Abstract

Ethosuximide (ETX) has become the drug of choice in the treatment of patients with absence seizures taking into account both its efficacy, tolerability and antiepileptogenic properties. However, 47% of subjects treated with ETX failed in therapy, and most antiepileptic drugs have cognitive side effects. VU0360172, a positive allosteric modulator (PAM) of mGluR5, acutely and chronically administered decreased seizures dose dependently in rats of the WAG/Rij strain, a genetic absence model. Here it is investigated whether anti-epileptogenesis induced by ETX alters the sensitivity of VU0360172 as an anti-absence drug, and cognition is affected during and after chronic ETX treatment.
Method: Male WAG/Rij rats were chronically treated with ETX for 4 months. EEG’s were recorded during and after treatment as well as challenged with VU0360172. Rats were also periodically exposed to a cue discrimination learning task in a Y-maze. mGlu5 receptors were quantified with Western Blot.
Results: Antiepileptogenesis was successfully induced by ETX and VU0360172 showed a time and dose dependent anti-absence action. However, chronic ETX treated rats showed a decrease in absences both during and after the end treatment, without clear time and dose related effects. The decrease of sensitivity for VU0360172 was not accompanied by a change in mGluR5 expression in cortex and thalamus. Chronic ETX enhanced motivation to collect sucrose pallets and this was followed by an increase in cued discrimination learning.
It is concluded that VU0360172 keeps its antiabsence effects after chronic treatment. Moreover, its differential effects in the two groups cannot be explained by a simple receptor down regulation suggesting a more downstream interaction between ETX and mGluR5. The cognitive enhancing effects of ETX, as found at the end of the experiment might be mediated to the antidepressant action of ETX as expressed by an increase in the rewarding properties of sucrose pallets.