The Journal of Neuroscience, July 15, 1999, 19(14):6169-6174
Addiction-Prone Lewis But Not Fischer Rats Develop Compulsive
Running that Coincides with Downregulation of Nerve Growth Factor
Inducible-B and Neuron-Derived Orphan Receptor 1
Martin
Werme1,
Peter
Thorén2,
Lars
Olson1, and
Stefan
Brené1
Departments of 1 Neuroscience and
2 Physiology and Pharmacology, Karolinska Institutet, S-171
77 Stockholm, Sweden
We have examined the effects of chronic voluntary running for
30 d on the levels of nerve growth factor inducilble-B
(NGFI-B) and neuron-derived orphan receptor 1 (NOR1)
mRNAs in Fischer and Lewis rats. The aim was to compare the
addiction-prone Lewis rat strain to the Fischer strain in a plausible
model for natural reward. The Lewis strain ran markedly more than the
Fischer strain, as indicated by the length of running per day when
given free access to running wheels. Both strains progressively
increased their amount of daily running. By day 14, Lewis rats had
reached a maximal level corresponding to 10 km/d, which slowly
decreased to ~8 km/d. Fischer rats ran considerably less, averaging
~1.5 km/d by day 30. After 30 d of running, levels of
mRNA encoding NGFI-B and Nor1 were decreased in cerebral cortex in
Lewis but not Fischer rats. The downregulation of NGFI-B mRNA in Lewis
rats could not be attenuated by the opioid receptor antagonist
naloxone. Instead, naloxone by itself downregulated NGFI-B in striatum
and cerebral cortex in both strains. In contrast, naloxone had no effect on Nor1 mRNA levels, although the running-induced downregulation of Nor1 was, in most cases, attenuated by naloxone. Data from the
present study suggest that the same genetic factors contributing to the
drug addiction-prone behavior of Lewis rats also control the excessive
running behavior and that this coincides with downregulation of
transcription factors of the NGFI-B family.
Key words:
abuse; basal ganglia; in situ
hybridization; exercise; stress; withdrawal; NR4A1; NR4A2; NR4A3
Copyright © 1999 Society for Neuroscience 0270-6474/99/19146169-06$05.00/0