Opposite effects of pentylenetetrazol on self-defensive and submissive postures in the rat

In a previous work, using the resident-intruder situation, we have shown that a benzodiazepine inverse agonist could exert a fear-promoting effect, in decreasing self-defensive behaviours while increasing submissive postures. To further test this hypothesis, the effects of pentylenetetrazol on different forms of defensive behaviour were examined in male intruder rats confronted with offensive residents. Administration of pentylenetetrazol (10 and 20 mg/kg, IP) increased submissive postures such as immobility and on-the-back, but reduced self-defensive postures. Other active behaviours were not reduced, thus excluding a non-specific behavioural suppression. These results suggest that self-defensive and submissive behaviours can be dissociated and that anxiogenic compounds are more likely to increase submissive behaviours than self-defensive ones.     

LY 171555-induced hyperdefensiveness in the mouse does not implicate benzodiazepine receptors

In naive mice the selective D2 agonist LY171555 dose-dependently (0.5–5 mg/kg) induces defensive responses toward non-aggressive conspecifics. In order to investigate possible anxiogenic properties of the D2 agonist, its behavioural effects were compared with those produced by the benzodiazepine receptor inverse agonist methyl--carboline-3-carboxylate(-CCM) in the elevated plus maze and in social interactions with non-aggressive opponents. When tested in the elevated plus maze, mice injected with LY 171555 (0.005–1 mg/kg) showed no decrease either of the number of entries or of the time spent in the open arms. At 5 mg/kg an actual increase of these two measures was observed. By contrast,-CCM (1–3 mg/kg) dose-dependently decreased both the number of entries and the time spent in the open arms without altering locomotion. The effects of-CCM were antagonized by the benzodiazepine receptor antagonist RO 15-1788 (3 mg/kg) showing a selective involvement of benzodiazepine receptors in their modulation. On the other hand,-CCM, (1–3 mg/kg) did not produce significant effects on defensive behaviour of mice interacting with non-aggressive opponents and the defensive responses of mice treated with 1 mg/kg LY 171555 were not prevented by 5 mg/kg chlordiazepoxide. These results show that DA D2-mediated hyperdefensiveness and anxiety modulated by benzodiazepine receptors are unrelated phenomena and suggest that this behavioural response may represent a model of those forms of fear-related reaction that do not respond to benzodiazepine treatment.     

The effect of the β-carboline FG 7142 on the behaviour of male rats in a living cage: An ethological analysis of social and nonsocial behaviour

The effects of FG 7142, a -carboline benzodiazepine receptor partial inverse agonist, on the social behavior of pair-housed rats were investigated. Four 6-min dyadic social encounters in a living cage were observed in a paradigm in which one member of a pair of rats was injected. The four injection groups (n=8) were vehicle control, and FG 7142 at 2.5, 5.0 and 10.0 mg/kg, respectively. All injections were administered 2 min before the start of the first observation trial. Compared to the effects of vehicle alone, FG 7142 decreased aggressive behaviour but did not change the level of total social interaction. Thus there were compensating increases in approaching and avoiding behaviours following the administration of FG 7142. Locomotion declined marginally and immobility increased in FG 7142-injected rats. FG 7142 decreased the incidence of self-grooming. The evidence is consistent with a relatively selective reduction in intraspecies aggression in male rats after the injection of the -carboline inverse agonist.     

Effects of a single or repeated administration of the benzodiazepine inverse agonist FG7142 on behaviour and cortical adrenoceptor binding in the rat

We have reported previously an increase in the number of -adrenoceptors in mouse cerebral cortex 7 days after kindling of seizures by repeated once-daily administration of the benzodiazepine receptor inverse agonist, FG7142. In subsequent experiments, an even larger increase in -adrenoceptor number was found 7 days after a single injection of this compound. The present experiments investigated whether FG7142-induced changes in adrenoceptor binding are also found in the rat and whether the effects of a single and repeated injections of this drug differ quantitatively. In view of the anxiogenic effects of FG7142, we have also tested for parallel changes in behaviours associated with anxiety and exploration. Nine days after a single injection of FG7142, the number of -adrenoceptors in the cerebral cortex was greater than that found after repeated administration of this compound; this difference was statistically significant. There was no difference in -adrenoceptor binding to tissues from chronically FG7142-treated and vehicle-injected animals and there were no changes in ₂-adrenoceptor binding or noradrenaline levels after either a single or repeated FG7142 treatment. Neither single nor repeated FG7142 treatment modified spontaneous behaviour in either the elevated plus-maze test of anxiety or the holeboard test of exploration. The behavioural effects of yohimbine and clenbuterol in these tests were also unaffected by FG7142. We discuss the possibility that the difference in the effects of a single and repeated administration of FG7142 on -adrenoceptor binding is related to the expression of kindled seizures.     

ZK 91296, a partial agonist at benzodiazepine receptors

ZK 91296 (ethyl 5-benzyloxy-4-methoxymethyl--carboline-3-carboxylate) is a potent and selective ligand for benzodiazepine (BZ) receptors. Biochemical investigations indicate that ZK 91296 may be a partial agonist at BZ receptors. Such partial agonism may explain to some extent why ZK 91296 needs higher BZ receptor occupancy than diazepam for the same effect against chemical convulsants and for behavioural effects. The lack of sedatiye effects, and the very potent inhibition of reflex epilepsy, spontaneous epilepsy and DMCM-induced seizures suggest, furthermore, that ZK 91296 may possess pharmacological selectivity for a particular type of BZ receptor interaction, perhaps including topographic as well as receptor subtype differentiation.     

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.     

Corticotropin releasing factor and amphetamine exaggerate partial agonist properties of benzodiazepine antagonist Ro 15-1788 in the conflict test

The central nervous system stimulants corticotropin releasing factor (CRF) and amphetamine were administered in combination with the benzodiazepine ligands Ro 15-1788 and FG 7142 in order to assess their benzodiazepine agonist and antagonist receptor properties in an operant conflict test in rats. Ro 15-1788, which was without behavioral activity in this test when given alone, reversed the suppression of punished responding produced by CRF and amphetamine in a dose-dependent manner. Chlordiazepoxide, which produced a release of punished responding by itself, also reversed the suppression of punished responding produced by CRF but not that of amphetamine. The benzodiazepine inverse agonist FG 7142, in contrast, enhanced the rate suppressing actions of both CRF and amphetamine. In a locomotor activity test, Ro 15-1788 failed to block the locomotor activation observed with CRF and amphetamine. The results suggest that anxiety or stress-enhancing compounds may enhance the partial agonist properties of Ro 15-1788 in certain test situations.     

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.     

A three-state model of the benzodiazepine receptor explains the interactions between the benzodiazepine antagonist Ro 15-1788, benzodiazepine tranquilizers, β-carbolines,and phenobarbitone

Summary The potent benzodiazepine receptor ligands -carboline-3-carboxylic acid ethyl ester (-CCM) and the corresponding methylester (-CCM) administered i.v. depressed segmental dorsal root potentials in spinal cats, reversed the prolongation of dorsal root potentials by phenobarbitone, and abolished the depression of a motor performance task induced by phenobarbitone in mice; -CCE enhanced the low-frequency facilitation of pyramidal population spikes in the hippocampus of anaesthetized rats. These effects of -carbolines reflect a depression of GABAergic synaptic transmission and, thus, are diametrically opposed to the enhancing action of benzodiazepine tranquilizers. The specific benzodiazepine antagonist, Ro 15-1788, while not affecting dorsal root potentials, hippocampal population spikes or phenobarbitone-induced motor performance depression, abolished the effects of -CCE on the three parameters and similar effects of -CCM on the spinal cord and motor performance.A three-state model of the benzodiazepine receptor is proposed in which benzodiazepine tranquilizers act as agonists enhancing the function of the benzodiazepine receptor as a coupling unit between GABA receptor and chloride channel, -carbolines act as inverse agonists reducing this coupling function, and Ro 15-1788 represents a competitive antagonist blocking both the enhancing effect of agonists and the depressant effect of inverse agonists on GABAergic synaptic transmission.     

Effects of GABAA receptor ligands on noradrenaline concentration and β-adrenoceptor binding in mouse cerebral cortex

The present experiments investigated changes in -adrenoceptor binding and noradrenaline stores in mouse cerebral cortex after single treatments with drugs which bind to the GABA_A receptor but which attenuate the actions of GABA. Neither the GABA antagonist, securinine, nor the picrotoxin/Cl^– channel ligand, picrotoxin, affected noradrenaline levels or -adrenoceptor binding. However, both the benzodiazepine inverse agonist, DMCM, and pentylenetetrazole increased noradrenaline levels 24 h after injection. Only pentylenetetrazol modified -adrenoceptor binding: there was a significant increase in receptor number 4 days after injection, but a significant decrease after 7 days. The anxiogenic, proconvulsant drug, yohimbine, was without effect. The changes induced by DMCM and pentylenetetrazole do not seem to be related to the behavioural effects of these drugs or to their affinity for binding to benzodiazepine receptors. The possibility that these compounds have actions in addition to those at the GABA_A receptor is discussed.     

Behavioral vigilance in rats: task validation and effects of age,amphetamine, and benzodiazepine receptor ligands

An operant task for the measurement of sustained attention or vigilance in rats was characterized. The task requires the animals to respond to the presentation of visual signals (presented for 25, 50, or 500 ms) by operating one lever (hits) and to the absence of a signal by operating the opposite lever (correct rejection). Incorrect responses (misses and false alarms, respectively) were not rewarded. Performance in this task is a function of signal length, i.e., the shorter the signals the higher the number of misses. An increase in background noise by flashing the chamber houselight (at 0.5 Hz) impaired the animals' ability to discriminate between signal and nonsignal events. Also, flashing the houselight augmented the vigilance decrement observed for shortest signals. An increase in the event-rate also resulted in a vigilance decrement. Finally, the inability of the animals to time signals was examined by testing the effects of an increase in event asynchrony. In a second experiment, the performance of differently aged rats (6- and 20 month-old male BNNia/F344 rats) was studied. Compared to young animals, 20-month-old rats showed a decrease in their ability to discriminate between shortest signals (25 ms) and non-signal events but did not differ in their ability to correctly reject nonsignal trials. Administration of the benzodiazepine receptor (BZR) agonist chlordiazepoxide (CDP; 3, 5, 8 mg/kg) resulted in an impairment of the animals' ability to discriminate between signal and non-signal events and, similar to the effects of age, this effect was exclusively due to an increase in the number of misses. CDP generally produced potent effects while affecting the aged animals to a greater degree. BZR-ligands with weak or selective inverse agonist properties (ZK 93426;-CCtB) did not affect vigilance performance. The BZR partial inverse agonist RU 33965 (0.1, 0.5 mg/kg) dose-dependently impaired vigilance performance. The administration of amphetamine (0.4, 0.8 mg/kg) also impaired performance, but these impairments were possibly based on effects unrelated to attentional mechanisms. The finding that performance in this task revealed the interactions between the effects of age and BZR agonists on attentional abilities further supports the validity of measures of performance generated by this task.     

Further studies of the aggressive behavior induced by Δ 9-Tetrahydrocannabinol in REM sleep-deprived rats

The aggressive behavior induced by ⁹-tetrahydrocannabinol in pairs of REM sleep-deprived rats was studied in five experiments by measuring dominant and submissive behavioral patterns. When 2 REM-deprived rats received ⁹-THC, one of the animals displayed very aggressive postures, while its partner assumed incomplete defensive postures. The intensity of these behavioral postures was dosedependent. In pairs composed of one REM-deprived rat injected with ⁹-THC and one normal or one REM-deprived partner injected with control solution the deprived/drugged rat showed an aggressive posture and catatonia, or a strikingly bizarre behavior, while the control partner displayed typical defensive postures. The behavioral alterations induced in REM-deprived rats by amphetamine, LSD-25, and pentobarbital failed to provoke defensive postures in the normal rats paired with them; however, apomorphine partially mimicked the ⁹-THC effects.It is concluded that in REM-deprived rats ⁹-THC not only provokes aggressive behavior but also impairs the defensive-submissive behavioral patterns.     

Diazepam withdrawal: effects of diazepam and gepirone on acoustic startle-induced 22 kHz ultrasonic vocalizations

It has proven difficult to demonstrate and study the anxiogenic quality of drug withdrawal states in animals. Ultrasonic vocalizations (USV) in response to acoustic startle stimuli have shown promise as a measure of affect and may represent distress responses during diazepam withdrawal. Three experiments evaluated the association between USV and distress by comparing the effects of diazepam as a prototypic benzodiazepine agonist and the putative anxiolytic gepirone with affinity for 5-hydroxytryptamine (5-HT_1A) receptors in naive and diazepam-withdrawn subjects. Adult male Long-Evans rats were exposed to acoustic startle sessions consisting of nine 105 dB and nine 115 dB stimuli. USV at 20–30 kHz were readily emitted during startle and often commenced after the third or fourth stimulus presentation. Acutely, intraperitoneal (IP) administration of diazepam (0.1–3 mg/kg) and gepirone (0.1–1 mg/kg) decreased USV dose-dependently without affecting the startle reflex; gepirone also decreased tail flick latency. Startle-induced USV were also sensitive to the anxiogenic effects of withdrawal from diazepam exposure (0, 2.5, 5, 10 mg/kg b.i.d. IP×5 days). Twenty-four hours after the last diazepam injection, rats were hyperreactive to startle stimuli and doubled their rate of USV over vehicle-treated controls. Gepirone (0.1–1 mg/kg IP), but not diazepam (3–20 mg/kg IP) antagonized the increased rate of USV in rats withdrawn from 10 mg/kg b.i.d. diazepam. Diazepam (2.5–10 mg/kg IP) antagonized the increased rate of USV in rats withdrawn from 2.5 mg/kg b.i.d. diazepam. USV induced by acoustic startle stimuli are sensitive to the anxiolytic effects of benzodiazepine and 5-HT_1A receptor agonists and permit the assessment of the anxiogenic properties of diazepam withdrawal. The potent effect of gepirone on USV suggests a serotonergic amelioration of the anxiogenic aspects of diazepam withdrawal.     

“Anxiolytic” and “anxiogenic” benzodiazepines and β-carbolines: effects on aggressive and social behavior in rats and squirrel monkeys

Ethopharmacological studies on the behavior of socially housed rats and squirrel monkeys were conducted to explore the role of the benzodiazepine GABA_A-coupled ionophore receptor complex in aggressive and social interactions. Benzodiazepine receptor (BZR) antagonists, ZK 93426 (1–10 mg/kg) and flumazenil (3–10 mg/kg), the partial agonist, ZK 91296 (1–10 mg/kg) and the partial inverse agonists RO 15-4513 (0.3–10 mg/kg), were administered to (1) squirrel monkeys prior to 1 h focal observations within established social groups or to (2) resident male rats before confrontations with a naive male intruder in their home cage for 5 min. Aggression was modified in a similar manner in both species, although squirrel monkeys were more sensitive to BZR challenges. Specifically, resident male rats showed dose dependent reductions in attack bites directed at intruder males that were significant at the highest dose of ZK 93426 (10 mg/kg). In squirrel monkeys, ZK 93426 (3 and 10 mg/kg) reduced aggressive grasps, threats and displays, as well as reducing the duration of being the target of aggression from untreated group members (1–10 mg/kg). The BZR partial agonist, ZK 91296 and the antagonist, flumazenil produced few effects on social behavior, low and high intensity aggression and motor activity in both species. Flumazenil (10–30 mg/kg) and ZK 91296 (10 mg/kg), but not ZK 93426, produced significant increases in foraging and feeding behaviors in squirrel monkeys. The hyperphagic effects of ZK 91296 and flumazenil, that are typical of BZR agonists compounds, were not observed in rats. Similarly, the inverse agonist-like reductions in social interactions produced by ZK 93426 (3–10 mg/kg) were observed only in squirrel monkeys. The partial inverse agonist Ro 15-4513 reduced aggression in rats, but low doses (1 mg/kg) produced tremors or seizures in 80% of the monkeys tested. Decreases in aggressive and social behaviors are often interpreted to reflect anxiogenic drug properties, whereas increased feeding has been associated with anxiolytic actions. The concurrent emergence of these apparent opposites suggests independent actions on social and alimentary functions.     

Differential effects of six structurally related benzodiazepines on some ethological measures of timidity,aggression and locomotion in mice

The effects were compared of three 2' chloro-phenyl-benzodiazepines (triazolam, clonazepam and lorazepam) and three corresponding 2' deschloro-phenylderivatives (alprazolam, nitrazepam and oxazepam, respectively) on the incidence of six ethological elements in both timid and aggressive singly-housed male mice, treated with drugs in paired interactions with untreated non-aggressive males. Alprazolam and oxazepam reduced defensive upright postures and escapes at doses which did not reduce rearing and actually increased walking, while their chlorinated counterparts (triazolam and lorazepam, respectively) decreased incidence of defenses and escapes mostly at doses decreasing locomotor acts involving a similar movement (rears and walks, respectively). Alprazolam and oxazepam also reduced attacks at doses not reducing rears, in contrast to triazolam and lorazepam which reduced attacks only at doses suppressing rearing. Nitrazepam stimulated sniffing partners much more than its chlorinated counterpart clonazepam. The 2 deschloro-phenyl-benzodiazepines were more potent in reducing defensive-escape activities than attacks or locomotion. Yet, none of the benzodiazepines tested produced a complete inhibition of timid defensive-escape behavior at non-sedative doses. The present study suggests that 2 deschloro-phenyl-benzodiazepines are less sedative with respect to their anxiolytic activity.     

Cannabinoids modulate ultrasound-induced aversive responses in rats

Rationale Mechanisms and brain substrates mediating cannabinoid-induced modulation of behaviour towards aversive stimuli are poorly understood.Objectives To investigate the effects of systemic and intra-dorsal periaqueductal grey (PAG) administration of the cannabinoid receptor agonist HU210 on behaviour and plasma corticosterone levels in rats exposed to ultrasound and determine the contribution of CB₁ receptors.Methods In experiment 1, rats received vehicle or CB₁ receptor antagonist SR141716A (3 mg/kg, IP) 30 min prior to a second injection of vehicle or HU210 (5, 20 or 80 g/kg, IP). In experiment 2, rats received intra-dorsal PAG vehicle or SR141716A (30 g/rat) 10 min prior to intra-dorsal PAG vehicle or HU210 (5 g/rat). Following injections, rats were exposed to an aversive 20 kHz ultrasonic tone for 3 min. Behaviour, including hyperlocomotor activity and freezing, was monitored during and post-ultrasound. Plasma corticosterone levels 10 min post-ultrasound were measured.Results Ultrasound induced explosive running and freezing behaviour. Systemic administration of HU210 attenuated the expression of ultrasound-induced hyperlocomotor activity and increased freezing. The HU210-induced attenuation of hyperlocomotor activity was blocked by SR141716A. Intra-PAG administration of HU210 reduced the expression of ultrasound-induced hyperlocomotor activity, an effect not blocked by SR141716A. Systemic and intra-PAG administration of HU210 increased plasma corticosterone levels, an effect not blocked by SR141716A.Conclusions The cannabinoid receptor agonist HU210 modulates behaviour towards an aversive ultrasound stimulus in rats, an effect accompanied by increased HPA axis activity. These effects may be mediated, at least in part, by the dorsal PAG but cannot be explained solely by an action at CB₁ receptors.Both D.P.F. and M.D.J. contributed equally to this study.     

Opposite effects mediated by CCKA and CCKB receptors in behavioural and hormonal studies in rats

We compared the influence of two cholecystokinin (CCK) antagonists, devazepide and L,365,260 [3R-(+)-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1 H-1,4-benzodiazepine-3y1)-N-(3-methyl-phenyl)urea], upon two distinct phenomena, behavioural and hormonal effects of caerulein (5 g/kg s.c.), and unselective CCK agonist, in rats. Behavioural effects were assessed in the elevated plusmaze and open field tests. In separate experiments, effects on thyrotropin (TSH), prolactin (PRL) and growth hormone (GH) levels in serum of male rats were studied.Caerulein inhibited the exploratory behaviour in the plus-maze. Time spent in the open part, the number of line crossings and closed arm entries were significantly decreased, whereas the ratio of failed attempts/closed arm entries was increased. The anti-exploratory effect of caerulein was antagonized by the pretreatment with L-365,260 (10 g/kg), a preferential antagonist at CCK_B receptors, but was increased by devazepide (1–100 g/kg), a preferential CCK_A antagonist. L-365,260 (1–100 /kg) and devazepide (1–100 Fig/kg) given alone did not change the behaviour of rats in the plusmaze test. Caerulein (5 g/kg) itself did not modify the locomotor activity of rats in open field. However, the concomitant administration of caerulein with devazepide (1–10 g/kg) reduced the frequency of line crossings and rearings. In the hormonal studies caerulein significantly decreased the cold-induced increase of TSH levels in serum. GH and PRL levels were not markedly affected by caerulein. Pretreatment with devazepide (100 g/kg) antagonized, while Lr365,260 (100 Ng/kg) even increased, the suppressing effect of caerulein on TSH levels. The concomitant administration of L-365,260 and caerulein reduced the levels of GH, whereas the combination of CCK agonist with devazepide caused the opposite effect. L-365,260 and devazepide alone did not change the levels of hormones in serum.The results support the idea that CCK_A and CCK_B receptors exert an opposite influence not only upon the exploratory behaviour in rats (CCK_A receptor activation mediates an increase, CCK_B receptor activation a decrease) but also upon the secretion of two anterior pituitary hormones, TSH and probably GH (CCK_A receptor activation mediates a decrease, CCK_B receptor activation an increase). Correspondence to: P. T. Mannisto at the above address     

A β-carboline antagonizes benzodiazepine actions but does not precipitate the abstinence syndrome in cats

The -carbolines, which are potent ligands for benzodiazepine receptors, antagonize the pharmacological actions of benzodiazepines. In the cat, the stable -carboline derivative methylamide--carboline-3-carboxylate, FG 7142, and the specific benzodiazepine antagonist Ro 15-1788 reversed behavioral and electroencephalographic (EEG) changes produced by a single dose of diazepam. Surprisingly, the -carboline did not elicit signs of withdrawal when given after 22 days of a daily dose regimen of diazepam, while Ro 15-1788 precipitated an acute abstinence syndrome largely characterized by tremors, increased muscle tone, back arching, myoclonic jerks and pupil dilatation. Unlike Ro 15-1788, the -carboline produced effects of its own such as behavioral states of arousal and fearfulness. These findings indicate that the -carboline functionally interacts with benzodiazepine receptors in a manner unlike that seen with typical agonists and antagonists.     

Bidirectional effects of benzodiazepine binding site ligands on active avoidance acquisition and retention: differential antagonism by flumazenil and β-CCt

Rationale The pharmacological approach, using subtype selective ligands, complements genetic studies on the specific contribution of individual receptor subtypes to the various effects of benzodiazepines.Objective The aim of this study was to examine the relative significance of ₁-containing GABA_A receptors in the effects of modulators at the benzodiazepine site on anxiety and memory processes.Methods We tested the effects of the nonselective antagonist flumazenil, the preferential ₁-subunit selective antagonist -carboline-3-carboxylate-t-butyl ester (-CCt), the nonselective agonist midazolam, the preferential ₁-subunit selective agonist zolpidem, and the nonselective inverse agonist methyl 6,7-dimethoxy-4-ethyl--carboline-3-carboxylate (DMCM) in a two-way active avoidance task in rats. The influence of flumazenil (10.0 mg/kg) and -CCt (30.0 mg/kg) on the effects of the two agonists were also examined. In the schedule 2×30 trials, drugs were administered i.p. 20 min before the training session. Avoidance responses in the training session are an anxiety-mediated behavior, whereas performance in the retention session relates to the effects on memory.Results Flumazenil and -CCt did not affect behavior. Midazolam (2.0 mg/kg) facilitated acquisition performance, while DMCM (1.0 and 2.0 mg/kg) induced the opposite effect. Flumazenil antagonized both effects. -CCt potentiated the effect of midazolam, and partly antagonized the effect of DMCM. Midazolam (0.5 and 1.0 mg/kg) and zolpidem (1.0–3.0 mg/kg) impaired, while DMCM (0.1 mg/kg) facilitated the subjects performance in the retention test. The amnesic effects were attenuated but not fully reversed, while the effect of DMCM was counteracted by both antagonists.Conclusion The results indicate the ₁-subunit interferes with the anxiolytic effect of a benzodiazepine site agonist and may contribute to the DMCM-induced anxiogenic effect. It is also substantially involved in the bidirectional memory processing in the active avoidance paradigm.     

Chronic administration of a selective dopamine D-2 agonist: factors determining behavioral tolerance and sensitization

The locomotor stimulant effects of sustained administration of a potent and selective dopamine (DA) D-2 receptor agonist, [+]-4-propyl-9-hydroxynaphthoxazine (PHNO), in rats were assessed 24 h a day during 12 h light-dark cycles. PHNO was administered continuously with subcutaneous implants of Alzet osmotic minipumps (5 g/h), for 12 h a day with modified osmotic minipumps (5 g/h), or by daily injections (15 g, SC). Tolerance was observed to occur only with 24 h continuous infusions and only during the light period. The other treatment regimens produced sensitization of the locomotor response. Daytime tolerance to continuous infusions of PHNO was reversed following reversal of the light-dark cycle. A normally arousing stimulus also reversed (temporarily) daytime tolerance. The present results indicate that the temporal pattern of administration of DA agonists, the phase of the circadian cycle and environmental stimuli associated with arousal are important determinants of the behavioral consequences of long-term treatment.