Effect of noradrenalin and serotonin on synaptic transmission in the rat spinal cord

Experiments on superfused isolated spinal cord preparations from rats aged 8–13 days showed that noradrenal in and serotonin have only a weak effect on monosynaptic reflex discharges but a substantial effect on polysynaptic motoneuronal discharges: noradrenalin potentiates whereas serotonin inhibits them. Both amines inhibit dorsal root potentials evoked by stimulation of high-threshold afferents. Potentiation of polysynaptic motoneuronal discharges induced by noradrenalin is connected with hyperpolarization of high-threshold afferents due to inhibition of the function of neurons in the substantia gelatinosa, and with increased excitability of interneurons participating in the generation of motoneuronal discharges. Serotonin inhibits polysynaptic motoneuronal discharges through its direct depolarizing effect on terminals of high-threshold afferents and depression of interneuron activity responsible for these discharges. Adrenergic and serotonin receptors, mediating these effects of noradrenalin and serotonin, were subjected to pharmacologic analysis.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 241–247, May–June, 1982.     

Electrophysiological and chemoreceptive characteristics of pontomedullary and thalamic neurons during ontogenetic development

Spontaneous and evoked activity of reticular neurons in the medulla, pons, and ventrobasal complex of the thalamus was studied in 54–65-day cat fetuses and kittens aged 1–60 days. Responses to microionophoretic application of noradrenalin, acetylcholine, and glutamate were studied. In the fetuses 63% of pontine cells and 92% of medullary cells were spontaneously active. The largest number of evoked responses (60% in the fetuses) was observed to stimulation of the tongue. Repetition of the stimulation facilitated discharges in the intertrial interval, and this effect was particularly marked in the early stages. Sensitivity to noradrenalin and glutamate in the fetuses was maximal (87 and 70%, respectively), and to acetylcholine minimal (43%). With increasing age, the number of neurons sensitive to noradrenalin decreased, the number sensitive to acetylcholine increased, and the number sensitive to glutamate remained unchanged. It is concluded that synaptic processes in the early stages are effected mainly through adrenergic and glutamate transmission.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 43–53, January–February, 1979.     

Convergence of corticofugal impulses on pontine neurons

Convergence of corticofugal impulses in reticular and intrinsic pontine nuclei during stimulation of the frontobasal cortex (proreal, posterior orbital, and basal temporal regions) and also of the dorsal hippocampus was studied in acute experiments on cats anesthesized with a mixture of pentobarbital and chloralose. Three foci of convergence of corticofugal impulses were found in these structures: one in the reticular formation and two in the intrinsic nuclei—in their medial and lateral portions. Neurons with an excitatory type of response were shown to predominate in the reticular formation and neurons with an inhibitory or mixed type of response of neurons activated antidromically by stimulation of one brain region and synaptically during stimulation of another, that the pontine nuclei play an integrative role in the functional unification of structures of the frontobasal zones of the neocortex and hippocampus.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 472–480, September–October, 1980.     

Role of the reticular formation in motor control. Study of some intrareticular mechanisms and functional properties of the reticulospinal system

Participation of the reticular formation and descending reticulospinal system in the motor control functions of the spinal cord is examined. The data indicate that the reticular formation may participate in the regulation of specific motor actions. This is shown by the results of experiments to analyze the properties of membranes of reticulospinal neurons and the principles of organization of cortico-reticular monosynaptic relays, and to the investigation of characteristics of responses of "ensembles" of reticular neurons in cats, and also by data obtained in a study of correlation of unit activity in the reticular formation with movements elaborated in rats. The functional role of differential characteristics of the reticular formation is discussed and prospects for future research into reticular membranous, neurochemical, and neuronal mechanisms as a step toward the understanding of reticular control of motor functions are described.Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 16, No. 5, pp. 637–651, September–October, 1984.     

Activation of bulbar reticular neurons by visceral afferents

Transmission of impulsation from the visceral nerves to the bulbar reticular formation in the cat is effected by two systems of conductive pathways. The first (fast-conducting) is formed by the spinoreticular pathways of the lateral funiculi. This system activates reticular neurons with a latent period of 8–10 msec. The second system is made up of the polysynaptic pathways of the ventrolateral and ventral funiculi. Activation of reticular neurons through this pathway requires 10–20 msec or longer. Transection of the dorsal funiculi and the dorsal portion of the lateral funiculi causes no material changes in the synaptic activation of reticular neurons by visceral nerves.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 177–185, September–October, 1969.     

Effects of bulbar stimulation on smooth muscle tone in the feline airway

Changes induced in tracheal smooth muscle tone by bulbar electrical stimulation were investigated in 30 cats anesthetized with a chloralose-urethane mixture and paralyzed with succinyl choline bromide. Raised tonus was mainly observed during stimulation of the caudal section of the dorsal motor nucleus of the vagus nerve, the vicinity of the nucleus ambiguus, and the adjoining reticular formation structures. Attenuation, however, was produced by stimulating bulbar reticular formation nuclei at a level 1 mm caudal and 6 mm rostral to the obex. Raised tonus is thought to be connected with activation of efferent neurons belonging to the motor nucleus of the vagal nerve, as well as axons of nucleus ambiguus neurons in transit through the medial zone, whilst attenuation is connected with excitation of sympathotonic reticular neurons, inhibitory neurons activated by pulmonary stretch receptors, and possibly with vagal efferent neurons activating the non-adrenergic inhibitory nervous system of the bronchi.Medical Institute, Latvian Ministry of Health, Riga. Cardiology Research Institute. Latvian Ministry of Health, Riga. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 320–326, May–June, 1989.     

Involvement of mesencephalic reticular formation neurons in cat conditioned reflexes

Traditional defensive and operant food reflexes were used to investigate neuronal responses of the mesencephalic reticular formation. It was found that these neurons may be divided into different groups according to function, depending on how they respond to positive conditioning stimuli. Of the two main groups of neurons with sustained tonic reactions one is activated in response to positive acoustic conditioning stimulation; it no longer reacts to the same stimulus after extinction of the reflex, while the other only becomes involved in response to positive stimulation accompanying the initiation of movement. Neurons belonging to the second group begin to respond directly to acoustic stimulation after extinction of the conditioned reflex. Neurons of the mesencephalic reticular formation can thus exercise additional tonic ascending effects both in the production and inner inhibition of the conditioned reflex. The group of neurons with a phasic reaction, i.e., a double response (a direct response to sound and another produced by movement) displayed a drop in spontaneous activity during the shaping of inhibition of differentiation and of extinction in particular. It was found that the initial changes in the spike response of reticular formation neurons during conditioning and pseudo-conditioning are similar. There are thus grounds for stating that neurons of the mesencephalic reticular formation participate in the shaping, production, and inner inhibition of traditional and operant conditioned reflexes in a differentiated capacity rather than as a population reacting identically.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 161–171, March–April, 1986.     

Effect of pentobarbital on unit activity of reticular and ventrolateral thalamic nuclei in cats

Responses of single units in the reticular and ventrolateral thalamic nuclei were studied in acute experiments on curarized cats before and after intravenous injection of small doses (0.5–15 mg/kg) of pentobarbital, with simultaneous derivation of activity by two electrodes. After injection of pentobarbital, unit activity in the reticular nucleus consisted of high-frequency grouped (52.5% of 40 neurons) or continuous (30%) discharges as long as barbiturate spindles were present in the electrocorticogram. Activity of only four neurons (10%) of this nucleus was inhibited during the presence of spindles. In all other neurons of the reticular nucleus (7.5%) the character of discharges was unchanged after injection of pentobarbital. The appearance of grouped discharges, repeated several times (66.5% of 40 neurons), or blocking of activity (30%) throughout the period of spindle recording was observed in neurons of the ventrolateral nucleus. The remaining neurons of that nucleus (3.5%) did not respond to intravenous pentobarbital. The appearance of high-frequency discharges in neurons of the reticular nucleus while spindles were recorded coincided with a period of silence in neurons of the ventrolateral nucleus (58.5% of 34 pairs of neurons). High-frequency electrical stimulation of the mesencephalic reticular formation led to asynchronous activation of neurons of the ventrolateral nucleus (82%) and inhibition of unit activity in the reticular nucleus (88%).I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 517–524, September–October, 1982.     

Relative numbers of neurons with different mediator mechanisms in motor nuclei of the cat cervical spinal cord

Motor nuclei of the cat cervical spinal cord are formed by groups of neurons differing in their mediator metabolism. From 40 to 65% are true motor (cholinergic) neurons. The localization of the precipitate of the reaction for acetylcholinesterase in the perinuclear space, on the membranes of the granular reticulum, axolemma, neurofilaments, and neurotubules of the axons, and in the synaptosomes and synaptic space are evidence of the possible perinuclear synthesis of the enzyme and of its transport with the flow of axoplasm. Comparison with the autoradiographic detection of glycine showed that large motor neurons form groups with small short-axon glycine-containing neurons, which make contact with them. The motor neurons have polyreceptive properties, for endings containing cholinesterase, glycine, noradrenalin, and serotonin, as well as unidentified endings are present on their soma and processes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 191–197, March–April, 1977.     

Comparative analysis of the role of the second and first somatosensory cortical areas in somatic responses of the medullary reticular formation in rats

Evoked potentials and unit activity in the medullary reticular formation were investigated in unanesthetized, curarized rats during cold blocking or after extirpation of the cortical representation of one of the stimulated limbs. Local cooling or extirpation in area SII, unlike blocking of area SI, leads to a small (up to 30%) decrease in amplitude and a very small change (up to 10 msec) in the temporal parameters of evoked potentials arising in the reticular formation in response to electrodermal stimulation of the contralateral limb, whose representation in the cortex was blocked. Predominance of corticofugal influences from SI over those from SII was discovered both in experiments with evoked potentials and during analysis of somatic spike responses of reticular formation neurons. Corticofugal control over activity of the medullary reticular formation in rats exerted by neuronal mechanisms of somatosensory areas SII and SI thus differs both qualitatively and quantitatively.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 15, No. 1, pp. 42–49, January–February, 1983.     

Effect of noradrenalin and serotonin on spontaneous unit activity in hippocampal area CA3 in vitro

The effect of noradrenalin and serotonin on spontaneous unit activity in hippocampal slices (area CA₃)in vitro was studied by the addition of mediators to the incubation medium. Both drugs were found to have both an inhibitory (32 and 49%, respectively) and an activating (52 and 35%, respectively) action. The effect of noradrenalin correlated with the type of spontaneous unit activity. Mainly cells without spontaneous discharges or with single irregular discharges were activated Cells with "complex discharges" were inhibited. Unlike the effect of serotonin, the activating action of noradrenalin was stimulated by the agonist phenylephrine and inhibited by the -adrenoblocker phentolamine. The action of the monoamines persisted in medium with an increased Mg⁺⁺ concentration.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 482–490, September–October, 1981.     

Reticular unit responses in rats during functional blocking of cortical representation of the stimulated paw

Responses of single reticular units to electrodermal stimulation were studied in unanesthetized, immobilized rats during cold blocking of the cortical representation of the stimulated limbs. Local cooling of the somatosensory cortex caused reversible and opposite changes in responses of 60 of the 86 neurons tested. In 25 cells responses only to stimulation of the limb whose sensory projection was in the cooled zone were modified. In 31 neurons changes in responses to this stimulation predominated and in 22 they were comparable with changes in responses of the same neurons to electrodermal stimulation of the other limb, whose cortical representation was intact. Cold blocking of the cortical response to presentation of one of the stimuli thus modifies the conditions for information processing in the neuron net of the reticular formation selectively for the response to presentation of that same stimulus.I. M. Sechenov Institute of Evolutionary Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 179–186, March–April, 1981.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Chemical sensitivity of Limnaea stagnalis neurons and their responses to synaptic stimulation

Responses of nerve cells to puncture, to touching the surface of the mollusk leg, osmotic stimulation, and extracellular microiontophoretic injection of acetylcholine, noradrenalin, serotonin, atropine, and propranolol were recorded intracellularly in the right parietal, left pedal, and visceral ganglia of the unisolated circumpharyngeal ring ofLimnaea stagnalis. Selective sensitivity of the neurons to the biologically active substances was observed. Results indicative of the functional differences between the various ganglia and of their neurochemical organization were obtained. Selective blocking of the unit responses to puncture of the surface of the mollusk leg by atropine or propranolol suggests that different forms of excitation reaching the central neurons evoked different and specific neurochemical processes on their subsynaptic membranes which can retain the essential informativeness of the widely different afferent volleys converging on a single nerve cell.I. M. Sechenov First Moscow Medical Institute. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 510–518, September–October, 1973.     

Neurochemical mechanisms in inhibitory effects of stimulation of the periaqueductal gray matter on high-threshold reflex activity of the reticular formation

A study was made of microinjections of antagonists of various neuromodulators on the dynamics of inhibition of the spino-bulbo-spinal reflexes which were evoked by stimulation of the central gray matter (PAG) in rats anesthetized with chloralose. Injections were made into the reticular gigantocellular nucleus (GN), which is the basic supraspinal center of this reflex. Administering methysergide (a blocker of serotonin receptors) was accompanied by significant (two to four times) diminution of inhibition evoked by PAG stimulation with a short, high-frequency series of stimuli. Long inhibition caused by long, rhythmic stimulation of the PAG was diminished less significantly: from 6–10 to 2.5–4 min. When the opiate receptors of the GN neurons were blocked with naloxone, duration of inhibition was reduced by two to five times. The most clearly expressed diminution of both types of inhibitions was noted with injections of haloperidol, an antagonist of catecholamines. Our data indicate that evidently all of these neuromediator (neuromodulator) systems participate in inhibition of high-threshold, reflex activity of the reticular formation evoked by stimulation of the PAG, but their participation in this process is unequal.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 455–463, July–August, 1991.     

Role of the reticular formation of the midbrain in the process of formation of background activity of cortex neurons

In strict experimental conditions the basic activity of optic-cortex neurons in the rabbit was depressed after transverse section at the level of the rostral part of the reticular formation of the midbrain. Electrolytic destruction or functional blockage of the midbrain reticular formation (nucleus reticularis tegmenti) produces a decrease in frequency and magnitude in the grouping indexes of the cortex-neuron pulses that manifest the activity in these conditions. Destruction of specific nuclei in the optic pathway (those of the lateral geniculate body and the corpora bigemina) made no substantial change in the nature of the cortex-neuron pulses. Comparison of the parameters of pulsation activity of the same cortex neurons, as recorded before and after functional exclusion of the midbrain reticular formation, revealed that the increase in grouping of these pulses after the reticular formation was blocked induced changes in the intervals between groups of pulses, while the frequency of pulses within the groups remained constant. On the basis of the data obtained we may assume that the midbrain reticular formation plays an important role in generation of the background activity of cortex neurons, being a triggering mechanism that sets off a group of pulses. Distribution of pulses within the group is apparently due to the activity of cortex mechanisms only.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 43–51, January–February, 1970.     

Role of cholinergic mechanisms in the genesis of some cortical responses

The dynamics of evoked potentials during blocking of cholinergic cortical structures was investigated in unanesthetized cats. Application of the anticholinergic drug benactyzine inhibits the negative phases of cortical responses to stimulation of the reticular formation and non-specific thalamic nuclei and also of responses to direct cortical stimulation. Direct cortical responses (DCRs), inverted by -aminobutyric acid, are also depressed, indicating the role of cholinergic mechanisms in the genesis of these responses. During blocking of cholinergic synapses, negative phases of the primary response (PR) and response to stimulation of the specific thalamic nucleus are facilitated. A tendency is then observed toward grouping of spontaneous unit discharges and abolition of inhibition of cortical neurons produced by high-frequency stimulation of the reticular formation. One cause of the increase in amplitude of the primary response (PR) to the action of anticholinergic drugs may be widening of the zone of cortical neurons involved in the response because of abolition of the localizing effect of inhibitory neurons.Institute of Physiology, Siberian Division, Academy of Sciences of the USSR, Novosibirsk. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 406–411, July–August, 1970.     

Convergence and interaction of reticulofugal and peripheral afferent impulses on caudate neurons in the cat

Extracellular investigations on the activity of 269 caudate neurons during electrical stimulation of the midbrain reticular formation were carried out during chronic experiments on cats. Stimuli of different sensory modalities were used: auditory, mechanical, and visual. A response was observed to both reticular and peripheral stimulation in single neurons. The former produced an orthodromic response in 53% of caudate neurons, notable for its high probability of occurrence. A total of 23% of caudal neurons responded to this type of stimulation and application of stimuli of a single modality, while 14% responded polymodally. An excitatory response pattern prevailed during all types of stimulation. By applying twin stimuli to 100 caudate neurons, a capacity for interaction between reticular and acoustic inputs was discovered. Interaction was similarly observed in neurons which had reacted neither to separate application of both stimuli nor to either of the stimuli in isolation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 101–110, January–February, 1987.     

Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Reflex discharges in intercostal nerves and activity of reticulospinal fibers of the ventral and lateral funiculi, evoked by stimulation of the reticular formation and of the splanchnic and intercostal nerves were investigated in cats anesthetized with chloralose (50 mg/kg). Brain-stem neuronal structures participating in the "relaying" of spino-bulbo-spinal activity were shown to lie both in the medial zones of the medullary and pontine reticular formation and in its more lateral regions; they include reticulospinal neurons and also neurons with no projection into the spinal cord. Structures whose stimulation led to prolonged (300–800 msec) inhibition of reflex spino-bulbo-spinal activity were widely represented in the brain stem, especially in the pons. Analogous inhibition of this activity was observed during conditioning stimulation of the nerves. Reticulospinal fibers of the ventral (conduction velocity 16–120 m/sec) and lateral (17–100 m/sec) funiculi were shown to be able to participate in the conduction of spino-bulbo-spinal activity to spinal neurons. In the first case fibers with conduction velocities of 40–120 m/sec were evidently most effective. Evidence was obtained that prolonged inhibition of this activity can take place at the supraspinal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 373–383, July–August, 1976.     

Single unit responses of the reticular and ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum

In acute experiments on cats anesthetized with thiopental (30–40 mg/kg, intraperitoneally) and immobilized with D-tubocurarine (1 mg/kg) responses of 145 neurons of the reticular and 158 neurons of the ventral anterior nuclei of the thalamus to electrical stimulation of the centrum medianum were investigated. An antidromic action potential appeared after a latent period of 0.3–2.0 msec in 4.1% of cells of the reticular nucleus and 4.4% of neurons of the ventral anterior nucleus tested in response to stimulation. The conduction velocity of antidromic excitation along axons of these neurons was 1.7–7.6 m/sec. Neurons responding with an antidromic action potential to stimulation both of the centrum medianum and of other formations were discovered, electrophysiological evidence of the ramification of such an axon. Altogether 53.8% of neurons of the reticular nucleus and 46.9% of neurons of the ventral anterior nucleus responded to stimulation of the centrum medianum by orthodromic excitation. Among neurons excited orthodromically two groups of cells were distinguished: The first group generated a discharge consisting of 6–12 action potentials with a frequency of 130–640 Hz (the duration of discharge did not exceed 60 msec), whereas the second responded with a single action potential. Inhibitory responses were observed in only 0.7% of neurons of the reticular nucleus and 4.4% of the ventral anterior nucleus tested. Afferent influences from the relay nuclei of the thalamus, lateral posterior nucleus, and motor cortex were shown to converge on neurons responding to stimulation of the centrum medianum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 36–45, January–February, 1980.