Comment in Sensory systems: the hungry sense. [Nat Rev Neurosci. 2014] Inhaling: endocannabinoids and food intake. [Nat Neurosci. 2014]International audienceHunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior

Thousand of local interneurons reach the olfactory bulb of adult rodents every day, but the functional effect of this process remains elusive. By selectively expressing channelrhodopsin in postnatal-born mouse neurons, we found that their activation accelerated difficult odor discrimination learning and improved memory. This amelioration was seen when photoactivation occurred simultaneously with odor presentation, but not when odor delivery lagged by 500 ms. In addition, learning was facilitated when light flashes were delivered at 40 Hz, but not at 10 Hz. Both in vitro and in vivo electrophysiological recordings of mitral cells revealed that 40-Hz stimuli produced enhanced GABAergic inhibition compared with 10-Hz stimulation. Facilitation of learning occurred specifically when photoactivated neurons were generated during adulthood. Taken together, our results demonstrate an immediate causal relationship between the activity of adult-born neurons and the function of the olfactory bulb circuit.

Somatostatin is abundantly expressed in mammalian brain. The peptide binds with high affinity to six somatostatin receptors, sst1, sst2A and B, sst3 to 5, all belonging to the G-protein-coupled receptor family. Recent advances in the neuroanatomy of somatostatin neurons and cellular distribution of sst receptors shed light on their functional roles in the neuronal network. Beside their initially described neuroendocrine role, somatostatin systems subserve neuromodulatory roles in the brain, influencing motor activity, sleep, sensory processes and cognitive functions, and are altered in brain diseases like affective disorders, epilepsia and Alzheimer's disease.