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The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced hypersensitivity of striatal dopaminergic receptors. The ascending dopaminergic pathway of adult rats was unilaterally lesioned using 6-hydroxydopamine. Three weeks later a cell suspension obtained from the mesencephali of ED 14 rat embryos was implanted into the denervated striatum. Rotational responses to dopaminergic agonists were tested five months after implantation. One month later animals were killed and striatal dopaminergic receptor densities were quantified using autoradiography, the dopaminergic reinnervation of the host striatum being visualized with [3H]GBR 12935, a ligand labelling dopamine uptake sites. The lesion induced a behavioural hypersensitivity to dopaminergic agonists and lesioned animals displayed a strong rotation contralateral to the lesion in response to a test dose of the D1 agonist compound SKF 38393 (2.5 mg/kg) or of the D2 agonist LY 171555 (0.15 mg/kg). These responses were completely abolished by the graft. The normal distribution of D1 and D2 dopaminergic receptors in the rat striatum was similar to that described previously. Seven months after the lesion of the nigrostriatal dopaminergic pathway, the density of D1 receptors was not significantly affected while the density of D2 receptors was increased by about 25-50%. The implantation of embryonic dopaminergic neurons into the denervated striatum led to a slight decrease of D1 receptor densities and to a reversal of the lesion-induced increase of striatal dopaminergic D2 receptors six months later. Moreover, this reversal concerned not only the reinnervated striatal region but also extended into non-reinnervated areas of the striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the density of dopaminergic D2 receptors.

The aim of the present study was to test whether intrastriatal implants of embryonic dopaminergic neurons are able to normalize the lesion-induced dysfunction of striatal enkephalinergic neurons, one of the major output systems of the striatum. The ascending dopaminergic pathway of adult rats was unilaterally lesioned. Three weeks later a cell suspension obtained from the mesencephali of ED14 rat embryos was implanted into the denervated striatum and striatal methionin enkephalin immunostaining was quantified six months later by the use of an image analyser. Methionin enkephalin immunostaining was unevenly distributed in the striatum of control animals. Besides the classical patch/matrix pattern, a mediolateral gradient was also present and, moreover, immunostaining decreased towards caudal levels. Seven months after the lesion of the nigrostriatal dopaminergic pathway, methionin enkephalin immunostaining was found to be increased in the denervated striatum by about 50%. However, relative increases were more sustained in the areas where basal methionin enkephalin immunostaining were lowest, i.e. the lateral striatum and posterior striatal areas. This resulted in an attenuation of the global gradients seen in the normal striatum. Increased immunostaining was also found in the ipsilateral globus pallidus. The implantation, into the denervated striatum, of embryonic dopaminergic neurons led to a reversal of the lesion-induced increase of striatal and pallidal methionin enkephalin immunostaining six months later. Moreover, this reversal resulted in an overshoot, as the level of immunostaining in the graft-bearing striatum was found to be lower than the levels found in the normal striatum. It is concluded that grafts of embryonic dopaminergic neurons can normalize the function of one of the major output systems of the striatum and, through it, influence more distant targets of this structure. This suggests a physiological basis for the behavioral effects observed previously with such grafts.

The glyoxylic acid fluorescence technique was applied to the study of catecholamine fibres in the caudate-putamen (neostriatum) of control and experimental adult rats. Cryostat or vibratome sectioning procedures were used; in the last case, either incubations of brain slices in gamma-methyl-noradrenaline or pre-treatment of animals with gamma-hydroxybutyrate were performed, in order to increase the intensity of fluorescence. In control animals and in the contralateral side of rats lesioned in the substantia nigra, the fluorescence of the dense plexus of dopamine nerve fibres appeared under the form of densely packed varicosities. However, some regions differed from the ordinary fluorescence of the neostriatum by their stronger intensity and more visible varicosities. They were located principally in the ventro-medial regions bordering either the nucleus accumbens, the dorsal nucleus interstitialis striae terminalis and the ventricle in the anterior part, or the amygdala, the globus pallidus and the ventricle in the posterior part. Moreover, islands of stronger fluorescence also were observed in the head of the caudate-putamen along the dorsal and lateral corpus callosum, as well as scattered in the central region. These particular neostriatal structures might correspond to a separate system of ascending dopamine nerve fibres. Therefore, restricted electrolytic lesions of the substantia nigra pars compacta were undertaken in order to study the morphology of the remaining catecholaminergic fibres in the ipsilateral neostriatum. In largely denervated areas, different types of fluorescent axons were evident. Presumed noradrenergic nerve fibres characterized by a very coarse appearance and closed varicosities were rare. They contrasted markedly with numerous delicate fibres which might belong to several dopaminergic systems. Both first types exhibited long, clearly visible intervaricose segments and ovoid triangular varicosities. The second type, which was thicker and more strongly fluorescent, probably formed the islands observed in unlesioned striata. The third type had very closed, small spherical varicosities and poorly fluorescent intervaricose segments. Dopamine nerve fibres of the same morphology were described previously in the neocortex [43,44] and the possibility of a common origin for nerve fibres of the same type is discussed. When rats were treated with the anaesthetic gamma-hydroxybutyrate, all the dopamine nerve fibres appeared to develop a strong fluorescence within the neostriatum, but more fluorescent islands were always visible. Additionally, some swollen fluorescent fibres were seen; these could be abnormal dopamine fibres whose metabolism had been pathologically altered by the drug.

Intrathecal (i.t.) administration of apomorphine at the upper thoracic level lowered blood pressure and heart rate in awake rats. This decrease was dose-dependent and competitively antagonized by haloperidol (i.v. and i.t.) or domperidone (i.t.) but not by domperidone (i.v.). Furthermore, these effects of apomorphine were not affected by alpha- and beta-blocking drugs (i.t.). The results suggest a spinal site, at least in part, for the cardiovascular effect of apomorphine.

[3H]Haloperidol as dopaminergic ligand used on pooled microdiscs punched from the rat dorsal spinal cord allowed detection of a stereospecific binding. Characteristics of such a binding: dissociation constant, Hill's slope and IC50 of different specific drugs were nearly the same as those found in the striatum, which suggests the presence of individualized dopaminergic receptor sites in the rat dorsal horn. Their density (Bmax) is about three times lower than in the whole striatum.

Immunohistochemistry of three specific synthesizing catecholamine enzymes was used in the rat spinal cord to determine precisely the distribution of catecholaminergic perikarya and the nature of the neurotransmitter they contain. Single and double labeling experiments were performed on cryostat sections from perfused rats. The peroxidase anti-peroxidase (PAP) and the indirect fluorescence techniques were used for labeling spinal catecholaminergic somata and separated into two completely different populations. The first is located in the upper cervical cord and includes three apparently distinct groups: a lateral cluster, of probably a noradrenergic nature, and two central subgroups where noradrenergic and dopaminergic neurons are intermingled. It is likely that these cervical cells represent caudal extensions of the medullary catecholaminergic cell groups. In the remaining cord, only tyrosine hydroxylase immunoreactive cell bodies have been found. Accordingly, this second population is probably dopaminergic. It is present almost exclusively in the first sacral segments, where it is located in the commissural (mostly lateral) grey matter and in the marginal dorsal horn.