In vivo and in vitro effects of pilocarpine: relevance to ictogenesis.
OBJECTIVE
A common experimental model of status epilepticus (SE) utilizes intraperitoneal administration of the cholinergic agonist pilocarpine preceded by methyl-scopolamine treatment. Currently, activation of cholinergic neurons is recognized as the only factor triggering pilocarpine SE. However, cholinergic receptors are also widely distributed systemically and pretreatment with methyl-scopolamine may not be sufficient to counteract the effects of systemically injected pilocarpine. The extent of such peripheral events and the contribution to SE are unknown and the possibility that pilocarpine also induces SE by peripheral actions is yet untested.


METHODS
We measured in vivo at onset of SE: brain and blood pilocarpine levels, blood-brain barrier (BBB) permeability, T-lymphocyte activation and serum levels of IL-1beta and TNF-alpha. The effects of pilocarpine on neuronal excitability was assessed in vitro on hippocampal slices or whole guinea pig brain preparations in presence of physiologic or elevated [K+](out).


RESULTS
Pilocarpine blood and brain levels at SE were 1400 +/- 200 microM and 200 +/- 80 microM, respectively. In vivo, after pilocarpine injection, increased serum IL-1beta, decreased CD4:CD8 T-lymphocyte ratios and focal BBB leakage were observed. In vitro, pilocarpine failed to exert significant synchronized epileptiform activity when applied at concentrations identical or higher to levels measured in vivo. Intense electrographic seizure-like events occurred only in the copresence of levels of K+ (6 mM) mimicking BBB leakage.


CONCLUSIONS
Early systemic events increasing BBB permeability may promote entry of cofactors (e. g. K+) into the brain leading to pilocarpine-induced SE. Disturbance of brain homeostasis represents an etiological factor contributing to pilocarpine seizures.
Marchi
Nicola
N
Department of Cerebrovascular Research, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Oby
Emily
E
Batra
Ayush
A
Uva
Laura
L
De Curtis
Marco
M
Hernandez
Nadia
N
Van Boxel-Dezaire
Anette
A
Najm
Imad
I
Janigro
Damir
D
D000818:Animals; D001812:Blood-Brain Barrier / Q000187:drug effects* / Q000502:physiology; D001921:Brain / Q000187:drug effects* / Q000503:physiopathology*; D004195:Disease Models, Animal; D004569:Electroencephalography / Q000706:statistics & numerical data; D006168:Guinea Pigs; D006624:Hippocampus / Q000737:chemistry / Q000187:drug effects / Q000503:physiopathology; D066298:In Vitro Techniques; D007274:Injections, Intraperitoneal; D053583:Interleukin-1beta / Q000097:blood; D008297:Male; D018721:Muscarinic Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology; D010539:Permeability / Q000187:drug effects; D010862:Pilocarpine / Q000008:administration & dosage / Q000032:analysis / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D012601:Scopolamine / Q000494:pharmacology; D013226:Status Epilepticus / Q000097:blood / Q000139:chemically induced* / Q000503:physiopathology*; D013601:T-Lymphocytes / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000097:blood; D014743:Videotape Recording
D053583:Interleukin-1beta; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D014409:Tumor Necrosis Factor-alpha; D010862:Pilocarpine; D012601:Scopolamine