Prolonged Attenuation of Amygdala-Kindled Seizure Measures in Rats by Convection-Enhanced Delivery of the N-Type Calcium Channel Antagonists ω-Conotoxin GVIA and ω-Conotoxin MVIIA

Abstract

Convection-enhanced delivery (CED) permits the homogeneous distribution of therapeutic agents throughout localized regions of the brain parenchyma without causing tissue damage as occurs with bolus injection. Here, we examined whether CED infusion of the N-type calcium channel antagonists -conotoxin GVIA (-CTX-G) and -conotoxin MVIIA (-CTX-M) can attenuate kindling measures in fully amygdala-kindled rats. Rats were implanted with a combination infusion cannula-stimulating electrode assembly into the right basolateral amygdala. Fully kindled animals received infusions of vehicle, -CTX-G (0.005, 0.05, and 0.5 nmol), -CTX-M (0.05, 0.15, and 0.5 nmol), proteolytically inactivated -CTX-M (0.5 nmol), or carbamazepine (500 nmol) into the stimulation site. CED of -CTX-G and -CTX-M over a 20-min period resulted in a dose-dependent increase in the afterdischarge threshold and a decrease in the afterdischarge duration and behavioral seizure score and duration during a period of 20 min to 1 week after the infusion, indicating an inhibitory effect on the triggering and expression of kindled seizures. The protective effects of -conotoxins reached a maximum at 48 h postinfusion, and then they gradually resolved over the next 5 days. In contrast, carbamazepine was active at 20 min but not at 24 h after the infusion, whereas CED of vehicle or inactivated -CTX-M had no effect. Except for transient tremor in some rats receiving the highest toxin doses, no adverse effects were observed. These results indicate that local CED of high-molecular-weight presynaptic N-type calcium channel blockers can produce long-lasting inhibition of brain excitability and that they may provide prolonged seizure protection in focal seizure disorders.

Long-Lasting Attenuation of Amygdala-Kindled Seizures after Convection-Enhanced Delivery of Botulinum Neurotoxins A and B into the Amygdala in Rats

“…In the present study, when BoNT/A and BoNT/B were infused locally into the amygdala by CED, no effects on behavior were observed and the animals gained weight normally. We previously provided evidence that another class of nondiffusable toxins delivered by CED can remain restricted to the infusion zone; however, at supratherapeutic doses, neurobehavioral effects suggesting leakage into the cerebrospinal fluid did occur (Gasior et al, 2007). In the present study, we confirmed that potentially toxic peptides can be safely delivered into the brain by CED; however, approaches to mitigate the risks of toxin leakage must be developed before clinical application can be contemplated.…”

“…Localization of the infusion cannulastimulating electrode assembly was verified in the amygdala in all animals selected for histological analysis. In confirmation of a previous study (Gasior et al, 2007), minimal damage to the amygdala and surrounding brain structures along the path of the assembly occurred. No inflammation or neuronal damage was detected in the surrounding tissue.…”

“…Each rat was chronically implanted with a custom-made guide cannula-bipolar stimulating electrode assembly (Plastics One, Roanoke, VA) during an aseptic surgical procedure with the rats under general anesthesia induced by a mixture of ketamine (60-75 mg/kg) and medetomidine (0.25-0.5 mg/kg). The cannula-electrode assembly consisted of a 26-gauge, 6.5-mm-long stainless steel guide cannula with two 0.23-mmdiameter stainless steel electrode wires attached diametrically at the periphery (Gasior et al, 2007). The electrode wires were polyamideinsulated, with the exception of the 0.5-mm most distal extent; the tips of the wires were separated by 0.5 mm and projected 3.5 mm past the end of the guide cannula.…”

“…To overcome these limitations, we have sought to identify agents that provide prolonged seizure protection after local delivery. We previously demonstrated that local infusion of peptide N-type calcium channel toxins can confer protection against amygdala-kindled seizures in rats that persists for up to 1 week (Gasior et al, 2007).…”

“…In the present study, we sought to assess the potential of locally delivered botulinum neurotoxins to confer seizure protection in the amygdala kindling model, an experimental paradigm that allows assessment of the duration of toxin action for weeks to months. We administered the toxins using convection-enhanced delivery (CED), which provides a larger and more homogeneous distribution than conventional bolus injection and does not damage the surrounding tissue (Gasior et al, 2007;Rogawski, 2009). …”