Cortico-hippocampal relation of electrical activity during a motor polarization dominant in rabbits

By the method of spectral-coherent analysis, the intercentral relations were studied of the electrical activity of the sensorimotor and premotor cortices and of CAs field of the dorsal hippocampus of both hemispheres during the motor polarization dominant, created by the action of the direct current on the rabbits sensorimotor cortical area. The formation was shown of a new structure of the intercentral relations of electrical activity of the sensorimotor cortex and CA3 of the dorsal hippocampus. It should be noted that the dominant optimum and its inhibition are characterized by different interhippocampal relations: at the optimum a low range of the theta-rhythm is highly coherent while at the activation of "the non-dominant" hemisphere--a high range.     

Coherent analysis of the electrical activity of the rabbit brain during the formation of a motor polarization dominant

By the method of spectral-coherent analysis the dynamics was studied of successive changes in the structure the rabbit brain electrical activity coherent relations in the process of formation of motor polarization dominant created by DC anode action on the sensorimotor cortical region. It has been shown that at earlier stages, when the motor "dominant" reaction is absent, there appears an interhemispheric asymmetry in Coh spectra of electrical activity of the sensorimotor cortex and of the thalamus VPL. On the contrary, interhemispheric asymmetry in Coh spectra of electrical activity of the sensorimotor cortex and dorsal hippocampus CA3 field appears only at the stage when the motor "dominant" reaction is recorded. Asymmetry in alpha- and beta-frequencies ranges in biopotentials Coh spectra of the studied regions coinciding with the motor "dominant" reaction realization is connected with processes of movement organization.     

Evoked potentials in the reticular formation of the rabbit midbrain during formation of a dominant focus in it

During creation of a dominant focus in the midbrain reticular formation (RF) by its multiple stimulation with a high-frequency current (stimulation frequency 200 Hz, pulse duration 0.1-0.5 ms, voltage 1-3 V, duration 5 s) a statistically significant increase of the amplitude of the evoked potential (EP) in RF to light flashes was revealed in comparison with background data. Significant increase of EP amplitude was also observed in RF in response to the same stimuli applied in successive experiments without RF stimulation, which pointed to the existence of a latent dominant focus in the CNS.     

Modulation of the neuronal activity and evoked potentials of the cerebral cortex by stimulation of the dorsal hippocampus]

In experiments on alert rabbits high frequency stimulation of the CA1 field of the dorsal hippocampus reduced the peak latency of the main negative component of the evoked potential (EP) to a light flash in the sensorimotor and occipital tests areas of the cerebral cortex. A single stimulation of the same part of the hippocampus resulted in a gradually developing facilitation of secondary negativity of the EP 5th component, predominantly in the sensorimotor cortex. Investigation of neuronal responses in the same cortical areas to a stimulation of the CA1 field with different parameters has shown that the effects of EP modulation are due to dynamic reorganizations of cortical neuronal activity.     

Effect of hippocampal stimulation on the feeding behavior of cats

Influence of electrical stimulation (100 cps., 1.0 ms) of medial parts of dorsal and ventral hippocampus (field CA1), and the lateral parts of dorsal and posterior hippocampus (field CA3) on general behaviour, elaboration of instrumental and manifestation of delayed reactions was studied in chronic experiments on cats. Stimulation of medial parts of dorsal and ventral hippocampus elicited a reaction of orienting reflex type to natural stimuli. Stimulation of lateral parts of dorsal and posterior hippocampus evoked arrest reactions. Medial and lateral parts of hippocampus produced different influences on elaboration of conditioned reflexes. In the first case elaboration was possible, but developed slower, while in the second case the ability to learn during stimulation was completely lost due to development of arrest reaction. Stimulation of different parts of the hippocampus disturbed delayed reactions, reducing the number of correct responses.     

Attenuation of phrenic motor discharge by phrenic nerve afferents

Short latency phrenic motor responses to phrenic nerve stimulation were studied in anesthetized, paralyzed cats. Electrical stimulation (0.2 ms, 0.01-10 mA, 2 Hz) of the right C5 phrenic rootlet during inspiration consistently elicited a transient reduction in the phrenic motor discharge. This attenuation occurred bilaterally with an onset latency of 8-12 ms and a duration of 8-30 ms. Section of the ipsilateral C4-C6 dorsal roots abolished the response to stimulation, thereby confirming the involvement of phrenic nerve afferent activity. Stimulation of the left C5 phrenic rootlet or the right thoracic phrenic nerve usually elicited similar inhibitory responses. The difference in onset latency of responses to cervical vs. thoracic phrenic nerve stimulation indicates activation of group III afferents with a peripheral conduction velocity of approximately 10 m/s. A much shorter latency response (5 ms) was evoked ipsilaterally by thoracic phrenic nerve stimulation. Section of either the C5 or C6 dorsal root altered the ipsilateral response so that it resembled the longer latency contralateral response. The low-stimulus threshold and short latency for the ipsilateral response to thoracic phrenic nerve stimulation suggest that it involves larger diameter fibers. Decerebration, decerebellation, and transection of the dorsal columns at C2 do not abolish the inhibitory phrenic-to-phrenic reflex.     

Interactions between electrical activities of the sensomotor cortex and the hippocampus during 'animal hypnosis' in rabbits

The electrical activity of the left and right sensorimotor cortex and left and right dorsal hippocampus (CA3 fields) was recorded during "animal hypnosis" in rabbits. The "animal hypnosis" produced asymmetry in the spectral power of the hippocampal electrical activity due to an increase in the power of delta 1, delta 2, and theta 1 components in the left-hippocampus and decrease in the spectral power in the same ranges in the right-hippocampus. Hemispheric asymmetry in the electrical activity during the "animal hypnosis" was also expressed in the indices of coherence between the sensorimotor cortex and hippocampus. EEG coherence between the left sensorimotor cortex and left hippocampus in the delta 1, theta 1, and theta 2 ranges was higher than that between the right-side structures.     

An analysis of the differences in the effects of diazepam on the EEG of noninbred white rats with high and low expression of anxiolytic action in a conflict situation]

The effects of diazepam (5 mg/kg, i.p.) on the EEG power spectra of the sensorimotor cortex and the dorsal hippocampus were studied in albino rats with different types of conflict behaviour. "Active" rats were characterized by domination of the theta-activity in their background cortical EEG-spectra, "passive" ones--by that of the delta-activity. No differences were revealed in the background hippocampal EEG-spectra. Diazepam produced slowing of the theta-activity and increased the beta-activity in a band of 12-32 Hz in "active" rats and that in a band of 12-16 Hz in "passive" ones. The finding is usefull for studying individual animal sensitivity to drugs effects.     

Involvement of the GABAergic Septo-Hippocampal Pathway in Brain Stimulation Reward

The hippocampus is a structure related to several cognitive processes, but not very much is known about its putative involvement in positive reinforcement. In its turn, the septum has been related to instrumental brain stimulation reward (BSR) by its electrical stimulation with trains of pulses. Although the anatomical relationships of the septo-hippocampal pathway are well established, the functional relationship between these structures during rewarding behaviors remains poorly understood. To explore hippocampal mechanisms involved in BSR, CA3-evoked field excitatory and inhibitory postsynaptic potentials (fEPSPs, fIPSPs) were recorded in the CA1 area during BSR in alert behaving mice. The synaptic efficiency was determined from changes in fEPSP and fIPSP amplitudes across the learning of a BSR task. The successive BSR sessions evoked a progressive increase of the performance in inverse relationship with a decrease in the amplitude of fEPSPs, but not of fIPSPs. Additionally, we evaluated CA1 local field potentials (LFPs) during a preference task, comparing 8-, 20-, and 100-Hz trains of septal BSR. We corroborate a clear preference for BSR at 100 Hz (in comparison with BSR at 20 Hz or 8 Hz), in parallel with an increase in the spectral power of the low theta band, and a decrease in the gamma. These results were replicated by intrahippocampal injections of a GABA_B antagonist. Thus, the GABAergic septo-hippocampal pathway seems to carry information involved in the encoding of reward properties, where GABA_B receptors seem to play a key role. With regard to the dorsal hippocampus, fEPSPs evoked at the CA3-CA1 synapse seem to reflect the BSR learning process, while hippocampal rhythmic activities are more related to reward properties.     

Spectral correlation analysis of the potentials of the neocortex and certain subcortical structures during low-frequency electrical stimulation of nonspecific thalamic nuclei]

The spectral-correlation analysis of biopotentials in the cortex and some other brain structures (the anteroventral thalamic nucleus, dorsal hippocampus, lateral geniculate body, mid-brain reticular formation), in chronic experiments on alert rabbits, revealed that during electrical stimulation of thalamic mid-line nuclei within the ranges of 1-3, 4-7 and 8-10 c/s, there occured a rearrangement of the EEG frequencies; a dominant, narrow-band peak at the stimulation frequency, appeared. The coherence of the biopotentials of different cortical areas, of the cortex and subcortical formations increased during the stimulation at the frequency of the stimulation, reaching maximum values between the potentials of the visual and sensorimotor cortical areas.     

Hippocampal afterdischarges and localization of the stimulating electrodes

Electrically evoked hippocampal afterdischarges are used as a model of partial epileptic seizures with a complex symptomatology and for testing anticonvulsants and toxic substances. Stimulating electrodes were implanted in the dorsal hippocampus of 16 laboratory rats and when the animals had recovered they were stimulated (15-s series, 8 Hz, pulse length 1 ms) with a voltage double the threshold value for a tissue response. The following features of the evoked afterdischarge were evaluated: the duration of the first phase of the afterdischarge, the duration of the non-active interphase, the duration of the second phase and the number of "wet dog shakes" (a constant accompaniment of hippocampal afterdischarges). Localization of the electrodes in the CA1 (n = 7) and CA3 (n = 7) region of the hippocampus made no difference to these parameters and in both cases the measured and evaluated data were the same. The afterdischarges were always accompanied by a marked orientation reaction. The study showed that when using macroelectrodes to stimulate the dorsal hippocampus, their localization in the CA1/CA3 is not of critical importance.     

Frequency potentiation in the neonatal rabbit hippocampus

The formation of properties of frequency potentiation in the entorhinal afferent pathway of the hippocampus was studied in unanesthetized rabbits aged from 1 to 15 days. In areas CA₁ and CA₃ of the dorsal hippocampus in newborn rabbits repetitive (1–20 Hz) electrical stimulation of the perforant path led to an increase in amplitude of the slow wave of the field potential by 20–100% compared with the control and to an increase in the probability of response discharges from the neurons from 0–0.5 in the control to 0.8–1.0 during tetanization. In rabbits aged 2–3 days potentiation was more marked at a frequency of 4–6 Hz, whereas depression of the responses developed rapidly to a higher frequency of stimulation. The frequency optimum of 4–15 Hz was established on the 5th day. Potentiation of the first component of the field potential was observed starting from the 8th–10th day of life. The experimental results show that the property of frequency potentiation in the cortical afferent connections of the hippocampus is found in rabbits actually at birth, and it acquires the adult form at the beginning of the second week of life.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 533–539, November–December, 1979.     

Measurements of intracellular free Ca2+ in mammalian central neurons

Neutral carrier-containing Ca2+-selective microelectrodes were used to record the cytoplasmic free Ca2+ concentration [( Ca2+]i) in spinal cells in cats and in hippocampal cells of rats (in situ). The mean [Ca2+]i in motoneurons was close to 1 microM. Antidromic or direct stimulation for 30 s at 10 Hz increased [Ca2+]i by a mean of 90 nM. Such a small increase in [Ca2+]i and its slow decay (with a mean half-time of 23 (SD +/- 14.5) s) indicate very effective intracellular sequestration of Ca2+. Orthodromic stimulation consistently evoked smaller increases in [Ca2+]i. A much larger rise of interneuronal [Ca2+]i was evoked by stimulation of dorsal roots: by contrast intra-axonal recording (in motor or sensory fibres) failed to reveal any increase in [Ca2+]i in response to stimulation at 100 Hz. In the hippocampus, presumably because of poorer recording conditions, resting values of [Ca2+]i were higher (mean 8.5 microM). Repetitive stimulation of the fimbria--commissure at 5-20 Hz for 30 Hz, had variable effects on [Ca2+]i. Very large increases (to greater than 200 microM) were elicited repeatedly in some cells, either near the end of the tetanic stimulation or after a 20-30 s delay. Such major increases, which were associated with population cell discharges in bursts, may be related to long-term changes in hippocampal neuronal properties that are evoked by tetanic stimulation. Both in the spinal cord and the hippocampus, probable intraglial recordings showed relatively high mean levels of [Ca2+]i (about 30 microM).     

Motor polarization dominance and "animal hypnosis"

Two kinds of dominanta were simultaneously formed under conditions of chronic experiments in rabbits. The motor polarization dominanta was formed under exposure of the right sensorimotor cortex of an animal to direct anodic current, and the state of "animal hypnosis" (the second dominanta) was induced. Animal behavior and electrophysiological characteristics were recorded. It was shown that the "animal hypnosis" induced at the optimum of the right motor polarization dominanta inhibited the motor reaction of the "dominant" extremity to testing stimuli. After the "animal hypnosis session, exposure of the right sensorimotor cortex to anodic current produced the latent excitation focus, which did not reach the level of summation. Two days later, exposure to testing stimuli developed the latent foci at first in the right cortex and then in subcortical structures. In the course of recovery of the motor polarization dominanta and its further change for the state characteristic of the "animal hypnosis", the patterns of cortical EEG coherence in the delta range typical of each kind of dominanta alternated in parallel with the time course of state changes.     

磷酸化钙/钙调蛋白依赖性蛋白激酶Ⅱ在大鼠脊髓背角C-纤维诱发电位长时程增强的诱导和维持中的作用

实验旨在探讨钙/钙调蛋白依赖性蛋白激酶II(calcium／calmodulin-dependent protein kinase Ⅱ,CaMKⅡ)在脊髓背角C-纤维诱发电位长时程增强(long—term potentiation,LTP)的诱导和维持中的作用。用Western blot技术分别检测LTP形成30min和3h脊髓背角(L4-L6)CaMKⅡ的含量及其磷酸化水平。同时观察脊髓局部给予CAMKⅡ选择性抑制剂KN-93后对脊髓背角LTP和CaMKII磷酸化的影响。观察结果如下：(1)诱导LTP后30min,CaMK Ⅱ的磷酸化水平明显高于对照组,而CaMKⅡ的总量无变化;诱导LTP后3h CaMKⅡ的磷酸化水平进一步升高。而且CaMKⅡ的总量也明显增加(n=4);(2)强直刺激前30min于脊髓局部给予CaMKⅡ的特异性抑制剂KN-93(100μmol/L),可阻断LTP的诱导,同时明显抑制CaMKⅡ的磷酸化水平;(3)诱导LTP后30min给予KN-93,可显著抑制LTP的维持,同时CaMKⅡ的磷酸化水平与未用药组相比也明显降低（n=3);(4)LTP3h后给予KN-93,LTP的幅值不受影响,磷酸化的CaMKⅡ的含量与用药前相比也无差别（n=3)。根据上述实验结果可以认为,CaMKⅡ的激活参与脊髓背角C-纤维诱发电位LTP的诱导和早期维持过程。     

Long-term potentiation in the dentate gyrus of the anaesthetized rat is accompanied by an increase in extracellular glutamate: real-time measurements using a novel dialysis electrode

We have used a glutamate-specific dialysis electrode to obtain real-time measurements of changes in the concentration of glutamate in the extracellular space of the hippocampus during low-frequency stimulation and following the induction of long-term potentiation (LTP). In the dentate gyrus, stimulation of the perforant path at 2 Hz for 2 min produced a transient increase in glutamate current relative to the basal value at control rates of stimulation (0.033 Hz). This activity-dependent glutamate current was significantly enhanced 35 and 90 min after the induction of LTP. The maximal 2 Hz signal was obtained during post-tetanic potentiation (PTP). There was also a more gradual increase in the basal level of extracellular glutamate following the induction of LTP. Both the basal and activity-dependent increases in glutamate current induced by tetanic stimulation were blocked by local infusion of the N-methyl-D-aspartate receptor antagonist D-APV. In areas CA1 and CA3 we were unable to detect a 2 Hz glutamate signal either before or after the induction of LTP, possibly owing to a more avid uptake of glutamate in the pyramidal cell fields. These results demonstrate that LTP in the dentate gyrus is associated with a greater concentration of extracellular glutamate following activation of potentiated synapses, either because potentiated synapses release more transmitter per impulse, or because of reduced uptake by glutamate transporters. We present arguments favouring increased release rather than decreased uptake.     

Application of the glycine labelling method to the cerebellum, hippocampus and spinal cord

3H-glycine was applied to the cat cerebellar cortex under resting conditions and during inferior olive stimulation which activated the climbing fiber system on a restricted area. Electric recording was made. The autoradiograms showed, that under resting condition labelled glycine was incorporated mainly in granule, Golgi and basket cells and only a few Purkinje and stellate cells were active. Also cerebellar glomeruli remained without labelling. On climbing fiber stimulation Purkinje cells became activated singly and grouped, also Golgi and stellate cells increased in number. Granule cells were totally inhibited. 3H-glycine, when applied to the rat hippocampus, the dentate gyrus, CA1 and CA4 fields showed labelling at low frequency stimulation. When 400 Hz high frequency stimulation periods were interposed, long-term potentiation ensued. The overall labelling of each hippocampal region was intensified significantly, indicating that glycine incorporation may be a sign not only of excitation but also of long-term potentiation. 3H-glycine was applied to frog spinal cord during rest and dorsal root stimulation. Interneurons and motor neurons excited by the afferent fibers showed intensive glycine uptake. It is concluded that the glycine labelling method is suitable for detecting neural excitation in the structures dealt with in this paper.     

Participation of the hippocampus in regulating a pathologic inactive motor reaction in dogs

A local pathological inert motor reaction, involving a forced flexion of the forepaw, was formed after simultaneous stimulation with NaCl solution of a part of the tongue brought out to the cheek and electrical stimulation of the forepaw. The reaction decreased (by 70 to 80%) after electrical stimulation of the dorsal hippocampus (beyond CA3). At the same time the animal's emotional stress diminished, as evidenced by the reduced heart rate and a reduced theta-rhythm in the hippocampus.     

Mechanisms of gamma oscillations in the hippocampus of the behaving rat

Gamma frequency oscillations (30-100 Hz) have been suggested to underlie various cognitive and motor functions. Here, we examine the generation of gamma oscillation currents in the hippocampus, using two-dimensional, 96-site silicon probes. Two gamma generators were identified, one in the dentate gyrus and another in the CA3-CA1 regions. The coupling strength between the two oscillators varied during both theta and nontheta states. Both pyramidal cells and interneurons were phase-locked to gamma waves. Anatomical connectivity, rather than physical distance, determined the coupling strength of the oscillating neurons. CA3 pyramidal neurons discharged CA3 and CA1 interneurons at latencies indicative of monosynaptic connections. Intrahippocampal gamma oscillation emerges in the CA3 recurrent system, which entrains the CA1 region via its interneurons.     

The modulation of sensory transmission through the medullary dorsal horn during cortically driven mastication

During mastication, reflexes are modulated and sensory transmission is altered in interneurons and ascending pathways of the rostral trigeminal sensory complex. The current experiment examines the modulation of sensory transmission through the most caudal part of the trigeminal sensory system, the medullary dorsal horn, during fictive mastication produced by cortical stimulation. Extracellular single unit activity was recorded from the medullary dorsal horn, and multiple unit activity was recorded from the trigeminal motor nucleus in anesthetized, paralyzed rabbits. The masticatory area of sensorimotor cortex was stimulated to produce rhythmic activity in the trigeminal motor nucleus (fictive mastication). Activity in the dorsal horn was compared in the presence and absence of cortical stimulation. Fifty-two percent of neurons classified as low threshold and 83% of neurons receiving noxious inputs were influenced by cortical stimulation. The cortical effects were mainly inhibitory, but 21% of wide dynamic range and 6% of low threshold cells were excited by cortical stimulation. The modulation produced by cortical stimulation, whether inhibitory or excitatory, was not phasically related to the masticatory cycle. It is likely that, when masticatory movements are commanded by the sensorimotor cortex, the program includes tonic changes in sensory transmission through the medullary dorsal horn.