Acute induction of epileptiform discharges by pilocarpine in the in vitro isolated guinea-pig brain requires enhancement of blood–brain barrier permeability

Abstract

Systemic application of the muscarinic agonist, pilocarpine, is commonly utilized to induce an acute status epilepticus that evolves into a chronic epileptic condition characterized by spontaneous seizures. Recent findings suggest that the status epilepticus induced by pilocarpine may be triggered by changes in the blood-brain barrier (BBB) permeability. We tested the role of the BBB in an acute pilocarpine model by using the in vitro model brain preparation and compared our finding with in vivo data. Arterial perfusion of the in vitro isolated guinea-pig brain with <1 mM pilocarpine did not cause epileptiform activity, but rather reduced synaptic transmission and induced steady fast (20-25 Hz) oscillatory activity in limbic cortices. These effects were reversibly blocked by co-perfusion of the muscarinic antagonist atropine sulfate (5 μM). Brain pilocarpine measurements in vivo and in vitro suggested modest BBB penetration. Pilocarpine induced epileptiform discharges only when perfused with compounds that enhance BBB permeability, such as bradykinin (n=2) or histamine (n=10). This pro-epileptic effect was abolished when the BBB-impermeable muscarinic antagonist atropine methyl bromide (5 μM) was co-perfused with histamine and pilocarpine. In the absence of BBB permeability enhancing drugs, pilocarpine induced epileptiform activity only after arterial perfusion at concentrations >10 mM. Ictal discharges correlated with a high intracerebral pilocarpine concentration measured by high pressure liquid chromatography.We propose that acute epileptiform discharges induced by pilocarpine treatment in the in vitro isolated brain preparation are mediated by a dose-dependent, atropine-sensitive muscarinic effect promoted by an increase in BBB permeability. Pilocarpine accumulation secondary to BBB permeability changes may contribute to in vivo ictogenesis in the pilocarpine epilepsy model. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2009 November 9. Published in final edited form as:Neuroscience. Pilocarpine is a non-selective muscarinic agonist (Maslanski et al., 1994) with a relatively high affinity for CNS muscarinic receptors (Hedlund and Bartfai, 1981) commonly utilized to develop an experimental model of temporal lobe epilepsy (Turski et al., 1989;Cavalheiro et al., 2006; but see Sloviter, 2005). In different animal species, i.p. injection of pilocarpine induces a convulsive status epilepticus (SE; i.e. sub-continuous generalized seizures that recur for several hours), followed within 2 weeks by a chronic epileptic condition that mimics human temporal lobe epilepsy (Cavalheiro et al., 2006). The initial SE is thought to be triggered by a cholinergic activation of excitatory neurons in specific brain regions that include limbic cortices. Such an effect is supposedly mediated by micro-molar concentrations of pilocarpine, since this drug shows a relatively poor brain penetration (Omori et al., 2004). Although studies directly assessing pilocarpine penetration across the ...

Why mesial temporal lobe epilepsy with hippocampal sclerosis is progressive: Uncontrolled inflammation drives disease progression?

“…This observation was supported by another study [60] in which it was found that acute induction of epileptiform discharges by pilocarpine in the in vitro isolated guinea-pig brain requires enhancement of blood-brain barrier permeability. Cytokines can increase the expression of adhesion molecules and selectins (such as ICAM-1, VCAM-1, chemokines, and their receptors) on endothelial and epithelial cells in the BBB and blood-CSF barrier [61].…”

“…Recent compelling research has highlighted the involvement of BBB permeability in the development of epilepsy. Immune-mediated damage to the nervous system is emerging as an important contributor to epileptogenesis, both directly through inflammation and indirectly by causing BBB leakage [60,93,94]. Other factors contributing to the alteration of brain homeostasis and generation of seizures from BBB leakage may include albumin [59,95] or epileptogenic agents such as glutamate, which are more concentrated in serum than brain [96,97].…”

What Non-neuronal Mechanisms Should Be Studied to Understand Epileptic Seizures?

“…BBB disruption (BBBD) causes seizures in animal models and human subjects [19, 45, 46, 48, 50, 51, 85]. In particular, a model of temporal lobe epilepsy (pilocarpine, PILO) also depends on BBBD [19, 51, 84]. The currently accepted mechanism of BBBD-induced seizures predicts activation of adhesion molecules on endothelial cells and leukocytes [19].…”

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