Emerging cholinergic mechanisms and ontogeny of response inhibition in the mouse.

A total of 1,604 Swiss-Webster mice 7, 11, 15, 19, and 85–215 (adult) days of age, served as Ss in 5 experiments assessing effects of anticholinergics on the development of behavioral inhibition. The centrally active anticholinergic scopolamine produced a dose-dependent elevation in locomotor activity in 19-day-old and adult Ss. Acquisition and retention of a step-off passive avoidance response (PAR) was initially studied in nondrugged Ss. Ss as young as 7 days of age learned and retained the PAR for 1 hr. 24-hr savings, however, were not observed until 19 days of age. Simple PAR performance deficits following scopolamine injection were first seen at 15 days of age. Ss in those age groups exhibiting 24-hr retention (19-day-olds and adults) were used to assess carry-over effects of scopolamine on retest. Only in the case of juveniles did scopolamine, injected prior to training, disrupt 24-hr retest performance. Since methylscopolamine, a peripherally active anticholinergic, had no effect on activity and PAR performance, it is assumed that scopolamine's effects were of central origin. Results suggest that behavioral suppression comes under cholinergic control during the 2nd and 3rd postnatal weeks but that cholinergic mechanisms may not mediate response inhibition uniformly throughout development. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of photoperiod and social environment on sexual maturation in female deer mice (Peromyscus maniculatus bairdii).

Tested the reproductive response of young female deer mice to either a long or short photoperiod combined with the presence of adult males, adult females, or social isolation. 266 Ss were reared on either a long photoperiod (15 hrs light, 9 hrs dark) or on short days (8 hrs light, 16 hrs dark) from birth. Beginning at weaning, females were housed with an adult male, with an adult female, or in social isolation. In Exp I, vaginas opened more slowly in Ss on short days than in those on long days. Vaginal introitus was also retarded in Ss reared with an adult female in comparison with Ss reared in isolation. When examined at 37 days of age, Ss reared with an adult male had larger uteri than those reared alone; uteri were also larger in long-day than in short-day Ss. In Exp II, Ss were killed at 30 days of age; again, uterine growth was stimulated by exposure to either long days or an adult male. As was previously demonstrated for male deer mice, sexual maturation in females is regulated by photoperiod and social cues. Heterospecific social stimuli accelerate maturation in individuals that otherwise would be inhibited by having been reared on a short photoperiod. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Litter size and emotionality in two strains of mice.

Studied 90 mice from 2 emotionally divergent strains, SJL/J and SWR/J, obtained from the Jackson Laboratory. The mice belonged to litters of 3, 5, or 7. At 33 days of age they were placed in separate cages and at 60 days of age they were run through a battery of tests consisting of 19 measures of emotionality. Scores were factor analyzed by alpha factoring followed by varimax and promax rotations. Factor scores were computed for all Ss on the 6 factors obtained and analyzed on a 2 * 3 factorial design with main effects for strain and litter size. Strain differences were found on 5 factors and litter-size differences on 3. The differential effect of litter size on factors is discussed. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal Thyroxine Stimulation Accelerates the Maturation of Both Locomotor and Memory Processes in Mice.

In two experiments mice were injected with thyroxine on Postnatal Days 1, 2, and 3, and the subsequent effects upon the development of the swimming reflex and the emergence of instrumental learning/memory processes were examined. In agreement with past studies, early thyroxine treatment accelerated the maturation of swimming capacities and general physical development compared with littermate controls receiving saline injections. In the second study, thyroxine- and saline-treated mice received 25 training trials on a shock-escape T-maze task at 7, 9, 11, or 13 days of age with a retention test 24 hr later. The results indicated that while learning was equivalent within each of the ages between the treatment groups, onset of 24-hr retention capacity occurred approximately 2 days earlier in the thyroxine-treated mice than in controls. In addition, a performance deficit was observed in the thyroxine mice at the oldest age tested, in agreement with previous reports. The results of these experiments suggest that early hyperthyroidism results in earlier maturation of both locomotor and memory processes, followed by later performance deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of memory in the neonatal mouse.

Conducted 4 experiments with Swiss-Webster mice (N = 488) to examine the development of memory of an escape response between 3-11 days of age. Ss were given 25 training trials in a straight-alley escape task and then retested at various retention intervals. Results show that 5- and 7-day-old Ss had a retention capacity of less than 6 hr. At 9 days of age, however, retention capacity greatly increased to at least 96 hr., suggesting that a period of maturational development critical to long-term memory processes occurs at 9 days of age in the neonatal mouse. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal stimulation and accelerated maturation in BALB/c mice.

Investigated the effects of neonatal stimulation on maturation rate using 24 litters of BALB/c mice as Ss. At birth litters were randomly assigned to 1 of 4 treatment conditions: (a) handled, (b) tactile, (c) handled control, or (d) undisturbed control. Continuous measurements were taken by 2 raters on a variety of physical maturation indexes. No significant treatment effects were obtained, but strong litter effects were found for each dependent variable. These results contradict previous reports in the literature and suggest that the genetic component attending physical maturation rate is not readily modulated by nonspecific neonatal stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste salience depends on novelty, not concentration, in taste-aversion learning in the rat.

Conducted 2 experiments with 12 rat litters of albino-hooded-Brown-Swarthmore strain derivation. Ss formed stronger aversions to solutions that were either more concentrated or more novel than other solutions. From the results it is proposed that the data can be reinterpreted in terms of just one of these factors-novelty-since the more concentrated solution is also ordinarily more novel. When Ss were poisoned after drinking 2 concentrations of the same solute, Ss reared on water acquired aversions mainly to the more concentrated solution. Ss reared on a still more concentrated solution acquired aversions mainly to the less concentrated solution which for them was more novel. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Problems of undernutrition research with breeding mice

Rats undernourished throughout pregnancy and lactation lose few young during the suckling period and wean normal size litters of extremely growth-retarded offspring. Comparable treatment of maternal mice, on the other hand, resulted in considerable nestling mortality. Thus few young were reared to weaning and these were not nearly as growth-retarded. Detailed evidence is given of the effects of different schedules of undernutrition throughout pregnancy and lactation on the reproductive performance of mice. These findings are compared with those for rats and possible reasons for the difference in nestling mortality discussed.     

Development of pattern recognition in infant pigtailed macaques (Macaca nemestrina).

Examined the development of pattern recognition in 31 infant pigtailed macaques using the familiarization–novelty technique. Ss were familiarized with 2 identical black and white patterns and tested on the familiar pattern paired with a novel one. Cross-sectional data revealed that a novelty preference occurred with increasing age. Younger Ss (mean age 178 days postconception or 1 postnatal week) did not show a reliable visual preference for either the novel or the familiar patterns. Infants with a mean age of 203.2 days postconception (about 4 postnatal weeks) fixated novel patterns significantly longer than familiar ones. Data suggest that by 200 days postconception, infant macaques are able to remember some aspects of previously exposed stimuli and will perform consistently on a familiarization–novelty task. Results are discussed in relation to the development of human infant pattern-recognition abilities. Pigtailed macaques provide an excellent model for the investigation of human infant recognition memory, 1 wk of maturation in the pigtailed infant being equivalent to 1 mo in the human. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of spontaneous locomotor activity in rabbit, rat, and guinea pig.

Investigated postnatal locomotor activity in 3 experiments with 43 New Zealand white rabbits, 20 Sprague-Dawley albino rats, and 11 Dunkin-Hartley albino guinea pigs. A peak was found in this behavior at 5 days of age in the rabbit and, in confirmation of earlier studies, at 15-20 days in the rat. Neonatal guinea pigs showed no variation in activity levels due to age. The guinea pig is born at an advanced stage of neural maturation in comparison with the rat, and the rabbit is born at an intermediate stage. This difference accounts for the observed variations in postnatal activity profiles if it is assumed that the behavioral peak coincides with the transition from a stage of primarily mesencephalic arousal system maturation to a stage of primarily diencephalic and telencephalic inhibitory system maturation. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of meal patterning in rats and its recapitulation during recovery from lateral hypothalamic lesions.

Investigated the development of feeding patterns in weanling rats and in rats with lateral hypothalamic lesions. 2 experiments were conducted with a total of 39 male albino Sprague-Dawley rats. From 16 to 25 days of age, the weanlings demonstrated a preprandial intake pattern (i.e., a positive correlation between meal size and time since the preceding meal). This subsequently declined while the postprandial relationship (correlation with time until subsequent meal) such that by 30-35 days of age a full adult pattern was observed. Ss recovering from lateral hypothalamic lesions, for a brief period, also demonstrated a preprandial intake pattern. The postprandial relationship was abolished by the lesion. Results suggest that the development of adult meal patterning results from maturation of lateral hypothalamic mechanisms governing meal initiation. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of amount of original training upon onset of a 24-hour memory capacity in neonatal mice.

Administered 0, 10, 25, or 40 trials in a shock-escape straight alley to 128 Swiss-Webster mice (Mus musculus) when 7 or 9 days old. All groups received an additional 25 training trials 24 hrs later. During original training, both age groups improved escape performance as a function of number of training trials. However, during retention testing, only the Ss trained when 9 days old displayed differences in performance due to amount of original training. Results support earlier research suggesting that the capacity for 24-hr retention of the escape response develops between 7 and 9 days of age in mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental analysis of behavioral dysfunction in rats with septal lesions.

At 7 days of age, 48 male Long-Evans hooded rats received lesions of the septal nuclei or control operations. Ss then received 30 hrs of training on a DRL 20-sec schedule for 1 hr/day beginning at either 27 or 96 days of age. At 126 days of age, all Ss received 10 additional training sessions. After operant testing, all Ss received 10 additional training sessions. After operant testing, all Ss were tested on spontaneous alternation, spatial reversal, and passive avoidance. Results indicate that on a DRL 20-sec schedule Ss that received lesions of the septum neonatally and were tested at different ages performed in a similar manner. Approximately 50% of the Ss with lesions of the septal nuclei reached efficiency levels comparable with those of normal controls. When tested for retention, these efficient Ss still performed similarly to normal Ss. Ss with septal lesions were facilitated in the acquisition of a spatial habit, were deficient in spatial habit reversal, were less likely to demonstrate spontaneous alternation, and were deficient in passive avoidance. It is concluded that neonatal lesions of the septal nuclei produce permanent behavioral impairments on a diversity of measures and that, although juvenile animals with limbic system damage often manifest behaviors different from adult Ss, the difference is not evident during operant testing (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social stimulation of reproductive development in male deer mice housed on a short-day photoperiod.

Male deer mice (Peromyscus maniculatus), born of mothers housed on a long-day (LD) photoperiod (15:9 hrs light/dark), were either switched to a short-day (SD) photoperiod (6:18 hrs) at birth or continued on their prenatal LD photoperiod. From weaning until 6 wks of age, Ss were housed with an adult female or in social isolation. Ss reared on an SD photoperiod had smaller testes, seminal vesicles, and ventral sebaceous glands that did those reared on LD. Postweaning exposure of SD Ss to females stimulated reproductive organ growth as measured at 6 wks of age. Results indicate that both photic and social stimuli regulate reproductive development in male deer mice and that positive social cues can stimulate maturation even in the presence of negative photic cues. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental aspects of recovery of function following septal lesions in the infant rat.

In an experiment with 4 litters of Long-Evans hooded rats (14 pups/litter), 1/2 of each litter received septal lesions at the age of 7 days, and the remaining 1/2 received control operations (incision). Septal lesions in infant Ss resulted in hyperemotionality and altered open-field behaviors at the ages of 21, 42, 63, and 90 days. When Ss reached 90 days of age, their behavior was compared with that of normal adult rats and rats that had received septal lesions in adulthood. Measures of active avoidance, fixed-ratio responding, and social facilitation were collected for all groups. Results show that septal lesions in infancy or adulthood enhanced avoidance responding, fixed-ratio responding, and social behavior when compared with infant or adult controls. Failure to observe recovery of function was interpreted in terms of phylogeny and hierarchical cerebral organization. (26 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prenatal maternal X-irradiation: Maternal and offspring effects.

Reports an experiment in which Charles River rats, irradiated or sham irradiated on Day 16 of fetal life, were reared by irradiated or nonirradiated foster mothers (n = 24) in a dual-chambered maternity cage. Results show that irradiated mothers spent less time with their litters than controls independent of the nature of the pups. Irradiated Ss weighed less than controls and the prenatal effects on mortality during the immediate postweaning period were influenced by maternal factors. Ss reared by irradiated mothers weighed less, were less emotional, and were more susceptible to the lethal effects of subsequent X-irradiation than Ss reared by nonirradiated mothers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother's milk and adult presence: Two factors determining initial dietary selection by weanling rats.

Reports 3 experiments with (a) 10 female hooded rats and their litters (reduced to 6 pups/litter); (b) 1 male and 4 female wild rats (Rattus norvegicus) and 2 litters (6 pups/litter) born to colony members; and (c) 6 litters of wild and 4 litters of hooded rat pups. Results indicate that adult Ss were capable of influencing their pups' choice of diet during weaning in 2 ways: (a) cues transmitted from a mother to her pups during the nursing period were sufficient to determine the dietary preference of the young at weaning, and (b) the presence of adult Ss at a feeding site was sufficient to determine the choice of feeding site by the pups independent of cues transmitted during the nursing period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social-seeking and novelty-seeking behavior as a function of differential rearing histories.

Rats were handled daily from birth until weaning or were nonhandled controls. At weaning Ss were reared with littermates or in isolation. At 90 days some of the socially reared Ss were placed into isolation. Total N = 44 males, 1 from each of 44 different litters. At 100 days S was placed for 10 min. into the stem of a T shaped unit. S could remain where it was, enter a social chamber, or enter a novel chamber. Time in each chamber, activity, and defecation were recorded for 4 successive days. Handled Ss were significantly more active, and spent significantly more time in the social and novel chambers than nonhandled controls. Ss reared in a social environment until testing spent significantly less time in the novel chamber than Ss undergoing long-term or short-term social isolation. The handling variable was found to interact significantly with postweaning rearing and test days. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early undernutrition impairs hippocampal long-term potentiation in adult rats.

Investigated the effects of early malnutrition on the ability to establish and maintain hippocampal long-term potentiation (LTP), a relatively permanent enhancement of synaptic and cellular responses induced by high-frequency stimulation. Six control male rats and 8 previously undernourished Ss were used in the acute preparation, and 4 controls and 6 previously undernourished Ss in the chronic preparation. Following high-frequency stimulation of hippocampal dentate granule cells, potentiation was difficult to achieve in undernourished Ss. LTP showed a significant decline within 3–6 hrs and was completely absent at 24 hrs. Further trains of stimulation resulted in only small benefits in undernourished Ss. Coupled with previously reported morphological and behavioral deficits, these findings indicate a marked hippocampal dysfunction resulting from early undernutrition and provide a potentially valuable approach for relating nutritionally induced behavioral impairments to brain function. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alleviated forgetting of a learned contingency in 8-week-old infants.

To investigate retention by 8-wk-old infants (N?=?24) after lengthy intervals, the authors first determined that infants of this age reliably learned an operant contingency in 2 training sessions and evidenced no retention of it 14 days later (Exp I). To determine whether the memory of the contingency was permanently inaccessible or whether forgetting could be alleviated by a prior cueing procedure known to facilitate retrieval in older infants, a "reactivation" treatment was administered 17 days after training was completed, and cued recall was examined 24 hrs later (Exp II). Control groups received either no reactivation treatment prior to the retention test or a reactivation treatment but no prior training. Experimental Ss showed little or no forgetting, but Ss in the 2 control groups responded at their pretraining baseline rates during the long-term retention test. These data challenge the general assumption of deficits in memory processing by 8-wk-olds and demonstrate that memories acquired either prior to or during a period of major neurological and behavioral reorganization can be maintained through that period. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)