Mid-thoracic Segments Research Articles

Growth of the corticospinal tract and the development of placing reactions in the postnatal rat.

The growth of corticospinal axons into the spinal cord has been demonstrated using the autoradiographic and the Fink-Heimer silver degeneration methods. In addition, the development of several types of placing reactions have been studied. After unilateral injections of radioactive proline or unilateral ablations of the somatosensory-motor cortex, corticospinal axons were found to extend into the contralateral dorsal funiculus of the lower cervical cord at one day postnatally, into mid-thoracic segments at three days, into upper lumbar cord by five days and into coccygeal segments by nine days. Corticospinal axons are first present in the contralateral spinal gray of lower cervical cord at day 5 and in the contralateral spinal gray of lower lumbar and sacral cord by day 9. Little change in the topographical distribution or in the density of the projection is found at all levels of the spinal gray after the fourteenth postnatal day. Comparable results were found with both experimental techniques. Forelimb placing is first seen between 4 to 7 days and hind limb placing between 9 to 13 days. The last placing response to appear in both the forelimbs and the hindlimbs is placing in response to tactile and light proprioceptive stimuli. After the initial onset of the placing reactions, there is a gradual increase in the frequency and speed of the responses until 14 to 17 days postnatally, at which time the reactions appear to be mature. While a causative relationship between the growth of corticospinal axons into the spinal cord and the development of placing has not been established, a close temporal relationship has been found between first: the appearance of fore-or hindlimb placing responses and the appearance of corticospinal axons within the spinal gray at the appropriate levels of the cord and second: between the completion of the primary growth of corticospinal axons at the light microscopic level and the maturation of the placing reactions.

Extra-segmental reflexes derived from intercostal afferents: phrenic and laryngeal responses.

1. Phrenic and recurrent laryngeal efferent responses were evoked by brief tetani or single shocks to the cut external intercostal nerves of anaesthetized cats. The reflexes derived from middle thoracic segments (T5 and 6) were compared with those emanating from caudal thoracic segments (T9 and 10).2. During inspiration, middle intercostal nerve stimulation transiently inhibited the spontaneous discharge in both efferent neurograms, whereas stimulation of caudal intercostal nerves facilitated phrenic discharge and usually inhibited recurrent laryngeal activity.3. During expiration, stimulation at either thoracic level enhanced recurrent laryngeal discharge while provoking little or no phrenic response.4. Superficial lesions of the lateral cervical cord, ipsilateral to the stimulus sites, above or below the phrenic outflow, eliminated all reflex responses except the phrenic response to caudal thoracic stimuli. Similarly, in the spinal animal, middle intercostal afferents could not be shown to decrease phrenic excitability. Caudal intercostal afferents cause phrenic excitation by a spinal reflex.5. Group I afferents of the mid-thoracic segments and group II afferents of the caudal thoracic segments initiate these extra-segmental reflexes.6. The recurrent laryngeal responses manifest, for the most part, changes in the discharge of fibres innervating the posterior cricoarytenoid muscle. The responses fit the overall pattern of response to middle intercostal nerve stimulation, namely, inhibition of inspiratory muscles and excitation of expiratory muscles. Intercostal afferent stimulation also activated the laryngeal adductor muscles.7. The results support the view that intercostal mechanoreceptors initiate an array of extra-segmental respiratory reflexes, including spinal and supraspinal arcs. The simplest way to account for the various responses to stimulation of middle intercostal afferents is to postulate a reflex involving supraspinal respiratory neurones.8. The observed reflexogenic differences correlate with anatomical differences between the middle and caudal ribs. Possible functional implications of this relationship are discussed.

CARCINOMA OF THE ESOPHAGUS AND THE CARDIAC END OF THE STOMACH

Until 1938 when Phemister and his associates1performed the first successful transthoracic resection for carcinoma of the lower end of the esophagus invading the cardia, the prospect of treatment of this disease was dismal if not hopeless. In the majority of cases in which the tumor involved the midthoracic segment, the application of the Torek procedure2resulted in disappointment because of the failure of this operation to provide satisfactory palliation and its inefficacy as a method of controlling the disease.3 As a result of several years of experience with resection and primary anastomosis within the thorax, the entire situation has changed, and the immediate and late results of treatment by resection and primary esophagogastric anastomosis may be evaluated. The elimination of the distressing dysphagia provided by this operation has been most gratifying, and the fact that a recurrence of the tumor at the site of anastomosis is