Competing Sound Sources Reveal Spatial Effects in Cortical Processing

Neurons in the avian auditory forebrain show strong sensitivity to the spatial configuration of two competing sources, even though there is only weak spatial dependence for any single source

Mass spectrometric investigation of the neuropeptide complement and release in the pericardial organs of the crab, Cancer borealis

The crustacean stomatogastric ganglion (STG) is modulated by both locally released neuroactive compounds and circulating hormones. This study presents mass spectrometric characterization of the complement of peptide hormones present in one of the major neurosecretory structures, the pericardial organs (POs), and the detection of neurohormones released from the POs. Direct peptide profiling of Cancer borealis PO tissues using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) revealed many previously identified peptides, including proctolin, red pigment concentrating hormone (RPCH), crustacean cardioactive peptide (CCAP), several orcokinins, and SDRNFLRFamide. This technique also detected corazonin, a well-known insect hormone, in the POs for the first time. However, most mass spectral peaks did not correspond to previously known peptides. To characterize and identify these novel peptides, we performed MALDI postsource decay (PSD) and electrospray ionization (ESI) MS/MS de novo sequencing of peptides fractionated from PO extracts. We characterized a truncated form of previously identified TNRNFLRFamide, NRNFLRFamide. In addition, we sequenced five other novel peptides sharing a common C-terminus of RYamide from the PO tissue extracts. High K+ depolarization of isolated POs released many peptides present in this tissue, including several of the novel peptides sequenced in the current study

Masking sounds increase spatial sensitivity.

<p>(A) Two target song spectrograms (frequency range 500 Hz to 8 kHz), and the response of an example field L recording site to those two songs (10 trials each) as rasters. There is one set of rasters at each of the four azimuths for the two target songs; the effects of changing the location are minimal. (B) The same, with the addition of a song-shaped noise masker (whose spectrogram is shown below those of the targets), played from −90° for all target locations, at the same RMS amplitude as the target (represented by the black box with an “M” on it). The masker sound affects the responses at all target locations, but the effect is stronger (primarily as deleted spikes) when the target is at −90°. (C) Discrimination performance of the same example site. Discrimination of clean targets is reliable for all target locations. However, masked performance is worse when the target is ipsilateral to the site than when it is contralateral. (D) The effect of adding a masker (black bars: means ± 1 SEM, gray lines: individual sites, <i>n</i> = 33). The spatial sensitivity is much higher for the masked stimuli, succinctly demonstrating that the addition of masker to a stimulus increases the dependence of performance on location. (E) Average spike rates in response to clean songs (black line: mean ± 1 SEM, gray lines: individual sites).</p