Prenatal nicotine exposure alters glycinergic and GABAergic control of respiratory frequency in the neonatal rat brainstem-spinal cord preparation

Bath application of GABA-A receptor agonists in neonatal rat brainstem-spinal cord preparations (BSSC) reduces respiratory frequency, an effect that is enhanced by prenatal nicotine exposure. Here we test the hypothesis that these effects can be reproduced by microinjection of GABAergic and glycinergic agonists into the pre-Botzinger complex region (PBC). We recorded the activity of phrenic motor axons from the fourth cervical ventral root in 1-3 days old BSSC that were exposed to either nicotine (6 mg/(kg day)) or saline prenatally. Microinjection of glycine or muscimol into the PBC caused abrupt, reversible apnea in all experiments. Apnea duration with glycine averaged 50.3+/-5 s in saline-exposed (N=12), and 95.7+/-9.9 s in nicotine-exposed (N=12) neonates (P<0.001). Apnea duration with muscimol averaged 51+/-5.1 s in saline-exposed (N=10), and 86+/-10.6 s in nicotine-exposed (N=12) neonates (P<0.05). These data show that prenatal nicotine exposure alters development of central ventilatory control, and that neurons in the PBC region are involved.

Antibacterial activity of remifentanil and mixtures of remifentanil and propofol

STUDY OBJECTIVE

To investigate the antibacterial activity of glycine, which is contained in remifentanil, when combined with propofol.

DESIGN

Prospective study.

SETTING

Departments of anesthesiology and microbiology of a university hospital.

MEASUREMENTS

Growth of the microorganisms Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans in propofol 1%; saline dilutions of remifentanil at one-, 10-, and 100-microg/mL concentrations; and 1:1 mixtures of propofol with remifentanil solutions was determined.

MAIN RESULTS

Remifentanil inhibits bacterial growth in a concentration-dependent manner. The antibacterial effects were more pronounced with Staphylococcus aureus and Pseudomonas aeruginosa at cultures obtained at the fifth hour. The inhibition of bacterial growth was less influenced with Escherichia coli and Candida albicans.

CONCLUSIONS

Propofol and remifentanil mixtures decreased bacterial growth, and combinations may reduce the infectious complications from accidentally contaminated propofol.

GABAA and glycine receptor-mediated transmission in rat lamina II neurones: relevance to the analgesic actions of neuroactive steroids

Analgesic neurosteroids such as 5alpha-pregnan-3alpha-ol-20-one (5alpha3alpha) are potent selective endogenous modulators of the GABA(A) receptor (GABA(A)R) while certain synthetic derivatives (i.e. minaxolone) additionally enhance the function of recombinant glycine receptors (GlyR). Inhibitory transmission within the superficial dorsal horn has been implicated in mediating the analgesic actions of neurosteroids. However, the relative contribution played by synaptic and extrasynaptic receptors is unknown. In this study, we have compared the actions of 5alpha3alpha and minaxolone upon inhibitory transmission mediated by both GABA(A) and strychnine-sensitive GlyRs in lamina II neurones of juvenile (P15-21) rats. At the near physiological temperature of 35 degrees C and at a holding potential of -60 mV we recorded three kinetically distinct populations of miniature IPSCs (mIPSCs): GlyR-mediated, GABA(A)R-mediated and mixed GABA(A)R-GlyR mIPSCs, arising from the corelease of both inhibitory neurotransmitters. In addition, sequential application of strychnine and bicuculline revealed a small (5.2 +/- 1.0 pA) GlyR- but not a GABA(A)R-mediated tonic conductance. 5alpha3alpha (1-10 microm) prolonged GABA(A)R and mixed mIPSCs in a concentration-dependent manner but was without effect upon GlyR mIPSCs. In contrast, minaxolone (1-10 microm) prolonged the decay of GlyR mIPSCs and, additionally, was approximately 10-fold more potent than 5alpha3alpha upon GABA(A)R mIPSCs. However, 5alpha3alpha and minaxolone (1 microm) evoked a similar bicuculline-sensitive inhibitory conductance, indicating that the extrasynaptic GABA(A)Rs do not discriminate between these two steroids. Furthermore, approximately 92% of the effect of 1 microm 5alpha3alpha upon GABAergic inhibition could be accounted for by its action upon the extrasynaptic conductance. These findings are relevant to modulation of inhibitory circuits within spinally mediated pain pathways and suggest that extrasynaptic GABA(A)Rs may represent a relevant molecular target for the analgesic actions of neurosteroids.

Effect of glycine on the calcium signal of thrombin-stimulated platelets

In treatment of hemorrhagic shock, small-volume infusion of 7.5% NaCl gives immediate hemodynamic improvement, but in vitro experiments suggest it depresses the hemostatic system. Since previous reports showed that hyperosmotic glycine solutions preserved the platelet function better than hyperosmotic NaCl solutions, we investigated whether glycine changes the intracellular calcium ([Ca]i) signal. Platelets were incubated in hyperosmotic solutions containing sodium glycine or glycine base and stimulated with 0.1 IU/ml thrombin. [Ca]i increases were compared with an isosmotic control. Platelets incubated in zero calcium/EGTA were used to study separately the effect of glycine on calcium mobilization from intracellular stores and extracellular calcium entry. When NaCl was replaced by sodium glycine, the [Ca]i increase produced by thrombin was enhanced, because the calcium entry increased without changes in the mobilization of stored calcium. The addition of 50 mmol/l glycine base to the HEPES-buffered media increases the thrombin-induced entry of calcium or manganese. This study demonstrates that hyperosmotic glycine solutions increase the entry of calcium. This effect contrasts with the impairment of the thrombin-induced calcium signals by NaCl. The addition of low amounts of glycine in resuscitation solutions would be useful to reduce dysfunctional inflammatory responses without the risk of bleeding; however, concentrated solutions could cause toxic effects.

The effect of zinc on glycinergic inhibitory postsynaptic currents in rat spinal dorsal horn neurons

The effect of zinc on glycinergic spontaneous inhibitory postsynaptic currents (IPSCs) was investigated using the whole-cell patch-clamp technique in mechanically dissociated rat spinal dorsal horn neurons. Zinc at a concentration of 10 microM reversibly increased the spontaneous IPSC frequency without changing the current amplitudes, suggesting that zinc increases spontaneous glycine release from presynaptic nerve terminals. At a low concentration of 1 microM, on the other hand, zinc potentiated the amplitude of spontaneous IPSCs but had no effect on the frequency. At a high concentration of 100 microM, zinc increased the spontaneous IPSC frequency while it inhibited the IPSC amplitude. The current evoked by exogenously applied glycine was potentiated and inhibited by low and high concentrations of zinc, respectively. The increase in spontaneous IPSC frequency by 10 microM zinc was inhibited by blocking the voltage-dependent Ca(2+) channels in the presence of both omega-conotoxin-MVIIC and nifedipine. The facilitatory effect of zinc on spontaneous IPSC frequency was also inhibited in the presence of tetrodotoxin. In the slice preparation, 30 microM zinc potentiated the evoked IPSC amplitude and decreased the paired pulse ratio. These results suggest that, in addition to an action on the postsynaptic glycine receptors, zinc may depolarize the presynaptic nerve terminals, leading to an activation of voltage-dependent Na(+) and Ca(2+) channels that in turn increases glycine release. Since dorsal horn neurons receive nociceptive inputs, zinc may play an important role in the regulation of sensory transmission.

Novel therapeutics for schizophrenia: targeting glycine modulation of NMDA glutamate receptors

Currently, a major hypothesis for the pathophysiology of schizophrenia proposes that numerous risk factors converge on the N-methyl-D-aspartate (NMDA) receptor for the neurotransmitter glutamate, resulting in neurodevelopmental abnormalities at glutamate synapses and hypofunction of NMDA receptors.This hypothesis was presented in a previous “Trends in Psychopharmacology” column. Novel treatments are now in development that can theoretically boost the function of NMDA receptors by enhancing actions at the glycine co-transmitter site of this receptor complex. Early studies already indicate that this may lead to improvement in negative and cognitive symptoms of schizophrenia, especially when added as augmenting agents to atypical antipsychotics.

Glycine-induced long-term synaptic potentiation is mediated by the glycine transporter GLYT1

The negative symptoms of schizophrenia are reverted by treatment with glycine or other agonists of the glycine-B site which facilitate NMDA receptor function. On the other hand, there are experimental observations showing that exogenous application of glycine (0.5-10mM) results in a long-lasting potentiation of glutamatergic synaptic transmission (LTP-GLY). The characterization of the mechanisms underlying LTP-GLY could be useful to develop new therapies for schizophrenia. The main goal of this work is to deepen the understanding of this potentiation phenomenon. The present study demonstrates in rat hippocampal slices that superfusion of glycine 1mM during 30 min produces a potentiation of excitatory postsynaptic potentials in CA3-CA1 pathway lasting at least 1h. Glycine application does not modify neither presynaptic fiber volley nor paired-pulse facilitation of synaptic potentials. This LTP-GLY is independent of both strychnine-sensitive glycine receptors and nifedipine-sensitive calcium channels. Interestingly, LTP-GLY is not inhibited but strengthened by NMDA receptors antagonists such as AP-5 or MK-801. In contrast, LTP-GLY is partially or totally blocked with the antagonists of glycine transporter GLYT1, sarcosine or ALX-5407, respectively. These results indicate that LTP-GLY requires the activation of GLYT1, a glycine transporter co-localized and associated to NMDA receptors. In addition, the fact that NMDA receptor inhibition increases LTP-GLY magnitude, opens the possibility that these receptors could have a negative control on GLYT1 activity.

Glycine receptors of A-type ganglion cells of the mouse retina

A-type ganglion cells of the mouse retina represent the visual channel that transfers temporal changes of the outside world very fast and with high fidelity. In this study we combined anatomical and physiological methods in order to study the glycinergic, inhibitory input of A-type ganglion cells. Immunocytochemical studies were performed in a transgenic mouse line whose ganglion cells express green fluorescent protein (GFP). The cells were double labeled for GFP and the four alpha subunits of the glycine receptor (GlyR). It was found that most of the glycinergic input of A-type cells is through fast, alpha1-expressing synapses. Whole-cell currents were recorded from A-type ganglion cells in retinal whole mounts. The response to exogenous application of glycine and spontaneous inhibitory postsynaptic currents (sIPSCs) were measured. By comparing glycinergic currents recorded in wildtype mice and in mice with specific deletions of GlyRalpha subunits (Glra1spd-ot, Glra2-/-, Glra3-/-), the subunit composition of GlyRs of A-type ganglion cells could be further defined. Glycinergic sIPSCs of A-type ganglion cells have fast kinetics (decay time constant tau = 3.9 +/- 2.5 ms, mean +/- SD). Glycinergic sIPSCs recorded in Glra2-/- and Glra3-/- mice did not differ from those of wildtype mice. However, the number of glycinergic sIPSCs was significantly reduced in Glra1spd-ot mice and the remaining sIPSCs had slower kinetics than in wildtype mice. The results show that A-type ganglion cells receive preferentially kinetically fast glycinergic inputs, mediated by GlyRs composed of alpha1 and beta subunits.

Strychnine-sensitive glycine receptors mediate the analgesic but not hypnotic effects of emulsified volatile anesthetics

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in hypnosis and analgesia induced by emulsified volatile anesthetics. After having established the mice model of hypnosis and analgesia by intraperitoneally injecting (i.p.) appropriate doses of ether, enflurane, isoflurane or sevoflurane, we intracerebroventricularly (i.c.v.) or intrathecally (i.t.) injected different doses of strychnine and then observed the effects on the sleeping time using the awaken test and the pain index in hot-plate test (HPPI) using the hot-plate test. In the awaken test, strychnine 1, 2, 4 microg (i.c.v.) had no distinctive effect on the sleeping time of the mice treated with the four emulsified inhalation anesthetics mentioned above (p > 0.05); in the hot-plate test, strychnine 0.1, 0.2, 0.4 microg (i.t.) can significantly and dose-dependently decrease the HPPI of the mice treated with emulsified ether, enflurane and sevoflurane (p < 0.05, p < 0.01); strychnine 0.1 microg (i.t.) did not affect the HPPI of the mice treated with emulsified isoflurane (p > 0.05), but 0.2 and 0.4 microg (i.t.) can significantly decrease the HPPI of the mice treatedwith emulsified isoflurane (p < 0.05, p < 0.01). These results suggest that strychnine-sensitive glycine receptors may contribute to the analgesic but not to the hypnotic effects induced by ether, enflurane, isoflurane and sevoflurane.

Are pacemaker properties required for respiratory rhythm generation in adult turtle brain stems in vitro?

The role of pacemaker properties in vertebrate respiratory rhythm generation is not well understood. To address this question from a comparative perspective, brain stems from adult turtles were isolated in vitro, and respiratory motor bursts were recorded on hypoglossal (XII) nerve rootlets. The goal was to test whether burst frequency could be altered by conditions known to alter respiratory pacemaker neuron activity in mammals (e.g., increased bath KCl or blockade of specific inward currents). While bathed in artificial cerebrospinal fluid (aCSF), respiratory burst frequency was not correlated with changes in bath KCl (0.5-10.0 mM). Riluzole (50 microM; persistent Na(+) channel blocker) increased burst frequency by 31 +/- 5% (P < 0.05) and decreased burst amplitude by 42 +/- 4% (P < 0.05). In contrast, flufenamic acid (FFA, 20-500 microM; Ca(2+)-activated cation channel blocker) reduced and abolished burst frequency in a dose- and time-dependent manner (P < 0.05). During synaptic inhibition blockade with bicuculline (50 microM; GABA(A) channel blocker) and strychnine (50 muM; glycine receptor blocker), rhythmic motor activity persisted, and burst frequency was directly correlated with extracellular KCl (0.5-10.0 mM; P = 0.005). During synaptic inhibition blockade, riluzole (50 microM) did not alter burst frequency, whereas FFA (100 microM) abolished burst frequency (P < 0.05). These data are most consistent with the hypothesis that turtle respiratory rhythm generation requires Ca(2+)-activated cation channels but not pacemaker neurons, which thereby favors the group-pacemaker model. During synaptic inhibition blockade, however, the rhythm generator appears to be transformed into a pacemaker-driven network that requires Ca(2+)-activated cation channels.

Strychnine-sensitive glycine receptors mediate analgesia induced by emulsified inhalation anaesthetics in thermal nociception but not in chemical nociception

The present study was designed to investigate the role of strychnine-sensitive glycine receptors in analgesia induced by emulsified inhalation anaesthetics. After having established the mice model of analgesia by intraperitoneal or subcutaneous injections of appropriate doses of ether, enflurane, isoflurane or sevoflurane, we injected different doses of strychnine intrathecally and then observed the effects on the tail-flick latency using the tail-withdrawal test and the writhing times and acetic acid-induced writhing test. In the tail-withdrawal test, all four emulsified inhalation anaesthetics (intraperitoneally) significantly increased the tail-flick latency (P < 0.01) compared with baseline, and the increase of tail-flick latency induced by four emulsified inhalation anaesthetics can be abolished by intrathecally injected strychnine. In the acetic acid-induced writhing test, writhing times inhibition induced by subcutaneous administration of four emulsified inhalation anaesthetics was not effected by intrathecal strychnine (0.1, 0.2 and 0.4 microg). The data presented in this study suggest that glycine receptors are specifically involved in mediating the analgesic effect of ether, enflurane, isoflurane and sevoflurane on thermal-induced nociception but not chemically induced nociception.

Respiratory activity in brainstem of fetal mice lacking glutamate decarboxylase 65/67 and vesicular GABA transporter

The respiratory neural network in the mammalian medulla oblongata shows rhythmic activity before birth. GABA and glycine are considered to be involved in control of respiratory rhythm. Recently we have demonstrated respiratory failure in glutamic acid decarboxylase (GAD) 67-deficient mice [Tsunekawa N, Arata A, Obata K (2005) Development of spontaneous mouth/tongue movement and related neural activity, and their repression in mouse fetus lacking glutamate decarboxylase 67. Eur J Neurosci 21:173-178]. To further evaluate the involvement of GABA and glycine in fetal respiratory function, we studied neural activities in brainstem-spinal cord blocks prepared from GAD65-/-:67-/- and vesicular GABA transporter (VGAT)-/-mice on embryonic day 14 (E14)-E15 and E18. In these knockout mice, the synthesis of GABA and the vesicular release of GABA and glycine are completely absent, respectively. Spontaneous respiratory discharges were observed in the ventral roots at the cervical cord (C) 4 level from wild-type mice but not from the knockout mice on E18. Administration of substance P induced C4 discharges in GAD65-/-:67-/- preparations but not in VGAT-/- preparations. C4 discharges were observed in the knockout mice on E14-E15, although the frequency was lower than that in the wild-type. Neuronal activities in the respiratory network of the E18 brainstem were recorded using a "blind" patch-clamp technique. Expiratory and inspiratory neurons with their characteristic firing patterns were observed in the wild-type fetuses. Strychnine reversed inspiratory-phase hyperpolarization to large depolarization in expiratory neurons. On the other hand, neurons in the same area of the knockout mice fired spontaneously without any rhythm. Substance P induced hyperpolarizing potentials in medullary neurons of GAD65-/-:67-/- mice. Further administration of strychnine induced large depolarizing potentials. Rhythmic activities were not observed in VGAT-/- mice even in the presence of substance P and strychnine. These results indicate that the lack of GABA and glycine impairs the function of the respiratory network in mouse fetuses and the impairment progresses with fetal age.

Early electrophysiological abnormalities in lumbar motoneurons in a transgenic mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a lethal, adult-onset disease characterized by progressive degeneration of motoneurons. Recent data have suggested that the disease could be linked to abnormal development of the motor nervous system. Therefore, we investigated the electrical properties of lumbar motoneurons in an in-vitro neonatal spinal cord preparation isolated from SOD1(G85R) mice, which is a transgenic model of amyotrophic lateral sclerosis. The study was performed on young animals at the beginning of their second week, between postnatal days 6 and 10. Measurements of resting membrane potential and action potential characteristics of motoneurons were similar in wild-type and SOD1(G85R) mice. However, the input resistance of motoneurons from transgenic mice was significantly lower than that of wild-type animals, whereas their membrane capacitance was increased, strongly suggesting larger SOD1(G85R) motoneurons. Furthermore, the slope of the frequency-intensity curve was steeper in motoneurons from wild-type pups. Interestingly, the input resistance as well as the slope of the frequency-intensity curves of other spinal neurons did not show such differences. Finally, the amplitude of dorsal root-evoked potentials following high-intensity stimulation was significantly smaller in SOD1(G85R) motoneurons. The superoxide dismutase 1 mutation thus induces specific alterations of the functional properties of motoneurons early in development.

Facilitation of spontaneous glycine release by anoxia potentiates NMDA receptor current in the hypoglossal motor neurons of the rat

Deficiency in energy supply, such as occurs during hypoxia, anoxia, metabolic stress and mitochondrial failure, strongly affects the excitability of central neurons. Such lowered energy supply evokes various changes in spontaneous synaptic input to the hippocampal and cortical neurons. However, how this energy deprivation affects synaptic input to motor neurons, which are also vulnerable to energy deprivation, has never been addressed. Here we report for the first time the effect of metabolic stress on synaptic input to motor neurons by recording postsynaptic currents in the hypoglossal nucleus. Chemical anoxia with NaCN (1 mm) and anoxia with 95% N(2) induced a persistent inward current and a marked and robust increase in action potential-independent synaptic input. This increase was abolished by strychnine, but not by picrotoxin, CNQX or MK-801, indicating glycine release facilitation. Blockade of voltage-dependent Ca(2+) channels and extracellular Ca(2+) deprivation strongly attenuated this facilitation. The amplitude of inward currents evoked by local application of NMDA to the motor neurons in the presence of strychnine was significantly increased during NaCN application. A saturating concentration of d-serine occluded this potentiation, suggesting that released glycine activated the glycine-binding sites of NMDA receptors. By contrast, neurons in the dorsal motor nucleus of the vagus showed no detectable change in synaptic input in response to NaCN. These data suggest that increase in synaptically released glycine in response to metabolic stress may play an exacerbating role in NMDA receptor-mediated excitotoxicity in motor neurons.

High potassium-induced facilitation of glycine release from presynaptic terminals on mechanically dissociated rat spinal dorsal horn neurons in the absence of extracellular calcium

The high potassium-induced potentiation of spontaneous glycine release in extracellular Ca2+-free conditions was studied in mechanically dissociated rat spinal dorsal horn neurons using whole-cell patch-clamp technique. Elevating extracellular K+ concentration reversibly increased the frequency of spontaneous glycinergic inhibitory postsynaptic currents (IPSCs) in the absence of extracellular Ca2+. Blocking voltage-dependent Na+ channels (tetrodotoxin) and Ca2+ channels (nifedipine and omega-grammotoxin-SIA) had no effect on this potassium-induced potentiation of glycine-release. The high potassium-induced increase in IPSC frequency was also observed in the absence of extracellular Na+, although the recovery back to baseline levels of release was prolonged under these conditions. The action of high potassium solution on glycine release was prevented by BAPTA-AM, by depletion of intracellular Ca2+ stores by thapsigargin and by the phospholipase C inhibitor U-73122. The results suggest that the elevated extracellular K+ concentration causes Ca2+ release from internal stores which is independent of extracellular Na+- and Ca2+-influx, and may reveal a novel mechanism by which the potassium-induced depolarization of presynaptic nerve terminals can regulate intracellular Ca2+ concentration and exocytosis.

Glycine receptors are functionally expressed on bullfrog retinal cone photoreceptors

Using immunocytochemical and whole cell recording techniques, we examined expression of glycine receptors on bullfrog retinal cone photoreceptors. Immunofluorescence double labeling experiments conducted on retinal sections and isolated cell preparations showed that terminals and inner segments of cones were immunoreactive to both alpha1 and beta subunits of glycine receptors. Moreover, application of glycine induced a sustained inward current from isolated cones, which increased in amplitude in a dose-dependent manner, with an EC50 (concentration of glycine producing half-maximal response) of 67.3+/-4.9 microM, and the current was blocked by the glycine receptor antagonist strychnine, but not 5,7-dichlorokynurenic acid (DCKA) of 200 microM, a blocker of the glycine recognition site at the N-methyl-D-aspartate (NMDA) receptor. The glycine-induced current reversed in polarity at a potential close to the calculated chloride equilibrium potential, and the reversal potential was changed as a function of the extracellular chloride concentration. These results suggest that strychnine-sensitive glycine receptors are functionally expressed in bullfrog cones, which may mediate signal feedback from glycinergic interplexiform cells to cones in the outer retina.

A novel effect of cochlear efferents: in vivo response enhancement does not require alpha9 cholinergic receptors

Outer hair cells in the mammalian cochlea receive a cholinergic efferent innervation that constitutes the effector arm of a sound-evoked negative feedback loop. The well-studied suppressive effects of acetylcholine (ACh) release from efferent terminals are mediated by alpha9/alpha10 ACh receptors and are potently blocked by strychnine. Here, we report a novel, efferent-mediated enhancement of cochlear sound-evoked neural responses and otoacoustic emissions in mice. In controls, a slow enhancement of response amplitude to supranormal levels appears after recovery from the classic suppressive effects seen during a 70-s epoch of efferent shocks. The magnitude of post-shock enhancement can be as great as 10 dB and tends to be greater for high-frequency acoustic stimuli. Systemic strychnine at 10 mg/kg eliminates efferent-induced suppression, revealing a purely enhancing effect of efferent shocks, which peaks within 5 s after efferent-stimulation onset, maintains a constant level through the stimulation epoch, and slowly decays back to baseline with a time constant of approximately 100 s. In mice with targeted deletion of the alpha9 ACh receptor subunit, efferent-evoked effects resemble those in wild types with strychnine blockade, further showing that this novel efferent effect is fundamentally different from all cholinergic effects previously reported.

Identification of novel glycine sulfonamide antagonists for the EP1 receptor

A high-throughput screen targeting the EP(1) receptor identified non-acidic glycine sulfonamide derivative 2a with a pK(i) of 6.2. Analogue synthesis allowed a thorough investigation of the structure-activity relationship (SAR) and led to a 100-fold increase in recombinant potency.

Three types of inhibitory miniature potentials in frog spinal cord motoneurons: Possible GABA and glycine cotransmission

Miniature inhibitory postsynaptic potentials (mIPSP) of motoneurons in isolated frog spinal cord were recorded in conditions of blockade of the conduction of nerve spikes and ionotropic glutamate receptors (TTX, 1 microM, CNQX, 25 microM, D-AP5, 50 microM). Three types of mIPSP were identified: those with fast and slow time characteristics and mIPSP with two-component decays. Two-component mIPSP accounted for 8.7% of all selected responses, fast mIPSP for 64.5%, and slow mIPSP for 26.8%. Blockade of GABA(A) receptors with bicuculline (20 microM) led to decreases in the numbers of slow and two-component mIPSP and an increase in the number of mIPSP with fast kinetics. Strychnine (1 microM), a blocker of glycine receptors, led to a reduction in the number of fast receptors and an increase in the number of slow potentials. These data suggest that frog spinal cord motoneurons have three types of inhibitory mIPSP, mediated by GABA, glycine, and simultaneous release of these two transmitters from the same presynaptic terminals.

Excitatory interneurons dominate sensory processing in the spinal substantia gelatinosa of rat

Substantia gelatinosa (SG, lamina II) is a spinal cord region where most unmyelinated primary afferents terminate and the central nociceptive processing begins. It is formed by several distinct groups of interneurons whose functional properties and synaptic connections are poorly understood, in part, because recordings from synaptically coupled pairs of SG neurons are quite challenging due to a very low probability of finding connected cells. Here, we describe an efficient method for identifying synaptically coupled interneurons in rat spinal cord slices and characterizing their excitatory or inhibitory function. Using tight-seal whole-cell recordings and a cell-attached stimulation technique, we routinely tested about 1500 SG interneurons, classifying 102 of them as monosynaptically connected to neurons in lamina I-III. Surprisingly, the vast majority of SG interneurons (n = 87) were excitatory and glutamatergic, while only 15 neurons were inhibitory. According to their intrinsic firing properties, these 102 SG neurons were also classified as tonic (n = 49), adapting (n = 17) or delayed-firing neurons (n = 36). All but two tonic neurons and all adapting neurons were excitatory interneurons. Of 36 delayed-firing neurons, 23 were excitatory and 13 were inhibitory. We conclude that sensory integration in the intrinsic SG neuronal network is dominated by excitatory interneurons. Such organization of neuronal circuitries in the spinal SG can be important for nociceptive encoding.

Spontaneous IPSCs and glycine receptors with slow kinetics in wide-field amacrine cells in the mature rat retina

The functional properties of glycine receptors were analysed in different types of wide-field amacrine cells, narrowly stratifying cells considered to play a role in larger-scale integration across the retina. The patch-clamp technique was used to record spontaneous IPSCs (spIPSCs) and glycine-evoked patch responses from mature rat retinal slices (4-7 weeks postnatal). Glycinergic spIPSCs were blocked reversibly by strychnine (300 nM). Compared to previously described spIPSCs in AII amacrine cells, the spIPSCs in wide-field amacrine cells displayed a very slow decay time course (tau(fast) approximately 15 ms; tau(slow) approximately 57 ms). The kinetic properties of spIPSCs in whole-cell recordings were paralleled by even slower deactivation kinetics of responses evoked by brief pulses of glycine (3 mm) to outside-out patches from wide-field amacrine cells (tau(fast) approximately 45 ms; tau(slow) approximately 350 ms). Non-stationary noise analysis of patch responses and spIPSCs yielded similar average single-channel conductances (approximately 31 and approximately 34 pS, respectively). Similar, as well as both lower- and higher-conductance levels could be identified from directly observed single-channel gating during the decay phase of spIPSCs and patch responses. These results suggest that the slow glycinergic spIPSCs in wide-field amacrine cells involve alpha2beta heteromeric receptors. Taken together with previous work, the kinetic properties of glycine receptors in different types of amacrine cells display a considerable range that is probably a direct consequence of differential expression of receptor subunits. Unique kinetic properties are likely to differentially shape the glycinergic input to different types of amacrine cells and thereby contribute to distinct integrative properties among these cells.

Establishment of a mouse skin model of the lichenification in human chronic eczematous dermatitis

BACKGROUND

Repeated mechanical stresses, such as scratching and rubbing, on a lesional skin area induce a rough skin condition known as lichenification in patients with chronic eczematous dermatitis. For ethical reasons, the pathomechanisms involved are difficult to study, so an animal model is required.

OBJECTIVES

To study the pathomechanisms of the unique rough skin changes seen in chronic eczematous dermatitis, we established a mouse skin model by repeated tape stripping to inflict stratum corneum (SC) barrier disruption. The skin characteristics of the model were investigated biologically, histologically and pharmacologically.

METHODS

Tape stripping was done on mouse back skin three times a week for 4 weeks. The skin changes were studied by obtaining negative replicas, haematoxylin and eosin staining, immunostaining for CD31 and BrdU, and measuring epidermal and cutaneous thickness and skin capacitance. Activities of matrix metalloproteinase (MMP)-2, 9 and urokinase-type plasminogen activator (uPA) in the skin tissues were analysed by zymography. The effects of MMP inhibitor and glycine were assessed.

RESULTS

The repeated tape stripping produced crusting and desquamation at 48 h, followed 1 week later by the formation of shallow furrows, which became much deeper after 4 weeks, appearing as fine and regular wrinkles. The resultant wrinkled skin resembled lichenified skin seen in patients with chronic eczematous dermatitis. Histopathologically, we found acanthosis, hypergranulosis and hyperkeratosis even at 48 h, and the skin was 2.5 times thicker than untreated control skin at 4 weeks. We observed angiogenesis in the upper dermis at 1 and 4 weeks. Skin capacitance, a parameter of SC hydration, displayed consistently low levels throughout the experimental period. Although the dermis was also thickened, the activity of MMP-9 was sharply increased only at 24 and 48 h after tape stripping, declining thereafter to the control level. Topical applications of CGS-27023A (CGS), an MMP inhibitor, failed to suppress this tape-stripping-induced wrinkle formation. In contrast, topical applications of a barrier recovery accelerator, glycine, effectively inhibited the wrinkle formation induced by repeated tape stripping.

CONCLUSIONS

The induction of fine and regular wrinkles by inflicting chronic SC barrier disruption in this model involves mainly epidermal changes, which is in sharp contrast to the mainly dermal changes induced by chronic ultraviolet B irradiation.

GABA, not glycine, mediates inhibition of latent respiratory motor pathways after spinal cord injury

Previous work has shown that latent respiratory motor pathways known as crossed phrenic pathways are inhibited via a spinal inhibitory process; however, the underlying mechanisms remain unknown. The present study investigated whether spinal GABA-A and/or glycine receptors are involved in the inhibition of the crossed phrenic pathways after a C2 spinal cord hemisection injury. Under ketamine/xylazine anesthesia, adult, female, Sprague-Dawley rats were hemisected at the C2 spinal cord level. Following 1 week post injury, rats were anesthetized with urethane, vagotomized, paralyzed and ventilated. GABA-A receptor (bicuculline and Gabazine) and glycine receptor (strychnine) antagonists were applied directly to the cervical spinal cord (C3-C7), while bilateral phrenic nerve motor output was recorded. GABA-A receptor antagonists significantly increased peak phrenic amplitude bilaterally and induced crossed phrenic activity in spinal-injured rats. Muscimol, a specific GABA-A receptor agonist, blocked these effects. Glycine receptor antagonists applied directly to the spinal cord had no significant effect on phrenic motor output. These results indicate that phrenic motor neurons are inhibited via a GABA-A mediated receptor mechanism located within the spinal cord to inhibit the expression of crossed phrenic pathways.

Ion Channels Generating Complex Spikes in Cartwheel Cells of the Dorsal Cochlear Nucleus

Cartwheel cells are glycinergic interneurons that modify somatosensory input to the dorsal cochlear nucleus. They are characterized by firing of mixtures of both simple and complex action potentials. To understand what ion channels determine the generation of these two types of spike waveforms, we recorded from cartwheel cells using the gramicidin perforated-patch technique in brain slices of mouse dorsal cochlear nucleus and applied channel-selective blockers. Complex spikes were distinguished by whether they arose directly from a negative membrane potential or later during a long depolarization. Ca2+ channels and Ca2+-dependent K+ channels were major determinants of complex spikes. Onset complex spikes required T-type and possibly R-type Ca2+ channels and were shaped by BK and SK K+ channels. Complex spikes arising later in a depolarization were dependent on P/Q- and L-type Ca2+ channels as well as BK and SK channels. BK channels also contributed to fast repolarization of simple spikes. Simple spikes featured an afterdepolarization that is probably the trigger for complex spiking and is shaped by T/R-type Ca2+ and SK channels. Fast spikes were dependent on Na+ channels; a large persistent Na+ current may provide a depolarizing drive for spontaneous activity in cartwheel cells. Thus the diverse electrical behavior of cartwheel cells is determined by the interaction of a wide variety of ion channels with a prominent role played by Ca2+.

Glycinergic inputs cause the pause of pontine omnipause neurons during saccades

Pontine omnipause neurons (OPNs) are inhibitory neurons projecting to saccade-related premotor burst neurons. OPNs exhibit sustained discharge during fixations and cease firing before and during saccades. The pause in OPN discharge releases the burst neurons from tonic inhibition, resulting in generation of saccadic eye movements. OPNs are thought to receive two major inhibitory inputs during saccades: an early component that determines the pause onset and a late component that controls the pause duration. Although there is evidence that numerous glycinergic and GABAergic terminals contact OPNs, their physiological roles remain unclear. To reveal functions of glycinergic and GABAergic inputs, we investigated effects of iontophoretic application of strychnine, a glycine receptor antagonist, and bicuculline, a GABAA receptor antagonist, on discharge patterns of OPNs in alert cats. Application of strychnine reduced the ratio of pause duration to saccade duration. Analysis of the timing of pause relative to saccades showed that pause onset was delayed and pause end was advanced. These effects were observed for saccades in all directions. Application of bicuculline, in contrast, had no effect on the OPN pause duration or timing. Both strychnine and bicuculline increased tonic firing rate during intersaccadic intervals. These results suggest that glycinergic, but not GABAergic, afferents convey inhibitory signals that determine the onset as well as duration of pause in OPN activity during saccades.