Graduate student at the Freie Universität Berlin Olfaction in mammals involves the binding of odorants to a subset of the large number of different G protein-coupled receptors that are present in the cilia of olfactory sensory neurons (OSNs) 1 . These neurons are predominantly found in the MOE, which senses and discriminates myriad volatile compounds. In the mouse, the nose contains additional, apparently more specialized olfactory organs, such the septal organ of Masera and the VNO 2 . Sensory neurons in the VNO are morphologically distinct and use odorant receptors and signal transduction cascades that differ from those found in the MOE.In the canonical OSN signal transduction pathway, odorant binding to the receptor locally increases cytosolic cAMP through activation of the olfactory G protein G olf and adenylate cyclase type III 1,2 . cAMP then opens heteromeric cyclic nucleotide-gated (CNG) cation channels 3 . The resulting influx of Na + and Ca 2+ depolarizes the plasma membrane and raises the cytosolic Ca 2+ concentration ([Ca 2+ ] i ), thereby activating Ca 2+ -activated Cl -channels 1,4-10 . All these components of the signal transduction cascade are localized to sensory cilia, which are embedded in the mucus covering the MOE. These cilia provide a large interaction surface for odorants, and the cilia's small diameters facilitate large local increases in cytosolic cAMP and [Ca 2+ ].There has been broad consensus that Ca 2+ -activated Cl -channels powerfully amplify olfactory signal transduction 1,4-10 . These channels are thought to mediate an outward flow of Cl -, which generates a depolarizing current that, in rodents, is five-to tenfold larger than currents through CNG channels 8,11,12 . A prerequisite for Cl -efflux 3 is an inside-out electrochemical Cl --gradient. It is believed that cytosolic chloride concentration of OSNs is raised by the Na + K + 2Cl -co-transporter Nkcc1 9,10,13 and that [Cl -] is low in the mucus surrounding the cilia 14,15 . However, mucosal ion concentrations are difficult to measure in vivo, and Nkcc1 knockout mice display attenuated electro-olfactograms (EOGs) 11,16 , but normal olfactory sensitivity 17 .To investigate the role of Ca 2+ -activated Cl -channels in olfaction, we disrupted Ano2 in mice. Ano2 is a member of the Anoctamin (Tmem16) gene family, which encodes several Ca 2+ -activated Cl -channels [18][19][20] . Agreeing with recent results 13,21-23 , our knockout-controlled immunolabeling showed Ano2 expression in cilia of OSNs in the MOE, in microvilli of VNO sensory neurons and in synapses of photoreceptors. Additionally, we found Ano2 in the olfactory bulb. Ano1 expression overlapped with Ano2 in the VNO and the retina, but not in the MOE. Patch-clamp analysis showed that Ca 2+ -activated Cl -currents were undetectable in Ano2 -/-OSNs.Unexpectedly, however, EOGs of Ano2 -/-mice were reduced by only up to ~40%, and Ano2 -/-mice were able to smell normally. Our work calls for a revision of the current view that Ca 2+ -activated Cl -channels have a crucial role...

No abstract

Highlights d Glutamatergic neurons of the PPN and CnF show distinct biophysical differences d CnF neurons produce bilateral muscle activation and involuntary locomotor activity d PPN neurons elicit long-lasting muscle activity and decreased overall motor output

Feedforward and feedback inhibition are two fundamental modes of operation widespread in the nervous system. We have functionally identified synaptic connections between rat CA1 hippocampal interneurons of the stratum oriens (SO) and interneurons of the stratum lacunosum moleculare (SLM), which can act as feedback and feedforward interneurons, respectively. The unitary inhibitory postsynaptic currents (uIPSCs) detected with K-gluconate-based patch solution at -50 mV had an amplitude of 20.0 +/- 2.0 pA, rise time 2.2 +/- 0.2 ms, decay time 25 +/- 2.2 ms, jitter 1.4 +/- 0.2 ms (average +/- SEM, n = 39), and were abolished by the gamma-aminobutyric acid (GABA)(A) receptor antagonist 2-(3-carboxypropyl)-3-amino-6-methoxyphenyl-pyridazinium bromide (SR 95531). Post hoc anatomical characterization revealed that all but one of the identified presynaptic neurons were oriens-lacunosum moleculare (O-LM) cells, whereas the postsynaptic neurons were highly heterogeneous, including neurogliaform (n = 4), basket (n = 4), Schaffer collateral-associated (n = 10) and perforant path-associated (n = 9) cells. We investigated the short-term plasticity expressed at these synapses, and found that stimulation at 10-40 Hz resulted in short-term depression of uIPSCs. This short-term plasticity was determined by presynaptic factors and was not target-cell specific. We found that the feedforward inhibition elicited by the direct cortical input including the perforant path onto CA1 pyramidal cells was modulated through the inhibitory synapses we have characterized. Our data show that the inhibitory synapses between interneurons of the SO and SLM shift the balance between feedback and feedforward inhibition onto CA1 pyramidal neurons.

Accumulating evidence supports the role of astrocytes in endocannabinoid mediated modulation of neural activity. It has been reported that some astrocytes express the cannabinoid type 1 receptor (CB1-R), the activation of which is leading to Ca2+ mobilization from internal stores and a consecutive release of glutamate. It has also been documented that astrocytes have the potential to produce the endocannabinoid 2-arachidonoylglycerol, one of the best known CB1-R agonist. However, no relationship between CB1-R activation and 2-arachidonoylglycerol production has ever been demonstrated. Here we show that rat spinal astrocytes co-express CB1-Rs and the 2-arachidonoylglycerol synthesizing enzyme, diacylglycerol lipase-alpha in close vicinity to each other. We also demonstrate that activation of CB1-Rs induces a substantial elevation of intracellular Ca2+ concentration in astrocytes. Finally, we provide evidence that the evoked Ca2+ transients lead to the production of 2-arachidonoylglycerol in cultured astrocytes. The results provide evidence for a novel cannabinoid induced endocannabinoid release mechanism in astrocytes which broadens the bidirectional signaling repertoire between astrocytes and neurons.