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The development of the monoclonal antibody YC5/45 HLK (YC5/HLK) against a 5HT-bovine seroalbumin immunogen and its application for immunocytochemistry is described. The YC5/HLK antibody is the product of a rat x rat hybrid myeloma, producing a heavy chain and two light chains. In hemagglutination tests, the antibody cross-reacts to entirety with dopamine, serotonin, and tryptamine at high concentrations. The serotonin-albumin conjugate is 20,000 times more effective in displacing the binding antibody, while albumin itself goes unrecognized by the antibody. In fixed preparations of brain tissue, immunofluorescence is observed only in neurons known to contain serotonin, while no reaction is observed in dopamine-rich neurons. All immunofluorescence is extinguished by the use of agents that inhibit the biosynthesis of 5HT, but not of the catecholamines.

The effect of GM1 ganglioside treatment on the recovery of biochemical and behavioral parameters which define the activity of nigro-striatal dopaminergic systems has been investigated in rats after different types of lesion. GM1 favours the recovery of tyrosine-hydroxylase activity, of the number and affinity of 3H-N-n-propyl-norapomorphine binding sites in the striatum of the lesioned side and reduces the apomorphine-induced rotational behavior after mechanical (i.e. unilateral hemitransection) but not after chemical (i.e. 6-OHDA injected in the substantia nigra) lesion. The source of regrowing dopaminergic nerve terminals in the striatum after hemitransection is mainly a response of intact remaining axons of the ipsilateral side. Moreover the contralateral nigro-striatal systems seems to play, through intrathalamic connections, an important role in regulating the GM1-induced increase of the tyrosine-hydroxylase activity.

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