NINDS Anticonvulsant Data (Quantitative)
Each molecule is identified by a unique six digit ADD number assigned internally by the NINDS' Anticonvulsant Screening Program (ASP). A summary of quantitative screening results are provided for specific compounds. This data represents an overview of quantitative data generated in the NINDS Anticonvulsant Screening Program. Compounds are tested in several models (e.g., the maximal more ..
BioActive Compounds: 5
Each molecule is identified by a unique six digit ADD number assigned internally by the NINDS' Anticonvulsant Screening Program (ASP). A summary of quantitative screening results are provided for specific compounds. This data represents an overview of quantitative data generated in the NINDS Anticonvulsant Screening Program. Compounds are tested in several models (e.g., the maximal electroshock (MES), subcutaneous Metrazol (scMET), 6Hz, kindled rat) using 6-8 animals per dose level. More complete test results (including detailed dose-response data) will be available soon on the PANACHE database web site (Public Access to Neuroactive & Anticonvulsant CHemical Evaluations). This web site is currently being populated with a planned fall launch. We would encourage you to visit the PANACHE site in the coming months.
Maximum Electroshock (MES)
The MES is a model for generalized tonic-clonic seizures that provides an indication of a compound's ability to prevent seizure spread when all neuronal circuits in the brain are maximally active. These seizures are highly reproducible and are electrophysiologically consistent with human tonic-clonic seizures. For all tests based on MES seizures, a 60Hz alternating current (50 mA in mice and 150 mA in rats) is delivered for 2s by silver tipped corneal electrodes which have been primed with an electrolyte solution containing an anesthetic agent (0.5% tetracaine HCL). Efficacy is defined as the ability of a test substance to abolish the hind-limb tonic extensor component of the evoked seizure (Swinyard et al., 1989; White et al., 1995a; White et al., 1995b). Using a single high dose, the time to peak effect (TPE) is estimated by evaluating the responses over time using four animals per time point. A dose-response curve is completed at the TPE using 6-8 animals per dose level, and ED50 values are calculated using probit analysis. All doses are reported as milligrams of candidate drug utilized per kilogram of animal weight administered by the specific route of administration indicated.
Subcutaneous Metrazol (scMET)
Subcutaneous injection of the convulsant Metrazol (a GABAA receptor antagonist) produces clonic seizures in laboratory animals. The scMET test detects the ability of a test compound to raise the seizure threshold of an animal and thus protect it from exhibiting a clonic seizure. The dose of Metrazol which will induce convulsions in 97% of animals (CD97: 85 mg/kg mice or 56.4 mg/kg rats) is injected into a loose fold of skin in the midline of the neck. Animals are placed in isolation cages to minimize stress (Swinyard et al., 1961) and observed for the next 30 minutes for the presence or absence of a seizure. An episode of clonic spasms, approximately 3-5 seconds, of the fore and/or hindlimbs, jaws, or vibrissae is taken as the endpoint. Animals which do not meet this endpoint are considered protected. Using a single high dose, the time to peak effect (TPE) is estimated by evaluating the responses over time using four animals per time point. A dose-response curve is completed at the TPE using 6-8 animals per dose level, confidence limits, slopes, standard errors and ED50 values are calculated using probit analysis.
To assess undesirable side effects (toxicity), animals are monitored for overt signs of impaired neurological or muscular function. In mice, the rotorod (Dunham and Miya, 1957) procedure is used to disclose minimal muscular or neurological impairment. When a mouse is placed on a knurled rod that rotates at a speed of 6 rpm, the animal can maintain its equilibrium for long periods of time. The animal is considered toxic if it falls off this rotating rod three times during a 1-min period. In rats, minimal motor impairment (MMI) is indicated by ataxia, which is manifested by an abnormal, uncoordinated gait. Rats used for evaluating toxicity are examined before the test drug is administered, since individual animals may have peculiarities in gait, equilibrium, placing response, etc., which otherwise might be attributed erroneously to the test substance. In addition to MMI, animals may exhibit a circular or zigzag gait, abnormal body posture and spread of the legs, tremors, hyperactivity, lack of exploratory behavior, somnolence, stupor, and catalepsy, loss of placing response and changes in muscle tone. Using a single high dose, the time to peak effect (TPE) is estimated by evaluating the responses over time using four animals per time point. A dose-response curve is completed at the TPE using 6-8 animals per dose level, and ED50 and other values are calculated using probit analysis.
6 Hz psychomotor seizure model
Some clinically useful AEDs that are relatively ineffective in the standard MES and scMET tests may still have anticonvulsant activities in vivo (e.g., leviteracitam) (insert Barton, 2001). In order to identify potential AEDs with this profile, some compounds may be tested in the minimal clonic seizure (6Hz or psychomotor) test. Like the maximal electroshock (MES) test, the minimal clonic seizure (6Hz) test is used to assess a compound's efficacy against electrically-induced seizures but uses a lower frequency (6Hz) and longer duration of stimulation (3s). After dosing, individual mice are challenged with sufficient current delivered through corneal electrodes to elicit a psychomotor seizure in 97% of animals (32 mA for 3s) (Toman et al., 1952). Unprotected mice will display seizures characterized by a minimal clonic phase followed by stereotyped, automatistic behaviors described originally as being similar to the aura of human patients with partial seizures. Using a single high dose, the time to peak effect (TPE) is estimated by evaluating the responses over time using four animals per time point. A dose-response curve is completed at the TPE using 6-8 animals per dose level, and ED50 and other values are calculated using probit analysis. ED50 values may also be calculated for other stimulus intensities such as: 22mA and 44mA.
Hippocampal Kindled Rat Model
The hippocampal kindled rat is a model of temporal lobe epilepsy. This model helps to identify compounds potentially useful against this common and often drug-resistant type of adult focal epilepsy (Morimoto et al., 2004). Repetitive electrical stimulations of the hippocampus result in progressively stronger seizure responses triggered by stimuli that initially do not elicit such responses. As described by Goddard (1969), this acquired hyper-responsiveness is called kindling and results not only in increased seizure responses but also in an elongation of the afterdischarge duration seen on an EEG recording. Electrodes are implanted into the hippocampus of anesthetized rats, which are then allowed to recover for one week. Following the rapid kindling protocol (Lothman and Williamson, 1994), the rats are stimulated with 200 A for 10s, 50 Hz, every 30 minutes for six hours on alternate days until they are fully kindled (4-5 stimulus days). After one week stimulus-free period, the animals are given the same electrical stimulus. Their behavioral and electrographic responses serve as a baseline. The animals are then pretreated with the test compound (generally via i.p. injection) and tested at various intervals. At each time point, the behavioral seizure score (BSS) (Racine, 1972) and afterdischarge duration (ADD) are recorded.
Using a single high dose, the time to peak effect (TPE) is estimated by evaluating the responses over time. In this assay, an animal is considered "protected" if its BSS is decreased to 3.0 or below. A dose-response curve is completed at the TPE using 6-8 animals per dose level, with ED50 and other values calculated using probit analysis.
Frings Audiogenic Seizure Model
The audiogenic seizure model of reflex epilepsy measures the ability of a test compound to block sound-induced seizures in genetically predisposed mice (Castellion et al., 1965). Male and female Frings mice (18-30 g) in groups of eight mice each are treated i.p. with varying doses of the test compound. At the previously determined time of peak effect, individual mice are placed in a round Plexiglas jar and exposed to a sound stimulus of 110 decibels (11 KHz) delivered for 20 sec. Mice are observed for 25 sec for the presence or absence of hindlimb tonic extension. Mice not displaying hindlimb tonic extension are considered protected. The ability of a test substance to block audiogenic seizures can be quantified by varying the doses between 0% and 100% of mice tested. ED50 and other values are calculated using probit analysis.
Castellion AW, Swinyard EA and Goodman LS (1965) Effect of maturation on the development and reproducibility of audiogenic seizures in mice. Exp. Neurol. 13:206.
Dunham MS and Miya TA (1957) A note on a simple apparatus for detecting neurological deficit in rats and mice. J. Amer. Pharm. Ass. Sci. Ed. 46:208-209.
Lothman EW and Williamson JM (1994) Closely spaced recurrent hippocampal seizures elicit two types of heightened epileptogenesis: a rapidly developing, transient kindling and a slowly developing, enduring kindling. Brain Res 649:71-84.
Morimoto K, Fahnestock M and Racine RJ (2004) Kindling and status epilepticus models of epilepsy: rewiring the brain. Prog Neurobiol 73:1-60.
Racine RJ (1972) Modification of seizure activity by electrical stimulation. II. Motor seizure. Electroencephalogr Clin Neurophysiol 32:281-94.
Swinyard EA, Clark LD, Miyahara JT and Wolf HH (1961) Studies on the mechanism of amphetamine toxicity in aggregated mice. J Physiol 132:97-102.
Swinyard EA, Woodhead JH, White HS and Franklin MR (1989) General principles: experimental selection, quantification, and evaluation of anticonvulsants, in Antiepileptic Drugs (R.H.Levy RHM, B. Melrum, J.K. Penry and F.E. Dreifuss ed) pp 85-102, Raven Press, New York.
Toman JE, Everett GM and Richards RK (1952) The search for new drugs against epilepsy. Tex Rep Biol Med 10:96-104.
White HS, Johnson M, Wolf HH and Kupferberg HJ (1995a) The early identification of anticonvulsant activity: role of the maximal electroshock and subcutaneous pentylenetetrazol seizure models. Ital J Neurol Sci 16:73-7.
White HS, Woodhead JH and Franklin MR (1995b) General principles: experimental selection, quantification, and evaluation of antiepileptic drugs, in Antiepileptic Drugs (Levy RHM, R.H.; Meldrum, B.S. ed) pp 99-110, Raven Press, New York.
Data Table (Concise)