Interferon-alpha inhibits long-term potentiation and unmasks a long-term depression in the rat hippocampus.

Interferons (IFN) appear to have various neuromodulatory actions. Here, we characterized the actions of IFN-alpha on the electrophysiological properties of CA1 hippocampal neurons using intracellular recordings. Superfusion of this cytokine did not alter the resting membrane potential, cell input resistance, action potentials, nor GABA-mediated fast synaptic potentials. IFN-alpha inhibited glutamate-mediated excitatory postsynaptic potentials (gEPSPs) and reversed or prevented long-term potentiation (LTP) induced by high-frequency tetanic stimulation. IFN-alpha reduced gEPSP amplitude far below its control value. Only a short-term potentiation (STP) was observed when either IFN-alpha or D-2-amino-5-phosphonovalerato (APV; NMDA receptor antagonist) were present during tetanic stimulation. After this STP in presence of APV, IFN-alpha had no effect on gEPSPs. APV had no effect on LTP when applied after tetanic stimulation and did also not prevent IFN-alpha effect on LTP. Genistein (a tyrosine kinase inhibitor) or heat inactivation prevented IFN-alpha effects. IFN-alpha also decreased the depolarization induced by local application of glutamate but did not modify those induced by NMDA. Similarly, IFN-alpha reversed the potentiation (induced by tetanic stimulation) of glutamate-induced depolarizations. IFN-alpha did not affect long-term depression (LTD) induced by low-frequency tetanic stimulation. In conclusion, IFN-alpha-induced inhibition of LTP is, at least in part, mediated by a postsynaptic effect, by tyrosine kinase activity, and by non-NMDA glutamate receptors. Inhibition of LTP by IFN-alpha unmasks LTD which is induced by the same high-frequency tetanic stimulation.

Anxiolytic-like actions of melatonin, 5-metoxytryptophol, 5-hydroxytryptophol and benzodiazepines on a conflict procedure.

Male Wistar rats (120-230 g) were used in these experiments. Some rats were deprived of water for 48 h before testing in a conflict procedure. Then, after 20 licks from a water bottle with a metal drinking tube, the animal received an electric shock (0.5 mA/500 msec). The effects of two classical anxiolytic drugs, DIAZ (1.0, 2.0 and 4.0 mg/Kg b.wt), and CDP (5.0 and 10.0 mg/Kg b.wt) were compared to those produced by MEL (0.1, 0.2, 0.5, 1.0 and 2.0 mg/Kg b.wt), 5-MTOPHOL (1.0 and 2.0 mg/Kg b.wt), 5-HTOPHOL (1.0 and 2.0 mg/Kg b.wt) and vehicle solution. Anxiolytic drugs as well as MEL produced a dose-dependent increase in the number of shocks received. The results suggest that the three pineal indoles are involved in the modulation of the stress responses. MEL showed a higher potency than the other indoles.

ATP inhibits glutamate synaptic release by acting at P2Y receptors in pyramidal neurons of hippocampal slices.

It has been proposed that extracellular ATP inhibits synaptic release of glutamate from hippocampal CA1 synapses after its catabolism to adenosine. We investigated the possibility that at least part of this effect is mediated by ATP itself acting on P2Y receptors. ATP and various analogs decreased the amplitude and duration of glutamate-mediated excitatory postsynaptic potentials in all tested neurons. This effect was reversible and concentration-dependent and had the following rank order of agonist potency: AMP = ATP = adenosine-5'-O-(3-thio)triphosphate > adenosine = ADP. alpha,beta-Methylene ATP, beta,gamma-methylene ATP, 2-methylthioadenosine 5'-triphosphate, GTP, and UTP induced only a partial response. The depolarization induced by exogenous glutamate was not affected by ATP, indicating that this nucleotide acts presynaptically to inhibit glutamate-mediated excitatory postsynaptic potentials. Neither inhibition of ectonucleotidase activity with alpha,beta-methylene ADP, suramin, or pyridaxalphosphate-6-azophenyl-2',4'-disulfonic acid 4-sodium nor removal of extracellular adenosine (with adenosine deaminase) altered ATP effects. 8-Cyclopentyltheophylline competitively inhibited ATP effects, whereas P2 receptor antagonists (pyridaxalphosphate-6-azophenyl-2',4'-disulfonic acid 4-sodium, suramin, and reactive blue 2) were ineffective. ATP effects were by far more sensitive to pertussis toxin (PTX) than those of adenosine. After PTX, adenosine-5'-O-(3-thio)triphosphate induced only a partial response, and ATP concentration-response curve was biphasic. The second phase of this curve was blocked by adenosine deaminase, implying that it is mediated by adenosine as a result of ATP catabolism. Under control conditions, however, catabolism of ATP is not required to explain its actions. In conclusion, ATP inhibits synaptic release of glutamate by direct activation of P2Y receptors that are PTX- and 8-cyclopentyltheophylline-sensitive.

Interferon modulates glucose-sensitive neurons in the hypothalamus.

Interferon-alpha (IFN) therapy induces feeding suppression that resembles anorexia. The hypothalamic glucose-sensitive neurons engage in feeding behavior. Coronal sections of rat brains, containing both the lateral hypothalamus (LH) and the ventromedial hypothalamus (VMH), as well as single-cell recordings were used to study the interaction between IFN and glucose-sensitive neurons. IFN suppressed the majority (78%) of LH neurons, while reduction in glucose concentration elicited excitation in the majority (85%) of the same neurons. The opposite effects were observed in the VMH, where IFN excited the majority of neurons (61%), and reduction in glucose concentration exerted the opposite effects in 64% of VMH recordings. Concomitant IFN and glucose reduction exhibited only the effects elicited by IFN, regardless of whether the glucose reduction caused excitation (LH) or suppression (VMH). This observation suggests that IFN causes anorexia by modulating the LH and VMH glucose-sensitive neurons.