Use of horseradish peroxidase to trace nerve cell connections in turtles.

Abstract

An exogenous protein, horseradish peroxidase (HRP) was used to trace efferent neurons of the heart and retina LO the turtle (Pseudemys scriota). Small doses of HRP were injected into the subepicardial tissue of the heart and after a 4R-hour survival period HRP reaction-product accumulated in what appear to be neuron cell horlies along the vagus nerve. Control HRP injections into the external jugular vein dd not label these cells, so a vascular route was ruled out. After injection of HFP into the anterior chamber of the turtle eye, HRP reaction-product Has observer!. in a group of cells which constitute a restricted nucleus in the midbrain. Most of the cells traced by this technique were in the nucleus on the side of the midbrain contralateral to the injected eye, but a smaller number of cells were tracett to the ipsilateral nucleus.