Input-output organization of reticulospinal neurones,with special reference to connexions with dorsal neck motoneurones in the cat

Summary Dorsal neck motoneurones receive disynaptic tectal and pyramidal EPSPs via common reticulospinal neurones (RSNs). This study was aimed at identification of the RSNs projecting directly to neck motoneurones and mediating these EPSPs. 1. Stimulation of the tectum and the cerebral peduncle evoked monosynaptic descending volleys in the spinal cord, which were chiefly mediated by reticulospinal neurones in the pons and the medulla. Systematic tracking of the C3 and C7 segments was made to locate descending volleys in the spinal funiculi. The tectal monosynaptic volley was largest in the medial part of the ventral funiculus and decreased gradually as the recording electrode was moved to the lateral part of the ventral funiculus and the lateral funiculus. In contrast, the peduncle-evoked monosynaptic volley was distributed rather evenly in the ventral funiculus and the ventral half of the lateral funiculus. 2. Differences in funicular distribution of the two descending volleys suggest the existence of subgroups of RSNs which differed in strength of inputs from the two descending fibre systems and in the funicular location of descending axons. 3. The RSNs were classified into the following four groups; (1) mRSNs which descended in the medial part of the ventral funiculus, (2) in RSNs which descended in the ventrolateral funiculus, (3) 1RSNs which descended in the dorsal 2/3 of the lateral funiculus and (4) coRSNs which descended in the contralateral funiculi. The mRSNs were located in a fairly localized region corresponding to the nucleus reticularis pontis caudalis (N.r.p.c.), while inRSNs, 1RSNs and coRSNs were mainly in the nucleus reticularis gigantocellularis (N.r.g.), in the nucleus reticularis magnocellularis (N.r.m.) and in the nucleus reticularis ventralis (N.r.v.). RSNs were further divided into three types depending on the levels of projection. L-RSNs projected to the lumbar spinal segments. C-RSNs descended to the C6–C7 spinal segment but not to the lumbar segments. N-RSNs projected to the C3 but not to the C6–C7 segments. 4. Stimulation of the tectum and the cerebral peduncle produced monosynaptic negative field potentials in the medial two thirds of the reticular formation in the pons and medulla. Tectal field potentials were largest in the N.r.p.c. and the rostral part of the N.r.g., while pyramidal field potentials were largest in the N.r.g. Correspondingly, RSNs in the N.r.p.c. (mRSNs) received larger monosynaptic EPSPs from tectal than from pyramidal volleys, while RSNs in the N.r.g. (in-, 1- and coRSNs) received stronger input from the peduncle than from the tectum. 5. Stimulation of the C7 ventral but not the lateral funiculus evoked monosynaptic EPSPs on all the dorsal neck motoneurones tested. Stimulation of the L1 segment only produced monosynaptic EPSPs in 35% of the motoneurones. The L1 evoked EPSPs were much smaller than C7 evoked EPSPs. 6. The C7 evoked EPSPs (C7 EPSP) showed complete occlusion (collision) with the tectal or pyramidal disynaptic EPSPs. Similar results were obtained with L1 EPSPs. These results indicate that tectal and pyramidal disynaptic EPSPs in dorsal neck motoneurones were mediated chiefly by C-mRSNs and C-inRSNs and partly by L-RSNs.     

Trigeminal excitation of dorsal neck motoneurones in the cat

Summary Excitation of dorsal neck motoneurones evoked by electrical stimulation of primary trigeminal afferents in the Gasserian ganglion has been investigated with intracellular recording from -motoneurones in the cat. Single stimulation in the Gasserian ganglion ipsi-and contralateral to the recording side evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating the lateral head flexor muscle splenius (SPL) and the head elevator muscles biventer cervicis and complexus (BCC). The gasserian EPSPs were composed of early and late components which gave the EPSPs a hump-like shape. A short train of stimuli, consisting of two to three volleys, evoked temporal facilitation of both the early and late EPSP components. The latencies of the gasserian EPSPs ranged from 1.6 to 3.6 ms in SPL motoneurones and from 1.6 to 5.8 ms among BCC motoneurones. A rather similar latency distribution between 1.6 and 2.4 ms was found for ipsi- and contralateral EPSPs in SPL and BCC motoneurones, which is compatible with a minimal disynaptic linkage between primary trigeminal afferents and neck motoneurones. Systematic transections of the ipsi- and contralateral trigeminal tracts were performed in the brain stem between 3 and 12 mm rostral to the level of obex. The results demonstrate that both the ipsi- and contralateral disynaptic and late gasserian EPSPs can be mediated via trigeminospinal neurones which take their origin in the nucleus trigeminalis spinalis oralis. Transection of the midline showed that the contralateral trigeminospinal neurones cross in the brain stem. Systematic tracking in and around the ipsilateral trigeminal nuclei demonstrated that the axons of ipsilateral trigeminospinal neurones descend just medial to and/or in the medial part of the nucleus. Spinal cord lesions revealed a location of the axons of the ipsilateral trigeminospinal neurones in the lateral and ventral funiculi. Interaction between the ipsi- and contralateral gasserian EPSPs showed complete summation of the disynaptic EPSP component, while the late components were occluded by about 45%. These results show that the disynaptic EPSPs are mediated by separate trigeminospinal neurones from the ipsi- and contralateral side, while about half of the late EPSPs are mediated by common neurones which receive strong bilateral excitation from commissural neurones in the trigeminal nuclei. Spatial facilitation was found in the late gasserian EPSP but not in the disynaptic gasserian EPSP by conditioning stimulation of cortico- and tectofugal fibres. Disynaptic pyramidal and tectal EPSPs, which are mediated by reticulospinal neurones, were facilitated by a single stimulation in the gasserian ganglion at an optimal interval of 2 ms. It is suggested that primary trigeminal afferents can excite the reticulospinal neurones via a disynaptic trigeminoreticular pathway.     

Mono- and disynaptic pathways from Forel's field H to dorsal neck motoneurones in the cat

Summary 1. We analysed the synaptic actions produced by Forel's field H (FFH) neurones on dorsal neck motoneurones and the pathways mediating the effects. 2. Stimulation of ipsilateral FFH induced negative field potentials of several hundred microvolts with the latency of about 1.1 ms in the medial ponto-medullary reticular formation, being largest in the ventral part of the nucleus reticularis pontis caudalis (NRPC), and in the dorsal part of the nucleus reticularis gigantocellularis (NRG). 3. Stimulation of ipsilateral FFH induced excitatory postsynaptic potentials (EPSPs) in 90% (47/52) and inhibitory postsynaptic potentials (IPSPs) in 19% (10/52) of the reticulospinal neurones (RSNs) in the NRPC and the NRG. Latencies of the EPSPs and IPSPs were 0.7–3.0 ms, the majority of which were in the monosynaptic range. The monosynaptic connexions were confirmed by spike triggered averarging technique both in excitatory (n=4) and inhibitory (n=2) pathways. 4. Single stimulation of FFH induced EPSPs at the segmental latencies of 0.3–1.0 ms in neck motoneurones, which were clearly in the monosynaptic range. Repetitive stimulation of FFH produced marked temporal facilitation of EPSPs in neck motoneurones. The facilitated components of the EPSPs had a little longer latencies and their amplitude reached several times as large as that evoked by single stimulation in all the tested motoneurones. These facilitated excitations are assumed to be mediated by RSNs in the NRPC and NRG, since RSNs were mono- and polysynaptically fired by stimulation of FFH and they were previously shown to directly project to neck moteneurones. 5. EPSPs were induced in 91% (82/91) of motoneurones supplying m. biventer cervicis and complexus (BCC; head elevator), 10% (3/29) of motoneurones supplying m. splenius (SPL; lateral head flexor). Eikewise, stimulation of FFH produced EMG responses in BCC muscles, while not in SPL muscle. Thus FFH neurones produce excitations preferentially in BCC motoneurones. 6. Systematic tracking in and around FFH revealed that the effective sites for evoking above effects were in FFH and extended caudally along their efferent axonal course. 7. These results suggested that FFH neurones connect with neck motoneurones (chiefly BCC, head elevator) mono-, diand/or polysynaptically and are mainly concerned with the control of vertical head movements.     

The projection from nucleus reticularis tegmenti pontis onto the cerebellum in the cat

Summary Following stereotactically performed lesions in nucleus reticularis tegmenti pontis (N.r.t.) degenerating fibers are traced to the contralateral N.r.t., to the pontine nuclei, through brachium pontis to restricted areas of the cerebellar nuclei and to most parts of the cerebellar cortex where they terminate in the granular layer. Most degenerating fragments are found in the contralateral half of the cerebellum with the greatest density in the vermal lobules VI and VIIA and in the flocculus.Following injections of HRP in the various cerebellar lobules labeled cells are mainly present within limited groups in the N.r.t.. Injections in vermal lobules VI-VIII B give rise to labeled cells within circumscribed areas in the dorsal and ventral parts throughout the rostrocaudal extent of the N.r.t.. In cases with injections in lobule IX or the ventral paraflocculus labeled cells are found ventrally in the rostral half of the N.r.t., while following injections in the vermal lobules I-V labeled cells are mainly found in the ventral and caudal part of the N.r.t.. Following injections in the intermediate and lateral parts of the anterior lobe, Crus I and II, the paramedian lobule and the dorsal paraflocculus labeled cells occur within groups in medial and lateral parts throughout the rostrocaudal extent of the N.r.t.. Following injections in the flocculus labeled cells are found in a very distinct group in the dorsal and rostral part of the N.r.t., While an injection in the nodulus (lobule X) gave rise to a smaller group of labeled neurons in the dorsolateral corner in the caudal part of the N.r.t.. Labeled cells within processus tegmentosus lateralis (p.t.l.) are only found following injections in lobules VI-VIIIA, Crus I and II and the dorsal paraflocculus.From what is known about afferents to the N.r.t., it is concluded that no cerebellar lobule gets information from one only of these sources via the N.r.t.. Visual information can probably be mediated from the superior colliculus via the N.r.t. to the flocculus and to a minor extent to the vermal lobules VI-VIII B, and from the pretectum via the N.r.t. to both vermal and lateral parts of the cerebellum.     

Direct connection of the nucleus reticularis gigantocellularis neurons with neck motoneurons in cats

Functional connections of single reticulospinal neurons (RSNs) in the nucleus reticularis gigantocellularis (NRG) with ipsilateral dorsal neck motoneurons were examined with the spike-triggered averaging technique. Extracellular spikes of single NRG-RSNs activated antidromically from the C6, but not from the L1 segment (C-RSNs) were used as the trigger. These neurons were monosynaptically activated from the superior colliculus and the cerebral peduncle. Single-RSN PSPs were recorded in 43 dorsal neck motoneurons [biventer cervicis and complexus (BCC) and splenius (SPL)] for 21 NRG-RSNs and 135 motoneurons tested. All synaptic potentials were EPSPs, and most of their latencies, measured from the triggering spikes, were 0.8–1.5 ms, which is in a monosynaptic range. The amplitudes of single-RSN EPSPs were 10–360 μV. Spike-triggered averaging revealed single-RSN EPSPs in multiple motoneurons of the same species (SPL or BCC), their locations extending up to nearly 1 mm rostrocaudally. Synaptic connections of single RSNs with both SPL and BCC motoneurons were also found with some predominance for one of them. The results provide direct evidence that NRG-RSNs make monosynaptic excitatory connections with SPL and BCC motoneurons. It appears that some NRG-RSNs connect predominantly with SPL motoneurons and others with BCC motoneurons. Received: 23 March 1999 / Accepted: 17 May 1999     

The pattern in the projection of the intracerebellar nuclei onto the nucleus reticularis tegmenti pontis in the cat. An experimental anatomical study

Summary Intensity and distribution of degeneration in the nucleus reticularis tegmenti pontis (N.r.t.) were mapped in silver impregnated sections following stereotactic lesions of the intracerebellar nuclei. Confirming previous results (Brodal and Szikla, 1972) fibres from the interpositus-lateralis-complex, reaching the N.r.t. by way of the crossed descending limb of the brachium conjunctivum, supply the main central part of the N.r.t. from rostral to caudal. The interpositus posterior does not appear to take part in this projection, nor do the ventralmost parts of the lateral cerebellar nucleus (NL). The caudal part of the latter appears to give off more fibres than its rostral part. Rostral and caudal parts of the interpositus anterior (NIA) appear to contribute approximately equally.Fibres from both nuclei terminate in a largely overlapping fashion in the central main regions of the N.r.t. On the whole the NIA projection is situated a little more medially than the NL projection (Fig. 8). Within both projections caudal parts of the nuclei tend to project somewhat more medially than lateral parts, especially caudally. Certain findings suggest that there may be more detailed topical relations.The organization in the cerebellar-nuclear projection onto the N.r.t. corresponds in principle to the pattern found for its other afferent contingents (especially from the cerebral cortex, Brodal and Brodal, 1971). In spite of wide overlapping there is some degree of topical order.Working in the Anatomical Institute in the University of Oslo with leave of absence from the Laboratory of Normal Anatomy, University of Coimbra, Portugal, with a grant from the Portugese Institute for Higher Culture.     

Eye movements and abducens motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis

Study Objectives:

The aim of this work was to characterize eye movements and abducens (ABD) motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis (NRPC).

Methods:

Six female adult cats were prepared for chronic recording of eye movements (using the scleral search-coil technique), electroencephalography, electromyography, ponto-geniculo-occipital (PGO) waves in the lateral geniculate nucleus, and ABD motoneuron activities after microinjections of the cholinergic agonist carbachol into the NRPC.

Results:

Unilateral microinjections of carbachol in the NRPC induced tonic and phasic phenomena in the oculomotor system. Tonic effects consisted of ipsiversive rotation to the injected side, convergence, and downward rotation of the eyes. Phasic effects consisted of bursts of rhythmic rapid eye movements directed contralaterally to the injected side along with PGO-like waves in the lateral geniculate and ABD nuclei. Although tonic effects were dependent on the level of drowsiness, phasic effects were always present and appeared along with normal saccades when the animal was vigilant. ABD motoneurons showed phasic activities associated with ABD PGO-like waves during bursts of rapid eye movements, and tonic and phasic activities related to eye position and velocity during alertness.

Conclusion

The cholinergic activation of the NRPC induces oculomotor phenomena that are somewhat similar to those described during REM sleep. A precise comparison of the dynamics and timing of the eye movements further suggests that a temporal organization of both NRPCs is needed to reproduce the complexity of the oculomotor behavior during REM sleep.

Citation:

Márquez-Ruiz J; Escudero M. Eye movements and abducens motoneuron behavior after cholinergic activation of the nucleus reticularis pontis caudalis. SLEEP 2010;33(11):1517-1527.     

Monosynaptic inhibition of neck motoneurons by the medial vestibular nucleus

Summary Stimulation of the brain stem in cats anesthetized with pentobarbital evoked short-latency IPSPs in many neck motoneurons. From the segmental delay of these IPSPs, and from comparison of their latencies with those of monosynaptic EPSPs evoked in the same motoneuron population by stimulation of the brain stem, it is concluded that the IPSPs are monosynaptic and are produced by descending inhibitory fibers.As many as thirteen electrodes were inserted into the medulla and pons to compare threshold stimuli required to evoke monosynaptic IPSPs from different locations. The points with the lowest threshold were in the medial vestibular nucleus and the medial longitudinal fasciculus. The IPSPs are apparently produced by fibers that originate in the medial vestibular nucleus and reach the upper cervical segments via the MLF.Electrical stimulation of the ipsilateral labyrinth often produces disynaptic IPSPs in neck motoneurons, very probably by means of a relay in the medial nucleus. This inhibitory pathway between labyrinth and neck motoneurons, together with the previously described excitatory pathway relaying in Deiters' nucleus, provides some of the pathways utilized by the labyrinth in regulation of head position.     

Disynaptic tectal and pyramidal excitation of hindlimb motoneurons mediated by pontine reticulospinal neurons in the cat

Summary 1 The pathway mediating disynaptic tectal and pyramidal excitation of hindlimb motoneurons was analyzed in cats anesthetized with chloralose or pentobarbital. Stimulation of the contralateral tectofugal fibers induced EPSPs in flexor and extensor hindlimb motoneurons (118/171). EPSP latencies, measured from the monosynaptically evoked descending volley, were 0.8 ms or less in 34 of the 118 motoneurons, suggesting disynaptic linkage from the tectum. The latencies tended to be shorter in motoneurons innervating proximal muscles than in those innervating distal muscles. 2. Stimulation of the cerebral peduncle induced EPSPs only in a small proportion of motoneurons (7/32). But the peduncular stimulation exhibited a marked facilitatory effect on the tectal EPSPs in most of the tested motoneurons (23/27), showing convergence of tectal and peduncular inputs onto relay cells. 3. In animals whose pyramid was transected, the tectal EPSPs were still facilitated by peduncular stimulation in 45 of 48 tested motoneurons. The time course of facilitation indicated convergence of tectofugal and corticofugal fibers onto brainstem relay neurons. 4. Projection of single neurons in the nucleus reticularis pontis caudalis (NRPC) to the gray matter of the hindlimb segments was examined by mapping thresholds of antidromic activation. Twelve of 13 tested neurons were excited by contralateral tectal stimulation at short latencies, probably monosynaptically. Four of them were found to project to lamina IX. Two of the 3 tested neurons projecting to lamina IX were found to receive excitatory input from the cerebral peduncle. 5. Stimulation of NRPC induced monosynaptic EPSPs in hindlimb motoneurons. In 19 motoneurons, the NRPC-induced monosynaptic EPSPs were facilitated by a conditioning tectal shock. This indicated that the tectal stimulus lowered thresholds of direct activation of cell bodies of premotor NRPC neurons. The time course of the facilitation indicated that the NRPC neurons received monosynaptic tectal excitation. The results provide strong evidence that NRPC neurons are involved in mediating disynaptic tectal excitation of hindlimb motoneurons.     

Responses of medullary reticulospinal neurones to stimulation of cutaneous limb nerves during locomotion in intact cats

The present study was designed to determine whether the transmission of cutaneous afferent information from the limbs to the medullary reticular formation is phasically modulated during locomotion. Experiments were carried out in three chronically prepared, intact cats in which nerve cuff electrodes were placed, bilaterally, on the superficial radial and the superficial peroneal nerves. Thirty-seven reticulospinal neurones (RSNs) were identified by stimulation of their axons in the lumbar spinal cord (L2); 29 of 37 of these were recorded with the cat at rest, 28 of 37 during locomotion and 20 of 37 both at rest and during locomotion. Low-threshold stimulation of the cutaneous nerves evoked excitatory responses in the majority of RSNs both at rest and during locomotion. In the 28 of 37 RSNs recorded during locomotion, it was possible to record the evoked response to stimulation of all four limb nerves, giving a total of 184 tested cases [RSNs testedxnumber of nerves stimulatedxphase of stimulation (swing or stance)]. The responses of most RSNs to cutaneous stimulation were modulated in a phase-dependent manner during locomotion. The maximal responses in most, but not all, cases were obtained during the swing phase of the limb that was stimulated and were largely independent of the discharge pattern of the cell. We interpret this result as indicating that the efficacy of transmission of the afferent information is determined more by the excitability of the spinal relay neurones than by the level of excitability of the RSNs in the brainstem. It is suggested that the base discharge pattern of RSNs might be largely determined by their central afferent input, while peripheral afferent inputs would primarily serve to modify the RSN discharge pattern in response to perturbations.     

Torque vectors of neck muscles in the cat

Summary Anatomical texts describe the neck musculature without measurements of muscle locations or quantitative estimates of pulling actions (torques). This study is based on measurements in stereotaxic coordinates of cat neck muscle origins and insertions, and neck intervertebral rotation axes. Torque vectors in three dimensions were calculated for 14 pairs of dorsal and ventral muscles that insert on the skull or first cervical vertebra. Predicted torque vectors were in general agreement with qualitative statements in the literature. Biventer cervicis and the rectus capitis major, medius, and minor muscles act mainly to raise the head, and longus capitis acts almost exclusively to lower the head. Longissimus capitis, sternomastoid, and cleidomastoid act mainly to roll the head. Complexus acts about equally to raise the head and roll it. Splenius and occipitoscapularis have torque in all three coordinate directions. Torques were altered by changing the pitch of the head with respect to the neck. The calculated neck muscle torques did not correspond to previously reported directions of neck muscle excitation during the vestibulocollic reflex. The neck musculature appears to be a complex, multidimensional system that presents interesting problems in motor control.     

Hypothalamic control of nocireceptive and other neurones in the marginal layer of the dorsal horn of the medulla (trigeminal nucleus caudalis) in the rat

Summary The effect of electrical stimulation of the preoptic area of the hypothalamus on the discharge of neurones in the marginal layer (lamina I) of the trigeminal nucleus caudalis was studied in the anaesthetised rat. There was a powerful suppression of the discharge evoked by noxious thermal stimuli in 49/49 specific nociceptor driven (nocireceptive) neurones. The inhibitory effect increased with graded increases in the intensity of preoptic stimulation. Stimulation, however, produced only a small reduction in the discharge of 14/17 cold receptive neurones. Thresholds for producing suppression of cold receptive neurones were generally higher than those for nocireceptive neurones. There was no effect on the activity of 12/12 low threshold mechanoreceptive neurones. The inhibitory action generated on the activity of nocireceptive neurones was reduced by electrolytic lesions in the nucleus raphe magnus (NRM) or the nucleus paragigantocellularis lateralis (PGCL) or the dorsolateral and ventrolateral periaqueductal gray matter (PAG). Lesions made in the ventral or dorsal aspect of PAG were, however, ineffective in reducing the suppression. It is suggested that the powerful descending inhibitory control of nociceptive transmission in the trigeminal nucleus caudalis is one of the neuronal mechanisms mediating analgesia from the preoptic area of the hypothalamus.     

Spatial frequency and orientation tuning curves of visual neurones in the cat: Effects of mean luminance

Summary Experiments have been performed on unanaesthetized and paralysed cats. The tuning curves for spatial frequency of retinal, lateral geniculate and simple and complex cells of the cortex have been determined in response to sinusoidal gratings of various spatial frequencies at different levels of mean luminance. For all neurones, decreasing the mean luminance leads to a progressive loss of spatial resolution and contrast sensitivity. Retinal ganglion cells of type X show, for scotopic levels of luminance, a flattening of their spatial frequency tuning curves in the low spatial frequency range. For geniculate and cortical neurones, on the contrary, the spatial frequency characteristics at the various levels of luminance remain practically invariant in their bandwidth. On the average, complex cells still respond to mean luminances ten times lower than simple cells. The tuning curves for orientation of cortical cells maintain, to a first approximation, the same shape at the various levels of mean luminance. The results are discussed, comparing the electrophysiological with psychophysical data.     

Monosynaptic connexions of low threshold muscle afferents with hindlimb motoneurones in the turtle spinal cord

Summary Excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from hindlimb motoneurones of the anaesthetized fresh water turtle. The EPSPs were evoked from low threshold muscle afferents and the amplitudes saturated for stimuli less than two times the nerve threshold. The segmental latencies of these EPSPs, measured from the initial positive peak of the triphasic cord dorsum potential to the onset of the EPSP, ranged from 1.5 to 3.1 ms. The intraspinal conduction time of afferents was estimated by recording afferent volleys in the grey matter along the vertical course of intraspinal afferent fibres. The synaptic delay was estimated by subtracting the latency of the afferent volley at the deepest region of the dorsal horn from the segmental latency of the EPSP (in the range from 1.6 to 2.1 ms) recorded in the same microelectrode track. The average value was 0.99 ms (range: 0.9–1.1 ms), which was close to the known synaptic delay of cold-blooded animals. Therefore, the EPSPs in this range of segmental latencies were regarded as monosynaptic. Taking account of the intraspinal afferent conduction time (0.8 ms on average) and another synaptic delay, the latency for disynaptic transmission would be 2.8 ms or more. Thus, EPSPs having segmental latencies of 1.5–3.1 ms were suggested to be almost all monosynaptic in nature, at least under the present conditions of deep anaesthesia. On the basis of the above criteria for the monosynaptic nature of EPSPs, the pattern of convergence of monosynaptic excitatory inputs from various muscle afferents was investigated. Monosynaptic EPSPs were induced from the homonymous muscle nerve and the nerve innervating the synergist at the same joint. The heteronymous EPSPs were also found between muscles within each group of the anterodorsal musculature and the posteroventral musculature. No monosynaptic connexions were found between anterodorsal and posteroventral muscles except between the muscles innervated by the peroneal and the tibial nerve.     

Pyramidal excitation in long propriospinal neurones in the cervical segments of the cat

Summary 1. The effect of stimulating the contralateral pyramid has been investigated with intracellular recording from 128 long propriospinal neurones (long PNs) in the C3-Th1 segments of the cat. Long PNs were identified by the antidromic activation from the Th13 segment. They were located in laminae VII–VIII of Rexed. Single pyramidal stimulation evoked monosynaptic EPSPs in 15/40 of the long PNs in cats with intact pyramid. In 15 other long PNs, a train of three to four pyramidal stimuli evoked EPSPs with latencies indicating a minimal disynaptic linkage. The remaining 25% of the long PNs lacked mono- or disynaptic pyramidal EPSPs. In a few cases longer latency excitation was observed. 2. The location of the intercalated neurones which mediate the disynaptic pyramidal EPSPs was investigated by making four different lesions of the corticofugal fibres: 1) at the border of the C5 and C6 segments, 2) at the border of the C2 and C3 segments, 3) at the caudal part of the pyramid; three mm rostral to the decussation and 4) at the level of the trapezoid body. Stimulation of the corticofugal fibres was made either rostral to lesion 3 (rPyr) in order to activate neurones in a cortico-bulbospinal pathway or caudal to lesion 3 (cPyr) to activate neurones in a corticospinal pathway. In the former case, in one experiment, stimulation was made in the pyramid between lesions 3 and 4 (double pyramidal lesion). In case of cPyr stimulation, lesions 1 and 2 were added sequentially in order to investigate if the corticospinal excitation was mediated via C3–C4 PNs. All lesions were made mechanically, except lesion 2 which in some of the experiments was performed by reversible cooling. 3. Stimulation in the pyramid rostral to lesion 3 and in between lesions 3 and 4 evoked disynaptic EPSPs in the long PNs, which shows that they were mediated via reticulospinal neurones. Stimulation in cPyr after lesion 3 elicited disynaptic EPSPs, which remained after lesion 1 but were abolished after adding lesion 2. It is concluded that the disynaptic cPyr EPSPs were mediated via intercalated neurones in the C3–C4 segments. 4. When the disynaptic cPyr EPSP was conditioned with a single volley in nucleus ruber and/or in tectum, it was markedly facilitated, especially when the conditioned volley was applied simultaneously with the effective cPyr volley. The results show that the intercalated neurones in the C3–C4 segments receive monosynaptic convergence from cortico-, rubro- and tectospinal] fibres. Stimulation in the lateral reticular nucleus (LRN) evoked monosynaptic EPSPs. These EPSPs had similar latencies and shapes as those previously recorded in forelimb motoneurones and which have been shown to be due to activation of ascending branches of the C3–C4 PNs. This finding in addition to the striking similarity of the descending input pattern of long PNs as compared to the forelimb motoneurones strongly suggest that short C3–C4 PNs project both to long PNs as well as to forelimb motoneurones. 5. Spatial facilitation of disynaptic EPSPs in long PNs was also observed between rPyr volleys and tectal volleys. The results suggest that common reticulospinal neurones which project to the long PNs receive monosynaptic convergence from corticofugal and tectofugal fibres but in some of the reticulospinal neurones the main input is cortical and in others tectal. Monosynaptic EPSPs were evoked from the medial part of the reticular formation, from 2 mm caudal to 6 mm rostral of the obex level. These EPSPs were presumably due to direct activation of reticulospinal neurones. 6. Convergence of disynaptic excitation mediated by cortico-propriospinal and cortico-reticulospinal routes was observed in about 12% of the long PNs. Convergence of monosynaptic corticospinal and disynaptic corticoreticulospinal and/or cortico-propriospinal input was observed in about 15% of the long PNs. 7. The role of the monosynaptic pyramidal input and disynaptic corticoreticulospinal and cortico-propriospinal (mediated by short C3–C4 PNs) inputs to long PNs is discussed in relation to postural control during movements of head and forelimb.     

Bulbar neurones with axonal projections to the trigeminal motor nucleus in the cat

Summary The location of bulbar neurones with axons projecting to the ipsi- and contralateral trigeminal motor nucleus were investigated in cats anaesthetized with sodium pentobarbital. Wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected in amounts of 5–24 nl. A volume-calibrated microelectrode was used for recording of evoked potentials and pressure injection of WGA-HRP. The injection site was guided by the position where a maximal antidromic response was evoked by electrical stimulation of the masseteric nerve. The survival time was 19–22 h. In preparations with the depot located in the masseteric subnucleus retrogradely stained neurones were found bilaterally in the borderzone of the trigeminal motor nucleus. Dense populations of stained neurones were observed ipsi- and contralaterally in the dorsal division of the main sensory trigeminal nucleus and the subnucleus- of the oral nucleus of the spinal trigeminal tract. Clusters of WGA-HRP-neurones were observed bilaterally in the lateral tegmental field at the level of the subnucleus- of the oral nucleus of the spinal trigeminal tract, bilaterally dorsal to the facial nucleus and contralaterally adjacent to the hypoglossal nucleus. No stained neurones were found in the gigantocellular reticular nucleus. A group of stained neurones was located in the marginal nucleus of brachium conjunctivum and some were found in the raphé nuclei near obex. Cell profiles were of two types: medium-sized neurones with a triangular profile and 30–40 m diameter, and fusiform neurones 10×50–70 m. Convergence of descending cortical and trigeminal afferent inputs on interneurones located in the lateral borderzone of the trigeminal motor nucleus, i.e. the intertrigeminal area, is reported in the preceding paper.List of Abbreviations BCM Marginal nucleus of the brachium conjunctivum - CAE Nucleus caeruleus - CI Inferior central nucleus - Cu Cuneate nucleus - Cux External cuneate nucleus - DMV Dorsal motor nucleus of the vagus - FTG Gigantocellular tegmental field - FTL Lateral tegmental field - FTP Paralemniscal tegmental field - Gr Gracile nucleus - Mb Medial borderzone of NVmt - NintV Intertrigeminal area - NsV Supratrigeminal nucleus (area) - NVmes Mesencephalic trigeminal nucleus - NVmt Trigeminal motor nucleus - NVsnpr Main sensory trigeminal nucleus - NVsnpr-d Main sensory trigeminal nucleus, dorsal division - NVsnpr-v Main sensory trigeminal nucleus, ventral division - NVspc Caudal nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - V Spinal trigeminal tract - NVII Facial nucleus - VII Facial nerve - NXII Hypoglossal nucleus - XII Hypoglossal nerve - Ols Superior olive - Rb Rostral borderzone of NVmt - Vb Ventral borderzone of NVmt - VIN Inferior vestibular nucleus - VSL Superior vestibular nucleus, lateral division     

Segmental reflex inputs to motoneurons innervating dorsal neck musculature in the cat

Summary The responses to Stimulation of upper cervical muscle and cutaneous afferents were studied in motoneurons innervating splenius, complexus, and biventer cervicis dorsal neck muscles of cats. Motoneurons innervating complexus and biventer cervicis fibers, which are in the deeper, longitudinally oriented muscles, were monosynaptically excited by ipsilateral Group I afferents from each of these muscles, but they did not receive significant input from splenius Group I afferents. Likewise, splenius motoneurons were not monosynaptically excited by ipsilateral afferents from complexus and biventer cervicis. Stimulation of ipsilateral cutaneous afferents produced predominant excitation in splenius motoneurons, predominant inhibition in biventer cervicis motoneurons, and inhibition or mixed responses in complexus motoneurons.None of the neck motoneurons studied showed postsynaptic potentials following single or multiple shock stimulation of contralateral muscle nerves at stimulus intensities expected to excite exclusively Group I afferents. Higher intensity stimulation of contralateral muscle afferents, as well as fibers in the greater auricular nerves, produced predominant inhibition in all three neck motoneuron pools.Segmentally-excited afferents to neck motoneurons, like those from supraspinal systems, appear to evoke different patterns of synaptic responses in splenius motoneurons than they do in motoneurons innervating fibers in the deeper, longitudinally oriented complexus and biventer cervicis muscles.     

Binocular interaction in the dorsal lateral geniculate nucleus of the cat

Summary We have investigated binocular interaction in the dorsal lateral geniculate nucleus (LGN) of the cat. Neurons were recorded extracellularly during visual stimulation with sinusoidal gratings which were presented at different interocular phases (disparities). The large majority of cells (91%) exhibited some type of binocular interaction. For 75% and 16% of the total number of cells, the binocular interaction was inhibitory or facilitatory, respectively. For the remaining 9% of cells, no interaction was evident. In marked distinction from visual cortex, the facilitatory and inhibitory interactions in the LGN are independent of the relative interocular phase of the patterns. Neurons in the LGN are therefore insensitive to the stereoscopic depth cue, retinal disparity.