Accumulation of 3H-glycine in interneurons of the cat spinal cord

Summary After in vivo njections of ³H-glycine into the cat spinal cord autoradiography at the light and electron microscopic level revealed high concentrations of radioactivity over certain nerve endings, often containing flat vesicles, over glial cells and over neuronal cell bodies probably representing spinal interneurons. Motoneurons, on the other hand, showed only a low activity.     

Viscerosomatic somatic convergence at lumbar interneurons in the dorsal horn of the cat and rat spinal cord

In experiments on spinal cats, when branches of the pelvic nerve innervating the rectum were electrically stimulated at the same time as the peroneal nerve it was found that 12 out of 20 neurons, to which the effects of both these supplies converged, were activated by both A- and C-fibers. Responses to stimulation of the pelvic nerve were apparently mediated via fibers with a conduction velocity not less than 2.2 m·s^–1. In studies in spinal rats it was shown that distension of the more distal regions of the large intestine could excite neurons in laminae IV–V, and inhibit neurons in deeper laminae. In seven out of 18 cases the inhibition evoked by visceral stimulation was due to a direct effect on the postsynaptic membrane of these cells, and in 11 cases it was localized to presynaptic structures. Naloxone, strychnine, and atropine did not block this inhibition, thus providing evidence against the possible participation of opioids, glycine, and acetylcholine in its generation. Phaclofen, a GABA_B-receptor antagonist, was also without effect, but bicuculline suppressed this inhibition in three out of 12 cases, indicating that GABA_A-receptors are involved.I. M. Sechenov Medical Academy, Russian Ministry of Public Health, Moscow. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 3–11, January–February, 1992.     

Cortico- and rubrofugal activation of interneurons forming the propriospinal pathways of the dorsolateral funiculus of the cat spinal cord

Interneurons of the lumbar division of the cat spinal cord responding after a short latent period with intensive excitation to stimulation of the medullary pyramids and red nucleus but not responding (or excited after a long latent period) to stimulation of peripheral nerves were investigated by microelectrode recording. Most of these neurons, located in the lateral zones of Rexed's laminae IV–VII of the gray matter, were identified as propriospinal cells sending axons into the dorsolateral funiculus of the white matter (mean velocity of antidromic conduction in the group 34.6 m/sec). Marked convergence of corticofugal and rubrofugal excitatory influences was found on the overwhelming majority of neurons. Some neurons were activated monosynaptically by fast-conducting fibers of both descending systems. The minimal and mean values of the latent periods of the pyramidal EPSPs for the neurons tested were 4.5 and 6.28 msec, and for the rubral EPSPs 3.3 and 4.94 msec respectively. A distinguishing feature of the activation of these neurons is the intensive potentiation of their synaptic action on the arrival of a series of corticofugal and rubrofugal waves.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 489–500, September–October, 1972.     

Synaptic organization of supraspinal control over propriospinal ventral horn interneurons in cat and monkey spinal cord

Synaptic responses evoked in propriospinal neurons of the upper lumbar segments (L₃–L₄) by reticulo-, vestibulo-, and corticospinal impulses were studied in experiments on cats and monkeys. Propriospinal cells, identified by antidromic stimulation, were stained with Procion red, so that they could be localized in the different zones of the ventral horn. Monosynaptic reticular and vestibular excitatory influences were discovered in cats; convergence of these influences on the same neurons was demonstrated. In monkeys bulbospinal monosynaptic effects were supplemented by monosynaptic influences arriving from the motor cortex; convergence of monosynaptic excitatory influences from all supraspinal sources studied was found on some propriospinal neurons. The propriospinal neurons studied also had synaptic inputs from primary afferents.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 177–184, March–April, 1977.     

Repetitive firing of Renshaw spinal interneurons

A model of the Renshaw spinal interneuron has been developed. The model consists of a nonhomogeneous cylinder divided into three compartments: dendrites, soma and axon initial segment (I.S). The soma and dendrites are represented as a cylindrical cable by the method of Rall (1962); anatomical data of Jankowska and Lindström (1971) from fluorescent dye injections were used to construct the cable. The soma and I.S. membranes are assumed to have Hodgkin-Huxley-like membrane activity. In comparison with our previous model of a tonic motorneuron (Traub, 1977), the Renshaw cell has a faster membrane time constant, faster Hodgkin-Huxley rate functions, _h and _h shifted to the right on the voltage axis, and no slow potassium conductance. With appropriate input conductances, the Renshaw cell model exhibits the following features: it develops very high frequency bursts (over 1000 impulses per s) which trail off over a period of 10–20 ms; the second spike has small amplitude and successive spikes develop progressively larger amplitudes. Comparisons are drawn with the experimental observations of Eccles et al. (1961) and Willis and Willis (`966). With this model, it is feasible to compute the steady firing rate for a large number of steady synaptic excitatory and inhibitory conductances by direct integration of the differential equations.     

The effect of SHF waves on the evoked potentials in the cat spinal cord

In experiments with adult cats there revealed a pronounced effect of SHF radiation on the electrogenesis of spinal cord, the beam density being 15 mW/cm2 and time of exposure 10 min. The estimates of the induced somatosensory brain potentials indicate that there is a phase of a 20 per cent response inhibition with the effect reaching maximum 2-3 h following irradiation. Subsequently, potential characteristics are exponentially restored to be the same with the control values. The evidence is presented that the synaptic neuron contacts within the reflex arc are highly susceptible to SHF radiation.     

Neuropeptides in interneurons of the insect brain

A large number of neuropeptides has been identified in the brain of insects. At least 35 neuropeptide precursor genes have been characterized in Drosophila melanogaster, some of which encode multiple peptides. Additional neuropeptides have been found in other insect species. With a few notable exceptions, most of the neuropeptides have been demonstrated in brain interneurons of various types. The products of each neuropeptide precursor seem to be co-expressed, and each precursor displays a unique neuronal distribution pattern. Commonly, each type of neuropeptide is localized to a relatively small number of neurons. We describe the distribution of neuropeptides in brain interneurons of a few well-studied insect species. Emphasis has been placed upon interneurons innervating specific brain areas, such as the optic lobes, accessory medulla, antennal lobes, central body, and mushroom bodies. The functional roles of some neuropeptides and their receptors have been investigated in D. melanogaster by molecular genetics techniques. In addition, behavioral and electrophysiological assays have addressed neuropeptide functions in the cockroach Leucophaea maderae. Thus, the involvement of brain neuropeptides in circadian clock function, olfactory processing, various aspects of feeding behavior, and learning and memory are highlighted in this review. Studies so far indicate that neuropeptides can play a multitude of functional roles in the brain and that even single neuropeptides are likely to be multifunctional.The original research in the authors’ laboratories was supported by DFG grants HO 950/14 and 950/16 (U.H.) and Swedish Research Council grant VR 621-2004-3715 (D.R.N).     

The inhibitory effect of xanthine derivatives on alkaline phosphatase in the rat brain

Summary Histochemical and biochemical studies were carried out on the inhibition of alkaline phosphatase (Al-P) activity in rat cerebral cortex with various methylxanthine derivatives.The histochemical study revealed that Al-P activity was completely inhibited with 2 mM theophylline or aminophylline, only slightly inhibited with 5 mM of xanthine, and no way inhibited even with 5 mM of diprophylline or caffeine.The biochemical study showed that Al-P activity was markedly inhibited by 1 mM theophylline, to 36% of the control value, and equally markedly by 1 mM aminophylline to 26% of the control value. It was only inhibited to 99% of the control value even by 5 mM diprophylline and conversely slightly activated, to 110% of the control value, by caffeine.The relationship between the pharmacological activities of methylxanthine derivatives and Al-P was studied, and the biological role of Al-P in the central nervous system was also discussed.     

Functions of mammalian spinal interneurons during movement

The major recent advances in understanding the role of spinal neurons in generating movement include new information about the modulation of classic reflex pathways during fictive locomotion and in response to pharmacological probes. The possibility of understanding movements in terms of spinal representations of a basic set of movement primitives has been extended by the analysis of normal reflexes. Recordings of the activity of cervical interneurons in behaving monkeys has elucidated their contribution to generating voluntary movement and revealed their involvement in movement preparation.     

The effect of GABA on lumbar terminations of rubrospinal neurons in the cat spinal cord

Although GABA and piperidine-4-sulphonic acid depolarize I a afferent terminations in the cat spinal cord by activation of bicuculline-sensitive GABA receptors, no evidence was obtained for a bicuculline-sensitive alteration by either gabamimetic of the electrical threshold of rubrospinal terminations in the spinal intermediate nucleus. The terminal axonal arborizations in the spinal cord of neurons in the red nucleus thus do not have GABA receptors similar to those on the cell bodies. The results are discussed in relation to the depolarizing action of GABA on some central neurons, and on neurons with peripheral cell bodies, and to probable differences in the intracellular chloride content of neurons having peripheral or central cell bodies, and thus of different embryological origin. A presynaptic depolarizing inhibitory process mediated by GABA appears to be confined to the terminals of primary afferent fibres in the mammalian central nervous system.     

The absence of an effect of L-tryptophan on the C-fiber reflex in the chronic spinal cat

L-tryptophan (150 mg/kg) had no effect on the C-fiber reflex in the acute decerebrate chronic spinal cat. L-tryptophan had been previously shown to facilitate this reflex in the acute decerebrate acute spinal cat. This finding supports the hypothesis that tryptaminergic neurons in the brain have axons which descend the spinal cord to produce modulation of some spinal reflexes.     

The synchronization properties of a network of inhibitory interneurons depend on the biophysical model

The synchronization properties of a pair of coupled fast spiking interneurons are studied by using the theory of weakly coupled oscillators. Four different biophysical models of the single fast spiking interneuron are used and the corresponding results are compared. It is shown that for a pair of identical coupled cells, the synchronization properties are model-dependent. In particular, the firing coherence of the network is strongly affected by the reversal potential, the kinetics of the inhibitory postsynaptic current and the electrical coupling; the activation properties of the sodium and potassium currents play a significant role too.     

The inhibitory effect of xanthine derivatives on alkaline phosphatase in the rat brain.

Histochemical and biochemical studies were carried out on the inhibition of alkaline phosphatase (A1-P) activity in rat cerebral cortex with various methylxanthine derivatives. The histochemical study revealed that A1-P activity was completely inhibited with 2 mM theophylline or aminophylline, only slightly inhibited with 5 mM of xanthine, and no way inhibited even with 5 mM of diprophylline or caffeine. The biochemical study showed that A1-P activity was markedly inhibited by 1 mM theophylline, to 36% of the control value, and equally markedly by 1 mM aminophylline to 26% of the control value. It was only inhibited to 99% of the control value even by 5 mM diprophylline and conversely slightly activated, to 110% of the control value, by caffeine. The relationship between the pharmacological activities of methylxanthine derivatives and A1-P was studied, and the biological role of A1-P in the central nervous system was also discussed.     

Control of dendritic outputs of inhibitory interneurons in the lateral geniculate nucleus

The thalamic relay to neocortex is dynamically gated. The inhibitory interneuron, which we have studied in the lateral geniculate nucleus, is important to this process. In addition to axonal outputs, these cells have dendritic terminals that are both presynaptic and postsynaptic. Even with action potentials blocked, activation of ionotropic and metabotropic glutamate receptors on these terminals increases their output, whereas activation of metabotropic (M2 muscarinic) but not nicotinic cholinergic receptors decreases their output. These actions can strongly affect retinogeniculate transmission.