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Alpha-conotoxin-PnVIIA, an alpha-carboxyglutamate-containing peptide agonist of neuronal pacemaker cation currents, was characterized from the venom of the molluscivorous snail Conus pennaceus from specimens obtained in the northern Red Sea. The PnVIIA stimulates depolarization and action potential burst in the caudodorsal neurons of Lymnaea. The results were attributed to the enhanced slow inward cation current that may underly the neuron's bursting activity. The PnVIIA may thus serve as a prototype of a conotoxin class called alpha-conotoxins.

The venom of the molluscivorous snail Conus textile produces a hydrophobic omega-conotoxin-TxVII that affects dihydropyridine (DHP)-sensitive calcium channels. Amino acid sequence analysis reveals similarities to the cysteine framework of omega-conotoxins but the peptide is highly hydrophobic and has a negative charge. The toxin has no influence on sodium and potassium channels in caudodorsal cells. TxVII blocks the slowly inactivating DHP-sensitive calcium channel though it has no action on the fast inactivating channel.

Two conotoxins obtained from the venom of molluscivorous snail Conus pennaceus, PnIVA and PnIVB, block the sodium channels in the neurons of molluscs but are ineffective on the sodium channels in bovine chromaffin cells and rat brain synaptosomes. The amino acid sequences of the conotoxins reveal the presence of a cysteine framework, hence the nomenclature IV is used. Peptide toxins from snail venom are small and fall into pharmacological or chemical groups based on structure and activities on target receptors.

A new set of conotoxins extracted from the venom of Conus marmoreus and Lymnaea stagnalis (fresh water snail) behave indifferently towards both sodium and calcium currents. These toxins inhibit the function of voltage dependent sodium currents and fast-inactivating calcium current in snail neurons, by blocking them. The block of calcium current can be reversed quickly while the recovery of sodium current demands extensive wash. Both conotoxins allow extensive studies on sodium and L-type calcium channels in a voltage regulated environment.

Gonadal steroid feedback to oxytocin neurons during pregnancy is in part mediated via the neurosteroid allopregnanolone (3[Alpha]-OH-DHP), acting as allosteric modulator of postsynaptic [Gamma]-aminobutyric acid type A ([GABA.sub.A]) receptors. We describe here a form of nongenomic progesterone signaling by showing that 3[Alpha]-OH-DHP not only potentiates [GABA.sub.A] receptor-channel activity but also prevents its modulation by protein kinase C (PKC). Application of oxytocin or stimulation of PKC suppressed the postsynaptic GABA responses of oxytocin neurons in the absence, but not in the presence of 3[Alpha]-OH-DHP. This finding was true at the juvenile stage and during late pregnancy, when the [GABA.sub.A] receptor is sensitive to 3[Alpha]-OH-DHP. In contrast, after parturition, when the [GABA.sub.A] receptors expressed by oxytocin neurons are less sensitive to 3[Alpha]-OH-DHP, this neurosteroid no longer counteracts PKC. The change in [GABA.sub.A]-receptor responsiveness to 3[Alpha]-OH-DHP helps to explain the onset of firing activity and thus the induction of oxytocin release at parturition.

To identify coding and non-coding suppressor genes of anchorage-independent proliferation by efficient loss-of-function screening, we have developed a method for enzymatic production of low complexity shRNA libraries from subtracted transcriptomes. We produced and screened two LEGO (Low-complexity by Enrichment for Genes shut Off) shRNA libraries that were enriched for shRNA vectors targeting coding and non-coding polyadenylated transcripts that were reduced in transformed Mouse Embryonic Fibroblasts (MEFs). The LEGO shRNA libraries included ~25 shRNA vectors per transcript which limited off-target artifacts. Our method identified 79 coding and non-coding suppressor transcripts. We found that taurine-responsive GABAA receptor subunits, including GABRA5 and GABRB3, were induced during the arrest of non-transformed anchor-deprived MEFs and prevented anchorless proliferation. We show that taurine activates chloride currents through GABAA receptors on MEFs, causing seclusion of cell volume in large membrane protrusions. Volume seclusion from cells by taurine correlated with reduced proliferation and, conversely, suppression of this pathway allowed anchorage-independent proliferation. In human cholangiocarcinomas, we found that several proteins involved in taurine signaling via GABAA receptors were repressed. Low GABRA5 expression typified hyperproliferative tumors, and loss of taurine signaling correlated with reduced patient survival, suggesting this tumor suppressive mechanism operates in vivo. [ABSTRACT FROM AUTHOR]

Endocannabinoids control hippocampal inhibitory synaptic transmission through activation of presynaptic CB1 receptors. During depolarization-induced suppression of inhibition (DSI), endocannabinoids are synthesized upon postsynaptic depolarization. The endocannabinoid 2-arachidonoylglycerol (2-AG) may mediate hippocampal DSI. Currently, the best studied pathway for biosynthesis of 2-AG involves the enzyme diacylglycerol lipase (DAGL). However, whether DAGL is necessary for hippocampal DSI is controversial and was not systematically addressed. Here, we investigate DSI at unitary connections between CB1 receptor-containing interneurons and pyramidal neurons in CA1. We found that the novel DAGL inhibitor OMDM-188, as well as the established inhibitor RHC-80267, did not affect DSI. As reported previously, effects of the DAGL inhibitor tetrahydrolipstatin depended on the application method: postsynaptic intracellular application left DSI intact, while incubation blocked DSI. We show that all DAGL inhibitors tested block slow self-inhibition in neocortical interneurons, which involves DAGL. We conclude that DAGL is not involved in DSI at unitary connections in hippocampus. [ABSTRACT FROM AUTHOR]

Repeated exposure to drugs of abuse causes persistent behavioral sensitization and associated adaptations of striatal neurotransmission, which is thought to play an important role in certain aspects of drug addiction. Microdialysis and neurochemical studies suggest that intermittent morphine treatment may lead to a long-term increase in both ACh and dopaminergic neurotransmission in the nucleus accumbens (NAc). This implies that both cholinergic modulation of GABA synapses and their sensitivity to dopaminergic transmission might be changed, ultimately leading to a modified NAc output. Here we investigate to what extent cholinergic modulation and sensitivity to amphetamine, causing endogenous dopamine efflux, of GABAergic transmission in the nucleus accumbens are affected 3 weeks after a period of daily morphine injections in adult rats. To this end, we recorded medium spiny neurons using whole cell voltage clamp and monitored the frequency and amplitude of spontaneous GABAergic synaptic currents. We observed that the effect of nicotine on the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was suppressed in rats pretreated with morphine, whereas the effects of mecamylamine and tetrodotoxin (TTX) were increased. These results indicate that the probability of GABA release was increased and that this effect resulted from an upregulation of the endogenous activation of presynaptic nicotinic receptors. In addition, we observed an increased sensitivity to in vitro application of amphetamine. This suggests that the long-term increase in dopaminergic transmission caused by the morphine treatment affects GABA synapses in the NAc. Hence, there may be two parallel synaptic mechanisms by which drugs of abuse may affect processing and integration of NAc inputs. Synapse 55:17-25, 2005. © 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]