Some effects of meprobamate on conditioned fear and emotional behavior

Animal models of anxiety based on classical conditioning: the conditioned emotional response (CER) and the fear-potentiated startle effect

Stimuli consistently paired with shock become capable of suppressing ongoing operant or consummatory behavior (the conditioned emotional response--CER) or elevating the amplitude of the startle reflex (fear-potentiated startle). These changes are used to infer a central state of fear which involves the central nucleus of the amygdala and its efferent projections to the brainstem. The present paper reviews how psychoactive drugs affect these measures. Both the CER and fear-potentiated startle are reduced by benzodiazepines, barbiturates and opiates. Advantages and disadvantages of these animal tests of anxiety are discussed.

Behavioral analogues of anxiety. Animal models

In the absence of fully characterized biological indexes, anxiety is at present measured as unpleasant effects reported verbally by patients. Because of the subjective nature of the syndrome, animal analogues have been difficult to design, but quests for new anxiolytics and a deeper understanding of the neurobiology of anxiety have fostered the development of several animal models. Usually, animals are exposed to exteroceptive or interoceptive stimuli which can be interpreted as capable of causing anxiety in humans. Then, the animals are observed for responses or behavioral deficits resulting from those stimuli in order to provide an index of anxiety. Behavioral responses that are reliably produced by those stimuli and that are also antagonized by anxiolytic drugs are accepted as analogues of anxiety. Exteroceptive stimuli, useful in this respect, consist of a variety of noxious treatments such as exposure to conflict-situations or unavoidable electric shock, whereas interoceptive stimuli consist of treatment with anxiogenic drugs or electrical stimulation of selected brain areas. Elicitation of unconditioned behavior or changes in the rate of conditioned (learned) responding have been employed as measures of anxiety responses following application of either exteroceptive or interoceptive stimuli. These measures, although useful in detecting anxiolytic drugs, possess several weaknesses. They suffer from difficulties in obtaining quantitative and objective data, they do not differentiate between anxiety and stress or fear, they are unable to measure further deterioration of behavior expected to occur when more potent anxiogenic stimuli are tested and they often present difficulty in differentiating direct motor effects of a number of stimuli are not related to anxiety. More recently, interest in the development of other analogues of anxiety has led to the use of drug-discrimination paradigms. In this approach, interoceptive discriminative stimuli, produced by anxiogenic drugs, are used as analogues of anxiety in animals. As an example of this approach, data are reviewed showing that pentylenetetrazol, an anxiogenic drug in humans, produces interoceptive stimuli which can be readily discriminated by rats. Further, these stimuli can be easily quantified through dose-response analysis. All known anxiogenic drugs generalize to pentylenetetrazol-induced interoceptive discriminative stimuli. Similarly, other anxiety-provoking situations in humans, such as withdrawal from dependence on benzodiazepines, also generalize to the pentylenetetrazol-induced stimuli. Alternatively, all known anxiolytic drugs antagonize these stimuli with a relative potency similar to

The effects of chronic morphine administration upon a modified Sidman avoidance schedule that utilizes response-independent shock

Six male squirrel monkeys were subjected to a Sidman nondiscriminated avoidance schedule (R-S, S-S-20 sec) that superimposed 3-min conditioned stimuli (CS) unavoidable shock pairings upon the ongoing avoidance behavior. Five of the 6 animals demonstrated facilitated avoidance response rates during the CS, while one animal demonstrated suppressed rates during the CS. Morphine sulfate (0.5, 1.0, 2.0, 3.0, 4.0 mg/kg) altered these patterns, causing the suppressor to facilitate, while the facilitators demonstrated reduced levels of response elevation during the aversive CS. Morphine also led to a reliable reduction in overall response rate and an increase in the number of shocks received. No consistent drug effects were noted with regard to general motor activity. These results were interpreted to suggest that a potent analgesic agent, such as morphine, was able to reduce the level of fear motivation normally generated by the aversive CS. Since changes in relative rate during the aversive CS were quite reliable both within and between animals, it was suggested that this behavioral schedule might prove useful in assaying the fear-reducing qualities of a variety of drugs. A cautionary note, however, indicated that other explanations, most notably, a rate dependent hypothesis, could account for the data without assuming the level of fear was altered.

Anxiety, meprobamate, d-amphetamine and the intrasubject variability of word associates

Two experiments on the intra-subject variability of word associates are reported. Exp. 1 indicates that Ss high in anxiety have more variable word associates than Ss low in anxiety. Exp. 2 investigated the joint effects of anxiety and the drugs, meprobamate and d-Amphetamine. Meprobamate reduced variability, d-Amphetamine increased variability. There was a significant drug × anxiety interaction. High-anxiety Ss were more variable than low-anxiety Ss under meprobamate and placebo conditions but less variable under d-Amphetamine conditions. The results are discussed in conjunction with the Hullian proposal of additivity of different sources of drive. It is concluded that other sources of drive detract from the drive-arousing properties of anxiety.

Effect of chlorpromazine on septal hyperactivity in the rat

The effect of chlorpromazine on the overt emotional activity of a hybrid strain of rats has been measured using an altered "emotionality rating scale." It has been found that 8 mg/kg of chlorpromazine intraperitoneally reduced the activity of rats with the septal nuclei destroyed, normal rats and control rats to the same emotional rating. This effect has been related to the postulated interrelationship of the septal area and the amygdaloid complex of nuclei. It seemed that impulses traversing the septal nuclei might be re-routed, so that destruction of the septal area need not necessarily cause total abolition of "septal-function."

Effect of Lesions in the Septal Forebrain of the Rat on Sleeping Time under Barbiturate

Rats with electrolytic lesions in the septal forebrain show increased sleeping times after injection with thiopental sodium or barbital, as compared with normal and other control rats and rats with lesions in the cerebral cortex or caudate nucleus.