Footshock given immediately after rats are placed in a strange inescapable environment produces no diminution in movement. However. if a brief exploration period is allowed before shock. freezing is the dominant defensive behavior seen. Thus. the topographical similarity of postshock reactions to unconditioned defensive behaviors elicited by a cat also involves a similar flight-to-freezing shift when the subject is permitted prior familiarization with the inescapable threat situation. Blanchard, Fukunaga, and Blanchard (1976) have reported that a brief familiarization period in a novel, inescapable chamber changes the dominant defensive behavior of a rat to a cat in that chamber, from flight to freezing. In view of the similarity between cat-elicited defensive behaviors and reactions to conditioned threat stimuli (Blanchard & Blanchard, 1971), it seems likely that a similar shift might occur with familiarization of a chamber in which foot shock is given. Thus, in order to assess the generality of effects of familiarity with the inescapable test situation on defensive reactions to threat, th.e procedure employed in Blanchard, Fukunaga, and Blanchard (I 976) was repeated, using shock rather than a cat as the threat stimulus. METHOD SubjectsTwenty-four naive albino rats from 135 to 192 days of age were randomly· assigned to three groups of eight rats each. These rats Were from the colony maintained by the University of Hawaii Psychology Department. ApparatusA l1at-gray 50 x 50 x 15 em wooden box with a solid wood cover containing an 18 x 18 cm Plexiglas insert served as the test chamber. The chamber was placed on a grid 1100r consisting of 64-<:m stainless steel rods which were suspended over a Formica base divided by lines into four 25 x 25 cm areas.Shock was delivered to the grids by a Grason-Stadler E 1 064 shock source. A 60-W bulb suspended 20 em over the Plexiglas insert in the ceiling of the chamber provided illumination. A 65-

Attacks by dominant colony males of a domesticated rat strain on conspecific strangers introduced into the colony include both a full range of threat displays and actual biting attack. These dominant males attack and bite both anesthetized and unanesthetized strangers, but threat displays and bites to anesthetized rats are limited. Lesions resulting from these bites are nonrandomly distributed, with most damage to the head and upper back and very few bites to ventral surfaces. When introduced strangers were left in the colonies for several days, 66% were killed, indicating that domesticated rats are capable of lethal attacks on conspecifics without external provocation.

Rats with hippocampal damage show a marked deficit in a variety of experiments requiring prolonged movement arrest. It is suggested that this inability of the hippocampal rat to "hold still" may be central in our understanding of the hippocampal syndrome. Requests for reprints should be sent to D.

No abstract