tetrodotoxin and nisoxetine

Experimental data suggest that halothane anesthesia is associated with significant changes in dopamine (DA) concentration in some brain regions but the mechanism of this effect is not well known. Rat brain cortical slices were labeled with [(3)H]DA to further characterize the effects of halothane on the release of this neurotransmitter from the central nervous system. Halothane induced an increase on the release of [(3)H]DA that was dependent on incubation time and anesthetic concentration (0.012, 0.024, 0.048, 0.072 and 0.096 mM). This effect was independent of extracellular or intracellular calcium. In addition, [(3)H]DA release evoked by halothane was not affected by TTX (blocker of voltage-dependent Na(+) channels) or reserpine (a blocker of vesicular monoamine transporter). These data suggest that [(3)H]DA release induced by halothane is non-vesicular and would be mediated by the dopamine transporter (DAT) and norepinephrine transporter (NET). GBR 12909 and nomifensine, inhibitors of DAT, decreased the release of [(3)H]DA evoked by halothane. Nisoxetine, a blocker of NET, reduced the release of [(3)H]DA induced by halothane. In addition, GBR 12909, nisoxetine and, halothane decrease the uptake of [(3)H]DA into rat brain cortical slices. A decrease on halothane-induced release of [(3)H]DA was also observed when the brain cortical slices were incubated at low temperature and low extracellular sodium, which are known to interfere with the carrier-mediated release of the neurotransmitter. Ouabain, a Na(+)/K(+) ATPase pump inhibitor, which induces DA release through reverse transport, decreased [(3)H]DA release induced by halothane. It is suggested that halothane increases [(3)H]DA release in brain cortical slices that is mediated by DAT and NET present in the plasma membrane.

Topics: Anesthetics, Inhalation; Animals; Cerebral Cortex; Dopamine; Dopamine Plasma Membrane Transport Proteins; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Female; Fluoxetine; Halothane; Male; Nomifensine; Norepinephrine Plasma Membrane Transport Proteins; Piperazines; Rats; Rats, Wistar; Tetrodotoxin; Transport Vesicles; Tritium

In order to further characterize the actions of cocaine on synaptic activity in the hippocampus, recordings of field excitatory postsynaptic potentials in the CA1 region of the rat hippocampal slice preparation were used to monitor drug effects on long-term potentiation (LTP) evoked in response to stimulation of the Schaffer collateral pathway. Cocaine had dose-dependent, biphasic effects on the magnitude of LTP at these excitatory synapses in the stratum radiatum ranging from a significant enhancement of LTP at intermediate drug concentrations (5-10 microM), to an inhibition of LTP at a relatively high drug concentration (30 microM). The local anesthetic lidocaine had only inhibitory effects on the induction of LTP at all concentrations examined (10-75 microM), whereas the monoamine transporter antagonists, WIN 35348 (1 microM) or GBR 12935 (5 microM) significantly enhanced the magnitude of LTP. The D(2)-like dopamine receptor antagonist, eticlopride was effective in preventing this action of cocaine, whereas pretreatment with the D(1/5) antagonist, SCH 23390 was ineffective. These results suggest that endogenously released dopamine, in the presence of cocaine (5-10 microM), can act via D(2)-like receptors to significantly increase the magnitude of LTP in the CA1 region of the hippocampus.

Topics: Adrenergic beta-Antagonists; Anesthetics, Local; Animals; Benzazepines; Cocaine; Desipramine; Dopamine Antagonists; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Drug Interactions; Electric Stimulation; Enzyme Inhibitors; Excitatory Postsynaptic Potentials; Fluoxetine; Hippocampus; In Vitro Techniques; Lidocaine; Long-Term Potentiation; Neurotransmitter Uptake Inhibitors; Piperazines; Propranolol; Rats; Rats, Sprague-Dawley; Salicylamides; Tetrodotoxin

1. The mechanism of stimulation of noradrenaline (NA) release by nicotine (NIC) was investigated in human cerebral cortex slices preloaded with 3H-noradrenaline. 2 NIC (10-1000 micro M) increased 3H-NA release in a concentration-dependent manner. 3. NIC (100 micro M)-evoked 3H-NA release was largely dependent on external Ca2+, and was attenuated by omega-conotoxin GVIA (0.1 micro M) but not by nitrendipine (1 micro M). 4. Tetrodotoxin (1 micro M) and nisoxetine (0.1 micro M) attenuated the NIC (100 micro M)-evoked release of 3H-NA. 5. Mecamylamine (10 micro M), dihydro-beta-erythroidine (10 micro M) and d-tubocurarine (30 micro M), but not alpha-bungarotoxin (alpha-BTX, 0.1 micro M), attenuated the NIC (100 micro M)-evoked release of 3H-NA. 6. NIC (100 micro M)-evoked release of 3H-NA was not affected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 30 micro M) and D(-)-2-amino-5-phosphonopentanoic acid (D-AP5, 100 micro M), but attenuated by MK-801 (10 micro M). MK-801 (0.1-1000 micro M) displaced the specific binding of 3H-nisoxetine with K(i) values of 91.2 micro M. NIC (100, 300 and 1000 micro M) did not induce 3H-D-aspartate release in human cerebral cortex slices. 7. NIC (100 micro M)-evoked release of 3H-NA was attenuated by 7-nitroindazole (10 micro M), N(G)-nitro-L-arginine methyl ester HCl (L-NAME, 30 micro M), N(G)-monomethyl-L-arginine acetate (L-NMMA, 300 micro M). [(3)H]-NA release induced by NIC (100 micro M) was attenuated by methylene blue (3 micro M) and 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ, 10 micro M), and enhanced by zaprinast (30 micro M). 8. In conclusion, NIC stimulates the release of 3H-NA through activation of alpha-BTX-insensitive nicotinic acetylcholine receptors in the human cerebral cortex slices and this action of NIC is associated with modulation of the NO/cGMP pathway.

Topics: Adolescent; Adult; Arginine; Calcium; Calcium Channel Blockers; Cerebral Cortex; Dihydro-beta-Erythroidine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Enzyme Inhibitors; Fluoxetine; Ganglionic Stimulants; Guanylate Cyclase; Humans; In Vitro Techniques; Indazoles; Male; Mecamylamine; Methylene Blue; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Nicotine; Nicotinic Antagonists; Nitrendipine; Nitric Oxide Synthase; Norepinephrine; omega-Conotoxin GVIA; Oxadiazoles; Purinones; Quinoxalines; Tetrodotoxin; Tritium; Tubocurarine

We previously reported that p-synephrine has antidepressant-like activity in the murine models of forced swimming and tail suspension. In the present study, we characterized antidepressant-like effects of p-synephrine stereoisomers in both in vivo and in vitro systems. In the tail suspension test, S-(+)-p-synephrine (3 mg/kg, p.o.) reduced the duration of immobility, while R-(-)-p-synephrine (0.3-3 mg/kg, p.o.) had no effect. S-(+)-p-synephrine (0.3, 1 and 3 mg/kg, p.o.) and R-(-)-p-synephrine (1 mg/ kg and 3 mg/kg, p.o.) significantly reversed the reserpine (2.5 mg/kg, i.p.)-induced hypothermia. S-(+)-p-synephrine was more effective than R-(-)-p-synephrine in inhibition of both [3H]noradrenaline uptake in rat cerebral cortical slices (maximal inhibition 85.7 +/- 7.8% vs. 59.8 +/- 4.3%; EC50 5.8 +/- 0.7 microM vs. 13.5 +/- 1.2 microM) and [3H]nisoxetine binding (Ki 4.5 +/- 0.5 microM vs. 8.2 +/- 0.7 microM). In contrast, R-(-)-p-synephrine was more effective than S-(+)-p-synephrine in stimulation of [3H]noradrenaline release from rat cerebral cortical slices (maximal stimulation 23.9 +/- 1.8% vs. 20.1 +/- 1.7%; EC50 8.2 +/- 0.6 microM vs. EC50 12.3 +/- 0.9 microM). The stimulatory effect of R-(-)-p-synephrine on [3H]noradrenaline release was inhibited by nisoxetine (100 nM), but tetrodotoxin (1 microM) and elimination of extracellular calcium had no effect. It is suggested that S-(+)-p-synephrine has more effective antidepressant-like activity than R-(-)-p-synephrine.

Topics: Adrenergic alpha-Agonists; Adrenergic Uptake Inhibitors; Anesthetics, Local; Animals; Antidepressive Agents; Cerebral Cortex; Fluoxetine; Hindlimb Suspension; Hypothermia; In Vitro Techniques; Male; Norepinephrine; Rats; Rats, Sprague-Dawley; Reserpine; Stereoisomerism; Swimming; Synephrine; Tetrodotoxin; Tritium

The aim of our study was to investigate the effect of different monoamine uptake blockers on the nicotine-evoked release of [3H]noradrenaline ([3H]NA) from rat hippocampal slices. We found that desipramine (DMI), nisoxetine, cocaine, citalopram, and nomifensine inhibit the nicotine-evoked release of [3H]NA with an IC50 of 0.36, 0.59, 0.81, 0.93, and 1.84 microM, respectively. These IC50 values showed no correlation with the inhibitory effect (Ki) of monoamine uptake blockers on the neuronal NA transporter (r = 0.17, slope = 0.02), indicating that the NA uptake system is not involved in the process. In whole-cell patch clamp experiments neither drug blocked Na+ currents at 1 microM in sympathetic neurons from rat superior cervical ganglia, and only DMI produced a pronounced inhibition (52% decrease) at 10 microM. Comparison of the effect of DMI and tetrodotoxin (TTX) on the electrical stimulation- and nicotine-evoked release of [3H]NA showed that DMI, in contrast to TTX, inhibits only the nicotine-induced response, indicating that the target of DMI is not the Na+ channel. Our data suggest that monoamine uptake blockers with different chemical structure and selectivity are able to inhibit the nicotinic acetylcholine receptors in the CNS. Because these compounds are widely used in the therapy of depressed patients, our findings may have great importance in the evaluation of their clinical effects.

Topics: Animals; Culture Techniques; Desipramine; Electric Stimulation; Electrophysiology; Fluoxetine; Hippocampus; Male; Neurons; Neurotransmitter Uptake Inhibitors; Nicotinic Antagonists; Nomifensine; Norepinephrine; Rats; Rats, Wistar; Receptors, Nicotinic; Sodium Channels; Superior Cervical Ganglion; Tetrodotoxin

Microdialysis was used to compare the effect of local perfusion of cocaine with that of functionally similar compounds on extracellular norepinephrine, dopamine, and serotonin (measured simultaneously) in the ventral tegmental area of freely moving rats. Tetrodotoxin (1 microM) potently inhibited both basal and cocaine-induced dialysate monoamine outputs. The local anesthetic lidocaine produced little or no effect on the monoamine output, whereas all uptake blockers tested (at 0.1-1,000 microM) increased the monoamine output in a dose-dependent manner. The selective norepinephrine-uptake blockers desipramine and nisoxetine did not show any selectivity for norepinephrine, whereas the selective serotonin-uptake blockers fluoxetine and citalopram, as well as the selective dopamine-uptake blocker GBR 12935, preferentially (but not exclusively) increased their target amine. Cocaine at low concentrations (1-10 microM) increased the three amines similarly, but at higher concentrations (100-1,000 microM) caused a relatively higher dopamine output. A positive relationship between blocker-induced dialysate norepinephrine and dopamine outputs suggests significant interactions between monoamine systems. The present results indicate that cocaine's action in the ventral tegmental area involves not only a dopamine-, but also a norepinephrine- and a serotonin-related component, and that cocaine-induced monoamine increase is independent of its local anesthetic property.

Topics: Animals; Biogenic Monoamines; Citalopram; Cocaine; Desipramine; Dopamine; Dose-Response Relationship, Drug; Fluoxetine; Lidocaine; Ligands; Male; Microdialysis; Movement; Norepinephrine; Piperazines; Rats; Serotonin; Tetrodotoxin; Ventral Tegmental Area