Pavlovian conditioning to a diazepam cue with yohimbine as the unconditional stimulus.

On multiple occasions, rats were administered diazepam (2.0 mg/kg, ip) followed 30 min thereafter by yohimbine hydrochloride (2.5 or 5. 0 mg/kg) or isotonic saline (forward conditioning groups). Three additional groups (backward conditioning controls) were given equivalent injections, but in reverse order. After eight such pairings, the effects of a single injection of diazepam on motor performance (balancing on a rotating drum) was assessed. Rats that had received either dose of yohimbine during forward conditioning trials maintained their balance longer than the saline controls. After four additional conditioning trials, the animals' activity patterns in a plus-maze screening test for anxiolytics were examined. Placed into the maze after a single test injection of isotonic saline, the behavior of all groups was virtually identical: less than 16% of total entries into or time spent in the four arms of the maze was spent in the two "open" arms (unprotected by surrounding walls). When tested in the maze again, but 35 min after a single injection of diazepam, the groups that had received diazepam but not yohimbine during the conditioning phase exhibited the expected increase in open-arm activity, and equivalent increases were found in backward conditioning groups. However, the group previously conditioned with 2.5 mg/kg of yohimbine following diazepam also showed an increased open-arm activity when tested with diazepam alone, but it was significantly greater than that seen in the control group. In contrast, the group conditioned with 5.0 mg/kg yohimbine following diazepam exhibited no effect of diazepam upon their plus maze activity; consequently, these animals spent less time in the open arms than either of the other groups. Yohimbine alone normally decreases open-arm activity (a putative "anxiogenic" effect) in a linear dose-dependent fashion. The fact that it had a bidirectional conditional effect on the diazepam cue drug demonstrates that a conditional response in drug --> drug conditioning cannot always be predicted on the basis of the behavioral response to the signaled drug. Consideration is given to possible reasons for these effects of diazepam --> yohimbine pairings in terms of the known neuropharmacological properties of yohimbine.

Conditional attenuation of the antipentylenetetrazol activity of chlordiazepoxide.

In a study of drug-drug conditioning, chlordiazepoxide (CDP) was administered to rats 30 min before chlorpromazine (CPZ) every 3-4 days for 5 weeks. Thereafter, CDP was tested for its ability to a) increase animals' exploration of the normally avoided "exposed" arms of a plus-maze (a screening method for anxiolytic substances) and b) protect against seizures induced by pentylenetetrazol (PTZ). The CDP-CPZ conditioning procedure potentiated the usual increase in open-arm activity seen in CDP-injected rats but attenuated the anti-PTZ effect. When injected with CDP 60 min prior to PTZ, rats with a previous history of CDP-CPZ pairings had shorter latencies to seizure onset and showed a greater likelihood of progression to the most severe behavioral indices of a maximal seizure relative to control subjects with a history of backward drug pairings (CPZ-CDP) or pairings of CDP with isotonic saline.

Yohimbine potentiates active defensive responses to threatening stimuli in Swiss-Webster mice.

Yohimbine HCl, an antagonist at alpha 2-noradrenaline receptors with putative panicogenic effects in human subjects, was administered to Swiss-Webster mice at doses of 0.5, 1.0, and 2.0 mg/kg. Animals were then tested in two defense test batteries. Yohimbine produced increases in flight from an approaching/contacting human and potentiated animals' reactions to dorsal contact. During a 5-min exposure to a cat (separated from the mouse by a wire-mesh screen) and the 15-min period thereafter, yohimbine produced a dose-dependent pattern of changes in defensive behaviors that included increases in locomotion, transits from one segment of the test chamber to another, fore- and hindpaw wall climbing, screen climbing and hanging, and roof pushing. Crouching (relative immobility while in a hunched-back posture) was notably decreased at all doses. During the postcat period, two different response patterns, "high-escape" and "low-escape," characterized in part by high and low frequencies of wall climbing, were observed in cat-exposed groups. In yohimbine-injected mice, the low-escape behavior pattern also included a tendency to avoid the segment of the test chamber closest to the cat compartment. Both patterns differed from the crouching and immobility generally exhibited by vehicle-injected, cat-exposed controls. It was suggested that yohimbine effected these behavioral changes by either potentiating neural mechanisms mediating flight or inhibiting mechanisms mediating freezing. This model may have some utility for the investigation of panicogenic and antipanic compounds and may contribute insights into the etiology of panic disorder.

High-frequency (35-70 kHz) ultrasonic vocalizations in rats confronted with anesthetized conspecifics: effects of gepirone, ethanol, and diazepam.

The effects of three anxiolytics--gepirone, diazepam, and ethanol--on high-frequency ultrasonic vocalizations elicited from rats via a new method are described. Subjects confronted with an anesthetized, same-sex conspecific in a neutral test cage emitted ultrasonic vocalizations in the 35- to 70-kHz range. The great majority of these were calls with frequencies higher than 40 kHz; of these, short calls (< 50 ms) occurred significantly more frequently than long calls (> 50 ms). Female subjects emitted far more of these high-short and high-long vocalizations than males did. In females, but not males, these calls were reduced in number by gepirone, 5-hydroxytryptamine1A (5-HT1A) agonist, at both 1.0- and 10.0-mg/kg doses and by diazepam, a benzodiazepine, at 3.0 but not 1.0 mg/kg. Ethanol (0.6 and 1.2 g/kg) had no detectable effect. The utility of this method, both for the study of ultrasounds and assessment of serotonergic anxiolytics, is discussed.

Neuroleptic-induced changes in the anxiolytic and myorelaxant properties of diazepam in the rat.

Diazepam (2.0 mg/kg) was injected (IP) into rats 30 min before chlorpromazine (2.5, 5.0, or 10.0 mg/kg) on ten occasions. All doses of chlorpromazine enhanced the capacity of diazepam to increase rats' exploration of the exposed arms of an elevated plus-maze, an animal screening test for anxiolytic and anxiogenic substances. When maze testing occurred during each of the ten diazepam----chlorpromazine trials (after diazepam but before chlorpromazine), this enhancement effect appeared on Trial 6 and persisted thereafter. Haloperidol (3.0 mg/kg, IP) changed diazepam-elicited plus-maze activity in the same manner as chlorpromazine; however, thioridazine (10.0 mg/kg) and pimozide (2.0 mg/kg) were ineffective. Additionally, haloperidol, like chlorpromazine, was found to reduce diazepam's muscle relaxation effect (inclined plane test) as a consequence of diazepam----haloperidol pairings; once again, thioridazine and pimozide proved ineffective. These results suggested that not all neuroleptics will alter diazepam activity, and also that dopamine blockade per se is not sufficient to induce such changes. While the reasons for the enhanced plus-maze effects of diazepam induced by haloperidol and chlorpromazine remain elusive, the diminished myorelaxant effect may be linked to a neuroleptic's capacity to induce muscular side effects: thioridazine and pimozide are far less likely to yield such effects than are chlorpromazine and haloperidol. Haloperidol administered chronically by itself was found to have an effect on diazepam-induced myorelaxation. Administration of this butyrophenone either orally (2.0 mg/kg daily for 22 days) or in depot form (haloperidol decanoate, 60.0 mg/kg IM once a month for four months) caused a diminished effect of diazepam in rats subjected to the inclined plane test.(ABSTRACT TRUNCATED AT 250 WORDS)

Diazepam-stress interactions in the rat: effects on autoanalgesia and a plus-maze model of anxiety.

On six occasions spaced at least a week apart, two groups of rats were subjected to a variety of stressful conditions consisting of a restraint/bright light complex, either alone or in combination with a tail pinch, whole-body inversion, or partial immersion in cold water. One of these groups was injected with diazepam (2.0 mg/kg) 30 min prior to the stressors, while the other group experienced the drug in their home cages the following day. A third group also received the diazepam but was not exposed to the stressors. In three test sessions all animals were injected with either diazepam or saline and were then exposed to a novel stressor: a plus-maze used as a screening device for anxiolytic drugs. This was immediately followed by a tail-flick measure of analgesia. The longest tail-flick latencies, indicating stress-induced analgesia ("autoanalgesia"), were observed in the group that had not been exposed to stress prior to testing. The other two groups exhibited substantially shorter latencies but did not differ from one another, thus showing a "stress inoculation" effect that was uninfluenced by diazepam. In the plus-maze, diazepam tends to increase the amount of time rats will spend in the two exposed arms of the maze relative to the two enclosed arms. This effect was significantly attenuated in the group that had previously experienced the variety of stressors after a diazepam injection, suggesting a learned association between drug and stress that resulted in a diminution of the drug's anxiolytic property.

Therapeutic and hypothermic properties of diazepam altered by a diazepam-chlorpromazine association.

Rats were injected (IP) with diazepam (2.5 mg/kg) and chlorpromazine (10.0 mg/kg) with a 30-min interval between the two injections. After 10-12 repeated drug pairings of this type, the thermic, muscle relaxant, and anxiolytic responses of the animals to diazepam alone were tested. These tests revealed: 1) an enhanced hypothermia (rectal temperature), 2) an attenuated muscle relaxant effect (inclined plane test), and 3) a potentiated anxiolytic effect (plus-maze test). Although various interdrug associations have previously been demonstrated using other measures of conditioning, this is the first instance in which changes in the therapeutic effects of a drug (in this case, muscle relaxation and anxiety reduction) have been obtained with this procedure.

Conditional shifts in thermic responses to sequentially paired drugs and the "conditional hyperactivity" hypothesis.

Previous experiments have demonstrated that upward shifts in a rat's thermic response to certain drugs may be observed when these drugs have been paired on several occasions with agents that induce hypothermia. A "conditional hyperactivity" hypothesis suggests that these upward shifts may simply reflect drug elicited increases in body movements which translate into higher temperatures. The present experiment explored this hypothesis. Atropine sulfate (10 mg/kg) was paired with sodium pentobarbital (40 mg/kg) on multiple occasions and several tests were conducted with both drugs. This treatment yielded a conditional hyperthermic response to atropine, but the drug was not found to elicit an increase in gross motor movements. Of greatest interest was the finding that the atropine, when injected 30 min prior to a hypnotic dose of pentobarbital (80 mg/kg), attenuated the hypothermia normally induced by this barbiturate while leaving the duration of hypnosis unaffected. This upward thermic shift cannot be accounted for by the "conditional hyperactivity" hypothesis because the animals were immobile while under pentobarbital's influence. These findings suggest that autonomic events, as yet unspecified, may underlie certain conditional temperature increases.

Conditional hyperthermia in response to atropine associated with a hypothermic drug.

In a set of experiments designed to examine learned associations between drug states, atropine sulfate (10 mg/kg) elicited a conditional hyperthermia in rats following ten treatment sessions in which the drug was paired with either chlorpromazine hydrochloride (10 mg/kg) or ethanol (2.3 g/kg), both hypothermia-inducing agents. Atropine methyl nitrate, a quaternary analogue with similar peripheral effects but little central action, was ineffective as a cue in this situation. These experiments demonstrated that a sequential pairing of drug states can yield a change in an organism's response to the cue drug (the first drug in the sequence).

Thyrotropin-releasing hormone (TRH) potentiates pentobarbital-based flavor aversion learning.

Thyrotropin-releasing hormone (TRH), a hypothalamic polypeptide, will antagonize some of pentobarbital's major effects (sleep time and hypothermia) in rodents when administered in low doses (1-10 mg/kg). At higher doses (30 and 100 mg/kg), TRH has been shown to increase the lethality of high doses of pentobarbital in mice. The present experiments demonstrated that 10 mg/kg of TRH will potentiate the conditioned flavor aversion normally induced in rats by 20 mg/kg of pentobarbital, suggesting that the TRH-pentobarbital combination may have sublethal toxic effects even at low doses of both substances. Furthermore, this result suggests that the mechanism whereby pentobarbital produces a flavor aversion is independent of the drug's hypothermic and sleep-inducing effects.

Attenuation of pentobarbital-elicited hypothermia in rats with a history of pentobarbital-LiCl pairings.

Rats were given five separate pairings (sequential IP injections) of pentobarbital and lithium chloride, both hypothermia-inducing agents. When the animals were subsequently tested with a single injection of pentobarbital alone, they exhibited an attenuated hypothermia relative to controls that had either (a) received pentobarbital-LiCl pairings spaced twenty-four hours apart, or (b) received only placebo injections of normal saline. This phenomenon provides further evidence that rats can learn an association between drug states and may help to explain why pentobarbital-LiCl pairings tend to eliminate pentobarbital's capacity to produce a conditioned flavor aversion.