Single muscle organization of interposito-rubral projections

_E A.imentai Exp Brain Res 39, 261-267 (1980) BranResearch 9 Springer-Verlag 1980 Single Muscle Organization of Interposito-rubral Projections* R. Giuffrida, G. Li Volsi, M . R . Pant6, V. Perciavalle, S. Sapienza and A. Urbano Institute of Human Physiology,Universityof Catania, Viale Andrea Doria, 6, 1-95125 Catania, Italy Summary. In unanesthetized neuraxis intact cats microstimulation of the interpositus nucleus (IN) which activated a single flexor or extensor muscle in limbs, was used to investigate changes of unitary discharges of rubrospinal (RST) cells. Recordings were made from sites the stimulation of which excited the same muscle activated by the IN (agonist cells), its antagonist (antagonist cells) or heteronymous muscles (heteronymous cells). Cats submitted to chronic cerebellar decortication, acute brachium conjunctivum (BC) section, acute prerubral hemidecerebration or chronic prerubral hemidecerebration and contralateral BC section, were used as controls. It was shown that agonist RST cells were monosynaptically fired from IN, while antagonist cells were inhibited and the heteronymous ones were not influenced. Cerebellar efferents within the BC mediate both excitatory and inhibitory effects, but cerebellar cortex and prerubral structures were not involved in their production. Key words: Interpositus nucleus - Rubrospinal cells Microstimulation Recent experiments have furnished a series of new data about the role played by the pars intermedia of the cerebellum in motor control. These data are the following: (1) stimulation of cerebellar afferents within the brachium pontis (BP; Perciavalle et al. 1977, 1978a) and the restiform body (RB; Perciavalle et al. 1978b) evokes contraction of single limb * Supported by a grant from ConsiglioNazionale delle Ricerche Prof. A. Urbano, M.D. (address see above) Offprint requests to: muscles directly (Perciavalle et al. 1979) via the interpositus nucleus (IN) and the rubrospinal tract (RST); (2) BP and RB activations which elicit contraction of a given muscle monosynaptically only excite IN cells located within the area from which that muscle is controlled (Perciavalle et al. 1979); (3) IN microstimulation is capable of provoking single limb muscle contractions which are mediated by the brachium conjuctivum (BC) and the RST (Asanuma and Hunsperger 1975); (4) activation of tendon receptor afferents in a given muscle produces, via the cerebellar cortex, inhibition of interposito-rubral cells belonging to the efferent zone for that muscle as well as the excitation of cells located in the focus for its antagonist (Licata et al. 1978). Previous findings had shown that activation of discrete zones within the red nucleus (RN) induces contraction of individual muscles via the RST (Ghez 1975). Therefore, it seemed likely that IN efferents, the stimulation of which provokes contraction of a single muscle, could only activate RST cells included within the area of the same muscle (agonist RST cells). Furthermore, stimulation of an IN focus could produce inhibition of RST cells located in an antagonist focus (antagonist RST cells). The present study was undertaken to investigate these points. Parts of the results presented in this report have been communicated elsewhere (Giuffrida et al. 1978). Methods The experiments were carried out on sixteen unanesthetized, head-restrained cats. Nine cats had the neuraxis intact, whereas those remaininghad been submitted to chroniccerebellar decortication (2), acute BC section (2), acute prerubral hemidecerebration (1) or chronicprerubral hemidecerebrationand contralateral BC section (2). General procedures as well as methods for central lesions have been described elsewhere (Perciavalle et al. 1978b). 0014--4819/80/0039/0261/$ 1.40 262 R. Giuffrida et al.: Interposito-rubral Projections Surgery was performed under gaseous anesthesia ( 0 2 40 ~ N20 60% supplemented with halothane 0.5-1%) and wounds were infiltrated with 1% Xylocaine (Astra). Sedative doses of sodium pentobarbitai (Nembutal, 5 mg i.m.) were administered once or twice in the course of the experiment. IN microstimulation was performed as reported elsewhere (Perciavalle et al. 1978c). The objective was to identify a site within the nucleus that, when stimulated with a threshold current equal or below 50 ~A, elicited a single limb muscle contraction after a latency (15-24 ms) which indicated an involvement of the rubrospinal pathway (Perciavalle et al. 1978e). IN stimulating electrodes were tungsten wires. insulated up to 7--15 ~m from the tip (resistance 1-4 Mf~). They were inserted along sagittal planes 3.6-5.2 (Berman 1968) a t an angle of about 35~ from the vertical axis. The selected IN zone was thereafter activated with 0.2 ms single or double (500-800 Hz) stimuli while extraeellular spike potentials were recorded from RN with tungsten mieroelectrodes having 2-4 ~m bare tips (resistance 7--10 MQ). The indifferent electrode (Ag-AgC1) was positioned at the cranial bone or at face or neck muscles. The explored RN portion was enclosed between planes Fr 3.0 and 6.0 (Jasper and Ajmone-Marsan 1954). RST cells were identified by antidromie invasion from the contralateral RST which was stimulated with three shocks (0.2 ms, 300-600 Hz, 150 ~tA) monopolarly delivered through nickel-chrome wires insulated up to about 100 ~tm from the top, stereotaxically placed in planes P 15.0, L 4.1-4.7, H -7.5 (Verhaart 1964). Antidromically activated cells were those showing a two step invasion (Tsukahara et al. 1972), a variation in latency not greater than 100 ~s (Padel et al. 1972) and the capability to follow stimulation frequencies above 300 Hz. As a rule, the RN recording sites were stimulated in order to produce muscle activation (Ghez 1975), and when cells were not encountered RN stimulation was applied every 100-200 ~m at the most in the course of penetration. RN ceils were characterized on the basis of the relation between the IN focus stimulated and the RN focus in which they were located. According to this criterion, IN and RN loci were expressed in terms of single muscles and RN cells were defined as agonist, antagonist or heteronymous, depending on whether they were located in a focus from which contraction was obtained in the same muscle as that activated from IN, in its antagonist or in heteronymous muscles. Muscle activation was examined by eleetromyography as already described (Perciavalle et al. 1977). Small electrolytic reference lesions (negative 15 ~tA current for 20 s) were made at the end of each electrode penetration within RN. After completion of the observations, IN and RST stimulating sites were also marked. At the end, the animals were anesthetized with Nembutal and the head perfused with 10% formalin solution. Histological examinations were performed on sagittal (cerebellum) and frontal (brain stem) sections stained with Kltiver-Barrera's method (1953). Muscles from which eleetromyograms (EMGs) had been recorded were identified through post mortem examination. Details of experimental procedures will be given in Results. The responsiveness of RN cells to IN stimulation was evaluated by converting 60 trials into post-stimnius time histograms (PSTHs) and cumulative frequency distributions (CFDs) in the conventional manner. Averaged PSTHs were also found by calculating from all trials of the examined cells the mean number of spikes for each bin after the onset of stimulation. Activity in absence of any intentional stimulation (spontaneous activity) was also computed from an equal number of trials in order to evaluate the mean number (-+ standard deviation, S.D.) of spikes for bins of 0.1-2 ms. As a rule, the PSTHs were compared with cumulative sums derived according to the method described by Ellaway (1978). Latency as well as duration and intensity of RN responses were determined by comparing evoked and spontaneous activities (Neafsey et al. 1978). Excitatory and inhibitory responses were defined as sequences of at least three bins with frequency values more than 2 S.D. above or below the mean value during spontaneous activity. Latency was expressed by the time interval of the first bin of the sequence from the stimulus, and duration was measured as the interval between the first and the last bin of the sequence. Response intensity (r) was calculated from the ratio between the number of spikes recorded in an equal time interval during evoked (E) and spontaneous (S) sequences (r = E/S). Results I. I N Influences on R S T Cells The observations were made stimulating 12 IN sites while recording extracellular spike potentials from 87 RN cells in the course of 56 electrode penetrations. Each IN site was capable of activating, when stimulated, an individual limb muscle (Asanuma and Hunsperger 1975). No excitation was observed by recording EMGs from other muscles (up to 8) in the same or other limbs. The threshold of the IN-induced motor effect was controlled at different times in the course of the experiment, taking care that the animal was in relaxed wakefulness and maintained the initial posture. The RN cells examined were included within 90 loci, the stimulation of which produced contraction of single limb muscles at a current intensity equal to or below 30 ~A. Distribution of IN Table 1. Types of muscles activated by interpositus nucleus (IN) and red nucleus (RN) stimulations and mean excitation threshold current (~A -+ standard error) IN Forelimb Flexors 6 (13.33+1.80) Extensors Flexors 1 (14.00) 1 (9.00) Extensors 3 (15.00+1.73) RN Hindlimb Forelimb Hindlimb 29 (13.22+].36) 11 (10.91+1.22) 20 (11.70+1.51) 6 (13.36_+3.72) 6 (11.50+1.33) 7 (15.57_+2.42) 7 (9.00+2.43) 4 (14.50_+5.23) 62 (12.20+0.92) 28 (12.71+1.09) Proximal i (13.00) Distal Total 11 (13.45+1.14) 1 (13.00) R. Giuffrida et al.: Interposito-rubral Projections 20 Agonist Antagonist 263 and RN loci according to the part of the limb involved in the movement and the flexor or extensor action of the muscle excited, is reported in Table 1 together with the mean threshold current (+ standard error) for muscle activation from different loci. Up to 3 cells could be recorded from a single RN focus. A different threshold was usually found in a different recording site of the same focus. Effects of IN stimulation on RN discharges were routinely tested with stimuli having an intensity equal to or below that used for muscle excitation. Agonist, antagonist and heteronymous RN cells were identified according to the criterion described in Methods. Of all RN cells studied, 42 were RST cells, while for the remaining 45, RST stimulation was ineffective in producing antidromic firing (non-RST cells). The histograms in Fig. 1 show the effect elicited by IN stimulation for the different types of RN cells. As can be seen, all agonist RST cells were activated and all the antagonists inhibited (see Dis, cussion) from the IN, whereas the heteronymous cells were unaffected with the exclusion of one cell located within an RN area for m. brachialis, which was activated from an IN focus for a synergic muscle (m. biceps brachii, BIB). Effects on non-RST cells were similar in nature; however, some agonist cells (5) were unresponsive and one of the antagonists was excited (interneuron?). Moreover, two heteronymous non-RST cells were excited and one inhibited. Results obtained from all RST cells examined in neuraxis intact animals are shown by the averaged PSTHs of Fig. 5A. No significant differences were Heteronymous U) 15 q) o I"O3 10-- 5-- (n 4) o 5~ 10- I'O3 cO Z 15- 20-- iiiiiiiii=" W////A Ex In Un Fig. 1. Responses of rubrospinal tract (RST) and non-rubrospinal tract (non-RST) cells to interpositus nucleus (IN) microstimulation. Cells were distinguished in agonist, antagonist and heteronymous according to whether the motor effect produced upon activation of the recording site involved the same muscle, its antagonist or heteronymous muscles, with respect to the muscle activated from the IN. Abbreviations: Ex, excited cells; In, inhibited cells; Un, unresponsive cells I&TRB 2A 3A 511 4iBIB 6 9 BIF Ft. 5 . 0 Threshold ( g A ) l L 2 9 ./div. ms 40 ms Idiv. /div. Fig. 2. Discharge changes (poststimulus time histograms, PSTHs, and cumulative frequency distributions, CFDs) of six (1-6) RST cells recorded in the red nucleus (RN) of a neuraxis intact cat upon IN stimulation (arrows) of a focus for m. biceps brachii (BIB; 17 gA). Recording sites at different depths (filled circles in the camera lueida drawing) and corresponding thresholds for the motor effect produced by their stimulation are reported at the top. Symbols represent the muscles excited from the RN. Abbreviations: BIF, m. biceps femoris, TRB, m. triceps brachii; others as in Fig. 1 264 R. Giuffrida et al.: Interposito-rubral Projections A B ~o 220 N=11 ,/9 = 0.32+0.95 x ~ = 0.8493 140. 9 / N:11 x1'37y =109 = 0.7393 = 120- o Fig. 3, Relationship of excitation latency (A) and inhibition duration (B) to threshold intensity for the motor effect elicited through stimulation of RN sites from which unitary responses to IN had been recorded. Threshold intensity is expressed as a multiple of the lowest threshold at different sites for each muscle (I/I 9 The number of cells, the equation of the relation and the correlation coefficient are reported in each case E 2 o J~ i- = o 1oo- I 9 ~= 8 0 - o 9 9 --~ 6 0 --= 4 0 200 Latency (ms ) found between the thresholds for excitatory and inhibitory effects. An electrode penetration within RN is illustrated in Fig. 2. At the top, the electrode trajectory and depth-threshold relation of the motor effect are drawn. Symbols represent RN recording sites from which activation of three distinct muscles was produced. Sites 1-3 elicited the contraction of m. triceps brachii (TRB), or the antagonist of the muscle activated from the IN focus for the BIB, at decreasing stimulus threshold, whereas sites 4 and 5 produced a contraction of this muscle and site 6 controlled m. biceps femoris. PSTHs and CFDs at the bottom were constructed from unitary discharges recorded from cells 1-6. They were all antidromically fired from RST. It can be seen that cells 1-3 (antagonist) were inhibited (r = 0.085, 0.069 and 0.14, respectively) whereas cells 4-5 (agonist) were excited (r= 117.5 and 83.9), and no discharge change was displayed by the heteronymous cell (6). It should be noted that CFDs from excited cells show plateaus which were not produced by instrument saturation. Although a late inhibition cannot be excluded, it seems probable that these plateaus as well as the plateau in Fig. 4, are dependent on very low background activity of the cells, as indicated by the spontaneous values (straight lines). Excitation had a latency of 0.7-1.7 ms (2:1.15 + 0.34 S.D.). The latency at different recording sites within a given focus decreased in parallel with the lowering of the threshold current for the motor effect (Fig. 3A). Most frequently, a single minimal intensity stimulus delivered to the IN was capable of evoking a single spike in the target RN cell; in the other cases, two stimuli were necessary, to provoke such a Threshold I/Io response. All cells examined followed stimulation frequencies up to 100 Hz. Inhibition lasted longer (up to 220 ms) when the threshold of the motor effect evoked from the recording site was lower (Fig. 3B). Low frequency discharge of RST cells (X: 8.85 Hz + 3.16 S.D.) rendered the evaluation of the inhibition onset impossible. For this reason, in some experiments conditioning stimulation of IN was followed by test stimulation of a site within the BC which with very low current (11-15 ~A) induced contraction of the antagonist muscle with respect to that activated from IN. The RST cells tested were located within a focus, the stimulation of which excited the same muscle activated from the BC (antagonist cells with respect to IN). After recording excitatory (monosynaptic spikes) and inhibitory responses, respectively from BC and IN, single conditioning stimuli were delivered to IN, followed by testing stimuli to BC at different intervals. Under these conditions, it was found that inhibition (suppression of the BC evoked spike) started 3.9-4.5 ms after the conditioning stimulus and persisted for 18--52 ms. An experiment of this type is illustrated in Fig. 4A-C. II. Control Experiments Chronic CerebeIlar Decortication. These experiments were performed on 2 cats submitted to cerebellar cortex suction 4 and 5 weeks before the experimental session. Stimulation of both INs was programmed in the experimental plan. Therefore, corticocerebellar areas which project to the IN (Jansen and Brodal 1954) were bilaterally sucked out together with the 265 R. Giuffrida et al.: Interposito-rubral Projections TRB BIB A IN -- . . . . . . ,,,,h ib BC 40ms B 3o :ti 3~] Jr "E = f C .hl.,L,- ,-~'.,,I...4- d.d.,-.dmul I I I [ t I I I I I 2 ms .A I ] I I I I /div. I i L I BC i l Fig. 4. Latency and duration of inhibitory responses of RST cells to IN stimulation of neuraxis intact cat. A electromyograms recorded from the BIB and TRB upon threshold stimulation of a focus within the IN (11 Wk) and a focus within the brachium conjunctivum (BC, 15 pA). B PSTHs and CFDs to single pulse stimulation (arrows) of IN (upper) and BC (lower): the RST cell recorded from was at a site from where contraction of the TRB was obtained with 18 pA intensity. C IN single pulse conditioning stimulation (filled circles) followed at different intervals by BC test activation (filled triangles). Note the disappearance of the RST cell response (single spike) to the BC for intervals between 4.3 and 22 ms "I IN I /div, 40ms 5ms vermal cortex b e t w e e n them. Five electrode penetrations within R N w e r e m a d e during which 3 agonist, 4 antagonist and 6 h e t e r o n y m o u s R S T cells were examined with I N stimulation. A v e r a g e d P S T H s are shown in Fig. 5B. It is evident that no significant differences were f o u n d in these cats with respect to intact animals. Acute BC Interruption. Previous experiments had shown that I N - i n d u c e d single muscle contractions persisted in cats chronically submitted to bilateral section of b o t h B P and R B (Perciavalle et al. in preparation). In the p r e s e n t study, two cats were used to examine w h e t h e r B C interruption abolished R S T responses to the IN. A s was expected, u n d e r these conditions no responses were o b s e r v e d in either agonist or antagonist cells. Acute Prerubral Hemidecerebration. This intervention was p e r f o r m e d on one acute cat. It was o b s e r v e d that I N stimulation p r o d u c e d inhibition of antagonist R S T cells as in preparations with intact neuraxis. Chronic Prerubral Hemidecerebration and Contralateral BC Section. I n chronic decorticated cats R N microstimulation evokes single limb muscle contractions via the R S T ( G h e z 1975). H o w e v e r , it was not possible to exclude that u n d e r the present conditions m o t o r effects f r o m R N could be p r o d u c e d by activa- 266 R. Giuffrida et al.: Interposito-rubral Projections ANTAGONIST AGON}ST HETERONVMOUS ~2 10 N=I~ A = N=2o N=11 2 to N=4 N=3 N=6 [3 i t ...... 2 ms I /clim i .... 40 tion o f afferents within the nucleus coming from other forebrain structures and/or from the cerebellum. Experiments were therefore carried out on two cats to test if single muscle responses to RN persisted after a chronic nuclear deafferentation which included descending fibers from the ipsilaterat hemisphere and cerebeUar afferents in the contralaterat BC. The experiment took place 11 and 14 days after the intervention. RN microstimulation was performed in the course of 5 electrode penetrations in deafferented RN and 4 in normal ones, It was found that activation of deafferented RN elicited single muscle contractions which were similar to those obtained from the normal nucleus. Discussion Microstimulation of IN in chronic BP and RB sectioned cats is capable of evoking, as in neuraxis intact cats (Asanuma and Hunsperger 1975), single muscle contractions which disappear after BC and RST interruption (Perciavalte et al. in preparation), Therefore, we exclude that the motor effects from IN observed in the present study could be provoked by presynaptic activation of BP and RB motor afferents. Furthermore, it is very unlikely that IN-induced muscle contractions could be produced by tile actiwltion of cotlaterah, if they exist, to RN of cerebellar afferents within the BC. Indeed, this should implicate that these collaterals exhibit a single muscle arrangement. There is, therefore, no doubt that in these experiments efferent zones of single muscles were stimulated in the IxN. However, an overlapping ms Fig. 5. Averaged PSTHs constructed from unitary responses to IN microstimutation (arrows) of 42 RST cells in neuro.xis intact cats CA) and 13 in ones with the cerebetlar cortex removed (t3). RST cells were distS_nguishedin agonist, antagonist and heteronymous according to the criterion in Fig, 1 /dl~ of contiguous zones cannot be excluded. For this reason, the above effects on RN cells were studied from IN zones exhibiting very low thresholds for motor effects (below 50 ~A). It has been observed that in chronic motor cortex ablated cats, RN stimulation induces single muscle contractions which m'e abolished by contratateral RST interruption (Ghez 1975). In this study we excluded that the motor effects from RN could be dependent on the activation of terminal and/or passage fibers of forebrain and cerebellar origin. Therefore, it is ,,'cry likely that under the present conditions the effects of IN stimulation were really tested on agonist, antagonist and heteronymous RST cells. A reciprocal spinal reflex regulation of muscular activity was already described by Sherrington (1906), and experiments in the recent past indicate that spinal elements are reciprocally influenced by corrico- and rubrospinal systems (Phillips and Porter 1964; Hongo et al. 1969; Jankowska et aL 1975). Besides giving direct evidence for the excitation of agonist RST cells, it is demonstrated herein that IN does exert inhibitory influences via BC on the RST cells located in antagonist loci. Observation of cats with chronic ablation of the cerebellum cortex showed that the activation of Purkinje axons was not responsible for inhibitory effects. Hence, both excitation and inhibition of RST celg (Massion 1961; Massion and Albe-Fessard 1963) were mediated by IN efferents within the BC. As expected (Tsukahara et al. 1967), the excitation of agonist cells was monosynaptic (mean latency: 1.15 ms). On the other hand, experiments using conditioning pulses from IN (Fig, 4), which allowed calculation of the latency of R. Giuffrida et al.: Interposito-rubrai Projections inhibitory responses (3.9-4.5 ms), indicate a short latency, p e r h a p s d i s y n a p t i c p a t h w a y . T h e m e m b r a n e mechanism subserving the discharge reduction or s u p p r e s s i o n o f a n t a g o n i s t R S T cells was n o t investig a t e d in this study. H o w e v e r , e f f e r e n t n e u r o n s w i t h i n i n t r a c e r e b e l l a r n u c l e i a r e c o n s i d e r e d to b e e x c i t a t o r y ( T o y a m a et al. 1970), a n d n o significant n u m b e r o f i n t e r n e u r o n s has b e e n d e s c r i b e d w i t h i n t h e s e nuclei ( M a t s u s h i t a a n d I w a h o r i 1971). T h e r e f o r e , it is m o s t likely t h a t I N - i n d u c e d i n h i b i t i o n w o u l d b e d e p e n d e n t o n the a c t i v a t i o n o f i n h i b i t o r y i n t e r n e u r o n s w i t h i n t h e R N . I n fact, i n t e r n e u r o n s h a v e b e e n o b s e r v e d with a n a t o m i c a l ( C o n d 6 a n d C o n d 6 1973; K i n g et al. 1974) a n d e l e c t r o p h y s i o l o g i c a l ( T s u k a h a r a et al. 1968) e x p e r i m e n t s a n d it is c o n c e i v a b l e t h a t t h e i r a c t i v a t i o n is p r o d u c e d b y c o l l a t e r a l s o f fibers w h i c h m o n o s y n a p t i c a l l y e x c i t e t h e R S T cells l o c a t e d in agonist loci. P r e r u b r a l s t r u c t u r e s a r e c e r t a i n l y n o t i n v o l v e d in m e d i a t i n g i n h i b i t i o n , b e c a u s e t h e l a t t e r was also o b s e r v e d in h e m i - d e c e r e b r a t e d animals. I n c o n c l u s i o n , this s t u d y c l e a r l y d e m o n s t r a t e s t h a t I N p r o j e c t i o n s to R N a r e o r g a n i z e d for single muscles a n d in a r e c i p r o c a l m a n n e r . F r o m a funct i o n a l p o i n t o f view, such an o r g a n i z a t i o n c o u l d b e utilized as a s u p r a s p i n a l m e c h a n i s m p r o v i d i n g m u s c u l a r synergy. Acknowledgments: We wish to thank Mr. G. Maugeri for the illustrations. References Asanuma H, Hunsperger W (1975) Functional significance of projection from cerebellar nuciei to the motor cortex in the cat. Brain Res 98:73-92 Berman AL (1968) The brain stem of the cat. Univ. of Winsconsin Press, Madison Milwaukee London Cond6 F, Cond6 H (1973) l~tude de la morphologie des cellules du noyau rouge du chat par la m6thode de Golgi-Cox. Brain Res 53:249-271 Ellaway PH (1978) Cumulative sum technique and its application to the analysis of peristimulus time histograms. Electroenceph Clin Neurophysiol 45:302-304 Ghez C (1975) Input-output relations of the red nucleus in the cat. Brain Res 98:93-108 Giuffrida R, Li Volsi G, Pant6 MR, Perciavalle V, Sapienza S, Urbano A (1978) Organizzazione a singofi musc~oli delte proiezioni interposito-rubrali nel gatto. Atti XXX Congr Naz Soc It Fisiol, com. N. 115, Ferrara, 28-30 september i978 Hongo T, Jankowska E, Lundberg A (1969) The rubrospinal tract. I. Effects on alpha-motoneurones innervating hindlimb muscles in cats. Exp Brain Res 7:344-364 Jankowska E, Padel Y, Tanaka R (1975) Projections of pyramidal tract cells to a-motoneurones innervating hind-limb muscles in the monkey. J Pliysiol (Lond) 249:637-667 267 Jansen J, Brodal A (1954) Aspects of cerebellar anatomy. Tanum, Oslo Jasper HH, Ajmone-Marsan C (1954) A stereotaxic atlas of the diencephalon of the cat. The National Research Council of Canada, Ottawa King JS, Dora RM, Martin GF (1974) Anatomical e~-idencefoJ:an intrinsic neuron in the red nucleus. Brain Res 67:317-323 Klfiver H, Barrera E (1953) A method for the combined staining of cells and fibers in the nervous system. J Neuropathol Exp Neurol 12:400-403 Licata F, Perciavalle V, Santangelo F, Sapienza S, Urbano A (1978) Input-output relationships of interpositus nucleus for single muscles. Neurosci Letters (Suppl) 1:$149 Massion J (1961) Contribution ~ l'~tude de la r~gulation cdrdbelleuse du syst~me extrapyramidal. Contr61e r4flexe et tonique de la voie rubrospinale par le cervelet. Masson, Bruxelles Arscia Paris Massion J, Albe-Fessard D (1963) Dualit6 des voies sensorielles affdrentes contr6Iant l'activit6 du noyau rouge. Electroenceph Clin Neurophysiol 15:435454 Matsushita M, Iwahori N (1971) Structural organization of the interpositus and dentate nuclei. Brain Res 35:17-36 Neafsey EJ, Hull CD, Buchwald NA (1978) Preparation for movement in the cat. I. Unit activity in the cerebral cortex. Electroenceph Clin Neurophysiol 44:706-713 Padei Y, Armand J, Smith AM (1972) Topography of rubrospinat units in the cat. Exp Brain Res 14:363-371 Perciavalle V, Santangelo F, Sapienza S, Savoca F, Urbano A (1977) Motor effects produced by microstimulation of brachium pontis in the cat. Brain Res 126:55%562 Perciavalle V, Santangelo F, Sapienza S, Savoca F, Urbano A (1978a) A ponto4nterposito-rubrospinal pathway for single muscle contractions in limbs of the cat. Brain Res 155: 124-129 Perciavalle V, Santangelo F, Sapienza S, Serapide MF, Urbano A (1978b) Motor responses evoked by microstimulation of restiform body in the cat. Exp Brain Res 33:241-255 Perciavalle V, Santangelo F, Sapienza S, Serapide MF, Urbano A (1978c) Dentate nucleus incapability to trigger movement in the eat. Neurosci Letters (Suppl) 1:$152 Perciavalle V, Santangelo F, Sapienza S, Serapide MF, Urbano A (1979) Direct afferents to interpositus nucleus responsible for triggering movement. Brain Res 177:367-372 Phillips CG, Porter R (1964) The pyramidal projection to motoneurones of some muscle groups of the baboon's forelimbs. In: Eccles JC, Shad6 YP (eds) Progress in brain research. Physiology of spinal neurons. Elsevier, Amsterdam London New York, pp 222-242 Sherrington CS (1906) The integrative action of the nervous system. Yale Univ Press, New Haven Toyama K, Tsukahara N, Kosaka K, Matsunami K (1970) Synaptic excitation of red nucleus neurones by fibres from interpositus nucleus. Exp Brain Res 11:187-198 Tsukahara N, Fuller DRG, Brooks VB (1968) Collateral pyramidal influences on the corticorubrospinat system. J Neurophysiol 31:467-484 Tsukahara N, Toyama K, Kosaka K (1967) Electrical activity of red nucleus neurones investigated with intracellular microelectrodes. Exp Brain Res 4:18-33 Verhaart WJC (/964) A stereotactic atlas of the brain stem of the cat. Van Gorcum, Assen Received July 16, 1979