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Cerebellum: a pressor response elicited from the fastigial nucleus and its efferent pathway in brainstem
BRAIN RESEARCH
595
Short Communications Cerebellum: a pressor response elicited from the fastigial nucleus and its efferent pathway in brainstem While it has long been recognized that the cerebellum may influence the blood pressure and other cardiovascular functions6,11,15, the intracerebellar organization and the relay nuclei of the brainstem through which these autonomic actions of the cerebellum are mediated are unknown. In a recent electrophysiological study we have discovered that the carotid sinus nerve projects monosynaptically into the paramedian reticular nucleusg, 1°, a small nucleus of unknown function lying in the reticular formation near the obex. Since this nucleus is innervated by, and projects to, the cerebellum 2,3, it seemed that it might be of importance in relaying cerebellar activity concerned with cardiovascular function to the spinal sympathetic outflow. In this report evidence will be presented to show that the paramedian nucleus transmits a powerful pressor effect elicited by electrical stimulation within a highly localized region of the fastigial nucleus of cerebellum of cat. Adult cats were anesthetized with chloralose (50 mg/kg) or decerebrated at the midcollicular level under ether anesthesia and anesthesia discontinued. The trachea and femoral artery were cannulated and the animal was placed in a stereotaxic frame while aortic blood pressure, heart rate and end-expired COz were recorded continuously on a polygraph. In many experiments the animals were paralyzed with Flaxedil (gallamine triethiodide 5 mg/kg) and artificially ventilated. Care was taken to maintain end-expired CO2 at 2-3 % and body temperature at 37°C. Stimulating electrodes consisted of small insulated dental broaches with an exposed tip of around 300 # (ref. 5). Monopolar (cathodal) square wave stimulation of pulse duration of 0.10.5 msec was delivered from an isolated Grass stimulator with constant display of stimulus current and wave form on an oscilloscope. Lesions were made by passing 5-10 mA for 30 sec from a constant DC current source through similar electrodes with an exposed tip of 1 mm. Electrodes were placed in the brainstem by a micromanipulator under direct vision with stereotaxic coordinates referred to the obex. At the end of the experiment the animal was perfused with a mixture of potassium ferri- and ferrocyanide (in order to identify the tip of the stimulating electrode) followed by 10 % formalin. Brains were cut using a frozen technique and appropriate sections mounted and stained for cells or fiber. During a systematic exploration of the cerebellum for effects of punctate electrical stimulation on cardiovascular function we discovered a point localized to the fastigial nucleus, which produced a very large pressor response. Subsequently this pressor response has been reproduced in 50 animals. It consists of rise of both systolic and diastolic blood pressure to as much as 100 mm Hg each. The latency of the response is less than 2 sec and it rapidly falls after cessation of the stimulus (see Fig. 2). Associated is a tachycardia which may revert to a bradycardia after stimulation stops. The threshold for the response is quite low, averaging 0.05 mA, Brain Research, 13 (1969) 595-599
596
S H O R T C O M M U N I C A TI()NS
and the response increases in magnitude with c o n c o m i t a n t increase in the stimulus intensity up to 0.5 mA when signs appear of current spread to the brainstem. The optimal stimulus frequency eliciting the fastigial response is 30-80 c/sec. Three pieces o f evidence indicated that the fastigial pressor response was not due to a spread of the stimulus current to the brainstem: (a) with threshold stimulation the pressor response disappeared as the electrode penetrated below the fastigial nucleus and reappeared only when the electrode entered the brainstem; (b) following a small electrolytic lesion made at a positive fastigial locus the pressor response disappeared : (c) the pattern o f the pressor response elicited f r o m the fastigial nucleus and that from the brainstem differed, the latter having a longer duration and an associated bradycardia and often prominent associated m o t o r signs, particularly facial twitching. The locus for the lowest threshold in the fastigial nucleus did not extend over 1 mm on a vertical plane. It was localized within the ventromedial border o f the rostral pole of the fastigial nucleus as shown in Fig. 1. Electrical stimulation t h r o u g h o u t each o f the other cerebellar nuclei failed to produce any changes in blood pressure. Punctate electrical stimulation o f the cortex o f the vermis of the anterior lobe in ani-
A
B
Caudal
Rostral
'
' ] mm
Lateral
Medial
.....
No response • Pressor response >45mm Hg • Pressor response <45 mm Hg
Fig. 1. Localization within a reconstruction of the fastigial nucleus of cat of regions from which a pressor response was elicited by electrical stimulation in two representative experiments. The dotted lines represent electrode tracts. At 100 /~ steps the cerebellum was briefly stimulated (0.5 msec, pulse duration 50 c/sec, 10 sec train duration at about 5 × threshold current, i.e., between 0.3 and 0.5 mA). Positive responses of different magnitude are represented by circles of different sizes. A, Parasagittal section of cerebellum through body of fastigial nucleus to show localization of responses to rostral third of nucleus. B, Coronal section of cerebellum in another experiment to show localization of maximal responses in ventromedial quadrant of the nucleus. Abbreviations: FN, fastigial nucleus; IN, interposed nucleus. Brain Research, 13 (1969) 595-599
SHORT COMMUNICATIONS
597
mals with high basal blood pressures resulted in a mild fall of blood pressure confirming Moruzzi's observations 11. In order to ascertain which of the principal cerebellofugal pathways serve to mediate the fastigial presser response, a series of experiments were undertaken in which lesions were selectively placed within cerebellar outflow tracts or relevant brainstem nuclei. The response persisted after transection of the brachium conjunctivum rostral to the Hook Bundle of Russell and of the brachium pontis, but disappeared with destruction of the restiform body. Transection of the brainstem at the level of the inferior colliculus did not abolish the response nor did bilateral lesions of the lateral reticular nucleus, nucleus of the solitary tract, dorsal nucleus of the vagus, hypoglossal nucleus, the inferior olivary nucleus, or most of the giant cellular nucleus (which lies in the pens just rostral to the paramedian nucleus). On the other hand, unilateral lesions of the paramedian reticular nucleus reduced the amplitude of the response by about half, and the response disappeared almost completely after bilateral lesions of this nucleus in 16 consecutive experiments. A representative experiment is illustrated in Fig. 2. Bilateral lesions of the vestibular complex abolished the presser response in 4 cases, but in all instances the lesions involved the bulbar continuation of the fastigio-bulbar tracts 7,1a,14 passing just lateral to Deiters' nucleus.
CONTROL
AFTER PARAMEDIAL LESION //
,NTS IXII
////× 250 BP 200 {mm Hg) 150 i0£ 5C
!. t..I.I,
\ _
.
:
:
~
HI
Sti m
i;/
FN
Lesion
'-~3,_L_~
\Oi Pyr
mR
FN i
i
12 sec Fig. 2. Effect of bilateral lesions within the paramedian reticular nucleus on presser responses evoked by electrical stimulation of fastigial nucleus (FN). Polygraphic tracings (on left) show blood pressure (BP) and heart rate (HR) responses - in beats per minute (bpm) - to F N stimulation before and after placement of the lesion depicted in the reconstruction (on right) which is primarily restricted to the paramedian reticular nucleus bilaterally. Stimulus parameters as in experiment described in Fig. 1. Abbreviations: NTS, nucleus of the solitary tract; Oi, inferior olivary nucleus; Pyr, pyramid; V, nucleus of the trigeminal nerve; X, dorsal motor nucleus of the vagus nerve; XII, nucleus of the hypoglossal nerve. Note increase in heart rate following lesion, probably as result of interruption of cardio inhibitory fibers in brainstem.
Brain Research, 13 (1969) 595-599
598
SH()R1 ('()MMI~ NI('AI It1N~;
Since the vestibular nucleus does not project to the paramedian reticular nucleus ~, it is likely that the effects of this last lesion were due to brainstem rather than interruption of vestibulo-reticular pathways. These experiments indicate that electrical stimulation of discrete loci within the fastigial nucleus of the cat cerebellum elicits a potent pressor response. ]-he difference between the fastigial effect on blood pressure and those evoked from the cerebellar cortex indicates that the effect is probably not due to stimulation of Purkinje cell axons projecting directly to brainstem but results from excitation of fastigiobulbar pathways. In the only other systematic survey of the effects of electrical stimulation of the fastigial nucleus on blood pressure, Zanchetti and Zoccolini 15 discovered that electrical stimulation of similar regions of the fastigial nucleus in decorticate cats elevated the blood pressure. In their experiments, however, the rise of blood pressure was always part of the patterned autonomic and somatic outbursts of sham rage and depended on the integrity of the hypothalamus. Our study, on the other hand, proves that other, powerful pressor effects may be mediated by direct fastigio-bulbar tracts. These projections which are crossed and uncrossed enter the brainstem in the restiform body and pass through most portions of the vestibular nuclei7, 8, ~, i,~ Bilateral lesions in this pathway invariably abolish the response. Of the various nuclei to which the fastigial nucleus is known to project only the paramedian reticular nucleus seems essential to the response. The fact that bilateral lesions of this nucleus are required to abolish the response when elicited from a unilateral fastigial point while unilateral lesions only reduce it by about 50~o indicates that fastigial stimulation excites both crossed and uncrossed fastigio-bulbar pathways and that the crossing occurs in the cerebellum, in accord with anatomical data. That the paramedian reticular nucleus is the principal relay for a cerebellar effect on blood pressure is not surprising since we have recently shown that this nucleus receives a heavy monosynaptic and polysynaptic projection from the carotid sinus nerve9,1°, and as Crill and Reis have shown 5, probably the aortic depressor nerve as well. In addition, it is located well within the so-called depressor zone of the brainsteml, 4. Since the cerebellum does not project to those portions of the nucleus of the solitary tract receiving baroreceptor innervation9,10, the paramedial nucleus may be the principal site of tonic and phasic interactions of cerebellum with the carotid sinus baroreceptor vasomotor reflexes which Moruzzi 11 and Reis and Cu6nod 12 have demonstrated. In summary, this study provides the first clear demarcation of a specific region of the cerebellum with an effect on blood pressure, as well as its efferent path and the principal relay nucleus in brainstem. Such information may be useful in further elucidation of cerebellar mechanisms in autonomic control.
The authors thank Mr. Fumio K a w a m u r a and Mrs. Athelene Sawyer for technical assistance. This study has been supported by research grants NB06911, NB04876 and Brain Research, 13 (1969) 595-599
SHORT COMMUNICATIONS
599
NB03346-08 and a R e s e a r c h C a r e e r D e v e l o p m e n t A w a r d ( K 3 - N B - 3 1 , 7 5 6 ) to D . J . R . f r o m the N a t i o n a l Institutes o f Health.
Department of Neurology, Cornell University Medical College, New York, N.Y. 10021 (U.S.A.)
MITSUHIKO MIURA* DONALD J. REIS
1 ALEXANDER,R. S., Tonic and reflex functions of medullary sympathetic cardiovascular centers, J. Neurophysiol., 9 (1946) 205-217. 2 BRODAL,A., AND GOGSTAD,A. C., Afferent connexions of the paramedian reticular nucleus of the medulla oblongata in the cat, Acta Anat. (Basel), 30 (1957) 133-151. 3 BRODAL,A., ANDTORVIK,A., The cerebellar projection of the paramedian reticular nucleus of the medulla oblongata in the cat, J. Neurophysiol., 17 (1954) 484-495. 4 CHAI, C. Y., AND WANG, S. C., Localization of central cardiovascular control mechanism in lower brain stem of the cat, Amer. J. Physiol., 202 (1962) 25-34. 5 fRILL, W. E., AND REIS, D. J., Distribution of carotid sinus and depressor nerves in cat brain stem, Amer. J. Physiol., 214 (1968) 269-276. 6 Dow, R. S., AND MORUZZI, G., The Physiology and Pathology of the Cerebellum, University of Minnesota Press, Minneapolis, 1958, 675 pp. 7 FLOOD,S., ANDJANSEN,J., The efferent fibres of the cerebellar nuclei and their distribution on the cerebellar peduncles in the cat, Acta Anat. (Basel), 63 (1966) 137-166. 8 LADPL1, R., AND BRODAL, A., Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat, Brain Research, 8 (1968) 65-96. 9 MIURA,M.,AND REIS, D. J.,Electrophysiologicalevidencethat carotid sinus nerve fibers terminate in the bulbar reticular formation, Brain Research, 9 (1968) 394--399. 10 MIURA, M., AND REIS, D. J., Mono- and polysynaptic organization of carotid sinus nerve afferents in brainstem of cat, Proc. XX1V int. Congr. physiol. Sci., 7 (1968) 299. 11 MORUZZI, G., Paleocerebellar inhibition of vasomotor and respiratory carotid sinus reflexes, J. Neurophysiol., 3 (1940) 20-32. 12 REIS, D. J., AND CUI~NOD, M., Central neural regulation of carotid baroreceptor reflexes in the cat, Amer. J. Physiol., 209 (1965) 1267-1277. 13 THOMAS,D. M., KAUFMAN,R. P., SPRAGUE,J. M., AND CHAMBERS,W. W., Experimental studies of the vermal cerebellar projections in the brain stem of the cat (fastigiobulbar tract), J. Anat. (Lond.), 90 (1956) 371-385. 14 WALBERG, F., POMPEIANO, O., WESTRUM, L. E., AND HAUGLIE-HANSSEN,E., Fastigioreticular fibers in the cat: An experimental study with silver methods, J. comp. Neurol., 119 (1962) 187-199. 15 ZANCHETTI,A., AND ZOCCOLINI,A., Autonomic hypothalamic outbursts elicited by cerebellar stimulation, J. Neurophysiol., 17 (1954) 475-483. (Accepted February 21st, 1969)
* On leave from the Department of Physiology, Chiba University School of Medicine, Chiba, Japan.
Brain Research, 13 (1969) 595-599
595
Short Communications Cerebellum: a pressor response elicited from the fastigial nucleus and its efferent pathway in brainstem While it has long been recognized that the cerebellum may influence the blood pressure and other cardiovascular functions6,11,15, the intracerebellar organization and the relay nuclei of the brainstem through which these autonomic actions of the cerebellum are mediated are unknown. In a recent electrophysiological study we have discovered that the carotid sinus nerve projects monosynaptically into the paramedian reticular nucleusg, 1°, a small nucleus of unknown function lying in the reticular formation near the obex. Since this nucleus is innervated by, and projects to, the cerebellum 2,3, it seemed that it might be of importance in relaying cerebellar activity concerned with cardiovascular function to the spinal sympathetic outflow. In this report evidence will be presented to show that the paramedian nucleus transmits a powerful pressor effect elicited by electrical stimulation within a highly localized region of the fastigial nucleus of cerebellum of cat. Adult cats were anesthetized with chloralose (50 mg/kg) or decerebrated at the midcollicular level under ether anesthesia and anesthesia discontinued. The trachea and femoral artery were cannulated and the animal was placed in a stereotaxic frame while aortic blood pressure, heart rate and end-expired COz were recorded continuously on a polygraph. In many experiments the animals were paralyzed with Flaxedil (gallamine triethiodide 5 mg/kg) and artificially ventilated. Care was taken to maintain end-expired CO2 at 2-3 % and body temperature at 37°C. Stimulating electrodes consisted of small insulated dental broaches with an exposed tip of around 300 # (ref. 5). Monopolar (cathodal) square wave stimulation of pulse duration of 0.10.5 msec was delivered from an isolated Grass stimulator with constant display of stimulus current and wave form on an oscilloscope. Lesions were made by passing 5-10 mA for 30 sec from a constant DC current source through similar electrodes with an exposed tip of 1 mm. Electrodes were placed in the brainstem by a micromanipulator under direct vision with stereotaxic coordinates referred to the obex. At the end of the experiment the animal was perfused with a mixture of potassium ferri- and ferrocyanide (in order to identify the tip of the stimulating electrode) followed by 10 % formalin. Brains were cut using a frozen technique and appropriate sections mounted and stained for cells or fiber. During a systematic exploration of the cerebellum for effects of punctate electrical stimulation on cardiovascular function we discovered a point localized to the fastigial nucleus, which produced a very large pressor response. Subsequently this pressor response has been reproduced in 50 animals. It consists of rise of both systolic and diastolic blood pressure to as much as 100 mm Hg each. The latency of the response is less than 2 sec and it rapidly falls after cessation of the stimulus (see Fig. 2). Associated is a tachycardia which may revert to a bradycardia after stimulation stops. The threshold for the response is quite low, averaging 0.05 mA, Brain Research, 13 (1969) 595-599
596
S H O R T C O M M U N I C A TI()NS
and the response increases in magnitude with c o n c o m i t a n t increase in the stimulus intensity up to 0.5 mA when signs appear of current spread to the brainstem. The optimal stimulus frequency eliciting the fastigial response is 30-80 c/sec. Three pieces o f evidence indicated that the fastigial pressor response was not due to a spread of the stimulus current to the brainstem: (a) with threshold stimulation the pressor response disappeared as the electrode penetrated below the fastigial nucleus and reappeared only when the electrode entered the brainstem; (b) following a small electrolytic lesion made at a positive fastigial locus the pressor response disappeared : (c) the pattern o f the pressor response elicited f r o m the fastigial nucleus and that from the brainstem differed, the latter having a longer duration and an associated bradycardia and often prominent associated m o t o r signs, particularly facial twitching. The locus for the lowest threshold in the fastigial nucleus did not extend over 1 mm on a vertical plane. It was localized within the ventromedial border o f the rostral pole of the fastigial nucleus as shown in Fig. 1. Electrical stimulation t h r o u g h o u t each o f the other cerebellar nuclei failed to produce any changes in blood pressure. Punctate electrical stimulation o f the cortex o f the vermis of the anterior lobe in ani-
A
B
Caudal
Rostral
'
' ] mm
Lateral
Medial
.....
No response • Pressor response >45mm Hg • Pressor response <45 mm Hg
Fig. 1. Localization within a reconstruction of the fastigial nucleus of cat of regions from which a pressor response was elicited by electrical stimulation in two representative experiments. The dotted lines represent electrode tracts. At 100 /~ steps the cerebellum was briefly stimulated (0.5 msec, pulse duration 50 c/sec, 10 sec train duration at about 5 × threshold current, i.e., between 0.3 and 0.5 mA). Positive responses of different magnitude are represented by circles of different sizes. A, Parasagittal section of cerebellum through body of fastigial nucleus to show localization of responses to rostral third of nucleus. B, Coronal section of cerebellum in another experiment to show localization of maximal responses in ventromedial quadrant of the nucleus. Abbreviations: FN, fastigial nucleus; IN, interposed nucleus. Brain Research, 13 (1969) 595-599
SHORT COMMUNICATIONS
597
mals with high basal blood pressures resulted in a mild fall of blood pressure confirming Moruzzi's observations 11. In order to ascertain which of the principal cerebellofugal pathways serve to mediate the fastigial presser response, a series of experiments were undertaken in which lesions were selectively placed within cerebellar outflow tracts or relevant brainstem nuclei. The response persisted after transection of the brachium conjunctivum rostral to the Hook Bundle of Russell and of the brachium pontis, but disappeared with destruction of the restiform body. Transection of the brainstem at the level of the inferior colliculus did not abolish the response nor did bilateral lesions of the lateral reticular nucleus, nucleus of the solitary tract, dorsal nucleus of the vagus, hypoglossal nucleus, the inferior olivary nucleus, or most of the giant cellular nucleus (which lies in the pens just rostral to the paramedian nucleus). On the other hand, unilateral lesions of the paramedian reticular nucleus reduced the amplitude of the response by about half, and the response disappeared almost completely after bilateral lesions of this nucleus in 16 consecutive experiments. A representative experiment is illustrated in Fig. 2. Bilateral lesions of the vestibular complex abolished the presser response in 4 cases, but in all instances the lesions involved the bulbar continuation of the fastigio-bulbar tracts 7,1a,14 passing just lateral to Deiters' nucleus.
CONTROL
AFTER PARAMEDIAL LESION //
,NTS IXII
////× 250 BP 200 {mm Hg) 150 i0£ 5C
!. t..I.I,
\ _
.
:
:
~
HI
Sti m
i;/
FN
Lesion
'-~3,_L_~
\Oi Pyr
mR
FN i
i
12 sec Fig. 2. Effect of bilateral lesions within the paramedian reticular nucleus on presser responses evoked by electrical stimulation of fastigial nucleus (FN). Polygraphic tracings (on left) show blood pressure (BP) and heart rate (HR) responses - in beats per minute (bpm) - to F N stimulation before and after placement of the lesion depicted in the reconstruction (on right) which is primarily restricted to the paramedian reticular nucleus bilaterally. Stimulus parameters as in experiment described in Fig. 1. Abbreviations: NTS, nucleus of the solitary tract; Oi, inferior olivary nucleus; Pyr, pyramid; V, nucleus of the trigeminal nerve; X, dorsal motor nucleus of the vagus nerve; XII, nucleus of the hypoglossal nerve. Note increase in heart rate following lesion, probably as result of interruption of cardio inhibitory fibers in brainstem.
Brain Research, 13 (1969) 595-599
598
SH()R1 ('()MMI~ NI('AI It1N~;
Since the vestibular nucleus does not project to the paramedian reticular nucleus ~, it is likely that the effects of this last lesion were due to brainstem rather than interruption of vestibulo-reticular pathways. These experiments indicate that electrical stimulation of discrete loci within the fastigial nucleus of the cat cerebellum elicits a potent pressor response. ]-he difference between the fastigial effect on blood pressure and those evoked from the cerebellar cortex indicates that the effect is probably not due to stimulation of Purkinje cell axons projecting directly to brainstem but results from excitation of fastigiobulbar pathways. In the only other systematic survey of the effects of electrical stimulation of the fastigial nucleus on blood pressure, Zanchetti and Zoccolini 15 discovered that electrical stimulation of similar regions of the fastigial nucleus in decorticate cats elevated the blood pressure. In their experiments, however, the rise of blood pressure was always part of the patterned autonomic and somatic outbursts of sham rage and depended on the integrity of the hypothalamus. Our study, on the other hand, proves that other, powerful pressor effects may be mediated by direct fastigio-bulbar tracts. These projections which are crossed and uncrossed enter the brainstem in the restiform body and pass through most portions of the vestibular nuclei7, 8, ~, i,~ Bilateral lesions in this pathway invariably abolish the response. Of the various nuclei to which the fastigial nucleus is known to project only the paramedian reticular nucleus seems essential to the response. The fact that bilateral lesions of this nucleus are required to abolish the response when elicited from a unilateral fastigial point while unilateral lesions only reduce it by about 50~o indicates that fastigial stimulation excites both crossed and uncrossed fastigio-bulbar pathways and that the crossing occurs in the cerebellum, in accord with anatomical data. That the paramedian reticular nucleus is the principal relay for a cerebellar effect on blood pressure is not surprising since we have recently shown that this nucleus receives a heavy monosynaptic and polysynaptic projection from the carotid sinus nerve9,1°, and as Crill and Reis have shown 5, probably the aortic depressor nerve as well. In addition, it is located well within the so-called depressor zone of the brainsteml, 4. Since the cerebellum does not project to those portions of the nucleus of the solitary tract receiving baroreceptor innervation9,10, the paramedial nucleus may be the principal site of tonic and phasic interactions of cerebellum with the carotid sinus baroreceptor vasomotor reflexes which Moruzzi 11 and Reis and Cu6nod 12 have demonstrated. In summary, this study provides the first clear demarcation of a specific region of the cerebellum with an effect on blood pressure, as well as its efferent path and the principal relay nucleus in brainstem. Such information may be useful in further elucidation of cerebellar mechanisms in autonomic control.
The authors thank Mr. Fumio K a w a m u r a and Mrs. Athelene Sawyer for technical assistance. This study has been supported by research grants NB06911, NB04876 and Brain Research, 13 (1969) 595-599
SHORT COMMUNICATIONS
599
NB03346-08 and a R e s e a r c h C a r e e r D e v e l o p m e n t A w a r d ( K 3 - N B - 3 1 , 7 5 6 ) to D . J . R . f r o m the N a t i o n a l Institutes o f Health.
Department of Neurology, Cornell University Medical College, New York, N.Y. 10021 (U.S.A.)
MITSUHIKO MIURA* DONALD J. REIS
1 ALEXANDER,R. S., Tonic and reflex functions of medullary sympathetic cardiovascular centers, J. Neurophysiol., 9 (1946) 205-217. 2 BRODAL,A., AND GOGSTAD,A. C., Afferent connexions of the paramedian reticular nucleus of the medulla oblongata in the cat, Acta Anat. (Basel), 30 (1957) 133-151. 3 BRODAL,A., ANDTORVIK,A., The cerebellar projection of the paramedian reticular nucleus of the medulla oblongata in the cat, J. Neurophysiol., 17 (1954) 484-495. 4 CHAI, C. Y., AND WANG, S. C., Localization of central cardiovascular control mechanism in lower brain stem of the cat, Amer. J. Physiol., 202 (1962) 25-34. 5 fRILL, W. E., AND REIS, D. J., Distribution of carotid sinus and depressor nerves in cat brain stem, Amer. J. Physiol., 214 (1968) 269-276. 6 Dow, R. S., AND MORUZZI, G., The Physiology and Pathology of the Cerebellum, University of Minnesota Press, Minneapolis, 1958, 675 pp. 7 FLOOD,S., ANDJANSEN,J., The efferent fibres of the cerebellar nuclei and their distribution on the cerebellar peduncles in the cat, Acta Anat. (Basel), 63 (1966) 137-166. 8 LADPL1, R., AND BRODAL, A., Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat, Brain Research, 8 (1968) 65-96. 9 MIURA,M.,AND REIS, D. J.,Electrophysiologicalevidencethat carotid sinus nerve fibers terminate in the bulbar reticular formation, Brain Research, 9 (1968) 394--399. 10 MIURA, M., AND REIS, D. J., Mono- and polysynaptic organization of carotid sinus nerve afferents in brainstem of cat, Proc. XX1V int. Congr. physiol. Sci., 7 (1968) 299. 11 MORUZZI, G., Paleocerebellar inhibition of vasomotor and respiratory carotid sinus reflexes, J. Neurophysiol., 3 (1940) 20-32. 12 REIS, D. J., AND CUI~NOD, M., Central neural regulation of carotid baroreceptor reflexes in the cat, Amer. J. Physiol., 209 (1965) 1267-1277. 13 THOMAS,D. M., KAUFMAN,R. P., SPRAGUE,J. M., AND CHAMBERS,W. W., Experimental studies of the vermal cerebellar projections in the brain stem of the cat (fastigiobulbar tract), J. Anat. (Lond.), 90 (1956) 371-385. 14 WALBERG, F., POMPEIANO, O., WESTRUM, L. E., AND HAUGLIE-HANSSEN,E., Fastigioreticular fibers in the cat: An experimental study with silver methods, J. comp. Neurol., 119 (1962) 187-199. 15 ZANCHETTI,A., AND ZOCCOLINI,A., Autonomic hypothalamic outbursts elicited by cerebellar stimulation, J. Neurophysiol., 17 (1954) 475-483. (Accepted February 21st, 1969)
* On leave from the Department of Physiology, Chiba University School of Medicine, Chiba, Japan.
Brain Research, 13 (1969) 595-599