The general lack of pain experience is a rare occurrence in humans, and the molecular causes for this phenotype are not well understood. Here we have studied a Canadian family from Newfoundland with members who exhibit a congenital inability to experience pain. We have mapped the locus to a 13.7 Mb region on chromosome 2q (2q24.3-2q31.1). Screening of candidate genes in this region identified a protein-truncating mutation in SCN9A, which encodes for the voltage-gated sodium channel Na(v)1.7. The mutation is a C-A transversion at nucleotide 984 transforming the codon for tyrosine 328 to a stop codon. The predicted product lacks all pore-forming regions of Na(v)1.7. Indeed, expression of this altered gene in a cell line did not produce functional responses, nor did it cause compensatory effects on endogenous voltage-gated sodium currents when expressed in ND7/23 cells. Because a homozygous knockout of Na(v)1.7 in mice has been shown to be lethal, we explored why a deficiency of Na(v)1.7 is non-lethal in humans. Expression studies in monkey, human, mouse and rat tissue indicated species-differences in the Na(v)1.7 expression profile. Whereas in rodents the channel was strongly expressed in hypothalamic nuclei, only weak mRNA levels were detected in this area in primates. Furthermore, primate pituitary and adrenal glands were devoid of signal, whereas these two glands were mRNA-positive in rodents. This species difference may explain the non-lethality of the observed mutation in humans. Our data further establish Na(v)1.7 as a critical element of peripheral nociception in humans.

Voltage-gated ion channels generate cellular excitability, cause diseases when mutated, and act as drug targets in hyperexcitability diseases, such as epilepsy, cardiac arrhythmia and pain. Unfortunately, many patients do not satisfactorily respond to the present-day drugs. We found that the naturally occurring resin acid dehydroabietic acid (DHAA) is a potent opener of a voltage-gated K channel and thereby a potential suppressor of cellular excitability. DHAA acts via a non-traditional mechanism, by electrostatically activating the voltage-sensor domain, rather than directly targeting the ion-conducting pore domain. By systematic iterative modifications of DHAA we synthesized 71 derivatives and found 32 compounds more potent than DHAA. The most potent compound, Compound 77, is 240 times more efficient than DHAA in opening a K channel. This and other potent compounds reduced excitability in dorsal root ganglion neurons, suggesting that resin-acid derivatives can become the first members of a new family of drugs with the potential for treatment of hyperexcitability diseases.

Desensitization of ligand-gated ion channels plays a critical role for the information transfer between neurons. The current view on γ-aminobutyric acid (GABA)A and glycine receptors includes significant rapid components of desensitization as well as cross-desensitization between the two receptor types. Here, we analyze the mechanism of apparent cross-desensitization between native GABAA and glycine receptors in rat central neurons and quantify to what extent the current decay in the presence of ligand is a result of desensitization versus changes in intracellular Cl− concentration ([Cl−]i). We show that apparent cross-desensitization of currents evoked by GABA and by glycine is caused by changes in [Cl−]i. We also show that changes in [Cl−]i are critical for the decay of current in the presence of either GABA or glycine, whereas changes in conductance often play a minor role only. Thus, the currents decayed significantly quicker than the conductances, which decayed with time constants of several seconds and in some cells did not decay below the value at peak current during 20-s agonist application. By taking the cytosolic volume into account and numerically computing the membrane currents and expected changes in [Cl−]i, we provide a theoretical framework for the observed effects. Modeling diffusional exchange of Cl− between cytosol and patch pipettes, we also show that considerable changes in [Cl−]i may be expected and cause rapidly decaying current components in conventional whole cell or outside-out patch recordings. The findings imply that a reevaluation of the desensitization properties of GABAA and glycine receptors is needed.

Background: Studies of family reactions following teenage suicide are hampered by the psychological difficulties of approaching families and recruiting an unbiased sample of study subjects. By using a small but consecutive series of cases, we examined the qualitative aspects of loosing a teenage family member due to suicide. Such an understanding is important for future organisation of proper programs that provide professional support in the grief process.

Methods: Effects of fatty acids and fatty-acid analogues on mouse dorsal root ganglion neurons and on the human K V 7.2/3 channel expressed in Xenopus laevis oocytes were studied using electrophysiology. Conclusions: These findings suggest that circulating polyunsaturated fatty acids, with a minimum requirement of multiple double bonds and a charged carboxyl group, dampen excitability by opening neuronal M-channels. Collectively, our data bring light to the molecular targets of polyunsaturated fatty acids and thus a possible mechanism by which polyunsaturated fatty acids reduce neuronal excitability. Results

Neurotransmitter release is known to be triggered by Ca¥ that enters presynaptic terminals through voltage-gated Ca¥ channels. Voltage-gated Ca¥ channels have been classified as T-, L_, N-, P-, Q-or R-type, depending on their voltage dependence, kinetic and pharmacological properties. A majority of electrophysiological reports suggest that high-threshold channels of the N-type in combination with P-type channels are responsible for transmitter release at central mammalian synapses (Horne & Kemp, 1991;Luebke, Dunlap & Turner, 1993;Takahashi & Momiyama, 1993;Ohno-Shosaku, Hirata, Sawada & Yamamoto, 1994;Regehr & Mintz, 1994;Mintz, Sabatini & Regehr, 1995;Poncer, McKinney, G ahwiler & Thompson, 1997). Involvement of Q-type channels (Wheeler, Randall & Tsien, 1994), and to a smaller extent L-type channels (Reuter, 1995), has also been suggested. In several of the above reports, the cells show a considerable homogeneity in the relative fraction of presynaptic Ca¥ influx that each channel type is responsible for. A few recent reports, however, have suggested a heterogeneous distribution of Ca¥ channel types in presynaptic terminals of the hippocampus (Reuter, 1995;Poncer et al. 1997;Reid, Clements & Bekkers, 1997). The medial preoptic nucleus (MPN) is possibly involved in several of the major functions ascribed to the preoptic area, such as control of sexual behaviour, thermoregulation, slowwave sleep and feeding. The inhibitory neurotransmitter ã_aminobutyric acid (GABA) has been suggested to be important for several of these functions. GABAergic synaptic contacts are widespread in the MPN, possibly forming local circuits in this region (Hoffman, Kim, Gorski & Dudek, 1994a 1. Voltage-dependent Ca¥ channels triggering GABA release onto neurons from the medial preoptic nucleus of rat were investigated. Acutely dissociated neurons with adherent functional synaptic terminals were investigated by tight-seal whole-cell recordings from the postsynaptic cells. 2. Spontaneous current events similar to miniature postsynaptic currents were recorded. They were blocked by bicuculline (100 ìÒ), showed a roughly unimodal amplitude distribution and a reversal potential consistent with a Cl¦ current, and were therefore attributed to GABAA receptors activated by synaptically released GABA. 3. Application of 140 mÒ KCl, expected to depolarize presynaptic terminals, evoked currents that were ascribed to a more massive release of GABA. The KCl-induced synaptic currents were abolished in Ca¥-free solutions and showed a roughly hyperbolic relation to external Ca¥ concentration with half-saturation at 0·15 mÒ. They further depended on the concentration of applied KCl in a way expected for high-threshold Ca¥ channels. 4. The KCl-evoked synaptic currents were completely blocked by 200 ìÒ Cd¥, but only partially blocked by 200 ìÒ Ni¥. 5. The KCl-evoked synaptic currents were insensitive to the L-type Ca¥ channel blocker nifedipine (10 ìÒ). However, the synaptic currents were sensitive to either 1 ìÒ ù_conotoxin GVIA, 25 nÒ ù_agatoxin IVA or 1 ...

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