title: Differential serotonergic modulation across the main and accessory olfactory bulbs.
abstract: There are serotonergic projections to both the main (MOB) and the accessory olfactory bulb (AOB). Current-clamp experiments demonstrate that serotonergic afferents are largely excitatory for mitral cells (MCs) in the MOB where 5-HT2Areceptors mediate a direct excitatory action. Serotonergic afferents are predominately inhibitory for MCs in the AOB. There are two types of inhibition: indirect inhibition mediated through the 5-HT2receptors on GABAergic interneurons and direct inhibition via the 5-HT1receptors on MCs. Differential 5-HT neuromodulation of MCs across the MOB and AOB could contribute to select behaviours such as olfactory learning or aggression.
  
  
  
  Mitral cells (MCs) contained in the main (MOB) and accessory (AOB) olfactory bulb have distinct intrinsic membrane properties but the extent of neuromodulation across the two systems has not been widely explored. Herein, we investigated a widely distributed CNS modulator, serotonin (5-HT), for its ability to modulate the biophysical properties of MCs across the MOB and AOB, using an in vitro, brain slice approach in postnatal 15-30 day mice. In the MOB, 5-HT elicited three types of responses in 93% of 180 cells tested. Cells were either directly excited (70%), inhibited (10%) or showed a mixed response (13%)- first inhibition followed by excitation. In the AOB, 82% of 148 cells were inhibited with 18% of cells showing no response. Albeit located in parallel partitions of the olfactory system, 5-HT largely elicited MC excitation in the MOB while it evoked two different kinetic rates of MC inhibition in the AOB. Using a combination of pharmacological agents, we found that the MC excitatory responses in the MOB were mediated by 5-HT2Areceptors through a direct activation. In comparison, 5-HT-evoked inhibitory responses in the AOB arose due to a polysynaptic, slow-onset inhibition attributed to 5-HT2receptor activation exciting GABAergic interneurons. The second type of inhibition had a rapid onset as a result of direct inhibition mediated by the 5-HT1class of receptors. The distinct serotonergic modulation of MCs between the MOB and AOB could provide a molecular basis for differential chemosensory behaviours driven by the brainstem raphe nuclei into these parallel systems.
authors.affiliation: Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.|Department of Biological Science, The Florida State University, Tallahassee, FL, USA.
authors.forename: Zhenbo
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.|Department of Biological Science, The Florida State University, Tallahassee, FL, USA.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Thiebaud
authors.affiliation: Program in Neuroscience, The Florida State University, Tallahassee, FL, USA.|Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL, USA.|Department of Biological Science, The Florida State University, Tallahassee, FL, USA.
authors.forename: Debra Ann
authors.identifier: 0000-0002-0546-3720
authors.initials: DA
authors.lastname: Fadool
mesh_terms: D000818:Animals; D005260:Female; D007395:Interneurons / Q000378:metabolism / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009830:Olfactory Bulb / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000378:metabolism / Q000502:physiology; D059326:Serotonergic Neurons / Q000378:metabolism* / Q000502:physiology; D012701:Serotonin / Q000378:metabolism*; D055366:Synaptic Potentials
chemical_list: D044402:Receptor, Serotonin, 5-HT2A; D012701:Serotonin
keywords: 5-HT; mitral cell; olfaction; olfactory bulb; serotonin