Blood pressure reflexes to stimulation of tibial nerve a fibers in mesencephalic and bulbar cats

The role of the various subgroups of A fibers of the tibial nerve (pulse frequency of electrical stimulation 10/sec) in the formation of reflex changes in blood pressure (BP) was investigated in unanesthetized cats with total transection of the brain stem at the level of the pontomedullary junction (bulbar animals) or at the rostral border of the mesencephalon (mesencaphalic animals), and also in anesthetized cats with an intact brain. The lowest thresholds for the reflexes were found in anesthetized animals with an intact brain, the highest in bulbar cats. Excitation of A fibers in anesthetized cats with an intact brain evoked only depressor reflexes. In some bulbar and mesencephalic animals only pressor reflexes appeared. In the experiments of this group excitation of fibers with a conduction velocity of over 15 m/sec in mesencephalic cats evoked reflexes of near maximal strengths, whereas in bulbar cats excitation of thinner A fibers also was necessary. In unanesthetized animals disconnection of the suprabulbar structures thus lowers the sensitivity of the central mechanisms of vasomotor regulation to impulses in lowthreshold A fibers. No such effect was found in another group of experiments in which depressor reflexes appeard in response to stimulation of fast-conducting A fibers only. In these experiments, if slower A fibers also were stimulated, the reflexes became pressor but the difference between their magnitude in the bulbar and mesencephalic cats was not signicant.Laboratory of Biophysics and Pathophysiology of the Circulation, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 84, No. 10, pp. 393–396, October, 1977.     

The rhombencephalon and vasomotor reflexes to impulses in somatic A-fibers

Cats were decerebrated so that the medulla preserved its connections with a greater or lesser part of the pons, after which they were immobilized with flaxedil or succinylcholine and the response of their arterial blood pressure (BP) to volleys of impulses in various subgroups of fibers of the tibial nerve (frequency of volleys 10 sec^–1) was investigated. Impulses in A + A₁-afferents and the most excitable fraction of A₂-afferents lowered BP in all animals. Application of impulses in all A₂-afferents potentiated the fall in BP in 79% of the experiments and led to a rise in BP in only 21% of the experiments. The addition of impulses in A₃-fibers to the afferent flow either did not change the mean decrease in BP or led to a small or sometimes more considerable increase in BP. The critical factor producing a sharp reduction in the pressor reflexes or their replacement by depressor reflexes was the integrity of the structures of the pontobulbar junction and the most rostral part of the medulla. This region of the hindbrain thus contains formations causing tonic depression of the excitatory action of impulses in somatic A-afferents on vasoconstrictor neurons and which thereby unmask the existence of an inhibitory component of their action on these neurons. In unanesthetized cats this action of hindbrain structures is depressed tonically by the mesencephalon.Laboratory of Biophysics and Pathophysiology of the Circulation, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 11, pp. 519–522, November, 1978.     

The brain stem and the very late reflex response of vasoconstrictor neurons to impulses of somatic A-afferents

Single stimulation of A-fibers of the tibial nerve evoked not only a late response — a discharge of the latent period 60–140 msec — in the renal nerve of unanesthetized decrebrate cats, but also a very late response (VLR), with a latent period of about 0.35 sec. This response was easily elicited in nearly all experiments on mesencephalic animals, but after division of the brain stem at different levels of the pons, including the region of the pontobulbar junction and the most rostral portions of the medulla, it was discovered in only 1 of 18 animals. After division of the brain stem rather more caudally (in bulbar animals) VLR was found in 10 of 11 animals. In the region of the pontobulbar junction there are thus structures which tonically inhibit the activity of the system generating the VLR. It is shown that the activity of this system is potentiated by two types of summation processes: Some taking place during long (seconds) and others taking place during short (milliseconds) time intervals.Laboratory of Biophysics and Pathophysiology of the Circulation, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii Meditsiny, Vol. 88, No. 10, pp. 390–393, October, 1979.     

The selective effect of certain chemical stimultants on the interoceptive reflexes

Summary Experiments on cats have shown that the selective inhibitory effect of streptomycin on the chemoreceptive afferent paths is accomplished at the level situated below the mesencephalon.Presented by Prof. V. N. Chernigovsky, Active Member of the USSR Academy of Medical Sciences     

Changes in the antinociceptive effect of mesencephalic stimulation produced by analgesics and tranquilizers

Chronic experiments on cats showed that analgesics, in subanalgesic doses, not only exhibit an antinociceptive effect when accompanied by subthreshold stimulation of the mesencephalon, but also potentiate the analgesic action of central stimulation. Tranquilizers only facilitate the development of an analgesic effect during subthreshold mesencephalic stimulation. The possible reasons for differences in the action of these substances are discussed.Department of Pharmacology, I. P. Pavlov First Leningrad Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR S. V. Anichkov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 1, pp. 36–41, January, 1978.     

Electroanatomy of tectal efferent connections related to eye movements in the horizontal plane

1. Excitatory and inhibitory oligosynaptic pathways from the superior colliculus (CS) to ocular motoneurons engaged in horizontal eye movements were investigated in cats using acute and chronic brain stem transections in combination with intracellular recordings. 2. Isolation of the medial ponto-bulbar tegmentum from vestibular nuclei and adjacent lateral tegmental structures did not impair short-latency EPSPs and IPSPs induced by collicular stimulation in lateral rectus motoneurons (LR-MNs). On the contrary, responses were enhanced after chronic de-efferentation of vestibular nuclei. This suggests compensatory synaptic rearrangement in the tecto-reticulo-abducens pathways. 3. Midsagittal mesencephalic transections eliminated not only crossed excitatory but also ipsilateral inhibitory CS action on LR-MNs indicating that underlying pathways undergo decussation within the midbrain. 4. Midsagittal transections at different pontine and bulbar levels were performed to locate the second decussation of the inhibitory pathway. Ipsilateral IPSPs were eliminated only by deep lesions extending for about 1.5 mm rostral and caudal to the 6th nuclei. 5. Investigation of medial rectus motoneurons (MR-MNs) revealed two types of excitatory responses to CS-stimulation: (a) di- or trisynaptic EPSPs characterized by a fast rising phase and pronounced frequency potentiation; (b) slowly rising EPSPs displaying little or no frequency potentiation. 'Fast' EPSPs were abolished by all types of pontine lesions interrupting transmission through the contralateral 'abducens region' and may thus be relayed by internuclear neurons within or adjacent to the 6th nucleus. 'Slow' EPSPs persisted after transverse sections at midpontine and rostral pontine levels. 6. The trajectory of tectofugal inhibitory pathway to MR-MNs could not be followed due to a marked suppression of IPSPs under pentobarbital anesthesia. Persistence of IPSPs in LR-MNs under same conditions indicated that reciprocal inhibition of LR- and MR-MNs is mediated by different populations of inhibitory interneurons.     

Continuity of the bulbar locomotor strip is not essential for walking

Bilateral destruction of the medulla, interrupting both locomotor strips, was carried out on mesencephalic cats. After the operation walking could still be induced by stimulation of the more rostral (and also caudal) portion of the strip, although in some experiments the threshold of walking was raised. The connection of the locomotor strip with other structures of the brain stem and spinal cord is discussed on the basis of these findings.A. N. Belozerskii Interfaculty Laboratory, M. V. Lomonosov Moscow State University. Laboratory of Physiology of Movements, Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR M. I. Kuzin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 1, pp. 3–6, January, 1980.     

Mechanism of action of nonachlazine on nervous control over the coronary circulation

The new antiaginal drug nonachlazine, in experiments on anesthetized cats and dogs, inhibited the response of reflex decrease of the blood flow into the coronary arteries. In freely behaving cats nonachlazine also inhibited reflex changes in the blood flow in the system of the common carotid artery and reduced pressor vasomotor reflexes. Nonachlazine selectively inhibited vasoconstrictor impulses from A-afferent fibers of spinal nerves, i.e., it acts on the vasomotor component of the primary nociceptive response. This mechanism may perhaps lie at the basis of the relief of the pain syndrome by nonachlazine in ischemic heart disease.Laboratory of Pharmacology of the Cardiovascular System, Institute of Pharmacology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 3, pp. 319–322, March, 1976.     

Effect of narcotic analgesics on transmission of excitation in the spinal cord

In experiments on unanesthetized, curarized spinal cats, morphine, trimeperidine, and fentanyl caused no change in the amplitude of evoked potentials in the ventrolateral columns in the lumbar region of the spinal cord in response to single or repetitive stimulation of a cutaneous or pelvic nerve. In some experiments these preparations inhibited neurons of the posterior horns of the spinal cord that are activated by nociceptive stimulation of peripheral receptors or by intraarterial injection of bradykinin. It is suggested that a spinal component exists in the action of the narcotic analgesics.Laboratory of Pharmacology of the Nervous System, Institute of Pharmacology, Academy of Medical Sciences of the USSR. Department of Pharmacology, I. M. Sechenov First Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 2, pp. 182–185, February, 1978.     

Experimental model of a secondary pacemaker center of feeding motivation

The possibility of simulating the functions of the feeding motivation pacemaker by various structures of the limbico-reticular complex was studied in chronic experiments on rabbits. In response to combined stimulation of the feeding center of the lateral hypopthalamus and various formations of the limbico-reticular complex, a secondary pacemaker of feeding motivation excitation was shown to be formed only in the mesencephalic reticular formation.P. K. Anokhin Research Institute of Normal Physiology, Academy of Medical Sciences of the USSR. Department of Normal Physiology, I. M. Sechenov First Moscow Medical Institute. Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 11, pp. 515–517, November, 1978.     

Effect of mesencephalic stimulation on responses to nociceptive stimulation of the dental pulp

Chronic experiments on cats showed that stimulation of certain zones of the mesencephalon reduces or completely suppresses responses to pain caused by stimulation of the dental pulp. Depending on the parameters of brain stimulation the antinociceptive effect was manifested as differential changes in individual motor, autonomic, emotional, and behavioral components of the integral nociceptive response. After-analgesia was found and the dynamics of the return of the various manifestations of pain after cessation of brain stimulation was noted. The possible mechanisms of the antinociceptive effect are discussed.Department of Pharmacology, I. P. Pavlov First Leningrad Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR S. V. Anichkov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 10, pp. 1158–1161, October, 1976.     

Effect of morphine and azidomorphine on cortical unit activity

In acute experiments on unanesthetized curarized cats and rats morphine and azidomorphine, in analgesic doses, inhibited spontaneous and bradykinin-evoked unit activity in the sensomotor cortex. The depriming action of both drugs was abolished by nalorphine. It is suggested that the inhibitory action of morphine and azidomorphine is due to their direct action on the cerebral cortex.Laboratory of Pharmacology of the Nervous System, Institute of Pharmacology, Academy of Medical Sciences of the USSR. Department of Pharmacology, Faculties of Therapeutics and Environmental Health, I. M. Sechenov First Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 6, pp. 698–699, June, 1977.     

Activity of neurons of the bulbar pressor structures in reflexes from the mechanoceptors of the urinary bladder and the afferent fibers of the tibial nerve

Summary Experiments were carried out on cats under urethane anesthesia. The action potentials of neurons of various bulbar pressor structures were taken off extracellularly by means of microelectrodes (d-2 to 25 mc). The vasomotor function of the neuron was judged according to: 1) the pressor reaction to stimulation of the point where the neuron was located; 2) the reflex charge in the frequency of neuron discharges during reduction of pressure in the carotid sinus or during rapid mechanical elevation and decrease of the general arterial pressure. It has been found that: 1) different neurons show dissimilar changes of the impulse activity in reflexes both from the urinary bladder mechanoceptors and from the afferent fibers of the tibial nerve. The afferent impulses from one and the same source produced no influence on certain neurons, while in others they caused excitation of a variable degree, and in some neurons, an inhibition of the activity; 2) some neurons respond to afferent impulses both in distention of the urinary bladder and in stimulation of the tibial nerve; 3) neurons reacting in one and different directions are not delimited anatomically. It is concluded that during arrival at the VMC of afferent impulses from some receptors in the bulbar pressor structures a functional system of neurons is formed there, characteristic of a given afferentation, which are distinguished by a variable degree of stimulation and inhibition.Laboratory of the Physiology and Pathology of Circulation and Respiration, Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow (Presented by Active Member of the Academy of Medical Sciences of the USSR V. V. Parin). Translated from Byulleten Éksperimental'noi Biologii i Meditsiny, Vol. 62, No. 7, pp. 8–12, July, 1966.     

The pontomedullary area integrating the defence reaction in the cat and its influence on muscle blood flow

1. In anaesthetized cats the effects were investigated of electrical stimulation of regions in the caudal mesencephalon, pons and medulla on muscle blood flow, skin blood flow and arterial blood pressure.2. It was found that within the dorsal part of the well known pressor area there is a narrow strip, 2.5 mm lateral from the mid line, starting ventral to the inferior colliculus and ending in the medulla close to the floor of the IV ventricle, from which vasodilatation in skeletal muscles is selectively obtained. This strip is quite separate from the more ventral, efferent pathway for active vasodilatation running from the hypothalamic and rostral mesencephalic ;defence centre'.3. As in the case of the hypothalamic and rostral mesencephalic ;defence centre', the muscle vasodilatation obtained from the caudal strip is accompanied not only by a rise of arterial blood pressure, but also by tachycardia, vasoconstriction in the skin, pupillary dilatation and piloerection.4. Stimulation, restricted to the caudal strip, via implanted electrodes in unanaesthetized animals, produced a behavioural response resembling the defence reaction. The strip, therefore, is probably a caudal extension of the ;defence centre'.5. Unlike the vasodilatation elicited from the more rostral part of the ;defence centre' in the hypothalamus and mesencephalon, the muscle vasodilatation obtained on stimulation of the caudal strip was resistant to atropine, but was blocked by guanethidine.6. It is suggested that during naturally occurring defence reactions in the normal animal the ponto-medullary area is activated together with the hypothalamo-mesencephalic area, inhibition of vasoconstrictor tone then accompanying activation of the vasodilator nerve fibres in skeletal muscle.     

Acid mucopolysa ccharides of the inner zone of the renal medulla in albino rats kept under different conditions

In albino rats kept without water reactions for acid mucopolysaccharides in the interstitial tissue of the distal part of the inner zone of the renal medulla remained highly stable in experiments carried out under conditions of higher relative atmospheric humidity.Department of Geographic Pathology, Research Institute of Human Morphology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. P. Avtsyn.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 10, pp. 1271–1274, October, 1976.     

Brain catecholamines in the early stage of emotional stress

To study central neurochemical mechanisms leading to a disturbance of self-regulation of the arterial blood pressure (BP) under conditions of emotional stress the dynamics of BP and the catecholamine level in different parts of the brain were studied in August and Wistar rats after immobilization for 2 h. The BP level was virtually indistinguishable from normal throughout the experiment. The catecholamine concentration in the hypothalamus, mesencephalon, the region of the isthmus cerebri, and the medulla was significantly changed. it is suggested that the mechanism of the changes in catecholamine concentration during stress in rats of both strains is similar in the region of the hypothalamus and medulla. Activity of the noradrenalinsynthesizing neurons of the isthmus cerbri and of the dopamine-synthesizing neurons of the mesencephalon in the rats of these two strains, however, is specific, and that is evidently one of the factors responsible for differences in the resistance of cardiovascular functions in the later stages of immobilization.P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Scineces of the USSR N. Ya. Fedorov.) Translated from Byulleten'Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 9, pp. 275–278, September, 1979.     

Mechanism of mesencephalic reticular influences on the hypothalamicpituitary-thyroid system

The role of the posterior hypothalamic nucleus in the transmission of mesencephalic reticular influences on thyroid hormone secretion was studied. In response to stimulation of the mesencephalic reticular formation in anesthetized cats the concentration of iodine bound with plasma proteins was increased. After bilateral coagulation of the posterior hypothalamic nucleus this effect disappeared. The results confirm the hypothesis of the leading role of the posterior hypothalamic nucleus in stimulation of thyroid hormone secretion.Laboratory of Neuroendocrine Regulation, P. K. Anokhin Institute of Normal Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 8, pp. 916–920, August, 1976.     

Restoration of blood supply and intensity of phospholipid metabolism in various parts of the postischemic rat brain

A marked increase in the blood supply to the cerebral hemispheres, diencephalon, and mesencephalon and a simultaneous decrease in blood supply to the cerebellum and medulla were observed 15 min after restoration of the blood flow through the common carotid arteries, which had been arrested by application of ligatures. The blood supply after 60 min was restored completely in all parts of the brain except the cerebral hemispheres. Complete restoration of the intensity of phospholipid metabolism also was found in parts of the brain in which it had been considerably depressed during the period of ischemia.Laboratory of Regulation of Brain Metabolism, Academician I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 2, pp. 139–142, February, 1979.     

Reaction of intracranial and extracranial vessels to noradrenalin in experimental cardiogenic shock

Weakening of the constrictor response of the intracranial and extracranial vessels to noradrenalin in animals with cardiogenic shock was established by resistography and rheoencephalography in acute experiments on anesthetized cats. Under these conditions elevation of the systemic arterial pressure by noradrenalin leads to passive dilatation of the brain vessels and to an increase in the volume of blood in them.Department of Pharmacology, Irkutsk Medical Institute. Department of Pharmacology, Pyatigorsk Pharmaceutical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 1, pp. 15–17, January, 1977.