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Psychedelics produce fast and persistent antidepressant effects and induce neuroplasticity resembling the effects of clinically approved antidepressants. We recently reported that pharmacologically diverse antidepressants, including fluoxetine and ketamine, act by binding to TrkB, the receptor for BDNF. Here we show that lysergic acid diethylamide (LSD) and psilocin directly bind to TrkB with affinities 1,000-fold higher than those for other antidepressants, and that psychedelics and antidepressants bind to distinct but partially overlapping sites within the transmembrane domain of TrkB dimers. The effects of psychedelics on neurotrophic signaling, plasticity and antidepressant-like behavior in mice depend on TrkB binding and promotion of endogenous BDNF signaling but are independent of serotonin 2A receptor (5-HT2A) activation, whereas LSD-induced head twitching is dependent on 5-HT2Aand independent of TrkB binding. Our data confirm TrkB as a common primary target for antidepressants and suggest that high-affinity TrkB positive allosteric modulators lacking 5-HT2Aactivity may retain the antidepressant potential of psychedelics without hallucinogenic effects.

Extinction and reinstatement of morphine-induced conditioned place preference were studied in glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-receptor GluA1 subunit-deficient mice (global GluA1-KO mice). In line with previous findings, both acquisition and expression of conditioned place preference to morphine (20 mg/kg, subcutaneously) were fully functional in GluA1 KO mice compared with wild-type littermate controls (GluA1-WT), thus enabling the study of extinction. With a 10-session extinction paradigm, the GluA1 KO mice showed complete extinction similar to that of the GluA1-WT mice. Morphine-induced reinstatement (10 mg/kg, subcutaneously) was detected in both mouse lines. GluA1 KO mice moved more during all the phases of the experiment, including the place conditioning trials, extinction sessions, and place preference tests. The results suggest that the GluA1 subunit may be dispensable or prone to compensation at the neural circuitries delineating extinction and reinstatement. The GluA1 KO mice show altered long-term between-session habituation, which extends longer than previously anticipated.

Adaptation of the nervous system to different chemical and physiologic conditions is important for the homeostasis of brain processes and for learning and remembering appropriate responses to challenges. Although processes such as tolerance and dependence to various drugs of abuse have been known for a long time, it was recently discovered that even a single pharmacologically relevant dose of various drugs of abuse induces neuroplasticity in selected neuronal populations, such as the dopamine neurons of the ventral tegmental area, which persist long after the drug has been excreted. Prolonged (self-) administration of drugs induces gene expression, neurochemical, neurophysiological, and structural changes in many brain cell populations. These region-specific changes correlate with addiction, drug intake, and conditioned drugs effects, such as cue- or stress-induced reinstatement of drug seeking. In rodents, adolescent drug exposure often causes significantly more behavioral changes later in adulthood than a corresponding exposure in adults. Clinically the most impairing and devastating effects on the brain are produced by alcohol during fetal development. In adult recreational drug users or in medicated patients, it has been difficult to find persistent functional or behavioral changes, suggesting that heavy exposure to drugs of abuse is needed for neurotoxicity and for persistent emotional and cognitive alterations. This review describes recent advances in this important area of research, which harbors the aim of translating this knowledge to better treatments for addictions and related neuropsychiatric illnesses.

The γ-aminobutyric acid (GABA) type A receptor system, the main fast-acting inhibitory neurotransmitter system in the brain, is the pharmacological target for many drugs used clinically to treat, for example, anxiety disorders and epilepsy, and to induce and maintain sedation, sleep, and anesthesia. These drugs facilitate the function of pentameric GABAAreceptors that exhibit widespread expression in all brain regions and large structural and pharmacological heterogeneity as a result of composition from a repertoire of 19 subunit variants. One of the main problems in clinical use of GABAAreceptor agonists is the development of tolerance. Most drugs, in long-term use and during withdrawal, have been associated with important modulations of the receptor subunit expression in brain-region-specific manner, participating in the mechanisms of tolerance and dependence. In most cases, the molecular mechanisms of regulation of subunit expression are poorly known, partly as a result of neurobiological adaptation to altered neuronal function. More knowledge has been obtained on the mechanisms of GABAAreceptor trafficking and cell surface expression and the processes that may contribute to tolerance, although their possible pharmacological regulation is not known. Drug development for neuropsychiatric disorders, including epilepsy, alcoholism, schizophrenia, and anxiety, has been ongoing for several years. One key step to extend drug development related to GABAAreceptors is likely to require deeper understanding of the adaptational mechanisms of neurons, receptors themselves with interacting proteins, and finally receptor subunits during drug action and in neuropsychiatric disease processes.

TASK two-pore-domain leak K(+) channels occur throughout the brain. However, TASK-1 and TASK-3 knockout (KO) mice have few neurological impairments and only mildly reduced sensitivities to inhalational anesthetics, contrasting with the anticipated functions and importance of these channels. TASK-1/-3 channel expression can compensate for the absence of GABA(A) receptors in GABA(A) alpha6 KO mice. To investigate the converse, we analyzed the behavior of TASK-1 and -3 KO mice after administering drugs with preferential efficacies at GABA(A) receptor subtypes: benzodiazepines (diazepam and flurazepam, active at alpha1betagamma2, alpha2betagamma2, alpha3betagamma2, and alpha5betagamma2 subtypes), zolpidem (alpha1betagamma2 subtype), propofol (beta2-3-containing receptors), gaboxadol (alpha4betadelta and alpha6betadelta subtypes), pregnanolone, and pentobarbital (many subtypes). TASK-1 KO mice showed increased motor impairment in rotarod and beam-walking tests after diazepam and flurazepam administration but not after zolpidem. They also showed prolonged loss of righting reflex induced by propofol and pentobarbital. Autoradiography indicated no change in GABA(A) receptor ligand binding levels. These altered behavioral responses to GABAergic drugs suggest functional up-regulation of alpha2beta2/3gamma2 and alpha3beta2/3gamma2 receptor subtypes in TASK-1 KO mice. In addition, female, but not male, TASK-1 KO mice were more sensitive to gaboxadol, suggesting an increased influence of alpha4betadelta or alpha6betadelta subtypes. The benzodiazepine sensitivity of TASK-3 KO mice was marginally increased. Our results underline that TASK-1 channels perform such key functions in the brain that compensation is needed for their absence. Furthermore, because inhalation anesthetics act partially through GABA(A) receptors, the up-regulation of GABA(A) receptor function in TASK-1 KO mice might mask TASK-1 channel's significance as a target for inhalation anesthetics.

The TASK-3 channel is an acid-sensitive two-pore-domain K(+) channel, widely expressed in the brain and probably involved in regulating numerous neuronal populations. Here, we characterized the behavioral and pharmacological phenotypes of TASK-3 knockout (KO) mice. Circadian locomotor activity measurements revealed that the nocturnal activity of the TASK-3 KO mice was increased by 38% (P < 0.01) compared with wild-type littermate controls, light phase activity being similar. Although TASK-3 channels are abundant in cerebellar granule cells, the KO mice performed as well as the wild-type mice in walking on a rotating rod or along a 1.2-cm-diameter beam. However, they fell more frequently from a narrower 0.8-cm beam. The KO mice showed impaired working memory in the spontaneous alternation task, with the alternation percentage being 62 +/- 3% for the wild-type mice and 48 +/- 4% (P < 0.05) for the KO mice. Likewise, during training for the Morris water-maze spatial memory task, the KO mice were slower to find the hidden platform, and in the probe trial, the female KO mice visited fewer times the platform quadrant than the male KO and wild-type mice. In pharmacological tests, the TASK-3 KO mice showed reduced sensitivity to the inhalation anesthetic halothane and the cannabinoid receptor agonist WIN55212-2 mesylate [(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate] but unaltered responses to the alpha2 adrenoceptor agonist dexmedetomidine, the i.v. anesthetic propofol, the opioid receptor agonist morphine, and the local anesthetic lidocaine. Overall, our results suggest important contributions of TASK-3 channels in the neuronal circuits regulating circadian rhythms, cognitive functions, and mediating specific pharmacological effects.

Inhalation anesthetics activate and cannabinoid agonists inhibit TWIK-related acid-sensitive K(+) channels (TASK)-1 two-pore domain leak K(+) channels in vitro. Many neuromodulators, such as noradrenaline, might also manifest some of their actions by modifying TASK channel activity. Here, we have characterized the basal behavioral phenotype of TASK-1 knockout mice and tested their sensitivity to the inhalation anesthetics halothane and isoflurane, the alpha(2) adrenoreceptor agonist dexmedetomidine, and the cannabinoid agonist WIN55212-2 mesylate [R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3,-de]-1,4-benzoxazinyl]-(1-naphtalenyl)methanone mesylate)]. TASK-1 knockout mice had a largely normal behavioral phenotype. Male, but not female, knockout mice displayed an enhanced acoustic startle response. The knockout mice showed increased sensitivity to thermal nociception in a hot-plate test but not in a tail-flick test. The analgesic, sedative, and hypothermic effects of WIN55212-2 (2-6 mg/kg s.c.) were reduced in TASK-1 knockout mice. These results implicate TASK-1-containing channels in supraspinal pain pathways, in particular those modulated by endogenous cannabinoids. TASK-1 knockout mice were less sensitive to the anesthetic effects of halothane and isoflurane than wild-type littermates, requiring higher anesthetic concentrations to induce immobility as reflected by loss of the tail-withdrawal reflex. Our results support the idea that the activation of multiple background K(+) channels is crucial for the high potency of inhalation anesthetics. Furthermore, TASK-1 knockout mice were less sensitive to the sedative effects of dexmedetomidine (0.03 mg/kg s.c.), suggesting a role for the TASK-1 channels in the modulation of function of the adrenergic locus coeruleus nuclei and/or other neuronal systems.

Inhaled anesthetics are believed to produce anesthesia by their actions on ion channels. Because inhaled anesthetics robustly enhance GABA A receptor (GABAA-R) responses to GABA, these receptors are considered prime targets of anesthetic action. However, the importance of GABAA-Rs and individual GABAA-R subunits to specific anesthetic-induced behavioral effects in the intact animal is unknown. We hypothesized that inhaled anesthetics produce amnesia, as assessed by loss of fear conditioning, by acting on the forebrain GABAA-Rs that harbor the α1 subunit. To test this, we used global knockout mice that completely lack the α1 subunit and forebrain-specific, conditional knockout mice that lack the α1 subunit only in the hippocampus, cortex, and amygdala. Both knockout mice were 75 to 145% less sensitive to the amnestic effects of the inhaled anesthetic isoflurane. These results indicate that α1-containing GABAA-Rs in the hippocampus, amygdala, and/or cortex influence the amnestic effects of inhaled anesthetics and may be an important molecular target of the drug isoflurane.

BackgroundA rat line developed by selective breeding for high alcohol sensitivity has blunted corticosterone responses to alcohol and stress. In the present study, we determined possible differences in adrenal activation after alcohol and motor performance testing between the alcohol‐sensitive alcohol‐nontolerant and alcohol‐insensitive alcohol‐tolerant rats.

An increase in the activity of brain stem locus coeruleus noradrenergic neurons has been hypothesised to be a major factor accounting for opiate withdrawal symptoms. These neurons are under GABAergic inhibition. Their GABAAreceptors have unique pharmacological properties, most likely due to the enriched expression of GABAAreceptor subtypes containing novel and subunits. Using in situhybridisation of cryostat sections, we now report a significant increase in the subunit mRNA expression after precipitation of opioid withdrawal by naloxone. Similar changes were detected in tyrosine hydroxylase mRNA expression. The results suggest increased formation of unique GABAAreceptor subtype(s) in the locus coeruleus neurons during increased neuronal activity.

Mg2decreased basal and GABA-inhibited t-butylbicyclophosphoro35Sthionate binding to GABAAreceptor ion channels in rat brain sections up to 1 mM, but increased the binding at 10 mM. The Mg2-effect was detectable in the presence of a specific GABA site competitive antagonist. Two-electrode voltage clamp recordings of recombinant α1β2γ2S, α1β2, α2β2γ2S and α2β2 GABAAreceptors revealed a potentiation by 0.1-1 mM Mg2of EC20GABA-evoked ion currents. At 10 mM, Mg2decreased the currents. In the absence of GABA, Mg2did not evoke any currents. The results show that physiologically relevant Mg2concentrations affect the GABA responses on GABAAreceptors in native and the main recombinant receptor subtypes, suggesting putative Mg2binding sites on the receptor complex.

We searched for subunit correlations for GABAAreceptor-associated atypically GABA-insensitive [35S]TBPS binding. The homomeric β3 subunit receptors could be excluded, as GABA-insensitive [35S]TBPS binding was present in β3−/− mice. Localization of GABA-insensitive [35S]TBPS binding correlated best with those of δ, α4 and α6 subunit mRNAs. The amounts of GABA-insensitive [35S]TBPS binding components were increased in δ−/− mice, but dramatically reduced in α6−/− mice, suggesting a role for α6 but excluding δ subunits.

γ-Aminobutyric acid type A (GABAA) receptor ionophore ligand t-[35S]butylbicyclophosphorothionate ([35S]TBPS) was used in an autoradiographic assay on brain cryostat sections to visualize and characterize atypical GABA-insensitive [35S]TBPS binding previously described in certain recombinant GABAAreceptors and the cerebellar granule cell layer. Picrotoxinin-sensitive but 1-mM GABA-insensitive [35S]TBPS binding was present in the rat cerebellar granule cell layer, many thalamic nuclei, subiculum and the internal rim of the cerebral cortex, amounting in these regions up to 6% of the basal binding determined in the absence of exogenous GABA. Similar binding properties were detected also in human and chicken brain sections. Like the GABA-sensitive [35S]TBPS binding, GABA-insensitive binding was profoundly decreased by pentobarbital, pregnanolone, loreclezole and Mg2+. The binding was reversible and apparently dependent on Cl−ions. Localization of the GABA-insensitive [35S]TBPS binding was not identical to that of high-affinity [3H]muscimol binding and diazepam-insensitive [3H]Ro 15-4513 binding, two previously established receptor subtype-dependent binding heterogeneities in the rat brain. The present study reveals a component of the GABA-ionophore enriched in the thalamus and cerebellar granule cells, possibly representing poorly desensitized or desensitizing receptors.

We used positron emission tomography (PET) to study brain [11C]flumazenil (FMZ) binding in four Angelman syndrome (AS) patients. Patients 1 to 3 had a maternal deletion of 15q11‐q13 leading to the loss of β3 subunit of γ‐aminobutyric acidA/benzodiazepine (GABAA/BZ) receptor, whereas Patient 4 had a mutation in the ubiquitin protein ligase (UBE3A) saving the β3subunit gene. [11C]FMZ binding potential in the frontal, parietal, hippocampal, and cerebellar regions was significantly lower in Patients 1 to 3 than in Patient 4. We propose that the 15q11‐q13 deletion leads to a reduced number of GABAA/BZ receptors, which could partly explain the neurological deficits of the AS patients. Ann Neurol 2001;49:110–113

N-methyl-D-aspartate (NMDA) receptor function appears to be under complex control during physiological and pharmacological states. We have investigated the effects of acute administration of uncompetitive NMDA receptor antagonists on mRNA levels of NMDA receptor subunits and on molecules known to cluster or phosphorylate the receptor utilizing in situ hybridization on rat brain sections. A high dose (5 mg/kg; 4 hr) of dizocilpine (MK-801) decreased mRNA levels of NMDA receptor subunits NR2C and NR2B in the entorhinal and parietal cortices, respectively. MK-801 increased mRNA levels of synapse-associated protein-90/postsynaptic density-95 (SAP90/PSD-95) and a γ-isoform of protein kinase C (PKCγ) in cortical regions. Synapse-associated protein-97 (SAP97) mRNA levels were increased in the entorhinal cortex layer III after MK-801 or after relatively high doses of other uncompetitive NMDA receptor antagonists: phencyclidine (15 mg/kg; 6 hr) and memantine (50 mg/kg; 6 hr). Memantine also increased SAP97 mRNA expression in other cortical regions, but this effect was not observed with MK-801 or phencyclidine. NMDA receptor uncompetitive antagonists alter the expression of multiple receptor components and such events may ultimately play a role in adaptation or toxic responses.

Transgenic mice deficient in the α6 subunit of the GABAAreceptor show reduced levels of the δ subunit protein and an altered GABAAreceptor pharmacology, suggesting selective assembly mechanisms. δ reduced the binding of [3H]Ro15–4513 or t-butylbicyclophosphoro[35S]thionate and, to a lesser extent, [3H]muscimol to recombinant α1β1γ2(δ), α4β1γ2(δ) and α6β1γ2(δ) receptors, paralleled by diminished GABA-evoked maximal currents in electrophysiological recordings for the latter one. The δ subunit gave rise to a lower EC50for GABA and a slowed desensitization indicating its assembly in α6β2δ, α6β1γ2δ and α6β2γ2δ receptors. The data show that the δ subunits assemble in various functional GABAAreceptor subtypes in vitroto reduce GABA-evoked maximal currents and ligand binding, but increase the potency for GABA.

• Serotonin (5-HT) and 5-hydroxyindoleacetic acid concentrations were determined in various brain areas of nonschizophrenic suicide victims, chronic schizophrenic patients with or without suicide as the cause of death, and normal control subjects without psychiatric or neurologic disorders. Serotonin concentrations in the basal ganglia were significantly elevated in suicide victims and chronic schizophrenic patients, as were 5-hydroxyindoleacetic acid concentrations in the occipital cortex. These differences were not specific to either patient group and may have been caused by neuroleptic or antidepressant treatment. A decreased 5-HT concentration was found in the hypothalamus of nonschizophrenic suicide victims. Among the chronic schizophrenic patients, there was no significant difference in the hypothalamic 5-HT content between the suicide victims and others, indicating that low 5-HT levels in the hypothalamus are not characteristic of schizophrenic patients who died of suicide.

The loop diuretic furosemide is known to antagonize the function of γ‐aminobutyric acid type A (GABAA) receptors. The purpose of the present study was to examine the direct interaction of furosemide with the GABAAreceptors by autoradiography and ligand binding studies with native rat and human receptors and with recombinant receptors composed of rat subunits.Autoradiography with [35S]‐t‐butylbicyclophosphorothionate ([35S]‐TBPS) as a ligand indicated that furosemide (0.1–1 mm) reversed the 5 μmGABA‐induced inhibition of binding only in the cerebellar granule cell layer of rat brain sections. In all other regions studied, notably also in the hippocampal and thalamic areas, furosemide failed to antagonize GABA. Furosemide 1 mmdecreased [35S]‐TBPS binding only in a limited number of brain regions, but facilitation of the GABA‐inhibition of the binding was much more widespread.In well‐washed rat cerebellar, but not cerebrocortical, membranes, furosemide enhanced the [35S]‐TBPS binding over basal level in the absence of added GABA. The GABAAantagonist, SR 95531, and the convulsant, Ro 5–4864, blocked this furosemide‐induced increase. Both interactions with the furosemide enhancement are likely to be allosteric, since furosemide affected the binding of [3H]‐SR 95531 and [3H]‐Ro 5–4864 identically in the cerebellar and cerebrocortical membranes. Maximal GABA‐antagonism induced by furosemide in cerebellar membranes was further increased by SR 95531 but not by Ro 5–4864, indicating additive antagonism only for SR 95531. In human cerebellar receptors, only GABA antagonism by furosemide, but not the enhancement without added GABA, was observed.In recombinant GABAAreceptors, furosemide antagonism of GABA‐inhibition of [35S]‐TBPS binding depended only on the presence of α6 and β2/3 subunits, irrespective of the presence or absence of γ2 or δ subunits.In α6β3γ2 receptors, clozapine reversed the enhancement of [35S]‐TBPS binding by furosemide in the absence of GABA. However, it failed to affect the GABA‐antagonism of furosemide, suggesting that the enhancement of basal binding and the GABA antagonism might represent two different allosteric actions of furosemide.In conclusion, the present results indicate that furosemide is a subtype‐selective GABAAantagonist with a mode of action not shared by several other antagonists, which makes furosemide a unique compound for development of potential GABAAreceptor subtype‐specific and ‐selective ligands.

A series of benzodiazepine receptor ligands with different chemical structures were evaluated for their affinities at diazepam-sensitive and diazepam-insensitive binding sites for [ 3 H]Ro 15-4513 (ethyl-8-azido-5,60dihydro-5-methyl-6-oxo-4H-imidazo-[1,5a][1,4]benzodiazepine-3-carboxylate) in cerebellar GABA A receptors. Rats of Wistar strain and of alcohol-sensitive (ANT) and alcohol-insensitive (AT) lines were used. The ANT rats possess a single point mutation in their GABA A receptor α6 subunit, which makes their diazepam-insensitive sites sensitive to benzodiazepine agonists, unlike those of AT and Wistar rats. All compounds evaluated displayed high-affinity binding to diazepam-sensitive sites (K i &lt; 50 nM ) . In contrast, a wider range of affinities were observed at diazepam-insensitive sites which depended upon the basic structure and substitutions. The 7- and 8-halogen substituted imidazobenzodiazepines and 12-halogen substituted diimidazoquinazolines displayed the highest affinities (K i &lt; 15 nM ) , while intermediate to low affinities (100 &lt; K i &lt; 4000 nM ) were displayed by imidazoquinazolines, thienopyrimidines, one oxoimidazoquinoxaline, and some cyclopyrrolones. The imidazoquinoxalines evaluated displayed the lowest affinity (K i > 10000 nM ) . The oxoimidazoquinoxaline, 6-chloro-3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-4,5-dihydro-5-isopropyl-4-oxo-imidazol[1,5-a]quinoxaline (NNC 14-0578) and suriclone represent the first benzodiazepine receptor full agonists to bind with relatively high affinity (K i ∼ 100 nM ) to diazepam-insensitive sites. The 5 position substituted methoxybenzyl, dimethylallyl, and 4-fluorobenzyl oxoimidazoquinoxaline analogs demonstrated a 58-336-fold higher affinity for ANT than AT diazepam-insensitive sites. Classical benzodiazepines having a 5-phenyl substituent have demonstrated a similar preference for ANT sites, suggesting that all these structures bind to diazepam-insensitive sites in the same orientation. The other compounds evaluated demonstrated only a more modest selectivity (1-12-fold), indicating different structural requirements for binding to mutant ANT and wild-type AT and Wistar receptors. These results expand the range of ligands which display high affinity for diazepam-insensitive sites. Such compounds shoudl be helpful in determining intrinsic actions of high-affinity ligands at these sites and in assessing the contribution of these sites in enhanced sedative sensitivity of cerebellar function in the ANT rats.

In order to evaluate comprehensively haloperidol pharmacokinetics under fixed-dose treatment conditions, psychiatric patients were studied after treatment with an acute dose, during maintenance therapy, and after withdrawal from haloperidol following steady-state conditions. After single doses, haloperidol appeared rapidly in serum, achieving peak concentration at a mean of 4.5 hours. The range of observed elimination half-life was broad, between 8.5 and 66.6 hours, with a mean of 19.5 hours. Under conditions of chronic dosing, serial measurements of steady-state serum concentration revealed intrapatient coefficients of variation between 2 and 72. The mean for all patients was 26.4. Body clearance decreased nonsignificantly, and elimination half-life increased significantly after chronic dosing compared with kinetic parameters determined after a single dose. The concentration of haloperidol in serum obtained at 8 hours after a single dose correlated most strongly (r= 0.73; p< 0.0001) with steady-state concentration resulting from chronic dosing. A value of 4 ng/ml or lower determined 8 hours after a single oral dose of 0.2 mg/kg identified patients who did not accumulate haloperidol during chronic dosing of 0.4 mg/kg per day above a presumed therapeutic range for haloperidol of 5 to 15 ng/ml. The implications of these data for the clinical use of haloperidol are discussed.

Molecular biological tools have revealed receptor proteins for excitatory and inhibitory neurotransmitters on cell membranes as targets of ethanol action. Behavioral and pharmacogenetic assays using rodent lines have supported this neurotransmitter theory of ethanol action and given a firm basis for future identification of the relevant genes and the central physiological processes vulnerable to ethanol.

Serum or plasma samples from haloperidol-treated patients were analyzed by high performance liquid chromatography (HPLC) with electrochemical detection, radioimmunoassay (RIA), and radioreceptor assay (RRA). The HPLC assay allows simultaneous quantitation of the reduced alcohol metabolite of haloperidol. The HPLC and RIA haloperidol results correlated fairly well (r= 0.63), while the HPLC reduced haloperidol and the RIA haloperidol had a weak correlation (r= 0.28). The RRA haloperidol results had a fair correlation with those of the HPLC (r= 0.55), but their correlation with the HPLC reduced haloperidol was almost as good (r= 0.52). The RIA tended to give lower and the RRA higher apparent haloperidol concentrations than the HPLC assay. The results indicate that the reduced haloperidol does not interfere with the RIA procedure used in this study, but it may partially account for higher concentrations obtained with the RRA.

Literature concerning quantification of plasma concentrations of neuroleptics is reviewed with a particular emphasis on the radioreceptor assay. Based on previously published reports and their own data, the authors conclude that further studies on factors influencing the results of the radioreceptor assay are needed prior to its application in the clinic. Furthermore, the original suggestion of using a single standard reference drug for all neuroleptics may be misleading. Rather, known concentrations of each neuroleptic quantified need to be used as standards.

In a double-blind, placebo-controlled study, 15 drug-free chronic schizophrenic inpatients were treated with a fixed dose of haloperidol for 6 weeks. Haloperidol and its metabolite, reduced haloperidol, were measured in plasma and red blood cells after 2, 4, and 6 weeks of treatment. Behavioral change was rated using the Brief Psychiatric Rating Scale (BPRS). Not only the raw concentrations, but also blood compartment sums and ratios of these four drug measurements were tested for their strength of association with behavioral improvement. Positive associations with some BPRS subscales at some time points emerged; however, no significant correlations were found to extend across all time points measured. There was a trend in this cohort for negative symptom improvement to be associated with the ratio of haloperidol to reduced haloperidol in red blood cells. The ratio of haloperidol to reduced haloperidol in plasma was always greater than that in the red blood cells for all patients, reflecting an accumulation of the metabolite in red blood cells.

Maximal L-glutamate/glycine-evoked currents were inhibited by ethanol in Xenopus laevisoocytes expressing recombinant heteromeric NMDA receptors consisting of NR1-NR2A, NR1-NR2B, and NR1-NR2C subunit combinations. Concentration-dependent inhibition was observed at ethanol concentrations of 50 mM both in Ca2-containing and Ca2-deficient, Ba2-containing Mg2-free media. The NR1-NR2C channels were slightly less sensitive to ethanol inhibition than the other heteromeric channels in Ca2-deficient, Ba2-containing medium. The inhibition was unaffected by the clamping-voltage and by a mutaion [NR1-NR2A(N595Q)] that prevents the Mg2-blockade of the channels, indicating that the mechanism of action of ethanol differs from that of Mg2. The results are consistent with the hypothesis that the NMDA receptor subtypes can mediate many behavioural actions of ethanol.

t-Aminobutyric acid (GABA), the most prevalent inhibitory neurotransmitter in the mammalian brain, exerts its main action through GABAA receptors. They belong to the superfamily of ligand-gated ion channels and respond to GABA by the opening of an intrinsic anion channel. Multiple GABAA receptor subtypes in the brain show differential regional and developmental expression patterns. The receptors have a pentameric structure and are formed from members of at least three different subunit families (a1–6, ß1–3, and t1–3). The regulation of functional properties by GABA and its analogs and by benzodiazepine (BZ) receptor ligands differs dramatically with the type of a variant in the receptor complex. Additional variations of GABAA receptors result from substitution of ? subunits. The role of the ß subunits, which are essential for receptor assembly, is less well defined on a functional basis. Besides their involvement in anxiolysis and sedation, GABAA receptors clearly have an impact on motor coordination. However, with the possible exception of the alcohol-and BZ-sensitive alcohol non-tolerant (ANT) rat line, it is not well documented whether a genetic alteration in this receptor system is directly involved in the impairment of animal or human motor activity.

Clozapine, an atypical neuroleptic, functionally antagonizes the ?-aminobutyric acid-induced chloride uptake via the main central inhibitory receptor, ?-aminobutyric acid type A (GABA A) receptor, in brain vesicles. GABA A antagonism by micromolar concentrations of clozapine is more efficient in rat cerebrocortical and hippocampal membranes than in cerebellar membranes, as evidenced by clozapine reversal GABA-inhibition of [ 35S] t-butylbicyclophosphorothionate ([ 35S]TBPS) binding. A typical neuroleptic, haloperidol, failed to antagonize GABA in any of these brain regions, while the specific GABA A antagonist 2'-(3'-carboxy-2',3'-propyl)-3-amino-6- p-methoxyphenylpyrazinium bromide (SR 95531) was efficient in all three brain regions. Clozapine action on [ 35S]TBPS binding was unaffected by the benzodiazepine receptor antagonist flumazenil. Clozapine inhibited the binding of [ 3H]muscimol and [ 3H]SR 95531 to the GABA recognition site, but this effect only partially correlated with the regional differences in and the potency of clozapine antagonism of GABA-inhibition of [ 35S]TBPS binding, suggesting that also other than GABA sites may mediate clozapine actions. Autoradiography of [ 35S]TBPS binding revealed GABA antagonism by clozapine in most brain regions. Main exceptions were cerebellar granule cell and molecular layers, olfactory bulb external plexiform and glomerular layers and primary olfactory cortex, where clozapine antagonized GABA inhibition less than average, and lateral hypothalamic and preoptic areas where its antagonism was greater than average. Recombinant a6ß2?2 receptors, the predominant a6 subunit-containing receptor subtype in cerebellar granule cells, failed to show GABA antagonism by clozapine up to 100?µM. In contrast, recombinant a1ß2?2 receptors, forming the predominant receptor subtype in the brain, were clozapine sensitive. Recombinant a6ß2?2 and a6ß3?2 receptors resulted in clozapine-insensitive receptors, whereas a6ß1?2 receptors were clozapine sensitive. The efficacy of clozapine to antagonize GABA in a1ßx?2 receptors decreased in the order of a1ß1?2>a1ß2?2>a1ß3?2. The results indicate that clozapine antagonizes the function of most GABA A receptor subtypes, and that the interaction is determined by the interaction of the a and ß subunit variants. GABA antagonism is a unique property of clozapine, not shared by haloperidol, which might be involved in the pharmacological mechanism for the increased seizure susceptibility associated with clozapine treatment.

The histaminergic system is thought to regulate brain reward, but the exact mechanisms are poorly understood. This study aims to reveal the pathophysiological differences in the brain histaminergic system between selectively outbred alcohol‐preferring AA and alcohol‐avoiding ANA rats by using a combination of biochemical, immunohistochemical, and molecular biological methods. We also want to test the functional significance of the system by using operant ethanol self‐administration method. We show that alcohol‐preferring AA rats, when compared with alcohol‐avoiding ANA rats, display higher levels of brain histamine and its first metabolite as measured by HPLC and mass spectrometry, a higher density of histamine‐immunoreactive nerve fibers, and lower H1receptor mRNA expression and H1and H3receptor binding as studied by using in situhybridization and autoradiography. Two H3receptor antagonists, thioperamide and clobenpropit, reduced and an agonist, R‐α‐methylhistamine, increased operant responding for ethanol by the alcohol‐preferring rats, whereas an H1receptor ligand, mepyramine, was inefficient. The results indicate that high alcohol preference is correlated with enhanced histaminergic mechanisms, most likely via H3receptor‐mediated processes. Central histaminergic mechanisms may thus participate also in other addictive behaviors.

Previous studies have reported a therapeutic window (i.e., a curvilinear relationship between clinical response and drug level) for haloperidol concentrations in serum or plasma. The authors treated 30 acutely decompensated schizophrenic inpatients with a fixed dose of haloperidol (.4 mg/kg/day). After 6 weeks there was no statistically significant correlation between clinical improvement and serum haloperidol concentration. Fifteen subjects with serum concentrations of 5–15 ng/ml did not differ in clinical improvement compared with 15 subjects who had concentrations above 15 ng/ml. These data are consistent with a therapeutic plateau, rather than a window, and suggest that in most cases there is no clinical advantage to the use of haloperidol doses greater than approximately 30 mg/day in schizophrenic patients.