The GABA and substance P input to dopaminergic neurones in the substantia nigra of the rat

Cholinergic input to dopaminergic neurons in the substantia nigra: a double immunocytochemical study

In order to determine whether the cholinergic fibres that innervate the substantia nigra make synaptic contact with dopaminergic neurons of the substantia nigra pars compacta, a double immunocytochemical study was carried out in the rat and ferret. Sections of perfusion-fixed mesencephalon were incubated first to reveal choline acetyltransferase immunoreactivity to label the cholinergic terminals and then tyrosine hydroxylase immunoreactivity to label the dopaminergic neurons. Each antigen was localized using peroxidase reactions but with different chromogens. At the light microscopic level, in confirmation of previous observations, choline acetyltransferase-immunoreactive axons and axonal boutons were found throughout the substantia nigra. The highest density of these axons was found in the pars compacta where they were often seen in close apposition to tyrosine hydroxylase-immunoreactive cell bodies and dendrites. In the ferret where the choline acetyltransferase immunostaining was particularly strong, bundles of immunoreactive fibres were seen to run through the reticulata perpendicular to the pars compacta. These bundles were associated with tyrosine hydroxylase-immunoreactive dendrites that descended into the reticulata. The choline acetyltransferase-immunoreactive fibres made "climbing fibre"-type multiple contacts with the tyrosine hydroxylase positive dendrites. At the electron microscopic level the choline acetyltransferase-immunoreactive axons were seen to give rise to vesicle-filled boutons that formed asymmetrical synaptic specializations with nigral dendrites and perikarya. The synapses were often associated with sub-junctional dense bodies. On many occasions the postsynaptic structures contained the tyrosine hydroxylase immunoreaction product, thus identifying them as dopaminergic. It is concluded that at least one of the synaptic targets of cholinergic terminals in the substantia nigra are the dendrites and perikarya of dopaminergic neurons and that in the ferret at least, the dendrites of dopaminergic neurons that descend into the pars reticulata receive multiple synaptic inputs from individual cholinergic axons.

Convergence of synaptic inputs from the striatum and the globus pallidus onto identified nigrocollicular cells in the rat: a double anterograde labelling study

Two major sources of afferent synaptic inputs to projection neurons in the rat substantia nigra reticulata are the striatum and the globus pallidus. In order to understand better the functional relationships between these two afferents in the control of the activity of nigrofugal neurons, experiments have been performed to test the possibility that single nigrofugal cells receive convergent synaptic inputs from the striatum and the globus pallidus. To address this question we have used two different approaches. First, we have developed a double anterograde labelling technique suitable for both light and electron microscopy and combined this procedure with the retrograde transport of lectin-conjugated horseradish peroxidase in order to retrogradely label the nigrocollicular cells. Second, we have combined the anterograde transport of Phaseolus vulgaris-leucoagglutinin from the globus pallidus and immunocytochemistry for DARPP-32 as a marker for the striatal terminals, with the retrograde transport of lectin-conjugated horseradish peroxidase from the superior colliculus. In the double anterograde labelling experiment, biocytin was injected in the striatum, Phaseolus vulgaris-leucoagglutinin in the globus pallidus and lectin-conjugated horseradish peroxidase in the superior colliculus. Following these injections, rich plexuses of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals were found in the ventral two-thirds of the substantia nigra. The biocytin-positive terminals (striatonigral) were generally small and formed rich plexuses without any apparent neuronal association whereas the Phaseolus vulgaris-leucoagglutinin-labelled terminals (pallidonigral) were much larger and formed baskets around the perikarya of retrogradely and non retrogradely labelled cells in the substantia nigra reticulata. In areas of the substantia nigra reticulata where the fields of biocytin- and Phaseolus vulgaris-leucoagglutinin-labelled terminals overlapped, the perikarya and the proximal dendrites of retrogradely and non retrogradely labelled cells were found to be apposed by numerous Phaseolus vulgaris-leucoagglutinin-immunoreactive pallidonigral terminals and a few biocytin-labelled striatonigral terminals. In the sections prepared for electron microscopy, the biocytin was localized using 3,3'-diaminobenzidine tetrahydrochloride whereas Phaseolus vulgaris-leucoagglutinin was localized using benzidine dihydrochloride. It was thus possible to distinguish the biocytin- from the Phaseolus vulgaris-leucoagglutinin-labelled terminals in the electron microscope by the texture of the reaction product associated with them.4+ Examination of 231 biocytin-labelled (striatonigral) terminals and 105 Phaseolus vulgaris-leucoagglutinin-immunoreactive (pallidronigral) terminals revealed that the striatonigral terminals were generally small, contained few mitochondria and formed symmetric synapses predominantly with the distal dendrites (77%) and far less frequently with the perikarya (3%) of substantia nigra reticulata cells.(ABSTRACT TRUNCATED AT 400 WORDS)