Gastrodin Reduces the Severity of Status Epilepticus in the Rat Pilocarpine Model of Temporal Lobe Epilepsy by Inhibiting Nav1.6 Sodium Currents.

Temporal lobe epilepsy (TLE) is one of the most refractory types of adult epilepsy, and treatment options remain unsatisfactory. Gastrodin (GAS), a phenolic glucoside used in Chinese herbal medicine and derived from Gastrodia elata Blume, has been shown to have remarkable anticonvulsant effects on various models of epilepsy in vivo. However, the mechanisms of GAS as an anticonvulsant drug remain to be established. By utilizing a combination of behavioral surveys, immunofluorescence and electrophysiological recordings, the present study characterized the anticonvulsant effect of GAS in a pilocarpine-induced status epilepticus (SE) rat model of TLE and explored the underlying cellular mechanisms. We found that GAS pretreatment effectively reduced the severity of SE in the acute phase of TLE. Moreover, GAS protected medial entorhinal cortex (mEC) layer III neurons from neuronal death and terminated the SE-induced bursting discharge of mEC layer II neurons from SE-experienced rats. Furthermore, the current study revealed that GAS prevented the pilocarpine-induced enhancement of Nav1.6 currents (persistent (INaP) and resurgent (INaR) currents), which were reported to play a critical role in the generation of bursting spikes. Consistent with this result, GAS treatment reversed the expression of Nav1.6 protein in SE-experienced EC neurons. These results suggest that the inhibition of Nav1.6 sodium currents may be the underlying mechanism of GAS's anticonvulsant properties.

Rhynchophylline Protects Against the Amyloid ß-Induced Increase of Spontaneous Discharges in the Hippocampal CA1 Region of Rats.

Accumulated soluble amyloid ß (Aß)-induced aberrant neuronal network activity has been recognized as a key causative factor leading to cognitive deficits which are the most outstanding characteristic of Alzheimer's disease (AD). As an important structure associated with learning and memory, the hippocampus is one of the brain regions that are impaired very early in AD, and the hippocampal CA1 region is selectively vulnerable to soluble Aß oligomers. Our recent study showed that soluble Aß1-42 oligomers induced hyperactivity and perturbed the firing patterns in hippocampal neurons. Rhynchophylline (RIN) is an important active tetracyclic oxindole alkaloid isolated from Uncaria rhynchophylla which is a traditional Chinese medicine and often used to treat central nervous system illnesses such as hypertension, convulsions, tremor, stroke etc. Previous evidence showed that RIN possessed neuroprotective effects of improving the cognitive function of mice with Alzheimer-like symptoms. In the present study, we aimed to investigate the protective effect of RIN against soluble Aß1-42 oligomers-induced hippocampal hyperactivity. The results showed that (1) the mean frequency of spontaneous discharge was increased by the local application of 3 µM soluble Aß1-42 oligomers; (2) 30 µM RIN did not exert any obvious effects on basal physiological discharges; and (3) treatment with RIN effectively inhibited the soluble Aß1-42 oligomers-induced enhancement of spontaneous discharge, in a concentration-dependent manner with an IC50 = 9.0 µM. These in vivo electrophysiological results indicate that RIN can remold the spontaneous discharges disturbed by Aß and counteract the deleterious effect of Aß1-42 on neural circuit. The experimental findings provide further evidence to affirm the potential of RIN as a worthy candidate for further development into a therapeutic agent for AD.

Synaptic mechanisms underlying thalamic activation-induced plasticity in the rat auditory cortex.

Electrical stimulation of ventral division of medial geniculate body (MGBv) neurons evokes a shift of the frequency-tuning curves of auditory cortical (AC) neurons toward the best frequency (BF) of the stimulated MGBv neurons (frequency-specific plasticity). The shift of BF is induced by inhibition of responses at the BF of the recorded AC neuron, with coincident facilitation of responses at the BF of the stimulated MGBv neuron. However, the synaptic mechanisms are not yet understood. We hypothesize that activation of thalamocortical synaptic transmission and receptor function may contribute to MGBv stimulation-induced frequency-specific auditory plasticity and the shift of BF. To test this hypothesis, we measured changes in the excitatory postsynaptic currents in pyramidal neurons of layer III/IV in the auditory cortex following high-frequency stimulation (HFS) of the MGBv, using whole cell recordings in an auditory thalamocortical slice. Our data showed that in response to the HFS of the MGBv the excitatory postsynaptic currents of AC neurons showed long-term bidirectional synaptic plasticity and long-term potentiation and depression. Pharmacological studies indicated that the long-term synaptic plasticity was induced through the activation of different sets of N-methyl-d-aspartate-type glutamatergic receptors, γ-aminobutyric acid-type receptors, and type 5 metabotropic glutamate receptors. Our data further demonstrated that blocking of different receptors with specific antagonists significantly inhibited MGBv stimulation-induced long-term plasticity as well as the shift of BF. These data indicate that these receptors have an important role in mediating frequency-specific auditory cortical plasticity.

Gastrodin suppresses the amyloid ß-induced increase of spontaneous discharge in the entorhinal cortex of rats.

Accumulated soluble amyloid beta- (Aß-) induced aberrant neuronal network activity may directly contribute to cognitive deficits, which are the most outstanding characteristics of Alzheimer's disease (AD). The entorhinal cortex (EC) is one of the earliest affected brain regions in AD. Impairments of EC neurons are responsible for the cognitive deficits in AD. However, little effort has been made to investigate the effects of soluble Aß on the discharge properties of EC neurons in vivo. The present study was designed to examine the effects of soluble Aß(1-42) on the discharge properties of EC neurons, using in vivo extracellular single unit recordings. The protective effects of gastrodin (GAS) were also investigated against Aß(1-42)-induced alterations in EC neuronal activities. The results showed that the spontaneous discharge of EC neurons was increased by local application of soluble Aß(1-42) and that GAS can effectively reverse Aß(1-42)-induced facilitation of spontaneous discharge in a concentration-dependent manner. Moreover, whole-cell patch clamp results indicated that the protective function of GAS on abnormal hyperexcitability may be partially mediated by its inhibitory action on Aß(1-42)-elicited inward currents in EC neurons. Our study suggested that GAS may provide neuroprotective effects on Aß(1-42)-induced hyperactivity in EC neurons of rats.

Modulation of action potential trains in rabbit saphenous nerve unmyelinated fibers.

Usually, the main axon is assumed to faithfully conduct action potentials (APs). Recent data have indicated that neural processing can occur along the axonal path. However, the patterns and mechanisms of temporal coding are not clear. In the present study, single fiber recording was used to analyze activity-dependent modulation of AP trains in the main axons of C fibers in the rabbit saphenous nerve. Trains of 5 superthreshold electrical pulses at interstimulus intervals of 20 or 50 ms were applied to the nerve trunk for 200 s. The interspike intervals (ISIs) for these trains were compared to the input interstimulus intervals. Three basic types of C fibers were observed in response to repeated stimuli: first, the ISI between the first and second AP (ISI1-2) of type 1 was longer than the interstimulus interval; second, the ISI1-2 of type 2 showed wavelike fluctuations around the interstimulus interval, and third, the ISI1-2 of type 3 exhibited shorter intervals for a long period. Furthermore, both 4-aminopyridine-sensitive potassium and hyperpolarization-activated cation currents were involved in the modulation of ISI1-2 of train pulses. These data provide new evidence that multiple modes of neural conduction can occur along the main axons of C fibers.

Riluzole ameliorates soluble Aß1-42-induced impairments in spatial memory by modulating the glutamatergic/GABAergic balance in the dentate gyrus.

Soluble amyloid beta (Aß) is believed to contribute to cognitive deficits in the early stages of Alzheimer's disease (AD). Increased soluble Aß1-42 in the hippocampus is closely correlated with spatial learning and memory deficits in AD. Riluzole (RLZ), an FDA-approved drug for amyotrophic lateral sclerosis (ALS), has beneficial effects for AD. However, the mechanism underlying the effects remains unclear. In this study, its neuroprotective effect against soluble Aß1-42-induced spatial cognitive deficits in rats was assessed. We found that intrahippocampal injection of soluble Aß1-42 impaired spatial cognitive function and suppressed long-term potentiation (LTP) of the DG region, which was relevant to soluble Aß1-42-induced shift of the hippocampal excitation/inhibition balance toward excitation. Interestingly, RLZ ameliorated Aß1-42-induced behavioral and LTP impairments through rescuing the soluble Aß1-42-induced excitation/inhibition imbalance. RLZ attenuated Aß1-42-mediated facilitation of excitatory synaptic transmission by facilitating glutamate reuptake and decreasing presynaptic glutamate release. Meanwhile, RLZ attenuated the suppression of inhibitory synaptic transmission caused by Aß1-42 by potentiating postsynaptic GABA receptor function. These results suggest that RLZ exerts a neuroprotective effect against soluble Aß1-42-related spatial cognitive deficits through rescuing the excitation/inhibition imbalance, and it could be a potential therapy for AD.

Rhynchophylline suppresses soluble Aß1-42-induced impairment of spatial cognition function via inhibiting excessive activation of extrasynaptic NR2B-containing NMDA receptors.

Rhynchophylline (RIN) is a significant active component isolated from the Chinese herbal medicine Uncaria rhynchophylla. The overproduction of soluble amyloid ß protein (Aß) oligomers in the hippocampus is closely involved in impairments in cognitive function at the early stage of Alzheimer's disease (AD). Growing evidences show that RIN possesses neuroprotective effects against Aß-induced neurotoxicity. However, whether RIN can prevent soluble Aß1-42-induced impairments in spatial cognitive function and synaptic plasticity is still unclear. Using the combined methods of behavioral tests, immunofluorescence and electrophysiological recordings, we characterized the key neuroprotective properties of RIN and its possible cellular and molecular mechanisms against soluble Aß1-42-related impairments in rats. Our findings are as follows: (1) RIN efficiently rescued the soluble Aß1-42-induced spatial learning and memory deficits in the Morris water maze test and prevented soluble Aß1-42-induced suppression in long term potentiation (LTP) in the entorhinal cortex (EC)-dentate gyrus (DG) circuit. (2) Excessive activation of extrasynaptic GluN2B-NMDAR and subsequent Ca2+ overload contributed to the soluble Aß1-42-induced impairments in spatial cognitive function and synaptic plasticity. (3) RIN prevented Aß1-42-induced excessive activation of extrasynaptic NMDARs by reducing extrasynaptic NMDARs -mediated excitatory postsynaptic currents and down regulating GluN2B-NMDAR expression in the DG region, which inhibited Aß1-42-induced Ca2+ overload mediated by extrasynanptic NMDARs. The results suggest that RIN could be an effective therapeutic candidate for cognitive impairment in AD.

Anticonvulsant effect of Rhynchophylline involved in the inhibition of persistent sodium current and NMDA receptor current in the pilocarpine rat model of temporal lobe epilepsy.

Rhynchophylline (RIN) is a significant active component isolated from the Chinese herbal medicine Uncaria rhynchophylla. Several studies have demonstrated that RIN has a significant anticonvulsant effect in many types of epilepsy models in vivo. However, the mechanisms of the anticonvulsant effect remain elusive. Using combined methods of behavioral testing, immunofluorescence and electrophysiological recordings, we characterized the anticonvulsant effect of RIN in a pilocarpine-induced status epilepticus (SE) rat model of temporal lobe epilepsy (TLE) and investigated the underlying cellular mechanisms. In one set of experiments, rats received RIN treatment prior to pilocarpine injection. In a second set of experiments, rats received RIN treatment following the onset of stage 3 seizures. Pretreatment and posttreatment with RIN effectively reduced the seizure severity in the acute phase of TLE. Furthermore, RIN protected medial entorhinal cortex (mEC) layer III neurons from neuronal death and terminated spontaneous epileptiform discharge of mEC layer II neurons in SE-experienced rats. Whole-cell voltage-clamp recordings indicated that RIN inhibited neuronal hyperexcitability via inhibition of the persistent sodium current (INaP) and NMDA receptor current. Immunofluorescence experiments also demonstrated that RIN rectified the pilocarpine-induced upregulation of Nav1.6 and NR2B protein expression. In conclusion, our results identified RIN as an anticonvulsant agent that inhibited ictal discharge via INap and NMDA receptor current inhibition.

Riluzole prevents soluble Aß1-42 oligomers-induced perturbation of spontaneous discharge in the hippocampal CA1 region of rats.

Abnormal accumulation of soluble amyloid beta (Aß) is believed to cause malfunction of neurons in Alzheimer's disease (AD). The hippocampus is one of the earliest affected brain regions in AD. However, little effort has been made to investigate the effects of soluble Aß1-42 oligomers on discharge properties of hippocampal neurons in vivo. This study was designed to examine the effects of soluble Aß1-42 oligomers on the discharge properties of hippocampal CA1 neurons using extracellular single-unit recordings in vivo. The protective effects of riluzole (RLZ) were also investigated for the prevention of soluble oligomers of Aß1-42-induced alterations in the spontaneous discharge of hippocampal neurons. The results showed that (1) the mean frequency of spontaneous discharge was increased by the local application of 100 µM Aß1-42 oligomers; (2) Aß1-42 oligomers also induced alterations of the neuronal firing patterns in the hippocampal CA1 region; and (3) pretreatment with 20 µM RLZ effectively inhibited the Aß1-42-induced enhancement of spontaneous discharge and alterations of neuronal firing patterns in CA1 neurons. Our study suggested that Aß1-42 oligomers induced hyperactivity and perturbed the firing patterns in hippocampal neurons. RLZ may provide neuroprotective effects on the Aß1-42-induced perturbation of neuronal activities in the hippocampal region of rats.