Brain Research, 169 (1979) 615-619 © Elsevier/North-HollandBiomedicalPress
Cervical control of posture and movements
DIEGO MANZONI, OTTAVIO POMPEIANO* and GIULIA STAMPACCHIA Istituto di Fisiologia Umana, Cattedra lI, Universitd di Pisa, 56100 Pisa (Italy)
(Accepted March 1st, 1979)
Unilateral section of the dorsal roots C1-C3 in rabbits produces rotation of the head towards the contralateral side 11, hypotonia of the ipsilateral limbs with lateropulsion, and a tendency of the animal to fall towards the side of the denervation3. The conclusion of these experiments, i.e. that the postural asymmetry produced by unilateral deafferentation of the neck is similar to that elicited by ipsilateral labyrinthectomy3, contrasts with the results of stimulation experiments, which show an antagonistic integration of the cervical and tonic labyrinthine inputs in the control of posture 9. Ataxia of the hindlimbs associated with defects of gait and difficulty in turning have also been observed in cats and monkeys after cervical deafferentation or denervation of the neck musculature; however, no indication about the type of postural asymmetry in the limb musculature has been reported in these studies1, ~,7,17. The main aim of the present experiments was to investigate the mechanisms responsible for the postural and motor deficits which occur in cats following unilateral section of the upper cervical dorsal roots. The experiments were carried out on 13 cats subjected, under Nembutal anesthesia (35 mg/kg i.p. of sodium pentobarbital) to unilateral section of the dorsal roots C1-Cs. All procedures and observations were defined as ipsilateral or contralateral with reference to the side of the cervical deafferentation. Unilateral section of the dorsal roots C1-Cz produced a slight tilt of the head to the contralateral side, due to asymmetric innervation of the dorsal neck musculature (Fig. 1A). Moreover, marked motor deficits involving the entire body were observed. In particular one day after the operation the cats tended to lie on the contralateral side, with the corresponding limbs flexed and the ipsilateral limbs extended (Fig. 1A, B). They began to right themselves and stand within 1-2 days; however, they showed much bodily sway, often interrupted by falling in the contralateral direction. By the third to the fifth day these effects disappeared and the animals were able to walk without apparent impairment, although the direction of the locomotor activity was still oriented towards the intact side. Seventeen days after deafferentation, the animals * To whom correspondenceshould be addressed.
Fig. 1. Effects of unilateral deafferentation of the neck on posture in the unanesthetized preparation. Cat no. 3, 1 day after section of the dorsal roots C1-Ca of the left side. A and B: the animal tended to lie on the right side, with the contralateral right limbs flexed and the ipsilateral left limbs extended. There was also tilting of the head with the right side down. C and D: both in supine (C) and in prone (D) position the animal showed an increase of the extensor tonus in the ipsilateral limbs and a decrease of the extensor tonus associated with mild flexor tonus in the contralateral limbs. This postural asymmetry affected both fore- and hinalimbs and was also observed when the head of the animal was kept in symmetric position (C and D).
were still hesitant d u r i n g l o c o m o t i o n ; however, 20 days after this lesion, the cats were able to walk for long distances w i t h o u t showing changes in intended direction or interr u p t i o n due to falling. The a n i m a l ' s b e h a v i o r was, at least in p a r t , due to p o s t u r a l a s y m m e t r y o f the l i m b musculature, as shown b y an increased tonic c o n t r a c t i o n o f the ipsilateral extensor muscles a n d a decreased c o n t r a c t i o n o f the c o n t r a l a t e r a l extensors (Fig. I C, D). M o r e o v e r , there was a selective suppression o f the tactile placing reaction and a depression o f the p r o p r i o c e p t i v e placing r e a c t i o n in b o t h the fore- a n d h i n d l i m b ipsilateral to the side o f the cervical deafferentation (Fig. 2). A c o m p e n s a t i o n o f the p o s t u r a l a s y m m e t r y described a b o v e o c c u r r e d within 20 days after cervical deafferentation, while the deficits in the tactile placing reactions were still present, a l t h o u g h slightly a t t e n u a t e d , after this period. Both spinal ascending and cortical descending m e c h a n i s m s intervene in the c o m p e n s a t i o n o f the p o s t u r a l s y n d r o m e described above, since the p o s t u r a l a s y m m e t r y elicited by cervical deafferentation r e a p p e a r e d in the
Fig. 2. Effects of unilateral deafferentiation of the neck on the placing reaction. Cat no. 9, 2 days after section of the dorsal roots C1-C3 of the left side. The postural asymmetry produced by this lesion was similar to that illustrated in Fig. 1. The tactile placing reaction occurred in the contralateral fore- and hindlimb when the animal was placed near the edge of the experimental table, so that a light touch was applied to the dorsum of the feet. On the contrary the placing reaction was absent in the ipsilateral fore- (A and B) and hindlimb (C and D).
c o m p e n s a t e d a n i m a l after p o s t b r a c h i a l section o f the spinal c o r d at T12 o r b i l a t e r a l a b l a t i o n o f the f r o n t a l cortex (two experiments). The p o s t u r a l a s y m m e t r y p r o d u c e d in the f o u r limbs b y unilateral deafferentation o f the neck was still present after pre- o r r e t r o c o l l i c u l a r d e c e r e b r a t i o n , b u t was reversed b o t h in i n t a c t a n d d e c e r e b r a t e p r e p a r a t i o n s either b y section o f the ipsilateral V I I I nerve or b y a b l a t i o n o f the c o n t r a l a t e r a l vermal cortex o f the cerebellar a n t e r i o r l o b e (3 experiments). O n the o t h e r h a n d a section o f the V I I I nerve ipsilateral to the side o f the cervical deafferentation did n o t m o d i f y the deficits o f the tactile p l a c i n g reactions p r o d u c e d in the i n t a c t p r e p a r a t i o n b y the cervical d o r s a l r o o t section. A c o m p l e t e
618 bilateral lesion of the vermal cortex of the cerebellar anterior lobe and the tastigial nucleus greatly reduced the postural asymmetry elicited in decerebrate animals by unilateral deafferentation of the neck, due to the increased rigidity of the four limbs following the cerebellar lesion (two experiments). This asymmetry, however, was clearly observed when the cervical deafferentation was performed 16 days after the cerebellar lesion (one experiment). In conclusion, unilateral section of the cervical dorsal roots C1-C3 produced a postural asymmetry in the limb musculature characterized by hypertonia of the ipsilateral limbs and hypotonia of the contralateral limbs. This postural asymmetry could still be observed after bilateral ablation of the cerebellar vermis and the fastigial nucleus, indicating that the neck input may control the posture of the four limbs even in the absence of the cerebellum. The neck input may then act on limb motoneurons by utilizing propriospinal and/or supraspinal descending pathways (cf. ref. 8). It is of interest that the postural asymmetry produced by unilateral deafferentation of the neck was just opposite in sign to that elicited by unilateral section of the VIII nerve. Recent experiments have shown that the neck input of one side exerts a prominent excitatory influence on the ipsilateral cerebellar vermis, in contrast to the labyrinthine input which acts mainly on the contralateral cerebellar vermis 6. Unilateral deafferentation of the neck may therefore produce a disfacilitation of the ipsilateral vermal cortex of the cerebellar anterior lobe, leading to disinhibition of the corresponding Deiters' nucleus. Since this vestibular structure excites the ipsilateral extensor motoneurons (ref. 10, cf. refs. 13 and 18), the activity in the extensor musculature ipsilateral to the side of the deafferentation will increase. On the other hand, the increased discharge of Deiters' nucleus of one side may lead to reciprocal depression in the contralateral Deiters' nucleus thus producing a suppression of the extensor tonus of the corresponding side. This effect can be attributed to descending vestibulospinal volleys acting on neurons of the crossed spinoreticulocerebellar pathway (refs. 5 and 16, cf. refs. 14 and 15). This proposed relationship is supported by the results of secondary lesions, showing that the postural asymmetry produced by unilateral section of the cervical dorsal roots was reversed either by section of the VIII nerve ipsilateral to the side of the cervical deafferentation or by ablation of the contralateral vermal cortex of the anterior lobe. In addition to the postural change described above, unilateral section of the dorsal roots C1-C3 abolished or greatly depressed the placing reactions ipsilaterally to the side of the lesion. These effects did not depend upon the postural changes produced by the cervical deafferentation, since the reversal of the postural asymmetry elicited by section of the ipsilateral VIII nerve was not associated with a parallel reversal in the pattern of the placing reactions produced by the cervical deafferentation. It is known that the tactile placing reaction depends, in part at least, upon the anatomical integrity of the interpositus nucleus (cf. ref. 5), which activates ipsilateral flexor motoneurons via the contralateral red nucleus (cf. ref. 12). The loss of the tactile placing reaction following deafferentation of the neck may therefore be attributed to disfacilitation of the ipsilateral interpositus nucleus. This hypothesis is supported by the results of recent experiments, showing that interpositus neurons respond to static changes in neck position 4.
619 This work was s u p p o r t e d by the Public H e a l t h Service Research G r a n t NS 07685-10 from the N a t i o n a l I n s t i t u t e of Neurological a n d C o m m u n i c a t i v e Disorders a n d Stroke, N . I . H . , U.S.A., a n d by a research g r a n t from the Consiglio Nazionale delle Ricerche, Italy. D. M a n z o n i is a s t u d e n t of the Scuola N o r m a l e Superiore, Pisa.
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