Recent advances on autosomal dominant nocturnal frontal lobe epilepsy: "understanding the nicotinic acetylcholine receptor (nAChR)"

The role of nicotinic acetylcholine receptors in autosomal dominant nocturnal frontal lobe epilepsy

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a focal epilepsy with attacks typically arising in the frontal lobe during non-rapid eye movement (NREM) sleep. It is characterized by clusters of complex and stereotyped hypermotor seizures, frequently accompanied by sudden arousals. Cognitive and psychiatric symptoms may be also observed. Approximately 12% of the ADNFLE families carry mutations on genes coding for subunits of the heteromeric neuronal nicotinic receptors (nAChRs). This is consistent with the widespread expression of these receptors, particularly the α4β2^* subtype, in the neocortex and thalamus. However, understanding how mutant nAChRs lead to partial frontal epilepsy is far from being straightforward because of the complexity of the cholinergic regulation in both developing and mature brains. The relation with the sleep-waking cycle must be also explained. We discuss some possible pathogenetic mechanisms in the light of recent advances about the nAChR role in prefrontal regions as well as the studies carried out in murine models of ADNFLE. Functional evidence points to alterations in prefrontal GABA release, and the synaptic unbalance probably arises during the cortical circuit maturation. Although most of the available functional evidence concerns mutations on nAChR subunit genes, other genes have been recently implicated in the disease, such as KCNT1 (coding for a Na⁺-dependent K⁺ channel), DEPD5 (Disheveled, Egl-10 and Pleckstrin Domain-containing protein 5), and CRH (Corticotropin-Releasing Hormone). Overall, the uncertainties about both the etiology and the pathogenesis of ADNFLE point to the current gaps in our knowledge the regulation of neuronal networks in the cerebral cortex.

Hydrophobic residues at position 10 of α-conotoxin PnIA influence subtype selectivity between α7 and α3β2 neuronal nicotinic acetylcholine receptors

Neuronal nicotinic acetylcholine receptors (nAChRs) are a diverse class of ligand-gated ion channels involved in neurological conditions such as neuropathic pain and Alzheimer's disease. α-Conotoxin [A10L]PnIA is a potent and selective antagonist of the mammalian α7 nAChR with a key binding interaction at position 10. We now describe a molecular analysis of the receptor-ligand interactions that determine the role of position 10 in determining potency and selectivity for the α7 and α3β2 nAChR subtypes. Using electrophysiological and radioligand binding methods on a suite of [A10L]PnIA analogs we observed that hydrophobic residues in position 10 maintained potency at both subtypes whereas charged or polar residues abolished α7 binding. Molecular docking revealed dominant hydrophobic interactions with several α7 and α3β2 receptor residues via a hydrophobic funnel. Incorporation of norleucine (Nle) caused the largest (8-fold) increase in affinity for the α7 subtype (Ki=44nM) though selectivity reverted to α3β2 (IC50=0.7nM). It appears that the placement of a single methyl group determines selectivity between α7 and α3β2 nAChRs via different molecular determinants.

Central Nicotinic Receptors: Structure, Function, Ligands, and Therapeutic Potential

The growing interest in nicotinic receptors, because of their wide expression in neuronal and non-neuronal tissues and their involvement in several important CNS pathologies, has stimulated the synthesis of a high number of ligands able to modulate their function. These membrane proteins appear to be highly heterogeneous, and still only incomplete information is available on their structure, subunit composition, and stoichiometry. This is due to the lack of selective ligands to study the role of nAChR under physiological or pathological conditions; so far, only compounds showing selectivity between alpha4beta2 and alpha7 receptors have been obtained. The nicotinic receptor ligands have been designed starting from lead compounds from natural sources such as nicotine, cytisine, or epibatidine, and, more recently, through the high-throughput screening of chemical libraries. This review focuses on the structure of the new agonists, antagonists, and allosteric ligands of nicotinic receptors, it highlights the current knowledge on the binding site models as a molecular modeling approach to design new compounds, and it discusses the nAChR modulators which have entered clinical trials.

Topiramate in frontal lobe epilepsy

BACKGROUND

Frontal lobe epilepsy (FLE) is a type of epilepsy that is difficult to treat and there are few studies about the use of topiramate (TPM).

AIM OF THE STUDY

To evaluate the efficacy and tolerability of TPM monotherapy in FLE.

METHODS

The study group consisted of 55 (33 male; 22 female) patients. TPM was administered as a first drug (n = 16) or converted after previous treatment (n = 39). All patients were followed every 3 months for at least 1 year. The patients were subdivided into two groups: 'newly diagnosed' patients and 'difficult-to-treat' patients.

RESULTS

Overall, all patients completed the 1-year study. At the end of follow-up, 10 patients showed disappearance of seizures and 33 patients showed improvement in seizure frequency. In particular, among the newly diagnosed patients 6/16 patients showed complete cessation of seizures and 5/16 patients showed very good response; in the other group, 4/39 patients showed complete cessation and 4/39 patients showed a very good response. No patients of both groups had worsening of seizures. No treatment-limiting adverse events associated with TPM were reported.

CONCLUSIONS

TPM is effective in newly diagnosed patients with FLE; TPM can be considered for the treatment of FLE.

Sleep and epilepsy

This article examines the relationship between sleep and epilepsy, an association that has been recognized since antiquity. The mechanisms whereby sleep facilitates seizures are under investigation, although the synchronizing role of thalamocortic networks seems contributory. Recognition of the variety of generalized and partial epileptic syndromes associated with sleep, familiarity with the differential diagnosis of nocturnal spells, and awareness of the role that antiepileptic drugs and sleep disorders may play in epilepsy are helpful in evaluating patients presenting with behavioral and motor disturbances of sleep.