Drug effects on afterdischarge and seizure threshold in lissencephalic ferrets: an epilepsy model for drug evaluation

Care, management, and use of ferrets in biomedical research

The ferret (Mustela putorius furo) is a small domesticated species of the family Mustelidae within the order Carnivora. The present article reviews and discusses the current state of knowledge about housing, care, breeding, and biomedical uses of ferrets. The management and breeding procedures of ferrets resemble those used for other carnivores. Understanding its behavior helps in the use of environmental enrichment and social housing, which promote behaviors typical of the species. Ferrets have been used in research since the beginning of the twentieth century. It is a suitable non-rodent model in biomedical research because of its hardy nature, social behavior, diet and other habits, small size, and thus the requirement of a relatively low amount of test compounds and early sexual maturity compared with dogs and non-human primates. Ferrets and humans have numerous similar anatomical, metabolic, and physiological characteristics, including the endocrine, respiratory, auditory, gastrointestinal, and immunological systems. It is one of the emerging animal models used in studies such as influenza and other infectious respiratory diseases, cystic fibrosis, lung cancer, cardiac research, gastrointestinal disorders, neuroscience, and toxicological studies. Ferrets are vulnerable to many human pathogenic organisms, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), because air transmission of this virus between them has been observed in the laboratory. Ferrets draw the attention of the medical community compared to rodents because they occupy a distinct niche in biomedical studies, although they possess a small representation in laboratory research.

Moving Forward: Recent Developments for the Ferret Biomedical Research Model

Since the initial report in 1911, the domestic ferret has become an invaluable biomedical research model. While widely recognized for its utility in influenza virus research, ferrets are used for a variety of infectious and noninfectious disease models due to the anatomical, metabolic, and physiological features they share with humans and their susceptibility to many human pathogens. However, there are limitations to the model that must be overcome for maximal utility for the scientific community. Here, we describe important recent advances that will accelerate biomedical research with this animal model.

LIS1-associated classic lissencephaly: A retrospective, multicenter survey of the epileptogenic phenotype and response to antiepileptic drugs

BACKGROUND

Patients with LIS1-associated classic lissencephaly typically present with severe psychomotor retardation and drug-resistant epilepsy within the first year.

AIM

To analyze the epileptogenic phenotype and response to antiepileptic therapy in LIS1-associated classic lissencephaly.

METHOD

Retrospective evaluation of 22 patients (8 months-24 years) with genetically and radiologically confirmed LIS1-associated classic lissencephaly in 16 study centers.

RESULTS

All patients in our cohort developed drug-resistant epilepsy. In 82% onset of seizures was noted within the first six months of life, most frequently with infantile spasms. Later in infancy the epileptogentic phenotype became more variable and included different forms of focal seizures as well generalized as tonic-clonic seizures, with generalized tonic-clonic seizures being the predominant type. Lamotrigine and valproate were rated most successful with good or partial response rates in 88-100% of the patients. Both were evaluated significantly better than levetiracetam (p<0.05) and sulthiame (p<0.01) in the neuropediatric assessment and better than levetiracetam, sulthiame (p<0.05) and topiramate (p<0.01) in the family survey. Phenobarbital and vigabatrin achieved good or partial response in 62-83% of the patients.

CONCLUSION

Our findings suggest that patients with LIS1-associated lissencephaly might benefit most from lamotrigine, valproate, vigabatrin or phenobarbital.

Surgery for malformations of cortical development causing epilepsy

Malformations of cortical development (MCD) are responsible for many cases of refractory epilepsy in adults and children. The results of surgical treatment are difficult to assess from the published literature. Judging from the limited number of adequately reported cases, approximately 40% of all cases of MCD treated surgically may be rendered seizure-free over a minimum 2-year follow-up period. This figure is the same for focal cortical dysplasia (FCD), the most common variety of MCD in surgical reports. In comparison with outcome for epilepsy associated with hippocampal sclerosis, this figure is low. Part of the difference may be artificial and related to limited reporting. Much of the difference is likely to relate to the complex underlying biology of MCD. Analysis of epileptogenesis in MCD has been undertaken. Different types of MCD have different sequelae. Some varieties are intrinsically epileptogenic; these include FCD and heterotopia. Although in most cases, the visualized MCD lies within the region of brain responsible for generating seizures (the epileptogenic zone), it may not constitute the entire epileptogenic zone in all cases. For polymicrogyria and schizencephaly in particular, the visualized abnormalities are probably not the most important component of the epileptogenic zone. There is evidence that the epileptogenic zone is spatially distributed and also, in some cases, temporally distributed. These findings may explain poor surgical outcome and the inadequacy of current presurgical evaluative methods. New preoperative techniques offer the opportunity of improved presurgical planning and selection of cases more likely to be rendered seizure-free by current surgical techniques. Of paramount importance is improved reporting. The establishment of a central registry may facilitate this aim. Specific recommendations are made for surgical strategies based on current experience and understanding.

Seizure susceptibility in immature rats with micrencephaly induced by prenatal exposure to methylazoxymethanol acetate

The administration of the alkylating neurotoxin methylazoxymethanol acetate (MAM) to pregnant rats on day 15 of gestation induces, in the offspring, a marked micrencephaly, characterized by an impaired formation of interneurons at cortical, hippocampal and striatal levels. Since in man developmental CNS malformations are often associated with severe epileptogenic encephalopathies with seizures appearing in the first months or years of life, we have studied the development of kainic-acid- and bicuculline-induced seizures in 15- and 30-day-old rats, prenatally exposed to MAM. Compared to controls, a higher susceptibility to seizures has been found in micrencephalic rats aged 15 days, while no significant differences have been observed in those aged 30 days. It is hypothesized that the cerebral global anatomical dysgenesis caused by MAM underlies the higher seizure susceptibility shown by animals during the first periods of life. Successively, the processes of adjustment occurring between the cerebral regions affected by the neurotoxic action of MAM and the afferent and efferent pathways spared by the substance may re-establish adequate interneuronal relationships and, therefore, a normal convulsive susceptibility.

Benzo[b]thiophenes, II: Novel benzo[b]thienylhydrazine and 1,3,4-oxadiazole derivatives as potential antidepressant agents

Three novel series of benzo[b]thiophene derivatives bearing various hydrazone, hydrazine and 1,3,4-oxadiazole moieties were synthesized as potential antidepressant agents. 22 Compounds were evaluated for their in vitro inhibitory effect on monoamine oxidase enzyme (MAO) type A. Several compounds inhibited MAO stronger than pargyline hydrochloride. Maximum inhibitions of 83% and 90% were observed with 1-benzyl-2-(3-chlorobenzo[b]thienyl-2-carbonyl)hydrazine (24) and 1-[2-(4-chlorophenyl)ethyl]-2-(3-chlorobenzo[b]thienyl-2- carbonyl)hydrazine (35), respectively.

Differences in antiepileptic drug efficacy in hippocampally kindled normal and microcephalic rats

The difference in antiepileptic drug efficacy was investigated in two groups of animals: 5 normal and 4 microcephalic rats. The latter were produced by a single i.p. injection of 30 mg/kg methylazoxymethanol acetate in the mother on the 15th day of gestation. Hippocampal kindling was performed to a seizure criterion in all animals followed by testing of the antiepileptic drugs vs placebo. Besides carbamazepine (CBZ), two new anticonvulsants were tested: (E)-2-[(alpha-amino)phenylmethylene]-benzo-[b]-thiophene-3(2H)-one (AF-CX 921) and its metabolite (E)-2-[alpha-amino)phenylmethylene]-benzo-[b]-thiophene-3(2H)-one- 1- oxide (AF-CX 1325). Frequency of occurrence and duration of afterdischarges and seizures were statistically examined. The duration of early afterdischarges (AD1) tended to be shorter in microcephalic than in normal animals in control and placebo periods. In contrast, during treatment with the antiepileptic drugs, AD1 durations were longer in microcephalic than in normal animals. This suggests that the drugs inhibited AD1 to a lesser extent in the microcephalics. Two other characteristics of EEG epileptic activity, focal spiking (FS) and late afterdischarges (AD2) also varied in the two groups. Both were significantly lower in occurrence in the microcephalic rats independent of treatment. Three types of behavioral manifestations were also examined: convulsive seizures (CS), epileptic behavior (EB) and quiet states (Q). The two groups of animals responded differently to the drugs with respect to Q and CS. In the microcephalics, AFCX 1325 and AFCX 921 were superior to CBZ, which in turn, was superior to placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of carbamazepine, AF-CX 921, and AF-CX 1325 on epileptic discharges and seizures in hippocampally kindled rats

In nine hippocampally kindled rats (5 normal and 4 microcephalic) a comparative study of the antiepileptic effects of carbamazepine, and AF-CX 921 [(E)-2-[(alpha-amino)-phenylmethylene]-benzo-[b]-thiophene-3(2H)- one] and its metabolite AF-CX 1325 [(E)-2-[(alpha-amino)-phenylmethylene]-benzo-[b]-thiophene-3-(2H)- one-1-oxide], were compared with placebo. The treatment effects were tested 1, 2, 3, 4, and 5 h after drug administration, and the testings were executed twice for each treatment and animal. The following biological parameters were evaluated and statistically analyzed: duration of first AD (AD1); frequency of occurrence of focal spiking (FS) which followed AD1; frequency of occurrence of second AD (AD2) which followed FS; duration of total EEG epileptic activity (AD1 + FS + AD2); frequency of occurrence of convulsive seizures (CS); frequency of occurrence of partial seizures (epileptic behavior, automatisms); and frequency of occurrence of a quiet state of the animal, indicating no behavioral kindling response. All three drugs had clear antiepileptic effects on EEG epileptic activity and clinical seizures in comparison with placebo. The strongest antiepileptic effect was produced by AF-CX 1325. It reduced AD1 duration to approximately 50% of that in the placebo treatment, and was most effective in reducing occurrence of FS to 20% and AD2 to 33% of that in the placebo. It was the only drug that decreased AD2 duration, and total EEG epileptic activity was reduced to less than 50% of that in the placebo. These EEG results were paralleled by clinical effects.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG and seizure threshold in normal and lissencephalic ferrets

Changes in EEG and susceptibility to electrically induced seizures were examined in the ferret with lissencephaly produced by exposure to a single injection of methylazoxymethanol acetate (MAM Ac) given to the pregnant jill on gestation day 32. Ten lissencephalic and 11 normal ferrets were chronically implanted with 14 cortical stainless steel electrodes. EEG records were sampled from various stages of the sleep/awake cycle. Six of each group were subjected to electrical stimulation for seizure threshold. Although the number of stimulations and the current intensity required to produce epileptiform afterdischarges (AD) and seizures were not different between the two groups, the lissencephalic ferrets had significantly longer AD and seizures, and a greater number of generalized seizures, indicating an enhanced seizure susceptibility. The EEG of the lissencephalic ferrets was characterized by increased slow wave activity within the low theta band range, extreme spindle activity, focal or multifocal slow and sharp waves, spikes, or spike and slow wave complexes. The differences in the EEG were more pronounced during drowsiness and sleep stages. The brains of all of the treated animals were lissencephalic and hydrocephalic, and weighed significantly less than those of the normals. The cerebral cortex was thin and flattened, with the parieto-occipital region most severely affected. Heterotopic foci were found in the cerebellum as well as in the cerebral cortex. Abnormalities in the configuration of the cerebellar folia were also seen. Comparison between the electrophysiological and neuropathological data suggests that the extent of the extreme spindle activity, and longer AD and seizure duration depended on the degree of cerebellar dysplasia, whereas the EEG focal abnormalities were related to lesions in the cerebral hemispheres.