Anatomical demonstration of the involvement of the substantia nigra in contraversive circling elicited by electrical stimulation of the medial forebrain bundle in the cat: a retrograde transport study using horseradish peroxidase subsequent to an electrolytic lesion.

A method is described for the anatomical identification of groups of neurones likely involved in the elaboration of component acts of a centrally elicited behaviour, when involvement of fibres of passage is suspected. The contraversive circling which accompanied the predatory attack of a cat upon a rat elicited electrical stimulation within the hypothalamic and ventral midbrain trajectory of the medial forebrain bundle (MFB) was used as a model because of the established role played by the nigrostriatal dopamine system in the production of the circling. Following horseradish peroxidase (HRP) injections, made after electrolytic lesion at such MFB sites, substantial numbers of labelled cells were found in the substantia nigra, pars compacta (SNC). In contrast, many fewer SNC neurones were labelled following:(1) HRP injections made after electrolytic lesion at MFB sites at which the elicited predatory behaviour was not accompanied by contraversive circling; and (2) HRP injections made without a prior lesion at MFB sites at which the elicited predatory behaviour was accompanied by contraversive circling.