Long-term behavioral and biochemical effects of 6-hydroxydopamine injections in rat caudate-putamen

Quantitative in situ hybridization evidence for differential regulation of proenkephalin and dopamine D2 receptor mRNA levels in the rat striatum: effects of unilateral intrastriatal injections of 6-hydroxydopamine

Nigrostriatal (NS) dopaminergic (DA) neurons are thought to exert an inhibitory influence on striatal enkephalinergic systems through their DA D2 receptors. In order to investigate the effects of partial lesions of the NS DA on striatal proenkephalin (PEK) and D2 receptor mRNAs, animals were allocated to High, Intermediate, and Low rotators on the basis of amphetamine-induced rotation observed after intrastriatal injections of 6-hydroxydopamine (6-OHDA). On the ipsilateral side of the lesions, there were significant increases in PEK mRNA in the total aspect of the caudate-putamen (CPu) of the High (+204%), the Intermediate (+125%), and of the Low (+67%) rotation groups in comparison to controls; these changes correlated positively with increases in rotation rate. Unexpectedly, there were also significant increases in striatal PEK mRNA on the contralateral side although these changes were much less prominent than those observed on the side of the lesions. Conversely, only the High rotation group showed significant increases (+112%) in D2 receptor mRNA which occurred only on the lesioned side. Interestingly, the low rotation group actually showed some non-significant decreases (-25%) on the side of the lesions. These results indicate that partial lesions of the NS DA projections are sufficient to cause substantial increases in PEK mRNA but not in D2 receptor mRNA. These data also provide evidence that the two nigrostriatal DA projections and the systems which they modulate might be under interdependent sets of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilateral modulation of [3H]neurotensin binding by unilateral intrastriatal 6-hydroxydopamine injections: evidence from a receptor autoradiographic study

The present study was carried out in order to re-evaluate the issue of the localization of neurotensin receptors in the caudate-putamen and in the nucleus accumbens of rat. Intrastriatal injections of 6-hydroxydopamine which cause almost complete destruction of the mesostriatal dopaminergic pathway also caused a marked loss of neurotensin receptors in the caudate-putamen (CPu), the nucleus accumbens (NAc) and in the olfactory tubercle (OT). These decreases corresponded to a mean loss of 98, 93 and 41% in the CPu, the NAc, and the OT, respectively. There were corresponding decreases in the substantia nigra pars compacta (SNpc) (-94%) and pars reticulata (SNpr) (-97%), and in the ventral tegmental area (-78%). Moreover, there were also decreases in neurotensin receptors on the contralateral side of the intrastriatal injections which occurred in the CPu but not in the NAc nor in the OT. These results indicate that almost all NT receptors measured within the CPu and the NAc are located on the terminals of dopaminergic neurons within those structures. The bilaterality of the changes which occur in the CPu provide further support for the notion of the interdependence of the two nigrostriatal dopaminergic projections and the peptidergic systems with which they interact.

Intrastriatal implants of fetal mesencephalic cells attenuate the increases in striatal proenkephalin mRNA observed after unilateral 6-hydroxydopamine-induced lesions of the striatum

Unilateral injections of 6-hydroxydopamine (6-OHDA) cause significant bilateral increases in striatal proenkephalin (PEK) mRNA in rat brain. We have tested the possibility that implantation of fetal mesencephalic cells can normalize these changes. Two types of grafts were used: 1) embryonic day-15 mesencephalic cells and 2) embryonic day-15 cells which have been modified with a retroviral vector containing a cDNA for protein kinase C (PKC). At two months after grafting, both cell types cause significant attenuation of the increases which occurred on the side of the lesion. However, only the PKC-modified cells cause normalization of the changes on the contralateral side. These observations indicate that, in addition to normalizing supersensitive striatal dopamine (DA) D2 receptors, embryonic cells can also attenuate the alterations in PEK mRNA observed after lesions of the nigrostriatal DA system. The finding that the PKC-modified cells caused bilateral effects in the striatum suggests that second messenger systems may play a role in the bilateral improvement reported in parkinsonian patients who had gotten unilateral intrastriatal transplants.