Pcpa-Produced effects on behavior in rats
505
usually found after such damage. The animals with hippocampal lesions
developed hyperactivity at about the anticipated postoperative time (sec-
ond week after surgery) and were impaired in acquisition of a passive
avoidance response. It was in the passive avoidance task that some
decreased impairment was found after pretreatment with the
catecholamine depletor AMT by Lanier et al. (1974).
The effect ofPCPA treatment on brain 5-HT levels was not measured in
the present experiment due to the extended testing of all subjects, but the
data reported by Koe and Weissman (1966) indicate that after similar
treatment 5-HT returns to control levels about 2 weeks after being re-
duced to less than 20% of control values in the first postinjection week
and about 60% of control values in the second postoperative week.
The failure to find PCPA effects on the locomotor behavior of intact
animals is consistent with the lack of locomotor changes found by Isaac-
son et al. (1977) for adult rats with about 70% reduction in forebrain 5-HT
levels after intracisternal 5,6-DHT administration at 5 days of age.
Locomotion in an open field depends on the activity in specific ascending
5-HT tracts (Srebro and Lorens, 1975) rather than the brain content of
5-HT remaining after the lesion. These authors found that lesions of the
medial raphe nuclei produce decreases in locomotor activity with only a
26% decrease in forebrain 5-HT. Damage to other raphe nuclei failed to
alter locomotor behavior despite much greater reductions in forebrain
5-HT content.
A reduction in grooming was not found after hippocampal lesions by
Kim et al. (1970) or Jarrard (1968) in rats or by Glickman et al. (1970) in
the gerbil. In all of these studies, however, grooming was observed in the
home environments of the animals. In this study grooming was evaluated
in a relatively novel, open field arena. It is possible that the act of being
transported to the arena or its novelty acts to induce grooming in the
control animals but not those with hippocampal lesions.
The hyper-responsiveness to footshock that has been reported as a
consequence ofPCPA (e.g., Harvey and Yunger, 1973) and some residual
effect of PCPA may account for the fact that the control group treated with
PCPA received fewer shocks than the nontreated control group during
acquisition of the passive avoidance task. However, this was not found in
animals with either hippocampal or neocortical damage. This supports the
suggestion that certain serotonergic influences are mediated by dorsal
hippocampal areas (Jacobs et al., 1975).
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