Abstract
It is accepted that the main- and accessory- olfactory systems exhibit overlapping responses to pheromones and odorants. We performed whole-cell patch-clamp recordings in adult rat olfactory bulb slices to define a possible interaction between the first central relay of these systems: the accessory olfactory bulb (AOB) and the main olfactory bulb (MOB). This was tested by applying electrical field stimulation in the dorsal part of the MOB while recording large principal cells (LPCs) of the anterior AOB (aAOB). Additional recordings of LPCs were performed at either side of the plane of intersection between the aAOB and posterior-AOB (pAOB) halves, or linea alba, while applying field stimulation to the opposite half. A total of 92 recorded neurons were filled during whole-cell recordings with biocytin and studied at the light microscope. Neurons located in the aAOB (n = 6, 8%) send axon collaterals to the MOB since they were antidromically activated in the presence of glutamate receptor antagonists (APV and CNQX). Recorded LPCs evoked orthodromic excitatory post-synaptic responses (n = 6, aAOB; n = 1, pAOB) or antidromic action potentials (n = 8, aAOB; n = 7, pAOB) when applying field stimulation to the opposite half of the recording site (e.g., recording in aAOB; stimulating in pAOB, and vice-versa). Observation of the filled neurons revealed that indeed, LPCs send axon branches that cross the linea alba to resolve in the internal cellular layer. Additionally, LPCs of the aAOB send axon collaterals to dorsal-MOB territory. Notably, while performing AOB recordings we found a sub-population of neurons (24% of the total) that exhibited voltage-dependent bursts of action potentials. Our findings support the existence of: 1. a direct projection from aAOB LPCs to dorsal-MOB, 2. physiologically active synapses linking aAOB and pAOB, and 3. pacemaker-like neurons in both AOB halves. This work was presented in the form of an on SfN 2014 (719.14/EE17).
Highlights
Successful decoding of complex environmental stimuli by the nervous system relies upon central convergence of primary sensory systems
In the present study we report whole-cell patch-clamp recordings of 92 neurons of the anterior and posterior regions of the accessory olfactory bulb (AOB) made with the primary goal of determining connectivity principles within the AOB and between the latter and the main olfactory bulb (MOB)
When recordings were performed on the anterior AOB (aAOB) (n = 72), field electrical stimulation was applied in the dorsal-posterior region of the MOB and in the pAOB, whereas recordings from the pAOB (n = 20) were accompanied by field electric stimulation of the aAOB and the MOB
Summary
Successful decoding of complex environmental stimuli by the nervous system relies upon central convergence of primary sensory systems. Volatile and pheromonal stimuli that are sensed by the MOS and AOS, respectively, bring about functionally and behaviorally overlapping responses in these systems (Sam et al, 2001; Trinh and Storm, 2003; Lin et al, 2004; Xu et al, 2005; Spehr et al, 2006; Larriva-Sahd, 2008, 2012b). In the absence of a structural interaction between the main olfactory epithelium (MOE) and the vomeronasal organ (VNO) or between the main- (MOB) and accessory olfactory (AOB) bulbs, synergistic responses of the MOS and AOB are largely attributed to the anatomical overlap beyond these primary and secondary sensory structures, respectively (Boehm et al, 2005; Kang et al, 2011). Mitral neurons in the MOB project to secondary olfactory areas (Ojima et al, 1986; Stettler and Axel, 2009; Kang et al, 2011), whereas in the AOB, large principal cells (LPCs; Larriva-Sahd, 2008) project to the so-called vomeronasal amygdala (Scalia and Winans, 1975; Boehm et al, 2005; Mohedano-Moriano et al, 2007; Kang et al, 2011)
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