Journal of Neuroscience, Vol 12, 4281-4297, Copyright © 1992 by Society for Neuroscience
Influence of mesostriatal afferents on the development and transmitter regulation of intrastriatal grafts derived from embryonic striatal primordia
FC Liu, SB Dunnett and AM Graybiel
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Embryonic striatal grafts develop a modular organization in which patches
of tissue enriched in many transmitter substances characteristic of
striatum (P regions) are embedded in surrounds (NP regions) expressing only
low levels of these substances. Catecholaminergic fibers from the host
brain, identified by their expression of tyrosine hydroxylase (TH), grow
into such grafts and selectively terminate in the striatum-like P regions.
This terminal pattern suggests that cell-cell affinities between neurons of
the substantia nigra and striatum may play a role either in the aggregation
of the striatal cells into P regions, or in the targeting of the TH-
positive fibers to the cell clusters. In the present study, we tested the
first of these possibilities. Striatal grafts derived from embryonic day 15
striatal primordia were implanted into the ibotenate- damaged host striatum
of rats previously treated with 6-hydroxydopamine (6-OHDA) to destroy
TH-containing dopaminergic nigrostriatal afferents. The 6-OHDA lesions that
eliminated nearly all TH-like immunostaining in the host striatum also
resulted in disappearance of nearly all TH- positive fibers in the grafts.
In this dopamine-depleted environment, the grafts nevertheless developed a
clear modular organization. They contained striatum-like patches with
neurons expressing many of the neurochemicals characteristic of striatum
(ACh, ChAT, calbindin-D28KD, met-enkephalin, and dopamine- and adenosine
3':5'-monophosphate- regulated phosphoprotein-32,000 or DARPP-32), and
these patches were surrounded by graft tissue expressing few of these
striatal markers. These observations suggest that the ingrowth of
TH-positive fibers from the host is not obligatory for the sorting out of
striatal from nonstriatal cells during the formation of P regions in
embryonic striatal grafts. Despite the fact that dopaminergic denervation
of the host striatum did not disrupt either the aggregation of grafted
cells into P regions or the acquisition of striatal neurochemical
phenotypes by cells in the P regions, there were clear differences between
the staining patterns of these grafts and grafts placed into dopamine-
innervated striatum. Most striking was a sharp increase of met-
enkephalin-like immunostaining in the P zones of the denervated grafts.
Upregulation of met-enkephalin is known to occur in the dopamine- depleted
mature striatum, and was observed in the parts of host striatum surrounding
the grafts on the side ipsilateral to the 6-OHDA lesions. This result
suggests that functional interactions between dopaminergic and
enkephalinergic systems can occur in the striatal circuits reconstructed by
embryonic striatal grafting. More generally, our results suggest that
TH-containing afferents from the host striatum, though not required for
induction and maintenance of striatal phenotypy in striatal grafts, can
chronically regulate neurotransmitter/neuromodulator expression in neurons
of the striatum- like P zones in a manner similar to that found for the
normal striatum.