A large body of evidence has shown the involvement of serotonin (5-HT) in anxiety. Anxiety level appears to be correlated with brain 5-HT level. A selective serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), reduces brain 5-HT content, and produces anxiolytic effect when administered to adult rats. When a 5,7-DHT is administered to neonatal rats, it produces anxiogenic effect in elevated plus-maze test (Yamada & Iwasaki, 2002). In the elevated plus-maze test, passive avoidance of open platforms is the major index of anxiety, while in the defensive burying test, the major index of anxiety is the active burying of a spatially discrete shock-source. In the present study, we examined the effects of neonatal 5,7-DHT treatment on anxiety level in the defensive burying test. The results showed that neonatal 5,7-DHT treatment decreased 5-HT levels in cortex, hippocampus, and striatum, but increased in hypothalamus, midbrain, and medulla oblongata. In behavioral test, neonatal 5,7-DHT treatment decreased the latency to defensive burying and increased the duration of burying. These behavioral results suggest that the neonatal 5,7-DHT produces anxiogenic effect. The results demonstrate the differential effects of neonatal 5,7-DHT treatment on anxiety level and brain 5-HT system as compared with adult 5,7-DHT treatment.

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The present experiment was performed to investigate the interactive effects of different prior photoperiods and stress on testicular weight in Syrian hamsters under the neutral photoperiod. Seasonality was experimentally manipulated by the change of photoperiod. One group was exposed to LD 12.5 : 11.5 for 12 weeks following 8-week long photoperiod (LP)exposure. The other group was exposed to the same neutral photoperiod for 12 weeks after 8-week short photoperiod(SP). Stress was produced by food deprivation of fixed days or random days throughout the 12 weeks of the neutral photoperiod. The results clearly showed that unpredictable food deprivation on 25% days throughout the 12-week testing period induced more detrimental effects on testes than predictable deprivation once every 4 days in the LP group. Stress tolerance associated with food deprivation was weaker for the animals transferred from LP than for the ones transferred from SP. This finding suggests that stress tolerance varies with season.

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This study aimed to examine object manipulation in 2 to 4-year-old hand-reared infant African great apes, two bonobos and three gorillas. Humans and the great apes differ from other primate species in terms of their ability to use tools. Orienting manipulation (or combinatory manipulation), especially object-to-object manipulation, is considered to be a precursor of tool use. Although developmental changes in object manipulation that lead toward tool use have been investigated in chimpanzees, studies concerning bonobos and gorillas are extremely scarce. We observed free play in ape infants manipulating three kinds of objects: wooden blocks, nesting cups, and rings and a stalk. The size of the behavioral repertoire was measured by focusing on four variables: body parts used, number of objects manipulated, motor patterns, and types of orienting manipulation. Both species showed orienting manipulation (or combinatory manipulation) comparable to chimpanzee infants of similar ages. The gorillas' repertoire included fewer behaviors involving the use of the foot than the bonobos'. They showed the tendency of manipulating single object not in a single motor pattern but in multiple motor patterns.

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