Infant monkeys' visual responses to drawings of normal and distorted faces.

Face-like patterns attract attention from both human and nonhuman primates. The present study explored the facial preferences in infant pigtailed macaques (Macaca nemestrina). Twenty-five subjects looked at 20 paired drawings of adult conspecific monkey faces, and their looking time was recorded. The facial features in the drawings were arranged in positions ranging from a normal to a scrambled face. The subjects looked at the normal face more than expected by chance (P < .02), suggesting a preference, whereas the distorted faces were observed randomly. The normal face may have been preferred because the eyes were in a normal position within the facial outline.

Infant monkey hyperexcitability after prenatal exposure to antiepileptic compounds.

PURPOSE: A monkey (Macaca fascicularis) model was previously used to assess infant hyperexcitability after prenatal exposure to phenytoin (PHT), stiripentol (STP) or PHT+STP. To explore this issue further, we studied additional monkey infants in those groups, as well as groups prenatally exposed to carbamazepine (CBZ) in monotherapy (n = 5) or CBZ+STP polytherapy (n = 10). METHODS: The drug-exposed groups were compared with a group of control infants (n = 10) for whom procedures were matched except that there was no prenatal drug exposure. All adult female monkeys were equipped with tether systems and stomach catheters so that drug administration (or water for controls) could be initiated before they were mated and continued throughout pregnancy. During pregnancy, PHT, STP, and CBZ plasma levels were maintained between 4-12, 4-10, and 1-6 micrograms/ ml, respectively (for both monotherapy and polytherapy). At birth, infants were separated from mothers and transferred to the University of Washington's (Seattle, WA, U.S.A.) Infant Primate Research Laboratory (IPRL) for postnatal care and follow-up testing. During tests of recognition memory administered between 2 weeks and 3 months of age, infants were rated on a hyperexcitability scale. RESULTS: Previously reported data indicated that infants prenatally exposed to PHT, in monotherapy or polytherapy with STP, were at increased risk for hyperexcitability (screeching, refusing to attend to stimuli, lack of visual orientation). This was not the case for infants prenatally exposed to STP monotherapy. CONCLUSIONS: Our results confirm previous findings and also demonstrate that infants prenatally exposed to CBZ or CBZ+STP, like controls, are not hyperexcitable during testing.

Phenytoin and/or stiripentol in pregnancy: infant monkey hyperexcitability.

A monkey (Macaca fascicularis) model was used to assess infant hyperexcitability after prenatal exposure to phenytoin (PHT, n = 4), stiripentol (STP, n = 5), or PHT + STP (n = 4). Adult female monkeys were equipped with tether systems and stomach catheters so that drug administration could start 1 month before mating and could be continued throughout gestation. During pregnancy, PHT and STP plasma levels were maintained between 4-12 and 4-10 micrograms/ml respectively (for both monotherapy and polytherapy). Infants were separated from mothers at birth and transferred to the University of Washington's (Seattle) Infant Primate Research Laboratory (IPRL) for postnatal care and testing. Data on a hyperexcitability scale were obtained during cognitive testing for visual and cross-modal recognition memory in 13 infant monkeys when they were between 2 weeks and 3 months of age. The data indicated that infants prenatally exposed to PHT, whether alone or in combination with STP, were at increased risk for hyperexcitability (screeching, refusing to attend to stimuli, lack of visual orientation). This was not true of infants prenatally exposed to STP monotherapy (drug group differences, p < 0.05).

Feasibility and safety of vagal stimulation in monkey model.

The feasibility, safety, and preliminary effects of chronic vagal stimulation were studied in an aluminagel monkey model. Pilot studies to perfect the equipment, determine stimulation thresholds, and insure the comfort and safety of the animals preceded this study. Four monkeys were equipped with an indwelling, 2-electrode cuff (titanium bands spaced 7 mm apart; silicone encased; 1.5 cm total length) in contact around the right vagus nerve; avoidance of the cardiac branch was confirmed by electrocardiograms. After postsurgical recovery, the intact and awake animals received constant-current stimulation (5 mA; 83 Hz, 143 Hz, or 50-250 Hz randomly; 0.5-ms pulse width) at the onset of every spontaneous seizure for the duration of the seizure or every 3 h for 40 s if stimulation had not occurred in the preceding hour. Stimulation periods of 2-6 weeks, with differing levels of stimulation, were preceded and followed by at least a 2-week baseline period of no stimulation. During the stimulation periods, the seizure rate decreased to zero in two monkeys and the interseizure intervals became invariable in the remaining two monkeys. These effects carried over temporarily into the poststimulation baseline periods. Vagal stimulation had no consistent effects on seizure severity or EEG interictal spikes. Histological studies of six vagus nerves were unable to separate electrode cuff damage from any direct effects stimulation may have had on the nerves. Although it appears that chronic vagal stimulation is feasible and that epileptogenic processes are influenced, the safety and efficacy of the procedure are still in question.

Carbamazepine plus stiripentol: is polytherapy by design possible?

To test the idea that the combination of carbamazepine (CBZ) plus stiripentol (STP) is synergistic, an alumina-gel monkey model (N = 4) was used to compare polytherapy electroencephalographic (EEG) effects to those of CBZ monotherapy. The research design included five consecutive phases (2-3 weeks each): baseline, CBZ, CBZ + STP, CBZ, and postdrug baseline. Both drugs were administered in suspension through a chronic gastric catheter every 4 h (to minimize plasma level oscillations). Doses of CBZ were adjusted to maintain CBZ concentration at the same level in the drug periods (except during the initial polytherapy phase, where levels were allowed to increase prior to adjustment). Phased-reversed interictal spikes were manually counted (expressed as a rate per minute). Relative to baseline, CBZ (Cmin = 0.59; Cmax = 2.36 micrograms/ml) increased interictal EEG spikes by an average of 42%. Relative to CBZ monotherapy, the addition of STP (Cmin = 12.02; Cmax = 13.21 micrograms/ml) was associated with an average decrease in spike rate of 39%. This effect was reversible since removal of STP was associated with an increase in spike rate of 66%. The CBZ-epoxide/CBZ ratio decreased from 0.29 to 0.06 when STP was added and increased to 0.30 when STP was removed. The data fit a pharmacodynamic interpretation and suggest that in the case of CBZ + STP the benefits may outweigh the usual disadvantages of polytherapy.

Metabolic fate of valproic acid in the rhesus monkey. Formation of a toxic metabolite, 2-n-propyl-4-pentenoic acid.

The metabolic fate of an iv bolus dose (13.5 mg kg-1) of valproic acid (VPA) was studied in adult male rhesus monkeys. Renal excretion proved to be the major route of elimination of the drug and a total of 17 metabolites, accounting collectively for some 82% of the administered dose, were identified in urine by GC-MS techniques. Many of these metabolites were present largely in the form of glucuronide conjugates, as was VPA itself. The principal pathways of VPA biotransformation were, in order of decreasing quantitative importance, ester glucuronide formation, omega-oxidation, beta-oxidation and (omega-1)-hydroxylation. In addition, three mono-unsaturated metabolites, identified as (E)-delta 2-, (E)-delta 3-, and delta 4-VPA, were detected in both plasma and urine. Quantitative analysis of these unsaturated VPA metabolites indicated that the delta 4 olefin, which is known to be a potent hepatotoxic agent, was the predominant isomer of the group.

A gestational monkey model: effects of phenytoin versus seizures on neonatal outcome.

In the present research, an animal model was developed to ascertain the potential effects of gestational drug concentrations and/or maternal seizures on the neonate. The rhesus monkey (Macaca mulatta) was the species of choice as previous research has demonstrated its validity as a model for partial epilepsy. Phenytoin (PHT) was tested because it is effective in the treatment of partial epilepsy in patients and is efficacious in nonpregnant monkeys with focal motor seizures. Data were obtained on the outcomes of nine pregnancies from five mothers, all of whom received PHT during gestation. Infant motor and social development and maternal/offspring interactions were systematically monitored for 12 weeks postnatally. Results indicated that impairment of infant motor development was directly correlated with greater drug exposure during the third trimester of pregnancy and unrelated to maternal seizure frequency during gestation. Also, developmental problems were more serious in infants exposed to higher drug levels, including difficulty nursing, grasping, and/or clasping; an upper lip anomaly; fetal death in one case; and infant death in another. Though the sample size of this study was small and the methodology experimental, the findings indicate that the gestational model is a valuable paradigm with potential clinical relevance. The results also support the notion that high third-trimester phenytoin levels may have significant impact on newborn reflexes and initial development of gross motor skills.

Stiripentol in acute/chronic efficacy tests in monkey model.

Acute and chronic efficacy tests of stiripentol (4,4-dimethyl-1-[3,4-(methylenedioxy)-phenyl]-1-penten-3-ol) were conducted in alumina-gel rhesus monkeys. In the acute study (n = 6), discrete serial seizures precipitated by 150 mg/kg of 4-deoxypyridoxine hydrochloride were challenged by intravenous administration of stiripentol and the data compared with those obtained with valproate similarly tested in other monkeys (reported here) and with those from four other standard anticonvulsants (phenytoin, carbamazepine, phenobarbital, and diazepam--data published previously). In the acute challenge (Study 1), stiripentol performed comparably to valproate by delaying the onset of seizures but not eliminating them as did the other four drugs. In two separate chronic studies (at different doses, n = 6 each), stiripentol was given every 4 h by gastric catheter for 4 weeks, preceded and followed by 4 weeks of baseline. In these studies, stiripentol significantly reduced EEG interictal spike rates at mean plasma concentrations from 20 to 27 micrograms/ml in Study 2 and 11 to 14 micrograms/ml in Study 3. From these results, and those evinced in other studies, it appears that stiripentol should be evaluated for absence epilepsy and possible synergistic effects in polytherapy.

Diurnal oscillations of CSF valproate in monkey.

Valproate (VPA) was administered to four rhesus monkeys by constant-rate intravenous infusion for two weeks under controlled conditions. Plasma and CSF samples were collected for a period of 27 hours at 3-hour intervals during steady-state and post-infusion periods. The mean correlation coefficient between total plasma and CSF VPA concentrations was found to be 0.78 +/- 0.09. The CSF VPA levels reflected the changes in free VPA in plasma but the two were not equivalent. Diurnal fluctuations in CSF VPA concentration were similar to those found in plasma but the inter-animal variation was greater in CSF than in plasma.

Absence of seizures or mirror foci in experimental epilepsy after excision of alumina and astrogliotic scar.

In 15 rhesus monkeys (Macaca mulatta) made epileptic by the sensorimotor cortical injection of alumina, the roles of alumina and of "mirror foci" were investigated by serial surgical excisions of the granuloma, surrounding epileptic focus, and contralateral homotopic sensorimotor cortex. Electroencephalographic and electrocorticographic recordings documented foci and transmitted contralateral epileptic activity. After the granuloma was removed, seizures continued but without alumina. After the epileptic cortex was removed, no seizure activity remained and no contralateral independent foci occurred. These findings indicate that the epilepsy incident to alumina injection into the sensorimotor cortex in monkey is not dependent on the continual presence of alumina and is not associated with independent or "mirror foci."

Na+ + K+-ATPase in serially excised segments of epileptic monkey cortex.

The membrane-bound enzyme Na+ + K+-ATPase was measured in serially excised specimens of cerebral cortex in epileptic and control monkeys. Experimental chronic epileptic cortex showed significantly lower values than controls, as is seen in some other models and human epilepsy, but is different from the increased enzyme values in cobalt and freezing lesion epilepsy.

Slow-speed EEG for chronic monitoring of clinical seizures in monkey model.

A method for utilizing slow-speed EEG (1/4 mm sec) to detect and quantify gross-motor clinical seizures in a chronic monkey model is described. The technique is particularly useful in the detection of small clinical seizures that may occur in studies of drug efficacy. It estimates the reams of paper generated by standard EEG recording (30 mm/sec) that heretofore precluded easy data collation and thereby essentially prevented continuous monitoring of EEG paroxysms. (This method, however, does not allow the detection of single or non-clumped interictal spikes.) The headplug and recording procedures employed in our laboratory are detailed. The technique can be used alone or, for greater precision, in conjunction with either the recording of motor-activity envelopes or a videotape seizure-confirmation system, or both (Lockard and Barensten, 1967; Lockard et al., 1976c). Unlike our motor-activity and closed-circuit TV method for detecting clinical seizures, the technique of slow-speed EEG could be easily employed in other laboratories already equipped with EEG polygraphs. This method also permits the simultaneous recording of slow-speed and standard-speed EEGs (on separate polygraphs) to facilitate periodically the discrimination between artifacts and clinical seizures.

Cinromide's metabolite in monkey model: gastric administration and seizure control.

In a previous study (Lockard et al., 1979) Cinromide (3 bromo-N-ethylcinnamamide), an experimental anticonvulsant (Burroughs-Wellcome Pharmaceutical Co.), was given a preliminary evaluation. Since that research was concerned primarily with EEG paroxysms, the present study was conducted to address drug efficacy in terms of clinical seizures. Cinromide's major metabolite (3-bromocinnamamide, BC) was the main focus. Eight alumina-gel monkeys were given by gastric bolus every 6 hr for 10 days (Phase I) either the solvent alone (Tween 80), Cinromide (BEC), or its synthetic metabolite (SBC). Subsequently (Phase II), four animals were given BEC or SBC by chronic gastric infusion for 20 days. In both phases Cinromide's metabolite (either via BEC or especially SBC) was effective in half of the animals in reducing seizure frequency and/or duration at plasma levels above 5 mcg/m. The data suggest that the drug's efficacy is individually specific. Another species of Cinromide metabolism, 3-bromocinnamic acid, is also discussed.

Clonazepam in a focal-motor monkey model: efficacy, tolerance, toxicity, withdrawal, and management.

Since the clinical data have been equivocal in regard to the effects of clonazepam (CZP) in focal-motor seizures, an alumina gel monkey model was used to evaluate quantitatively its efficacy with respect to this seizure category. The insolubility of CZP and its short biological half-life in monkey necessitated its evaluation in the model via constant-rate intravenous administration in a solution of polyethylene glycol 400 (PEG). Two groups of monkeys were given CZP in PEG (N = 6) or a PEG solution alone as a control compound (N = 5) for 6 weeks; these treatments were bordered at both ends by 3 weeks of treatment with saline only in order to establish a baseline. CZP was administered at a concentration sufficient to achieve a plasma level of 30 ng/ml in drug step I (3 weeks) and at least double that level in drug step II (3 weeks). As a solute for CZP, and when given by itself, PEG was always administered at a concentration of 35%. The results indicate that CZP is effective for focal-motor seizures and secondarily generalized tonic-clonic seizures, particularly when its concentration in plasma is higher than 60 ng/ml. Withdrawal seizures were evident on cessation of CZP administration. CZP appears to be a useful broad-spectrum anticonvulsant when managed carefully. An unexpected finding was the irreversibility of the pharmacological effect of PEG. Cessation of PEG administration significantly reduced seizure frequency in subsequent weeks to a level below the initial baseline level.

Experimental anticonvulsant cinromide in monkey model: preliminary efficacy.

Cinromide (3 brono-N-ethylcinnamide), an experimental anticonvulsant (Burroughs-Wellcome Pharmaceutical Co.), was given a preliminary evaluation in our alumina-gel monkey model. The parent drug has a biological half-life in monkey of 1-2 hr and its active metabolite, 3-bromocinnamide, a half-life of 4-6 hr. In phase 1, 6 chronically epileptic monkeys, with focal motor and secondarily generalized tonic-clonic seizures, received the drug in a vehicle of 65% polyethylene glycol 400 (PEG) by constant-rate intravenous infusion followed by baseline days of saline only and PEG only. Three different concentrations of Cinromide (12, 24, and 36 mg/ml/hr) were administered, respectively, to achieve mean steady state plasma levels of approximately 5, 10 and 20 micrograms/ml of the metabolite (0.5 to 5.0 micrograms/ml of the parent drug). In phase 2, Cinromide was administered for 7 days at the middle concentration to all monkeys. Baseline periods similar to those of phase 1 were used as controls. The data tentatively suggest that Cinromide is efficacious in the monkey model at a plasma concentration range of 7-14 micrograms/ml of the metabolite. With the exception of one animal, no secondarily generalized seizures were exhibited during drug administration (but were evident in the baseline periods), and EEG bursting decreased significantly in several monkeys. Minimal side effects were manifested at these plasma levels but withdrawal seizures were evinced with cessation of the drug. Further evaluation of Cinromide by gastric administration in our animal model is planned.