974 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



The rhinencephalic structures act in turn upon the 

 neurosecretory mechanisms of the hypothalamus. 



In the past it has frequently been proposed that the 

 cerebellum participates in autonomic activities, but 

 most of these suggestions were not substantiated by 

 adequate evidence. For instance, in cases of stimula- 

 tion of the cerebellum it was not at the time possible 

 to guard against spread of current to adjacent medul- 

 lary and pontine mechanisms. The first work which 

 demonstrated with any authority that the cerebellum 

 may have an effect on autonomic functions was re- 

 ported by Moruzzi, starting in 1938 and summarized 

 more recently (125). Using cats with the brain stem 

 transected at the precollicular level, Moruzzi was 

 able to demonstrate inhibition of ijoth vasoconstrictor 

 and vasodilator reflexes. The same was also true for 

 the increased vasoconstrictor and respiratory activity 

 produced by ligation of the common carotid arteries. 

 Moruzzi also stimulated the cerebellum during fits 

 of sham rage. Here a remarkable effect, presumably 

 upon the hypothalamus, was produced, since the 

 somatic and autonomic manifestations of the sham 

 rage were immediately inhibited. /After cessation of the 

 stimulation, a characteristic cerebellar type of re- 

 bound manifestation was seen in that the somatic and 

 autonomic characteristics of the sham rage reap- 

 peared. Moruzzi also observed diphasic pupillary 

 responses upon cerebellar stimulation in which a 

 parasympathetic miotic effect during stimulation was 

 followed by a sympathetic mydriatic response during 

 the rebound period. To quote, "Apparently the cere- 

 bellum, or at least its median structures, can play 

 upon many central functions besides postural tonus, 

 but the diphasic response to an electrical stimulation 

 seems to be a permanent feature of all cerebellar 

 effects, as if the cerebellum were mainly concerned 

 with sending a sequence of inhibitory and facilitating 

 volleys to the brain stem neurons, the type of the 

 response depending upon the structure to which the 

 cerebellar impulses arrive"' (125). 



More recently, Zanchetti & Zoccolini (177) stimu- 

 lated the fastigial nuclei of the cerebellum in acute 

 thalamic cats. Such stimulation caused outbursts of 

 the sham rage type, including autonomic effects. 

 These were also produced by stimulation of the mid- 

 line structures and from the buried folia of the tuber, 

 pyramid and uvula. Diencephalic centers were neces- 

 sary for these responses, since they were abolished by 

 rostral midbrain coagulation. Ban and his co-workers 

 (11) studied cerebellohypothalamic relationships as 

 revealed by electrical recording methods. There was a 



marked increase in the frequency and voltage of the 

 EEG of the ventromedial hypothalamic nucleus, 

 together with sympathetic manifestations, when the 

 anterior lobe of the cerebellum was stimulated. That 

 of the lateral hypothalamic nucleus showed slight 

 increases in frequency. In the reverse direction, the 

 EEG of the anterior lobe of the cerebellum was also 

 increased in frequency and voltage by stimulation of 

 the ventromedial hypothalamic nucleus. Peripheral 

 autonomic responses produced by stimulation of the 

 lateral hypothalamic area were prevented by stimu- 

 lation of the cerebellar anterior lobe. The authors 

 postulate that the cerebellum not only modulates 

 autonomic activity at the level of the lower brain stem 

 but also may modulate the autonomic activities of 

 the hypothalamus. 



One of the more striking evidences of cerebellar 

 participation in autonomic reflexes is presented by 

 the work of Bard et al. (15) who demonstrated that 

 motion sickness in dogs is prevented by excision of the 

 flocculonodular lobe of the cerebellum. 



CONCLUSION 



Central autonomic mechanisms exhibit a crescendo 

 of complexities. In the isolated spinal cord many of 

 the autonomic mechanisms are truly capable of auton- 

 omous activity. These reflexes resemble somatic re- 

 flex circuits in many ways, and are capable of anal- 

 ysis as to their synaptic relationships and reflex times. 

 They appear, under normal circumstances, to be 

 subject to facilitatory and inhibitory influences from 

 higher areas, and here some restriction of their auton- 

 omous status appears. There is also good evidence 

 that these spinal circuits may be capable of project- 

 ing to the higher regions, even as high as the cerebral 

 cortex, over definite afi'erent pathways by which they 

 may bring the modulating feed-back influence of the 

 higher regions into action. Separated from the higher 

 brain, these segmental mechanisms function only for 

 the needs of the moment. They are largely incapable 

 of functioning in the broad sense of maintaining the 

 homeostasis and homeokinesis of the body after the 

 influence of the brain has been removed by spinal 

 transection. 



As we go on to the lower brain-stem complexes, 

 again we find circuits of different types so arranged as 

 to make feed-back and reverl)eration possible, making 

 use of the innumerable internuncial neurons of the 

 reticular formation for elaborating patterns of control 



