Selective effect of lithium on cognitive performance in man

The effects of lithium on psychomotor performance were examined in six healthy male volunteers (aged 26-31 years) and compared with those of a similar control population. Three computerised psychomotor tests (serial reaction time, semantic reasoning and syntatic reasoning) were administered before lithium, after 5 and 22 days of lithium carbonate (800 mg/d) and 4 days and 1 month after stopping the lithium. The only significant effect was an impairment of semantic reasoning during the chronic (22 day) test. This suggests a selective effect of lithium on associative mental tasks and may explain the subjects' experience of slowing in recall of object names whilst taking lithium.

Platelet binding studies in panic disorder

Binding parameters of the alpha 2-adrenoceptor (using [3H]yohimbine) and the 5-HT uptake site (using [3H]imipramine) were measured in intact platelets in a group of 15 patients with a DSM-III diagnosis of panic disorder. When compared with an age- and sex-matched control population no differences in either Bmax or Kd were found. This result is discussed in light of the reports of platelet binding abnormalities in depression.

Kindling and withdrawal changes at the benzodiazepine receptor

Drugs acting at benzodiazepine receptors can have two types of pharmacological profile: benzodiazepine agonists are anxiolytic, anticonvulsant and sedative, whilst benzo diazepine inverse agonists cause anxiety and convulsions. In 1982 we showed that a benzo diazepine antagonist, Ro 15-1788, prevented the effects of both types of compound at doses without intrinsic activity in the tests used. We put forward the hypothesis that the benzo diazepine receptor complex could undergo two possible conformational changes, resulting in increases (benzodiazepine agonists) or decreases (benzodiazepine inverse agonists) in the effects of the inhibitory transmitter γ-aminobutyric acid (GABA). This concept has been widely accepted. We have now studied the effects of inverse agonists after chronic treatment with inverse agonists themselves and with benzodiazepine agonists, in order to see if tolerance develops (as seen with the agonists) or whether an opposite change occurs.

Effects of chronic treatment with benzodiazepine receptor ligands on cortical adrenoceptors

We report the effects of kindling with the benzodiazepine partial inverse agonist, FG 7142 on adrenoceptor binding in mouse cerebral cortex. Twelve once-daily injections of FG 7142 caused a statistically significant increase in the density of both alpha 2- and beta-adrenoceptor binding sites, seven days after the last injection. Despite the marked effects of FG 7142 on adrenoceptors, there were no changes in either alpha 2- or beta-adrenoceptor binding after prolonged treatment with the benzodiazepine, flurazepam.

Optimizing the pentetrazol infusion test for seizure threshold measurement

Seizure thresholds in mice were determined using the pentetrazol infusion method. Concentration of infusate and rate of infusion were varied to assess the optimal parameters for seizure threshold detection. Seizure threshold elevations were produced by flurazepam and threshold decreases by FG 7142. An infusion rate of 1.1 ml min-1 was best for detecting both increases and decreases in threshold. However a concentration of 2.5 mg ml-1 gave optimal measurement of elevations in threshold whereas decreased thresholds were best detected with a concentration of 10 mg ml-1.

Mice and rats are sensitized to the proconvulsant action of a benzodiazepine-receptor inverse agonist (FG 7142) following a single dose of lorazepam

Rats and mice were treated with lorazepam (1.0 mg/kg) or its vehicle. Six h later seizure threshold to i.v. pentylenetetrazole was determined following treatment with the benzodiazepine-receptor inverse agonist FG 7142, the antagonist Ro 15-1788 or a second dose of lorazepam. Although lorazepam alone was anticonvulsant 6 h after its administration, animals pretreated with lorazepam were more sensitive to the proconvulsant action of FG 7142 and less sensitive to the effects of a second treatment with lorazepam.

The effects of drugs acting at the GABAA-receptor/ionophore after chemical kindling with the benzodiazepine receptor ligand FG 7142

Repeated administration of the beta-carboline benzodiazepine receptor ligand FG 7142 produces sensitization to its effects so that full seizures develop (chemical kindling); initially it is only pro-convulsant. The present study investigated alterations in the function of drugs which act at the different sites at the gamma-aminobutyric acid (GABA) benzodiazepine receptor complex, after repeated administration of FG 7142. In FG 7142 kindled mice decreased anticonvulsant and hypothermic effects of the GABA agonist muscimol were observed. The hypothermic effects of the GABA agonist progabide were reduced. In contrast a small increase in the hypothermic effect of pentobarbitone was seen. The convulsant effects of bicuculline and picrotoxin were unaltered when they were given intravenously but marginally increased when they were given by the intraperitoneal route. No changes were seen in the hypothermic effects of these drugs. No significant changes were seen in the convulsant or hypothermic effects of pentylenetetrazol. These results suggest that kindling with FG 7142 may alter GABA receptor function.

The effect of diazepam on indices of 5-HT function in man

The effects of acute and chronic diazepam administration on L-tryptophan induced prolactin release was studied in seven male volunteers. Acute diazepam diminished the prolactin neuroendocrine response to L-tryptophan. On chronic administration this effect was lost, suggesting tolerance had developed. The sedative effects of L-tryptophan were unaltered by either acute or chronic diazepam administration. A possible explanation for the tolerance development to the neuroendocrine effects may be the observed reduction in platelet 3H-imipramine binding that was observed.

Benzodiazepine-receptor mediated convulsions in infant rats: effects of beta-carbolines

The effects of anticonvulsant and proconvulsant benzodiazepine-receptor ligands were studied in infant rats. The agonist flurazepam increased myoclonic twitching of the limbs as has previously been reported. In contrast, the convulsant beta-carbolines DMCM and beta-CCM did not produce twitching, but did produce marked increases in locomotor activity and whole body shakes. The standard convulsants pentylenetetrazol and bicuculline similarly increased locomotor activity and shaking. These findings suggest that the effects of agonist benzodiazepines cannot be interpreted as convulsant-type behaviour. In addition, the finding that DMCM and beta-CCM have equivalent effects despite showing preferential affinities for benzodiazepine-receptor subtypes argues against one particular subtype having proconvulsant effects.

Increased central alpha 2-adrenoceptor sensitivity in panic disorder

Cardiovascular responses to an intravenous challenge dose of clonidine (1.5 micrograms/kg) were measured in eight patients with DSM III panic disorder. In comparison with an age- and sex-matched control population panic patients showed significantly greater falls in systolic and diastolic blood pressure, with similar falls in heart rate. These observations support the view of a biological abnormality in panic disorder.

The effect of clonidine on plasma MHPG: evidence against tonic alpha 2-adrenoceptor control of noradrenergic function

The effect of the alpha 2-adrenoceptor agonist clonidine on plasma free MHPG levels was assessed in 12 normal volunteers. A significant fall in MHPG was produced by 1.5 microgram X kg-1 clonidine IV whereas saline had no effect. The peak fall in MHPG correlated strongly with the area under the curve (AUC). In addition, a strong correlation was seen between basal MHPG and the extent of the clonidine-induced fall. This suggests that plasma MHPG levels are not simply a reflection of central alpha 2-adrenoceptor function and argues against tonic alpha 2-adrenoceptor-mediated inhibitory control of noradrenergic output.

The effect of lithium on 5-HT-mediated neuroendocrine responses and platelet 5-HT receptors

The effect of lithium on serotonin (5-HT)-mediated responses in the brain was assessed by measuring changes in the prolactin (PRL) and growth hormone (GH) responses to L-tryptophan (LTP) in eight normal subjects. On the 4th day of lithium treatment the PRL responses were significantly enhanced, and this enhancement was still apparent after 20 days' treatment. In contrast, GH responses to LTP were not altered. Lithium had no effect on platelet 5-HT content, platelet imipramine binding and platelet 5-HT receptor binding. The ability of lithium to enhance some aspects of brain 5-HT function may be important in its mode of action in manic-depressive illness and may be particularly relevant to its potentiation of the antidepressant effect of tricyclic antidepressants.

The benzodiazepine antagonist, Ro 15-1788 does not decrease ethanol withdrawal convulsions in rats

The effects of the benzodiazepine antagonist, Ro 15-1788 on ethanol withdrawal convulsions were investigated in rats. The study originated from recent reports of benzodiazepine binding activity in urine of alcoholics during withdrawal. No alleviation of convulsions was found with Ro 15-1788. This suggested that this component of the withdrawal syndrome is not due to endogenous production of a benzodiazepine inverse agonist (contragonist), as Ro 15-1788 prevents the action of this type of compound.

A benzodiazepine agonist and contragonist have hypothermic effects in rodents

The effects on body temperature of the benzodiazepine contragonists FG 7142 (N-methyl-beta-carboline-3-carboxamide) and DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate), the benzodiazepine antagonist Ro 15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-7-oxo-4H-imidazo-(1,5-a)(1,4)benzod iazepin e -3-carboxylate) and the benzodiazepine agonist, flurazepam, were investigated in mice. Both of the contragonists and flurazepam reduced the body temperature. The antagonist Ro 15-1788 did not alter body temperature alone but significantly antagonised the effects of FG 7142 and of flurazepam. The effects of the latter two drugs on locomotor activity in animals in a familiar environment were also investigated. Flurazepam reduced the activity counts in these circumstances but FG 7142 did not cause a significant change, at doses which considerably reduced body temperature. The drug FG 7142 also reduced the body temperature in rats. The effects on body temperature of the benzodiazepine contragonists and flurazepam were unusual in that they were changes in the same direction, both antagonised by Ro 15-1788. However, they differed in that while the effects of flurazepam on locomotor activity might contribute to its hypothermic effect this did not appear to be the case for FG 7142.

Acute and chronic effects of the benzodiazepine receptor ligand FG 7142: proconvulsant properties and kindling

The effects of the acute and chronic administration of the beta-carboline benzodiazepine receptor ligand, FG 7142 were studied in mice. On acute administration FG 7142 (at doses between 10 and 40 mg kg-1) lowered seizure thresholds to infused pentylenetetrazol (PTZ) but showed an unusual dose-response curve in that higher doses had less effect. The duration of action was considerably longer than that of other beta-carbolines, such as ethyl-beta-carboline-3-carboxylate (beta CCE). During repeated administration, doses of FG 7142 which were initially proconvulsant subsequently produced generalized seizures on average in 60% of animals after 12 once daily treatments. This seemed to be a form of chemical kindling. The effects of different drug administration regimes were studied. Once daily dosage was shown to be the optimum for kindling production, and was therefore used for subsequent experiments. Kindling lasted for at least one month after 12 single once daily doses of 40 mg kg-1 (FG 7142). The administration of the benzodiazepine antagonist Ro 15-1788 concurrent with FG 7142 prevented kindling. When Ro 15-1788 was given to kindled animals along with a challenge dose of FG 7142, it prevented the expression of kindled seizures. These data show that kindling is mediated via the benzodiazepine receptor.

The effect of repeated electroconvulsive shock on the function of THIP, a GABA agonist

Repeated electroconvulsive shock did not alter the anticonvulsant effect of THIP in rats, although it did elevate basal rectal temperature and abolish the hypothermic response to THIP.

Investigating benzodiazepine receptor function in vivo using an intravenous infusion of DMCM

A method for measuring seizure thresholds using an intravenous infusion of a convulsant beta-carboline benzodiazepine receptor ligand (DMCM) is reported. Seizure thresholds to DMCM are elevated by the benzodiazepine receptor agonist, flurazepam and antagonist, Ro 15-1788, and the proconvulsant beta-carboline, FG 7142. Various other anticonvulsant also antagonise DMCM seizures. Selectivity for the benzodiazepine/GABA receptor complex is demonstrated since bicuculline and pentylenetetrazol lowered thresholds whereas strychnine and N-methyl DL-aspartate did not.

On the convulsant action of Ro 5-4864 and the existence of a micromolar benzodiazepine binding site in rat brain

The benzodiazepine Ro 5-4864 (60 mg/kg) produced convulsions in mice that could be antagonised either by diazepam (2-4 mg/kg) or by Ro 15-1788 (10-20 mg/kg). In mice and rats subconvulsant doses of Ro 5-4864 were proconvulsant when combined with subconvulsant doses of picrotoxin or pentylenetetrazole. Ro 15-1788 antagonised the tonic convulsions triggered by the drug combinations when it was given at the same time as Ro 5-4864; this antagonism was not observed when the drugs were injected at different times. In contrast to a previous report, we could find no evidence that Ro 5-4864 antagonised seizures induced by electroshock. Using two different ligand-binding techniques, no evidence was seen for the existence in rat brain of the previously reported "micromolar" benzodiazepine receptor, a suggested site of action of Ro 5-4864.

Studies on [3H]diazepam and [3H]ethyl-beta-carboline carboxylate binding to rat brain in vivo. II. Effects of electroconvulsive shock

In vivo specific binding of [3H]diazepam was not altered by a single electroconvulsive shock given 5, 30, or 60 min, or 24 h previously, nor 24 h after the last of 10 daily shocks. Similarly, in vivo [3H]ethyl-beta-carboline carboxylate binding was not changed in the brains of animals that had been given a single electroconvulsive shock 30 min previously or a series of 10 daily shocks. Brain areas examined included cerebral cortex, hippocampus, cerebellum, and striatum. However, cortical binding of [3H]diazepam was increased by 32% in animals which were present in the same room while another was being injected and killed. This may represent a response to stress and/or anxiety.

Studies on [3H]diazepam and [3H]ethyl-beta-carboline carboxylate binding to rat brain in vivo. I. Regional variations in displacement

The binding of [3H]diazepam and [3H]ethyl-beta-carboline carboxylate (beta-CCE) to rat brain membranes has been studied following injection of the ligand via a tail vein. "Ex vivo" binding was avoided by homogenising the tissue in an excess of unlabelled ligand. The dissociation rate constant for [3H]diazepam and [3H]beta-CCE was approximately 0.46 min-1 at 0 degree C. Displacement of [3H]diazepam by beta-CCE in vivo showed regional variation: the dose of beta-CCE required to inhibit 50% of [3H]diazepam binding in the cerebellum was one quarter of that required in the cortex, hippocampus, or striatum. However, when diazepam was used to displace [3H]beta-CCE in vivo the converse occurred: the dose needed for 50% inhibition in the cerebellum was more than four times that required in the other three regions. These findings support suggestions from in vitro experiments that two receptors exist with different affinities for benzodiazepines and beta-carbolines. The benzodiazepine receptor antagonist Ro 15-1788 did not differentiate between the two receptor subtypes.

Hypophysectomy alters both 5-hydroxytryptamine- and alpha 2-adrenoceptor-mediated behavioural changes in the rat

Hypophysectomy, but not sham-hypophysectomy, reduced tranylcypromine/L-tryptophan hyperactivity when compared with unoperated controls although brain 5-hydroxytryptamine concentrations were not different. Hypophysectomy also reduced quipazine locomotor activity but did not alter spontaneous locomotion. Hypophysectomy potentiated clonidine hypoactivity but did not itself produce sedation. Furthermore, noradrenaline concentrations were not altered in either hypothalamus or nucleus accumbens. This suggests that pituitary function is necessary for the normal manifestation of behaviours mediated by postsynaptic 5-hydroxytryptamine receptors and presynaptic alpha 2-adrenoceptors.

Regional GABA concentration and [3H]-diazepam binding in rat brain following repeated electroconvulsive shock

It has been confirmed that 24 hours following a series of electroconvulsive shocks (ECS) given once daily for 10 days (ECS X 10) to rats there is an increase in GABA concentration in the corpus striatum. A similar change was seen after the ECS had been given to rats anaesthetised with halothane, or when 5 ECS were given spread out over 10 days, the rats being anaesthetised during the ECS. A daily convulsion for 10 days elicited by flurothyl exposure resulted in an increased striatal GABA concentration, but also increased the GABA concentration in the hypothalamus, hippocampus and cortex. The increase in striatal GABA concentration was present 24 hours after ECS daily for 5 days or 3 days after ECS daily for 10 days. No change in [3H]-diazepam binding was seen in hippocampus, cortex or corpus striatum 24 hours after the last of 10 once daily ECS. The increase in striatal GABA concentration was therefore seen at all times when enhanced monoamine-mediated behaviours have been demonstrated following seizures.

Comparison of the effects of chronic desmethylimipramine administration on alpha 2- and beta-adrenoceptors in different regions of rat brain

The effects of ten once-daily injections of desmethylimipramine (10 mg/kg i.p.) on alpha 2- and beta-adrenoceptor binding were investigated in the rat cortex, hippocampus and hypothalamus. [3H]clonidine and [3H]dihydroalprenolol were used as ligands for alpha 2- and beta-adrenoceptors, respectively. Twenty-four hours after the last injection, the density of beta-adrenoceptors was reduced in all regions studied. In contrast, there was no change in alpha 2-adrenoceptor binding in the cortex, while increased binding was found in the hypothalamus. The effects of desmethylimipramine are discussed in relation to those of other antidepressant treatments.