[Experience with the use of horseradish peroxidase for light and electron microscope studies of interneuronal connections].

By the method based on a retrograde axonal transport of exogenous horseradish peroxidase (HRP), the origins of afferentation of the motor cortex of adult cats, kittens and albino rats were studied. HRP-positive neurons were found by light and electron microscopy in the somatosensory cortex (C1) of the ipsilateral hemisphere and in the portions of the cortex of the contralateral hemisphere which were symmetrical to the site of injection of HRP. The disposition of neurons, marked by HRP, in the Vth layer of the motor cortex suggest that these neurons may send their axons into the bundles of comissural fibres going to the motor cortex of the opposite hemisphere. This method considerably expands possibilities of revealing the origins of afferentation of the investigated portion of the nervous system and allows more complete and reliable investigation of interneuronal connections.