Inhibitory effects of N-valproyl-L-tryptophan on high potassium, low calcium and low magnesium-induced CA1 hippocampal epileptiform bursting activity in rat brain slices.

N-valproyl-L-tryptophan (VPA-Tryp), new antiepileptic drug, was tested on CA1 hippocampal epileptiform bursting activity obtained by increasing potassium and lowering calcium and magnesium concentrations in the fluid perfusing rat brain slices. Each slice was treated with a single concentration (0.2, 0.5, 1 or 2 mM) of Valproate (VPA) or VPA-Tryp. Both burst duration and interburst frequency during and after treatment were off-line compared with baseline values. For both parameters, the latency and the length of statistically significant response periods as well as the magnitude of drug-induced responses were calculated. VPA-Tryp evoked fewer and weaker early excitatory effects than VPA on bursting activity. On the contrary, VPA-Tryp induced powerful and long-lasting inhibitory effects on epileptiform discharge in a significantly higher number of slices than VPA. In fact, greater length and magnitude of VPA-Tryp-induced inhibition on both interburst frequency and burst duration were observed. Furthermore, VPA-Tryp showed antiepileptic activity at lower concentration than VPA and, when testing both drugs at analogue concentrations, VPA-Tryp evoked responses with either shorter latency or greater effect length and magnitude than VPA.

Modulation of in vivo GABA-evoked responses by nitric oxide-active compounds in the globus pallidus of rat.

Nitric oxide (NO) is a gaseous molecule acting as a messenger in both the peripheral and the central nervous systems. NO affects synaptic activity by modulating neurotransmitter release and/or receptor function. We previously observed that NO-active compounds modify the bioelectric activity of basal ganglia (BG) units. In this study, we applied microiontophoresis to extracellular in vivo recordings to investigate the effect of NO-active compounds on GABA-evoked responses in the globus pallidus (GP) of anesthetized rats. The changes induced by NO-active drugs on the GABA-induced inhibition were used as indicators of NO modulation. The response to GABA release was tested on recorded GP neurons before and during the administration of S-nitroso-glutathione (SNOG, a NO donor) and/or Nω-nitro-L: -arginine methyl ester (L: -NAME), an inhibitor of nitric oxide synthase (NOS); furthermore, SNOG and L: -NAME were tested at different ejection currents in order to highlight the possibility of a current-dependent effect in the nitrergic modulation of GABA transmission. In general, during SNOG ejection the magnitude of GABA-evoked responses was reduced, whereas the administration of L: -NAME produced the opposite effect. The results suggest that NO-active drugs modulate the response of GP neurons to GABA transmission; the effects induced by SNOG and L: -NAME were strictly related to the ejection currents. Then, the modulation of GABAergic transmission by NO could represent a mechanism to finely regulate the GP neurons activity with important consequences on the overall BG function.

Nitric oxide-active compounds modulate the intensity of glutamate-evoked responses in the globus pallidus of the rat.

AIM: The effects of local applied NO-active compounds on glutamate (GLU)-evoked responses were investigated in globus pallidus (GP) neurons. MAIN METHODS: Extracellularly recorded single units from anesthetized rats were treated with GLU before and during the microiontophoretic application of S-nitrosoglutathione (SNOG), a NO donor, and Nω-nitro-l-arginine methyl ester (L-NAME), a NOS inhibitor. KEY FINDINGS: Most GP cells were excited by SNOG whereas administration of L-NAME induced decrease of GP neurons activity. Nearly all neurons responding to SNOG and/or L-NAME showed significant modulation of their excitatory responses to the administration of iontophoretic GLU. In these cells, the changes induced by NO-active drugs in the magnitude of GLU-evoked responses were used as indicators of NO modulation. In fact, when a NO-active drug was co-iontophoresed with GLU, significant changes in GLU-induced responses were observed: generally, increased magnitudes of GLU-evoked responses were observed during SNOG ejection, whereas the administration of L-NAME decreased responses to GLU. SIGNIFICANCE: The results suggest that the NO-active drugs modulate the response of GP neurons to glutamatergic transmission. Nitrergic modulation of glutamatergic transmission could play an important role in the control of GP bioelectric activity, considered a fundamental key in the BG function.

N-valproyl-L-tryptophan for CNS-targeting: synthesis, characterization and efficacy in vitro studies of a new potential antiepileptic drug.

A new aminoacidic derivative of valproic acid (VPA) has been synthesized and characterized by analytical and spectral data. The rationale for the preparation of such potential antiepileptic agent is based on the observation that chemical combination of the anticonvulsant pharmacophore, VPA with essential aminoacids could afford more effective and less toxic actives. The synthesis, characterization, physico-chemical parameters functional for crossing Blood Brain Barrier of N-valproyl-L-tryptophan (4) are reported. The Log D (pH7.4) (0.3) indicates that (4) is adequate to cross biological membranes. Its chemical and enzymatic stability were assessed. The experiments indicate high stability of compound (4) at pH conditions of physiological fluids. Moreover, both in plasma and in cerebral enzymatic environments compound (4) doesn't undergo cleavage after 24 h. The anticonvulsant activity of the new compound was assessed against epileptic burst discharges evoked in vitro in rat hippocampal slices (Seizure like events - SLEs) and compared with that of the widely used VPA. Compound (4), even at the lower tested concentration, when compared to VPA, showed an improved protective effect against hippocampal seizures. The collected data suggest that compound (4) could be considered a very valuable candidate for subsequent in vivo evaluation as new potential antiepileptic drug.