Background firing in cortical neurons with blockade of synaptic inhibition in guinea pig neocortical slices maintained in vitro

The effects of 100 µM picrotoxin on neuronal background firing were investigated in guinea pig neocortical slices maintained in vitro. Picrotoxin or bicuculline application is known to bring about an abrupt increase in background firing or the onset of spontaneous epileptiform volleys at a higher excitatory and inhibitory level in the in vivo than in the in vitro cortex. Blocking GABA-ergic inhibition hardly affected the pattern of background spike trains, although stimuli-induced response did become epileptiform. Findings from this research would thus indicate that any inhibitory processes taking place during in vitro background activity are only very slight and exert no significant effect on this activity.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 16–24, January–February, 1989.     

Ionizing radiation alters neuronal excitability in hippocampal slices of the guinea pig

To investigate the effects of ionizing radiation on an isolated neuronal network without complicating systemic factors, slices of hippocampus from the guinea pig were isolated and studied in vitro. Slices were irradiated with a 60Co source and compared to paired, sham-irradiated controls. Electrophysiological activity in the CA 1 population of pyramidal cells was evoked by stimulation of the stratum radiatum. Analysis of the somatic and dendritic responses suggested sites of radiation damage. Orthodromically evoked activity was significantly decreased in slices receiving greater than 75 Gy gamma radiation. The effects were dose and dose-rate dependent. At 20 Gy/min, doses of 50 Gy and greater produced synaptic impairment while doses of 75 Gy and greater also produced postsynaptic damage (i.e., the ability of the synaptic response to generate an action potential). A lower dose rate, 5 Gy/min, reduced the sensitivity of synaptic damage to radiation exposure; synaptic impairment required a dose of 100 Gy or greater at the lower dose rate. In contrast, postsynaptic damage was not sensitive to dose rate. This study demonstrates that ionizing radiation can directly affect the integrated functional activity of neurons.     

Structure of background neuronal activity in thin slices of guinea-pig neocortex

We recorded background neuronal discharges extracellularly in guinea-pig cerebral cortex slices maintainedin vitro. The following types of activity were delineated: 1) regular single discharges (38.5%), 2) irregular spikes (6.5%), 3) bursts (6.5%), 4) burst-and-single discharge (mixed) activity (26.5%), 5) group discharges (2.5%), 6) multicellular volleys (18.5%). Each of these types corresponds to a characteristic distribution of interspike intervals in the form of an autocorrelogram. Regular pacemaker-type discharges, which are never observed in normal or isolated cortex, appeared in small volumes of grey matter and in the absence of afferentation.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 441–449, July–August, 1985.     

Temperature dependence of neuronal activity in Guinea pig hypothalamic and hippocampal slices

Neuronal activity was recorded in surviving hippocampal and medial preoptic thalamic slices from guinea pigs using extracellular techniques during thermal changes. Rate of generating action potentials changed in seven of the 19 hypothalamic cells tested once a threshold temperature of 36–38°C had been reached. Above this range, activity in these neurons was temperature dependent. It is suggested that these neurons form a sensory element in the system controlling brain temperature over a narrow (1–2°C) range. In the hippocampus (the control structure), pyramidal layer cells were insensitive to temperatures in the 32–40°C range.Institute of Physiology, Academy of Sciences of the Byelorussian SSR, Minsk. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 358–365, May–June, 1989.     

Dynamics of spontaneous activity in neocortical slices.

The flow of activity in the cortical microcircuitry is poorly understood. We use calcium imaging to reconstruct, with millisecond and single-cell resolution, the spontaneous activity of populations of neurons in unstimulated slices from mouse visual cortex. We find spontaneous activity correlated among networks of layer 5 pyramidal cells. Synchronous ensembles occupy overlapping territories, often share neurons, and are repeatedly activated. Sets of neurons are also sequentially activated numerous times. Network synchronization and sequential correlations are blocked by glutamatergic antagonists, even though spontaneous firing persists in many "autonomously active" neurons. This autonomous activity is periodic and depends on hyperpolarization-activated cationic (H) and persistent sodium (Na(p)) currents. We conclude that the isolated neocortical microcircuit generates spontaneous activity, mediated by a combination of intrinsic and circuit mechanisms, and that this activity can be temporally precise.     

Background activity pattern of guinea pig septal neurons in vitro

Activity of medial septum-diagonal band cells (MS-DB neurons) was investigated in slices of guinea pig septum. Four types of activity were distinguished on the basis of interspike interval distribution and coefficient of variation (CV): extremely regular (CV<0.3), regular (CV>0.3<0.7), irregular (CV>0.7), and rhythmic bursting patterns. Activity of cells belonging to the first group was resistant to superfusion with a medium low in Ca²⁺ and high in Mg²⁺ which produces blockade of synaptic effects. The same applied to a percentage of neurons with a rhythmic bursting pattern. Activity pattern of Mg²⁺-resistant bursting cells also remained unchanged by the effects of GABA and acetylcholine antagonists. It is concluded that cells with properties of regular and bursting endogenous pacemakers are found in the MS-DB.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 586–595, September–October, 1987.     

DNA repair synthesis in guinea pig pancreatic slices following in vitro exposure to N-nitrosomethylurethane.

The incorporation of thymidine into DNA in the presence of hydroxyurea (HU) by guinea pig pancreatic slices following exposure to N-nitrosomethylurethane (NMUT) was used to follow DNA repair synthesis. HU was used to suppress normal replicative DNA synthesis. Slices from the duodenal segment of the pancreas were exposed for periods of 15 to 90 min to NMUT at concentrations of 2 to 20 mM, then incubated in tritiated thymidine ([H3]-TdR) free of carcinogen, and radioactivity in DNA was determined. NMUT induced a a dose- and time-dependent increase in HU-insensitive thymidine incorporation. This stimulated incorporation, which could be attributed to repair synthesis, occurred immediately following the treatment and was largely complete within 3 h.     

Cross-correlation analysis of the background activity of visual cortex cells separated by different distances in the alert rabbit

Values of correlation coefficients (CC) and forms of cross-correlation functions of impulse activity were studied in neurones recorded with one microelectrode or simultaneously with two sticked together microelectrodes with tangential distance between tips of 70 and 140 mcm. Three main types of cross-correlation functions were singled out differing by peaks form and modes positions. The greatest variety of forms and the greatest percentage of significantly correlated discharges of cellular pairs were found among the neurones recorded with one electrode. Mean CC of cells recorded with one electrode was significantly greater than mean CC of the neurones recorded with two microelectrodes. Comparison of the character of intercellular correlation with amplitudes of recorded spikes showed that discharges of neurones with greater amplitude mainly forestalled discharges of cells with low amplitude.     

Comparative characteristics of the neuronal activity of the anterodorsal and anteroventral nuclei in thalamus slices from guinea pigs

Extracellular investigation of neurons of the anterodorsal (AD) and anteroventral (AV) nuclei in the incubated slices of the thalamus of guinea pigs and rabbits revealed unusual properties of the AD units. They responded only to electrical stimuli of considerable duration (1-5 ms) by multispike initial bursts or by prolonged (1-15 s) high frequency phasic discharges. Summation of effects of successive stimuli following with intervals of 2-30 s was necessary for development of phasic discharges. Prolonged refractory state (up to 2-15 s) followed the discharges. They were blocked in low Ca2+, high Mg2+ medium and facilitated in a medium with high concentration of K+. The nature of unusual properties of AD neurons, not present in the neighbouring AV nucleus, are discussed.     

Proteolytic activity of guinea pig spermatozoa after induction of the acrosomal reaction in vitro

After inducing the acrosomal reaction in guinea pig spermatozoa in vitro, the sperm were tested for proteolytic activity by applying them to membranes of fixed gelatin. One to 5% of them showed slight evidence of proteolytic activity, while the rest were completely negative. Sperm that had retained their acrosomes throughout the incubation period displayed intense proteolytic activity. These results suggest that proteinases may be lost from spermatozoa as a result of the acrosomal reaction.     

Cross-correlation analysis of unit activity in spinal locomotor centers

Correlation analysis of unit activity in spinal locomotor centers was carried out in immobilized thalamic cats. Within a short time interval (the time shift of one spike train relative to the other during plotting of the cross-correlation histogram did not exceed 54 msec) correlation between the spike flows of these cells was absent, irrespective of the distance between them, both at rest and during efferent discharge generation. Spike flows of neurons could correlate only in the case of a long time interval (maximal time shift of one spike train relative to the other not less than 4–8 sec during plotting of the cross-correlation histogram). Weak correlation with a long time interval (4–8 sec) was found between changes in the momentary frequency of a neuron and the intensity of the discharge in the motor nerve, but no correlation was found between changes in momentary frequency of the neuron and intensity of discharge. The possible causes of the absence of correlation with a short time interval and its presence with a long time interval are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 283–289, May–June, 1980.     

Metabolism of homovanillamine to homovanillic acid in guinea pig liver slices.

BACKGROUND/AIMS: Homovanillamine is a biogenic amine that it is catalyzed to homovanillyl aldehyde by monoamine oxidase A and B, but the oxidation of its aldehyde to the acid derivative is usually ascribed to aldehyde dehydrogenase and a potential contribution of aldehyde oxidase and xanthine oxidase is usually ignored. METHODS: The present investigation examines the metabolism of homovanillamine to its acid derivative by concurrent incubation with monoamine oxidase and aldehyde oxidase. In addition, the metabolism of homovanillamine in freshly prepared and cryopreserved liver slices is examined and the relative contribution of aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase activity by using specific inhibitors of each oxidizing enzyme is compared. RESULTS: Homovanillamine was rapidly converted mainly to homovanillic acid when incubated with both momoamine oxidase and aldehyde oxidase. Homovanillic acid was also the main metabolite in the incubations of homovanillamine with freshly prepared or cryopreserved liver slices, via the intermediate homovanillyl aldehyde. The acid formation was 70-75 % inhibited by disulfiram (specific inhibitor of aldehyde dehydrogenase), whereas isovanillin (specific inhibitor of aldehyde oxidase) inhibited acid formation to a lesser extent (50-55 %) and allopurinol (specific inhibitor of xanthine oxidase) had almost no effect. CONCLUSIONS: Homovanillamine is rapidly oxidized to its acid, via homovanillyl aldehyde, by aldehyde dehydrogenase and aldehyde oxidase with little or no contribution from xanthine oxidase.     

Propagation of excitation in surviving neocortical slices

Propagation of excitation was investigated in neocortical guinea-pig slices maintained in vitro. Stimuli were applied at different distances from the chosen neuron. A comparison between latencies of induced spike responses would point to complex structure and configuration of vertically oriented columnar array. Such arrays of relatively synchronously activated neurons have a narrow peak in layer II (of up to 300 µm), a broad central portion in layer V about 600 µm or above), and a narrower base in layer VI (of about 300 µm). Layer-by-layer diversity in excitation propagation was found within the array, moreover.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 472–481, July–August, 1990.     

Quantal analysis of long-term potentiation of combined neuronal postsynaptic potentials on hippocampal slices in vitro

Excitatory postsynaptic potentials (EPSP) were recorded from 14 neurons in guinea pig hippocampal slices (area CAl) after stimulating the stratum radiatum (Schaffer collaterals) and stratum oriens. An increase occurring in EPSP amplitude in 7 units (9 pathways) recorded 15–45 min after tetanic stimulation of Schaffer collaterals is viewed as long-term potentiation (LTP). Statistical analysis conducted according to two sets of quantal theory (histogram and variance methods) showed an increase in mean quantal content (m) during LTP. An increase in quantal size, found only when using the histogram method, did not correlate with LTP level. This increase is thought to be associated with the considerably greater sensitivity of the histogram method to noise level in comparison with the variance method, the latter being more reliable with signals of high noise level. The increase found in m using both methods matches findings previously obtained for the whole brain; it also points to presynaptic location of mechanisms responsible for raised synaptic efficacy during LTP.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Max-Planck Institute of Biophysical Chemistry, Göttingen, West Germany. Institute of Zoology, Jagiellonian University, Cracow, Poland. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 465–472, July–August, 1990.