Effects of Lesions of the Periaqueductal Gray Matter in the Cat ∗

Abstract

The great epidemic of lethargic encephalitis directed the attention of neurologists to the region of the midbrain and hypothalamus. A long series of experimental and pathological studies has demonstrated the importance of the gray masses which surround the inferior and posterior parts of the third ventricle, but the posterior extension of the juxta-ventricular gray matter, which surrounds the aqueduct of Sylvius in a cylinder of considerable size, has been neglected. This periaqueductal gray matter is of such a shape, and so located, as to make its destruction very difficult by the usual means-such as the Horsley-Clarke machine-without such extensive damage to neighboring structures as to obscure the interpretation of results.

After much experimentation we developed an electrode which could be inserted by an opening in the occipitoatlantoid ligament through the fourth ventricle into the aqueduct and, in this manner, made electrolytic lesions confined to the periaqueductal gray matter of the cat. During the process of development of an electrode which would follow the aqueduct we produced numerous lesions, in all parts of the midbrain, which served as controls since in none of them did the symptoms appear which regularly follow destruction of the periaqueductal gray matter. The lesions were made with an electrolytic apparatus, built for us by Mr. Craig Goodwin, which delivers a constant amperage regardless of variations in the resistance. The location of the lesion was, in each case, verified by serial sections stained alternately with the methods of Nissl and Weil.

When the electrode is merely inserted into the aqueduct, without making an electrolytic lesion, the subsequent behavior of the animals is entirely normal. When the electrode jumps the aqueduct and an electrolytic lesion is made outside the periaqueductal gray matter only alterations in motor performance are noted.