ABSTRACT
Insects and mammals share similarities of neural organization underlying the perception of odors, taste, vision, sound, and gravity. We observed that insect somatosensation also corresponds to that of mammals. In Drosophila, the projections of all the somatosensory neuron types to the insect's equivalent of the spinal cord segregated into modality-specific layers comparable to those in mammals. Some sensory neurons innervate the ventral brain directly to form modality-specific and topological somatosensory maps. Ascending interneurons with dendrites in matching layers of the nerve cord send axons that converge to respective brain regions. Pathways arising from leg somatosensory neurons encode distinct qualities of leg movement information and play different roles in ground detection. Establishment of the ground pattern and genetic tools for neuronal manipulation should provide the basis for elucidating the mechanisms underlying somatosensation.
Subject(s)
Drosophila melanogaster/physiology , Sensory Receptor Cells/physiology , Sensory Receptor Cells/ultrastructure , Somatosensory Cortex/cytology , Somatosensory Cortex/physiology , Animals , Axons/physiology , Axons/ultrastructure , Behavior, Animal/physiology , Dendrites/physiology , Dendrites/ultrastructure , Interneurons/cytology , Interneurons/physiology , Locomotion , Motor Activity , Neural Pathways/cytology , Neural Pathways/physiology , Spinal Cord/physiology , Synapses/physiology , Synapses/ultrastructureABSTRACT
Elimination of granule cells (GCs) in the olfactory bulb (OB) is not a continual event but is promoted during a short time window in the postprandial period, typically with postprandial sleep. However, the neuronal mechanisms for the enhanced GC elimination during the postprandial period are not understood. Here, we addressed the question of whether top-down inputs of centrifugal axons from the olfactory cortex (OC) during the postprandial period are involved in the enhanced GC elimination in the OB. Electrical stimulation of centrifugal axons from the OC of anesthetized mice increased GC apoptosis. Furthermore, pharmacological suppression of top-down inputs from the OC to the OB during the postprandial period of freely behaving mice by γ-aminobutyric acid (GABA)A receptor agonist injection in the OC significantly decreased GC apoptosis. Remarkable apoptotic GC elimination in the sensory-deprived OB was also suppressed by pharmacological blockade of top-down inputs. These results indicate that top-down inputs from the OC to the OB during the postprandial period are the crucial signal promoting GC elimination, and suggest that the life and death decision of GCs in the OB is determined by the interplay between bottom-up sensory inputs from the external world and top-down inputs from the OC.
Subject(s)
Neurons/physiology , Olfactory Bulb/physiology , Olfactory Cortex/physiology , Postprandial Period/physiology , Animals , Apoptosis/drug effects , Apoptosis/physiology , Axons/drug effects , Axons/physiology , Catheters, Indwelling , Cell Count , Electric Stimulation , Electrodes, Implanted , Electroencephalography , GABA-A Receptor Agonists/pharmacology , Immunohistochemistry , Male , Mice, Inbred C57BL , Muscimol/pharmacology , Neurons/drug effects , Olfactory Bulb/drug effects , Olfactory Cortex/drug effects , Olfactory Pathways/drug effects , Olfactory Pathways/physiology , Postprandial Period/drug effects , Receptors, GABA-A/metabolism , Sensory Deprivation/physiologyABSTRACT
Granule cells (GCs) in the mouse olfactory bulb (OB) continue to be generated in adulthood, with nearly half incorporated and the remainder eliminated. Here, we show that elimination of adult-born GCs is promoted during a short time window in the postprandial period. Under restricted feeding, the number of apoptotic GCs specifically increased within a few hours after the start of feeding. This enhanced GC apoptosis occurred in association with postprandial behaviors that included grooming, resting, and sleeping, and was particularly correlated with the length of postprandial sleep. Further, deprivation of olfactory sensory experience in the local OB area potentiated the extent of GC elimination in that area during the postprandial period. Sensory experience-dependent enhancement of GC elimination also occurred during postprandial period under natural feeding condition. These results suggest that extensive structural reorganization of bulbar circuitry occurs during the postprandial period, reflecting sensory experience during preceding waking period.