An N-methyl-D-aspartate-receptor dependent, late-phase long-term depression in middle-aged mice identifies no GluN2-subunit bias.

Late-phase long-term depression (L-LTD) in middle-aged mice has been difficult to achieve and maintain. Here we report an electrically induced, homosynaptic, input-specific form of LTD that could be stably maintained for at least 4 h in the CA1 area of hippocampal slices of 10-14 months old mice. This form of L-LTD was similar in magnitude in aged, middle-aged and young mice and was blocked by high concentrations of broad-spectrum N-methyl-d-aspartate receptor (NMDAR) antagonists such as d(-)-2-amino-5-phospho-pentanoic acid (d-AP5) and (R)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP). Extracellular and whole cell recordings revealed a decreased sensitivity to d-AP5 with age, without any differences in NMDAR conductance between the age groups tested. This L-LTD could be inhibited neither by common doses of NMDA-subunit specific antagonists like zinc, ifenprodil and Ro-25-6981, nor by various co-applications of these compounds. In addition to the lack of any GluN2 subunit bias, L-LTD did not show any discernible involvement of L-type voltage-gated calcium channels. In conclusion, our results do not support any specific role of NMDAR subunits in LTD.

Cell cycle-related changes in regulatory volume decrease and volume-sensitive chloride conductance in mouse fibroblasts.

Cell cycle-related changes in the ability to regulate cell volume following hyposmotic swelling were studied in mouse fibroblasts using videomicroscopy and the whole-cell patch clamp technique. Regulatory volume decrease (RVD) and volume-sensitive Cl- conductance (G(Cl,vol)) were measured: (1) in proliferating cells of different sizes; (2) in cells arrested in defined phases of the cell cycle (G1, G1/S, S, and M phases) using mevastatin, mimosine, hydroxyurea, aphidicolin, cytosine beta-D-arabinofuranoside, and taxol; and (3) in serum-starved cells (G(0) state). Cells in all groups were able to undergo RVD, although the cells approaching mitosis (i.e., the largest cells in proliferating cultures and the taxol-treated cells) had the lowest rates of shrinkage during RVD. In agreement with this finding, the density of G(Cl,vol) was stable in proliferating and cell cycle-arrested cells for most of the cell cycle, with the exception of the cells approaching mitosis and the new daughter cells where the density was decreased to half. The impairment of RVD was greatest in serum-starved cells which also had the lowest density of G(Cl,vol). We conclude that proliferating cells maintain an ability to recover from osmotic swelling as they progress through the cell cycle, although this ability may be compromised during mitosis.

Dual role of ATP in supporting volume-regulated chloride channels in mouse fibroblasts.

The effects of inhibitors of protein tyrosine kinases (PTKs) on the Cl(-) current (I(Cl(vol))) through volume-regulated anion/chloride (VRAC) channels whilst manipulating cellular ATP have been studied in mouse fibroblasts using the whole-cell patch clamp technique. Removal of ATP from the pipette-filling solution prevented activation of the current during osmotic cell swelling and when the volume of patched cells was increased by the application of positive pressure through the patch pipette to achieve rates exceeding 100%/min. Equimolar substitution of ATP in the pipette solution with its non-hydrolyzable analogs, adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) or adenylyl-(beta,gamma-methylene)-diphosphonate (AMP-PCP), not only supported activation of the current but also maintained its amplitude. The PTK inhibitors, tyrphostins A25, B46, 3-amino-2,4-dicyano-5-(4-hydroxyphenyl)penta-2,4-dienonitrile++ + and genistein (all at 100 microM), inhibited I(Cl(vol)) in a time-dependent manner. Tyrphostin A1, which does not inhibit PTK activity, did not affect the current amplitude. The PTK inhibitors also inhibited I(Cl(vol)) under conditions where ATP in the pipette was substituted with ATPgammaS or AMP-PCP. We conclude that in mouse fibroblasts ATP has a dual role in the regulation of the current: it is required for protein phosphorylation to keep VRAC channels operational and, through non-hydrolytic binding, determines the magnitude of I(Cl(vol)). We also suggest that tyrosine-specific protein kinases and phosphatases exhibit an interdependent involvement in the regulation of VRAC channels.

The changes in the nervous structures under the chemical sympathectomy with guanethidine.

The process of sympathectomy of white rats was achieved by injecting guanethidine intraperitoneally every day for 5.5 weeks at doses of 75 mg/kg of animal's weight. This process of sympathectomy was checked according to ganglion cervicothoracicum neurocytes state. The material was taken on days 1, 14, 30, 90 and 180 after cessation of guanethidine injections. It was ascertained that full sympathectomy under prolonged injections of high doses of guanethidine is reached at 5-6 months after the cessation of the injections, though pronounced total degeneration of gnl. stellatum neurocytes is marked on the 14th-30th days after cessation of the guanethidine injections. The following gradient of damaging influence of guanethidine was revealed: sympathetic gnl. cervicothoracicum neurocytes gnl. nodosum afferent neurocytes-neuromuscular synapsis skeletal muscle.

Static tilt may modify the value of nystagmus asymmetry.

In awake pigeons (Columba livia) we investigated the horizontal cervical and ocular nystagmuses which were induced by monaural stimulation of the lateral semicircular canals by the parathreshold sinusoidal currents. The value of nystagmus asymmetry (by the average velocities of slow components) with a normal orientation of the bird's head was compared with that in static head tilts in the sagittal and frontal planes. In the normal head position depolarization of the lateral canals evoked a stronger response than hyperpolarization of an equal value indicating that Ewald's second law is justified for the weak suprathreshold stimuli. It was found that the static tilts modify the value of nystagmus asymmetry. These changes are connected with the asymmetric modifications of the otolithic activities in tilts. This feature of the canal-olithic interaction should be taken into consideration in estimation of the results of the caloric test one of the obligatory conditions of which is static tilt.

Chloride channels in brown adipocyte plasma membranes: candidates for mediation of alpha 1-adrenergic depolarization?

The presence of plasma membrane Cl- channels was investigated in brown-fat cells differentiated in culture. Single channel activity was followed by the patch-clamp technique, with an NMDG+ Cl- pipette solution and a NaCl bath solution. Only rarely was putative Cl- channel activity encountered in the cell-attached mode. However, after excision, ion channel activity of two types was observed in inside-out patches: one type represented the earlier observed non-selective cation channel, and one a putative Cl- channel, with the following characteristics: practically non-rectifying current-voltage relationship with a conductance of approximately 50 pS and a reversal potential of approximately 0 in symmetrical Cl- solutions, voltage dependent channel activity (Po approached 0.5 at positive holding potentials), and rapid flickering activity in the open state. It is discussed whether this Cl- channel may be responsible for the initial depolarization phase observed after alpha 1-adrenergic stimulation of brown-fat cells.

[The metasympathetic mechanisms supporting the constancy and stability of the internal environment in vertebrates]. / Nekotorye metasimpaticheskie mekhanizmy podderzhaniia postoianstva i ustoichivosti vnutrennei sredy pozvonochnykh.

The data were obtained with the aid of extracellular recording of unit activity in the cardial, enteral and respiratory parts of the metasympathetic nervous system, staining of the neural tissue preparations of atrial walls, intestine and lower part of the guinea pig trachea. The neurons were shown to be very sensitive to the main homeostatic contants: pH of the perfusion solution, its temperature and the grade of oxygenation. These structures were shown to take a direct part in maintenance of the constancy and stability of the organism inner milieu. Sympathetic nervous system differs from the above system in that the former is the system of transmission, defence, mobilisation of resources which is necessary for active interaction of the organism with ambient milieu.

[The interaction of vestibular inputs with differing orientations of the otoliths in a gravitational field]. / Vzaimodeistvie vestibuliarnykh vkhodov pri razlichnoi orientatsii otolitov v gravitatsionnom pole.

In alert pigeons Columba livia effects of static tilts about fore-aft and binaural axes (angles of tilts: 30-40 deg) on neck and ocular nystagmus elicited by monaural galvanic stimulation of the lateral semicircular canals with sinusoidal currents (peak amplitudes: 20-100 microA; period: 35 sec) were investigated. It was shown that the same angles of the tilts elicited different changes of horizontal nystagmus parameters in different animals. In some of them changes of quantitative characteristics of opposite-directed nystagmus differed with signs. Data support the correctness of recently (Stolbkov, 1989) proposed scheme of forming vestibulomotor reactions, according to which signals from heterolateral vestibular nuclei, during nystagmus, which are integrated, contain both canal and otolith components independent of stimulus mode addressed to canals or otoliths (separately or jointly). Results suggest also that caloric test may be a source of incorrect conclusions concerning state of vestibular system during static tilts the responses of functionally asymmetric semicircular canals may be symmetric ones. Moreover data suggest that sensitivity of convergent vestibular neurons to the canal signals is different depending on separated or combined canal and otolith stimulations.

[Effect of microelectrophoretic application of GABA on the formation of a cellular analog of a conditioned reaction]. / Vliianie mikroélektroforeticheskoi applikatsii GAMK na formirovanie kletochnogo analoga uslovnoi reaktsii.

Influence of GABA application on ability of sensorimotor cortical neurones to form conditioned cellular reactions was studied in chronic experiments on rabbits. Neuronal reactions were analysed at the initial stage of eye-lid conditioning. GABA application in a period of presentation of paired conditioned and unconditioned stimuli disturbed formation of inhibitory conditioned cellular reactions and did not influence elaboration of activating responses. Plastic changes underlying the process of formation of inhibitory conditioned neuronal reactions are supposed to be of intracortical nature.