Robert W. Bell

Maternal responses to infant vocalizations and olfactory cues in rats and mice

In Experiment I lactating female Long-Evans rats (Rattus norvegicus) and in Experiment II lactating female C57BL/10 mice (Mus musculus) were tested for retrieval of young in a Y-maze using the home cage as a start box. Retrieval-eliciting stimuli compared were: (1) a pup emitting ultrasounds, (2) a tape loop of neonatal vocalizations, (3) a chilled pup which could not emit ultrasounds, and (4) an empty maze arm to control for random and/or exploratory activity. For both rats and mice the absence of any olfactory cue in the maze arms was accompanied by an absence of differential choice behavior. Given the presence of olfactory cues neonatal ultrasounds were effective directional cues for retrieval. The rat seemed incapable of utilizing olfactory cues alone for directional information, whereas the mouse utilized vocalizations and olfactory cues equally well.

Ultra-sounds in three inbred strains of young mice

Ultrasonic vocalizations of young mice of three inbred strains: C57B1/6/J, BALB/c/J, and C3H/He/J; were recorded at 3, 6, 9, 12, 15, and 18 days of age. Recordings were made under conditions of separation from the nest and isolation, at room temperature (23.5 ± 1.5°C) which produces a mild degree of hypothermic stress. The modal peak frequencies of signals emitted from pups of all the strains were between 70 and 80 kHz. The major strain differences obtained were differential age functions of signaling. The C57B1/6/J signaled frequently at 3 days of age but had virtually ceased signaling by 6 days of age. The BALB/c/J displayed a similar age function, except that signaling persisted until 9 days of age. The C3H/He/J increased their rate of signaling from 3 to 9 days of age, with a marked reduction in signaling by 12 days of age. No signals were detected at 15 or 18 days of age. The strains also differed in terms of peak frequencies and mean durations of signals. These differences in signaling characteristics suggest a basis for strain differences in mother-infant interactions which have been reported previously. Further, they should be useful indices for monitoring responsiveness to various environmental manipulations by neonatal mice.

The effects of prenatal injections of adrenalin chloride and d- amphetamine sulfate on subsequent emotionality and ulcer-proneness of offspring

Twenty pregnant female rats were each given one injection of (1) 1.5cc/kg body weight of a 1:1000 solution of adrenalin chloride, (2) 3.0mg/kg body weight of a 0.9mg/l.0cc solution of d-amphetamine sulfate, or (3) 1.5cc/kg body weight of distilled water. Injections were administered intraperitoneally either between 6 and 9 days post-conception, during which time the fetal stomach and intestine are developing, or between 12 and 15 days post-conception. Following normal rearing, offspring were subjected to immobilization stress, with pre- and post-measures of emotionality, following which they were assayed for ulcers. The results indicate modified emotionality as a function of the prenatal treatments, and a significantly higher frequency of ulceration in those Ss whose mothers had been injected with adrenalin at the time of the fetal stomach development.

Prenatal maternal conditioned fear and subsequent ulcer-proneness in the rat

Increased ulceration under immobilization stress was observed in rats which had been subjected to prenatal maternal fear conditioning coincident with the development of the fetal gut. Presentation of the CS (Buzzer) or UCS (Shock) alone did not affect ulceration, nor did the conditioning procedure if it occurred after the fetal gut development was complete.

Effects of magnesium pemoline on avoidance behavior in rats

Following oral injections of either 0, 5, or 20 mg/kg of magnesium pemoline mixed with tragacanth in an equal volume solution, 60 Long-Evans hooded rats were given 70 trials in a two-compartment one-way avoidance apparatus. Type of CS (light vs buzzer) and interval between drug injection and conditioning (30 vs 60 min) were varied factorially with drug dosage. Ss receiving either 5 or 20 mg/kg of magnesium pemoline performed significantly better than did controls, independent of the other two variables. These results fail to support the Beach & Kimble (1967) hypothesis that the major effects of magnesium pemoline on avoidance conditioning are due to an increased aversive responsiveness to a buzzer CS, which has typically been employed in studies of the drug, rather than directly affecting the avoidance learning.

Interactive effects of shock intensity and delay of reinforcement on escape conditioning

A 3 (levels of shock) by 4 (delays of shock termination) design investigated effects of delay of reinforcement in escape conditioning in 60 rats in a 2-compartment shuttle box. Different delay gradients were obtained under different levels of shock intensity (p<.01), with all delay groups showing marked inhibition of performance when compared to non-delay groups (p <.01). The significant drive level (controlled by shock intensity) by delay of reinforcement interaction is inconsistent with results of investigations varying degree of food deprivation and delay of food reward (Ramond, 1954; Renner, 1963), and suggest that Spence’s (1956) theory of delay of reinforcement in appetitive learning cannot be generalized to aversive conditioning.

Note: Emotionality after Mild, Chronic Stress as a Function of Infantile Handling

Increased or decreased emotionality following mild, chronic stress was obtained as a function of handling rats at different ages during infancy.

EFFECTS OF VALUE OF REINFORCEMENT UPON EXPECTANCY STATEMENTS IN "GAMBLING" AND ACHIEVEMENT TASKS

The effects of probability of reinforcement and reward value on expectancy of success were investigated in both learning and gambling tasks. Forty-eight college students were asked to predict their success rate in correctly anticipating which of four lights would next be turned on. For some Ss the pattern of lights was random. For others a systematic pattern was repeated, permitting learning. Different probabilities of reinforcement effectively varied the level of expectancy, as did the gradual learning of the pattern in the learning task. Amount of reward, using poker chips with cash value, did not significantly alter expectancies of success in either the learning or gambling (random pattern) task. The implications of the results for expectancy theories were discussed.

Developmental effects of variable population density and dietary protein sufficiency upon morphology, neurochemistry, and behavior in the rat

Male Wistar rats were housed in groups of 2, 16, or 30 from 21 to 48 days of age. Each housing condition was factorially combined with one of three levels of dietary protein: 5%, 15%, or 25%. Body weight, brain weight, adrenal weight, and pituitary weight, as well as brain protein concentration, varied directly with protein level in the diet. Indices of neurotransmitter activity and nucleic acid concentrations were not differentially affected. The major effect of differential population density was associated with the combination of largest group size (30) and protein-enriched diet (25%). The large group size tended to minimize the effects of the protein-enriched diet. This combination also produced an increased responsiveness to extrinsic stress, as measured in the open field.