• The Korean Journal of Physiology
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• v.25 no.2
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• pp.211-221
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• 1991

Although the existence of nerve cells which determine the activity of sympathetic nervous system in ventrolateral medulla is advocated recently, there are wide varieties on the location and function of them according to authors. Present study aimed to identify and characterize the medullospinal tract cells in rostral and caudal medulla of cats .which branch to the lateral horn of the upper thoracic spinal cord. Cats were anesthetized with ${\alpha}-chloralose$. The upper thoracic spinal cord and floor of the IVth ventricle were exposed. Medullospinal tract cells in rostral and caudal medulla were identified by anti-dromic stimulation of the intermediolateral nucleus in the upper thoracic cord and then the location and physiological characteristics of these cells were studied. A total of seventy cells in medulla had constant latency and responded to high frequency stimulation to thoracic cord. Among them fifty-six cells were identified as medullospinal tract cells either by collision with spontaneous activities or activities evoked by sciatic nerve stimulation(27/56), or by determining the refractory period (29/56). Thirty-one of these cells branched to the contralateral thoracic spinal cord, twenty-one cells to the ipsilateral side and remaining four cells branched to both sides. The conduction velocity of cells branching to the contralateral side was $29{\pm}2.9\;m/sec$ and that of cells to the ipsilateral side was $39.1{\pm}6.0\;m/sec$. When medulla was devided into two by a horizontal plane at 3 mm rostral to the obex, fifty-one among seventy cells were in the rostral medulla and nineteen were in the caudal medulla. The conduction velocities of these two groups were $21.6{\pm}1.0\;and\;33.3{\pm}3.9\;m/sec$, respectively. In this study, we confirmed the existence of two groups of medullospinal tract cells in rostral and caudal ventrolateral medulla, which branch to the lateral horn of thoracic cord and these cells have relatively few spontaneous activities and rapid conduction velocity, so we concluded that these cells are different from the previously known sympatho-related cells in ventrolateral medulla.

• Journal of Chest Surgery
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• v.23 no.5
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• pp.833-843
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• 1990

Vasomotor areas were identified by stimulating various sites of the medulla electrically in adult cats anesthetized with a-chloralose and their correlation with somatosympathetic pressor or depressor responses was investigated. Followings are the results obtained: 1. Pressor areas were found in the rostral ventrolateral, the caudal ventrolateral and the rostral dorsolateral medulla. 2. Separate depressor areas were found dorsal and ventral to the rostral ventrolateral pressor area. 3. Some areas showed biphasic responses: depressor responses to low frequency[1 \ulcorner2 Hz] and pressor responses to high frequency[20 \ulcorner100 Hz] stimulation 4. Lesions on the rostral ventrolateral pressor areas abolished the somatosympathetic pressor responses to the stimulation of peripheral afferent nerves, while the depressor responses remained. Lesions on the caudal ventrolateral pressor area affected neither the pressor nor depressor responses to the peripheral nerve stimulation. 5. Lesions on the depressor areas resulted in decreased depressor responses to the peripheral nerve stimulation, but to a lesser degree than that resulted from lesions on the pressor areas. 6. A microinjection of glutamate solution to the pressor area resulted in a prolonged pressor response, while glutamate injection to the depressor areas did not elicit depressor responses. From the above results, it is concluded that there are separate pressor and depressor areas in the rostral medulla of cats and each area plays a role in somatosympathetic pressor and depressor responses, respectively.

• The Korean Journal of Physiology
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• v.26 no.1
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• pp.75-88
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• 1992

It is well established that neurons in ventrolateral medulla play a key role in determining the vasomotor tone. The purpose of present study is to identify sympathetic related, medullospinal tract neurons in ventrolateral medulla and to show that these mediate somato-sympathetic reflex. Medullospinal tract cells were identified by antidromic stimulation to intermediolateral nucleus (IML) of the second thoracic ($T_2$) spinal cord in anesthetized cats. Peripheral nerves were stimulated for orthodromic activation of these cells and peripheral receptive fields were determined. Post R wave histogram of unit and spike triggered averaging of sympathetic nerve discharge (SND) were used to define sympathetic related cell. A total of 113 neurons was recorded in ventrolateral medulla that had the axonal projections to $T_2$ spinal cord. Thirty four of these medullospinal cells showed spontaneous discharges and the others not. Between these two groups, rostro-caudal coordinate of the distribution from obex [$4.7{\pm}0.2\;$ (mean S.E.) mm, 4.1 0.1 mm], depth from dorsal surface ($5.5{\pm}0.2mm,\;4.9{\pm}0.1mm$ and conduction velocity ($9.9{\pm}1.7m/sec,\;16.7{\pm}1.9\;m/sec$) were significantly different (p<0.05). In spontaneously discharging group, characteristics of rostral and caudal groups were significantly different and we demonstrated that cells in rostral group mediate somatosympathetic reflex. From these results, we conclude that a certain portion of spontaneously discharging medullospinal tract cells in rostral ventrolateral medulla comprise the efferent outputs of somatosympathetic reflex to sympathetic preganglion neurons.