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HANDBOOK OF PHYSIOLOGY 



NEt;ROPHVSIOLOGV U 



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FIG. 14. Tambour records of cystometric determination with manometric notations. B. Two 

 successive records after intercoUicular decerebration. C. After spinal transection. The reconstructed 

 cystometrogram also shows a control normal cur\e. In this and subsequent cystometrograms the 

 following abbreviations are used. 



SUB.C, subcollicidar transection SUP.D., supracollicular decerebration 



I.D., intercoUicular decerebration T.D., transhypothalamic decerebration 



[From Tang & Ruch (32).] 



component is identified. Although the threshold 

 volume needed to elicit micturition is smaller than 

 normal (fig. 4), it is sometimes only slightly smaller 

 and is always considerably larger than the small 

 volumes sufficing in the intercoUicular decerebrate 

 preparation. Converting a rostral midi^rain prepara- 

 tion into an anterior pontine preparation by per- 

 forming an intercoUicular transection results in a 

 pronounced lowering of the threshold (fig. 16, 

 right). Thus, the pontine facilitatory area is partially 

 balanced by a midbrain inhibitory area.^ One can 

 visualize two descending streams of impulses, one 

 increasing and one decreasing the excitability of the 

 preganglionic neurons supplying the bladder, the 

 two summing algebraically. The midbrain area may, 

 of course, be inhibiting the pontine area rather than 

 or as well as the final common pathway. Both areas 

 must receive an afferent input from below since both 

 act when the brain rostral to each has been ablated. 



" Focal lesions (33) have localized this area bilaterally in the 

 tegmentum, just lateral to the central gray matter, at the 

 caudal superior coUicular level. 



POSTERIOR HYPOTHALAMIC PREPARATION. An initial 



transection slightly rostral to the superior coUicular 

 level (transhypothalamic decerebration) yields a very 

 low micturition threshold, averaging 8 ml in seven 

 experiments. A subsequent supracollicular transec- 

 tion elevates the micturition threshold dramatically 

 (fig. 16, right), the average now being 29 ml as 

 would be predicted. The threshold change for six 

 of the seven animals was an increase of threefold or 

 more. Thus, again, two conclusions can be drawn: 

 a) that the wedge-shaped block of tissue between 

 the two levels of decerebration contains a powerful 

 facilitatory area^ and b) that the net eflfect of the tis- 

 sue rostral to the transhypothalamic area is strongly 

 inhibitory to the micturition reflex. The marked 

 reduction in threshold to 4 to 12 ml documents a 

 powerful, rostral, net inhibitory effect, presumably 

 from the cerebral cortex and the rostral hypo- 

 thalamus, although this point was not specifically 

 examined. 



' Localizing experiments placed the effective locus in the 

 mammillary region (33). 



