Effects of diazepam and triazolam on auditory and visual thresholds and reaction times in the baboon

Perceptual and motor effects of morphine and buprenorphine in baboons

The effects of morphine and buprenorphine on auditory perceptual discriminations and response latency ("reaction time") in baboons are compared. The task employed synthetic human vowel sounds that are readily generated in the laboratory, and closely approximate natural baboon "grunt" vocalizations [J. Acoust. Soc. Am. 101 (1997) 2951]. Baboons pressed a lever to produce one repeating "standard" vowel, and released the lever only when one of four other "comparison" vowels occasionally occurred in place of the standard vowel. The percentage of correct detections and median reaction time for each comparison were measured following intramuscular drug administrations of morphine (0.01-1.8 mg/kg) and buprenorphine (0.00032-0.032 mg/kg). Both morphine and buprenorphine impaired vowel discriminability, and greater impairments occurred for those comparison vowels that were more similar in formant structure to the standard vowel. Morphine increased reaction time in all baboons, and buprenorphine increased reaction time in two of three baboons. Morphine's perceptual effects occurred within 20-40 min following drug administration; buprenorphine's perceptual effects occurred 50-100 min following drug administration. Morphine and buprenorphine did not differ in the time course of their maximal reaction time effects. The results demonstrate that both morphine and buprenorphine can impair auditory discriminations involving human vowel sounds in baboons, as well as lengthen reaction times to the stimuli.

Impulsivity as a confounding factor in certain animal tests of cognitive function

Performance in cognitive tasks which require the subject to wait and/or to process a large amount of information can be disrupted by an increase in impulsive-like behaviour. Accordingly, a decrease in impulsive-like behaviour can improve performance in such tasks. Conversely, impulsive-like behaviour may improve performance in cognitive tasks where simple and fast responses and/or only little information processing is required. Thus, impulsivity constitutes a confounding factor in studies of cognitive function. Impulsive-like behaviour may be modified by serotonergic (5-HT) activity, with underactivity in 5-HT neurotransmission increasing impulsivity and vice versa. Drug- or lesion-induced alteration in 5-HT neurotransmission may, therefore, constitute suitable tools to investigate the role of impulsivity in animal tests of cognitive function. Benzodiazepines also increase impulsive-like behaviour, possibly by decreasing 5-HT neurotransmission. Hence, the effects of modulation of 5-HT systems and of the benzodiazepine-binding site on performance in animals tests of cognitive function will be discussed. It is predicted that the effects of manipulations of serotonergic activity or of benzodiazepine administration depend upon the nature of the response required, and that these effects may be mediated through changes in impulse control.

The effects of scopolamine, lorazepam, and glycopyrrolate on classical conditioning of the human eyeblink response

Human eyeblink conditioning, a relatively simple form of learning and memory, has previously been shown to be impaired by the central and peripheral anticholinergic scopolamine. The present study compared the behavioral effects of scopolamine with the benzodiazepine lorazepam and a peripherally active anticholinergic, glycopyrrolate. Thirty-six healthy normal volunteers (mean age: 23.7 years) were studied with 12 assigned double-blind to each of three drug conditions (0.5 mg scopolamine IV, 2 mg lorazepam PO, or 0.2 mg glycopyrrolate IV). Subjects underwent classical conditioning of the eyeblink response in which the conditioned stimulus was an 80 dB binaural tone, and the unconditioned stimulus was a 2 psi airpuff to the right eye. Ten trials of unpaired stimulus presentations were followed by 60 paired trials and finally by an extinction period of five tone-alone presentations. An eyeblink response that occurred during the tone but before the airpuff was scored as a conditioned response (CR). Subjects treated with lorazepam (43% mean CRs) and scopolamine (51% mean CRs) exhibited a significantly lower asymptotic level of conditioning than those treated with glycopyrrolate (85% mean CRs; P < 0.01). However, during extinction, lorazepam-treated subjects (35% CRs) showed a lower overall level of responding to the tone than either scopolamine (60% CRs) or glycopyrrolate (62% CRs) treated subjects (P < 0.05). It seems unlikely that these differences could be accounted for by drug-induced alterations in motor responses because there were no significant differences between the three drug conditions in the frequency, latency, or amplitude of unconditioned responses to the airpuff. Overall, our data indicate that scopolamine and lorazepam impair eyeblink conditioning and suggest that some of the effects of benzodiazepines and anticholinergics on learning and memory can be differentiated using this paradigm.

Primacy and recency effects in rhesus monkeys (Macaca mulatta) using a serial probe recognition task. I. Effects of diazepam

In this study, we evaluated the effects of diazepam (0.2, 0.8, 1.6 and 3.2 mg/kg; IM) on the primacy and recency memory effects in four rhesus monkeys trained on a six-item serial probe recognition (SPR) task. Only the highest dose of diazepam (3.2 mg/kg) consistently affected the shape of the monkeys' serial position curves. Accuracy on the probe trials was disrupted for list items which occurred in the middle portion and recency memory component of the serial position curve, without affecting the primacy component. Diazepam, however, also produced several nonspecific effects on SPR performance. Both the 1.6 and 3.2 mg/kg diazepam doses disrupted accuracy on the non-matching probe trials, and the 3.2 mg/kg dose caused an increase in response latencies which were unrelated to any one component of the serial position curve. This is the first demonstration in nonhuman primates showing that the primacy and recency memory effects can be differentiated on the basis of diazepam dose.

Effects of cocaine on sensory motor function in baboons

The effects of cocaine on auditory and visual threshold functions and reaction times were studied in baboons. Single IM injections of cocaine HCl (0.001-1.0 mg/kg) were administered once or twice weekly and were followed immediately by psychophysical tests designed to assess cocaine's effects on sensory thresholds and reaction times. Consistent reductions in reaction times were observed in the cocaine dose range of 0.032-0.32 mg/kg. Reaction times were decreased by 5-8% at the more effective cocaine doses. Concurrently measured auditory and visual threshold sensitivities showed no systematic changes at any of the cocaine doses studied.

Triazolam and ethanol effects on human matching-to-sample performance vary as a function of pattern size and discriminability

The effects of placebo, triazolam (2.0, 4.0 and 8.0 micrograms/kg) and ethanol (0.25, 0.5, 1.0 g/kg) on perceptual-motor performance were examined using a visual pattern matching-to-sample procedure in which pattern size and comparison stimulus discriminability were systematically varied. Baseline response rates and accuracy increased as the discriminability of the comparison stimuli increased. At the highest dose, both drugs decreased response accuracy. This disruption of accuracy was attenuated by increasing the discriminability of non-matching stimuli. Triazolam produced dose-related decreases in response rate while ethanol produced only slight decreases at the highest baseline rates of responding. Thus, triazolam produced response rate slowing at relatively lower doses than ethanol.

Animal models for assessing drugs of abuse

A major toxic effect that has limited the clinical usefulness of medicinal drugs has been their susceptibility to nonmedical use and abuse by significant segments of the population. Major research efforts have been directed toward the development of safer and more effective therapeutic agents that would not be subject to such misuse, and laboratory animal assessment models have contributed importantly to the evaluation of such compounds. There are now several converging lines of evidence that testify to the reliability and broad generality of observations concerning drug abuse liability in humans based upon such animal laboratory models. The most important point of contact that characterizes the interaction between such animal assessment models and the human drug abuse arena is the demonstrated relationship between the biochemical/pharmacological/toxic properties of drugs on the one hand, and their environmental/behavioral stimulus functions on the other. As a result of these developments in animal model research technology and the consequent advances in knowledge of drug action, an operational basis has been provided for redefining the bewildering range of phenomena and experiential pseudo-phenomena loosely identify with such terms as "addition," "dependence" and "abuse."

Benzodiazepine-induced impairment of matching-to-sample performance in humans

The effects of benzodiazepines on a visual pattern matching-to-sample (MTS) task were examined in nine healthy male volunteers. The MTS task employed randomly generated checkerboard-like stimuli presented on a video display. The sample and two comparison stimuli were simultaneously presented. Nonmatching comparison stimuli were randomly generated to be 3.125, 6.25, 12.5, 25.0, 37.5, or 50.0 percent different from the sample. Subjects responded on left or right button manipulanda to identify the matching comparison stimulus. The nonmatching stimulus condition was maintained constant for a 60-sec component and the percentage difference of the nonmatching stimuli was systematically varied across multiple components. The effects of triazolam (2.25-9.0 micrograms/kg) and lorazepam (7.5-45 micrograms/kg) were examined in a within-subjects, double-blind, placebo-controlled study. Under placebo conditions, response rates and accuracy were a positive function of the nonmatching stimulus discriminability. Triazolam produced dose-related decreases in response rate at nonmatching stimulus conditions greater than or equal to 25%. Only the 9.0 micrograms/kg dose of triazolam decreased accuracy and this occurred across all nonmatching stimulus conditions. Lorazepam effects were qualitatively similar but less robust than those of triazolam.

Ethanol's effects on auditory thresholds and reaction times during the acquisition of chronic ethanol self-administration in baboons

Baboons were trained to ingest ethanol at successively higher ethanol concentrations using oral self-administration techniques. Concurrently, animal psychophysical procedures were employed to determine auditory thresholds and reaction times daily. Maximal consumption of ethanol occurred at concentrations of 6-8% (w/v). During the initial period of ethanol self-administration, both auditory reaction times and auditory thresholds became elevated as animals consumed larger amounts of ethanol. For both the threshold and reaction time measures, the degree of elevation was correlated with the amount of ethanol consumed. These correlations decreased, however, with continued ethanol consumption. The elevations in sensory and motor function recovered to near-baseline levels when ethanol was no longer available.

Multiple behavioral effects of diazepam in rhesus monkeys

The acute effects of diazepam (Valium) were assessed using a battery of complex food-reinforced operant tasks that included responding in delayed matching to sample (DMTS, n = 5), conditioned position response (CPR, n = 7) progressive ratio (PR, n = 8), temporal response differentiation (TRD, n = 4), and incremental repeated acquisition (IRA, n = 9) tests. Diazepam (0.25-4.0 mg/kg IV) produced significant dose-dependent decreases in the number of reinforcers obtained in the TRD and IRA tasks only. TRD accuracy was significantly decreased at doses of 0.25, 1.0, 2.0, and 4.0 mg/kg when compared to vehicle injections. Significant decreases in IRA accuracy generally did not occur at doses below 1.0 mg/kg. DMTS accuracy was decreased at 0.5 mg/kg for some time delays but showed no clear dose-delay interaction. Performance in the CPR and PR tests showed no significant effects of diazepam exposure over the dose range tested. These results indicate that diazepam selectively disrupts performance of operant tasks in monkeys designed to model human correlates of time perception, learning ability and visual attention/short-term memory while not affecting tasks designed to model motivation and position/color discrimination.

Diazepam and delta-9-THC: contrasting effects on the discrimination of speech sounds in nonhuman primates

The adult male baboons were trained on a psychophysical procedure to discriminate five synthetic, steady-state vowel sounds (/a/, /ae/, /e/, /U/, and /c/) from one another. A pulsed train of one vowel comprised the reference stimulus during a session. Animals were trained to press a lever and release the lever only when this reference vowel sound changed to one of the comparison vowels. All animals learned the vowel discriminations rapidly and, once learned, performed the discriminations at the 95-100% correct level. The IM administration of diazepam (0.32, 1.0, 3.2, and 10.0 mg/kg) produced dose-dependent decrements in vowel discriminability. The diazepam-induced decrements in vowel discriminability were correlated with the degree of spectral frequency differences found among the different vowels, with lower vowel discriminability scores found for those vowels with smaller spectral differences from the reference vowel. In contrast, oral administration of delta-9-THC (0.32, 1.0, 3.2, and 5.6 mg/kg) produced no decrements in vowel discriminability.

Effects of mephenytoin and methsuximide on the reaction time of pigeons

Although antiepilepsy drugs are used clinically, their behavioral effects are poorly understood. The present study examined the effects of mephenytoin and methsuximide, two antiepilepsy medications, on the reaction times of pigeons. Pigeons were trained to depress and hold a foot treadle until a stimulus change occurred. Releases within 2 sec of the stimulus change were reinforced with access to mixed grain; premature releases or releases occurring after the 2-sec limited hold were not reinforced. Mephenytoin (40, 60, 80, 120, and 160 mg/kg) and methsuximide (25, 50, 75, and 100 mg/kg) produced generally dose-dependent increases in median reaction times and decreases in percent responses that were reinforced. The present procedure has not previously been used with pigeons and is a promising technique for the study of reaction time with this species.

CGS 8216, a benzodiazepine receptor antagonist, enhances learning and memory in mice

Mice pretreated with the benzodiazepine antagonist, CGS 8216 (2.5, 10, or 40 mg/kg, i.p.) learned a T-maze discrimination to a fixed performance criterion more rapidly than vehicle-treated mice. In retention tests conducted one week later, the drug-treated groups had better first-trial recall and greater difficulty reversing the previously trained maze habit when compared with controls, suggesting improved memory for the previously trained maze habit. The enhanced acquisition and retention following CGS 8216 was similar to that observed previously with another benzodiazepine antagonist, flumazenil (Ro 15-1788). It is postulated that CGS 8216 and flumazenil could act at benzodiazepine receptors to antagonize a tonic inhibitory influence of endogenous, diazepam-like, benzodiazepine receptor ligands on memory processes.

Effects of benzodiazepines on acquisition and performance: a critical assessment

Evidence related to the effects of benzodiazepines on learning and memory is reviewed in the contexts of human verbal learning studies and animal studies using both aversive and non-aversive paradigms. While the impairment of acquisition by benzodiazepines appears to be a robust phenomenon generalizing across species and experimental conditions, the impairment in the performance of an already-learned task by such drugs appears to be more restrictive and highly dependent upon experimental contingencies. Thus far, performance impairment appears to be found mainly in animal studies using non-aversive, food-motivated tasks, with such tasks being particularly well suited for investigating such a phenomenon. At present, there is a noticeable lack of knowledge regarding the neurochemical substrates underlying BDZ-induced impairment. Finally, some issues that may contribute to the presence or absence of a BDZ-induced performance impairment in published studies are briefly considered.