Aversive Footshock Research Articles

In vitro Adrenocortical Responsiveness to ACTH in Rats Subjected to Different Emotional Situations

Corticosterone production in isolated adrenocortical cells from adult male Wistar rats subjected to different emotional situations and the possible relationship between adrenocortical and behavioral responses were studied. On the basis of an inhibitory avoidance paradigm (IAP), in which the innate preference of rats for a dark environment is suppressed by application of an aversive electric footshock (acquisition trial, AT), the following set of conditions was studied: Rats trained in the IAP (a) without application of electric footshock; (b) with application of electric footshock; (c) rats trained as in (b) but subjected to forced extinction (by staying for 5 min in the dark compartment 24 h after the AT, the animals overcome their fear for the dark box). Rats trained in conditions (a) and (c) displayed significantly shorter retention latencies, and concomitantly showed a significantly lower adrenocortical responsiveness than rats trained under condition (b). However, no significant differences in circulating ACTH or corticosterone levels among the various experimental groups were found. Furthermore, animals tested for retention 24, 48, 72 or 168 h after the AT showed an increased loss of the behavioural response so that the greater the time lapse, the more the retention behavior diminished concomitantly with the adrenocortical responsiveness to ACTH. Our results suggest that a good retention of the newly acquired behavior is related to an increased adrenocortical responsiveness to ACTH. Forced or innate extinction of the same behavior is accompanied by a diminished adrenocortical responsiveness. Taken together, these results also emphasize that altered adrenal responsiveness to ACTH is a better and more accurate index of the degree of emotionality associated with different behavioral performances than 'punctual' ACTH or corticosterone plasma levels.

Brain stimulation of the ventral tegmental area attenuates footshock escape: an in vivo autoradiographic analysis of opiate receptors

An in vivo autoradiographic technique was employed to visualize discrete neuroanatomical changes in opiate receptor binding as a result of aversive footshock (FS) and rewarding electrical brain stimulation (ICS). Footshock-induced escape responding was shown to be attenuated by the simultaneous presentation of non-contingent ICS. Rats were divided into 4 groups ( n = 6) receiving ICS, FS, ICS + FS or neither stimulus in an escape paradigm. During the final behavioral test session, rats were injected with 0.002 mg/kg [ 3H]diprenorphine ([ 3H]Dpr) and subsequently prepared for autoradiography. Results indicated two groups of brain areas distinguishable by their treatment-induced changes in [ 3H]Dpr binding. One group of areas included the nucleus accumbens, claustrum, claustrocortex, perirhinal cortex and ventral tegmental area. These structures showed increased binding due to both FS and ICS. The other group consisted of the diagonal band of Broca, bed nucleus of the stria terminalis, lateral hypothalamus-medial forebrain bundle and amygdala. In these regions, an increase in binding ipsilateral to the electrode was observed in animals receiving ICS with no apparent effect of FS. These results demonstrate that non-contingent ICS may not be strictly aversive and suggest an anatomic, opioid-sensitive basis for both a rewarding and aversive component of this stimulus. It appears, further, that ICS can inhibit the release of endogenous opioid peptides in areas along the mesotelencephalic dopamine pathways, possibly to regulate the activity of neurons conveying reward information. Finally, the observed changes in opiate receptor binding may indicate a mechanism for ICS to produce both drive and reward.

Exploratory response habituation and the attenuating effect of an amphetamine-barbiturate mixture.

Mutual potentiation between dl-amphetamine (0.75 mg/kg) and amylobarbitone (15.0 mg/kg) can occur, measured as a marked increase in locomotor exploratory responses in the rat (Rushton and Steinberg, 1963). Experiment 1 confirms the potentiation between amphetamine and amylobarbitone, and extends the finding to a distinctly different type of exploratory behaviour (the 'head-poke' response). However, the same amphetamine-barbiturate mixture did not affect the preference for responses rewarded by a light-onset contingency (Expt. 1), and also did not affect the threshold of a response elicited by aversive footshock (Expt. 2). The mixture may facilitate the occurrence of exploratory responses by a direct attenuation of the rate of habituation of the exploratory responses, and not secondarily by altering the reward or aversion of external stimuli, or by changing the animal's level of arousal.