Chemical neuroanatomy of the olfactory neuropil in honey bees: The GABAergic circuitry

PROTAS D.; SINAKEVITCH, I; LOCATELLI F; SMITH B

San Diego, EEUU

Congreso; XL Annual meeting of the Society for Neuroscience; 2010

American Society for Neuroscience

Chemical neuroanatomy of the olfactory neuropil in honey bees: The GABAergic circuitry D. T. PROTAS1, I. SINAKEVITCH1, F. LOCATELLI2, B. H. SMITH1; 1Arizona State Univ., Tempe, AZ; 2Univ. of Buenos Aires, Buenos Aires, Argentina This study focuses on organization of the inhibitory network in the glomerular neuropil of the honey bee (Apis mellifera) antennal lobe (AL), which is the functional analog to the mammalian Olfactory Bulb. The long-term objective of our study is to provide a detailed analysis of the neural circuitry of glomeruli in support of ongoing computational modeling studies. Each glomerulus consists of an outer cortex and inner core. The injection of a retrograde fluorescent dye into one glomerulus revealed three major types of neurons that make up the circuitry of a glomerulus: olfactory receptor neurons (ORN); 25-30 interneurons that have cell bodies in the lateral cell cluster of the AL; and 5 to 6 uniglomerular projection neurons (uPN) that send the axons into higher order brain processing centers. The second group of cells is comprised of both local interneurons and multiglomerular PNs, and their processes are branched only in the core region of each glomerulus. Finally, varicose fibers from modulatory cells that contain biogenic amines are evident in the majority of glomeruli. Processes that contain octopamine, tyramine and serotonin are homogenously distributed within glomeruli, whereas fibers containing dopamine are confined to the core area. The lateral cluster of the local interneurons contains a dense population of approximately 80 GABAergic neurons. We used anti-GABA antibodies to stain the GABAergic processes in glomeruli in which the PN dendrites and ORN terminals were mapped by two dyes. Antibodies to the presynaptic protein synapsin (SYNORF1) revealed the structure of the synaptic neuropil core in each glomerulus. Synaptic contacts are confined to the glomeruli; regions outside of glomeruli (containing cell soma clusters and cell processes) were devoid of synapses. The distribution of SYNORF is heterogeneous across different glomeruli: some glomeruli have high levels in the cortex, some glomeruli have high levels throughout the core, and some are homogenously labeled throughout the cortex and core. In most glomeruli, ORN axons innervate the cortex area, forming presynaptic contacts onto GABAergic processes. The majority of the PN fibers were not co-labeled with SYNORF indicating that PNs have postsynaptic arborizations in glomeruli. The dense population of GABA fibers within the glomeruli suggest that GABA is presynaptic to both PNs and ORNs, while it is also postsynaptic to ORNs. In conclusion, our studies reveal a more complex organization of the AL synaptic circuitry than has been reported to date. Heterogeneity of glomerular organization could be related to types of plasticity recently shown in the AL.