Selective specificity of calcium-binding proteins calbindin and calretinin expression in the magnocellular neurosecretory hypothalamic nuclei of tortoises and turtles.

We have studied the distribution of calcium-binding proteins in the magnocellular neurosecretory nuclei of nonapeptidergic neurosecretory nuclei of the preoptic-hypothalamic complex in a tortoise (Testudo horsfieldi) and a pond turtle (Emys orbicularis) using immunohistochemistry. We have found that different types of cells in the paraventricular and supraoptic nuclei predominantly express calbindin and, to a lesser extent, calretinin, but not parvalbumin. The selective calbindin/calretinin control of the neurohormone secretion in these hypothalamic nuclei is an evolutionary conservative feature typical of reptiles and mammals.

[INTERACTION OF GLUTAMATE AND GABA RECEPTORS IN THE CENTRAL NERVOUS SYSTEM].

The article provides an overview of postsynaptic interaction of GABA and glutamate receptors in central neurons. Co-localization of GABA and glutamate in synapses, structure and function of their receptors and interaction of both ionotropic and metabotropic glutamate and GABA receptors are being discussed.

[SECOND MESSENGERS IN PRESYNAPTIC REGULATION OF GLYCINERGIC SYNAPSE ON THE FROG MOTONEURON].

The possible pathways of inhibitory influences mediated by two kinds of metabotropic receptors, group III metabotropic glutamate receptors (mGluRs III) and GABAB receptors (GABABRs) to the miniature glycinergic events were investigated in the isolated spinal cord of the frog Rana ridibunda. The glycinergic events prevailed within the miniature inhibitory activity of motoneurons [3]. Selective agonists of GABABRs (baclofen) and group III mGluR (LAP4) reduce the frequency of miniature events to 48.0 ± 5.56% (n = 8) and 48.5 ± 8.6% (n = 5) respectively. The mean amplitude of miniature potentials was not modified significantly which indicates the presynaptic mode of their action on the synaptic transmission. To reveal the stages of metabotropic receptors regulatory effects on the glycine exocitosis the application of their selective agonists was performed after selective blockade of putative links of glycinergic transmission modulation. It was shown that the mGluRsIII influences are due to the negative feedback with adenylyl cyclase (AC) whereas the following step is formed by protein kinase A (PKA), because their selective blockade eliminate the effect of group III mGluRs activation. The AC is not involved in transdusing the GABABRs signal to the glycine miniature activity because SQ22536, an AC-inhibitor does not eliminate the inhibitory action of baclofen. The action of GABABRs depends on the activity of the phospholipase C (PLC) because its inhibition with U73122 prevents the effect of baclofen. The next possible link of this pathway could be the protein kinase C (PKC); but it is not involved in the realization of GABABRs influences because the PKC blocker (GF 109302X) does not modify the baclofen effect. The common link of group III mGluRs and GABABRs influences on the glycinergic miniature activity realization can be the inositol trisphosphate receptors (IP3Rs) that regulate the Ca2+ outflow from the nerve terminal depots and are connected (according to the literature data) with PKA, cAMP and PLC. In our experiments 2-APB, an IP3Rs antagonist, reduced to 26 ± 8% (n = 7) the frequency of glycinergic miniature activity and prevented the inhibitory effects of group III mGluRs and GABABRs. Our data suggest that collision and cross-talk of these Glu- and GABA-metabotropic pathways which was described earlier [2] may take place at this level.

[Modulation of GABA- and kainate-activated currents by metabotropic receptors in isolated rat cortical neurons].

Whole-cell patch-clamp recordings from isolated neurons from rat prefrontal cortex have been made to study GABAb and mGluR receptor modulation of currents induced by applications of GABA and kainate. The GABAb-receptor antagonist CGP-55845 (5 microM) enhanced the peak by 26 +/- 13% (n = 6) but had no effect on the steady-state of GABA-activated current. Bath application of GABAb-receptor agonist baclofen (50 microM) enhanced the GABAa currents by 9 +/- 2% (n = 8). Kainate-activated currents were not affected by baclofen. Both GABA-activated currents and kainate-activated currents were not affected by trans-ACPD (MGluR agonist). These results suggest that in cortex postsynaptic response of GABAa-receptors can be modulated by GABAb-receptors.

[Desensitization of glycine mediated currents in frog spinal cord neurons].

Whole-cell patch clamp recordings from isolated frog spinal cord neurons were made to study the desensitization of glycine-mediated currents. The decay phase of current induced by application of glycine (1 mM) could be either monoexponential or biexponential. Monoexponential decays had either tau1 = 1693 +/- 135 ms (n = 8) or tau2 = 364 +/- 42 ms (n = 9) time constants, while biexponential decays had both tau1 and tau2. Currents with fast monoexponential decay (tau2) remained reproducible through the experiment. Currents with slow monoexponential (tau1) and biexponential decay gradually became faster while whole-cell patch clamp recordings were being taken. These results suggest that, at least, two different glycine receptor subtypes are present in frog spinal cord neurons.

[Effect of antagonists of 5-HT receptors on modulation with serotonin of synaptical activity of projectional neurons of dorsolateral nucleus of rat amygdala].

The work deals with study of role of different serotonin (5-HT) receptor types in the process of synaptic activity modulation of rat dorsolateral amygdale projection neurons with serotonin. The selective antagonist of 5-HT1,2 receptors methylsergide maleate was shown to suppress the 5-HT inhibitory action on amplitude of the postsynaptic currents evoked by glutamate and GABA, whereas the antagonist of 5-HT3,4 receptors SDZ202-557 produced no effect on the above-mentioned 5-HT action. The obtained action indicates that the 5-HT modulatory effect on the projectional neuron synaptic inputs is mediated by 5-HT receptors of the 1 and 2 types.

[Effect of GABA and glycine neuromediator interaction in the central nervous system].

Today it is well accepted that GABA can be co-localized and co-released with glycine in the same synapse. This article provides an overview of GABA and glycine co-localization and the effects of simultaneous activation of GABAA and glycine receptors. The review deals with mechanisms of direct and indirect receptor interaction, as well as with the effect of non-selective activation of glycine receptors by GABA.

[Inhibitory regulation of glutamate receptors in the frog motoneuron].

The interaction of exogenously applied excitatory (glutamate and their agonists NMDA, AMPA, kainate) and inhibitory (glycine and GABA) amino acid effects was studied intracellularly in the motoneurones of the isolated frog spinal cord. During simultaneous glycine or GABA bath applications GLU-, AMPA-, KA- and NMDA-evoked responses were, respectively, decreased up to 45.8 +/- 2.9% (n = 12) and 67.8 +/- 3.9% (n = 16), 13.9 +/- 4.3% (n = 9) and 32.1 +/- 8.3% (n = 12), 36.8 +/- 8.2% (n = 7) and 48.0 +/- 11.8% (n = 6), 7.7 +/- 3.5% (n = 9) and 18.1 +/- 3.8% (n = 14) from the control. Sequential applications of EAA after glycine or GABA as well as the applications of EAA-agonist and glycine (GABA) mixture demonstrated similar results. The decrease of EAA-responses by glycine and GABA was abolished by selective GlyR antagonist strychnine (1 microM) and the selective GABAR antagonist SR95531 (gabazine, 20 MM), respectively. The data revealed differences in inhibitory effect of glycine and GABA on the excitation responses mediated by different types of glutamate receptors in the frog motoneurones: the predominant inhibitory effect of glycine and GABA on NMDA-responses and weak inhibitory effect on KA- and GLU-responses. Inhibitory effect of glycine was twice as much as that of GABA at the same concentration.

[Summation of GABA- and glutamate-mediated currents in rat cortical neurons].

Whole-cell patch clamp recordings from isolated neurons from rat prefrontal cortex have been made to study the interaction of responses induced by application of GABA and glutamate. Two different pipette solutions were used in this research: the first one was based on CsCl, while the second one was CsF-based. With CsCl-based pipette solution being used, co-application of GABA (200 microM) and glutamate (200 microM) resulted in producing a total current smaller than the sum of the two individual responses. But with CsF-based pipette solution being used, the response to co-application of GABA (200 microM) and glutamate (200 microM) was equal to the sum of the two individual responses. These results suggest that there is a cross-modulation between GABA- and glutamate-mediated responses.

[Role of long-term potentiation in mechanism of the conditioned learning].

The review analyzes the fundamental problem of study of the neuronal mechanisms underlying processes of learning and memory. As a neuronal models of these phenomena there was considered one of the cellular phenomena that has characteristics similar with those in the process of "remembering"--such as the long-term potentiation (LTP). LTP is easily reproduced in certain synapses of the central nervous system, specifically in synapses of hippocampus and amygdala. As to the behavioral model of learning, there was used the conditioned learning, in frames of which production of the context-dependent/independent conditioned reaction was considered. Analysis of literature data has allowed showing that various stages of LTP produced on synapses of hippocampus or amygdala can be comparable with certain phase of the process of learning. Based on the exposed material the authors conclude that plastic changes of synapses of hippocampus and amygdala can represent the morphological substrate of some kinds of learning and memory.

[Mechanisms of interactions between glycine- and GABA-mediated responses in spinal cord neurons].

The interactions of GABA- and glycine-mediated responses have been analyzed, the whole cell patch-clamp method being used. The response induced by co-application of glycine and GABA was a lesser one than the sum of responses induced by applying two transmitters separately. The molecular mechanisms underlying this effect have been determined. Due to applications of high concentrations of neurotransmitters it was revealed that GABA could activate glycine receptors in frog spinal motoneurons with relatively high efficiency (EC50 = 1.2 mM). The sequential application of neurotransmitters showed that even a single application of glycine could significantly boost the "run-down" of the GABA-mediated current, suggesting that there was a strong phosphorylation-dependent mechanism of GABAa-receptors inhibition. These mechanisms are likely to take place in frog spinal motoneurons when GABA and glycine are co-released from the same synaptic terminal.

[The contribution of glycine and GABA(A) receptors to generation of the inhibitory postsynaptic potentials in the frog spinal cord motoneurones].

The contribution of glycine and GABA(A) receptors to generation of the inhibitory postsynaptic potentials (IPSPs) evoked by microstimulation of the inhibitory fibers was studied intracellularly in the motoneurones of the isolated frog spinal cord. IPSPs were isolated by bloking EPSPs with kynurenate or CNQX and AP-5. The reversion under the small depolarising current (1-10) nA was used for the identification of IPSPs. The selective GlyR antagonist strychnine (1-5 microM) reduced the amplitude of IPSPs by a factor of 4.7 on the average in all studied motoneurones, while the selective GABA(A)R antagonist bicuculline (50-70 microM)--only by a factor of 1.6 and had no effect in 44% of motoneurones. Sequential applications of strychnine and bicuculline completely blocked the IPSPs. The results suggest that postsynaptic inhibition in the frog motoneurones is mediated by glycine (predominantly) and GABA(A) (to a smaller extent) receptors. It is possible the GABA(A) receptors are partly extrasynaptic.

[Gaba- and glycine-immunoreactive synapses in the spinal cord of the frog Rana temporaria].

Postembedding immunogold method was used to examine the distribution of gamma-aminobutyric acid- and glycine-immunoreactives synapses on the motoneurons and primary afferent axons in frog spinal cord. Analysis of all labeled boutons on dendrites and somata of motoneurons showed that 7% were labeled for GABA, 23% only for glycine and approximately 70% were immunoreactive for both GABA and glycine. These results confirm the predominant role of glycine in postsynaptic inhibition of motoneuronal activity. Three populations of synaptic boutons were found on primary afferent axons: GABA-immunoreactive (25%), glycine-immunoreactive (5%) and the majority of the immunoreactive synapses exhibited colocalization of two inhibitory transmitters. Greater proportion of axo-axonal synases was organized in synaptic triads. The possible roles of glycine in the axo-axonal synapses on the primary afferent fibers are discussed.

Characteristics and interaction of GABAergic and glycinergic processes in frog spinal cord neurons.

Whole-cell patch clamp recordings from isolated spinal cord neurons from the frog Rana temporaria were made to study the interaction of processes induced by application of GABA and glycine. The amplitudes of currents evoked by application of glycine did not change with time, while the amplitudes of GABA-mediated currents decreased two-fold during the first 15 min of the experiment and stabilized at the new level. Neuron responses to simultaneous application of GABA and glycine were always smaller than the sum of the responses to separate application of these neurotransmitters. On application of GABA and glycine at the same concentration (5 mM), the amplitude of the response to simultaneous application decreased with time, reaching the level of the glycine-mediated response. A mixture of glycine and GABA at 8 microM and 5 mM, respectively, gave settled responses which were larger than the largest individual response by more than obtained with other mixtures. These data provide evidence that frog motoneurons may express receptors activated by both GABA and glycine.

[Principles of organization and evolution of systems of regulation of functions].

Evolution of living organisms is closely connected with evolution of structure of the system of regulations and its mechanisms. The functional ground of regulations is chemical signalization. As early as in unicellular organisms there is a set of signal mechanisms providing their life activity and orientation in space and time. Subsequent evolution of ways of chemical signalization followed the way of development of ways of delivery of chemical signal and development of mechanisms of its regulation. The mechanisms of chemical regulation of the signal interaction is discussed by the example of the specialized system of transduction of signal from neuron to neuron, of effect of hormone on the epithelial cell and modulation of this effect. These mechanisms are considered as the most important ways of the fine and precise adaptation of chemical signalization underlying functioning of physiological systems and organs of the living organism.