B. Soderpalm et al., Bovine growth hormone transgenic mice display alterations in locomotor activity and brain monoamine neurochemistry, ENDOCRINOL, 140(12), 1999, pp. 5619-5625
Recent clinical and experimental data indicate a role for GH in mechanisms
related to anhedonia/hedonia, psychic energy, and reward. In the present st
udy we have investigated whether bovine GH (bGH) transgenic mice and nontra
nsgenic controls differ in spontaneous locomotor activity, a behavioral res
ponse related to brain dopamine (DA) and reward mechanisms, as well as in l
ocomotor activity response to drugs of abuse known to interfere with brain
DA systems. The animals were tested far locomotor activity once a week for
4 weeks. When first exposed to the test apparatus, bGH transgenic animals d
isplayed significantly more locomotor activity than controls during the ent
ire registration period (1 h). One week later, after acute pretreatment wit
h saline, the two groups did not differ in locomotor activity, whereas at t
he third test occasion, bGH mice were significantly more stimulated by d-am
phetamine (1 mg/kg, ip) than controls. At the fourth test, a tendency for a
larger locomotor stimulatory effect of ethanol (2.5 g/kg, ip) was observed
in bGH transgenic mice. bGH mice displayed increased tissue levels of sero
tonin and 6-hydroxyindoleacetic acid in several brain regions, decreased Db
levels in the brain stem, and decreased levels of the DA metabolite 3,4-di
hydroxyphenylacetic acid in the mesencephalon and diencephalon, compared wi
th controls. In conclusion, bGH mice display more spontaneous locomotor act
ivity than nontransgenic controls in a novel environment and possibly also
a disturbed habituation process. The finding that bGH mice were also more s
ensitive to d-amphetamine-induced locomotor activity may suggest that the b
ehavioral differences observed are related to differences in brain DA syste
ms, indicating a hyperresponsiveness of these systems in bGH transgenic mic
e. These findings may constitute a neurochemical basis for the reported psy
chic effects of GH in humans.