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

• Published in: Neuroscience Vol. 151; no. 1; pp. 303 - 312
• Main Authors: Uva, L, Librizzi, L, Marchi, N, Noe, F, Bongiovanni, R, Vezzani, A, Janigro, D, de Curtis, M
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 02.01.2008; Elsevier
• Subjects: Acute Disease; Animals; Biological and medical sciences; Blood-Brain Barrier - drug effects; Blood-Brain Barrier - physiopathology; Brain - metabolism; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; Dose-Response Relationship, Drug; Epilepsy - chemically induced; Epilepsy - physiopathology; Evoked Potentials - drug effects; extracellular potassium; Fundamental and applied biological sciences. Psychology; Guinea Pigs; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; In Vitro Techniques; limbic cortex; Medical sciences; Microinjections; muscarinic; Muscarinic Agonists - administration & dosage; Muscarinic Agonists - pharmacokinetics; Nervous system (semeiology, syndromes); Neurology; Pilocarpine - administration & dosage; Pilocarpine - pharmacokinetics; Tissue Distribution; Vertebrates: nervous system and sense organs; mpc; BBB; extracellular potassium; DAD; piriform cortex; entorhinal cortex; lateral olfactory tract; high pressure liquid chromatography; LOT; muscarinic; status epilepticus; SE; blood–brain barrier; monosynaptic population component; PC; dpc; disynaptic population component; diode array; limbic cortex; EC; HPLC; Nervous system diseases; Acute; Epilepsy; Rodentia; Central nervous system; Pilocarpine; Permeability; Blood brain barrier; Extracellular; In vitro; Cerebral disorder; Encephalon; Cholinergic receptor; Vertebrata; Mammalia; Guinea pig; Central nervous system disease; Muscarinic receptor; Potassium
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2007.10.037

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.