Synedrella nodiflora Extract Depresses Excitatory Synaptic Transmission and Chemically-Induced In Vitro Seizures in the Rat Hippocampus

Abstract

Extracts of the tropical Cinderella plant Synedrella nodiflora are used traditionally to manage convulsive conditions in the West African sub-region. This study sought to determine the neuronal basis of the effectiveness of these plant extracts to suppress seizure activity. Using the hippocampal slice preparation from rats, the ability of the extract to depress excitatory synaptic transmission and in vitro seizure activity were investigated. Bath perfusion of the hydro-ethanolic extract of Synedrella nodiflora (SNE) caused a concentration-dependent depression of evoked field excitatory postsynaptic potentials (fEPSPs) recorded extracellularly in the CA1 region of the hippocampus with maximal depression of about 80% and an estimated IC₅₀ of 0.06 mg/ml. The SNE-induced fEPSP depression was accompanied by an increase in paired pulse facilitation. The fEPSP depression only recovered partially after 20 min washing out. The effect of SNE was not stimulus dependent as it was present even in the absence of synaptic stimulation. Furthermore, it did not show desensitization as repeat application after 10 min washout produced the same level of fEPSP depression as the first application. The SNE effect on fEPSPs was not via adenosine release as it was neither blocked nor reversed by 8-CPT, an adenosine A₁ receptor antagonist. In addition, SNE depressed in vitro seizures induced by zero Mg²⁺ and high K⁺ -containing artificial cerebrospinal fluid (aCSF) in a concentration-dependent manner. The results show that SNE depresses fEPSPs and spontaneous bursting activity in hippocampal neurons that may underlie its ability to abort convulsive activity in persons with epilepsy.

Keywords: SNE; adenosine; field excitatory postsynaptic potentials; hippocampal slices; seizure.

FIGURE 1

High performance liquid chromatography chromatogram of SNE monitored at 315 nm.

FIGURE 2

(A) Effect of SNE (0.01, 0.1 and 1.0 mg/ml) on slope of fEPSPs in rat hippocampal slices after a stable baseline perfused with normal aCSF. (B) The bar graph represents the total effect (calculated as AUCs from the graph above). (C) Concentration-response curve from SNE (0.01, 0.1, and 1.0 mg/ml) on slope of fEPSPs. Data is mean ± SEM (n = 5). ***p < 0.001 compared with baseline, one-way ANOVA followed by a Dunnett’s multiple comparison test.

FIGURE 3

(A) A typical recording of paired fEPSP showing pair-pulse facilitation (B) Effect of SNE (0.01, 0.1, and 1.0 mg/ml) on paired pulse ratio in rat hippocampal slices after a stable baseline perfused with normal aCSF. Data is mean ± SEM (n = 5). ***p < 0.001 compared with baseline, one-way ANOVA followed by a Dunnett’s multiple comparison test.

FIGURE 4

(A) Effect of SNE (1 mg/ml) on the slope fEPSPs without stimulation (*SNE 1.0 mg/ml) and with stimulation (SNE 1.0 mg/ml). (B) The box and whiskers graph is the total effect calculated form the AUCs of the graph above it. Data is mean ± SEM (n = 5). ***p < 0.001 compared with baseline, one-way ANOVA followed by a Dunnett’s multiple comparison test.

FIGURE 5

(A) Administration of 8-CPT (4 µM) before SNE (0.01, 0.1 and 1.0 mg/ml) on slope of fEPSPs in rat hippocampal slices after a stable baseline perfused with normal aCSF. (B) The box and whiskers graph is the total effect calculated form the AUCs of the graph above it. Data is mean ± SEM (n = 3). ***p < 0.001 compared with baseline, one-way ANOVA followed by a Dunnett’s multiple comparison test.

FIGURE 6

(A) Administration of 8-CPT (4 µM) after SNE (0.01, 0.1 and 1.0 mg/ml) on slope of fEPSPs in rat hippocampal slices after a stable baseline perfused with normal aCSF. (B) The box and whiskers graph is the total effect calculated form the AUCs of the graph above it. Data is mean ± SEM (n = 3). ***p < 0.001 compared with baseline, one-way ANOVA followed by a Dunnett’s multiple comparison test.

FIGURE 7

Chemically-induced seizure model produces two types of spontaneous response. (A): Typical recordings of bursts in a hippocampal slice exposed to zero-Mg²⁺ high K⁺ medium. (B,C): Expanded scales from A showing two types of spontaneous seizure activity induced by zero-Mg²⁺ high K⁺ medium: low frequency burst (LFB)-B and high frequency bursts (HFB)-C.

FIGURE 8

SNE suppresses the frequency and amplitude of spontaneous seizure activity induced by zero-Mg²⁺high K⁺ medium. (A): Trace showing effect of SNE on chemically induced seizure activity. (B1): Summary bar graph of effect of SNE (1 mg/ml) on the frequency of spontaneous activity. (B2): Summary bar graph showing concentration dependent effect of SNE on seizure activity. (C1): Summary bar graph of effect of SNE (1 mg/ml) on the amplitude of spontaneous events. (C2): Summary bar graph showing a concentration-dependent depression of event amplitude by SNE.