Thermostimulation-Induced Modulation of Conditioned Reflex Movement-Related Reactions of Cortical Neurons of the Cat

In awake cats trained to perform a food-procuring conditioned operant reflex (placing movement), we studied impulse reactions of 86 neurons of the motor cortex (field 4) related to realization of the above movements. As conditioning stimuli (CS) initiating the reflex, we used either non-noxious electrocutaneous stimulation (ECS) of the contralateral forelimb or an acoustic stimulus (sound click). Impulsation of cortical neurons was recorded under conditions of (i) isolated presentation of the CS (control), (ii) presentation of the CS (either ECS or acoustic stimulus) combined with thermostimulation (heating with a miniature electric bulb) of the skin of the working forelimb, and (iii) the same, but with stimulation of the resting forelimb. When we recorded spike activity of neurons within the projection motor zone of the resting limb subjected to ESC, alternating thermostimulation of both forelimbs resulted in considerable intensification and an increase in the duration of neuronal responses, especially in cases where thermostimulation was applied to the working limb ipsilateral to the recording site (a two- to threefold increase). When spike reactions were recorded within the motor cortex of the working forelimb, thermostimulation resulted in a considerable increase in the intensity of these reactions and a decrease in their latency, but only when such stimulation was applied to the working forelimb. Thermostimulation of the resting (ipsilateral, subjected to ESC) limb evoked opposite effects (the intensity of neuronal reactions dropped). In both situations, placing movements remained within the control limits. When sound click was used as a distant CS, thermostimulation of the working limb enhanced neuronal responses, increased their duration by 50-100%, and also increased the time of forestalling of the movement initiation by spike neuronal reactions. Thermostimulation of the resting forelimb in this situation also suppressed neuronal reactions. We conclude that foreign stimulations directed toward modifications of the receptor model of the operant reflex experimental situation formed in the animal result in a decrease in the intensity of the spike responses of field-4 neurons and prolongation of the latencies of these responses, while stimulations promoting the inflow of afferent information to the cortical projection of the working limb evoke opposite effects, an increase in the intensity of neuronal spike responses and a decrease in their latencies.     

Spatial tuning of neurons in the inferior colliculus of the big brown bat: effects of sound level, stimulus type and multiple sound sources

We examined factors that affect spatial receptive fields of single units in the central nucleus of the inferior colliculus of Eptesicus fuscus. Pure tones, frequency- or amplitude-modulated sounds, or noise bursts were presented in the free-field, and responses were recorded extracellularly. For 58 neurons that were tested over a 30 dB range of sound levels, 7 (12%) exhibited a change of less than 10° in the center point and medial border of their receptive field. For 28 neurons that were tested with more than one stimulus type, 5 (18%) exhibited a change of less than 10° in the center point and medial border of their receptive field.The azimuthal response ranges of 19 neurons were measured in the presence of a continuous broadband noise presented from a second loudspeaker set at different fixed azimuthal positions. For 3 neurons driven by a contralateral stimulus only, the effect of the noise was simple masking. For 11 neurons driven by sound at either side, 8 were unaffected by the noise and 1 showed a simple masking effect. For the remaining 2, as well as for 5 neurons that were excited by contralateral sound and inhibited by ipsilateral sound, the peak of the azimuthal response range shifted toward the direction of the noise.Abbreviations E/E excitation at either ear - I/E inhibition at the ipsilateral ear, excitation at the contralateral ear - O/E no effect from the ipsilateral ear, excitation at the contralateral ear - FM downward frequency modulation - FM upward frequency modulation - IC inferior colliculus - ICC central nucleus of the inferior colliculus - ILD interaural level difference - ITD interaural time difference - PT pure tone - SAM sinusoidally amplitude modulated sounds - SFM sinusoidally frequency modulated sounds     

Effects of high ambient temperatures on the metabolism of West African dwarf goats. II

32 West African dwarf goats were exposed in respiration chambers to temperature treatments of 20, 25, 30, 35, 35, 35, 30, 25, 20°C. Each treatment lasted three days. 16 goats were kept in individual pens (I); the others in two group pens of eight animals each (G). During each treatment, heat production and activity were recorded continuously over 48 hours. In addition, feed and water intake, rectal temperature, skin temperature and respiratory rate were measured during each treatment.Compared to 20°C, at 35°C rectal temperature increased from 39.0°C to 39.9°C, respiratory rate from 30 to 260 times. min^–1 and skin temperature from 37.1°C to 39.5°C. Hay intake decreased by 40%; concentrates (30 g. kg^–0.75. d^–1) were always completely consumed. Heat production was higher for the G animals at 20°C and higher for the I animals at 35°C. These differences in heat production between the two groups were reflected in differences in rectal and skin temperature and in respiratory rate but only very slightly in differences in hay intake.Tissue insulation was 0.014 K. m². W^–1 at 30°C and 35°C and 0.022 K. m². W^–1 at 20°C.It is concluded that the reactions of these dwarf goats to high ambient temperatures are not different in principle from those of other domestic ruminants and that they do not exhibit a specific suitability or unsuitability for ambient temperatures as prevailing in West Africa.     

Processing of antennal information in extrinsic mushroom body neurons of the bee brain

Summary In the bee brain neural activity of interneurons of the inner antenno-cerebral tract (inputs to the mushroom body) and extrinsic neurons of the-lobe (output cells) was recorded intracellularly. The cells were stained with Lucifer Yellow. The response characteristics of the neurons to light, various antennal stimuli and mechanical stimuli to thorax and abdomen were studied.The cells of the inner antenno-cerebral tract (ACT) have uniglomerular dendritic arborizations in the antennal lobe and send projections into the calyces of the ipsilateral mushroom body and the lateral protocerebral lobe. 93% of the neurons are bi- or multimodal. No responses to light stimuli were found. Tactile stimuli to the antennae are only effective when applied ipsilaterally. Only one neuron showed marked differences in the responses to the qualitative testing of three odors: rose, lavender and isoamyl acetate.The cells can be classified according to their response characteristics; the following response types were found: (1) inhibitory responses to the stimuli, (2) inhibitory responses to olfactory and excitatory responses to mechanical stimuli or vice versa, (3) excitatory responses to mechanical and sugar water stimuli, (4) excitation to olfactory stimuli and to touching the antenna with a drop of water or sugar water, (5) excitation to mechanical stimuli to head, thorax and abdomen and inhibition to sugar water stimuli.The recorded extrinsic-lobe neurons have small dendritic bands perpendicular to the Kenyon cells, their axons project to the contralateral median protocerebrum. These cells have ipsilateral antennal and mostly ipsilateral optic inputs and process information from thoracic and abdominal mechanoreceptors. All responses are excitatory.The recordings suggest that the mushroom bodies are multimodal integration centers, where antennal information is first combined with visual inputs.Abbreviation ACT antenno-cerebral tract     

Conditioned Salivation and Associated Dreams from REM Sleep

Although research has investigated the feasibility of establishing classically conditioned physiological responses during sleep, very few experimental studies have considered whether classically conditioned cognitive associations are possible. Since dreams have previously been described as a state of hyper-association, an experiment involving classical conditioning of the human salivary response and associated dream content was conducted. During wakefulness, repeated pairings of a conditioned stimulus (CS; a red light) with an unconditioned stimulus (UCS; citrus juice) yielded a conditioned autonomic response (CR; salivation) on presentation of the CS alone. After exposure to the CS during REM sleep, salivary excretion rates measured upon awakening were significantly higher than measures taken from baseline REM awakenings. However, no CR-related dreams were reported by the participants. This result could be interpreted as evidence that participants in this experiment did not experience higher-order memory associations to the external stimuli presented during REM. Alternatively, the lack of CR-related dreams could be explained by previous findings that the autonomic nervous system often works independently of higher-order cognitive activity. Therefore, if an autonomic association is formed, this does not necessarily imply a cognitive one.     

Physiological and pharmacological properties of responses to GABA and ACh by abdominal motor neurons in Manduca sexta

1. GABA, ACh, and other agents were applied by pressure ejection to the neuropil of the third abdominal ganglion in the isolated nerve cord of Manduca sexta. Intersegmental muscle motor neurons with dendritic arborizations in the same hemiganglion were inhibited by GABA (Fig. 2) and excited by ACh (Fig. 5).
2. Picrotoxin was a potent antagonist of GABA (Fig. 4A). Bicuculline reduced GABA responses in some motor neurons (Fig. 4C), but had no effect on many other motor neurons. Curare reduced ACh responses (Fig. 6A). Bicuculline was an effective ACh antagonist in most motor neurons tested (Fig. 6B).
3. Motor neurons with dendrites across the ganglion from the ejection pipette exhibited different responses to GABA and ACh. Contralateral motor neurons often showed smaller, delayed hyperpolarizing GABA responses (Fig. 7). On two occasions, contralateral motor neurons had excitatory responses (Fig. 8). Contralateral motor neurons were hyperpolarized by ACh (Fig. 9). The inhibitory responses had only slightly longer latencies than ipsilateral excitatory ACh responses (Fig. 10A). The contralateral inhibitory ACh responses, but not the ipsilateral excitatory ACh responses, were eliminated by TTX (Fig. 10B).
4. A model, which includes inhibitory interneurons that cross the ganglionic midline to inhibit their contralateral homologs and motor neurons (Fig. 11), is proposed to account for contralateral responses to GABA and ACh and antagonistic patterns of activity of motor neurons during mechanosensory reflex responses.

     

Convergence of synaptic influences of contralateral somatic afferents on interneurons in segmental inhibitory pathways to motoneurons

Convergence of contralateral somatic afferent synaptic influences on segmental inhibitory neurons was investigated by intracellular recording of postsynaptic potentials of -motoneurons in experiments on cats. Excitatory synaptic influences of afferents of the contralateral flexor reflex were shown to converge on interneurons of both segmental inhibitory systems studied: afferents of flexor reflex and group Ia muscle afferents. Interneurons of inhibitory systems are exposed not only to excitatory but also to inhibitory contralateral influences. Contralateral inhibitory PSPs of montoneurons are produced through ipsilateral inhibitory systems; a leading role is played by inhibitory neurons of the flexor reflex system of afferents. Inhibitory neurons of the Ia system as a rule do not make an important contribution to generation of contralateral IPSPs.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 476–484, September–October, 1973.     

Colonic Mechanoreceptor Input to Neurons in Guinea Pig Caudal Mesenteric Ganglion

The background activity of pacemaker-like neurons (PLN) of the guinea-pig caudal mesenteric ganglion (CMG) and their reflex responses to colonic distention were studied on combined isolated preparations including the CMG and a colon segment connected with the lumbar colonic nerves. The results allow us to suggest that the spontaneous and reflex activity of PLN is of a peripheral origin. Synaptic transmission in the peripheral colonofugal nerve pathways is mediated by acetylcholine and substance P (SP). The SP-induced excitation of PLN probably involves activation of the tachykinin NK₃ receptors.     

Sound localisation in crickets

Intracellular recordings were made in the brain of the cricket Gryllus bimaculatus from an ascending auditory interneuron (AN1). Acoustic stimuli with calling song temporal pattern were delivered via earphones in a preparation with the acoustic trachea cut (attenuation of crossing sound > 30 dB). The input-output function of this cell was then determined by recording its responses to stimulation of the ipsilateral ear alone, of the contralateral ear alone and to stimulation of both ears simultaneously with the same or different carrier frequencies and intensities.This interneuron was excited by the ear ipsilateral to its axon and dendritic field and unresponsive to stimuli presented to the axon-contralateral ear alone. However, in binaural stimulation experiments, the response to a constant ipsilateral stimulus was progressively reduced as the intensity of a simultaneous contralateral stimulus was increased, above a threshold intensity.Tuning curves for threshold of this inhibition, determined in binaural stimulation experiments, indicated significant inhibition in the range 3–20 kHz with lowest threshold at 4–5 kHz. The inhibition was unaffected by sectioning of the contralateral circumoesophageal or neck connective, indicating that the inhibitory influence crosses the midline at the level of the prothoracic ganglion. Intracellular recordings from AN1 in the prothoracic ganglion confirmed that it was indeed neurally inhibited by inputs from the contralateral ear.Tuning curves for excitation of an omega neuron (ON1) by the ear ipsilateral to its soma and also the tuning of inhibition of ON1 by its contralateral ON1 partner, closely match the tuning of inhibition of AN1 and to a lesser extent, of AN2. This was taken as evidence that each AN1 is inhibited by the contralateral ON1. The significance of this interaction for directional hearing and phonotaxis is discussed.Abbreviations AP/CHP action potentials per chirp - AN1, AN2 ascending auditory interneurons 1, 2 - ON1 omega neuron 1 - ipsi ipsilateral contra contralateral - PTG prothoracic ganglion loc lateral ocellar nerve - On optic nerve an antennal nerve - coc circum-oesophageal connective so sound off     

Lateral ocellar nerve projections in the dragonfly brain

Summary The central projections of the lateral ocellar neurons of the dragonfly were examined using whole nerve cobalt iontophoresis, supplemented by sectioning of the nerve and brain for inspection in the light and electron microscopes. At E.M. level the presence of cobalt in filled axon profiles and cell bodies was confirmed by analysis of X-ray energy spectra in the microscope.The pathways, cell body sites and terminal arborizations of four large (7–25 m diameter) lateral ocellar neurons are described. Two of these fibers arborize in the ipsilateral posterior neuropil of the protocerebrum and two cross the brain and arborize in the contralateral posterior neuropil. Within each half of the posterior neuropil, two spatially separated regions of ocellar input have been identified. These regions receive median ocellar input plus input from either the ipsi- or contralateral ocellus, but not both. The arborizations of the contralateral fibers are more extensive than those of the ipsilateral fibers.One of the contralateral neurons crosses the brain in the region of the protocerebral bridge giving off a collateral in that region before descending to the posterior neuropil. This collateral arborizes almost immediately in a region receiving input from arborizations of a number of small ocellar neurons (those less than 5 m in diameter) from the ipsilateral ocellar nerve, together with small neurons from the median ocellar nerve, forming a region in each half of the brain which receives input from all three ocelli. The small lateral ocellar neurons associated with these arborizations have cell bodies adjacent to the lateral ocellar tracts.This work was supported in part by National Institute of Health Grants 2 RO1 EY-00777 and 1 KO4 EY-00040     

Functional implications of the projections of neurons from individual labellar sensillum of Drosophila melanogaster as revealed by neuronal-marker horseradish peroxidase

Summary Earlier studies using Golgi silver impregnations from the labellar sensilla of adult Drosophila melanogaster revealed seven types of sensory axons projecting into the suboesophageal ganglion of the brain. These sensory terminals were designated as coiled fibres (type-I), shrubby fibres (type-II), ipsilateral ventral fibres (type-III), ipsilateral dorsal fibres (type-IV), contralateral ventral fibres (type-V), contralateral dorsal fibres (type-VI), and central fibres (type-VII). The present study identifies the projections of sensory neurons present in a single labellar taste-sensillum, using the neuronal marker horseradish peroxidase (HRP). Although the taste sensillum in question has five neurons, in a given experiment only one or at the most two neurons are labelled. The type of neuron labelled was usually specific to the stimulant solute (sucrose, sodium chloride or potassium chloride) present in the HRP solution. Although type-II fibres get labelled most of the time, irrespective of the stimulant present in HRP solution, type-IV fibres are labelled when attractants (0.1 M sucrose or 0.1 M sodium chloride) are used as stimulants in HRP solution. Type-VI fibres are labelled when the stimulant is 0.1 M potassium chloride, a repellent. HRP dissolved in distilled water revealed type-I coiled fibres. Besides revealing projections of sensillar neurons to the brain the present technique also inferred their possible function. Incubation of whole-brain tissue with 0.04% 3,3-diaminobenzidine tetrahydrochloride in presence of 0.06% hydrogen peroxide suggested that the glomerular organization is also present in the taste-sensory region as it is in olfactory neuropile.     

The neuronal basis of the anesthetic state: A comparative physiological approach

The sensitivity of specific neuronal pathways to Halothane and N₂O has been investigated in flies. The effects were tested by monitoring the responses of photoreceptors and their second order neurons, as well as two behavioral responses-a leg reflex induced by light flashes and head movements induced by moving optical patterns-chosen because their neuronal substrates are fairly well known. Sensitivity to both agents rises with the length of dendrites and the number of input synapses of the neurons involved. The finding confirms the hypothesis, formulated in Part I of this paper, that neurons with long dendrites and/or axonal endings and large numbers of input synapses are the elements in the central nervous system with the highest sensitivity to anesthetic action. Under physiological conditions this kind of neuron is capable of gain-control: the relationship between input and output is modified according to functional requirements. Possible molecular mechanisms leading to functional impairment under anesthesia are discussed.     

Neuron activities of the motor cortex during conditioned eye blink reflex in rabbits (author's transl)]

Effects of the tone (CS) on neurons of the motor cortex were investigated in naive, pseudoconditioned, and conditioned rabbits. Conditioning to eye blink reflex was made by a combination of CS and air puff (US). Effects of electrical stimulation of the subcortical structures were also observed on the cortical neurons associated with the conditioned reflex. The results were as follows. (1) Proportion of neurons which significantly increased the firing rate in response to the CS, type E, was higher in the conditioned group than in other two groups. On the other hand, no group difference was found in the proportion of neurons which significantly decreased the firing rate to the stimulus, type I. (2) Most of the type E neurons in the conditioned rabbits began to fire at latencies of about 50 to 100 msec after the CS, preceding about 200 msec to the appearance of the peripheral conditioned responses (EMG). (3) Most of the type E neurons in the conditioned animals were more easily affected by stimulation of the medial geniculate body and the brain stem reticular formation. Based on the results mentioned above, it is concluded that in the rabbits conditioned to the eye blink reflex, excitability of neurons in the motor cortex is enhanced by the tone (CS), and by electrical stimulation to the medial geniculate body and the brain stem reticular formation.     

Effect of stimulating periaqueductal gray matter on low- and high-threshold response of pontine and bulbar reticular neurons

Electrical stimulation of the periaqueductal gray matter (PGM) bringing about inhibition of high-threshold mouth-opening reflex on somatosensory response of neurons belonging to the pontine caudal reticular nucleus (CN) and the reticular gigantocellular nucleus (GN) were investigated in cats under light chloralose-induced anesthesia. It was found that inhibitory effects on CN and GN neurons adhered to the principle of control over their main synaptic input: in GN neurons and particularly in high-threshold cells, inhibition mainly affected response to nociceptive stimuli, in contrast to CN neurons, and low-threshold cells in particular, where response to non-nociceptive stimulation was inhibited. The possible mechanisms and functional significance of the effects described are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 749–757, November–December, 1988.     

Contribution of L. Ya. Balonov and V. L. Deglin to Study of Verbal-Thinking Activity from the Viewpoint of Functional Brain Asymmetry

This paper summarized experimental data on the role of the right and left brain hemispheres in performance of the verbal and thinking activity, which were obtained by Lev Yakovlevich Balonov and Vadim L'vovich Deglin and published in numerous articles and monographs. The interpretation of these results, the concepts of Balonov and Deglin on regularities underlying division of functions between two hemispheres and on mechanisms of the hemispheric interaction are presented. The original concept is exposed, which consists in that the functional brain asymmetry is based on different relation of the right and left hemispheres to the language sign, its different vision and perception by each hemisphere. The data of study on the functional brain asymmetry also helped the authors to find answers to the questions concerning general scientific and general human problems dealing with the conscious and the unconscious, speech development in child, evolution of psychic activity. The authors understood clearly that the answers to these questions ...by no means will be exhaustive... and that ...this is merely one of possible points of view.     

Neuron activity in the motor cortex of a cat with inhibition of a conditioned postural change reflex

A study was made of the neuron spike reactions in the primary motor cortex of the cat in the projection zone of the contralateral forelimb with external and internal inhibition of the conditioned reflex for posture change that consisted of shifting the body weight to the forelimb being studied. Spike responses of the neurons to extraneous stimuli and the conditioned signal were determined to a significant degree by the condition of the animal and its habituation to the signal used. In trained animals, the duration of responses to extraneous stimulation was shorter than in the nontrained. With external and internal inhibition, we observed simultaneous disappearance of conditioned reflex movements and the trace spike discharges connected with them. Frequently extraneous stimulations could suppress trace discharges even when learned movement was present. Extraneous stimulations of a different modality inhibited the reflex to different degrees. The change in neuron spike reaction connected with a conditioned reflex change in posture was similar to well-learned local reflex phenomena.A. A. Bogomol'ets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 489–500, July–August, 1985.     

Effects of blockade of noradrenergic and serotonergic transmission in theCM-Pf complex on neuronal activity in the motor thalamus in cats

Effects of injections of blockers of the monoaminergic receptor structures into thecentrum medianum-nucl. parafascicularis (CM-Pf) on the activity of neurons in the motor thalamic nuclei (VA-VL) were studied in chronic experiments on awake cats. The animals were trained to perform an operant placing reflex by the forelimb. Injection of a-adrenoblocker, anapriline, into theCM-Pf resulted in enhancement of background activity of neurons of the motor thalamus and facilitation of their spike responses related to conditioned and unconditioned reflex movements. Application of a blocker of serotonin receptors, lysergoamide, evoked opposite changes in the neuronal activity in theVA-VL nuclei: depression of background activity, facilitation of inhibitory processes, and suppression of evoked activity related to conditioned and unconditioned movements. It is supposed that the monoaminergic system of thelocus coeruleus exerts a suppressing influence on the motor thalamus via theCM-Pf complex, while the system of the raphe nuclei facilitates motor thalamic structures.Neirofiziologiya/Neurophysiology, Vol. 28, No. 6, pp. 305–311, November–December, 1996.     

Detection of rotating gravity signals

It is shown in the preceding paper that neurons with two-dimensional spatio-temporal properties to linear acceleration behave like one-dimensional rate sensors: they encode the component of angular velocity (associated with a rotating linear acceleration vector) that is normal to their response plane. During off-vertical axis rotation (OVAR) otolith-sensitive neurons are activated by the gravity vector as it rotates relative to the head. Unlike one-dimensional linear accelerometer neurons which exhibit equal response magnitudes for both directions of rotation, two-dimensional neurons can be shown to respond with unequal magnitudes to clockwise and counterclockwise off-vertical axis rotations. The magnitudes of the sinusoidal responses of these neurons is not only directionally selective but also proportional to rotational velocity. Thus, responses from such two-dimensional neurons may represent the first step in the computations necessary to generate the steady-state eye velocity during OVAR. An additional step involving a nonlinear operation is necessary to transform the sinusoidally modulated output of these neurons into a signal proportional to sustained eye velocity. Similarly to models of motion detection in the visual system, this transformation is proposed to be achieved through neuronal operations involving mathematical multiplication followed by a leaky integration by the velocity storage mechanism. The proposed model for the generation of maintained eye velocity during OVAR is based on anatomical and physiological properties of vestibular nuclei neurons and capable of predicting the experimentally observed steady-state characteristics of the eye velocity.     

Exogenous glycosaminoglycans (GAG) differentially modulate GAG synthesis by anchorage-independent cultures of the outer cells from neonatal rat calvaria in the absence and presence of TGF-β

In anchorage-dependent (AD) cultures of the outer cell population (OCP) from neonatal rat calvaria, transforming growth factor-₁ (TGF-) specifically upregulated the synthesis of chondroitin sulfate (CS) proteoglycan (PG) and uncoupled the inhibitory effect of increasing cell density on CS PG synthesis (reference #30). Utilizing the same cell population, we have further examined the possibility that glycosaminoglycans (GAG) known to be synthesized and secreted by bone cells might exert feedback effects on GAG synthesis and/or its stimulation by TGF-. Although addition of TGF- alone stimulated net synthesis of HA and CS in both AD and anchorage-independent (AI) cultures, significant alterations of basal and TGF--stimulated GAG synthesis by exogenous GAGs were observed only in AI cultures. In AI cultures exogenously added hyaluronic acid (HA) markedly enhanced the basal synthesis of HA and CS while heparin (H) suppressed the basal synthesis of HA, CS as well as dermatan sulfate (DS). Also, the addition of HA markedly potentiated the stimulation by TGF- of HA and CS synthesis as did heparan sulfate (HS) for CS and DS synthesis. H suppressed the stimulation of the synthesis of HA, CS and DS by TGF-. Overall, our results indicate specific effects of individual GAGs on basal and TGF--stimulated GAG synthesis in OCP cultures. We suggest that some of the GAGs in the OCP microenvironment (which with the exception of HA are covalently linked to protein cores of secreted PGs), acting in concert with TGF-, may serve as an amplification system for upregulating GAG synthesis in the rapidly growing neonatal calvarium.     

Neuronal responses in area 7 of the cat cortex during defensive conditioning

Responses of neurons in area 7 of the parietal association cortex during and after formation of a defensive conditioned reflex to sound were recorded in waking cats. Changes in spike responses of the neurons as a result of the onset of conditioned reflex limb movements were observed in 68% of neurons. Spike responses of neurons formed as a result of learning appeared only if conditioned-reflex limb movements appeared, and they were not observed if, for some reason or other, movements were absent after presentation of the positive conditioned stimulus or on extinction of the reflex. Responses of 46% neurons to conditioned stimulation preceded the conditioned-reflex motor responses by 50–450 msec. The remaining responding neurons were recruited into the response after the beginning of movement. Characteristic spike responses of neurons to the conditioned stimulus appeared 500–900 msec before the beginning of movement and, in the case of appearance of special, "prolonged" motor responses of limb withdrawal, evoked by subsequent reinforcing stimulation.