Neuroanatomic projections related to biting attack elicited from ventral midbrain in cats

A single electrode was implanted in each of ten cats at a point in the ventral midbrain from which nonaffective biting attack on a rat could be elicited by electrical stimulation. A lesion was then made which was just large enough to eliminate the elicitation of attack at suprathreshold intensities from that electrode. After post-lesion survival times of 3-14 days the cats were sacrificed, and the degeneration resulting from the lesions was followed with the use of modified Nauta silver stains. Four additional cats were used as anatomic controls. Degenerating fibers were observed to descend bilaterally through the midbrain, pontine, and medullary tegmentum to the vicinity of the principal sensory and motor nuclei of the trigeminal nerve. There was, in addition, evidence of degenerating terminals within the nucleus of the facial nerve and the spinal nucleus of the trigeminal nerve. Of particular note was the observation that the degenerating fibers in the region of the nucleus of the spinal tract of the trigeminal nerve terminated in glomeruli in the rostral portion of the nucleus. Degenerating fibers ascending from the lesion were found to course along the medial forebrain bundle into the hypothalamus and the midline thalamus in a pattern very similar to that previously demonstrated after lesions of biting attack sites in the hypothalamus. The role that the neural pathways associated with ventral midbrain attack sites might play in the mediation of behavior patterns which are elicited during attack stimulation was discussed and it was concluded that the demonstrated neural pathway could provide a cogent explanation for some of the properties of centrally elicited attack behavior.