THE EFFECTS OF EARLY POSTNATAL STIMULATION MORRIS WATER-MAZE ACQUISITION IN ADULT MICE - GENETIC AND MATERNAL FACTORS

Following stressor exposure BALB/cByJ mice exhibit hypersecretion of c orticosterone and marked brain catecholamine alterations. In addition, mice of this strain exhibit impairments of performance in a Morris wa ter-maze, which may be exacerbated by footshock application. In the pr esent investigation it was demonstrated that early-life handling of mo use pups (coupled with brief separation periods from the dam over the course of 21 days postpartum) reduced the learning impairments seen wh en mice were tested in the Morris water-maze at 120 days of age and al so prevented stress-induced disturbances in this task. Likewise, cross -fostering BALB/cByJ mice with a C57BL/6ByJ dam prevented the performa nce deficits. In contrast, C57BL/6ByJ mice cross-fostered to a BALB/cB yJ dam exhibited proficient performance. Thus, maternal factors may be important in determining the Morris water-maze disturbances, provided that this was applied on the BALB/cByJ genetic background. Stressor e xposure exacerbated the performance disturbances in BALB/cByJ mice, wh ile diazepam treatment disrupted Morris water-maze performance in both BALB/cByJ and C57BL/6ByJ mice. Paralleling the behavioral changes ass ociated with handling, the stress-induced hypercorticosterone secretio n characteristic of the BALB/cByJ mouse was attenuated by the early ha ndling procedure. Stressor exposure also produced strain-dependent var iations of NE and 5-HT, but these effects were not appreciably influen ced by the handling procedure. These data are consistent with the prop osition that performance disturbances of BALB/cByJ mice tested in the Morris water-maze task are associated with excessive hypothalamic-pitu itary-adrenal reactivity. Moreover, it appears that the influence of e arly-life stimulation may interact with genetic factors in determining endocrine and behavioral stress responses.