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HANDBOOK OF PHNSIQLOGV 



NEUROPHYSIOLOGY II 



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PIG. 1 1. Vasodilator responses in the muscles of the hind leg to stimulation in the right part of the 

 tectum mesencephali, and the effect of physostigmine and atropine. Cat under Dial anesthesia; left 

 common carotid occluded. /) Stimulation, 1.25 v.; 10 sec; increase of flow, 50 per cent; .') phy- 

 sostigmine, o. I mg per kg, intra\cnously; j) stimulation, 1.25 v.; 10 sec; increase of flow, 50 per 

 cent; 4) stimulation, 1.25 v.; 10 sec; increase of flow, 70 per cent; j) stimulation, 1.25 v.; 10 sec; 

 increase of flow, 130 per cent; ff) stimulation, 1.25V.; 10 sec; increase of How, i 70 per cent; 7) stimu- 

 lation, 1.25 v.; 10 sec; increase of flow, 260 per cent; 8) atropine, 0.2 mg per kg, intravenously; 

 p) stimulation, 1.25 v.; 10 sec; increase of flow, 1 10 per cent; 10) atropine, 0.3 mg per kg, intra- 

 venously; //) stimulation, 1. 25V.; 10 sec; increase of flow, 70 per cent; /2) atropine, 0.5 mg per kg, 

 intravenously; 73) stimulation, 1.25 v.; 10 sec; increase of flow, 20 per cent. Note the potentiating 

 effect of physostigmine and the large doses of atropine necessary for abolishing the vasodilator re- 

 sponses. [From Lindgren (149).] 



Medulla Spinalis and Medulla Oblongata 



In the medulla oblongata the sympathetic vaso- 

 dilator pathway was found to lie in the ventral lateral 

 area [Lindgren & Uvnas (151, 152)]. It forms a longi- 

 tudinal band running i to 2 mm above the ventral 

 surface of the medulla and could be traced down to 

 the lateral horns of the cervical segments of the spinal 

 medulla. 



Electrical stiinulation of the medullary part of the 

 sympathetic vasodilator path produced in cats and 

 dogs ipsilateral vasodilatation in the skeletal muscles 

 of a hind leg (fig. 12) accompanied by ipsilateral 

 vasoconstriction in the skin of the hind leg (cat) and 

 in the ear (dog) and within the splanchnic region 

 [Lindgren (149)]. In addition, stimulation produced 

 a discharge of catechols from the adrenals [Grant 

 et al. (106)]. Evidently the vasodilator fibers were 

 accompanied by vasoconstrictor fillers and fibers 

 running to the adrenals. 



Lindgren (149) showed in chronically decerebrate 

 cats that the vasodilator and vasoconstrictor fibers 

 in the medulla oblongata degenerated after decerebra- 

 tion caudal to the inferior colliculus. This finding 

 suggests that these fibers pass through the medulla 

 oblongata without synapses. The vasodilator path 



passes outside those medullary regions which contain 

 the pressor and depressor centers. In point of fact, 

 Lindgren & L'vnas (153, 154) showed that with 

 cauterization it was possible to destroy the depressor 

 region and thus to abolish medullary depressor re- 

 flexes produced by stimulation of a sinus nerve, de- 

 pressor nerve or aff'erent nerve. Such local destruction 

 of the depressor area does not interfere with the sym- 

 pathetic vasodilator pathway, since Lindgren & 

 Uvnas demonstrated that hypothalamic stimulation 

 still produced \asodilatation in the muscles, which 

 finding must imply that this path passes intact throut^h 

 the medulla oblongata. 



Mesencephalon 



Lindgren (149) found that the sympathetic vaso- 

 dilator pathwav- from the h\pothalamus could be 

 traced towards the mesencephalon. He found it to 

 lie in the basal parts of the superior colliculus whence 

 it continued \entrocaudad to the upper part of the 

 medulla oblongata where it descended dorsolateral 

 to the pyramidal tract. He further observed that the 

 tectofugal pathway had a partial crossing ventral to 

 the substantia grisea centralis approximately in the 



