Altered intrinsic functional connectivity in the latent period of epileptogenesis in a temporal lobe epilepsy model.

The latent period, a seizure-free phase, is the duration between brain injury and the onset of spontaneous recurrent seizures (SRSs) during epileptogenesis. The latent period is thought to involve several progressive pathophysiological events that lead to the evolution of the chronic epilepsy phase. Hence, it is vital to investigate the changes in the latent period during epileptogenesis in order to better understand temporal lobe epilepsy (TLE), and to achieve early diagnosis and appropriate management of the condition. Accordingly, recent studies with patients with TLE using resting-state functional magnetic resonance imaging (rs-fMRI) have reported that alterations of resting-state functional connectivity (rsFC) during the chronic period are associated with some clinical manifestations, including learning and memory impairments, emotional instability, and social behavior deficits, in addition to repetitive seizure episodes. In contrast, the changes in the intrinsic rsFC during epileptogenesis, particularly during the latent period, remain unclear. In this study, we investigated the alterations in intrinsic rsFC during the latent and chronic periods in a pilocarpine-induced TLE mouse model using intrinsic optical signal imaging (IOSI). This technique can monitor the changes in the local hemoglobin concentration according to neuronal activity and can help investigate large-scale brain intrinsic networks. After seeding on the anatomical regions of interest (ROIs) and calculating the correlation coefficients between each ROI, we established and compared functional correlation matrices and functional connectivity maps during the latent and chronic periods of epilepsy. We found a decrease in the interhemispheric rsFC at the frontal and temporal regions during both the latent and chronic periods. Furthermore, a significant decrease in the interhemispheric rsFC was observed in the somatosensory area during the chronic period. Changes in network configurations during epileptogenesis were examined by graph theoretical network analysis. Interestingly, increase in the power of low frequency oscillations was observed during the latent period. These results suggest that, even if there are no apparent ictal seizure events during the latent period, there are ongoing changes in the rsFC in the epileptic brain. Furthermore, these results suggest that the pathophysiology of epilepsy may be related to widespread altered intrinsic functional connectivity. These findings can help enhance our understanding of epileptogenesis, and accordingly, changes in intrinsic functional connectivity can serve as an early diagnosis.

Development of miotic cross-tolerance between pyridostigmine and sarin vapor.

The organophosphorous nerve agent sarin (GB) and the carbamate pyridostigmine bromide (PB) both inhibit acetylcholinesterase (AChE), leading to overstimulation of muscarinic receptors. Both GB and PB produce miosis through stimulation of ocular muscarinic receptors. This study investigated 2 hypotheses: (1) that the miotic response to PB would decrease following repeated injections; and (2) that repeated administration of PB would result in tolerance to the miotic effect of GB vapor. Rats were injected intramuscularly with saline, 0.04 mg/kg, 0.5 mg/kg, or 1.4 mg/kg of PB twice daily for 8 consecutive days. After day 3, animals injected with 1.4 mg/kg PB developed miotic tolerance. Twenty-four (24) h following the final PB injection, the rats were exposed to GB vapor (4.0 mg/m(3)). A similar magnitude of miosis was observed in all groups after GB exposure. However, the rate of recovery of pupil size in animals pretreated with 0.5 and 1.4 mg/kg PB was significantly increased. Twenty (20) h following exposure to GB vapor, the pupils of animals pretreated with 1.4 mg/kg PB had recovered to 77% +/- 4% of their pre-exposure baseline, whereas the saline-injected controls had recovered to only 52% +/- 2% of their pre-exposure baseline. The increased rate of recovery does not appear to be a result of protection of pupillary muscarinic receptors by the higher doses of PB, as there was no longer PB present in the animal at the time of GB exposure. These results demonstrate the development of tolerance to the miotic effect of PB following repeated exposures, and also suggest that cross-tolerance between PB and GB occurs. However, because the magnitude of the response was not reduced, the PB pretreatment and its associated miotic cross-tolerance does not appear to diminish the effectiveness of miosis as a biomarker of acute exposure to nerve agent vapor.

Miotic effect and irritation potential of pilocarpine prodrug incorporated into a submicron emulsion vehicle.

Pilocarpine prodrug, O,O'-dipivaloyl(1,2-ethylene) bispilocarpic acid diester, was introduced to a submicron emulsion vehicle in a dose equivalent to 0.5% pilocarpine base, and the formulation was studied in albino rabbits using miotic assay. Compared with pilocarpine HCl 0.5% solution delayed and prolonged miosis was observed after application of the prodrug emulsion. AUC(0-6 h) values for the prodrug emulsion and pilocarpine solution were 9252+/-1345 and 6845+/-1967%xmin, respectively. The prodrug was also administered twice daily for 5 days in the form of aqueous solution or submicron emulsion in order to study ocular irritation. Irritation potential of the prodrug was significantly reduced when submicron emulsion was used as a vehicle.

Effects of epinephrine, benzalkonium chloride, and intraocular miotics on corneal endothelium.

Drugs formulated for use both inside and outside of the eye were tested for their potential toxic effects on the corneal endothelium. Commercially available epinephrine 1:1000 was toxic to the corneal endothelium, but solutions diluted fivefold caused no endothelial damage. The toxic agent was the sodium bisulfite 0.1% preservative. Benzalkonium chloride is highly toxic to corneal endothelium in its commonly used concentration of 0.01% and had to be diluted one thousand times to prevent endothelial damage. Ophthalmic medications for extraocular use should never be used intracamerally. Miotics commonly used in surgery during intraocular lens implantation are generally nontoxic to the cornea, though caution is advised in the use of carbachol in patients with preexisting endothelial disease and in patients having procedures in which substantial mechanical trauma to the endothelium may occur.