摘要:

AbstractThe orienting response to an auditory stimulus, as measured by a decrease in heart rate, habituates rapidly, and at the same rate in preweanling and adult rats. Although adult rats retain this nonassociative memory for at least 7 days, prewealing rats show extremely rapid forgetting. In the preweanling, forgetting of this nonassociative memory appears to be complete after just 24 hr (Richardson&Campbell, 1991b). The results of several experiments in the present study with preweanling rats demonstrated that this type of nonassociative memory could be reactivated by presenting a fractional component of the original eliciting stimulus just prior to testing. The effectiveness of the reactivation treatment was critically dependent upon both the number of reactivating stimuli presented and the duration of those stimuli. Reactivation was also found to be stimulus‐specific in that presentation of an auditory stimulus qualitatively different from that used in training (white noise instead of a pure tone) did not reactivate the memory. Control groups in each experiment demonstrated that the reactivation treatment facilitated retrieval of the prior nonassociative memory and did not produce new learning. A possible process through which nonassociative memories can be reactivated is discussed. © 1993 Johan Wiley&Sons, I

ISSN:0012-1630    

DOI:10.1002/dev.420260102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo correlational studies were undertaken to expolre the relationship between the sex ratio of the pups that a female Mongolian gerbil gestated and her behavior, morphology, and hormone levels late in pregnancy. In the first study, we found that the change in sex ratio between the first and second litters that a female gerbil delivered and the change in her frequency of scent marking late in her first and second pregnancies were significantly correlated. In the second study, we found significant positive correlations between both the percentage and the number of males in the litter a female delivered and (1) her plasma testosterone levels, (2) the size of her ventral gland, and (3) her frequency of scent marking, all measured late in pregnancy. Our data were entirely consistent with the hypothesis that fetal males excrete biologically significant quantities of testosterone into their dam's bloodstream and that this testosterone masculinizes both the behavior and morphology of dams late in pregnancy. © 1993 Johan Wiley&Sons, Inc

ISSN:0012-1630    

DOI:10.1002/dev.420260103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractOpioid ligands or drugs that act on dopaminergic pathways effect changes in the motor behavior of near‐term rat fetuses. In this study, selective manipulation of kappa opioid and D1 DA receptors was used to investigate opioid and dopamine involvement in mediating the behavioral effects of milk infusion. Milk reduced expression of the fetal facial wiping response to a tactile probe, and this effect was blocked by the kappa antagonist nor‐binaltorphimine as well as the D1 antagonist SCH‐23390. Administration of either the kappa agonist U50,488 or the D1 agonist SKF‐38393 mimicked the effects of milk and reduced fetal responsiveness to the probe in the absence of milk infusion. Administration of nor‐binaltorphimine reversed the effects of SKF‐38393 and resulted in a high incidence of the wiping response. However, administration of SCH‐23390 did not reverse the low incidence of facial wiping induced by U50,488. These findings suggest that milk modulates activity at dopamine receptors, which in turn promotes activity at kappa receptors of the opioid system to bring about changes in cutaneous responsiveness in the fetal rat. © 1993 Johan W

ISSN:0012-1630    

DOI:10.1002/dev.420260104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis study was designed to describe the development of posture control in sitting in response to a natural perturbation. Seven normal infants 2 to 5 months of age were tested at two stages of independent sitting development. Trunk support was removed from infants while sitting erect and the postural responses were videotaped and EMG recorded from the upper trunk extensors, lumbar paraspinals, gluteus maximus, rectus femoris, hamstrings, and abdominals. Kinematic variables (trunk displacement, trunk velocity, trunk curvature) and an EMG variable (pattern of muscle activation) were analyzed with computer programs. Between Stages 1 and 2 of sitting development, anterior trunk displacement and velocity decreased significantly, although the trunk extension curve did not change significantly. Infants had variable muscle responses during Stage 1; however, during Stage 2 EMG analysis revealed less variability and the emergence of postural synergies. Overall, lumbar paraspinals, hamstrings, and quadriceps were the muscles most frequently active during the postural response. Each subject had a preferred synergy, with the most common synergies being a lumbar paraspinalhamstring synergy and a lumbar paraspinal‐quadriceps synergy. These data provide evidence that trunk displacement and trunk velocity decrease in infants develop independent sitting posture, and these variables may be used to measure improvement in sitting control. We suggest that the control of sitting posture is related to the emergence and preferred use of the paraspinal‐hamstring and paraspinal‐quadriceps synergies. © 1993 Johan Wiley&Son

ISSN:0012-1630    

DOI:10.1002/dev.420260105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe stability of olfactory preferences for artificial odors was studied in young spiny mouse pups (Acomys cahirinus). Subjects aged between 2 and 20 days were exposed to the odor of either cinnamon or cumin for 1.5 hr. The durability of preferences for the familiar versus novel odor was subsequently monitored in a three‐choice preference test. The results suggest the existence of a sensitive phase for learning odor characteristics, through simple exposure, between Days 2 and 18 of the pups' postnatal life. The sensitive phase proved not be an “on‐off” process, but the strongest effect of exposure to odors took place at about Days 4 and 6. However, the duration of preference for exposed odors was dependent on later experience with the odors during retests. The results point to an unusual plasticity in rapid learning of odors through simple exposure in precocial young spiny mice. © 1993 Johan Wiley&S

ISSN:0012-1630    

DOI:10.1002/dev.420260106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0012-1630    

DOI:10.1002/dev.420260101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY