William P. Smotherman

Mother infant attachment in the squirrel monkey adrenal response to separation

The pituitary-adrenal response following separation was evaluated in mother and infant squirrel monkeys. Four mother-infant pairs and a pregnant female, living in a social group, were the subjects of this experiment. The plasma cortisol levels of the mothers and infants were determined after the following conditions: (1) basal levels at 1100 hr, (2) 30 min after momentary separation and reunion, (3) 30 min after infant removal from the group, and (4) 30 min after mother removal from the group. The levels of plasma cortisol were significantly elevated in both mothers and infants following separation and the response was not reduced by the presence of familiar animals (e.g., separated infants which were “aunted” by the pregnant female). Separation followed by immediate reunion did not result in elevated values. These data indicate that a specific attachment relationship develops between mother and infant, and that the agitation following separation is reduced only by reunion with the object of attachment.

Plasma corticosterone levels during recovery from LiCl produced taste aversions

In two experiments, rats drank sweetened milk while in a non-deprived state. After five presentations, the milk was paired with lithium chloride (LiCl). In Experiment 1 plasma levels of corticosterone were determined on the first day of recovery after flavor toxicosis. Under these nondeprived conditions, subjects avoided ingesting the sweetened milk. This avoidance behavior was not accompanied by an activation of the pituitary-adrenal system. In Experiment 2, following the flavor-toxicosis pairing, animals were deprived chronically of food and water and thus “forced” to ingest milk that had earlier been paired with LiCl. Forcing subjects to ingest the sweetened milk led to increased levels of plasma corticosterone. The results demonstrated the task generality of pituitary-adrenal activation during avoidance responding.

Conditioned taste aversion and the pituitary-adrenal system.

Plasma corticosterone levels of male rats were found to be elevated for 2–4 hr following injection of a toxic dosage of LiCl, while pretreatment with dexamethasone suppressed this pituitary-adrenal activation. These data suggest that both ACTH and corticosteroid levels are elevated at the time of taste aversion conditioning. It was also found that treatment of subjects with dexamethasone prior to conditioning attenuated the aversion to the taste of milk produced by LiCl. Pretreatment with ACTH during conditioning and recovery prolonged the aversion. The results were interpreted in terms of the effect of the stimulus/feedback characteristics of high circulating ACTH levels during illness upon the taste-illness association.

Maternal responsiveness following differential pup treatment and mother-pup interactions

Abstract Pituitary-adrenal and behavioral responsiveness to rat pups which had been handled or shocked was assessed in mothers at Days 2, 9, and 16 postpartum. Mothers were exposed to these pups either directly where mother-infant contact was permitted or indirectly (pups placed in a wire mesh basket) where mother-infant contact was prevented. Handled and shocked pups elicited differential pituitary-adrenal responsiveness when mother-infant contact was prevented following pup treatment. Mothers responded more to shocked than to handled pups. While pup treatments elicited different patterns of maternal behavior, direct mother-infant contact subsequent to pup treatment eliminated the differential pattern of pituitary-adrenal responsiveness. These findings were discussed in terms of a parallel between behavioral and pituitary-adrenal indices of maternal responsiveness and the proposed role of maternal mediation in early experience effects.

Early handling effects on neophobia and conditioned taste aversion

Abstract The purpose of this study was to determine whether early handling, a manipulation which affects both behavioral and pituitary-adrenal responsiveness to novel and aversive situations, will affect responses in adult rats confronted with novel substances (neophobia) or with substances associated with illness (conditioned taste aversion). We found that (1) early handling reduces the neophobia shown by adult animals and that handled animals appear better able to distinguish between a preferred and a nonpreferred substance. (2) Handling reduces the magnitude of the initial taste aversion and also increases the rate of recovery of drinking to pretoxicosis levels. (3) These behavioral differences between handled and nonhandled animals are not due to differential pituitary-adrenal responses to LiCl. (4) Early handling does affect the conditioned elevation of plasma corticoids upon reexposure to milk under a Forced Extinction procedure. In this situation nonhandled animals show greater corticoid elevations than handled animals. (5) Manipulation of the number of exposures to a substance prior to pairing that substance with LiCl affects the magnitude of both the aversion and the elevation of plasma corticoids which are produced upon reexposure. As number of preexposures increase, both the magnitude of the aversion and the elevation of corticoids decrease.

Prolonged cortisol elevation in the infant squirrel monkey after reunion with mother.

Abstract Pituitary-adrenal response in mother and infant squirrel monkeys was assessed following either 30 min separation or 5, 15 and 30 min after a brief separation and reunion of mother and infant. Basal (undisturbed) samples were also obtained. The results revealed that there was an increment (28%) in plasma cortisol levels in the separation-reunion condition. This change was slight however when compared to the changes in plasma cortisol following separation (120%). A second experiment assessed plasma cortisol levels in mothers and infants that were reunited following a 30 min separation. Blood samples obtained 30 min after reunion indicated that the plasma cortisol levels in mothers had returned to basal levels, whereas the infants remained highly elevated during this period. Thus the effects of reunion following a very brief separation show the operation of an inhibitory process which occurs as a result of the interaction between mother and infant. Reunion following a longer separation appears to be more effective in reducing the pituitary-adrenal response in the mother than in the infant.

Plasma corticosterone levels as an index of the strength of illness induced taste aversions

Data are presented which demonstrate the task generality of pituitary-adrenal changes that accompany avoidance conditioning. In two experiments a conditioned aversion to milk was established by pairing it with lithium chloride (LiCl). In Experiment 1 conditioned pituitary-adrenal activation occurred when, in a conflict situation, animals reexperienced milk that had earlier been paired with LiCl. The relationship between the strength of aversion and corticosterone levels was such that animals showing the greatest avoidance showed the largest elevations in plasma corticosterone. In Experiment 2 this behavior/steroid relationship was manipulated. Dexamethasone (DEX) pretreatment on the day of conditioning was used to attenuate the conditioned aversion. Compared to saline (SAL) controls when reexposed to milk, DEX animals showed an attenuated aversion (i.e., drank more) and a smaller conditioned response (i.e., less adrenocortical activity). The reduction of conditioned elevation in corticosterone was not due to any residual effects of DEX at the time of testing (Experiment 3). Plasma levels of corticosterone represent an index for assessing the strength of illness induced conditioned taste aversions.

Investigations into the nature of the dexamethasone and ACTH effects upon learned taste aversion

Abstract Dexamethasone injected prior to the conditioning trial will attenuate a learned taste aversion. ACTH injections will prolong the recovery from a taste aversion when administered prior to recovery trials. Two experiments are reported here. In the first, the interaction between these effects was studied. Using a factorial design, four groups of rats received dexamethasone or ACTH prior to conditioning and prior to recovery trials. An additional group received isotonic saline throughout training and recovery. The primary finding was that animals receiving dexamethasone prior to conditioning and ACTH prior to recovery trials did not differ from the group pretreated with ACTH during both conditioning and recovery. That is, given the parameters of these experiments, the ACTH effect was prepotent. In the second experiment it was shown that the ACTH effect upon the performance of a taste aversion can occur in one trial. Taken together, the results of the two experiments support the idea that ACTH influences memory retrieval when administered prior to a test for retention of an avoidance response.

Early Olfactory Enrichment Enhances Later Consumption of Novel Substances

Abstract Male rats were exposed to conditions of either postweaning olfactory enrichment or standard laboratory rearing. In later tests, rats exposed to olfactory enrichment consumed more of novel substances (sucrose and milk)_than did laboratory-reared controls. Animals presented with milk and then sucrose drank more of both substances than animals presented with the substances in the reverse order. The results suggest that the variety of odors to which the weanling rat is exposed affects its later preference for dietary variability.

An ACTH effect on recovery from conditioned taste aversion.

Recovery from LiCl-induced taste aversion was found to be affected by the administration of adrenocorticotrophic hormone (ACTH). When injected prior to recovery sessions, ACTH prolonged recovery from the aversion, while presession injections on the day of conditioning had no effect. The results were consistent with previous reports, and were interpreted in terms of the importance of ACTH as a component of the internal stimulus complex created by LiCl-induced illness.