Rat Sacral Dorsal Commissural Nucleus Research Articles

Potentiation of inhibitory amino acid receptors-mediated responses by lanthanum in rat sacral dorsal commissural neurons

Lanthanum is one of rare earth cations with extremely active chemical property and has been reported to influence neuronal transmitter systems. To date, little attention has been directed towards the sacral dorsal commissural nucleus (SDCN), which serves as a relay of sensory information from the pelvic viscera in the spinal cord. Therefore, the effect of lanthanum on the inhibitory neurotransmitter γ-aminobutyric acid (GABA) and glycine (Gly) responses in neurons acutely dissociated from the rat SDCN was investigated using the nystatin-perforated patch-recording configuration under voltage-clamp conditions. At a holding potential of − 40 mV, La 3+ reversibly potentiated GABA (3 μM)-activated currents ( I GABA) in a concentration-dependent manner over the concentration range of 10 μM to 30 mM, with the EC 50 value of 67.3 ± 16.4 μM. Similarly, La 3+ reversibly potentiated glycine (10 μM)-activated currents ( I Gly) in a concentration-dependent manner over the concentration range of 1 μM to 1 mM, with the EC 50 value of 52.3 ± 10.9 μM. The effects of La 3+ on I GABA and I Gly were voltage-independent. Moreover, both of the potentiations were not use-dependent and were overcome by increasing the concentration of agonist. Our results indicate that La 3+ potentiates the inhibitory amino acid receptors-mediated responses in SDCN, which may reduce the transmission of the pelvic visceral information. The information provided by this work may help to elucidate the mechanisms and effects of lanthanum on brain functions.

Adenosine suppresses GABA A receptor-mediated responses in rat sacral dorsal commissural neurons

The modulatory effect of adenosine on γ-aminobutyric acid (GABA)-activated whole-cell currents were investigated in the neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin perforated patch recording configuration under the voltage-clamp conditions. The results showed that: (1) GABA acted on GABA A receptor and elicited inward Cl − currents ( I GABA) at a holding potential ( V H) of −40 mV; (2) adenosine suppressed GABA-induced Cl − current without affecting the reversal potential of I GABA and the apparent affinity of GABA to its receptor; (3) N6-cyclohexyladenosine mimicked the suppression effect of adenosine on I GABA, whereas 8-cyclopentyl-1,3-dipropylxanthine blocked the suppression effect of adenosine; (4) adenosine fails to suppress I GABA on the neurons that were pretreated with bisindolylmaleimide I (BIM), while after pretreatment with H-89, the inhibitory effect of adenosine on I GABA were not affected; (5) the suppression effect of adenosine on I GABA remained in the presence of BAPTA-AM. The present results indicate that the suppression of adenosine on I GABA is mediated by adenosine A 1 receptor and through a Ca 2+-independent protein kinase C transduction pathway, and that the interactions between adenosine and GABA might participate in the modulation of nociceptive information transmission at the SDCN.

Suppression of Kainate-Evoked AMPA Receptor Mediated Responses by Lanthanum in Rat Sacral Dorsal Commissural Neurons

The effect of lanthanum (La) on kainate (KA) responses in neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) was investigated using the nystatin-perforated patch-recording configuration under voltage-clamp conditions. The responses to KA were mediated by activation of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in SDCN neurons. La³⁺ reversibly inhibited KA (100 µM) activated currents (I_KA) in a concentration-dependent manner over the range from 30 µM to 30 mM, with IC₅₀ values of 0.64 ± 0.06 mM at a holding potential (V_H) of –40 mV. Our further study indicated that the effects of La³⁺ on I_KA were voltage independent. Moreover, the inhibition was not use dependent and was not overcome by increasing the concentration of agonist. These findings indicate that La³⁺ is an efficacious inhibitor of AMPA receptor mediated responses which may contribute to its cytotoxic effect.

Asymmetric Cross-inhibition between GABAA and Glycine Receptors in Rat Spinal Dorsal Horn Neurons

Presynaptic nerve terminals of inhibitory synapses in the dorsal horn of the spinal cord and brain stem can release both GABA and glycine, leading to coactivation of postsynaptic GABAA and glycine receptors. In the present study we have analyzed functional interactions between GABAA and glycine receptors in acutely dissociated neurons from rat sacral dorsal commissural nucleus. Although the application of GABA and glycine activates pharmacologically distinct receptors, the current induced by a simultaneous application of these two transmitters was less than the sum of currents induced by applying two transmitters separately. Sequential application of glycine and GABA revealed that the GABA-evoked current is more affected by glycine than glycine-evoked responses by GABA. Activation of glycine receptors decreased the amplitude and accelerated the rate of desensitization of GABA-induced currents. This asymmetric cross-inhibition is reversible, dependent on the agonist concentration applied, but independent of both membrane potential and intracellular calcium concentration or changes in the chloride equilibrium potential. During sequential applications, the asymmetric cross-inhibition was prevented by selective GABAA or glycine receptor antagonists, suggesting that occupation of binding sites did not suffice to induce glycine and GABAA receptors functional interaction, and receptor channel activation is required. Furthermore, inhibition of phosphatase 2B, but not phosphatase 1 or 2A, prevented GABAA receptor inhibition by glycine receptor activation, whereas inhibition of phosphorylation pathways rendered cross-talk irreversible. Taken together, our results demonstrated that there is an asymmetric cross-inhibition between glycine and GABAA receptors and that a selective modulation of the state of phosphorylation of GABAA receptor and/or mediator proteins underlies the asymmetry in the cross-inhibition.

Biphasic action of midazolam on GABA A receptor-mediated responses in rat sacral dorsal commissural neurons

The effect of the benzodiazepine agonist midazolam on γ-aminobutyric acid A (GABA A) receptor-mediated currents was investigated in neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin-perforated patch-recording configuration under voltage-clamp conditions. Midazolam displayed a biphasic effect on GABA responses. Low concentrations of midazolam (1 nM–10 μM) reversibly potentiated GABA (3 μM)-activated Cl − currents ( I GABA) in a bell-shaped manner, with the maximal facilitary effect at 0.1 μM; whereas at higher concentrations (above 10 μM), midazolam had an antagonistic effect on I GABA. Our further study indicated that midazolam changed GABA A receptor affinity to GABA and the effects of midazolam on I GABA were voltage-independent. The benzodiazepine receptor antagonist, flumazenil, abolished the facilitary effect of low concentrations of midazolam rather than the antagonism of I GABA induced by high doses of midazolam. In addition, activation of protein kinase C prevented the inhibitory effect of midazolam at higher concentrations, but did not influence the effect of midazolam at low concentrations. These results indicate that midazolam interacts with another distinct site other than the central benzodiazepine receptors on GABA A receptors as an antagonist at higher concentrations in SDCN neurons.

β-ALANINE ACTS ON GLYCINE RECEPTORS IN THE RAT SACRAL DORSAL COMMISSURAL NEURONS

Whole-cell current responses to bath application of g -alanine ( g -ALA) were investigated in neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin perforated patch recording configuration under voltage-clamp conditions. g -ALA activated inward currents in a concentration-dependent manner over the range of 10 3000 µM with an EC50 of 80.8 µM. The reversal potential of g -ALA-activated currents (I g -ALA) was close to the Cl equilibrium potential. Strychnine and the chlo ride channel blocker picrotoxin suppressed the I g -ALA in a concentration-dependent manner with the IC50 values of 0.19 µM and 343.6 µM, respectively. At the concentration of 3 µM, strychnine was sufficient to completely block 100 µM g -ALA response, whereas it did not show a suppression of GABA response. In contrast, bicuculline, a potent GABAA receptor antag onist, at concentrations up to 10 µM, a dose that could block the GABA response completely, had little or no effect on I g -ALA. Further more, the I g -ALA was not affected by a preceding GABA response, but rather cross-desensitized with that evoked by glycine. The results indicate that g -ALA activates the strychnine-sensitive glycine receptors in the SDCN neurons, and suggest that g -ALA may act as a functional neurotransmitter in the mammalian SDCN.

Functional roles of presynaptic GABA(A) receptors on glycinergic nerve terminals in the rat spinal cord.

GABA(A) receptor-mediated presynaptic depolarization is believed to induce presynaptic inhibition of excitatory synaptic transmission. We report here the functional roles of presynaptic GABA(A) receptors in glycinergic transmission of the rat spinal cord. In mechanically dissociated rat sacral dorsal commissural nucleus (SDCN) neurons attached with native glycinergic and GABAergic nerve terminals, glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) were isolated from a mixture of both glycinergic and GABAergic sIPSCs by perfusing the SDCN nerve cell body with ATP-free internal solution. Under such experimental conditions, exogenously applied muscimol (0.5 microM) depolarized glycinergic presynaptic nerve terminals and significantly increased glycinergic sIPSC frequency to 542.7 +/- 47.3 % of the control without affecting the mean current amplitude. The facilitatory effect of muscimol on sIPSC frequency was completely blocked by bicuculline (10 microM) or SR95531 (10 microM), selective GABA(A) receptor antagonists. This muscimol-induced presynaptic depolarization was due to a higher intraterminal Cl(-) concentration, which is maintained by a bumetanide-sensitive Na-K-Cl cotransporter. On the contrary, when electrically evoked, this muscimol-induced presynaptic depolarization was found to decrease the action potential-dependent glycine release evoked by focal stimulation of a single terminal. The results suggest that GABA(A) receptor-mediated presynaptic depolarization has two functional roles: (1) presynaptic inhibition of action potential-driven glycinergic transmission, and (2) presynaptic facilitation of spontaneous glycinergic transmission.

Cu 2+ inhibition of glycine-activated currents in rat sacral dorsal commissural neurons

The effect of Cu 2+ on glycine (Gly) response was examined in neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin perforated patch clamp recording configuration under voltage-clamp conditions. Cu 2+, in the concentration range 10–1000 μM, reversibly inhibited chloride current activated by 30 μM Gly at a holding potential of −40 mV with an IC 50 of 88.4 μM. Cu 2+ shifted the Gly concentration response curve to the right in a parallel manner, which indicated that Cu 2+ decreased the apparent affinity of the receptor for Gly. Cu 2+ suppression of Gly-activated current was independent of membrane potential between −60 and +60 mV and did not involve a shift in the reversal potential of the current. Furthermore, Cu 2+ antagonized the inhibitory action of Zn 2+ in a concentration-dependent manner, suggesting a common site or mechanism of action of Cu 2+ and Zn 2+ on Gly receptors. The results show that Cu 2+ is a potent inhibitor of Gly receptor-mediated responses in rat spinal neurons.

Co-release and interaction of two inhibitory co-transmitters in rat sacral dorsal commissural neurons.

Conventional whole-cell recording configuration was used to characterize the interaction between two inhibitory neurotransmitters, GABA and glycine, in synaptic bouton preparation obtained from rat sacral dorsal commissural nucleus (SDCN). The co-release of GABA and glycine as well as the interaction between their corresponding receptors was demonstrated. Furthermore, taking advantage of pure glycinergic terminal preparation, the possible interaction between GABA and glycine at synaptic level was studied. The results revealed a novel cross-modulation between the two inhibitory cotransmitters systems. This interaction may contribute to sensory processing such as nociception in the mammalian deep dorsal horn under physiological and/or pathological conditions.

Cu2+ Suppresses GABAA Receptor-Mediated Responses in Rat Sacral Dorsal Commissural Neurons

The effect of copper ions (Cu²⁺) on γ-aminobutyric acid (GABA)-induced responses in acutely dissociated neurons from the rat sacral dorsal commissural nucleus (SDCN) was investigated using a nystatin-perforated patch recording configuration under voltage clamp conditions. The application of Cu²⁺ to SDCN neurons reversibly suppressed the GABA (10 µM)-activated Cl^– current (I_GABA) in a concentration-dependent manner (1–1,000 µM; IC₅₀ = 24.5 µM). In the presence of Cu²⁺ (30 µM), the concentration-response curve of GABA was shifted rightward without reducing I_GABA recorded under the maximally effective concentration of GABA, thus indicating a dependence of Cu²⁺ action on GABA concentration. Inhibition of GABA (10 µM) responses by 30 µM Cu²⁺ was essentially voltage independent and was not accompanied by a shift in the reversal potential of the currents. Cu²⁺ antagonized the suppressive effect of Zn²⁺ in a concentration-dependent manner, suggesting competition between Cu²⁺ and Zn²⁺ for similar binding sites. These data demonstrate that Cu²⁺ is a potent inhibitor of GABA_A receptor-mediated responses, implying a possible modulatory effect of Cu²⁺ on GABAergic synaptic transmission in the mammalian SDCN.

CAMP-dependent presynaptic regulation of spontaneous glycinergic IPSCs in mechanically dissociated rat spinal cord neurons.

Spontaneous miniature glycinergic inhibitory postsynaptic currents (mIPSCs) in mechanically dissociated rat sacral dorsal commissural nucleus (SDCN) neurons attached with intact glycinergic presynaptic nerve terminals and evoked IPSCs (eIPSCs) in the slice preparation were investigated using nystatin-perforated patch and conventional whole cell recording modes under the voltage-clamp conditions. Trans-ACPD (tACPD) reversibly reduced the mIPSC frequency without affecting the mean amplitude. The effect was mimicked by a specific metabotropic glutamate receptor (mGluR) II subtype agonist, (2S, 1'S, 2'S)-2-(carboxycyclo propyl) glycine (L-CCG-I), and a specific mGluRIII subtype agonist, 2-amino-4-phosphonobutyrate (L-AP4). These inhibitory effects on mIPSC frequency were blocked by the specific antagonists for mGluRII, alpha-methyl-1-(2S, 1'S, 2'S)-2-(carboxycyclo propyl) glycine and (RS)-alpha-cyclopropyl-4-phosphonophenylglycine. In the slice preparation, eIPSC amplitude and mIPSC frequency were decreased reversibly by L-CCG-I (10(-6) M) and L-AP4 (10(-6) M). In K(+)-free or K(+)-free external solution with Ba(2+) and Cs(+), Ca(2+)-free or Cd(2+) external solution, the inhibitory effect of tACPD on mIPSC frequency was unaltered. Forskolin and 8-Br-cAMP significantly increased presynaptic glycine release, and prevented the inhibitory action of tACPD on mIPSC frequency. Sp-cAMP, however, did not prevent the inhibitory action of tACPD on mIPSC frequency. It was concluded that the activation of mGluRs inhibits glycine release by reducing the action of cAMP/PKA pathway.

Mediation by calcium/calmodulin-dependent protein kinase II of suppression of GABAA receptors by NMDA

Using nystatin-perforated whole-cell recording configuration, the modulatory effect of N-methyl-D-aspartate (NMDA) on gamma-aminobutyric acid (GABA)-activated whole-cell currents was investigated in neurons freshly dissociated from the rat sacral dorsal commissural nucleus (SDCN). The results showed that: (i) NMDA suppressed GABA-and muscimol (Mus)-activated currents (I(gaba) and I(Mus)), respectively in the Mg(2+)-free external solution containing 1 mumol/L glycine at a holding potential (V ( H )) of -40 mV in SDCN neurons. The selective NMDA receptor antagonist, D-2-amino-5-phosphonovaleric acid (APV, 100 gammamol/L), inhibited the NMDA-evoked currents and blocked the NMDA-induced suppression of I(gaba); (ii) when the neurons were incubated in a Ca(2+)-free bath or pre-loaded with a membrane-permeable Ca(2+) chelator, BAPTA AM (10 mumol/L), the inhibitory effect of NMDA on I(GAba) disappeared. Cd(2+) (10 mumol/L) or La(3+) (30 mumol/L), the non-selective blockers of voltage-dependent calcium channels, did not affect the suppression of I(gaba) by NMDA application; (iii) the suppression of I(GAba) by NMDA was inhibited by KN-62, a calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor. These results indicated that the inhibition of GABA response by NMDA is Ca(2+)-dependent and CaMKII is involved in the process of the Ca(2+)-dependent inhibition.

N-methyl-D-aspartate enhancement of the glycine response in the rat sacral dorsal commissural neurons.

The effect of N-methyl-D-aspartate (NMDA) on the glycine (Gly) response was examined in neurons acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin-perforated patch-recording configuration under voltage-clamp conditions. The application of 100 microM NMDA to SDCN neurons reversibly potentiated Gly-activated Cl- currents (IGly) without affecting the Gly binding affinity and the reversal potential of IGly. A selective NMDA receptor antagonist, APV (100 microM), blocked the NMDA-induced potentiation of IGly, whereas 50 microM CNQX, a non-NMDA receptor antagonist, did not. The potentiation effect was reduced when NMDA was applied in a Ca2+-free extracellular solution or in the presence of BAPTA AM, and was independent of the activation of voltage-dependent Ca2+ channels. Pretreatment with KN-62, a selective Ca2+-calmodulin-dependent protein kinase II (CaMKII) inhibitor, abolished the NMDA action. Inhibition of calcineurin (CaN) further enhanced the NMDA-induced potentiation of IGly. In addition, the GABAA receptor-mediated currents were suppressed by NMDA receptor activation in the SDCN neurons. The present results show that Ca2+ entry through NMDA receptors modulates the Gly receptor function via coactivation of CaMKII and CaN in the rat SDCN neurons. This interaction may represent one of the important regulatory mechanisms of spinal nociception. The results also suggest that GABAA and Gly receptors may be subject to different intracellular modulatory pathways.

Functional properties of ionotropic glutamate receptor channels in rat sacral dorsal commissural neurons

Nystatin perforated patch and conventional whole-cell recording configurations were used to characterize the properties of ionotropic glutamate receptor (GluR) channels in neurons freshly dissociated from the rat sacral dorsal commissural nucleus (SDCN). l-Glutamate (Glu), N-methyl- d-aspartate (NMDA), quisqualate (QA), α-amino-3-hydroxy-5methyl-4-isoxazoleprop ionate (AMPA) and kainate (KA) applied via a Y-tube produced inward currents at −44 mV which increased in a concentration-dependent manner; they desensitized when induced at higher concentrations except for the KA-induced current ( I KA). (1 S-3 R)1-amino-cyclopentane-1,3-dicarboxylate (1 S-3 R-ACPD) evoked no response. The EC 50 and Hill coefficient ( n H) values of the GluR responses were 3.3×10 −5 M, 0.74 for Glu; 9.0×10 −5 M, 0.83 for NMDA; 6.4×10 −7 M, 1.30 for QA; 1.3×10 −4 M, 1.10 for AMPA and 9.6×10 −5 M, 1.30 for KA, respectively. The reversal potentials of the GluR responses were all near 0 mV. The 6-Cyano-7-nitroquinoxaline-2-3-dione (CNQX) and d-2-amino-5-phosphonovalerate ( d-APV) suppressed the non-NMDA and NMDA responses in a concentration-dependent manner, respectively. Cyclothiazide strongly potentiated both KA- and AMPA-induced responses while concanavalin A potentiated both the responses to a much lesser degree. NS-102 produced no significant effect on either KA- or AMPA-activated currents, while GYKI 52466 reversibly blocked both the currents. The Ca 2+ permeabilities ( P Ca/ P Cs) of the NMDA and AMPA receptor channels were 8.33 and 1.23, respectively. In addition, the current–voltage ( I– V) relationship of I KA showed little rectification. There was a poor correlation between the Ca 2+ permeability and the shape of the I– V curves of I KA. These results suggest that rat SDCN neurons possess NMDA and non-NMDA receptor channels, and express AMPA type receptors with unique properties (slow desensitization to AMPA, high Ca 2+ permeability but lack of inward rectification). These ionotropic receptor charnels may play important roles in mediating and regulating pelvic visceral information including nociception.

α2-adrenoceptor-mediated enhancement of glycine response in rat sacral dorsal commissural neurons

The effect of noradrenaline on the glycine response was investigated in neurons acutely dissociated from the rat sacral dorsal commissural nucleus using nystatin perforated patch recording configuration under voltage-clamp conditions. Noradrenaline reversibly potentiated the 10 −5M glycine-induced Cl − current in a concentration-dependent manner. Single channel recordings in a cell-attached mode revealed that noradrenaline decreased the closing time of the glycine-activated channel activity. Noradrenaline neither changed the reversal potential of the glycine response nor affected the affinity of glycine to its receptor. Clonidine mimicked and yohimbine blocked the noradrenaline action on glycine response. N-[2(methylamino)ethyl]-5-misoquinoline sulfonamide dihydrochloride, protein kinase A inhibitor, mimicked the effect of noradrenaline on glycine response. Noradrenaline failed to affect the glycine response in the presence of these intracellular cyclic AMP and protein kinase A modulators. However, noradrenaline further enhanced the glycine response even in the presence of phorbol-12-myristate-13-acetate and chelerythrine, a protein kinase C inhibitor. Pertussis toxin treatment for 6–8 h blocked the noradrenaline facilitatory effect on the glycine response. In addition, noradrenaline potentiated the strychnine-sensitive postsynaptic currents evoked in a slice preparation of sacral dorsal commissural nucleus. These results suggest that the activation of α2-adrenoceptor by noradrenaline coupled with pertussis toxin-sensitive G-proteins reduces intracellular cyclic AMP formation through the inhibition of adenyl cyclase. The reduction of cyclic AMP decreases the protein kinase A activity, thus resulting in the potentiation of the glycinergic inputs to the sacral dorsal commissural neurons. It is thus feasible that the noradrenergic input to the sacral dorsal commissural nucleus modulates such nociceptive signals as pain by intracellular enhancing the glycine response.

γ-Aminobutyric acid-induced responses in acutely dissociated neurons from the rat sacral dorsal commissural nucleus

The electrophysiological and pharmacological properties of GABA-activated Cl − currents ( I GABA) were investigated in enzymatically dissociated rat sacral dorsal commissural nucleus (SDCN) neurons using the nystatin perforated patch recording configuration under voltage-clamp conditions. Exogenous application of GABA to SDCN neurons induced Cl − currents which increased in a concentration-dependent manner. Bicuculline (BIC) and strychnine (STR) antagonized the I GABA in a concentration-dependent manner. Zn 2+ suppressed the I GABA with an IC 50 of 2.8×10 −5 M. Muscimol mimicked the I GABA, while baclofen evoked no response. Pentobarbital (PB) and 5β-pregnan-3α-ol-20-one (pregnanolone, PGN) also induced GABA A-mimic Cl − currents. Diazepam (DZP), PB and PGN all enhanced the I GABA by increasing the apparent affinity of the GABA A receptors to GABA. Moreover, spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) were observed in mechanically dissociated SDCN neurons attached with synaptic boutons, so called `synaptic bouton preparation'. These results indicate that SDCN neurons express GABA A receptors with relatively low sensitivity to Zn 2+ inhibition, and that GABA may have a functional role as an inhibitory transmitter in the SDCN regulating nociceptive, analgesic, and autonomic functions.

5-HT potentiation of the GABA(A) response in the rat sacral dorsal commissural neurones.

1. The modulatory effect of 5-hydroxytryptamine (5-HT) on the gamma-aminobutyric acid(A) (GABA(A)) response was investigated in the neurones freshly dissociated from the rat sacral dorsal commissural nucleus (SDCN) using the nystatin perforated patch recording configuration under the voltage-clamp conditions. 2. 5-HT potentiated GABA-induced Cl- current (IGABA) without affecting the reversal potential of IGABA and the apparent affinity of GABA to its receptor. 3. Alpha-Methyl-5-HT mimicked the potentiation effect of 5-HT on IGABA while ketanserine blocked it. 1-Oleoyl-2-acetyl-glycerol (OAG) potentiated IGABA, and the effect of 5-HT on IGABA was occluded by OAG pretreatment. In the presence of chelerythrine, 5-HT failed to potentiate IGABA, suggesting that protein kinase C (PKC) is involved in the pathway through which the activation of the 5-HT2 receptor potentiates the IGABA. 4. The facilitatory effect of 5-HT on IGABA remained in the presence of BAPTA-AM. LiCl also had no effect on 5-HT-induced potentiation of IGABA. 5. H-89, genistein, okadaic acid and pervanadate all had no effects on 5-HT potentiation of IGABA. Pertussis toxin treatment for 6-8 h did not block the facilitatory effect of 5-HT on IGABA. 6. The present results show that GABA(A) receptor in the rat SDCN could be modulated in situ by 5-HT, one of the major transmitters involved in the supraspinal control of nociception, and that the phosphorylation of GABA(A) receptor by PKC may be sufficient to support such modulation. The results also strongly support the hypothesis that the cotransmission by 5-HT and GABA has an important role in the spinal cord.

Taurine-activated chloride currents in the rat sacral dorsal commissural neurons

The electrophysiological and pharmacological properties of taurine (Tau)-activated Cl − currents ( I Tau) were investigated in the dissociated rat sacral dorsal commissural nucleus (SDCN) neurons using the nystatin perforated patch recording configuration under voltage-clamp conditions. The reversal potential of I Tau was close to the Cl − equilibrium potential. The I Tau was not affected by a preceding GABA response but cross-desensitized by a preceding glycine (Gly) response. Strychnine (STR), picrotoxin (PIC), bicuculline (BIC) and Zn 2+ suppressed the I Tau in a concentration-dependent manner. The pharmacology of the I Tau and Gly-induced response ( I Gly) was similar, though Zn 2+ inhibition on I Tau differed from that on I Gly in being much slower in recovery. Serotonin potentiated the I Tau via protein kinase C. The results indicate that both Tau and Gly act on a strychnine-sensitive site to open the same Cl − channels in the SDCN neurons, and suggest that Tau may act as a functional neurotransmitter in the mammalian SDCN.

Protein kinase C-mediated enhancement of glycine response in rat sacral dorsal commissural neurones by serotonin.

1. The modulatory effect of serotonin (5-hydroxytryptamine, 5-HT), on the glycine (Gly) response was investigated in neurones acutely dissociated from the rat sacral dorsal commissural nucleus (SDCN) using a nystatin-perforated patch recording configuration. 2. 5-HT potentiated the 10(-5) M Gly-induced Cl- current (IGly) in a concentration-dependent manner without changing the reversal potential of the Gly response or the affinity of Gly to its receptor. 3. alpha-Methyl-5-HT mimicked and ketanserine blocked the 5-HT action on IGly, thus indicating the 5-HT2 receptor-mediated enhancement. 4. Phorbol-12-myristate-13-acetate and 1-oleoyl-2-acetylglycerol potentiated IGly. The subsequent application of 5-HT slightly increase IGly. Chelerythrine blocked the enhancement of IGly by 5-HT, thus suggesting the involvement of protein kinase C (PKC) in the pathway of 5-HT action on IGly. 5. Pertussis toxin (IAP) treatment did not block the facilitatory effect of 5-HT on IGly. 6. BAPTA AM did not disturb the 5-HT-induced potentiation of IGly, thus suggesting that [Ca2+]i is not involved in the 5-HT effect. 7. In conclusion, activation of a 5-HT2 receptor coupled to an IAP-insensitive G-protein increases intracellular diacylglycerol (DAG) formation. The accumulation of DAG also increases the Ca(2+)-independent PKC activity, thus resulting in the potentiation of the Gly response in the SDCN neurones.