On the distribution of axonal terminals containing spheroidal and flattened synaptic vesicles in the hippocampus and dentate gyrus of the rat and cat

Summary A quantitative analysis has been made of the distribution of presynaptic profiles containing round (or spheroidal) and flattened (or ellipsoidal) synaptic vesicles in the apical and basal dendritic zones and in the layer of pyramidal cell somata of fields CA₁ and CA₃ of the hippocampus, and in the molecular and granular layers of the dentate gyrus of the rat and cat.In the apical and basal dendritic zones of fields CA₁ and CA₃ the overwhelming majority of the synapses are of the asymmetrical variety, the axon terminals ending principally upon dendritic spines, and to a lesser extent upon the shafts and secondary or tertiary branches of the dendrites. Between 1 and 8% of the axon terminals in these zones contained flattened vesicles: all of these formed symmetrical contacts upon medium-sized or large dendritic shafts. In the molecular layer of the dentate gyrus a slightly higher percentage of flattened vesicle containing profiles was observed (10%); again these formed symmetrical contacts upon dendritic shafts. In the stratum pyramidale of the hippocampal fields and the stratum granulosum of the dentate gyrus of the rat, flattened vesicle containing synapses are two or three times more numerous than those with spheroidal vesicles. In the cat hippocampus the axosomatic synapses are about equally distributed between those containing round, and those with flattened vesicles.The finding that at the focus of post-synaptic inhibition, at the level of the pyramidal cell somata, the majority of the axon terminals contains flattened synaptic vesicles, whereas in the region of termination of the extrinsic, commissural and long association pathways (all of which are excitatory) virtually all the synapses contain round vesicles, strongly supports the view that endings containing flattened vesicles mediate post-synaptic inhibition in the hippocampal formation.Supported in part by Grant EY-00599 from the National Eye Institute.We should like to thank Mr. Paul Myers and Mr. Milburn W. Rhoades for their technical assistance, and Mrs. Doris Stevenson for secretarial help.     

Effect of stimulation of neocortical regions and the subiculum on hippocampal neurons in rabbits

In chronic experiments on rabbits using extracellular recording of unit activity in hippocampal area CA₁ the effects of stimulation of the subiculum, posterior cingulate cortex, and anterior and posterior nonprimary areas of the neocortex were investigated. The effects of such stimulation were compared in the intact and chronically isolated hippocampus. It is concluded from the results that direct two-way connections exist between CA₁ and the subiculum. Polysynaptic influences of the subiculum on CA₁ are realized through the entorhinal cortex, for they are not present in the isolated hippocampus. Influences of the neocortical areas studied on CA₁ are transmitted to some extent through a relay in the subiculum. The entorhinal cortex plays no part in the realization of polysynaptic effects. The effectiveness of these influences increases with removal of the principal hippocampal afferent systems.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 315–323, May–June, 1982.     

Effect of electrical stimulation of the septum on subicular neurons with different kinds of spontaneous activity in rabbits

The effect of electrical stimulation of the medial nucleus of the septum and of hippocampal area CA₁ on subicular neurons with three different types of spontaneous activity (with theta-modulation, with delta-modulation and complex spikes, and with irregular single-spike activity) was studied in unanesthetized rabbits by extracellular recording of unit activity. Cells with theta-activity were found to respond in a distinctive functional manner to stimulation of the medial nucleus of the septum: Their reactivity was higher but latent periods of their responses were much shorter than those of cells with delta-activity and irregular discharges. Stability of modulation of theta-cell activity increased both during and after stimulation of the medial septal nucleus. Electrical stimulation of hippocampal area CA₁, on the other hand, led to disappearance of rhythm modulation. Average response latencies of all three types of cells to stimulation of area CA₁ were equal. The results indicate special properties of the septal input to subicular cells with theta-modulation.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 326–333, May–June, 1985.     

Excitatory postsynaptic potentials of hippocampal neurons and their extinction during repeated stimulation

A method of detecting "minimal" excitatory postsynaptic potentials (EPSP) in neurons of hippocampal area CA₃ of the unanesthetized rabbit during stimulation of the septo-fimbrial region and the dentate fascia is described. The method consists of presenting a strong (a current of up to 1 mA) conditioning stimulus, inducing a distinct inhibitory postsynaptic potential (IPSP), before a near-threshold (current of 0.03–0.35 mA) testing stimulus. The response to the testing stimulus, develoing after the previous conditioning IPSP, in most cases was purely depolarizing and, judging from the change in the latent period in some cases and the absence of correlation between its amplitude and that of the IPSP, it is a pure EPSP. If the testing stimuli are presented at low enough frequency (intervals of not less than 1 sec) the amplitude of the EPSP evoked by them gradually falls. This decrease exhibits some of the characteristic properties of extinction of behavioral responses (recovery after an interruption, a more rapid decrease during repeated series of stimuli, a slower decrease in amplitude during less frequent stimulation). The amplitude of the IPSP also fell or showed no significant change. The results are evidence in support of the hypothesis that extinction is based on a mechanism of homosynaptic depression.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 3–12, January–February, 1978.     

Investigation of heterosynaptic interactions in hippocampal areas CA1, and CA3 in vitro

Heterosynaptic interactions between synapses located at a considerable distance from the cell body (perforant path) and lying close to the body of the neuron (synapses of Schaffer's collaterals and axons of the dentate fascia) on guinea pig hippocampal neurons were investigatedin vitro. It was shown by the paired stimulus method that, using stimulation of subthreshold intensity for action potential generation, spatiotemporal summation takes place in both pairs of synaptic systems. If above-threshold stimulation was used, afferents lying close to the cell body suppressed responses evoked by stimulation of distant afferents for a longer time (up to 20 msec in area CA₁ and up to 300 msec in area CA₃) than during the opposite combination of stimuli (up to 3–8 msec). After tetanization of the dentate fascia depression of responses of area CA₃ neurons to stimulation of the perforant path was observed for 2–30 min. In the remaining cases, no significant prolonged heterosynaptic posttetanic changes were observed. The possible mechanisms of these interactions are discussed.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 524–532, November–December, 1979.     

Localization of aldosterone and corticosterone in the central nervous system,assessed by quantitative autoradiography

Nuclear localization of tritiated aldosterone in the CNS was studied in rats by numerical evaluation of silver grains, deposited over neuronal cell nuclei in thawmounted autoradiograms, and compared with the localization obtained after prior administration of a 100-fold excess of radioinert aldosterone, corticosterone or 18-hydroxy-11-deoxycorticosterone (18-OH-DOC). Corticosterone and 18-OH_DOC completely prevented nuclear localization in most regions examined. However, in contrast to pretreatment with aldosterone, pretreatment with corticosterone and 18-OH-DOC did not completely prevent the concentration of radio-activity in the cell nuclei of the indusium griseum. Traces of radioactivity were, furthermore, retained in areas CA₁ and CA₂ and the dentate gyrus in rats exposed to corticosterone, but not to 18-OH-DOC, prior to [³H]aldosterone. A similar profile of silver grain distribution to that noted with aldosterone was found for corticosterone except that with tritiated corticosterone the most intense concentration of radioactivity occurred in hippocampal areas CA₁ and CA₂ and not in the indusium griseum. Prior administration of excess deoxycorticosterone acetate abolished nuclear accumulation of tritiated corticosterone. Dihydrotestosterone, on the other hand, failed to compete with tritiated corticosterone at a dose 200-fold in excess of the tritiated steroid.We conclude that (1) a receptor readily shared by aldosterone, corticosterone, 18-OH-DOC and DOC, but not by dihydrotestosterone, is widely distributed throughout the CNS, (2) a receptor shared by aldosterone and 18-OH-DOC, but not by corticosterone may be present in hippocampal areas CA₁ and CA₂, (3) that both these as well as the receptor accepting dihydrotestosterone can be located within the same cell.Dedicated to K. A. C. Elliott on his 80th birthday.     

Short- and long-term potentiation in afferent pathways of the neonatal rabbit hippocampus

Vocal potentials were recorded in hippocampal area CA₁ and dentate fascia in unanesthetized rabbits aged from 1 to 50 days during stimulation of Schaffer's collaterals and the perforant path, respectively, with paired (interval 15–100 msec) and repetitive (20–40 Hz for 3–5 sec) electric pulses. Short-term potentiation of focal potentials during paired stimulation and post-tetanic potentiation lasting from a few minutes to 3 h were shown to be reproduced in the hippocampus from the first days after birth, whereas in the dentate fascia, which matures later, reproduction began on the 8th–10th day, when neurons first began to respond to stimulation of the corresponding afferent pathways.     

Excitatory and Inhibitory Effects of A1 and A2A Adenosine Receptor Activation on the Electrically Evoked [3H]Acetylcholine Release from Different Areas of the Rat Hippocampus

Abstract: The modulation by adenosine analogues and endogenous adenosine of the electrically evoked release of [³H]acetylcholine ([³H]ACh) was compared in subslices of the three areas of the rat hippocampus (CA1, CA3, and dentate gyrus). The mixed A₁/A₂ agonist 2-chloroadenosine (CADO; 2–10 µM) inhibited, in a concentration-dependent manner, the release of [³H]ACh from the three hippocampal areas, being more potent in the CA1 and CA3 areas than in the dentate gyrus. The inhibitory effect of CADO (5 µM) on [³H]ACh release was prevented by the A₁ antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 50 nM) in the three hippocampal areas and was converted in an excitatory effect in the CA3 and dentate gyrus areas. The A_2A agonist CGS-21680 (30 nM) produced a greater increase of the evoked release of [³H]ACh in the CA3 than in the dentate gyrus areas, whereas no consistent effect was found in the CA1 area or in the whole hippocampal slice. The excitatory effect of CGS-21680 (30 nM) in the CA3 area was prevented by the adenosine receptor antagonist 3,7-dimethyl-1-propargylxanthine (10 µM). Both adenosine deaminase (2 U/ml) and DPCPX (250 nM) increased the evoked release of [³H]ACh in the CA1 and CA3 areas but not in the dentate gyrus. The amplitude of the effect of DPCPX and adenosine deaminase was similar in the CA1 area, but in the CA3 area DPCPX produced a greater effect than adenosine deaminase. It is concluded that the electrically evoked release of [³H]ACh in the three areas of the rat hippocampus can be differentially modulated by adenosine. In the CA1 area, only A₁ inhibitory receptors modulate ACh release, whereas in the CA3 area, both A_2A excitatory and A₁ inhibitory adenosine receptors modulate ACh release. In the dentate gyrus, both A₁ inhibitory and A_2A excitatory adenosine receptors are present, but endogenous adenosine does not activate them.     

Long-term potentiation in vivo increases rat hippocampal tenascin-C expression

We investigated the expression of the extracellular matrix glycoprotein tenascin-C after induction of long-term potentiation (LTP) by high-frequency tetanization (HFT) in the rat dentate gyrus in vivo. Expression of tenascin-C was evaluated at the mRNA and protein levels by in situ hybridization and immunocytochemistry, respectively. Whereas no tenascin-C mRNA was detectable in control animals, an increase in tenascin-C mRNA levels was observed in the granule cell layer of the dentate gyrus 4 h after HFT. At 24 h after HFT, tenascin-C mRNA had returned to control levels. Expression of tenascin-C protein 4 h after HFT followed that of controls in that tenascin was detectable in the strata oriens and radiatum of CA1, in the molecular layer, and within a narrow area at the inner surface of the granule cell layer in the dentate gyrus. However, 24 h after HFT, additional patches of tenascin-C immunoreactivity were observed in the molecular layer of the dentate gyrus. No increase in tenascin mRNA or protein levels was detected in control animals that received no stimulation, low-frequency stimulation, or HFT in the presence of the N-methyl-D -aspartate receptor antagonist D (−)-2-amino-5-phosphonopentanoic acid or the metabotropic glutamate receptor antagonist (R,S)-α-methyl-4-carboxyphenylglycine. These observations implicate a role for tenascin-C in N-methyl-D -aspartate and metabotropic glutamate receptor–dependent changes accompanying induction and/or maintenance of LTP. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 393–404, 1998     

Evaluation of binaural interaction according to the characteristics of short latency acoustic evoked potentials in guinea pigs

Binaural interactions was evaluated in guinea pigs by plotting the difference between the algebraic sum of brainstem evoked potentials recorded during monaural stimulation of the right and left ears and those produced by binaural stimuli. This plot was distinguished by three peaks (N₁, P₁, and N₂) in the region of IV–IV wave latencies (short-latency acoustic evoked potentials) in the absence of masking noise, but using masking noise (signal-noise ratio: +20-0 dB), plots showed additional peaks No and Po in the region of wave III–III latencies. The amplitude of P₁N₂ in relation to that of wave IV of the summated potentials recording monaural stimulation of the right and left ear remains constant with an increase in the sound pressure level from 47 to 107 dB. This relationship grows with a decline in the signal-noise ratio when masking is used, while the P₁N₂ amplitude declines. It is postulated that binaural interaction pattern does not change when the clicking sound increases in intensity and that distinctive aspects of neurophysiological mechanisms underlying binaural interaction emerge during masking with a signal-noise ratio of +20-0 dB.Institute of Otolaryngology, Ministry of Public Health of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 579–586, September–October, 1987.     

Laminar analysis of hippocampal potentials evoked by peripheral stimulation

From areas SA₁ and SA₂ of the dorsal hippocampus of unanesthetized rabbits immobilized with d-tubocurarine a laminar analysis was made of evoked potentials (EP) in response to stimulation of the sciatic nerves. Inversion of the initial surface-positive phase of the EP was observed at the level of the pyramidal layer. The subsequent surface-negative phase reached a maximum value in the layer of basal dendrites of the pyramidal cells. The initial portion was inverted somewhat above the pyramidal layer and reached its maximum value approximately at the boundary of the pyramidal and radial layers. The change in sign of the remaining portion of this component occurred 0.3–0.4 mm deeper than the pyramidal layer. It is suggested that both components of the EP picked up from the hippocampal surface are due to an excitatory postsynaptic potential (EPSP) at the apical (positive phase), and basal (negative phase) dendrites. The positivity in the region of the pyramidal somata appears to be an extracellular reflection of a composite postsynaptic potential (IPSP) generated in this region.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 4. pp. 434–438, July–August, 1970.     

Posttetanic changes in hippocampal minimal evoked potentials

Changes in the EEG induced by a single spike were recorded in the hippocampus of an unanesthetized rabbit. Summation of focal electrical activity synchronous with spontaneous single unit discharges at the symmetrical point of contralateral hemisphere revealed no stable potentials which could reflect these changes. In two cases discharges identified as activity of Shaffer's collaterals were recorded in area CA₁. Summation of post-spike changes in evoked activity recorded by the same microelectrode showed stable negative waves with an amplitute of 40–60 µV, which could have been evoked by single spikes. The curve of amplitude of the averaged evoked potentials versus near-threshold current strength stimulating the intrahippocampal pathways was not smooth in most experiments but stepwise in character. It is suggested that the minimal evoked potential corresponding to the first step (amplitude 40–80 µV) reflects a response to stimulation of one fiber. After above-threshold tetanization prolonged posttetanic potentiation of the minimal evoked potentials did not arise in CA₁ in response to stimulation of Shaffer's collaterals. Minimal evoked potentials recorded in area CA₃ in response to stimulation of the dentate fascia showed clear potentiation. The results are in agreement with the hypothesis of the synaptic localization of the mechanisms responsible for prolonged posttetanic potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 124–134, March–April, 1977.     

Possible pathogenic mechanisms on trimethyltin-induced lesions in the hippocampus of adult and neonatal rats

The extent of trimethyltin (TMT) induced lesions in the rat hippocampal formation was reviewed. Adult rats were treated with a single dose of 6.0 mg TMT/kg body wt and were sacrificed between 3–60 d following exposure. In the hippocampal formation, the granule cells of fascia dentata showed early changes, which subsided considerably at a later time of the intoxication. On the other hand, destruction of the pyramidal neurons in the Ammon’s horn became more pronounced with time, resulting in an extensive destruction of this structure. It is interesting to note that the CA₃ neurons in the septal portion of the Ammon’s horn were more vulnerable than those located more temporally, whereas the reverse pattern was observed for the dentate granule cells as well as for the CA_1,2 neurons of the Ammon’s horn. Special stain for zinc (Timm’s method) also revealed a progressive depletion of zinc in the mossy fibers. When neonatal rats were treated at various times with a single injection of TMT, rapid and progressive destruction of the Ammon’s horn was observed in animals injected between postnatal day (PND) 5–15. The progression of neuronal involvement was CA_3b →CA_{3a, b} →CA_3(a,b,c)→CA₃+CA₂→entire Ammon’s horn (CA_1,2,3). This pattern of pathological lesion was in good concert with morphological development and functional maturity of the hippocampal formation. Destruction of the Ammon’s horn neurons was proposed to be the result of hyperexcitation of the dentate granule neurons under the influence of TMT. Other possible mechanisms are also discussed. Author to whom all correspondence and reprint requests should be addressed.     

Dynamic Expression Pattern of Neuro-oncological Ventral Antigen 1 (Nova1) in the Rat Brain after Focal Cerebral Ischemia/Reperfusion Insults

The present study aimed to evaluate the expression of neuro-oncological ventral antigen 1 (Nova1) in cerebral ischemia/reperfusion (I/R) insults by immunohistochemistry. The focal cerebral I/R model was induced by right middle cerebral artery occlusion (MCAO) for 120 min followed by 1 day, 7 days, and 14 days of reperfusion in Sprague-Dawley (SD) rats. The results showed that Nova1 was expressed in nearly the whole brain, although with higher density in hippocampus, hypothalamus, cingulate cortex, and medial habenular nucleus. The immunoreactivity of Nova1 neurons was increased dramatically, especially on both sides of the hippocampal CA₁ region, after 1 day of reperfusion. A strong response occurred at the ipsilateral CA₁ region between 1 day and 7 days of reperfusion. Likewise, strong compensatory responses of Nova1 expression were observed on the contralateral side of the striate cortex, dentate gyrus, and hypothalamus. Interestingly, more Nova1 neurons were observed to translocate to the dendrites and growth cones of the axons in the hypothalamus on the ischemic side after 7 days of reperfusion. In conclusion, our data suggest that Nova1 might mediate neuronal responsiveness, and its expression might positively correlate with neural repair after I/R insults in the rat brain.     

Noggin and BMP4 co-modulate adult hippocampal neurogenesis in the APPswe/PS1ΔE9 transgenic mouse model of Alzheimer’s disease

In addition to the subventricular zone, the dentate gyrus of the hippocampus is one of the few brain regions in which neurogenesis continues into adulthood. Perturbation of neurogenesis can alter hippocampal function, and previous studies have shown that neurogenesis is dysregulated in Alzheimer disease (AD) brain. Bone morphogenetic protein-4 (BMP4) and its antagonist Noggin have been shown to play important roles both in embryonic development and in the adult nervous system, and may regulate hippocampal neurogenesis. Previous data indicated that increased expression of BMP4 mRNA within the dentate gyrus might contribute to decreased hippocampal cell proliferation in the APP_swe/PS1_ΔE9 mouse AD model. However, it is not known whether the BMP antagonist Noggin contributes to the regulation of neurogenesis. We therefore studied the relative expression levels and localization of BMP4 and its antagonist Noggin in the dentate gyrus and whether these correlated with changes in neurogenesis in 6-12 mo old APP_swe/PS1_ΔE9 transgenic mice. Bromodeoxyuridine (BrdU) was used to label proliferative cells. We report that decreased neurogenesis in the APP/PS1 transgenic mice was accompanied by increased expression of BMP4 and decreased expression of Noggin at both the mRNA and protein levels; statistical analysis showed that the number of proliferative cells at different ages correlated positively with Noggin expression and negatively with BMP4 expression. Intraventricular administration of a chimeric Noggin/Fc protein was used to block the action of endogenous BMP4; this resulted in a significant increase in the number of BrdU-labeled cells in dentate gyrus subgranular zone and hilus in APP/PS1 mice. These results suggest that BMP4 and Noggin co-modulate neurogenesis.     

Action of an enkephalinase blocker on the effect of acupuncture in acupuncture sensitive and resistant rabbits]

In unanaesthetized acupuncture-sensitive rabbit d-phenylalanine injection didn't change the EP in response to tooth pulp electrostimulation, but prolonged the analgetic effect of auriculo-acupuncture stimulation 15 Hz expressed by decreasing of the amplitude of N1P2 component EP. In acupuncture-resistant rabbit d-phenylalanine injection induced analgetic effect which was enhanced and prolonged by auriculo-acupuncture stimulation. It's suggested that the recovery of pain sensibility after acupuncture analgesia is determined by enkephalinase's mechanism activation which is activated permanently in acupuncture-resistant rabbits.     

Functional characteristics of the principal intrinsic systems of hippocampal connections

By extracellular recording of unit activity and electrical stimulation of unanesthetized rabbits the character of the following principal intrinsic hippocampal connections was investigated: fascia dentata with area CA₃ (series FD-CA₃) and area CA₃ with area CA₁ (series CA₃-CA₁). Differences between the functional characteristics of these two systems of connections were shown. The CA₃-CA₁ system was highly efficient, with a sharply defined boundary between subthreshold and threshold intensities of stimulation and with a wide range of active frequencies; recruiting was negligible and no sign of prolonged potentiation was present. The FD-CA₃ system was characterized by low efficiency, a wide threshold zone, and narrow range of active frequencies, slow recruiting, and long preservation of incoming influences. The probability that these functional differences depend on the morphological characteristics of the systems of connections and their possible role in the function of the hippocampus are discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 259–266, May–June, 1976.     

Functional development of hippocampal mossy fiber synapses in rabbits

The course of functional maturation with age of mossy fiber synapses on pyramidal cells in areas CA_3,4 of the dorsal hippocampus was investigated by extracellular recording of focal potentials and single unit responses of the hippocampus to electrical stimulation of the dentate fascia in waking, unimmobilized rabbits aged from 1 to 14 days. After the 4th day of postnatal life focal potentials appeared in response to single stimulation, in the form of a biphasic short-latency wave, characteristic of responses of the mature hippocampus, accompanied by spike discharges with a latent period of 3 to 10 msec and inhibitory responses of the hippocampal neurons. During the next 10 days the amplitude of the focal potentials increased from several hundred millivolts, with the sharpest increase observed from the 4th through the 7th days. In early age periods global and unitary responses were shown to be capable of frequency potentiation and also of short-term after-potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 246–254, May–June, 1980.     

Influence of orotic acid upon post-excitatory facilitation released by stimulation of the tooth pulp]

The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred.     

Functional characteristics of Schaffer's collaterals studied in vivo and in vitro

A comparative analysis was made of the functional characteristics of connections between hippocampal areas CA₃ and CA₁ (Schaffer's collaterals) in experiments in vivo on unanesthetized rabbits and in vitro on surviving slices of guinea pig hippocampus, with extracellular recording in area CA₁. In the case of electrical stimulation of the collaterals in vitro, post-activational inhibition was weak, responses of inhibition of spontaneous discharges were absent, and low frequencies of stimulation were more effective than in vivo. Posttetanic changes were found more frequently in experiments in vitro and they lasted longer than in vivo. The predominant effect of tetanization under normal conditions was depression, but during incubation it was facilitation of responses. The possible causes of these differences are discussed.Institute of Biophysics, Academy of Sciences of the USSR, Puschino-on-Oka. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 208–217, May–June, 1979.