Brain sodium channels (NaChs) are regulated by various neurotransmitters such as acetylcholine, serotonin and dopamine. However, it is not known whether NaCh activity is regulated by glutamate, the principal brain neurotransmitter. We show here that activation of metabotropic glutamate receptor (mGluR) subtype 1 regulates fast transient (I NaT ) and persistent Na + currents (I NaP ) in cortical pyramidal neurons. A selective agonist of group I mGluR, (S)-3,5-dihydroxyphenylglycine (DHPG), reduced action potential amplitude and decreased I NaT . This reduction was blocked when DHPG was applied in the presence of selective mGluR1 antagonists. The DHPG-induced reduction of the current was accompanied by a shift of both the inactivation curve of I NaT and the activation curve of I NaP . These effects were dependent on the activation of PKC. The respective role of these two regulatory processes on neuronal excitability was determined by simulating transient and persistent Na + conductances (G NaT and G NaP ) with fast dynamic-clamp techniques. The facilitated activation of G NaP increased excitability near the threshold, but, when combined with the down-regulation of G NaT , repetitive firing was strongly decreased. Consistent with this finding, the mGluR1 antagonist LY367385 increased neuronal excitability when glutamatergic synaptic activity was stimulated with high external K + . We conclude that mGluR1-dependent regulation of Na + current depresses neuronal excitability, which thus might constitute a novel mechanism of homeostatic regulation acting during intense glutamatergic synaptic activity.
-Detecting olfactory perception in animals is a difficult task requiring indirect investigation at the peripheral level (e.g., using electroantennograms) or at the behavioral level (e.g., using choice behavior assays). We show in restrained honeybees that variations in antennal movements can be used to analyze odor detection. Two methods, based on the analysis of digital recordings during odor stimulations, have been used: manual or automatic (with image processing) data collection of the successive positions of the antennae. The results were similar for the two methods and showed that citral induced an increase in the velocity of the antennal movements. Comparing the olfactory stimulation (citral) to air alone stimulation and to stimulation consisting of air saturated with water or quinine solution, we conclude from these observations that only volatile molecules induce detectable movements of the antennae in the honeybee.Apis mellifera / antennal movements / olfaction / video frame analysis / automatic records
Regional brain variations of cytochrome oxidase (CO) staining were analyzed in the honeybee (Apis mellifera) after olfactory conditioning of the proboscis extension reflex. Identification of brain sites where stimuli converge was done by precise image analysis performed in antennal lobes (AL) and mushroom bodies (MB). In Experiment 1, bees received 5 odorant stimulations that induced a transient decrease of CO activity in the lateral part of the AL. In Experiment 2, bees were trained with 5-trial olfactory conditioning. CO activity transiently increased in the lips of the MB calyces. There was also a delayed increase in the lateral part of the AL. An olfactory stimulus presented alone and an odor paired to a sucrose stimulation are treated by different pathways, including both AL and MB.
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