Proconvulsant actions of intrahippocampal botulinum neurotoxin B in the rat

Abstract

Botulinum neurotoxins (BoNTs) may affect the excitability of brain circuits by inhibiting neurotransmitter release at central synapses. There is evidence that local delivery of BoNT serotypes A and E, which target SNAP-25, a component of the release machinery specific to excitatory synapses, can inhibit seizure generation. BoNT serotype B (BoNT/B) targets VAMP2, which is expressed in both excitatory and inhibitory terminals. Here we assessed the effects of unilateral intrahippocampal infusion of BoNT/B in the rat on intravenous pentylenetetrazol (PTZ) seizure thresholds, and on the expression of spontaneous behavioral and electrographic seizures. Infusion of BoNT/B (500 and 1000 unit) by convection-enhanced delivery caused a reduction in myoclonic twitch and clonic seizure thresholds in response to intravenous PTZ beginning about 6 days after the infusion. Handling-evoked and spontaneous convulsive seizures were observed in many BoNT/B-treated animals but not in vehicle-treated controls. Spontaneous electrographic seizure discharges were recorded in the dentate gyrus of animals that received local BoNT/B infusion. In addition, there was an increased frequency of interictal epileptiform spikes and sharp waves at the same recording site. BoNT/B treated animals also exhibited tactile hyperresponsivity in comparison with vehicle-treated controls. This is the first demonstration that BoNT/B causes a delayed proconvulsant action when infused into the hippocampus. Local infusion of BoNT/B could be useful as a focal epilepsy model.

Accelerated intoxication of GABAergic synapses by botulinum neurotoxin A disinhibits stem cell-derived neuron networks prior to network silencing

“…In ESNs, the accelerated intoxication of GABAergic synapses acutely disinhibits network behavior, driving a transition from stochastic firing to prolonged bursts, followed ultimately by network silencing as glutamatergic synapses are intoxicated. Observations of synapse subtype-specific latencies are consistent with in vitro observations of disinhibited network responses following addition of BoNT/A to primary cortical or spinal cord neurons on planar microelectrode arrays (Scarlatos et al, 2008 ; Pancrazio et al, 2014 ) as well as in vivo reports of seizures following the intrahippocampal administration of BoNT/B (Broer et al, 2013 ). The rapid elimination of GABAergic signaling by BoNT/A treatment also suggests that functional assays directly (MIST) or indirectly (network responses) measuring the integrity of inhibitory neurotransmission could be leveraged as highly sensitive, specific and rapid methods to detect the presence of active BoNT.…”

Calcium Channel Subunit α2δ4 Is Regulated by Early Growth Response 1 and Facilitates Epileptogenesis

“…This, in turn, renders the hippocampus more vulnerable to epileptiform discharges and their propagation into all-or-none pattern of seizure activity recruiting the whole network. Importantly, analogous reductions of PTZ seizure threshold have previously been documented after decreasing intrinsic or synaptic excitability of hippocampal neurons by elevating NaK-ATPase activity (Funck et al, 2015) or lowering transmitter release (Bröer et al, 2013). Furthermore, we previously observed that mice devoid of the presynaptic active zone protein RIM1␣, which exhibit a decrease in neurotransmitter release in the hippocampal CA1 region, also experience an increased seizure frequency in the chronic phase after pilocarpine-induced SE (Pitsch et al, 2012).…”

Blockade of p75 Neurotrophin Receptor Reverses Irritability and Anxiety-Related Behaviors in a Rat Model of Status Epilepticus

“…Responses were recorded as 1, the rat has no reaction; 2, the rat turned toward the object; 3, the rat moved away from the object; 4, the rat frozen; 5, the rat turned toward the touch; 6, the rat turned away from the touch; 7, the rat jumped with or without vocalizations [35,37] .…”

“…Responses were scored as 1, very easy; 2, easy with vocalizations; 3, some difficulties, the rat reared and faced the hand; 4, frozen (the rat); 5, difficult, the rat avoided the hand by moving away; 6, very difficult, the rat behaved defensively and may attacked the hand [35,37] . The behavioral tests were done by three independent observers, and the means of their scores were calculated for each animal for each test.…”