The Journal of Neuroscience, July 1, 1998, 18(13):5035-5044
Effects of Pedunculopontine Tegmental Nucleus Lesions on
Responding for Intravenous Heroin under Different Schedules of
Reinforcement
Mary C.
Olmstead1,
Elizabeth M.
Munn2,
Keith
B. J.
Franklin3, and
Roy A.
Wise2
1 Department of Psychology, Queen's University,
Kingston, Ontario K7L 3N6, Canada, 2 Centre for Studies in
Behavioral Neurobiology, Concordia University, Montréal,
Québec H3G 1M8, Canada, and 3 Department of
Psychology, McGill University, Montréal, Québec H3A 1B1,
Canada
The pedunculopontine tegmental nucleus (PPTg) is believed to play
important roles in reward and learning. We examined the effect of PPTg
lesions (0.5 µl of 0.1 M NMDA injected bilaterally over
10 min) on the learning of an operant response for opiate reward. In 14 adult male Long-Evans rats, bilateral lesions of the PPTg disrupted
the acquisition of responding for intravenous heroin (0.1 mg/kg infused
at a rate of 0.25 ml/28 sec) on a fixed ratio-1 (FR-1) schedule of
reinforcement. The 12 remaining lesioned animals increased their heroin
intake over the acquisition sessions but did not reach the response
levels of sham-lesioned animals on the 15th and final session. The
sham- and PPTg-lesioned animals that learned the FR-1 task exhibited
similar patterns of responding during extinction and reacquisition
sessions. When tested on a progressive ratio (PR) schedule of
reinforcement, however, PPTg-lesioned animals had lower break points
than sham-lesioned animals. Asymmetric lesions, which destroyed the
majority of the nucleus in one hemisphere only, did not produce any
behavioral deficits. Rats that were lesioned after training also did
not show deficits in responding under either FR or PR schedules. These
findings suggest that PPTg lesions reduce the rewarding effect of
opiates but do not disrupt the ability either to learn an operant
response or the response requirements of a PR schedule.
Key words:
brainstem; learning; opiates; PPTg; reward; self-administration
Copyright © 1998 Society for Neuroscience 0270-6474/98/18135035-10$05.00/0
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