Respiratory modulation of the startle reflex in cats

Phase respiratory influences on reflex after-discharges in response to stimulation of the segmental nerves as well as tactile and acoustic stimulation in the limb and intercostal nerves — physiological analogs of startle reflexes (SR) were studied in unanesthetized (decerebrate) or chloralose-anesthetized cats. It was found that the level of these reflexes in the inhalation phase of respiration was 8–58% lower than during exhalation. The difference between the inhalation and exhalation phases was determined for different types of reflexes and under varying experimental conditions. Evidence was obtained that respiratory modulation of reflexes occurs mainly at the level of suprasegmental (reticular) mechanisms. Clear distinctions could be drawn between the pattern of reflex modulation in the lower intercostal nerves and those of the limbs. Findings would lead to the conclusion that the likely mechanisms underlying suprasegmental respiratory influences on these reflexes differ, as does the organization of their reticular centers.S. V. Kurashov Medical Institute, Ministry of Public Health of the RSFSR, Kazan'. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 593–603, September–October, 1986.     

Change in reactions of visual cortex neurons to light flash upon hypothalamic and reticular stimulation

The effect of electrical stimulation of the hypothalamic positive reinforcement zone (PRZ), the neutral hypothalamic zone (NZ), and the reticular formation (RF), of the midbrain on the impulse activity of single neurons of the visual cortex evoked by light flashes was studied in unanesthetized and uncurarized white rats. Poststimulus histograms of the neurons's responses were compared. Under the influence of stimulation the evoked activity of the neurons which responded to light changed in a majority of them (from 63% for the NZ to 82% for the RF). Qualitative differences were found in the effects of PRZ and RF stimulation. The effects of PRZ stimulation consisted in the invariability or in a decrease in the frequency of the neuron's discharge comprising the short-latent response, and an increase in the frequency of the discharges in the long-latent response ("positive-motivation" type). The effects of RF stimulation were manifested in intensification of the neuronal discharges in the short-latent and a decrease in the discharges in the long-latent response ("reticular" type). The responses of a considerable number of the neurons changed to the "combined" type. The data obtained indicates the different natures and mechanisms of the ascending activating effects caused by stimulation of the PRZ and the RF and which brings about positive nonspecific reinforcements. These effects, which are manifested differently in different periods of the neuron's working cycle cannot be explained by "energizing" or "tonus" concepts; their explanation must be sought for in informational (systemic) concepts.N. I. Grashchenkov Laboratory of Problems of Functional Control in the Human and Animal Organism, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 359–368, July–August, 1971.     

Effect of reticular formation on hippocampal neurons (field CA1)

The reaction of field CA₁ hippocampal neurons to stimulation of the reticular formation (RF) with impulses of different frequencies was investigated in experiments on unanesthetized rabbits. The effect of electrical and sensory stimuli was compared and the effect of reticular stimulation on the sensory responses was determined. With an increase in the frequency of RF stimulation, the number of neurons of field CA₁ responding with inhibition of the activity increases. Multimodal neurons of the hippocampus depend on the reticular input to a greater degree than unimodal neurons. Neurons whose activity does not change in response to the effect of sensory stimuli also do not respond to stimulation of the RF. Neurons responding with inhibitory reactions to sensory stimulation show a higher correlation with the effects of RF stimulation than neurons with activation reactions and, especially those with "complex" responses to the effect of sensory stimuli. In a considerable number of hippocampal neurons the responses to sensory stimuli change in the course of 10–15 min after stimulation of the RF. The role of the RF in the organization of the reactions of hippocampal neurons is discussed.Division of Memory Problems, Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oke. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 227–235, May–June, 1971.     

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.     

Effects of substantia nigra stimulation on high- and low-threshold response in reticular neurons

The effects of electrical stimulation of the substantia nigra (NS) pars compacta on somatosensory response in pontine neurons (from n. reticularis pontis caudalis) and reticular cells (n. reticularis gigantocellularis) were investigated in chloralosed cats. These effects were found to be inhibitory and tended mainly towards high-threshold activation of reticular neurons: responses induced by activation of high-threshold somatic efferents were those mainly inhibited in 71% of test cells. Inhibition of low-threshold response induced by tactile stimuli emerged less clearly or not at all. Potential mechanisms and the functional significance of these SN influences on reticular neurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 772–780, November–December.     

The rhombencephalic "locomotor region" in turtles

Electrical stimulation (10–20 µA, 20–30 Hz) of the rhombencephalon in decerebrate turtles can induce cyclic coordinated limb movemnts. The "locomotor region" is a strip, oriented in the rostro-caudal direction, which coincides in its location with the lateral reticular formation. Both in the medial and in the lateral reticular formation extracellular ipsilateral and contralateral synaptic responses of single neurons evoked by stimulation of the "locomotor region," (10–30 µA, 2 Hz), were recorded. Usually these responses had latent periods of between 3 and 12 msec (mode 5–6 msec). Excitation of the "locomotor region" thus leads to extensive spread of activity in the rhombencephalon. The possible mechanisms of this spread are discussed.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 382–390, July–August, 1980.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Effect of phosphocreatine on reflex activity of the brain stem reticular formation

The effects of phosphocreatine (PCr) on startle reflexes, known to be relayed through the brain stem reticular formation (RF), were investigated on chloralose-anesthetized rats. PCr (10^–6 to 10^–3 M) was either applied superficially to the bottom of the fourth ventricle or microinjected into the reticular gigantocellular nucleus. The PCr effect was found to depend on its concentration. At low concentrations (10^–6 to 10^–5 M), PCr markedly facilitated the reflexes; sometimes its application gave rise to additional, later and longer, discharges following startle reflexes, whereas an inhibitory effect predominated at higher PCr concentration (10^–4 to 10^–3 M). Possible mechanisms of PCr action on the studied reflexes are discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 272–278, 1993.     

Corticofugal influences on pontine unit activity

Unit responses of the nuclei pontis (NP) and reticular pontine nuclei (RPN) to stimulation of the frontobasal cortex (proreal, orbital, and basal temporal regions) and of the dorsal hippocampus were studied in cats. Stimulation of the various cortical structures was found to induce phasic and (less frequently) tonic responses in neurons of NP and RPN. The main type of unit response in RPN was primary excitation, whereas in NP it was primary inhibition. The largest number of responding neurons in the pontine nuclei was observed to stimulation of the proreal gyrus. In the cerebro-cerebellar relay system neurons of the reticular tegmental nucleus and ventromedial portion of NP showed the highest ability to respond. In the oral and caudal reticular pontine nuclei the regions of predominant influence of cortical structures were located in zones of these nuclei where neurons with rostral and (to a lesser degree) caudal projections were situated.M. Gorkii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 358–367, July–August, 1980.     

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 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.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Effects of stimulating the periaqueductal gray matter on high- and low-threshold startle reflexes

The effects of stimulating the periaqueductal gray matter (PAG) on two types of startle reflex (spino-bulbo-spinal reflex produced by intensive stimulation of the peripheral nerves and low-threshold tactile spino-reticulo-spinal reflex) as well as high-threshold jaw-opening reflex arising in response to tooth pulp stimulation were investigated in cats anesthetized with chloralose. Simulating most PAG test sites led to pronounced inhibition of jaw-opening reflex, profound depression of spino-bulbo-spinal reflex, and moderate inhibition of tactile reflexes. The facilitatory effect of stimulating a number of PAG sites on the latter reflexes was demonstrated. Effects of PAG stimulation fell into two classes: brief, measurable in hundreds of msec and more prolonged, measured in minutes and seconds. Findings would indicate certain differences between the effects of PAG stimulation low-threshold (non-nociceptive) and high-threshold (nociceptive) startle reflexes, of which the possible mechanisms are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 71–78, January–February, 1989.     

Functional characteristics and topography of spinal pathways conducting high- and low-threshold startle reflexes

Electrophysiological and topographical properties of the spinal tract systems involved in two functional types of startle reflexes were studied in chloralose anesthetized cats: a high-threshold reflex produced by intense peripheral nerve stimulation (spinobulbo-spinal, SBS, reflex) and a low-threshold reflex evoked by tactile (T-reflex) and acoustic (A-reflex) stimulation. Maximum conduction velocity of descending transmission of the high-threshold reflex, at 30 m/sec, was perceptibly lower than that of low-threshold reflexes, at 85 m/sec for T-reflex and 100 m/sec for A-reflex. Mean conduction velocity for SBS and T-reflexes were 40.2 and 70.8 m/sec respectively. Perceptible differences were also found in the topography of spinal and especially ascending pathways of these reflexes. It was established by partial spinal cord destruction that accomplishment of T-reflex depended on the integrity of ascending pathways of the dorsal and dorsolateral funiculi and the SBS reflex on preservation of the dorsolateral, ventrolateral and (partially) of ventral funiculi. Descending pathways of the reflexes under study were revealed mainly in the ventrolateral and ventral funiculi and those of the SBS reflex mainly in the first of these. Findings also show the noticeable similarity between the organization of both T- and A-reflex descending pathways. The functional organization of the spinal pathways of a variety of startle reflexes is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 486–496, July–August, 1986.     

Convergence of visceral afferent impulses on hypothalamic neurons during vagal and splanchnic nerve stimulation

Responses of posterior and anterior hypothalamic neurons to stimulation of the vagus, splanchnic, and sciatic nerves, and also to photic stimulation were studied by extracellular recording of spike activity in cats anesthetized with chloralose and immobilized with succinylcholine. Most responding neurons of the posterior and anterior hypothalamus did so to stimulation of both vagus and splanchnic nerves. The responses of these polysensory neurons to stimulation of visceral afferents of parasympathetic nerves were identical in sign and mainly excitatory in type. The absence of a reciprocal character of the response to stimulation of "antagonistic" autonomic nerves and the marked polysensory convergence are evidence of the nonspecific "reticular" character of activation of most of the neurons in the posterior and anterior hypothalamus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 165–170, March–April, 1977.     

Effect of neurotropic drugs on cortical evoked potentials

In acute experiments on unanesthetized, curarized cats and rabbits and also on animals anesthetized with chloralose, recordings were made of direct cortical and transcallosal responses, responses in the pyramids of the medulla to peripheral stimulation and stimulation of the motor cortex, primary responses in area S-I, and interzonal somatomotor responses. The effect of narcotics on these cortical responses was shown to persist under conditions partially or completely excluding effects mediated through the reticular formation and other subcortical structures (intracarotid injection of the drugs or their local application to the cortex, experiments after premesencephalic section or on the isolated cortex). Neuroleptics have only a slight effect on these cortical evoked responses, mainly due to their blocking action on the reticular formation. Tranquilizers of the benzodiazepine series are active against the cortical responses studied, and this effect is due to their direct action on the cortex.Institute of Pharmacology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 582–591, November–December, 1971.     

Postnatal Temporal,Spatial and Modality Tuning of Nociceptive Cutaneous Flexion Reflexes in Human Infants

Cutaneous flexion reflexes are amongst the first behavioural responses to develop and are essential for the protection and survival of the newborn organism. Despite this, there has been no detailed, quantitative study of their maturation in human neonates. Here we use surface electromyographic (EMG) recording of biceps femoris activity in preterm (<37 weeks gestation, GA) and term (≥37 weeks GA) human infants, less than 14 days old, in response to tactile, punctate and clinically required skin-breaking lance stimulation of the heel. We show that all infants display a robust and long duration flexion reflex (>4 seconds) to a single noxious skin lance which decreases significantly with gestational age. This reflex is not restricted to the stimulated limb: heel lance evokes equal ipsilateral and contralateral reflexes in preterm and term infants. We further show that infant flexion withdrawal reflexes are not always nociceptive specific: in 29% of preterm infants, tactile stimulation evokes EMG activity that is indistinguishable from noxious stimulation. In 40% of term infants, tactile responses are also present but significantly smaller than nociceptive reflexes. Infant flexion reflexes are also evoked by application of calibrated punctate von Frey hairs (vFh), 0.8–17.2 g, to the heel. Von Frey hair thresholds increase significantly with gestational age and the magnitude of vFh evoked reflexes are significantly greater in preterm than term infants. Furthermore flexion reflexes in both groups are sensitized by repeated vFh stimulation. Thus human infant flexion reflexes differ in temporal, modality and spatial characteristics from those in adults. Reflex magnitude and tactile sensitivity decreases and nociceptive specificity and spatial organisation increases with gestational age. Strong, relatively non-specific, reflex sensitivity in early life may be important for driving postnatal activity dependent maturation of targeted spinal cord sensory circuits.     

Effects of intraoral mechanoreceptor stimulation on reticular formation neurones, in the rabbit

The effects of intraoral mechanoreceptor stimulation on the firing rate of single neurones of the brain stem reticular formation (RF) were investigated in rabbits. 30% of RF neurones responded to periodontal mechanoreceptor stimulation; 16% to mucosal mechanoreceptor stimulation and 6% to both types of stimuli. Periodontal stimulation induced mainly inhibitory effects localized within the mesencephalic and rostral pontine RF. Among periodontal afferents incisors were the most widely represented. The effects of mucosal mechanoreceptor stimulation were predominant in the medullary and pontine RF and they were mainly excitatory. The present results support the hypothesis that brain stem RF neurones can be recruited into regulating mastication and biting also by stimulation of intraoral mechanoreceptors.     

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.