Preservation of dopamine release in the denervated striatum.

Dopamine metabolism and release were determined in the striata of rats sustaining varying damage to the nigrostriatal dopamine (DA) projection. DA metabolism, inferred from concentrations of dihydroxy-phenylacetic acid (DOPAC) or homovanillic acid (HVA), decreased with DA denervation of more than 20%. Dopamine release, inferred from the concentration of 3-methoxytyramine (3-MT), did not decrease unless the denervation was at least 80%. The amount of 3-MT per surviving neuron exceeded that for DOPAC over most of the denervation range. Thus, striatal DA release is preserved at normal levels with the survival of only 20% of the striatal DA innervation. Decreases in DA release, rather than decreases in DA metabolism or the density of dopamine innervation, coincide with the appearance of behavioral impairments.