Direct inhibitory synaptic linkage of pontomedullary reticular burst neurons with abducens motoneurons in the cat

156

SUMMARY1. A hypothesis has been verified that laminae V-VI interneurones which mediate non-reciprocal inhibition of motoneurones from group I muscle afferents have collateral actions on other laminae V-VI interneurones. Stimulation within the areas of projection of these inhibitory interneurones in motor nuclei and in Clarke's column would be expected to give rise to monosynaptic i.p.s.p.s in interneurones with disynaptic i.p.s.p.s from group I afferents if the hypothesis were correct.2. Intracellular records were made from eighty-five laminae V-VI interneurones with input from group I a muscle spindle and/or group I b tendon organ afferents. Weak intraspinal stimuli applied in motor nuclei in L7 and S1 segments, or in the lateral funiculus just caudal to Clarke's column in L4, were found to evoke monosynaptic i.p.s.p.s in seventy-two interneurones. These i.p.s.p.s were systematically correlated with disynaptic inhibition from group I a or Ib afferents but not from other fibres.3. Such monosynaptic i.p.s.p.s evoked by intraspinal stimuli were seen in forty-two interneurones which themselves projected to the level of Clarke's column and therefore (on the basis of previous evidence) should mediate inhibition of motoneurones. For seven of these interneurones it was also shown directly that they projected to motor nuclei. The inhibition of such interneurones demonstrates mutual interactions between those interneurones which are interposed in inhibitory pathways from group I afferents. Only indirect indications have been obtained for inhibition of interneurones in the excitatory pathways.

Section: B)mentioning

confidence: 99%

Inhibitory interactions between interneurones in reflex pathways from group Ia and group Ib afferents in the cat.

Brink¹,

Jankowska²,

McCrea³

et al. 1983

156

“…in the set of brainstem neurones projecting monosynaptically on ocular motoneurones. The main afferent inputs to ABD neurones are organized in reciprocal excitatory and inhibitory synaptic connections (Escudero & Delgado-Garcia, 1988) arising from (i) the ipsilateral excitatory (Kaneko, Evinger & Fuchs, 1981;Strassman, Highstein & McCrea, 1986a) and the contralateral inhibitory burst neurones (Hikosaka, Igusa, Nakao & Shimazu, 1978b;Yoshida, McCrea, Berthoz & Vidal, 1982;Strassman, Highstein & McCrea, 1986b), located in the pontomedullary reticular formation; (ii) the contralateral excitatory and ipsilateral inhibitory medial vestibular neurones (Baker, Mano & Shimazu, 1969;Hikosaka, Nagao & Shimazu, 1980;McCrea, Yoshida, Berthoz & 540 VESTIBULAR AND PREPOSITUS AFFERENTS TO ABDUCENS 541 Baker, 1980;Berthoz, Droulez, Vidal & Yoshida, 1989); and (iii) the ipsilateral excitatory and contralateral inhibitory prepositus hypoglossi (PH) neurones (Escudero & Delgado-Garcia, 1988;Spencer, Wenthold & Baker, 1989).…”

Section: Introductionmentioning

confidence: 99%

A physiological study of vestibular and prepositus hypoglossi neurones projecting to the abducens nucleus in the alert cat.

Escudero

Cruz

Delgado-García

1992

173

112

SUMMARY1. Vestibular and prepositus hypoglossi (PH) neurones projecting to the abducens (ABD) nucleus were recorded in the alert cat. Their discharge characteristics were analysed to ascertain the origin of the horizontal eye position signal present in ABD neurones.2. Neurones were classified according to: their location with respect to the ABD nucleus; their antidromic activation from the ABD nucleus; the synaptic field potential they induced in the ABD nucleus with the spike-triggered averaging technique; and their activity during spontaneous and vestibularly induced eye movements.3. Vestibular neurones projecting to the ABD nucleus were located in the rostral medial vestibular nucleus. They were excitatory on the contralateral and inhibitory on the ipsilateral ABD neurones. Both types of premotor vestibular neurone showed a firing rate weakly related to eye position, increasing for eye fixations in the contralateral on-direction, and decreasing with ipsilateral fixation. Position sensitivity during eye fixations was (means + S.D.) 1-8 +09 spikes s-' deg-' for excitatory neurones and 2-2 + 1-3 spikes s-I deg-' for inhibitory neurones. Firing rate exhibited a high variability during eye fixations. Their responses during saccades in the off-direction were characterized by a pause that, although less defined, was occasionally present during saccades in the on-direction. Eye velocity sensitivity during spontaneous saccades in the on-direction was 0 17 +0.15 spikes s8-deg-' s-' for excitatory neurones and 0.15 + 0-07 spikes s-' deg-' s-' for inhibitory vestibular neurones. During sinusoidal head stimulation at 0-2 Hz, vestibular neurones showed a type I discharge rate with a phase lead over eye position of 86-0 + 14-1 deg for excitatory and 80-2 + 12-5 deg for inhibitory neurones. Position sensitivity during vestibular stimulation did not differ significantly from values obtained for spontaneous eye movements. However, the velocity sensitivity of premotor vestibular neurones during head rotation was significantly higher (I1 6 + 0-2 spikes s-1 deg-' s-' for excitatory and 1-5 + 0-3 spikes s-I deg-1 s-' for inhibitory neurones) than during spontaneous eye movements.4. PH neurones projecting to the ABD nucleus were located in the rostral one- MS 1118M. ESCUJDERO AND OTHERS third of the nucleus. These neurones were excitatory on the ipsilateral and inhibitory on the contralateral ABD nucleus. Their firing rates were correlated mainly with eye position, increasing for abducting eye positions of the ipsilateral eye and decreasing with adduction movements. Eye position sensitivities were 8 2 + 2-9 and 7-9 + 2-9 spikes s-' deg-' for excitatory and inhibitory neurones, respectively. Variability of the firing rate during eye fixations was lower than that shown by premotor vestibular neurones. During saccades, premotor PH neurones showed low eye velocity sensitivity (0 15 + 021 for the excitatory and 0 32 + 028 spikes s-' deg-' s-' for the inhibitory group) with low coefficients of correlation. During vestibular sinusoidal st...

“…Brink, Harrison, Jankowska, McCrea & Skoog, 1983) or along primary afferents (Solodkin, Jimenez & Rudomin, 1984), and recording of discharges of motoneurones, or muscles which they innervate (see e.g. Hikosaka, Igusa, Nakao & Shimazu, 1978;Fetz & Cheney, 1980). We have chosen the technique of Brink et al (1983) which was easiest to apply under our experimental conditions and is most suitable for screening the actions, if any, of single interneurones on a population of motoneurones.…”

Section: Introductionmentioning

confidence: 99%

Post‐synaptic actions of midlumbar interneurones on motoneurones of hind‐limb muscles in the cat.

Cavallari

Edgley

Jankowska

1987

139

102

SUMMARY1. The hypothesis that interneurones in the 4th lumbar segment (L4) are interposed between group I and group II afferents and hind-limb motoneurones has been tested. Action potentials of single interneurones were induced by ionophoretically applied homocysteate and recorded in parallel with post-synaptic potentials in motoneurones; the latter were recorded from motor axons in the ventral root of the first sacral segment as population potentials, using the sucrose gap technique.2. The action potentials of twenty-four L4 interneurones were found to be followed by either e.p.s.p.s. or i.p.s.p.s in motoneurones. The latencies of the majority of these p.s.p.s were consistent with monosynaptically evoked excitation or inhibition of motoneurones since they exceeded the latencies of antidromic activation of the interneurones from the S1 motor nuclei by only a fraction of a millisecond.3. The dominant input to both the excitatory and the inhibitory interneurones was from group II muscle afferents, in particular from the quadriceps nerve. The latencies of excitation of the interneurones by these afferents indicated a monosynaptic coupling between them. The same interneurones were co-excited by group I and cutaneous afferents and by descending fibres.4. We conclude that not only excitation but also inhibition of hind-limb motoneurones from group II afferents may be mediated disynaptically and that interneurones in the 4th lumbar segment contribute to both.