Inverse agonist properties of the THBC discriminative stimulus: asymmetrical generalization with FG 7142.

Male rats were trained to discriminate the stimulus properties of the beta-carbolines 1,2,3,4-tetrahydro-beta-carboline (THBC) (15.0 mg/kg) or FG 7142 (5.0 mg/kg) from vehicle in a two-lever, food-motivated operant task. Consistent with the serotonergic properties of THBC, administration of the 5HT1B agonists TFMPP and mCPP to THBC-trained rats resulted in THBC-appropriate responding. Norharmane, a beta-carboline metabolite of THBC, also mimicked the THBC discriminative stimulus. In contrast, the benzodiazepine receptor partial inverse agonist FG 7142, the anxiogenic/convulsant pentylenetetrazole (PTZ), two physiological stressors and the alpha 2 adrenergic antagonists yohimbine and idazoxan failed to produce THBC-appropriate responding. In the FG 7142-trained rats, THBC and norharmane dose-dependently mimicked the FG 7142 discriminative stimulus. This generalization was not based upon the serotonergic properties of THBC and norharmane since administration of the serotonin agonist mCPP to FG 7142-trained rats failed to produce FG 7142-appropriate responding. The ability of THBC to substitute for the FG 7142 discriminative stimulus was antagonized by the benzodiazepine receptor mixed agonist/antagonist CGS 9896 and the benzodiazepine receptor antagonist RO 15-1788, indicating that THBC produces an inverse agonist stimulus in FG 7142-trained rats. These results suggest that THBC produces a discriminative stimulus which consists of both serotonergic and inverse agonist components.     

Evidence for noradrenergic involvement in mediating the FG 7142 discriminative stimulus.

Rats were trained to discriminate the stimulus properties of the benzodiazepine receptor partial inverse agonist beta-carboline-3-carboxylate acid methyl amide (FG 7142) (5.0 mg/kg) or the alpha 2-adrenergic receptor antagonist 17 alpha-hydroxyyohimban-16 alpha-carboxylic acid methyl ester (yohimbine) (3.0 mg/kg) from vehicle in a two-lever, food-motivated operant task. These compounds have in common a beta-carboline structure and anxiogenic behavioral profiles. The yohimbine discriminative stimulus was mimicked by the alpha 2-adrenergic receptor antagonist idazoxan and antagonized by the alpha 2-adrenergic receptor agonist clonidine, indicating that the yohimbine stimulus was mediated through the alpha 2-adrenergic receptor. The anxiogenic beta-carbolines FG 7142, 1,2,3,4-tetrahydro-beta-carboline (THBC), and norharmane, the anxiogenic/convulsant agent pentylenetetrazole (PTZ), and two physiological stressors failed to mimic the yohimbine discriminative stimulus. In contrast, both yohimbine and idazoxan dose responsively mimicked the anxiogenic FG 7142 stimulus. The present results demonstrate that an asymmetrical generalization exists between the discriminative stimuli produced by yohimbine and FG 7142. Furthermore, these data suggest that yohimbine can produce a multicomponent discriminative stimulus, part of which may be anxiogenic in nature. The ability of alpha 2-adrenergic receptor antagonists to mimic the FG 7142 cue suggests that activation of the noradrenergic system may underlie cues produced by benzodiazepine receptor inverse agonists.     

Discriminative stimulus properties of β-carbolines characterized as agonists and inverse agonists at central benzodiazepine receptors

The discriminative stimulus properties of three -carboline derivatives were studied in three groups of rats trained, respectively, to discriminate diazepam (2.5 mg/kg IP), chlordiazepoxide (CDP, 5 mg/kg IP) or pentylenetetrazol (PTZ, 15 mg/kg IP) from saline in standard procedures employing two-lever operant chambers. Two -carbolines, ZK 91296 and ZK 93423, substituted for the benzodiazepines in both CDP- and diazepam-trained rats. The neutral benzodiazepine antagonist Ro 15-1788 blocked the diazepam discriminative stimulus and the ability of ZK 91296 to substitute for diazepam. A third -carboline, FG 7142, was not identified as benzodiazepine-like in generalization tests in either diazepam- or CDP-trained rats, but when administered together with CDP antagonized the benzodiazepine discriminative stimulus. In rats trained to discriminate PTZ from saline (a discrimination which is thought to depend on the anxiogenic properties of PTZ) the PTZ cue was antagonized by diazepam and ZK 93423, and partially antagonized by ZK 91296. The PTZ cue generalized to FG 7142 and this generalization was partially antagonized by Ro 15-1788. These results suggest that the three -carbolines provide more than one kind of discriminative stimulus, consistent with the classification of ZK 93423 as an agonist at central benzodiazepine receptors, with ZK 91 296 as a partial agonist, and with FG 7142 as an inverse agonist. Pharmacologically, ZK 93 423 and ZK 91 296 may exhibit anxiolytic qualities, whereas FG 7142 produces anxiogenic effects.     

Benzodiazepine receptor ligands have no specific action on working memory in a delayed conditional discrimination task in rats

We investigated effects of benzodiazepine (BDZ) receptor ligands on working memory in a delayed conditional discrimination (DCD) task. The BDZ receptor full agonist midazolam (0.1-1.0mg/kg) dose-dependently impaired performance independent of delay, indicating no specific effect on working memory. The non-sedative BDZ receptor partial agonist bretazenil (0.06-0.6mg/kg), the inverse agonist beta-CCM (0.05-0.45mg/kg), the partial inverse agonist FG 7142 (0.5-5.0mg/kg), the antagonist flumazenil (1-10mg/kg), and the antagonist ZK 93 426 (1-10mg/kg) did not significantly affect performance. It is concluded that BDZ ligands do not affect working memory in a positively-motivated DCD task. Midazolam also impaired performance in the no-delay condition, suggesting loss of stimulus control, possibly through an attentional impairment.     

FG 7142 specifically reduces meal size and the rate and regularity of sustained feeding in female rats: evidence that benzodiazepine inverse agonists reduce food palatability.

Benzodiazepine receptor inverse agonists reduce food intake in males, but their actions in females, in whom stress-related eating disorders are more common, as well as their behavioral mode of action remain unclear. The consummatory effects of benzodiazepine receptor ligands have alternately been hypothesized to reflect changes in the hedonic evaluation of food or secondary effects of anxiety-related or cognitive properties. To test the anorectic mode of action of benzodiazepine inverse agonists, the effects of FG 7142 on feeding microstructure were studied in nondeprived female Wistar rats (n=32). Microstructure analysis used a novel meal definition that recognizes prandial drinking. On pharmacologically synchronized diestrus I, rats were pretreated (-30 min dark onset) with the benzodiazepine partial inverse agonist FG 7142 (i.p. 0, 3.75, 7.5, 15 mg/kg) in a between-subjects design. FG 7142 delayed the onset of (16-541%), decreased the amount eaten (36-52%) and drunk (63-87%), and reduced the time spent drinking (59-87%) within the first nocturnal meal. Dose-dependent incremental anorexia continued 6 h into the dark cycle, whereas FG 7142 did not suppress the quantity, duration or rate of drinking past the first meal. Treated rats ate smaller meals (17-42%) of normal duration. This reflected that FG 7142 slowed feeding within meals (9-38%) by decreasing the regularity and maintenance of feeding from pellet-to-pellet. FG 7142 did not influence postprandial satiety; meal frequency and inter-meal intervals were unaffected. FG 7142 anorexia was blocked by the benzodiazepine receptor antagonist flumazenil in a 2:1 molar ratio (n=17 rats). The very early, nonspecific (+10 min), but not subsequent (2.5, 4.5 h) feeding-specific phase, of FG 7142 anorexia was mirrored by anxiogenic-like behavior in FG 7142-treated (7.5 mg/kg) female rats (n=48) in the elevated plus-maze. Thus, benzodiazepine receptor inverse agonists preferentially lessen the maintenance of feeding in female rats, effects opposite to those of palatable food.     

Benzodiazepine receptor ligands and the consumption of a highly palatable diet in non-deprived male rats

Non-deprived rats were familiarised with a highly palatable diet until baseline consumption in a 60-min daily access period had stabilised. The benzodiazepine receptor agonist midazolam (1.25–10.0 mg/kg, IP) produced a large, dose-related increase in food consumption during the first 30 min of access. It also produced significant, short-term hyperphagia in animals which had been partially pre-satiated on the diet before drug administration, an effect which was reversible by the benzodiazepine receptor antagonist Ro15-1788. Administered alone, Ro15-1788 (1.25–10.0 mg/kg, IP) had no intrinsic activity in the food consumption test. In contrast, CGS 8216 (2.5–40.0 mg/kg, IP) produced a marked dose-related suppression of food intake. This anorectic effect was shared by two benzodiazepine receptor inverse agonists, FG 7142 and DMCM, which also produced dose-dependent reductions in consumption. The effects on feeding produced by FG 7142 (20 mg/kg, IP) and DMCM (1.25 mg/kg, IP) were reversed by either Ro15-1788 (2.5 and 5.0 mg/kg) or midazolam (5.0 and 10.0 mg/kg). A matched anorectic effect produced by CGS 8216 (40 mg/kg) was not, however, reversed by either Ro15-1788 or midazolam. This suggests that at a high dose CGS 8216 may act by a mechanism different from that of the two inverse agonists. The feeding test described in the report proved sensitive to both hyperphagic and anorectic effects of drugs active at benzodiazepine receptors, pointing to a possible bi-directional control of palatable food consumption.     

Effects of benzodiazepine receptor ligands on the performance of an operant delayed matching to position task in rats: opposite effects of FG 7142 and lorazepam

The effects of a series of benzodiazepine (BZ) receptor ligands, ranging from a full agonist through to partial inverse agonists, were examined on short term working memory in the rat. The behavioural paradigm used was a discrete trial, operant delayed matching to position task, as originally described by Dunnett (1985), with delays of 0, 5, 15 and 30 s. The benzodiazepine receptor (BZR) full agonist lorazepam (0.25, 0.375 and 0.5 mg/kg) dose and delay dependently impaired matching accuracy. Lorazepam also increased the latency to respond and decreased the number of nose pokes made into the food tray during the delays. In contrast, the BZR partial agonist ZK 95 962 (1, 3, 10 mg/kg) did not affect matching accuracy, but did increase the speed of responding. The BZR antagonist ZK 93 426 (1.25, 5, 25 mg/kg) had no effects in this paradigm. The BZR weak partial inverse agonists Ro 15-4513 (0.1, 1 and 10 mg/kg) and ZK 90 886 (1, 3 and 10 mg/kg) did not affect accuracy of performance. However, both of these drugs increased the latency to respond and decreased nose poke responses. These motoric effects were particularly strong following 10 mg/kg Ro 15-4513. This shows that the effects of drugs on the accuracy of responding and on the speed of responding can be dissociated. The BZR partial inverse agonist FG 7142 had effects on matching accuracy that were dependent upon dose. The lowest dose of FG 7142 (1 mg/kg) significantly improved accuracy, whereas the highest dose (10 mg/kg) impaired accuracy. This impairment induced by FG 7142 (10 mg/kg) was accompanied by an increase in the latency to respond and a decrease in the number of nose pokes. Taken together, these results show that the accuracy of delayed matching performance can be modulated in opposite ways by the BZR full agonist lorazepam and a low dose of the BZR partial inverse agonist, FG 7142.     

A benzodiazepine receptor inverse agonist inhibits stress-induced ulcer formation

The effects of a benzodiazepine receptor inverse agonist (FG 7142) on gastric ulcer formation were studied in restrained rats. FG 7142 (10-50 mg/kg) reduced in a dose-dependent fashion both the number and cumulative length of gastric ulcers elicited by restraint for 2 hr at 4 degrees C, but did not affect ulcer formation in unrestrained animals maintained in this environment. FG 7142 also reduced gastric ulcer formation in restrained rats maintained at 22 degrees C for 5 hr. The ability of FG 7142 to reduce restraint-stress induced gastric ulcer formation was blocked by the benzodiazepine receptor antagonist ZK 93426 and the beta-adrenoceptor antagonist propranolol. These findings suggest that FG 7142 produces a benzodiazepine-receptor mediated reduction in gastric ulcer formation, which may result from its ability to increase activity of the sympathetic nervous system.     

Loss of Inositol Phospholipids in Epididymal Sperm Following Exposure of Mice to Long-Term Feeding of Organophosphates

Abstract: The action of central and peripheral type benzodiazepine ligands on growth hormone, luteinizing hormone and follicle stimulating hormone levels in serum were studied in male rats. Graded doses of Ro 5-4864, that binds to the peripheral type benzodiazepine receptors, clonazepam, a fairly pure central type agonist and diazepam, a mixed-type agonist, were given intraperitoneally. Also a benzodiazepine partial inverse agonist, FG 7142, was investigated. Clonazepam increased growth hormone levels at 0.2 mg/kg while higher doses were not active. Diazepam (5-25 mg/kg) was not effective. FG 7142 (15 mg/kg) and Ro 5-4864 (25 mg/kg) decreased growth hormone levels. Flumazenil, a central-type antagonist, reversed at least partially the effects of clonazepam and FG 7142, suggesting an effect through GABA-benzodiazepine complex. Elevation of growth hormone could be associated with anxiolysis and decrease of growth hormone with enhanced anxiety. Clonazepam (0.2-5 mg/kg) and diazepam (5-25 mg/kg) increased luteinizing hormone concentrations, but only the effects of 1 mg/kg of clonazepam and 5 mg/kg of diazepam reached statistical significance. Even FG 7142 caused a modest increase of luteinizing hormone at 5 mg/kg, but Ro 5-4864 rather decreased luteinizing hormone, although not significantly. Flumazenil (25 mg/kg) antagonized partially the effects of diazepam and clonazepam. Effects of Ro 5-4864 and FG 7142 were not modified by flumazenil or PK 11195, a peripheral-type mixed antagonist/agonist. Luteinizing hormone stimulation by benzodiazepine ligands may be a pituitary action while inhibition could be caused by the activation of the central GABAergic system. Serum follicle stimulating hormone levels were not significantly altered by central or peripheral type benzodiazepine agonists or antagonists.     

Effects of central and peripheral type benzodiazepine ligands on growth hormone and gonadotropin secretion in male rats.

The action of central and peripheral type benzodiazepine ligands on growth hormone, luteinizing hormone and follicle stimulating hormone levels in serum were studied in male rats. Graded doses of Ro 5-4864, that binds to the peripheral type benzodiazepine receptors, clonazepam, a fairly pure central type agonist and diazepam, a mixed-type agonist, were given intraperitoneally. Also a benzodiazepine partial inverse agonist, FG 7142, was investigated. Clonazepam increased growth hormone levels at 0.2 mg/kg while higher doses were not active. Diazepam (5-25 mg/kg) was not effective. FG 7142 (15 mg/kg) and Ro 5-4864 (25 mg/kg) decreased growth hormone levels. Flumazenil, a central-type antagonist, reversed at least partially the effects of clonazepam and FG 7142, suggesting an effect through GABA-benzodiazepine complex. Elevation of growth hormone could be associated with anxiolysis and decrease of growth hormone with enhanced anxiety. Clonazepam (0.2-5 mg/kg) and diazepam (5-25 mg/kg) increased luteinizing hormone concentrations, but only the effects of 1 mg/kg of clonazepam and 5 mg/kg of diazepam reached statistical significance. Even FG 7142 caused a modest increase of luteinizing hormone at 5 mg/kg, but Ro 5-4864 rather decreased luteinizing hormone, although not significantly. Flumazenil (25 mg/kg) antagonized partially the effects of diazepam and clonazepam. Effects of Ro 5-4864 and FG 7142 were not modified by flumazenil or PK 11195, a peripheral-type mixed antagonist/agonist. Luteinizing hormone stimulation by benzodiazepine ligands may be a pituitary action while inhibition could be caused by the activation of the central GABAergic system. Serum follicle stimulating hormone levels were not significantly altered by central or peripheral type benzodiazepine agonists or antagonists.     

Chronic treatment with lorazepam and FG 7142 may change the effects of benzodiazepine receptor agonists, antagonists and inverse agonists by different mechanisms

Treatment of mice with lorazepam 10 mg/kg p.o. or FG 7142 40 mg/kg i.p. once a day for 14 days changed the effects of benzodiazepine (BZ) receptor ligands injected acutely on the threshold of pentylenetetrazol (PTZ)-induced seizures. The effects of the two pretreatments differed qualitatively as well as quantitatively. Lorazepam elicited a shift in the effects of all BZ receptor ligands tested, whereby the agonists lorazepam and ZK 93423 now acted like partial agonists given acutely, the partial agonist ZK 91296 acted like an antagonist and the antagonists Ro 15-1788 and ZK 93426 like partial inverse agonists. The proconvulsant effects of the partial inverse agonist FG 7142 and the full inverse agonist DMCM on the PTZ-induced seizures did not change. However, FG 7142 became a full inverse agonist i.e. became convulsant, and DMCM may have increased in potency as a convulsant. After FG 7142 pretreatment lorazepam and ZK 93423 behaved like partial agonists given acutely whereas there was no change in effect for ZK 91296, Ro 15-1788 and ZK 93426. FG 7142 became convulsant (i.e. kindling occurred) and the potency of DMCM as a convulsant was non-significantly increased, while their proconvulsant effects with respect to PTZ-induced seizures were not altered. The fact that the effects of the two very different pretreatments on the BZ receptor ligand continuum were in the same direction may be explainable by assuming two different mechanisms, both of which may involve the GABA receptors.     

Discriminative stimulus control by the anxiogenic beta-carboline FG 7142: generalization to a physiological stressor

Drug discrimination was employed to investigate the similarities between FG 7142-induced anxiogenesis and the stress produced by exposure to either a novel environment or to footshock. Eight rats were trained to discriminate between the stimulus properties of the beta-carboline FG 7142 (5.0 mg/kg) and its vehicle in a two-lever, food motivated operant task. Once trained, decreasing doses of FG 7142 produced fewer FG 7142-appropriate responses and the dose-response relationship yielded an ED50 of 1.45 mg/kg. Rats were subsequently subjected to two physiological/environmental stressors, footshock and novelty, and then tested in the discriminative paradigm. Exposure to novelty resulted in partial FG 7142-appropriate responding, whereas footshock sessions produced responding predominately on the FG 7142-appropriate lever. This is the first report of stimulus control by FG 7142 and it is likely that the interoceptive cue state produced by this compound is anxiogenic in nature, as reported to occur in man. The anxiogenic nature of the FG 7142 discriminative stimulus is supported by the generalization of FG 7142 to the state produced following stressful environmental manipulation.     

Effects of diazepam and two beta-carbolines on epileptic activity and on EEG and behavior in rats with absence seizures

In the present series of experiments, effects of a full benzodiazepine receptor agonist (diazepam) are described and compared with those of a partial benzodiazepine receptor agonist (ZK 91296) and an inverse partial benzodiazepine receptor agonist (FG 7142), both compounds of the beta-carboline family. In a rat model for generalized absence epilepsy, the anticonvulsant, the hypnotic and the myorelaxant properties were investigated, as well as effects on on-going behavior and effects on the electroencephalogram (EEG). While diazepam showed all behavioral and electrophysiological changes characteristic for the benzodiazepines, the partial agonist ZK 91296 reduced seizure activity without inducing any signs of sedation, sleepiness, myorelaxation and changes in behavior or EEG spectral content. The partial inverse agonist FG 7142 aggrevated epileptic activity, with slightly enhanced immobile behavior, suggesting some anxiogenic properties. The results not only demonstrate that the multiple effects of the benzodiazepines could be separated by these compounds, but also that the anticonvulsant activity is not related to changes in spectral content of the EEG. Because of its selective activity, ZK 91296 appears to be more suitable than diazepam in reducing seizure activity. Finally, FG 7142 seems a genuine partial inverse agonist which has some, but not all, of the inverse effects of a full agonist.     

Conditioned place aversion produced by FG 7142 is attenuated by haloperidol

A place conditioning paradigm was used to examine the affective properties of FG 7142, a benzodiazepine receptor inverse agonist. At the highest dose tested (10 mg/kg, IP), FG 7142 produced a significant place aversion to the drug-paired compartment. In a second experiment, haloperidol injections were given before FG 7142. It was found that haloperidol (0.2 mg/kg) significantly reduced the measured conditioned place aversion produced by FG 7142, without exhibiting any aversive or rewarding effects by itself. These results suggest that dopamine receptors are involved in the learning or expression of conditioned place aversion induced by benzodiazepine receptor inverse agonists.     

Anxiogenic beta-carboline FG 7142 produces activation of noradrenergic neurons in specific brain regions of rats.

By measuring the levels of two major metabolites of rat brain noradrenaline (NA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), we investigated the effects of anxiogenic beta-carboline FG 7142, an inverse agonist of benzodiazepine (BZD) receptors, on brain noradrenergic activity of rats. Thirty min after treatment with FG 7142 (15 mg/kg IP), levels of both MHPG and DHPG in the hypothalamus, amygdala and thalamus, but not in the hippocampus and cerebral cortex, significantly increased. These increases were significantly antagonized by pretreatment with BZD receptor antagonist Ro 15-1788 (15 mg/kg, IP). Sixty min after treatment with FG 7142 at the same dose, significant increases in both metabolite levels occurred in the hypothalamus, amygdala, thalamus and cerebral cortex, and increases in MHPG levels only were observed in the hippocampus. These increases were significantly blocked by pretreatment with alpha 2-adrenoreceptor agonist clonidine (100 microgram/kg, IP). The present findings suggest that FG 7142 can produce increases in brain noradrenergic activity in specific brain regions by interacting with BZD receptors, and may support the hypothesis that hyperactivity of brain noradrenergic systems may be one neural mechanism in provocation of aversive emotional changes (anxiety, fear or panic).     

Prior exposure to the elevated plus-maze sensitizes mice to the acute behavioral effects of fluoxetine and phenelzine

A single undrugged experience of the elevated plus-maze modifies future drug responses in the test. The present study investigated the effects of maze-experience on the acute behavioral effects of the monoamine oxidase inhibitor phenelzine and the serotonin reuptake inhibitor fluoxetine. Phenelzine (2.5-12.5 mg/kg) had no clear effect on plus-maze behavior in test-naive Swiss Webster mice, but dose-dependently increased anxiety-like behavior in maze-experienced subjects. Similarly, fluoxetine (5-20 mg/kg) produced non-significant trends for increased anxiety-like behavior in maze-naive mice, but significantly and dose-dependently increased anxiety-like behavior and suppressed locomotor activity in maze-experienced mice. The anxiogenic effects of the benzodiazepine receptor inverse agonist N-methyl-beta-carboline-3-carboxamide (FG 7142) (20 mg/kg) was abolished by prior test experience, suggesting an alteration in gamma-aminobutyric acid (GABA)/benzodiazepine receptor function with maze-experience. However, the benzodiazepine receptor antagonist flumazenil (5-20 mg/kg) produced a silent profile regardless of maze-experience. Present findings provide further evidence demonstrating that prior test history is a critical consideration in mouse studies of anxiety-related behavior.     

Benzodiazepine receptor agonists and inverse agonists yield concordant rather than opposing effects on startle responses

Benzodiazepine receptor agonists and inverse agonists exert generally opposite actions at both the cellular and behavioural levels. The present study, however, reveals that both the benzodiazepine receptor agonist, chlordiazepoxide and the partial inverse agonist, FG7142, yield a dose-dependent (2-16 mg/kg, i.p) reduction in the amplitude of the acoustic startle response in the rat. The similarity in drug effects on startle was not attributable to congruent effects on basal somatic activity, as chlordiazepoxide resulted in a dose-dependent decrease in activity whereas FG7142 was associated with a small but non-significant increase in activity. As these results contrast with the bidirectional actions of benzodiazepine receptor agonists and inverse agonists in behavioural tests of fear or anxiety, the neuronal mechanisms mediating the effects of benzodiazepine receptor ligands on the acoustic startle response may be distinct from those that underlie the specific fear- attenuating and potentiating actions, respectively, of benzodiazepine receptor agonists and inverse agonists.     

Effects of diazepam,FG 7142, and RO 15-1788 on schedule-induced polydipsia and the temporal control of behavior

Although benzodiazepine agonists and inverse agonists have opposite effects on drinking elicited by water deprivation, there is much less information about the effects of these drugs on nonhomeostatic drinking. In this experiment the effects of diazepam (0.3–5.0 mg/kg), a benzodiazepine receptor agonist, and FG 7142 (1.0–9.0 mg/kg), an inverse agonist, were determined on drinking elicited by a FT-60 schedule of food delivery (SIP). Both diazepam and FG 7142 dose-dependently reduced SIP, measured as either licking or volume consumed. In addition, diazepam reduced panel pressing for food, decreased locomotor activity, and changed the time course of each behavior. In contrast, FG 7142 reduced schedule-induced drinking without significantly altering other behaviors. The antagonist RO 15-1788, when given in combination with these drugs, only partially restored the reductions in licking produced by diazepam, but was much more effective in reversing the effects of FG 7142 at doses of the antagonist that failed by themselves to affect responding. The opposite pattern of effects was seen on the volume of water consumed. These effects are discussed in terms of the behavioral and pharmacological specificity of these drugs.     

Strain differences in sensitivity to the hypothermic effects of benzodiazepine receptor ligands in mice

The hypothermic effects of intraperitoneal (IP) administration of the full benzodiazepine agonist lop razolam (1, 10 mg/kg); the partial agonist Ro 17-1812 (1, 10 mg/kg); the benzodiazepine receptor antagonist flumazenil (10, 20 mg/kg); the benzodiazepine inverse agonists Ro 15-4513 (1, 3, 10 mg/kg) and Ro 19-4603 (0.03, 0.1, 0.3 mg/kg) and the-carboline inverse agonists FG 7142 (10, 30 mg/kg) and DMCM (1, 3, 10 mg/kg) were investigated in three strains of mice. TO mice were less sensitive than CBA/cA and DBA/2 mice, since only loprazolam and the partial and full-carboline inverse agonists FG 7142 and DMCM lowered body temperature in these animals. CBA/cA mice were particularly sensitive to the hypothermic effects of loprazolam and Ro 17-1812, and also responded to the-carboline but not the benzo diazepine inverse agonists. In contrast, DBA/2 mice responded with moderate hypothermia to loprazolam, Ro 17-1812, and to the partial inverse agonist Ro 15-4513, and exhibited marked hypothermia in response to the more efficacious benzodiazepine inverse agonist Ro 19-4603 and to FG 7142 and DMCM. Flumazenil did not alter body temperature. DBA/2 mice were also more sensitive to the convulsant activity of inverse agonists than TO mice. CBA/cA mice exhibited enhanced sensitivity to the convulsant, but not the hypothermic, effects of Ro 19-4603, showing dissociation of these responses. The mechanisms underlying the genetic differences in sensitivity of mice to the hypothermic and convulsant action of the different ligands are unknown and warrant further investigation.     

Ro 15-4513, like anxiogenic beta-carbolines, increases dopamine metabolism in the prefrontal cortex of the rat

The effects of Ro 15-4513, FG 7142 and beta-CCM on the activity of the mesocortical dopaminergic system were examined by measuring the changes in the content of the principal dopamine (DA) metabolite, dihydroxyphenylacetic acid (DOPAC) in the prefrontal cortex of the rat. Ro 15-4513 increased the DOPAC content in the prefrontal cortex in a dose-dependent manner (5-40 mg/kg i.p.) but had no effect on DA concentrations. A similar increase in DOPAC content was induced by FG 7142 (40 mg/kg i.p.) and beta-CCM (8 mg/kg s.c.), two beta-carboline derivatives that interact with benzodiazepine recognition sites as partial inverse agonists. These effects of Ro 15-4513, FG 7142 and beta-CCM on DA metabolism in the prefrontal cortex are mediated via benzodiazepine recognition sites, since they were prevented by the administration of the benzodiazepine antagonists Ro 15-1788 and ZK 93426. These data indicate that Ro 15-4513 is an inverse agonist at benzodiazepine recognition sites.