2 component between congruent and incongruent trials or on post-error slowing. Thus, alprazolam was shown to affect brain correlates of error detection (ERN) and motor preparation (LRPs), while it did not disturb conflict monitoring on correct trials (N2) or post-error adjustments of behavior.

Differential effects of midazolam on inhibitory postsynaptic currents in CA1 pyramidal cells and dentate gyrus granule cells of rat hippocampal slices

To examine regional differences of synaptic transmission, the effects of midazolam were observed on inhibitory postsynaptic currents (IPSCs) in CA1 pyramidal cells (CA1-PCs) and dentate gyrus granule cells (DG-GCs) in rat hippocampal slices. Midazolam is one of the most popular benzodiazepines. The monosynaptic IPSCs in the CA1-PCs and DG-GCs were evoked by electrical stimulation of GABAergic interneurons and recorded by whole cell patch-clamp techniques. The effects of specific concentrations of midazolam (0.3, 1, 10 and 75 microM) on the IPSCs in CA1-PCs and DG-GCs were examined at particular membrane potentials (20 mV steps, from -120 to +40 mV). In all midazolam concentrations tested, the conductance of the IPSCs was significantly larger than that in control and was increased by increasing the concentration of midazolam in CA1-PCs (normalized conductance, 0.3 microM, 121%; 1 microM, 125%; 10 microM, 147%; 75 microM, 147%). However, midazolam did not significantly change the conductance of the IPSCs in DG-GCs (normalized conductance, 0.3 microM, 92%; 1 microM, 92%; 10 microM, 91%; 75 microM, 115%). The normalized conductance was significantly different between the CA1-PCs and DG-GCs in 1 and 10 microM midazolam. The results strongly suggest that the differential effects of midazolam on IPSCs in CA1-PCs and DG-GCs could be, at least in part, due to the different sensitivity to midazolam of the GABA(A) receptor subtypes.

Regional distribution of benzodiazepine binding sites in the human newborn and infant hypothalamus. A quantitative autoradiographic study

Using in vitro quantitative autoradiography and [3H]flunitrazepam we examined the rostrocaudal distribution of benzodiazepine binding sites in the human neonate/infant hypothalamus. The autoradiographic analysis shows the presence of a heterogeneous distribution throughout the rostrocaudal extent of this brain structure. High [3H]flunitrazepam binding corresponds primarily to the diagonal band of Broca and the preoptic region. The labelling in the preoptic region showed a rostrocaudal increase, contrasting in that with the other hypothalamic structures. Intermediate densities were present in the septohypothalamic, suprachiasmatic, periventricular and paraventricular nuclei as well as in the mammillary complex. Low binding was observed in the other hypothalamic structures. The benzodiazepine binding sites analyzed belong mostly to type II receptors. In an attempt to unravel possible differences related to age, we compared the autoradiographic distribution in three postnatal age ranges. The topographical distribution of these binding sites was almost identical in each period analyzed. We found, however, that benzodiazepine binding is generally low in the neonatal period and a tendency in increasing densities is observed during development. Taken together, these results provide evidence for a large distribution of benzodiazepine binding sites in neonate/infant hypothalamus, suggesting their implication in the development of this brain structure and the maintenance of its various functions.

New directions in anxiolytic drug research

Agents to treat anxiety have gained in acceptance and importance in the fast pace of life in the second half of this century. The discovery and refinement of the benzodiazepines represented a quantum leap in therapy from early compounds which were essentially sedatives. With the advent of molecular biology, an understanding of the basic mechanism by which the benzodiazepines exert their effects was revealed through the discovery and isolation of the GABAA receptor and its benzodiazepine binding site. This, in turn, has enabled benzodiazepines to be classified into a broad spectrum of pharmacological types ranging from agonist to inverse agonist, thus allowing fine tuning with respect to side-effects. Consequently, newer, more promising agents have emerged which bind at the GABAA BZD site and have reduced side-effects. An example of this is RWJ-51204 (92), a member of a novel structural type which is superior to several marketed benzodiazepines in animals in terms of efficacy and side-effects. The cost-conscious environment of managed health care presents continuing challenges to the discovery and development of safe, highly efficacious, and cost-effective anxiolytic agents.

Differential effects of a benzodiazepine on synaptic transmissions in rat hippocampal neurons in vitro

The effects of midazolam, one of the most popular benzodiazepines, on synaptic transmissions were compared with intracellular recordings between CA1 pyramidal cells (CA1-PCs) and dentate gyrus granule cells (DG-GCs) in rat hippocampal slices. First, we studied the effects of midazolam on orthodromically evoked spikes, membrane properties and synaptic potentials. Secondly, the effects of a GABA(A) receptor agonist, muscimol, were examined on membrane properties to determine whether or not the densities of GABA(A) receptors are different between CA1-PCs and DG-GCs. Midazolam (75 microM) markedly depressed orthodromically evoked spikes in CA1-PCs, compared with those in DG-GCs. A GABA(A) receptor antagonist, bicuculline (10 microM), almost completely antagonized the depressant effects of midazolam on spike generation in CA1-PCs, whereas it had little effect on midazolam in dentate gyrus granule cells. Midazolam produced either depolarizing or hyperpolarizing effects on resting membrane potentials (Vm) with an input resistance decrease in CA1-PCs, whereas it produced depolarized Vm in DG-GCs. Midazolam significantly increased the amplitude of monosynaptic inhibitory postsynaptic potentials in CA1-PCs, whereas midazolam slightly decreased these in DG-GCs. Midazolam significantly decreased the amplitude of excitatory postsynaptic potentials both in CA1-PCs and DG-GCs. Muscimol (100 microM) produced either depolarizing or hyperpolarizing effects on Vm with an input resistance decrease in CA1-PCs, and it depolarized Vm with an input resistance decrease in DG-GCs. These results demonstrate that midazolam has differential effects on excitatory and inhibitory synaptic transmissions in hippocampal neurons. The mechanism of this difference could be partly due to the different types of GABA(A) receptors between CA1-PCs and DG-GCs.

Immunohistochemical localization of the beta 2 and beta 3 subunits of the GABAA receptor in the basolateral amygdala of the rat and monkey

The basolateral amygdala has a strong intrinsic inhibitory system mediated by GABAA receptors and is the main site of the anxiolytic actions of benzodiazepines. In an effort to identify the anatomical substrates for these transmitter and drug actions, immunohistochemical techniques were used to analyse the neuronal localization of the beta 2 and beta 3 receptor subunits of the GABAA-benzodiazepine receptor complex in the rat and monkey basolateral amygdala. The overall pattern of GABAA-benzodiazepine receptor immunoreactivity was very similar in both species. The density of the immunoreactivity in the neuropil varied in different nuclei of the basolateral amygdaloid complex. In both species the neuropil of the lateral nucleus exhibited the most robust staining. Immunoreactivity was also seen in neuronal perikarya and dendrites where it was localized to the cytoplasm and/or surface membrane. The cell type with the strongest immunoreactivity was a subpopulation of small non-pyramidal neurons that had numerous thin dendrites. Other larger non-pyramidal neurons were also stained. Pyramidal neurons in the rat and monkey basolateral amygdala exhibited light to moderate perikaryal staining that varied in different nuclei. The results of this study indicate that the pattern of GABAA-benzodiazepine receptor immunoreactivity in the neuropil of the rat and monkey basolateral amygdala closely resembled the distribution of benzodiazepine receptors localized in previous radioligand autoradiographic studies. The finding of intense immunoreactivity in subpopulations of non-pyramidal neurons suggests the existence of disinhibitory mechanisms which may be important for the activation of basolateral amygdaloid projection neurons.

Changes in benzodiazepine-GABA receptor coupling in an accumbens-habenula circuit after chronic diazepam treatment

1. The effects of subacute and of chronic diazepam treatment upon binding to the GABAA receptor have been examined by use of receptor autoradiography for determining flunitrazepam (FNZP) binding, GABA enhancement of FNZP binding. SR 95531 2-(3'-carboxy-2',propyl)-3-amino-6-p-methoxyphenylpyridazinium bromide) binding and GABA binding in parallel sections from rat brain. Prior to the autoradiographic procedures, a behavioural assessment of the rats was made in the elevated plus-maze test of anxiety. 2. Rats receiving diazepam either subacutely (3 days) or chronically (28 days) by both continuous release, from previously implanted subcutaneous silastic capsules, or by daily injection (5 mg kg-1) did not display changes in FNZP or GABA binding in any of the 47 brain structures analysed. Similarly, there were no significant effects of treatment upon mean total entries or on the open:total ratio for entries in the elevated plus-maze. 3. There were reductions in the GABA enhancement of FNZP binding in the nucleus accumbens and central grey after subacute diazepam treatment. This effect persisted in the nucleus accumbens after chronic treatment. Less marked effects occurred in the lateral habenula, dorsal raphe and substantia nigra pars compacta. In the dorsal tegmental nucleus, GABA enhancement of FNZP binding was enhanced after chronic treatment and this was accompanied by reductions in SR 95531 binding. Treatment did not otherwise affect SR 95531 binding, with the exception of the dorsal raphe where binding was decreased after subacute treatment. 4. In general, the patterns of binding produced by the two different treatment routes were very similar. However, SR 95531 binding was lower in certain hippocampal fields in the i.p. treated animals compared to the rats implanted with silastic capsules. 5. It is concluded that repeated administration of diazepam evokes changes in benzodiazepine and GABA receptor coupling, and to a lesser extent changes in low affinity GABA binding, in certain interrelated brain structures of which an accumbens-habenula circuit is a central feature. These changes occur soon after the initiation of diazepam treatment, suggesting that they are unlikely to account for tolerance to the anxiolytic effects of diazepam but may trigger and/or accompany other critical neurochemical events.

Increased dopamine and norepinephrine release in medial prefrontal cortex induced by acute and chronic stress: effects of diazepam

We have examined the effects of diazepam on the stress-induced increase in extracellular dopamine and norepinephrine in the medial prefrontal cortex using in vivo microdialysis. In naive rats, acute tail pressure (30 min) elicited an increase in the concentrations of dopamine and norepinephrine in extracellular fluid of medial prefrontal cortex (+54 and +50%, respectively). Diazepam (2.5 mg/kg, i.p.) decreased the basal concentration of extracellular dopamine and norepinephrine. Diazepam also attenuated the stress-evoked increase in the absolute concentrations of extracellular dopamine (+17%), but did not alter the stress-induced increase in norepinephrine (+41%). However, when the drug-induced decrease in basal dopamine and norepinephrine concentration was taken into account, the stress-induced net increase in dopamine above the new baseline was equivalent to that obtained in vehicle pretreated rats, whereas the net increase in norepinephrine was almost twice that obtained in control subjects. In rats previously exposed to chronic cold (three to four weeks at 5 degrees C), tail pressure again produced an increase in the concentrations of dopamine and norepinephrine in the medial prefrontal cortex (+42% and +92%, respectively). However, in these chronically stressed rats, diazepam no longer decreased basal dopamine or norepinephrine in extracellular fluid, nor did it affect the stress-induced increase in the concentrations of these catecholamines. These data indicate that diazepam has complex effects on the extracellular concentrations of dopamine and norepinephrine which vary depending upon whether the rat is undisturbed or stressed during the period of drug exposure as well as the rat's prior history of exposure to stress. Moreover, these data raise questions regarding the role of catecholamines in the mechanism by which diazepam exerts its anxiolytic properties.

Quantitative autoradiography of somatostatin receptors in the rat limbic system

The distribution of somatostatin receptors (SRIF-R) was analyzed in the limbic system of the adult rat by in vitro autoradiography with [125I-Tyr0,DTrp 8]S14 as a radioligand. Precise quantification of the density of binding sites, at 0.2 mm intervals throughout the different areas revealed a marked heterogeneity of labeling in most structures. In particular, SRIF-R were concentrated in the basal (104.4 +/- 3.3 fmol/mg proteins) and basolateral amygdaloid nuclei (94.8 +/- 4.3 fmol/mg proteins), and in the nucleus of the lateral olfactory tract (121.6 +/- 2.4 fmol/mg proteins), whereas moderate densities were detected in the amygdalo-hippocampal nucleus (76.4 +/- 2.8 fmol/mg proteins). The medial (41.3 +/- 1.9 fmol/mg proteins) and the central (24.0 +/- 1.4 fmol/mg proteins) amygdaloid nuclei contained lower SRIF-R concentrations. It appears from these observations, in the light of the anatomical pathways of the amygdala, that intra-amygdalian SRIF-containing neurons project to the amygdalo-hippocampal nucleus, and that SRIF-R in the basolateral complex are the target of afferents from limbic cortical areas. SRIF-R were detected at different levels of the hippocampal formation but their distribution was more restricted than that of SRIF-containing fibers. The maximal density of sites was detected in the ventral and dorsal parts of the subiculum (115.0 +/- 3.4 and 87.0 +/- 2.8 fmol/mg proteins, respectively) and in the parasubiculum (100.1 +/- 5.4 fmol/mg proteins). In Ammon's horn, the stratum oriens and stratum radiatum of the CA1 field were the only sites enriched in SRIF-R (74.1 +/- 2.0 and 74.6 +/- 1.9 fmol/mg proteins, respectively). The apparent lack of receptors in the pyramidal cell layer indicated that, in Ammon's horn, SRIF is involved in intra-hippocampal communication. Low levels of receptors were found in the hippocampal CA2 and CA3 fields. SRIF-R in the dentate gyrus were mainly concentrated in the molecular layer (57.3 +/- 1.2 fmol/mg proteins). A very high density of sites was also observed in the entorhinal cortex (up to 123.1 +/- 1.5 fmol/mg proteins). A clear mismatch between SRIF and SRIF-R was detected in the septum and the habenula. In the profound layers of the cingulum and retrosplenial cortex, a heterogeneous distribution of SRIF-R was observed. High concentrations of sites were detected in the rostral zone of the cingulate cortex (93.4 +/- 2.0 fmol/mg proteins) while the posterior cingulate only exhibited moderate concentrations of sites (66.5 +/- 0.7 fmol/mg proteins).(ABSTRACT TRUNCATED AT 400 WORDS)

Localization of GABA-like immunoreactivity in the monkey amygdala

Neurons exhibiting GABA-like immunoreactivity were identified in the monkey amygdala using an avidin-biotin immunohistochemical technique. The pattern of GABA immunoreactivity was very similar in the basolateral and superficial amygdaloid nuclei. In these regions GABA-positive cells were nonpyramidal neurons that were often arranged in clusters or curvilinear rows. These GABA-positive nonpyramidal neurons constituted about 25% of the total neuronal population of the basolateral and superficial amygdaloid nuclei. Numerous GABA-positive puncta resembling axon terminals were observed both in the neuropil and encapsulating the perikarya of GABA-negative pyramidal cells. The pattern of GABA-like immunoreactivity was different in the central and medial amygdaloid nuclei. These regions contained a very dense array of GABA-positive puncta. There were numerous GABA-positive neurons in the lateral subdivision of the central nucleus and fewer cells in the medial nucleus and medial subdivision of the central nucleus. Many immunoreactive puncta were observed contacting the perikarya and dendrites of GABA-positive cells in these regions. The intercalated nuclei consisted of numerous, small, GABA-positive neurons and a few, larger, GABA-negative cells. Both cell types were contacted by GABA-positive puncta. This study indicates that neuronal subpopulations in each of the amygdaloid nuclei of the monkey are GABAergic. The pattern of immunoreactivity varies in different amygdaloid regions and is very similar to that described in the rat. Certain aspects of the functional organization of this rich GABAergic circuitry can be elucidated by correlating the findings of the present investigation with previous anatomical, physiological, and pharmacological studies of the amygdala.

Differential effects of picrotoxin and RO 15-1788 on high and low ethanol concentrations on rat locus coeruleus in vitro

In an in vitro electrophysiological single-cell recording model, ethanol had an inhibitory effect on locus coeruleus (LC) neurons at both low (0.1 mmol/l) and high (500 mmol/l) concentrations. In order to test if the benzodiazepine-GABA (gamma-aminobutyric acid) receptor complex could be implicated in this effect, we tested the interaction of these ethanol concentrations with picrotoxin (100 mmol/l) and RO 15-1788 (10 nmol/l). RO 15-1788 reversed the inhibitory effect induced by ethanol 500 mmol/l, but not by ethanol 0.1 mmol/l; picrotoxin reversed the effects of both concentrations. This indicates that the mechanisms of action of ethanol on LC neurons are not the same for high and low concentrations. Furthermore, the effect of concentrations related to a behavioral effect (greater than 10 mmol/l) was reversed by a low-calcium medium that abolishes transmitter release. Therefore, the inhibition induced by ethanol 500 mmol/l seems to be due to the release of an endogenous benzodiazepine-like compound.

Benzodiazepine-induced decreases in extracellular concentrations of dopamine in the nucleus accumbens after acute and repeated administration

In vivo microdialysis was used to assess the effects of acute and repeated injections of the benzodiazepine midazolam on extracellular dopamine (DA) concentrations in the nucleus accumbens. Acute administration of midazolam (5 mg/kg, SC) elicited a 22% decrease in extracellular DA in the nucleus accumbens but failed to affect DA concentrations in the striatum. Similarly, six spaced intravenous infusions of midazolam, at a dose that has previously been found to support self-administration (0.05 mg per infusion), produced a 50% decrease in extracellular DA in the nucleus accumbens. In order to assess the effects of subchronic midazolam injections, two groups of rats were given injections of saline or midazolam (5 mg/kg, SC) for 14 days (two injections per day). A subsequent challenge injection of midazolam (5 mg/kg) decreased extracellular DA in the nucleus accumbens by 25% in both groups, indicating that neither tolerance nor sensitization occurred during the repeated drug administration. These experiments indicate (1) that midazolam differentially affects meso-accumbens and nigrostriatal DA neurons, and (2) that the midazolam-induced decrease in extracellular DA in the nucleus accumbens is not affected by repeated drug administration. The data further suggest that the rewarding effects of midazolam are not associated with increased release of DA in the nucleus accumbens.

The neuroanatomical basis of anxiety

This review details the neural systems that are important in anxiety-related behaviours. In particular, the role of the amygdaloid complex, Papez circuit, septohippocampal formation and raphe nuclei are described and discussed. Evidence is gathered from a variety of experimental approaches. These include behavioural assessment of anxiety in animals after intracerebral injection of pharmacological agents and following lesions of discrete brain nuclei and selective neurotransmitter pathways. Further evidence is provided by functional brain mapping studies applied to animals and humans. It is proposed that the neural systems recruited in different experimental conditions of anxiety may differ, supporting the notion that clinical anxiety exists in several forms. This has implications for the identification of new anxiolytic treatments. In particular, the findings suggest that approaches aimed at identifying new anxiolytic agents must take into account both the distribution of receptors for the drug and the neuronal systems activated by the experimental protocol.

Perinatal diazepam exposure: alterations in exploratory behavior and mesolimbic dopamine turnover

Perinatal exposure to diazepam has been shown to lead to alterations in motor activity and exploratory behavior in neonatal animals. Exploratory and locomotor behavior have been associated with changes in mesotelencephalic dopamine function. We have therefore examined the effects of perinatal diazepam administration on both exploratory behavior and mesotelencephalic dopamine turnover in the adult rat. Animals exposed to the benzodiazepine during the perinatal period engaged in significantly less exploratory behavior than did control subjects. The diazepam-induced alterations in behavior were developmentally specific: decreased exploratory behavior was observed at 90, but not 60, days of age. At 90 days of age, specific changes in dopamine turnover in diazepam-treated animals were restricted to mesolimbic (nucleus accumbens and ventral tegmental area) sites; alterations in dopamine turnover were not seen in other mesotelencephalic sites examined. The findings indicate that perinatal exposure to benzodiazepines leads to behavioral changes that are present in adulthood. These changes in exploratory behavior may be associated with alterations in mesolimbic dopamine function.

Local administration of flurazepam has different effects on dopamine release in striatum and nucleus accumbens: a microdialysis study

The action of local administration of flurazepam on extracellular levels of dopamine (DA) and its metabolites 3,4 dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) in the anterior striatum and medial nucleus accumbens have been investigated using microdialysis. Flurazepam (10 microM), administered through the perfusion medium for 20 min, reduced levels of DA in dialysates from the nucleus accumbens by 60% while the same concentration of the drug had no effect on levels of DA in perfusates from the striatum. Pretreatment with the benzodiazepine antagonist Ro 15-1788 (flumazenil) or with picrotoxin, a drug which blocks the GABAA receptor-associated chloride channel, inhibited the effect of flurazepam on levels of DA in the nucleus accumbens, which suggests that the effect was mediated by the multimolecular GABAA/benzodiazepine receptor complex. Administration of flurazepam had little effect on the two metabolites of DA, DOPAC and HVA, in either the nucleus accumbens or striatum. The inverse partial benzodiazepine agonist, FG 7142, had no significant action on the release of DA in the nucleus accumbens. These results suggest that the dopaminergic projection to the nucleus accumbens is more sensitive to benzodiazepine-induced inhibition than the projection to the striatum.

Local cerebral glucose utilization following subacute and chronic diazepam pretreatment: differential tolerance

Local cerebral glucose utilization (LCGU) was determined in parallel groups of conscious rats receiving diazepam (0.3 mg/kg i.v.) either acutely or following subacute (5 mg/kg i.p. daily for 3 days) or chronic (5 mg/kg i.p. daily for 28 days) diazepam pretreatment, using 2-deoxyglucose quantitative autoradiography. Acute administration of diazepam reduced LCGU in 44 of the 66 structures examined compared to vehicle-treated controls. These included limbic, cortical and extrapyramidal structures, and areas associated with sensory processing. These data are consistent with many brain regions being functionally involved in the diverse acute pharmacological effects of diazepam and with the widespread distribution of benzodiazepine receptors throughout the neuroaxis. Following subacute treatment, when animals were tolerant to the sedative effects of diazepam, glucose use remained depressed in the majority of areas studied. However, in the locus coeruleus, dorsal tegmental nucleus and most structures associated with auditory processing, tolerance to the depressant effect of diazepam upon glucose use had occurred suggesting the importance of these structures in the sedative effect of diazepam. The most striking feature of the patterns of LCGU after chronic diazepam treatment was that tolerance had occurred in the mammillary body and subiculum. However, glucose use remained depressed in hippocampal layers and in structures that provide input to the hippocampus (e.g. raphe nuclei). These data suggest that the outflow of neuronal activity from the hippocampus to the mammillary body via the subiculum is restored after chronic treatment, and may implicate these pathways in the anxiolytic action of diazepam. Overall, it would appear that different neuroanatomical substrates underlie the various pharmacological effects of diazepam and that there may be regional differences in tolerance mechanisms.

Direct transfer into nitrocellulose and quantitative radioautographic anatomical determination of brain tyrosine hydroxylase protein concentration

An improved quantitative immunochemical determination of brain tyrosine hydroxylase (TH) concentrations was designed using direct transfer into nitrocellulose from 20-microns thick brain sections, followed by immunodetection and quantitative radioautography in three reference brain structures (locus ceruleus, substantia nigra, and ventral tegmental area). Results obtained by this methodology were similar to those obtained after extraction and Western blotting of the TH protein in control and reserpine-treated animals. Moreover, this methodology allows the combination of high sensitivity and high anatomical resolution in the study of the distribution of pharmacological effects. The locus ceruleus exhibited a significant posteroanterior distribution of TH protein concentration in control and reserpine-treated animals.

The effects of FG 7142 upon local cerebral glucose utilization suggest overlap between limbic structures important in anxiety and convulsions

The effects of the beta-carboline benzodiazepine receptor ligand FG 7142 upon local cerebral glucose utilization have been examined in conscious rats using the quantitative [14C]2-deoxyglucose autoradiographic technique. FG 7142 (1-10 mg/kg i.v.) produced behavioural changes consistent with an anxiogenic action. At the largest dose of FG 7142 (10 mg/kg) 30% of the animals experienced overt convulsions. In the data analysis animals were divided according to the behavioural response elicited by the drug. In animals not expressing convulsions, FG 7142 (1-10 mg/kg) effected increases in glucose utilization in 33 of the 65 regions examined. The majority of changes were confined to limbic structures with pronounced effects occurring in the mammillary body, anterior thalamic nuclei, septal nuclei and the oriens and molecular layers of the hippocampus. Glucose use in other structures associated with auditory and visual processing, such as the medial and lateral geniculate body, and associated cortical areas, was also significantly increased. However, brain regions involved in motor control were minimally affected. The patterns of local cerebral glucose use in animals expressing FG 7142-induced convulsions were contrasted with those from an equivalent non-seizure group. Some limbic structures which were significantly affected by FG 7142 (non-seizure group) displayed a further increase in glucose utilization during convulsions. These included the mammillary body and septum. Many other limbic structures (anterior thalamic nuclei, CA fields of the hippocampus and basolateral amygdala) did not display this further rise in glucose utilization. In the cortical amygdala, lateral preoptic area of the hypothalamus, nucleus accumbens and lateral elevations in glucose utilization were restricted to those animals experiencing overt convulsions.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepine receptors in the human hippocampal formation: a pharmacological and quantitative autoradiographic study

The pharmacological characteristics and anatomical distribution of benzodiazepine receptors in the human hippocampal formation were studied in seven cases aged 4-68 years. The pharmacology of the receptors was studied by computerized, non-linear least squares regression analysis of [3H]flunitrazepam displacement by flunitrazepam, CL218,872 and ethyl beta-carboline-3-carboxylate binding to membranes and the anatomical localization of these receptors was demonstrated using quantitative autoradiography following in vitro labelling of cryostat sections with [3H]flunitrazepam. The pharmacological studies indicated that the human hippocampal formation contained equal numbers of benzodiazepine receptors with high affinity (Type I) and low affinity (Type II) for CL218,872 and ethyl beta-carboline-3-carboxylate. The autoradiograms demonstrated that the benzodiazepine receptors were distributed in a heterogeneous fashion throughout the major regions of the human hippocampal formation; the highest concentrations of receptors were present in the dentate gyrus (molecular layer) and field CA1 of Ammon's horn (strata pyramidale, oriens, lacunosum), with moderate concentrations in field CA2 of Ammon's horn (stratum pyramidale) and in regions of the subicular complex and entorhinal cortex, and with considerably lower densities in fields CA3 and CA4. Quantitative analyses of the autoradiograms showed that the regions containing the highest densities of receptors (molecular layer of dentate gyrus and the strata oriens, pyramidale and lacunosum of CA1) were enriched with Type 1 receptors whereas other regions of lower receptor densities were enriched with either Type I or Type II receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepine receptor sites in the human brain: autoradiographic mapping

Receptor autoradiography was used to localize and quantify the distribution of benzodiazepine receptor sites in human post mortem materials using [3H]flunitrazepam. The distribution and density of these sites was analysed in the brains of 21 patients dying without reported neurological disease. The distribution of benzodiazepine receptors in the human brain was found to be comparable from case to case although differences in the density occurred among the brains examined. No influence of the post mortem delay, age, gender or pre mortem drug treatment on the distribution and densities was observed in our series. The highest densities of benzodiazepine receptors in human brain were localized in cortical and hippocampal areas, nucleus accumbens, amygdala and mammillary bodies. Intermediate densities were found in the basal ganglia and thalamic and hypothalamic nuclei. [3H]Flunitrazepam binding was low in the brainstem nuclei and very low in white matter. The triazolopyridazine Cl 218872, reported to differentiate between type I and type II benzodiazepine receptor sites, exhibited regional differences in affinity when used to block [3H]flunitrazepam binding. Benzodiazepine receptors in the cerebellar cortex were more sensitive to this compound than those in the dentate gyrus of the hippocampus and the tuberal nuclei of the hypothalamus. An enrichment in the concentration of type I benzodiazepine receptor Cl 218872-sensitive sites was observed in motor areas as compared to structures of the limbic system. The addition of GABA to the incubation medium resulted in an increase of [3H]flunitrazepam binding, suggesting the coupling of these sites to a GABAA receptor. The increase in binding was directly proportional to the density of benzodiazepine receptors but unrelated to the density of high-affinity GABAA sites. The distribution of benzodiazepine receptor sites in the human brain compares well with that previously described in the rat brain. The high densities of receptors localized in the limbic system and in the cortical areas suggest that the effects of benzodiazepines are mediated through an interaction with the sites we have visualized in these anatomical structures. Our results provide a detailed map of the distribution of benzodiazepine receptors and a basis for the understanding of pharmacological effects of these drugs in humans and for future studies of modifications of these receptors in neurological and neuropsychiatric conditions in humans.

Benzodiazepine binding sites in the cingulate cortex after lesion of the noradrenaline and dopamine containing afferents

The distribution of benzodiazepine binding sites was analysed in the cingulate cortex of the rat brain by quantitative radioautography of brain sections incubated with a full agonist benzodiazepine ligand, 3H-flunitrazepam (3H-FLU), or with a partial agonist with non benzodiazepine structure, (7-3H)-4hydroxy-N(4,5-dihydroxy-2-thiazolyl)-6 methoxy-3-quinoline (3H-RU 43028), after lesion of noradrenaline (NA) and dopamine (DA) containing afferents to this structure. NA denervation was obtained by systemic administration of N-(2-chlorethyl)-N ethyl-2-bromobenzylamine (DSP4) and destruction of both NA and DA containing afferents was induced by unilateral injection of 6-hydroxydopamine (6-OHDA) in the middle forebrain bundle (MFB). A similar caudo-rostral pattern of distribution was found in the cingulate cortex after incubation with these two ligands which bound a greater number of sites in the anterior portion of the structure. In spite of a very precise anatomical sampling (200 micron intervals along the postero-anterior axis) no significant difference was observed when intact and lesioned brains were compared. It is concluded that benzodiazepine binding sites eventually localized on catecholaminergic afferents to the cingulate cortex do not represent a significant proportion of the total population of these sites in this structure.

Are the effects of benzodiazepines on discrimination and punishment dissociable?

Studies have shown that benzodiazepines (BZs) both disrupt discrimination and increase resistance to punishment. Using a delayed response task, we provide evidence that effects of BZs on discrimination cannot be fully explained by deficits in either short or long term memory, or by intolerance for delay of reward. A schedule with rewarded, nonrewarded (Time out: TO) and conflict components was used to investigate effects in rats of compounds active at the BZ receptor on successive discrimination and punished responding in parallel. The GABA transaminase inhibitor ethanolamine-O-sulphate exerted additive effects with chlordiazepoxide (CDP) on punished but not TO responding. Both GABA and CDP injected into the amygdala selectively increased conflict rates, but with peripheral treatment CDP also increased TO rates. Two inverse BZ agonists, CGS 8216 and FG 7142 antagonzied the anti-conflict effects of GABA and CDP, given within the amygdala or peripherally, but the increase in TO rates induced by systemic CDP was counteracted only by peripheral treatments. These compounds also reduced rates of conflict responding below baseline, consistent with anxiogenic activity. Effects of the BZ antagonist Ro 15-1788 were broadly similar to those of the inverse agonists, except that it did not antagonise the anti-conflict action of intra-amygdaloid GABA, nor significantly reduce punished responding at the single dose used. We conclude from these results that the anti-conflict effects of BZs are mediated by a GABAergic amygdaloid mechanism, but that the same mechanism is not involved in BZ effects on discrimination.