Journal of Neuroscience, Vol 10, 1847-1854, Copyright © 1990 by Society for Neuroscience
Changes in striatal dopamine neurotransmission assessed with microdialysis following recovery from a bilateral 6-OHDA lesion: variation as a function of lesion size
E Castaneda, IQ Whishaw and TE Robinson
Department of Psychology, University of Lethbridge, Alberta, Canada.
Intracerebral microdialysis was used to measure the extracellular
concentration of striatal dopamine (DA) and its metabolites in freely
moving rats depleted of DA by the bilateral infusion of 6- hydroxydopamine
into the substantia nigra approximately 1 month earlier. It was found that
the basal extracellular concentration of DA remained within the same range
as seen in control animals until the size of the lesion exceeded 80%
(estimated by the postmortem tissue concentration of DA). In animals with
an 80-95% lesion there was only a modest decrease in basal extracellular
DA, but as lesion size exceeded 95% there was a marked drop in the basal
extracellular concentration of DA. In contrast, the basal extracellular
concentration of the DA metabolites showed a more steady decline as a
function of lesion size. To determine the ability of the residual
population of DA terminals to further increase DA release upon increased
demand, animals were given a challenge injection of 1.5 mg/kg of
d-amphetamine. Amphetamine-evoked DA release remained within the control
range until lesion size exceeded 95%. These results provide direct
confirmation for the hypothesis that following recovery from partial
bilateral damage to the nigrostriatal DA system in adulthood, there are
presynaptic compensatory changes in the remaining population of DA neurons
sufficient to "normalize" the extracellular concentration of striatal DA.
It is suggested that this normalization of extracellular DA is responsible
for the sparing of function seen following the loss of up to 80% of the DA
innervation to the striatum and contributes to the recovery of function
seen after even more extensive damage (80-95%).(ABSTRACT TRUNCATED AT 250
WORDS)