Social isolation contributes into the effect of 3-day hindlimb unloading
on dopaminergic transmission in the nigrostriatal system of mice
Abstract
The nigrostriatal system composed of the dorsal striatum and the
substantia nigra (SN) is highly involved in the control of motor
behavior. Various extremal and pathological conditions as well as social
isolation may cause an impairment of locomotor function; however,
corresponding alterations in the nigrostriatal dopaminergic pathway are
far from full understanding. Here we analyzed the effect of 3-day
hindlimb unloading (HU) and social isolation (SI) on the key players of
dopamine transmission in the nigrostriatal system of CD1 mice. Three
groups of mice were analyzed: group-housed (GH), SI, and HU. Our data
showed a significant decrease in the expression of tyrosine hydroxylase
(TH) in the SN and dorsal striatum of HU mice, but only in comparison
with SI group that suggested attenuation of dopamine synthesis in
response to HU, while TH phosphorylation was reduced in comparison with
both GH and SI animals. SI also led to a decrease in TH phosphorylation
in the dorsal striatum that pointed on an impact of isolation too.
Expression of dopamine receptors D1 in the dorsal striatum of HU mice
was increased suggesting a compensatory response, but the activity of
downstream signaling pathways involving PKA and CREB was inhibited. But
in the dorsal striatum of SI mice, expression of DA receptors and
activity of downstream signaling was not affected. Obtained data let us
to conclude that combination of short-term HU and isolation impaired
dopamine transmission in the nigrostriatal system.