Effects of population density and living space upon neuroanatomy, neurochemistry, and behavior in the C57Bl/10 mouse.

Abstract

One hundred fifty-six male C57B1/10 mice lived in groups of 1, 4, 8, 16, or 32 animals. For all group sizes animals were housed either in cages of a constant size, so that group size and crowding correlated, or were housed in cages with floor space varied proportional to the group size. Closed-maze exploration decreased with increased group size, irrespective of crowding, while wheel activity was an interactive effect of group size and degree of crowding. Reduced concentrations of brain protein and nucleic acids accompanied living in larger groups, whether crowded or not, but rate of intracellular synthesis of RNA and protein by DNA was more dependent upon the size of the living space.*A portion of the data reported here is also reported in an unpublished master's thesis by C. E. Miller, Population density and overcrowding: Possible confounding due to space. Northern Illinois University. 1969.2 Requests for reprints should be sent to R.

The Development of Social Interaction, Play, and Metacommunication in Mammals: An Ethological Perspective

“…Bekoff and Fo.x-(1972) have discussed variables that affect development of the central nervous system, particularly in rodents, and it is not unlikely that many of them, if not all of them, affect the ontogeny of both brain and behavior in other mammals. These include handling (see Morton, 1968, for a review of this literature), cage size (Bell, Miller, and Ordy, 1971), birth mode (caesarian versus vaginal delivery -Meier, 1964;Meier and Garcia-Rodriguez, 1966;Grota, Denenberg, and Zarrow, 1966), conditions at birth (e.g., hypoxia, asphyxia-see Meier, 1971, for a review of this literature), and litter size (LaBarba and White, 1971). Poole (1966), studying the agressive play of polecats, stated that the size and agility of the animal depended on the number in the litter from which it came.…”

Postnatal neural ontogeny: Environment‐dependent and/or environment‐expectant?

“…[See Morton (1968) for a review of the effects of handling in laboratory animals.] Cage size (Bell, Miller & Ordy, 1971), litter size (LaBarba & White, 1971;Poole, 1966), time of weaning, and the existence of possible endogenous rhythms must also be controlled for. Little is gained by knowing the genetic strain of the animal under study if the experiential life-history is only partially accounted for (see Denenberg, 1969).…”

Environmental enrichment and crowding: Behavioral and hormonal effects

“…However, several investigators have reported increased aggressiveness among crowded animals [9,15,28], and/or no adrenal hypertrophy [4,7,17,29,33 ].…”