Joel N. Kaplan

Maternal discrimination of infant vocalizations in squirrel monkeys

Responses of mother squirrel monkeys to vocalizations of their own and other infants were examined to determine whether mothers could discriminate their infants on the basis of auditory cues. Thirty mothers, whose infants ranged in age from one to seven months were tested in three conditions in which their own infant, a different infant, and no infant served as the stimulus. Mothers were tested in an enclosed alleyway with opaque end panels behind which stimuli were placed. The quantity and quality of maternal responses clearly differed in the three conditions and indicated that mothers recognized their own infants. Differences in maternal vocalizations were the most pronounced. All but one type of vocalization increased in the own-infant condition; the exception, a high-pitched shrill, decreased. Mothers also spent more time near the stimulus and were more active when tested with their own infants.

Separation distress and attachment in surrogate-reared squirrel monkeys ☆

Abstract Surrogate-reared infant squirrel monkeys were exposed to various conditions of separation from their surrogate. Infants showed significant increases in plasma levels of cortisol when they were placed in an unfamiliar environment during the separation period. Changes in behavior, but not cortisol, were observed under conditions in which the surrogate was removed and the infant left in the home cage. These results differ from those previously obtained with mother-reared infants. It is concluded that surrogate-reared infant squirrel monkeys do not show the same separation response or attachment to their rearing figure as do mother-reared infants.

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.

Responses of Mother Squirrel Monkeys to Dead Infants

The responses of mother squirrel monkeys to infants were examined by testing the mothers with bodies of their own and other infants. Mothers whose infants were stillborn or died at one day of age showed strong and equivalent maternal responses to all the bodies with which they were presented, while those whose infants died after two weeks of age responded mainly to the body of their own infant. These results suggest that the female squirrel monkey becomes more selective in responding to the body of a dead infant with the passage of time after parturition. The females post-parturient condition appears to be the prime cause for changes in her responsiveness, although other factors related to the infants growth and development might also be important.

Effects of synthetic odors on filial attachment in infant squirrel monkeys.

Abstract It was hypothesized that the frequent application of synthetic odors to squirrel monkey mothers ( Saimiri sciureus ) could affect filial attachment independently of odor preferences by their infants. Six control infants were reared by mothers who retained naturally produced odors, and 12 experimental infants were reared by mothers who were regularly sprayed with a synthetic odor. In the first experiment, control but not experimental animals preferred their mother to a stranger during monthly visual discrimination tests in Months 1–5 postpartum. In the second experiment, infants preferred their synthetic rearing odor to an unfamiliar synthetic odor, but only in Month 5. The results suggest that the frequent perception of alien odors on the mother may diminish a squirrel monkey infants behavioral attraction to her in spite of a preference developed for an early rearing odor.

The development of seasonal variation in gonadal hormones and body weight in the maturing squirrel monkey

Captive-born squirrel monkeys of three different subtypes (Colombian, Bolivian, Peruvian), ranging in age from 1 to 4.5 years for males and 1 to 3.5 years for females, were examined at 3-month intervals throughout the year for seasonal changes in levels of plasma testosterone and progesterone and in body weight. Cyclical activity of testosterone in males began between 2 and 3 years of age but became more defined by the time the animals were 3–4 years old. Peak values occurred in February and May and corresponded to the the time of year in which adults normally mate. Elevations of progesterone occurred initially at approximately 2.5 years of age in February and May, and mainly infernales of the Colombian subtype. However,unlike levels of testosterone in males of this age, which declined in August and November (following the typical breeding season), levels of progesterone in females continued to increase during these months. Seasonal changes in body weight were also found in males but these changes were less evident than, and did not correlate with, hormonal changes.

Oral Ethanol Intake and Levels of Blood Alcohol in the Squirrel Monkey

Oral alcohol ingestion and blood alcohol levels were examined in adult female squirrel monkeys to assess the feasibility of using this primate as a model for fetal alcohol effects. In one experiment, alcohol intake was evaluated in nonpregnant animals under conditions in which the concentration of ethanol, length of ethanol exposure, and degree of liquid deprivation were varied. In another experiment blood alcohol levels were measured in pregnant animals of two subtypes that had been drinking ethanol. In a third experiment, time-dependent blood alcohol levels and behavior were evaluated in nonpregnant monkeys following intubation of specific doses of ethanol. Results showed that nonpregnant monkeys drank ethanol at concentrations of 5 to 10%, and that the amount of ethanol consumed was related to the concentration and length of time ethanol was available. When given access to a 5% ethanol solution, pregnant animals drank quantities that varied between individuals and subtypes, with maximum blood levels, measured up to 6 hr after presentation, ranging from 1 to 196 mg%. Intubation of ethanol resulted in blood alcohol levels and incoordination scores that were linearly related to dose, with maximum effects occurring 1 hr after administration. Elimination of ethanol from the blood at levels above 50 mg% occurred at a rate of about 35 mg%/hr, while the rate of clearance from the body was calculated to be approximately 250 mg/kg/hr.

Maternal responsiveness in the squirrel monkey following chronic administration of Δ9-THC ☆

Abstract Mother squirrel monkeys were orally administered gradually increasing doses of Δ 9 -THC (from 0.5 to 5.0 mg/kg) 5 days/wk from 2 wk to approximately 6 mo after birth. After having received a dose of 5.0 mg/kg for an average of 3.5 mo, drug-treated mothers were then compared with control mothers in terms of their responsiveness both to their own and to unrelated infants. In contrast to the control mothers whose response pattern clearly showed differentiation of their own and other infants, the mothers that received Δ 9 -THC responded in much the same manner to the alien infant as they did to their own infant. The results show that the behavior of the THC-exposed mothers was not attributed simply to a general reduction in their responsiveness toward their offspring or to an overall reduction in their own state of arousal. Rather, the results suggest that chronic ingestion of Δ 9 -THC caused the mothers to be less disturbed by separation from their infants and/or produced some degree of perceptual distortion that prevented them from responding selectivity to the different infants.

The effect of pressurized air in establishing discriminative response suppression in stump-tailed macaques

Pressurized air was repeatedly associated with one of two frequencies of flashing light during performance of a VI 30-sec positive reinforcement schedule by stump-tailed monkeys. As revealed by the relative suppression of bar presses to each of the two visual stimuli, the Ss learned to discriminate between the different flicker frequencies. However, they also showed signs of adapting to the airblast during the course of training, and its location had to be changed in order to maintain discriminative suppression.