The role of glucose in synaptic transmission was examined in the rat dorsolateral septal nucleus (DLSN) with single-microelectrode voltage-clamp and slice-patch technique. Removal of glucose from the oxygenated Krebs solution caused an outward current associated with an increased membrane conductance. The current-voltage relationship (I-V curve) showed that the hypoglycemia-induced outward current was reversed in polarity at the equilibrium potential for K+. Exposure of DLSN neurons to the glucose-free solution for 5-20 min depressed the excitatory postsynaptic current (EPSC), the inhibitory postsynaptic current (IPSC), and the late hyperpolarizing current (LHC). Replacement of glucose with 2-deoxy-D-glucose (2DG), an antimetabolic substrate, mimicked the deprivation of glucose. Mannoheptulose (10 mM) and dinitrophenol, inhibitors of glucose metabolism, also depressed the PSCs, even in the presence of 10 mM glucose. Glucose-free perfusion did not significantly depress the glutamate-induced inward current, indicating that the inhibition of the EPSC by the glucose-free perfusion was presynaptic. gamma-Aminobutyric acid (GABA)-induced outward currents were depressed by the glucose-free solution. Intracellular dialysis of DLSN neurons with a patch-pipette solution containing 5 mM ATP attenuated the hypoglycemia-induced outward current. Glucose-free superfusion consistently inhibited the IPSC and the LHC without changing the GABA-induced outward current in ATP-treated DLSN neurons. It is suggested that glucose metabolism directly regulates the release of both excitatory amino acids and GABA from the presynaptic nerve terminals.

Intracellular recordings were made from neurons of vesical parasympathetic ganglia (VPG) isolated from the rabbit urinary bladder and maintained, in vitro. Bath-application of norepinephrine (NE, 500 nM-5 microM) caused a hyperpolarizing response at the postsynaptic membrane of VPG neurons in a concentration-dependent manner. NE blocked the action potential elicited by an orthodromic stimulation of preganglionic (pelvic) nerve fibers. At a relatively low concentration (5-100 nM), NE depressed the fast excitatory postsynaptic potential (EPSP), without producing the hyperpolarization. NE (100 nM) produced 49 +/- 17% (N = 5) decrease in the amplitude of the fast EPSP. NE did not depress the acetylcholine (ACh) potential produced by iontophoretic application of ACh to the ganglion cells. NE did not affect the amplitude of the miniature EPSP, while it reduced the frequency of miniature EPSPs. These results suggest that NE inhibits the nicotinic transmission in the rabbit VPG, probably reducing the ACh release from presynaptic nerve terminals. Epinephrine (1 microM) was more potent than NE (1 microM) in producing the hyperpolarization as well as the blockade of the fast EPSP amplitude. Isoproterenol was ineffective as an agonist for these inhibitory adrenoceptors. Clonidine mimicked the effect of NE on the fast EPSP. Yohimbine and idazoxan antagonized both the inhibition of the fast EPSP and the hyperpolarization produced by NE. These results suggest that alpha 2-adrenoceptors are responsible for the inhibition of the neuronal activity in parasympathetic ganglia of the rabbit urinary bladder. Immunohistochemical study demonstrated the presence of tyrosine hydroxylase (TH)-labelled neuronal elements in the VPG. They were a small proportion of principal neurons, their dendrites, and many varicose fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of gamma-aminobutyric acid-A (GABAA) and GABAC receptors in the GABA-induced biphasic response in neurons of the rat major pelvic ganglia (MPG) were examined in vitro. Application of GABA (100 microM) to MPG neurons produced a biphasic response, an initial depolarization (GABAd) followed by a hyperpolarization (GABAh). The input resistance of the MPG neurons was decreased during the GABAd, whereas it was increased during the GABAh. The GABAd could be further separated into the early component (early GABAd) with a duration of 27 +/- 5 s (mean +/- SE; n = 11) and the late component (late GABAd) with a duration of 109 +/- 11 s (n = 11). The duration of the GABAh was 516 +/- 64 s (n = 11). The effects of GABA (5-500 microM) in producing the depolarization and the hyperpolarization were concentration-dependent. GABA (5-30 microM) induced only late depolarizations. The early component of the depolarization appeared when the concentration of GABA was >50 microM. Muscimol produced only early depolarizing responses. Baclofen (100 microM) had no effect on the membrane potential and input resistance of MPG neurons. Bicuculline (60 microM) blocked the early GABAd but not the late GABAd and the GABAh. Application of picrotoxin (100 microM) with bicuculline (60 microM) blocked both the late GABAd and the GABAh. CGP55845A (3 microM), a selective GABAB receptor antagonist, did not affect the GABA-induced responses. cis-4-Aminocrotonic acid (CACA, 1 mM) and trans-4-aminocrotonic acid (TACA, 1 mM), selective GABAC receptor agonists, produced late biphasic responses in the MPG neurons. The duration of the CACA responses was almost the same as those of the late GABAd and GABAh obtained in the presence of bicuculline. Imidazole-4-acetic acid (I4AA, 100 microM), a GABAC receptor antagonist, depressed the late GABAd and the GABAh but not the early GABAd. I4AA (100 microM) and picrotoxin (100 microM) also suppressed the biphasic response to CACA. The early GABAd and the late GABAd were reversed in polarity at -32 +/- 3 mV (n = 7) and -38 +/- 2 mV (n = 4), respectively, in the Krebs solution. The reversal potential of the GABAh was -34 +/- 2 mV (n = 4) in the Krebs solution. The reversal potentials of the late GABAd and the GABAh shifted to -20 +/- 3 mV (n = 5) and -22 +/- 3 mV (n = 5), respectively, in 85 mM Cl- solution. These results indicate that the late GABA(d) and the GABAh are mediated predominantly by bicuculline-insensitive, picrotoxin-sensitive GABA receptors, GABAC (or GABAAOr) receptors, in neurons of the rat MPG.

SUMMARY1. Intracellular and single-electrode voltage-clamp recordings were made from neurones of vesical parasympathetic ganglia (VPG) isolated from the rabbit urinary bladder.2. Noradrenaline (NA, 0 5-5 ,UM) shortened the duration of the action potentials and depressed the amplitudes of both spike after-hyperpolarization and aftercurrent.3. Voltage-dependent calcium currents (ICa) were recorded by using microelectrodes filled with 2 M-caesium chloride in a superfusing solution containing tetraethylammonium (TEA, 50 mM) and tetrodotoxin (TTX, 500 nM). Noradrenaline 7. Noradrenaline reduced the IBa evoked at clamp potentials more positive than -20 mV from holding potentials near the resting membrane potential (-70 to -50 mV). Under these conditions, the IBa consisted primarily of N-and L-current components. In contrast, NA had no effect on the isolated T-and L-currents. It is concluded that NA selectively inhibits the N-type calcium channels by an action at a2-adrenoceptors in the rabbit VPG neurones.

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