Cortical processing of configurally perceived odor mixtures
Résumé
METHODS Animals Long-Evans hooded rats obtained from Envigo Lab animals (200-400g) and B6SJLF1/J mice (Jackson Labs, 20-50g) were used as subjects. All procedures were approved by the Institutional Animal Care and Use Committee of the Nathan Kline Institute and were in compliance with NIH guidelines. Testing was performed during the light phase and animals has ad lib food and water prior to data collection. Animals were anesthetized with urethane (1.5g/kg rats, 0.8g/kg mice) and placed in a stereotaxic apparatus. The scalp was resected and holes drilled in the skull overlying either the aPCX or pPCX. Tungsten microelectrodes (5Mohm; AM Systems) were directed toward Layer II/III of PCX and single-unit activity recorded. Recordings were amplified (500x), band-pass filtered (0.3-3kHz), and digitized at 10kHz for data collection and analyses with Spike2 software (CED, Inc.). Local field potentials (0.3-3kHz; 200x amplification, 1kHz sample rate) were recorded simultaneously to monitor brain state during the recordings. Once units were isolated, their basal activity rates (3 sec pre-odor onset) and response to odor (3 sec post-odor onset) were assessed. Single-units had at least 4:1 signal:noise ratio and at least 2 ms refractory period in an interval histogram. Odorant stimulation was a 2 sec pulse at 0.5 LPM directed to the nose of the freely breathing animal, with at least 30 sec between stimuli. Each stimulus was repeated three times in random order for each unit. Stimuli included ethyl isobutyrate (odor A; CAS 97-62-1; Sigma; stock solution 100.5mg in 10mL of 100% ethanol;), ethyl maltol (odor B; CAS 4940-11-8; Sigma; stock solution 100mg in 10mL of 100% ethanol), the binary mixture AB at a component ratio of 30/70 (A/B stock solutions), or the binary mixture A'B' at a component ratio of 68/32. Histology Following the termination of recording, animals were overdosed with urethane (3g/kg) and perfused transcardially with phosphate buffered saline and 4% paraformaldehyde. Brains were sectioned, stained with cresyl violet, and electrode placements verified with light microscopy. Data analyses Cumulative stimulus-evoked single-unit spike counts (number of spikes during a 3 sec period post odor onsetnumber of spikes during the 3 sec pre-odor onset) formed the primary dataset. Data were organized and presented as both normalized odor receptive fields and hierarchical cluster analysis (SPSS) of ensemble unit activity for each region in each species. Normalization involved expressing number of evoked spikes for a given single-unit as a proportion of the maximal response to the 'best' stimulus for that unit. The average response magnitude to a given odor was the mean of the proportional responses across cells for that odor. Thus, if all cells respond maximally (response mag. = 1.0) to EI, the mean proportional score for that odor would be 1.0. For hierarchical cluster analyses (HCA) of how single-unit ensemble activity organized their activity to the different stimuli, standard HCA routines in SPSS were used. An agglomerative protocol was used to determine clustering and squared-euclidian distance was used to determine distance between clusters. HCA was performed for single-unit ensemble data obtained in each brain region in each species.
Domaines
Neurosciences [q-bio.NC]
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