Drugs, shock intensity, and the CER

Facilitated Recovery from Punishment-Induced Suppression

14 rats were maintained at 80% of their free-feeding weights and trained to press a bar on a chained variable-interval 1/2 fixed-ratio 20 schedule of reinforcement. In Exp. I a discriminative stimulus paired with the ratio component of the chain was shown to control a high rate of responding. In Exp. II, it was demonstrated that this stimulus, when superimposed on a stimulus which had been associated with punishment and therefore controlled a low rate of bar-pressing, facilitated recovery from the effects of punishment.

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.

Effects of mild cardiovascular and cerebrovascular disorders on serial reaction time performance

Medical examinations were used to classify 271 adults aged 18-77 into 6 groups: normotensive, treated and untreated hypertensive, coronary heart disease (CHD), transient ischemic attack (TIA), and recovered stroke. They were also divided by age into 3 groups: 18-36, 37-55, and over 55 years. Each subject completed 12 reaction time (RT) tasks which involved making 16 consecutive responses without interruption. Serial RT increased with age throughout the lifespan. RT was also increased in treated hypertensive patients; this slowing was unrelated to type of drug treatment. Patients with cerebrovascular disorders showed greater slowing and also made more errors; TIA patients showed greatest impairment. No significant performance deficits were observed in untreated hypertensive or CHD groups. However, a trend toward slowing among untreated hypertensive patients with high plasma renin activity was observed. Behavioral deficits associated with both aging and diagnosed vascular disorders were interpreted as evidence of impaired brain function.

Amphetamine and conditioned 'anxiety'

1. Rats pressed a bar for milk reward at a steady rate, but this baseline responding was suppressed in the presence of an auditory stimulus associated with electric shock (conditioned suppression). The effects of (+)-amphetamine sulphate on this conditioned suppression were studied in two experiments.2. (+)-Amphetamine sulphate (0.5, 1.0 or 2.0 mg/kg) reduced the baseline rate of responding and also reduced the conditioned suppression, i.e. responding in the presence of the auditory stimulus was partially restored. Both these effects were dose related.3. In a further experiment the effects of 1.0 mg/kg on two levels of conditioned suppression were studied. Regardless of its degree, (+)-amphetamine attenuated suppression.4. The results were compared to previous research which found that amphetamine increased baseline responding and exaggerated conditioned suppression. It was concluded that the conditioned suppression procedure should be used with caution as an animal model of anxiety in psychopharmacological investigations.

Modification of the autonomic component of the conditioned emotional response

A series of experiments was conducted to clarify the role of the autonomic nervous system in the acquisition and maintenance of the conditioned emotional response (CER). In Exp. 1 the reactivity of either the sympathetic or the parasympathetic system was altered by drugs during maintenance testing of the CER. 12 rats were trained to bar-press for sugar water on a VI 30-sec. schedule; 6 CER trials were administered during each 2-hr. session. The intensity of the unconditioned stimulus (electric shock) was adjusted for each S so as to suppress responding during the CER signal (tone) to approximately 50% of normal pressing rate. Neither the sympathetic agents (adrenalin, Chlorpromazine, Dibenzyline), nor the parasympathetic agents (methacholine chloride, propantheline, atropine sulfate) reliably altered bar-press rates during the CER trials. Exp. 2 demonstrated that the autonomic agents, in the dosages used, were in fact altering autonomic reactivity as indexed by heart-rate measures. In Exp. 3 acquisition of the CER by 18 rats was found not to be affected by autonomic alteration as produced by drugs.