Thalamic control of dopaminergic functions in the caudate-putamen of the rat--III. The effects of lesions in the parafascicular-intralaminar nuclei on D2 dopamine receptors and high affinity dopamine uptake.

Dopamine receptor binding in the caudate-putamen was studied following bilateral lesions of the thalamostriatal pathway. Receptor binding was assayed using [3H]spiperone and defined with both (+)-butaclamol and S(-)-sulpiride. Radiofrequency lesions resulted in an increase in the Bmax of [3H]spiperone binding defined with both (+)-butaclamol and S(-)-sulpiride between 7 and 14 days following surgery. At longer survival times a fluctuating response was seen in which a decrease in receptor binding was observed at 28 days following lesion and a further rise again at 70 days. At no time point was significant change in Kd recorded. Further experiments were carried out to control for the possible effects of damage to fibres of passage and for inadvertent damage to habenula, as well as to define the receptor subtype involved. Ibotenic acid lesions resulted in similar effects to those reported with the radiofrequency method. Thus, 7 days following lesion, Bmax for (+)-butaclamol-defined [3H]spiperone binding increased by approximately 14-20% over that recorded in sham-lesioned animals. Using S(-)-sulpiride to define binding, Bmax was found to increase 13-17% in the same membrane preparations. Similar results were obtained in experiments at 14 days following ibotenic acid induced lesions. Again, no change in Kd was recorded. When radiofrequency lesions were made, which were largely restricted to habenula and associated fibres of passage, only small [(+)-butaclamol defined] or insignificant [S(-)-sulpiride defined] changes in Bmax were recorded. Combined radiofrequency lesions of habenula and ibotenic acid lesions of the thalamus resulted in a larger increase in Bmax for (+)-butaclamol defined binding than with S(-)-sulpiride defined binding. Our interpretation of these findings, in the light of the histology of the lesions, is that the predominant effect of removing thalamic input to the caudate-putamen is an increase in the number of D2 receptors, but without any change of affinity. A small component of the change in Bmax defined with (+)-butaclamol found with radiofrequency lesions may be due to a response at non-dopamine sites (possibly a 5-hydroxytryptamine receptor subtype) following damage to other caudate-putamen afferents which pass near the habenula or fasciculus retroflexus. Following unilateral ibotenic acid lesions of the thalamus, the number of high affinity uptake sites for dopamine was increased at long survival times.(ABSTRACT TRUNCATED AT 400 WORDS)