Behavioral manifestations of prolonged lead exposure initiated at different stages of the life cycle: I. Schedule-controlled responding.
While early development represents a period of particular sensitivity to the neurotoxic effects of lead (Pb), much less is known about CNS effects at later stages of the life cycle. It is conceivable that old age represents an additional period of vulnerability given the neurodegenerative processes that are the inevitable accompaniment of advanced age. The experiments described here examined that possibility. The effects of prolonged low-level Pb exposures were assessed in young (21 day old), adult (8 mon old) and old (16 mon old) F-344 rats performing on Fixed-Interval (F1) and Variable-Interval (VI) schedules of reinforcement, two behavioral baselines previously shown to be sensitive to Pb exposure in young rats. The profile of Pb effects within each age group was remarkably uniform across both reinforcement schedules, while the direction of effect differed by age group. Pb exposure was associated with shifts toward increased VI and FI response rates in both young and old rats. In contrast, adult rats exposed to Pb exhibited decreased rates of responding on both FI and VI schedules. Both patterns of response rate changes can be indicative of less efficient performance. Of the two reinforcement schedules, the FI appeared to be the more sensitive, as marginally significant behavioral effects were observed at both the 2 and 10 mg Pb/kg/day doses on the FI, while only occurring in response to the 10 mg/kg dose of Pb on the VI. The differential pattern of Pb effects across age groups does not appear to reflect a rate-dependency phenomenon, but its exact basis awaits further investigation. The detection of primarily marginally significant response rate changes here as compared to previous studies using similar Pb exposure levels suggests that the F-344 strain of rats is less sensitive to Pb than is the Long-Evans rat strain.
Cory-Slechta
D A
DA
Environmental Health Sciences Center, University of Rochester School of Medicine and Dentistry, New York 14642.
Pokora
M J
MJ
D000375:Aging / Q000523:psychology*; D000818:Animals; D001921:Brain / Q000378:metabolism; D003216:Conditioning, Operant / Q000187:drug effects*; D007854:Lead / Q000097:blood / Q000378:metabolism / Q000633:toxicity*; D008297:Male; D010865:Pilot Projects; D051381:Rats; D011916:Rats, Inbred F344; D012055:Reinforcement Schedule; D013997:Time Factors
D007854:Lead