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Behavioural Processes, 17 (1988) 63 -67 Elsevier

Letter Latency

Measures

Richard

J.

Indicate

New Place

in Rattus

Species

Wallace

Computer Science Department, (Accepted 28 April 1988) ABSTRACT Wallace, species.

Neophobia

R.J., 1988. Latency Behav . Process. 17:

University

measures 63-67

of

New Hampshire,

indicate

new place

Durham, NH 03824,

neophobia

U.S.A.

in Rattus

Latency to enter an unfamiliar wooden alley from the home cage was recorded All groups on successive daily trials in several populations of domestic rats. Latencies showed a decline in latency over days suggesting an initial neophobia. for individual rats on Trial 1 showed a bimodal distribution in most groups, Earlier reports of reflecting mild or intense avoidance of the unfamiliar area. new place reactions in wild Rattus suggesting an immediate neophilic reaction to a novel area may have overlookedinitial hesitations to enter the area because latency measures were not used systematically. novelty

exploration

neophobia

new place

reaction

INTRODUCTION Earlier reports have contrasted the reactions of commensal Rattus species and -R. rattus) to novel objects and novel places. If a new object (R, norvegicus appears in a location that is familiar to the animal, there is often pronounced avoidance (Barnett, 1958; Cowan, 1977; Cowan & Barnett, 1975; Shortan, 1954). On the other hand, access to a new area seems to produce immediate exploration by these animals (reviewed in Barnett 6 Cowan, 1976). Domestic Norway rats show a period of avoidance of novel objects that is short when compared to wild conspecifics (Barnett, 1958; Mitchell, 1976). Like their wild counterparts they readily explore a novel area (Barnett, Smart & Widdowson, 1971; Cowan, 1977; Montgomery, 1952). The most extensive data on the new place reaction have been obtained by Barnett and his coworkers using an automated maze apparatus (see Barnett et al., 1971; Cowan and Barnett, 1975 for details), These investigators found that, i) the number of visits to each arm declines markedly after the first day (or trial) in the maze, ii) if an arm is opened after several days in the maze, the greatest number of visits to that arm is recorded on the first day (or trial) of access (Cowan, 1977; Cowan & Barnett, 1975). Although these results undoubtedly reflect a greater tendency to approach and explore a new area before familiarization, they do not rule out an initial avoidance, or neophobia, that then gives way to “neophilia”. Unfortunately, measures of latency to enter an arm following access have not generally been reported in these studies. However, a recent analysis of movement in a plus maze by -R. rattus during daily five hour trials showed a significant decrease in latency across the seven or eight trials of the first condition (Wallace, 1987). At the same time the rats showed the usual decline in the number of visits across trials, indicating neophilia. Several studies of domestic Norway rats also suggest an initial avoidance of a newly accessible area adjacent to the place of residence. When rats are allowed to enter an.alley from their home cages, reported latencies indicate that entry is not immediate (Bindra, 1948; Meyers, Leary h Littman, 1965; Osborne, 1977; see also Montgomery, 1955). Fehrer (1956) showed that extended familiarization with a nesting box led to an increase in the time taken to enter a new locale. In a complementary paradigm, Blanchard, Kelley and Blenchard (1974) found that entry into a new area from the home cage was facilitated by 0376-6357/88/$03.50

0 1988 Elsevier Science Publishers B.V. (Biomedical Division)

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prior forced demonstrations Blanchard et

exposure to that area. These of escape from a novel area al., 1974).

latency data are corroborated into the home cage (Aulich,

by 1976;

This note presents further evidence for new place neophobia in domestic rats, based on entrance latencies. These data were collected over a period of years in experiments on object retrieval. During the initial “familiarization” trials, no objects were present, so these trials tested the response to a new location. latency to enter the new area was In contrast to prior reports, recorded for a series of daily trials. Data from two strains and a variety of sources indicate the generality of the basic phenomenon and the quantitative variation in this characteristic within different populations. NEW RESULTS AND DISCUSSION In these studies the new place was a wooden box or “alley”, usually 60 x 20 x 20 cm, that was set before the animal’s home cage for a limited time each day. Latency to place all four feet in the alley was recorded to the nearest five sec. Subjects received food and water ad libitum, and were handled daily for at least one week before the first trial. %-were given during the last few hours of the light period of a 12:12 or 13:ll LD cycle. Cages were never moved, unlike some studies of cage emergency (e.g., Harrington, 1971). Under these conditions subjects always approached and investigated the alleys at the beginning of each trial. Sprague-Dawley (several Three strains have been tested in this way: breeding populations: cf. Figures l-2)) Wistar and agouti.

Figure 1. Median latencies (logip scale) on successive trials beginning with the first opportunity to enter the a ey. Vertical lines indicate full interquartile ranges, i.e., to 01 and 03. Break in Carworth graph is for trial on which incomplete data were taken.

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Latencies declined over trials for all groups tested, the relation between mean or median latency and trials having a positively decelerating form (The function must be complex or suggesting a negative exponential function. Two composite, since this form obtains when the ordinate is logarithmic.) examples are shown in Figure 1 for populations that differed greatly in their initial avoidance of the alleys (see Wallace, 1983 (Exper. 1); Wallace & Tigner, a similar decline in median latency over trials 1972 for details). Despite this, and for every rat the difference between the first and is seen in both groups, Figure last latencies is positive (E

Latency measures indicate new place neophobia in Rattus species.

Latency to enter an unfamiliar wooden alley from the home cage was recorded on successive daily trials in several populations of domestic rats. All gr...
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