Parasympathetic innervation of the initial segments of the large intestine in cats

The locations and morphometric characteristics of efferent parasympathetic neurons in the dorsal motor nucleus of the vagus nerve and the cruciform parasympathetic nucleus of the spinal cord, innervating the area of the ileocecal sphincter and the ascending and transverse segments of the colon, were studied. Horseradish peroxidase solution was injected beneath the serous membranes of these parts of the intestine in urethane-anesthetized cats. After 48 h, animals were subjected to transcardiac perfusion with a fixative mixture and sections of the medulla oblongata and spinal cord were prepared and processed by the Mesulam method. The results showed that all these parts of the large intestine received parasympathetic innervation from neurons in the ventrolateral part of the dorsal motor nucleus, which were uniform in terms of their morphometric characteristics. The number of neurons of this group sending axons to the ileocecal area was greater than the number of neurons innervating the ascending colon. A second group of neurons, which were smaller cells, was located in the same part of the nucleus and innervated the transverse colon. The transverse colon also received innervation from neurons in the cruciform parasympathetic nucleus of the spinal cord.