Electrical activity of red nucleus neurones investigated with intracellular microelectrodes

Summary Microelectrodes were inserted into the magnocellular portion of cat's red nucleus (RN), and some basic physiological properties of RN cells were examined by both extra- and intracellular recording. During stimulation of the rubrospinal fibres at the spinal segmental level, the RN cells were invaded antidromically, producing conspicuous field potentials within RN. The somatotopical distribution of RN cells was confirmed by comparing the field potentials induced from C₂ and L₁ levels. When recorded intracellularly, antidromic action potentials showed three-step configuration as those in motoneurones and were followed by a remarkable after-hyperpolarization. The conduction velocity along the rubrospinal fibres ranged from 41–123 m/sec, with the peak frequency at 91–100 m/sec. The membrane properties were examined in some RN cells by intracellular application of current steps. The total membrane resistance was 4 M on the average, and the membrane time constant 6 msec, respectively.Excitatory postsynaptic potentials (EPSPs) were induced monosynaptically in RN cells by stimulation of the nucleus interpositus of the contralateral cerebellum. Their time course was analyzed in comparison with that of the potentials produced by current steps. Stimulation in the ventrolateral nucleus of the thalamus evoked monosynaptic EPSPs via the collaterals of the interpositus axons which innervate RN and thalamus commonly. It was further shown that impulses in cortico-rubral fibres produced EPSPs in RN cells. These cerebral-evoked EPSPs were characterized by much slower time courses than those from the nucleus interpositus.     

Calcium-dependent potentials in mammalian red nucleus neurons in vitro

Intracellular recordings were made from red nucleus (RN) neurons in guinea-pig slice preparations. The slow afterhyperpolarization (AHP) following an action potential was reversibly abolished by Co2+ or Mn2+. Its amplitude was dependent on the extracellular K+ concentration. When tetraethylammonium was added to the perfusing solution, a tetrodotoxin-resistant regenerative depolarization was evoked which was blocked by Co2+ or Mn2+. There results suggest that the slow AHP is produced by an increase in Ca2+-dependent K+ conductance and that RN neurons have a voltage-dependent Ca2+ conductance.     

Effects of amino acids on cat red nucleus neurons in vitro

Summary Intracellular records were obtained from neurons in the region of the red nucleus (RN) of cat brain slices. Both EPSPs and IPSPs were recorded in response to local electrical stimulation and these resembled similar electrophysiological responses observed in experiments conducted in vivo. Monosynaptic and polysynaptic IPSPs were observed, suggesting the existence of inhibitory interneurons near or within the RN region.When added to the bathing solution, L-glutamate and L-aspartate depolarized RN neurons with a decrease in input resistance. -Aminobutyric acid (GABA) and glycine hyperpolarized the cells with a decrease in input resistance. GABA also elicited a depolarizing response. These amino acid actions had direct postsynaptic effects, since the experiments were conducted in a low Ca²⁺/high Mg²⁺ medium which blocked synaptic transmission.     

GABA neurons in the cat red nucleus: a biochemical and immunohistochemical demonstration

Following unilateral kainic acid lesioning of neuronal cell bodies in the cat red nucleus (RN), a large decrease in glutamic acid decarboxylase (GAD) activity was detected in the injected RN, compared to the RN from control, non-injected animals. Using GAD immunohistochemistry, reactive perikarya were visualized dorsolaterally to the rostral part of the nucleus as well as within the RN proper. Taken together, these results point to the existence of an intrinsic GABAergic innervation in the RN area of the cat. The GABAergic neurons characterized here might thus correspond to the inhibitory interneurons previously detected electrophysiologically as a putative source of GABA for large-sized neurons of the RN.     

Light labeling of red nucleus neurons following an injection of peroxidase-conjugated wheat germ agglutinin into the inferior olivary nucleus of the rat

Since the rubro-olivary projection has not been demonstrated in the rat, unlike the monkey and cat (refs. in text). HRP or highly-concentrated wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the inferior olivary nucleus using a ventral approach. After processing with a modified technique, sections were examined under high power. Three rats injected with WGA-HRP showed labelling in the red nucleus. In one of those rats with a well-confined injection, 583 neurons contained grains of HRP reaction product consistent with light retrograde labeling. This observation lends support to the existence of a rubro-olivary projection in the rat.     

Sensitivity of rubrospinal neurons to excitatory amino acids in the rat red nucleus in vivo.

Responses of rubrospinal neurons (RSNs) to iontophoretic applications of L-glutamate (L-Glu), L-aspartate (L-Asp), quisqualate (Quis) and N-methyl-D-aspartate (NMDA) have been studied in the rat red nucleus (RN) in vivo. All agonists produced a dose-dependent increase of the firing rate and Quis was found to be the most efficient. The responses to NMDA and to a lesser extent to L-Asp were abolished by steady application of 2-amino-5-phosphonovalerate (2APV) whereas responses to Quis were unaffected and those to L-Glu poorly antagonized. On the other hand, NMDA-mediated excitations were insensitive to steady application of 6,7-dinitroquinoxaline-2,3-dione (DNQX) which abolished responses to Quis and to a lesser extent to L-Glu while those to L-Asp were less affected. These results show the presence of both NMDA and non-NMDA receptors on RSNs in the rat. A specific localization of the NMDA receptors on distal dendrites of these neurons is suggested.     

The red nucleus of the monkey

Summary The topographic organization of somatosensory input to the primate red nucleus was investigated by studying receptive fields of rubral neurons, and that of the motor output by delivering trains of microstimulating pulses to evoke movements. A receptive field was identified in 191 of 208 rubral neurons. Most neurons (172) responded to passive movement of one or two joints including digits but some (26) had a cutaneous input. Neurons in both the parvocellular (RN_pc) and magnocellular (RN_mc) divisions of the nucleus had receptive fields. Neurons which responded to stimulation of the forelimb were located in the dorsomedial part of the nucleus. Those responsive to stimulation of the hindlimb were in the ventrolateral part. Thin regions on the dorsal and ventrolateral borders of the nuclei, respectively, contained neurons responsive to face and tail stimulation. Within the regions representing each limb, neurons receiving an input from the extremity (hand or foot) formed a core surrounded by neurons with an input from more proximal segments. This core extended uninterrupted throughout the RN_pc and RN_mc.Movements of individual limb segments including digits were readily evoked by microstimulating in the RN_mc with thresholds as low as 3 A. In most cases, movements were evoked in the direction opposite to the passive movement which drove the neurons at the stimulating site, although fibers of passage limited the analysis of the sensory input-motor output organization with stimulation. We conclude that there is topographic localization of somatosensory input and motor output in the macaque red nucleus. Furthermore, the red nucleus of monkeys contributes to the control of independent movements of limb segments including digits, although the number of axons it sends to the spinal cord is less than 1% of the number of corticospinal axons.     

Synaptic responses of neurons in the parietal associative cortex of the cat to stimulation of the red nucleus

Acute experiments on anesthetized and immobilized cats using intracellular recording were used to study the responses of neurons in the parietal associative cortex to stimulation of the red nucleus. Efferent neurons of the parietal cortex were identified by antidromal activation on stimulation of the intrinsic nuclei of the pons and motor cortex. Oligo- and polysynaptic EPSP in response to stimulation of the red nucleus were seen. The results are discussed in the light of the morphological organization of the rubrothalamic and cerebellothalamocortical tracts. Laboratory for Central Nervous System Physiology (Director V. V. Fanardzhyan), L. A. Orbel' Institute of Physiology, Armenian National Academy of Sciences, Erevan. Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 81, No. 12, pp. 64–69, December, 1995.     

Discharge of primate magnocellular red nucleus neurons during reaching to grasp in different spatial locations

Reaching to grasp is of fundamental importance to primate motor behavior. One descending motor pathway that contributes to the control of this behavior is the rubrospinal tract. An important source of origin of the rubrospinal tract is the magnocellular red nucleus (RNm). Forelimb RNm neurons discharge vigorously during reach-to-grasp movements. RNm discharge is important for hand use, as coordinated whole-limb movements without hand use are not associated with strong discharge. Because RNm is functionally linked to muscles of the entire forelimb, RNm discharge may also contribute to use of the proximal limb that accompanies hand use. If RNm contributes to proximal limb use, we predict discharge to differ for reaches that differ in proximal limb involvement but require the same grasp. We tested this prediction by measuring discharge of individual RNm neurons while monkeys reached to grasp objects in four spatial locations in front of them. The animals reached from the waist to locations to the left, right, above, and below the shoulder of the "reaching" limb. RNm neurons of our sample were activated strongly during reach-to-grasp, and discharge of a third of the neurons tested depended on the spatial location of the object grasped. Discharge of RNm neurons and EMG activity of many of the distal and proximal forelimb muscles we tested were larger for reaching to grasp in the upper and/or right than lower and left target locations. Based on comparisons of each individual neuron's discharge patterns during reaches with and without preshaping the hand, we conclude that target location-dependent modulations in discharge rate of the majority of RNm neurons whose discharge differed for reaching to grasp in the four target locations contributed to aspects of hand preshaping that covaried with reach direction.