Facilitation of learning by delayed injections of pentylenetetrazol

Summary In the first experiment rats were trained in black-white discrimination, then injected with 7.5, 10.0, or 15.0 mg/kg of pentylenetetrazol (Metrazol) or saline. Injections were given immediately or 15 min following training. The animals were retested 24 hours later. Improved performance was observed for drug groups, but the extent of improvement was a joint function of the amount of drug and the time at which it was given. Animals given 10 mg/kg showed greater retention when injection was delayed. In a second experiment animals were given spaced trials in a position discrimination task, extending over a period of several days. Following each day's, session, animals were injected with pentylenetetrazol or saline at intervals of 0, 5 or 10 min. A maximum facilitation effect was obtained at the 10-min interval.This research partially supported by the U.S.Public Health Service, Grant MH 13673-01, and partially by the University of Washington Graduate School Research Fund. We wish to express our thanks to Patricia McGurk for her assistance in Experiment II.     

Modification of learning and memory in goldfish through the use of stimulant and depressant drugs

The effects of stimulants and depressants on learning and memory in goldfish were investigated in a series of four experiments. Avoidance performance in a two-way, light-cued shuttle task was significantly facilitated by intracranial injection of picrotoxin (1.50 mg/kg) but significantly impaired by injection of sodium pentobarbital (30 mg/kg) 5 min before 20 training trials were given. These drugs in the dosages used in the present study did not affect general activity of the fish. When identical doses of the drugs (along with saline controls) were given immediately after the first two of three 10-trial training sessions given 48 h apart, avoidance performance during the second and third sessions was facilitated and impaired by the posttrial injections of the stimulant and depressant drugs respectively. Moreover, it was found in an extended experiment that picrotoxin improved performance if injected 25 sec or 1 h after each of two 10-trial training sessions, but not if injected after a 4 h delay. Pentobarbital impaired performance if injected 25 sec after training, but not if injected after a 1/2 h or a 1 h delay.These stimulant and depressant effects demonstrated in goldfish were interpreted in terms of their effects on memory consolidation processes.This report is based upon dissertation research by the first author under the supervision of the second author in partial fulfillment of the requirements for the Ph. D. degree in the Department of Psychology at the University of Houston, 1972.     

Time dependent pentylenetetrazol-like cues subsequent to diazepam administration

Seventy male Sprague-Dawley rats were trained to discriminate which of two levers to press for milk reinforcement on a VI-20 schedule of reinforcement on the basis of whether they were injected subcutaneously with 0.75 mg/kg diazepam or 10.0 mg/kg pentylenetetrazol. Following discrimination acquisition, a dose-response function was generated for each drug during 5-min extinction periods. Subjects were then assigned to one of seven groups on the basis of their per cent responding during saline testing. Each group was injected with 5 mg/kg diazepam and then given a 5-min extinction test at intervals of 2, 4, 6, 8, 12, 16, 20, or 24 h subsequent to injection. The results indicated that at the shorter time intervals the animals responded on the diazepam lever. However, as the time interval between injection and testing lengthened, responding on the PTZ bar gradually increased until by 12 h following injection with diazepam the animals were responding as though they had received an injection of 5 mg/kg PTZ. Following this period of rebound, choice behavior returned to baseline by 24 h post-injection.     

The effect of para-chlorophenylalanine and scopolamine on passive avoidance in chicks

Four-day-old Vantress x Arbor Acre chicks were treated for key-peck passive avoidance (PA) learning following intraperitoneal injections of parachlorophenylalanine (PCPA) and/or scopolamine. In Experiment 1, chicks were pre-treated with either three or five injections of PCPA (150 mg/kg) or saline across th first three posthatch days and then tested for PA learning on the fourth posthatch day. In Experiment 2, chicks were first pre-treated with three injections of PCPA (150 mg/kg) or saline, and then injected with either scopolamine (0.5 mg/kg) or saline 20 min prior to PA testing on the fourth posthatch day. Major findings were: (a) Chicks pre-treated with PCPA did not significantly differ from saline control chicks in either the acquisition or maintenance of response suppression during PA testing; (b) chicks injected with scopolamine were significantly disrupted in PA learning as compared to saline control chicks; and (c) PCPA pre-treatment did not significantly affect the scopolamine-induced disruption of PA learning. These findings, therefore, suggest that cholinergic, but not serotonergic, mechanisms are involved in PA learning of the young chick.     

Amphetamine and the overtraining reversal effect

Rats were trained in a Y-maze on a two choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Animals in the Mastery group were trained until they reached criterion and were then switched to reversal, where the reinforcement contingencies of the original training were reversed. Animals in the Overtraining group received a further 110 trials before being switched to reversal. The administration of 1 mg/kg d-amphetamine facilitated dramatically reversal learning in Mastery group. Overtraining improved reversal in saline injected animals and slowed down reversal in amphetamine-treated animals. The drug also facilitated the acquisition of the initial brightness discrimination.     

The effects of multiple injections of morphine sulfate on shuttle-box behavior in the rat

F344 male rats were trained in shuttle-box avoidance to a criterion of over 90% avoidance, and independent groups of subjects (Ss) were then given 13 daily injections of 5, 10, or 20 mg/kg of morphine or saline (s.c.) 30 min prior to testing. In Experiment 1, Ss were injected and tested on each of the 13 days while in Experiment II, Ss were injected daily but tested only on Day 13. Five mg/kg of morphine did not decrease avoidance responding. While 10 mg/kg initially caused a decrease in avoidance responses, responding rapidly returned to the pre-injection level. For the groups receiving either 5 or 10 mg/kg there was an increase in locomotor activity and a decrease in response latencies when compared to saline controls on Day 13. The 20 mg/kg dose initially disrupted avoidance, but not escape, responses but after 13 daily injections avoidance responses were near pre-injection levels even though locomotor activity remained above baseline. Results of the two experiments were identical for drug Day 13 suggesting that Ss injected and run daily had not merely learned to respond under the influence of the drug but had developed tolerance to the drug.     

The long-term effects of diazepam and pentylenetetrazol on behavioral sensitivity to a stressor

Rats were trained to bar press for sucrose reinforcement following daily injections of 20 mg/kg pentylenetetrazol (PTZ), 5 mg/kg diazepam (DZ), or saline. At the end of 12 days of this training, all injections were suspended for the remainder of the experiment. Five days later, the rats were given 10 days of Pavlovian fear conditioning (two trials per day) to establish a light as a shock signal. Next, the rats were returned to the bar press situation to test the capacity of the light to suppress responding. Rats previously treated with DZ showed stronger conditioned fear of the light than did rats originally trained following injections of either PTZ or saline. In contrast, bar pressing by PTZ-treated rats was less suppressed by light than was control performance. The results indicate that modification of the behavioral effects of environmental stressors can be a long-term consequence of drug treatments. DZ treatments had the long-term effect of increasing behavioral disruption by a stressor, while treatment with PTZ reduced the stressor's negative behavioral impact. These findings appear compatible with the idea that behavioral sensitivity to stressors is dependent, in part, on learning about the stimulus properties of internal states.     

Protracted withdrawal: sensitization of the anxiogenic response to cocaine in rats concurrently treated with ethanol.

Rats were trained to respond on one lever following an injection of saline and the alternate lever after the anxiogenic drug pentylenetetrazol (PTZ 20 mg/kg), according to a fixed ratio (FR10) schedule of food reinforcement. The trained animals were then administered dependence-producing regimens of either cocaine (20 mg/kg, [IP], three times daily for 7 days) or ethanol (mixed 4.5% w/v with sweetened liquid diet given for 5 days). Separate groups of trained rats were given either subthreshold regimens of cocaine (20 mg/kg, IP, three times daily for 5 days), ethanol (2.25% w/v of the diet given for 5 days), or both. Additional groups were matched for control groups. After discontinuation of these regimens, rats were administered test injections of either saline or cocaine, and tested for elicitation of the PTZ-stimulus at selected intervals of withdrawal. After a saline injection, maximum elicitation of the PTZ-stimulus was observed 12 hours following chronic treatment with the higher dose of ethanol, and 120 hours following longer treatment with cocaine. During those periods of withdrawal when a saline injection failed to produce a PTZ-like stimulus, a test injection of cocaine (10 mg/kg) elicited the PTZ-stimulus in the ethanol withdrawn rats, although only partially eliciting the PTZ-stimulus in the cocaine withdrawn group. In the pair-fed controls, or rats withdrawn from the smaller dosage of either ethanol or cocaine, the test dose of saline or cocaine did not elicit the PTZ-stimulus; only 30% of rats selected the PTZ-appropriate level at the highest dose of cocaine tested (10 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)     

State dependent control of discrimination by morphine and pentobarbital

Rats were trained in state dependent discrimination to escape shock in a T-maze by turning one way under a drug and the other way under saline without aid of exteroceptive cues. In experiment 1, 9.0 nig/kg of morphine, 20 mg/kg of pentobarbital and 0.3 cc of saline were used with a balanced order of training which employed 18 training days under one condition followed by 18 days in the other condition; twelve test days were then given in which conditions were alternated daily. Pentobarbital produced strong state dependent behavior but morphine did not. Experiment 2 used 4.5, 9.0, 18.0, and 36.0 mg/kg of morphine and 0.3 cc of saline with the same procedures as for the first study. Orderly state dependent learning was not found. In experiment 3, the dose levels and procedures were the same as for the second study except that training under the two conditions was carried out concurrently, i.e. morphine and saline trials were given alternately in balanced order. Highly significant dose-related state dependent behavior occurred in both the training and test periods. The results were discussed in relation to state dependent learning, dissociation and opiate addiction.Retired.     

Tolerance,withdrawal, and supersensitivity to dopamine mediated cues in a drug-drug discrimination

Rats were trained to discriminate between 0.25 mg/kg amphetamine (AMPH) and 0.03 mg/kg haloperidol (HAL) in a two-lever drug discrimination task. In order to test for a drug-induced withdrawal state, animals were assigned to one of three chronic treatment groups and given injections of AMPH, HAL, or distilled water (DW) for 10 consecutive days. Subjects from each treatment condition were then tested at 24, 48, or 72 h after the final injection. At the 24 h retest interval, subjects injected with AMPH responded as though administered an acute dose of HAL (0.028 mg/kg) and subjects injected with chronic HAL responded as though administered an acute dose of AMPH (0.15 mg/kg). By 72 h choice behavior had returned to pretreatment values. To determine whether the rebound observed after 10 days of drug treatment was present after a single injection, independent groups of subjects were injected with single doses of either 10 mg/kg AMPH or 1.0 mg/kg HAL and then retested from 4 h to 48 h later. Single doses of both AMPH and HAL produced significant rebounds that peaked between 20 h (AMPH) and 24 h (HAL) following administration. In a third experiment, animals were tested with or without acute doses of drug following pretreatment with either HAL or AMPH. Receptor supersensitivity accounts for the tolerance observed to HAL 24 h after treatment with 1.0 mg/kg HAL, whereas receptor subsensitivity accounts for the tolerance observed 20 h after treatment with 10 mg/kg AMPH.Some of the data presented here was presented at the meeting of the Society for Neurosciences, New Orleans, 1991.     

Time-dependent retrograde amnesic effects of muscimol on conditioned taste aversion extinction

We explored how stimulation of GABA_A receptors at different times during conditioned taste aversion (CTA) acquisition or extinction influenced extinction. In Experiment 1, rats acquired a CTA to 0.3% saccharin-flavored water (SAC) when it followed an injection of lithium chloride (LiCl; 81.0 mg/kg, i.p.). Following conditioning, rats received extinction training in which the GABA_A agonist muscimol (1.0 mg/kg, i.p.), or control (saline) injections, were administered either before or after each extinction trial. Muscimol hindered extinction when administered after extinction trials. Muscimol's inhibitory effects may have impeded extinction learning by disrupting synaptic mechanisms required to consolidate information experienced during extinction training. In Experiment 2, we studied the effects of muscimol on CTA acquisition and subsequent extinction. Rats received muscimol (1.0 mg/kg, i.p.) either before or after CTA conditioning trials. Following CTA acquisition, all rats were given CTA extinction training without muscimol administration. All groups developed CTA, but the group that received muscimol before CTA conditioning trials extinguished rapidly in comparison to other treatment groups. Differences between muscimol's effects on CTA conditioning and CTA extinction indicate that fear conditioning and extinction involve, to some degree, different neuronal mechanisms.     

Lack of tolerance development to benzodiazepines in antagonism of the pentylenetetrazol discriminative stimulus.

In an operant procedure of lever pressing on FR 10 schedule of food reinforcement male hooded rats were trained to respond on a lever on one side of a food cup following a 20 mg/kg pentylenetetrazol (PTZ) injection and to respond on a lever on the alternate side following a 1 ml/kg saline injection. Upon acquisition of the PTZ-saline discrimination, diazepam and chlordiazepoxide were tested and found to antagonize the PTZ discriminative stimulus. The animals were then injected with 10 mg/kg diazepam or chlordiazepoxide for ten consecutive days. New dose-response curves obtained following this treatment indicated that tolerance did not develop to the antagonism of the PTZ discriminative stimulus by these benzodiazepines.     

The class I metabotropic glutamate receptor antagonist, AIDA, improves short-term and impairs long-term memory in a spatial task for rats.

Effects of the class I selective metabotropic glutamate receptor antagonist, 1-aminoindan-1,5-dicarboxylic acid (AIDA), on spatial procedural learning and episodic short-term memory of rats were investigated in an appetitively reinforced 3-choice delayed match-to-position task. First, an acute intraperitoneal injection of AIDA (2 mg/kg) was given 20 min before a single training session of 20 trials using repeated reward position in one alcove out of three. AIDA caused facilitated short-term acquisition within such a session compared to saline treated controls. Secondly, injections were given before each of ten sessions (48 h intervals) also using constant reward position. The results showed AIDA induced inhibition of procedural between-session acquisition. Finally, the use of reward positions in a non-repetitive but trial-specific version of the 3-choice test revealed a facilitating effect of AIDA on episodic short-term memory.     

Cycloheximide and passive avoidance memory in mice: Time-response,dose-response and short-term memory

The greatest loss of memory shown by mice 24 hr after learning was found to occur with cycloheximide (CXM) (120 mg/kg) administered subcutaneously 30 min before training. With injection at this time the extent of the amnesia was done dependent (30–150 mg/kg) and the resultant amnesia was found to be relatively constant when tested at 1, 7 or 14 days. An attempt was made to follow the development of this amnesia with 100 and 120 mg/kg CXM. However, the saline controls showed an unexpectedly low avoidance 6 hr after training. This was interpreted as a possible interaction between the stress of the injection and the 6 hr interval. An experiment designed to test this possibility showed that mice injected with 0.1 ml of 1% lignocaine gave high avoidance at 6 hr but mice receiving only a needle puncture of the skin gave performances similar to mice receiving saline injections. It was felt that these findings cast doubt on the usefulness of the passive avoidance task in the assessment of drug action on short term memory.     

Possible cholinergic-dopaminergic link in memory facilitation induced by oxotremorine in mice

The immediate post-trial injection of the centrally active muscarinic agonist oxotremorine (0.025, 0.050 and 0.100 mg/kg, IP) can facilitate the retention of a passive-avoidance response in mice, as indicated by performance on a retention test 24 h later. Injections given 10 min after training also significantly facilitated retention, but given 120 min after training did not affect retention. These findings suggest an action of oxotremorine on memory mechanisms. The enhanced retention was neither the result of a punishing effect of oxotremorine nor of a nonspecific proactive pharmacological action of the drug. The memory facilitation produced by oxotremorine (0.050 mg/kg, IP) was not antagonized by pretreatment with phentolamine (10 mg/kg, 30 min, IP), phenoxybenzamine (10 mg/kg, 120 min, IP) or piperoxane (20 mg/kg, 30 min, IP). The alpha-noradrenergic blocking agents had no effect by themselves. On the other hand, the immediate post-trial injection of oxotremorine (0.050 mg/kg, IP) did not enhance retention when mice were pretreated with haloperidol (0.5 mg/kg, 120 min, IP). Haloperidol injected either before training or before the retention test did not alter performance during the retention test. This suggests that haloperidol impairs neither acquisition of the avoidance response nor its retrieval. Thus, it is probable that haloperidol pretreatment impaired oxotremorine-induced memory facilitation. We suggest a possible participation of brain catecholamines in memory facilitation induced by oxotremorine in mice.     

State dependent learning produced by post trial intrathoracic administration of sodium pentobarbital

The state dependent learning paradigm was used with a one-trial, passive avoidance task. Forty male rats were equally distributed among four groups: One group received intrathoracic injections of sodium pentobarbital immediately after the acquisition trial and immediately before the retention test trial; a second group received equivalent injections of 0.9% saline; a third group was drugged after acquisition and given saline prior to retention testing and the fourth group was given saline after acquisition and drug prior to retention testing. All groups showed increased latencies on the retention trial but marked group differences in retention test latencies indicate that there was significantly more retention of training when drug states were the same during the memory storage interval and the memory retrieval interval. Intrathoracic injection proved to be a practical substitute for intravenous injection in assuring rapid onset of drug effect.     

Acute and chronic effects of LSD and 3,4-dimethoxyphenylethylamine on shuttlebox escape/avoidance in rats

Three experiments were conducted in rats to study the effects of acute and chronic LSD and 3,4-dimethoxyphenylethylamine (DMPEA) on acquisition of shuttlebox escape/avoidance and of acute DMPEA on performance in the shuttlebox of pretrained poor performers. In Experiments 1 and 2, separate groups of male hooded rats were injected (i.p.) either once with LSD (0.1 or 0.5 mg/kg),DMPEA (25, 50, or 100 mg/kg) or saline or daily for 5 days with LSD (0.5 mg/kg), DMPEA (25 or 100 mg/kg) or saline before an initial acquisition test. The acute drug groups were retested 24 h later under saline. In Experiment 3, pretrained rats which had achieved a low, stable baseline rate of shuttlebox performance were injected once with DMPEA (50 mg/kg) before a performance test and retested 24 h later under saline. It was found that all LSD treatments decreases escape/avoidance latencies (excitatory effect) on the acquisition test and saline retest, while all DMPEA treatments were without effect.This research was supported by grants No. ID5TI MH 6418, No. 5 KO5 MH 04177, and No. 5T5-GM1674 from the National Institutes of Health, U.S.A.     

Behavioral and biochemical correlates of chronic administration of quipazine

In Experiment 1 groups of rats received single injections of 1, 3, 10, 20 or 40 mg/kg quipazine, and their total 24-hr food and water intake after a 24-hr deprivation period was recorded; there was a dose-related reduction of both food and water intake. In Experiment 2 a group of 15 rats received 5 mg/kg/day, SC quipazine during 29 days, and a control group received saline injections. During treatment, all animals were exposed to a 24-hr food and water deprivation schedule, alternated with 24 hr of free access. Food and water consumption was measured 2 and 24 hr after drug injection; regional 5-HT concentrations were determined at 1 and 13 treatment days by fluorometric assay. Beginning the first treatment day, food and water intake decreased, but by the 13th day the quipazine group had returned to normal ingestion levels. 5-HT concentrations were increased in cerebellum and cortex in acute conditions, but after 13 days they had decreased in cerebellar samples. In Experiment 3 we found that the effects of quipazine on food and water ingestion were recovered after 14 days of discontinuing chronic drug administration.     

The effects of pentylenetetrazol, bicuculline and strychnine on the development of kindled seizures

Modification of the rate of acquisition of the kindled amygdaloid seizure by the convulsants pentylenetetrazol, bicuculline and strychnine was studied. Injections of saline, 25 mg/kg of pentylenetetrazol, 2 mg/kg of bicuculline or 1 mg/kg of strychnine were given 15 min prior to the daily electrical stimulation of the amygdala. The drug doses selected were capable of producing some behavioral and electrical epileptoid activity prior to stimulation without inducing generalized seizures. To determine whether pentylenetetrazol or bicuculline accelerated the rate of development of the kindled amygdaloid seizure or merely augmented the expression of each seizure, a crossover design was implemented. The crossover studies involved switching animals during the acquisition phase (between stimulations 3–6) from prestimulation saline to drug or drug to saline injections. It was found that pentylenetetrazol markedly augmented the expression of seizures during kindling development but the results of the crossover studies showed a less dramatic acceleration in the actual rate of the development of the fully generalized kindled amygdaloid seizure. The bicuculline-treated animals showed little augmentation in the expression of seizures during the kindling acquisition phase and in the actual rate of development of the kindled amygdaloid seizure. The strychnine treated animals showed no augmentation in expression of the seizures nor in the rate of development. The effects of prestimulation injections of bicuculline (1, 2 and 3 mg/kg) and strychnine (0.5, 1 and 2 mg/kg) on fully developed kindled amygdaloid seizures were also evaluated. Pretreatment with bicuculline minimally increased seizure afterdischarge duration at the highest dose. When fully kindled animals were pretreated with strychnine, a paradoxical decrease in afterdischarge length and an increase in severity (tonic hindlimb extension) was seen with the largest dose tested. This study emphasizes the potential importance of crossover studies in evaluating pharmacological manipulations of the rate of acquisition of the kindled seizure.     

A method to shorten the training phase of drug discrimination

Rats were trained to discriminate drug from no drug in a two-lever, food-reinforced task. One group was trained with cocaine (10 mg/kg) and a second group was trained with pentylenetetrazol (20 mg/kg). A method designed to shorten the time required for the training phase of drug discrimination experiments was assessed in subgroups for each drug. In one subgroup, single training sessions were conducted daily. In the other subgroup, a second session (either drug or saline) was conducted on days for which the first condition was saline. The training conditions were presented in an irregular sequence, with the same condition occurring in no more than two consecutive sessions. Rats trained by the accelerated method learned the discrimination in fewer days, with no decrement in acquisition per session, suggesting that drug discrimination training can be accomplished more rapidly by reducing inter-session interval.