Abstract
Combining intracellular electrophysiology and multi-photon calcium imaging in vivo, we studied the relationship between calcium signals (sampled at 500–750 Hz) and spike output in principal neurons in the locust antennal lobe. Our goal was to determine whether the firing rate of individual neurons can be estimated in vivo with calcium imaging and, if so, to measure directly the accuracy and resolution of our estimates. Using the calcium indicator Oregon Green BAPTA-1, we describe a simple method to reconstruct firing rates from dendritic calcium signals with 80–90% accuracy and 50 ms temporal resolution.
Highlights
Direct electrical measurements using extracellular electrode arrays and spike-sorting algorithms (Pouzat et al, 2002) are routinely used to examine neuronal activity in vivo (Dragoi and Buzsaki, 2006; Sargolini et al, 2006; Siapas et al, 2005)
Locust projection neurons and experimental considerations The locust antennal lobe contains about 830 PNs
Each locust PN projects to 10–14 glomeruli; correspondingly, individual ORN axons (∼90 000 in toto) project to several glomeruli (3–6). It is not known yet whether all ORN neurons of the same type converge to the same glomeruli, as they do in dipteras (Clyne et al, 1999; Hallem et al, 2004; Vosshall et al, 2000), nor whether the glomeruli visited by each PN are all innervated by ORNs of the same type, as observed with multi-glomerular mitral cells (MCs) in the mammalian accessory bulb (Del Punta et al, 2002; but see Wagner et al, 2006)
Summary
Direct electrical measurements using extracellular electrode arrays and spike-sorting algorithms (Pouzat et al, 2002) are routinely used to examine neuronal activity in vivo (Dragoi and Buzsaki, 2006; Sargolini et al, 2006; Siapas et al, 2005) Such techniques are very powerful; they allow the simultaneous recording of small groups of neurons, typically up to 25 in insects (Perez-Orive et al, 2002) and 100 in rodents (Buzsaki, 2004), with an excellent temporal resolution (
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