Coding of vibration by neurones of the dorsal column nuclei in the pigeon

Whereas the function of mechanoreceptors is well known in birds there are no detailed investigations of central processing. Therefore the characteristics of neurones in a first relay, the dorsal column nuclei (nuclei gracilis et cuneatus and the nucleus cuneatus externus), were studied electrophysiologically by recording responses from individual neurones to mechanical stimulation of skin and deep tissue.Of 140 units 84 were cutaneous neurones. The remainder were tap- and deep-neurones. Tap-neurones were activated by sharp brief taps. Activity in deep-neurones was comparable to joint and tendon receptors but not to muscle spindles. Thirty-four cutaneous neurones were vibration sensitive neurones, 36 were slowly adapting neurones and 14 neurones were rapidly adapting and fast habituating cells. Vibration sensitive neurones were most sensitive to 200 to 500 Hz. Frequencies above 100 Hz elicited phase coupled responses.Within the nn. gracilis et cuneatus 61 were cutaneous neurones, 13 were deep-neurones and 7 were tap-cells. Within n. cuneatus externus 17 were cutaneous units, 21 were deep-neurones and 11 were tap-neurones. No vibration sensitive neurones were found within n. cuneatus externus. This means that coding for vibration is represented in the nn. gracilis et cuneatus.Abbreviations CE n. cuneatus externus - DCN dorsal column nuclei - GC n. gracilis et cuneatus - HC Herbst corpuscle - PH phasic and habituating - Imps./s Impulses per second - INTH interval histogram - PSTH peristimulus time histogram - PHASE Phase histogram - RF receptive field - SA slowly adapting - Vec. vector strength     

Afferent connections of the nuclei of dorsal columns of spinal cord

The authors studied structural origins of the conduction of the dorsal chord afferent projections to contralateral dorsal column nucleus in cats, which were discovered after foreleg electrical stimulation by the evoked responses method. This evoked responses remain after unilateral section of the medial lemniscus. It was shown the existence of not classical connections which cross to another side at the level of spinal cord and caudal division of brain stem. The discovery fibres contact with other projection systems and form all known types of interneuronal contacts.     

Structural-functional connections of the lemniscus system with the caudate nucleus in the cat

Afferent projections were studied of nuclei of the spinal cord dorsal columns to the caudate nuclei. Evoked potentials (EPs) were recorded in the caudate nuclei and the nuclei of dorsal columns of the spinal cord to stimulation of the forelimb against the background and after unilateral elimination of the medial lemniscus. After the section, the EPs in the recorded nuclei sharply intensified in response to stimulation of the forelimb, ipsilateral to the section. Degenerative changes were also shown by electron microscopy in axonal terminals in the caudate nuclei at the operated side. Conclusion is drawn that the caudate nuclei receive direct connections from the contralateral nuclei of the spinal cord dorsal columns, which probably, conduct mainly kinesthetic afferent influences.     

Responses of septal nuclei neurons to microiontophoretically administered putative neurotransmitters

In halothane anesthetized rats, neurons of the medial and lateral septal nuclei were tested with iontophoretically applied putative neurotransmitters. GABA, norepinephrine, serotonin, and acelycholine in roughly this order of potency were inhibitory with respect to spontaneous and evoked activity of both medial and lateral septal nuclei cells. No specific effects of any of the compounds were observed on septal unit responses to fornix or fimbria stimulation.     

Pharmacological analysis of conditioning in sensorimotor cortex neurons in a model

In awake mobile rabbits, with electrodes implanted in the medial lemniscus, midbrain tegmental reticular nucleus, and pyramidal tract, combined stimulation of two brain of two brain structures resulted in elaboration of conditional connections in sensorimotor cortex neuronal populations. The main criterion of the conditioning was the appearance of changes in the neuronal activity on omission of the second stimulus. These changes represented a complex of electrical events, some of which were similar to and others different from the evoked responses to the second stimulus. Application of atropine, sulfate, chlorpromazine hydrochloride, serotonin creatinine sulfate, and gamma-aminobutyric acid (GABA) to the cortex at the site of the recording exerted a modulating effect on the conditional neuronal activity patterns. Of the above substances, GABA and atropine had the most pronounced effect. The GABA removed the short-latency components of the conditional changes which were similar to evoked responses. The atropine abolished the long-latency changes which differed from evoked responses.     

Effect of GABA on a temporary connection in a neuronal population of the sensorimotor cortex in rabbits

Evoked activity of sensorimotor cortical neurones in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum; driving reaction of cortical neurones at stimulation of these brain structures of growing frequency, and conditioned reflexes elaborated by combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation were studied in awake nonimmobilized rabbits. Application to the cortex of GABA solutions of low concentration (less than or equal to 1%) emphasizes the evoked neuronal responses, facilitates the appearance of driving reaction and contributes to the manifestation of the temporary connection. Application of GABA solutions of higher concentration (greater than 2%) leads to opposite effects. Positive correlation is found between electrical and behavioural phenomena. The described experimental approach may be used for analysis of various types of influences on temporary connection formation.     

Changes in somatosensory evoked potentials following an experimental focal ischaemic lesion in thalamus

Experiments have been performed to produce localized thalamic ischaemia in baboons anaesthetised with alpha-chloralose. Somatosensory evoked potentials to median nerve stimulation were recorded in the medial lemniscus. VPL of thalamus and the primary somatosensory cortex. Local blood flow was also recorded by the hydrogen clearance technique in these regions. The early potential recorded in thalamus has been shown to be generated from 3 sources: (i) a positivity generated outside the VPL, (ii) local wavelets, most likely from synaptic activity close to the recording electrode, and (iii) a local overall negativity. The first of these potentials alone remains after thalamic ischaemia. It arises below the level of the thalamus, being very likely generated by the afferent volley in the medial lemniscus, and is seen in the surface-recorded response as the early component P8 (corresponding to P15 in the human).     

Behavioural and cardiovascular responses to electrical stimulation of the medulla oblongata of the cat

Effects of stimulation of the nucleus tractus solitarii, the dorsal motor nucleus of the vagus, the nucleus reticularis paramedianus, and the nucleus cuneatus were studied in free-moving cats. Stimulation of the medullary nuclei that are known to be involved in the central nervous control of cardiovascular functions might activate preprogrammed motor responses such as licking and sniffing, and induce complex behavioural response patterns such as sleep or flight reaction. Moreover, both lever-pressing for rewarding brain stimulation, and eating in food deprived cats might be modulated by these stimulations. In a shuttle box the cats showed no tendency toward shuttling during stimulation, except the stimulation of the nucleus reticularis paramedianus which produced aversion. The cardiovascular and respiratory effects varied parallel with the behavioural responses. It is concluded that the medullary nuclei related to visceral functions are capable of affecting somatomotor behaviour either directly on the motor system, or by inducing complex response patterns in which somatomotor and visceral responses are integrated.     

Effects of GABA and picrotoxin on temporary bonds in neuronal populations of the motor cortex

The paired stimulations of some brain structures (the medial lemniscus, the reticular nucleus of the midbrain tectum, and the pyramidal tract) resulted in the formation of temporary bonds in the neuronal populations of the motor cortex of the non-immobilized awake rabbits. The changes in the neuronal impulsation observed in the absence of the supporting stimuli were used as the criteria of establishment of the temporary bond. The changes consisted of the elements reproducing an initial response pattern and generation of impulse sequences that appeared later and differed in their configuration from the responses evoked by the real stimuli. The application of GABA directly to the site from which the neuronal activity was recorded blocked the former changes and significantly facilitated the latter ones. Picrotoxin antagonized the GABA effect only in relation to the late rearrangements of the impulse activity (generation of the sequences that differed from the responses evoked by stimulation).Neirofiziologiya/Neurophysiology, Vol. 26, No. 2, pp. 115–121, March–April, 1994.     

HISTOCHEMICAL MAPPING OF LACTATE DEHYDROGENASE AND MONOAMINE OXIDASE IN THEMEDULLA OBLONGATA AND CEREBELLUM OF SQUIRREL MONKEY (SAIMIRI SCIUREUS)

Abstract— —The gross distribution of LDH and MAO was studied in a caudo-cranial series of 50 μ thick sections through the medulla oblongata and cerebellum. In general, LDH exhibited a stronger reaction in the neuropil and in the perikarya, whereas MAO showed moderate activity in the neurons and mild to moderate activity in the neuropil. The axonal processes and nerve fibres showed comparatively stronger MAO activity. The nuclei gracilis, cuneatus medialis and lateralis, cranial nerve nuclei, olivaris inferior, vestibularis and cochlearis nuclei showed particularly strong LDH and equally weak MAO activities. The lateral part of the formato reticularis myelencephali showed much more MAO than did the medial part, whereas the LDH reaction was uniformly strong. The reticularis lateralis showed uniformly strong LDH and very mild MAO activities.
In the cerebellar cortex, the MAO activity was concentrated in the molecular layer and nerve fibre layer, whereas LDH activity was particularly strong in the Purkinje cells and their processes in the molecular layer. The cerebellar nuclei showed strong LDH and weak MAO in the neutrons and stronger MAO and moderate LDH in the neuropil.     

Changes in the effect of acetylcholine on septo-hippocampal reactions after serotonin administration to rabbits

Impulse activity and focal evoked potentials appearing in the hippocampus in response to testing stimuli applied to the septum medial nucleus were recorded in nonimmobilized and unanaesthetized rabbits. The efficiency of acetylcholine (ACh) action on septo-hippocampal reactions was tested before and after microiontophoretic administration of the serotonin (5-OT) or stimulation of the raphe nuclei. The 5-OT and raphe stimulation produced significant changes in the ACh action on septo-hippocampal reactions. In most cases, after microiontophoretic administration of 5-OT, the efficiency of ACh diminished, independently of excitatory or inhibitory effect of the 5-OT. Thus, the modulating action of 5-OT consists not only in protracted trace changes of the magnitude of septo-hippocampal reactions but also in trace reduction of septo-hippocampal responses to ACh.     

Unit responses of the medial group of thalamic nuclei to stimulation of the frontobasal regions of the neocortex

In acute experiments on cats anesthetized with pentobarbital and chloralose, single-unit and focal responses of the medial group of thalamic nuclei (mediodorsal, central lateral, paracentral, central medianum, parafascicular) were studied to stimulation of the frontobasal regions of the cortex (proreal, posterior orbital, basal temporal regions). Depending on the number of neurons responding to cortical stimulation and on the length of the latent period of the responses three functionally heterogeneous subdividions of the medial nuclei were distinguished; the parvocellular and magnocellular portions of the mediodorsal nucleus and the intralaminar nuclei with the parafascicular complex. On the basis of responses of neurons activated antidromically by stimulation of the same cortical region and synaptically by stimulation of another region, the concept of the integrative function of nuclei of the medial group, integrating the frontobasal zones of the neocortex with the aid of neuron circuits in which the medial nuclei are included, is argued.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 11–18, January–February, 1977.     

Effect of strychnine on the neuronal reactivity of the sensorimotor cortex and the temporary connection in rabbits

On awake nonimmobilized rabbits, evoked activity was studied of the sensorimotor cortex neurons in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum by stimuli of different frequencies, and driving reaction of cortical neurons to stimulation of these brain structures by series of stimuli of increasing frequency. Conditioned reflexes were also studied, established on the basis of combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation. Application of the cortex of low concentration of strychnine solutions (less than 1%) heightened neurons reactivity and provides for the formation of temporary connection. Application of strychnine solutions of higher concentration (greater than 1%) led to opposite effects. Interconnection of electrical and behavioural effects is discussed.     

Effect of serotonin on cholinergic septo-hippocampal reactions in the rabbit

In noncurarized and unanaesthetized rabbits, the unit activity and field potentials evoked by testing stimulation of the medial septum were studied before, during (3-10 min), and in different periods (up. to 0.5 h) after microiontophoretic serotonin (5-OT) application or n. Raphe stimulation. In most of the cases, just during 5-OT application or n. Raphe stimulation, cholinergic septo-hippocampal responses decreased. Trace facilitatory effect of native and exogenously applied 5-OT on these responses was found. Increase of efficiency of cholinergic excitatory input was considered as a confirmation of the role of the serotonergic system in hippocampal long-term posttetanic potentiation after the stimulation of the medial septum. On the whole the data obtained indicate a complex modulatory 5-OT influence on the cholinergic septo-hippocampal responses.     

Hemodynamic changes during electrical stimulation of some bulbar cardiovascular structures

The effect of electrical stimulation was studied on the nucleus of the tractus solitarius, the nucleus cuneatus, and the dorsal motor nucleus of the vagus nerve, i.e., structures of the bulbar cardiovascular sector in which it has been postulated that impulses from the sinoaortic reflexogenic zone are relayed to the cardiovascular system. Stimulation of all the structures tested in acute experiments on cats under chloralose-Nembutal anesthesia evoked depressor responses of varied degree, the hemodynamic basis of which was a decrease in the cardiac output (CO). The effect of stimulation of the nucleus cuneatus on the development of the negative chronotropic effect was observed. The dorsal motor nucleus of the vagus nerve in cats is not the only or even the principal zone from which negative chronotropic influences are exerted on the heart.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.3, No.6, pp.631–636, November–December, 1971.     

Uptake and Release of d-Aspartate, GABA, and Glycine in Guinea Pig Brainstem Auditory Nuclei

Abstract: This study attempts to determine if the medial (MSO) and lateral superior olive (LSO), medial nucleus of the trapezoid body (MNTB), ventral nucleus of the lateral lemniscus (VNLL), and central nucleus of the inferior colliculus (ICc) contain glutamatergic synaptic endings. Micropunch and microdissection procedures provided fresh samples of these auditory nuclei for the measurement of the high-affinity uptake and electrically evoked release of exogenous d -[³H]ASP. The study also determined if the LSO and MSO contain glycinergic synaptic endings by measuring uptake and release of [¹⁴C]-Gly in these nuclei, and whether the MNTB, VNLL, and ICc contain GABAergic endings by assessing the uptake and release of [¹⁴C]GABA in these structures. Several strategies optimized the evoked Ca²⁺-dependent release of the labeled amino acids. These included the enhancement of high-affinity uptake during loading of the markers into the tissues, inhibition of uptake during the subsequent measurement of release, and use of an electrical stimulus current that evoked maximal Ca²⁺-dependent release. Each of these nuclei manifested the high-affinity uptake and the evoked Ca²⁺-dependent release of d -[³H]Asp, suggesting the presence of synaptic endings that may use Glu or Asp as a transmitter. Similar findings suggest the presence of glycinergic synaptic endings in the LSO and MSO, and of GABAergic synaptic endings in the MNTB, VNLL, and ICc.     

Frequency tuning and response latencies at three levels in the brainstem of the echolocating bat,Eptesicus fuscus

To determine the level at which certain response characteristics originate, we compared monaural auditory responses of neurons in ventral cochlear nucleus, nuclei of lateral lemniscus and inferior colliculus. Characteristics examined were sharpness of frequency tuning, latency variability for individual neurons and range of latencies across neurons.Exceptionally broad tuning curves were found in the nuclei of the lateral lemniscus, while exceptionally narrow tuning curves were found in the inferior colliculus. Neither specialized tuning characteristic was found in the ventral cochlear nuclei.All neurons in the columnar division of the ventral nucleus of the lateral lemniscus maintained low variability of latency over a broad range of stimulus conditions. Some neurons in the cochlear nucleus (12%) and some in the inferior colliculus (15%) had low variability in latency but only at best frequency.Range of latencies across neurons was small in the ventral cochlear nucleus (1.3–5.7 ms), intermediate in the nuclei of the lateral lemniscus (1.7–19.8 ms) and greatest in the inferior colliculus (2.9–42.0 ms).We conclude that, in the nuclei of the lateral lemniscus and in the inferior colliculus, unique tuning and timing properties are built up from ascending inputs.Abbreviations AVCN anteroventral cochlear nucleus - BF best frequency - CV coefficient of variation - DCN dorsal cochlear nucleus - FM frequency modulation - IC inferior colliculus - NLL nuclei of lateral lemniscus - PSTH post stimulus time histogram - PVCN posteroventral cochlear nucleus - SD standard deviation - SPL sound pressure level - VCN ventral cochlear nuclei - VNLLc ventral nucleus of the lateral lemniscus, columnar division     

Steady-state auditory evoked potentials (SSAEPs) in the rabbit. Contribution of the inferior colliculus

Steady-state auditory evoked potentials (SSAEPs) were recorded in rabbits with both surface and depth electrodes. Surface recording from the bregma provided the largest and most typical SSAEPs as compared to other surface locations when a stimulus rate of 50 Hz was used. The medial geniculate body (MGB) showed no potential corresponding to the surface SSAEP. On the other hand, the latency of SSAEP in the inferior colliculus (IC) corresponded closely to that of the surface potential. Furthermore, the amplitude of the IC potential tended to become large with the stimulus rate of 50 Hz as compared with transient stimuli. Although other auditory nuclei in the brain-stem, the ventral nucleus of the lateral lemniscus, the trapezoid body and the auditory nerve responded to transient stimuli with an amplitude larger than that of the IC, no amplification occurred with 50 Hz stimuli in these nuclei. These findings suggest that the IC contributes to the generation of SSAEP to a great extent.     

Depression of evoked potentials in rat thalamic ventro-basal complex and somatosensory cortex after reticular stimulation

Experiments on unanesthetized rats immobilized with D-tubocurarine showed that electrical stimulation (100/sec) of the central gray matter and the mesencephalic and medullary reticular formation considerably depressed potentials in the somatic thalamic relay nucleus and somatosensory cortex evoked by stimulation of the forelimb or medial lemniscus. The mean threshold values of the current used for electrical stimulation of these structures did not differ significantly and were 70 (20–100), 100 (20–120), and 120 (50–200) µA, respectively. On comparison of the amplitude-temporal characteristics of inhibition of evoked potentials during electrical stimulation of the above-mentioned structures by a current of twice the threshold strength, no significant differences were found. Immediately after the end of electrical stimulation the amplitude of the cortical evolved potential and the post-synaptic components of the thalamic evoked potential was 50–60% (P<0.01) below the control values. The duration of this depression varied from 0.5 to 1 sec. An increase in the intensity of electrical stimulation of brain-stem structures to between three and five times the threshold led to depression of the presynaptic component of the thalamic evoked potential also. Depression of the evoked potential as described above was found with various ratios between the intensities of conditioning and testing stimuli.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 467–475, September–October, 1976.     

Theta driving both inhibits and potentiates the effects of nicotine on dentate gyrus responses

The medial septal area of conscious rats was stimulated through previously implanted electrodes at a frequency of 7.7 Hz for 20 min each day for 7 days to evoke rhythmic slow activity in CA1 at a similar frequency to spontaneous theta. Two weeks later in the anaesthetized rats the effects of a single subcutaneous injection of nicotine (0.4 mg x kg(-1)) on fEPSPs, evoked in the dentate gyrus by separate stimulation of the MPP and LPP, were studied and compared with those obtained in controls. Nicotine increased the firing of locus coeruleus neurones and the slope of the fEPSPs evoked by LPP stimulation, but not by MPP stimulation. Prior theta driving considerably increased the effect of nicotine on the responses evoked by stimulation of the MPP and abolished the nicotine-induced potentiation of the responses evoked by stimulation of the LPP. The results are attributed to theta driving increasing the amount of noradrenaline released by nicotine and to noradrenaline producing a beta-adrenoceptor long-lasting potentiation at the medial perforant path synapse and a long-lasting depression at the lateral perforant path synapse.