doi:10.1016/j.taap.2005.03.007 
Copyright © 2005 Elsevier Inc. All rights reserved.
Anticonvulsant treatment of sarin-induced seizures with nasal midazolam: An electrographic, behavioral, and histological study in freely moving rats
E. Gilat
, 
, T. Kadar, A. Levy, I. Rabinovitz, G. Cohen, Y. Kapon, R. Sahar and R. Brandeis
Department of Pharmacology, Israel Institute for Biological Research, Ness Ziona, 74100 Israel
Received 22 November 2004;
accepted 16 March 2005.
Available online 22 April 2005.
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Abstract
Centrally mediated seizures and convulsions are common consequences of exposure to organophosphates (OPs). These seizures rapidly progress to status epilepticus (SE) and contribute to profound brain injury. Effective management of these seizures is critical for minimization of brain damage. Nasal application of midazolam (1.5 mg/kg) after 5 min of sarin-induced electrographic seizure activity (EGSA) ameliorated EGSA and convulsive behavior (238 ± 90 s). Identical treatment after 30 min was not sufficient to ameliorate ECoG paradoxical activity and convulsive behavior. Nasal midazolam (1.5 mg/kg), together with scopolamine (1 mg/kg, im) after 5 min of EGSA, exerted a powerful and rapid anticonvulsant effect (53 ± 10 s). Delaying the same treatment to 30 min of EGSA leads to attenuation of paroxysmal ECoG activity in all cases but total cessation of paroxysmal activity was not observed in most animals tested. Cognitive tests utilizing the Morris Water Maze demonstrated that nasal midazolam alone or together with scopolamine (im), administered after 5 min of convulsions, abolished the effect of sarin on learning. Both these treatments, when given after 30 min of convulsions, only decreased the sarin-induced learning impairments. Whereas rats which were not subject to the anticonvulsant agents did not show any memory for the platform location, both treatments (at 5 min as well as at 30 min) completely abolished the memory deficits. Both treatments equally blocked the impairment of reversal learning when given at 5 min. However, when administered after 30 min, midazolam alone reversed the impairments in reversal learning, while midazolam with scopolamine did not.
Rats exposed to sarin and treated with the therapeutic regimen with the exclusion of midazolam exhibited severe brain lesions that encountered the hippocampus, pyriform cortex, and thalamus.
Nasal midazolam at 5 min prevented brain damage, while delaying the midazolam treatment to 30 min of EGSA resulted in brain damage. The addition of scopolamine to midazolam did not alter the above observation. In summary, nasal midazolam treatment briefly after initiation of OP-induced seizure leads to cessation of EGSA and prevented brain lesions and behavioral deficiencies in the rat model.
Keywords: Organophosphate; Sarin; Seizures; Midazolam; Scopolamine; Nasal; EEG
Fig. 1. The experimental paradigm consisted of HI-6 and pyridostigmine (Pyr) pre-treatment (5 and 0.1 mg/kg), 20 min prior to sarin exposure (118 μg/kg, IM). One minute post-exposure to sarin (Sar), animal received atropine (Atr, 2 mg/kg). Within 2–5 min all animals developed abnormal electrographic discharges. Anticonvulsive treatment in the current study was tested after 5 min and 30 min of ongoing seizure.
Fig. 2. The effect of nasal midazolam and nasal midazolam + scopolamine (im) on weights of rats (survivants) exposed to sarin. *P < 0.01, **P < 0.001, decrease from base. #P < 0.02, ##P < 0.01, ###P < 0.001, increase from base.
Fig. 3. Cessation of EGSA by nasal midazolam (1.5 mg/kg) when given 5 min after onset of EGSA (A). When given after 30 min of EGSA, cessation was not achieved (B).
Fig. 4. Cessation of EGSA by nasal midazolam (1.5 mg/kg) and scopolamine (1 mg/kg, im) when given 5 min after onset of EGSA (A). Marked attenuation of EGSA, by nasal midazolam (1 mg/kg) and scopolamine (1 mg/kg, im), when given 30 min after onset of EGSA (B).
Fig. 5. The effect of midazolam treatment (at 5 min and 30 min EGSA) on the rat ECoG power following sarin exposure.
Fig. 6. The effect of nasal midazolam and scopolamine (im) on acquisition of MWM in rats exposed to sarin. (A) Escape latency: *P < 0.002–P < 0.0001, compared to sarin, #P < 0.05–P < 0.029, compared to control. (B) Path length: *P < 0.003–P < 0.0001, compared to sarin, #P < 0.047–P < 0.035, compared to control (Mid, midazolam; Sco, scopolamine; C-Medic, conventional treatment).
Fig. 7. The effect of nasal midazolam and scopolamine (im) on memory of MWM in rats exposed to sarin. *P < 0.01–P < 0.001, compared to Quadrant (1) (M, Midazolam; S, Scopolamine; C-Medic, conventional treatment).
Fig 8. Reversal learning in sarin-exposed rats treated with nasal midazolam and scopolamine (im). (A) Escape latency: *P < 0.003, **P < 0.001, compared to sarin, #P < 0.026, compared to control. (B) Path length: *P < 0.02–P < 0.0001, compared to sarin, #P < 0.033, compared to control (figure captions as in Fig. 7).
Fig. 9. Histological score of brain structures in the various treatment groups.
Fig. 10. Brain sections at the level of the striatum (A, C, and E) and the hippocampus (B, D, and F) 1 week following sarin exposure in rats and the effect of midazolam treatment. (A–B) Sarin (108 μg/kg), (C and D) sarin + midazolam at 5 min, and (E and F) Sarin + midazolam at 30 min. Note the severe damage (arrows) when midazolam was given at 30 min (E and F) and the normal morphology when midazolam was given at 5 min (C and D). H and E staining. Objective magnification: ×2.
Fig. 11. Brain damage 1 week following sarin exposure (A and C) and its prevention by nasal midazolam given 5 min after onset of convulsions (B and D). Note the enlargement of lateral ventricles (LV) and vacuolar degeneration in the piriform cortex (arrow in A) and in CA1 layer compared to the intact brain regions following midazolam treatment (B and D).
Abstract
Purchase PDF (474 K)
E-mail Article
Add to my Quick Links
Cited By in Scopus (3)
Purchase PDF (394 K)
