HTR2 Receptors in a Songbird Premotor Cortical-Like Area Modulate Spectral Characteristics of Zebra Finch Song

Abstract

Serotonin [5-hydroxytryptamine (5-HT)] is involved in modulating an array of complex behaviors including learning, depression, and circadian rhythms. Additionally, HTR2 receptors on layer V pyramidal neurons are thought to mediate the actions of psychedelic drugs; the native function of these receptors at this site, however, remains unknown. Previously, we found that activation of HTR2 receptors in the zebra finch forebrain song premotor structure the robust nucleus of the arcopallium (RA) led to increased excitation, and that endogenous 5-HT could roughly double spontaneous firing rate. Here, using in vivo single-unit recordings, we found that direct application of 5-HT to these same RA projection neurons, which are analogous to layer V cortical pyramidal neurons, caused a significant increase in the number of action potentials per song-related burst, and a dramatic decrease in signal-to-noise ratio. Injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine into the third ventricle greatly reduced telencephalic 5-HT and resulted in decreased fundamental frequency of harmonic syllables as well as increased goodness of pitch. Both of these results can be explained by the observed actions of 5-HT on RA projection neurons, and both effects recovered to baseline within 2 weeks following the toxin injection. These results show that 5-HT is involved in modulating spectral properties of song, likely via effects on RA projection neurons, but that adult zebra finches can partially compensate for this deficit within 7 d.

Network analysis of microRNA and mRNA seasonal dynamics in a highly plastic sensorimotor neural circuit

“…Previous studies found that miR-135 inhibits the expression of the serotonin transporter and the inhibitory serotonin receptor, thereby promoting an increase in serotonin signaling [ 53 ]. The up-regulation of miR-135 in RA coincides with increases in spontaneous firing activity [ 38 ] and the probable increased serotonin signaling in RA [ 54 , 55 ]. Another miR of interest up-regulated in RA during breeding conditions is miR-184.…”

A Daily Oscillation in the Fundamental Frequency and Amplitude of Harmonic Syllables of Zebra Finch Song

“…Cages were approximately 38x38x35 cm, with the microphone immediately outside the cage. All animals were part of a previous study investigating the actions of 5-HT in the robust nucleus of the arcopallium (RA), a premotor nucleus for song production [ 10 ].…”

“…One possible mediator of the daily rhythm is the monoaminergic neuromodulator, serotonin (5-HT), which is involved in sleep and other circadian behaviors [ 9 ]. We tested whether lesions of the serotonergic system disrupt the daily oscillation in FF by re-analyzing data from a previous study [ 10 ], and we rule 5-HT out as a causal factor. Song production in zebra finches is a valuable model system for studying complex learned behavior, and the daily oscillation described here thus promises to reveal new insights into how time of day influences our ability to accomplish complex learned motor tasks.…”

Context-dependent fluctuation of serotonin in the auditory midbrain: the influence of sex, reproductive state, and experience

“…Motor or premotor regions controlling the production of social vocalizations are also sensitive to serotonin in a range of vertebrate model communication systems (Yu and Yamaguchi, 2009;Wood et al, 2011;Wood et al, 2013). The centralized serotonergic system would thus exemplify motivational or modulatory neural machinery impinging on the social decision network (Goodson and Kabelik, 2009;O'Connell and Hofmann, 2011;Hoke and Pitts, 2012).…”