Imaging ensemble activity in arthropod olfactory receptor neurons in situ

Abstract

We show that lobster olfactory receptor neurons (ORNs), much like their vertebrate counterparts, generate a transient elevation of intracellular calcium (Ca i ) in response to odorant activation that can be used to monitor ensemble ORN activity. This is done in antennal slice preparation in situ maintaining the polarity of the cells and the normal micro-environment of the olfactory ilia. The Ca i signal is ligand-specific and increases in a dose-dependent manner in response to odorant stimulation. Saturating stimulation elicits a robust increase of up to 1 μM free Ca i within 1-2 sec of stimulation. The odor-induced Cai response closely follows the discharge pattern of extracellular spikes elicited by odorant application, with the maximal rise in Ca i matching the peak of the spike generation. The Ca i signal can be used to track neuronal activity in a functional subpopulation of rhythmically active ORNs and discriminate it from that of neighboring tonically active ORNs. Being able to record from many ORNs simultaneously over an extended period of time not only allows more accurate estimates of neuronal population activity but also dramatically improves the ability to identify potential new functional subpopulations of ORNs, especially those with more subtle differences in responsiveness, ligand specificity, and/or transduction mechanisms.

Cellular Basis for Response Diversity in the Olfactory Periphery

“…Fura-2AM was used to estimate the absolute calcium concentration (see [23] for details). The tube was shaken for about 1 hr on an orbital shaker (∼70 rpm).…”

Quantifying bursting neuron activity from calcium signals using blind deconvolution

“…The in situ preparation of the lobster (Panulirus argus) ORNs was conducted as previously described (Bobkov and Ache, 2007; Ukhanov et al, 2011). Briefly, a single annulus was excised from the lateral antennular filament.…”

Ligand-selective activation of heterologously-expressed mammalian olfactory receptor

“…Despite the fact that olfactory receptors (ORs) represent the largest family of mammalian GPCRs [12], their potential for ligand-selective signaling has received little attention, notwithstanding indirect evidence that activation of native ORNs can involve adenylate cyclase (AC)-as well as phosphoinositide (PI)-dependent signaling [13] and that activation of the two signaling pathways in native ORNs can be ligand selective [14, 15]. A major constraint to implicating ligand-induced selective signaling in ORNs is the identification of odorants that target each signaling pathway for a given OR, given that deorphanizing ORs for even a single ligand is not trivial.…”