DIET-INDUCED ALTERATIONS IN THE ONTOGENY OF LONG-TERM POTENTIATION

The ability of prenatally malnourished rats to establish and maintain long-term potentiation (LTP) of the perforant path/dentate granule cel l synapse was examined in freely moving rats at 15, 30, and 90 days of age. Measures of the population EPSP slope and population spike ampli tude (PSA) were calculated from dentate field potential recordings obt ained prior to and at various times following tetanization of the perf orant pathway. Significant enhancement of both population EPSP slope a nd PSA measures was obtained from all animals of both malnourished and well-nourished diet groups at 15 days of age. However, the magnitude of enhancement obtained from 15-day-old prenatally malnourished animal s was significantly less than that of age-matched, well-nourished cont rols. At 30 days of age, PSA measures obtained from approximately 50% of prenatally malnourished 30-day-old rats showed no significant effec t of tetanization, while measures obtained from the remaining 50% of t hese animals did not differ significantly from controls. EPSP slope me asures for this age group followed much the same pattern, i.e., malnou rished animals showing no significant enhancement of PSA measures exhi bited only slight increases in EPSP slope beginning 1 h after tetaniza tion and returned to baseline by 18 h post-tetanization. EPSP slope me asures obtained from PSA-enhanced malnourished animals did not differ significantly from controls. At 90 days of age, PSA measures obtained from 50% of malnourished animals declined from pretetanization levels immediately following tetanization. Three hours after tetanization, ho wever, this measure had increased to a level which did not differ sign ificantly from that of the control group. PSA measures obtained from t he remaining 50% of 90-day-old malnourished animals showed initial and sustained enhancement which did not differ significantly from those o btained from well-nourished age-matched controls. These results indica te that gestational protein malnutrition significantly affects the mag nitude of tetanization-induced enhancement of dentate granule cell res ponse in preweanling rats (15-day-old animals) and significantly alter s the time-course and magnitude of potentiation in approximately half of prenatally malnourished animals tested at 30 and 90 days of age. Gi ven the primarily postnatal development of the dentate granule cells, these results may reflect malnutrition-induced delays in the neurogene sis and functional development of granule cells previously reported by our group. Most striking is the fact that significant impairments in LTP establishment were obtained from prenatally malnourished animals a t 90 days of age, implying that dietary rehabilitation commencing at b irth is an intervention strategy incapable of ameliorating the effects of the gestational insult. (C) 1996 Wiley-Liss, Inc.