DISTRIBUTION OF THE INNERVATING NEURONS OF PUPILLARY DILATOR AND TARSAL MUSCLES IN THE SUPERIOR CERVICAL-GANGLION

In an experimental study using adult cats, we analyzed the distributio n of the sympathetic postganglionic neurons in the superior cervical g anglion (SCG) which innervate the pupillary dilator and tarsal muscles to determine whether there are direct fiber projections from the spin al cord to the iridic and tarsal muscles. This study consisted of thre e experiments. In Experiments 1 and 2, respectively, horseradish perox idase (HRP) was injected unilaterally into the iridic stroma or superi or tarsal muscles. The SCG and spinal cord were then removed for micro scopic analysis. In Experiment 3, the ganglion was examined microscopi cally after the injection of bisbezimide into the iris and of HRP into the ipsilateral superior tarsal muscle. Experiment 1 revealed more nu merous HRP-labeled neurons in the rostral part than in any other regio n of the ipsilateral superior cervical ganglion. In Experiment 2, HRP- labeled neurons were evenly distributed over the whole ipsilateral SCG . No HRP-labeled neurons were detected in the spinal cord in either of these experiments. In Experiment 3, no doubly-labeled neurons were di scernible in the ganglion. These results clearly indicate the localiza tion of internal carotid nerve cells in a specific region of the SCG, and provide evidence for the absence of postganglionic neurons that in nervate both the dilator muscle of the pupil and the tarsal muscles.