Resistance to extinction of the gradually increased (gI) or decreased (gD) ratio of partial reinforcement has been investigated in order to assess effectively partial-reinforcement theories. COGAN et al. (1975) reported greater resistance in gD than in gI employing an extensive acquisition training and the sucrose solution as a reinforcer, and interpreted the results as supporting AMSEL'S frustration hypothesis. ISHIDA (1978), however, found the opposite result with food reward after a moderate number of acquisition trials. Thus, the present study was desingned to determine the resistance to extinction after gI and gD schedules under appropriately arranged experimental conditions, and to assess partial-reinfocement hypotheses.
Three groups of 9 rats each were trained with extensive acquisition trials (12 trials a day for 9 days) and then extinguished (12 trials a day for 6 days) in a straight alley. Groups gI and gD received the reward sequences as shown in Table 1. Group RA, which was added as a control, received random sequence. All three groups were rewarded at 53% with food pellets.
There was not a significant difference among groups during acquisition, although performance of gI was below those of the other two groups in early trials (Fig. 1). During extinction three groups differed significantly, i. e., group gI was most resistant to extinction, RA was less, and gD was least (Fig. 2).
The extinction results did not support the AMSEL'S view that the later occuring nonreinforcements (the group of gD) should produce greater frustration and greatest resistance to extinction. The present findings are interpreted both by reinforcement-level view (CAPALDI, 1978) and attention theory (SUTHERLAND and MACKINTOSH, 1971). However, it is suggested that CAPALDI'S thesis is more appropriate one, considering the predictability of the results, especially the difference between RA and each of gI and gD.

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Five male and five female albino rats of the same litter (40 days of age) were put into about 7 m² enclosure, and thereafter their social behaviours were observed about for three months. Between male individuals dominance-subordination relationships came to be observed evidently on and after about 60 days of age. Three types of status were distinguished; one male called “alpha” was dominant or top individual, one called “bata” in the second rank, and three called “gamma” in the third. There was a linear hierarchy in the order of dominance, which continued during observation period. Alpha individual, who was superiorly strongest, often attacked and chased or threatened terribly the other male rats. Although it seemed that subordinate individuals sometimes displayed the appeasment behaviour toward alpha, this behaviour could hardly be recognized to be effective on preventing alpha's attack.
Male rats did not fight each other for copulation with the same litter's female when she was in the regularly cycling oestrus. Before and after the postpartum oestrus of the female, however, alpha male took up his position near the parturition nest and drive away all approaches of the other males to the female in the nest. Alpha, moreover, temporally formed a couple with the young female born and grown up in the observation enclosure when she came into the oestrus for the first time.
From these results, it is considered that albino rats domsticated from Norway rats, which are naturally territorial animals, may acquire the absolute dominance system in case they are put into the confined space. To establish this hierarchy system, albino rats might required wider space and larger population than Norway rats in the laboratory. The behaviour of alpha individual shows a evident territoriality. In the albino rat group under the loose housing condition, alpha seems to follow more closely to the behaviour of the adult male Norway rat.

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Behavioral effects of ACTH on habituation of the acoustic startle responses were examined. A tone stimulus (3, 400 Hz, 107 dB) was presented under three different conditions of inter-stimulus interval (variable 4, 8, and 16 sec). Animals underwent 100 habituation trials. Ten min prior to habituation, the baseline amplitude of the startle response was measured using 107 and 85 dB tones (Prehabituation test), and 5 min after the habituation period, the after-effect was examined by the same procedure (Post-habituation test).
Administration of ACTH (4 i. u./animal, s. c.) facilitated habituation when the inter-stimulus-interval (ISI) was short, but retarded habituation when the ISI was long. No such phenomena was observed in the saline treated animals. The effects of ACTH became more marked in the post-habituation test.
The results mentioned above suggest that the effects of ACTH on habituation are dependent upon the ISI condition.

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