Adult Male Zebra Finches Research Articles

Neural Circuits Underlying Nest Building in Male Zebra Finches.

Nest building consists of a series of motor actions, which are concomitant with activity in regions of the anterior motor pathway, the social behavior network, and the reward circuity in nest building adult male zebra finches (Taeniopygia guttata). It is not clear, however, whether this activity is due to nest building, collection, and/or manipulation of nest material. To identify which areas of the brain are specifically involved, we used immunohistochemistry to quantify the immediate early gene c-Fos in male zebra finches that were nest building (Building), birds given a nest box but could interact only with tied down nest material (Fixed), and birds that were not given a nest box or nest material (Control). We investigated the following brain regions: the anterior motor pathway (anterior ventral mesopallium [AMV], AN, anterior striatum [ASt]), areas of the social behavior network (bed nucleus of the stria terminalis, dorsomedial subdivision [BSTmd], lateral septum [LS]), the dopaminergic reward circuitry (ventral tegmental area), and the cerebellum. We found that there was greater Fos immunoreactivity expression in the BSTmd, LS, and AMV with increased material deposition; in LS, AMV ASt, and Folium VI with increased material carrying; in LS, AMV, and ASt with increased nest material tucking; and in LS and all folia (except Folium VIII) with increased tugging at tied down material. These data confirm a functional role for areas of the anterior motor pathway, social behavior network, and the cerebellum in nest material collection and manipulation by birds.

Serotonin Expression in the Song Circuitry of Adult Male Zebra Finches

Serotonin is an important neurotransmitter of the brain, but its role in song control remains to be fully demonstrated. Using male zebra finches (Taeniopygia guttata) that have song learning and production capabilities, we analysed the serotonin expression levels in the song nuclei and adjacent areas (peri-song nuclei) using immunohistochemistry. Key song nuclei were identified using combinations of Hoechst, choline acetyltransferase, and a neurofilament (NN18) marker in reference to the ZEBrA atlas. Mean serotonin expression was highest in interfacial nucleus (Nif) and lower in the other song nuclei in the following order (in order of highest first): interfacial nucleus (Nif) > Area X > dorsomedial part of the intercollicular nucelus (DM) > robust nucleus of the archistriatum (RA) > lateral magnocellular nucleus of the anterior neostriatum (LMAN) > ventral respiratory group (VRG) > dorsolateral nucleus of the medial thalamus (DLM) > the nucleus HVC (proper name) > tracheosyringeal motor nucleus (nXIIts). However, the mean serotonin expression (in order of highest first) in the peri-song nuclei regions was: peri-DM > peri-nXIIts > supra-peri-HVC > peri-RA > peri-DLM > peri-Area X > infra-peri-HVC > peri-VRG > peri-LMAN > peri-Nif. Interestingly, serotoninergic fibers immunostained for serotonin or the serotonin transporter can be found as a basket-like peri-neuronal structure surrounding cholinergic cell bodies, and appear to form contacts onto dopaminergic neurones. In summary, serotonin fibers are present at discrete song nuclei, and peri-song nuclei regions, which suggest serotonin may have a direct and/or modulatory role in song control.

Dopamine Modulates Excitatory Synaptic Transmission by Activating Presynaptic D1-like Dopamine Receptors in the RA Projection Neurons of Zebra Finches.

Songbirds are useful vertebrate study models for vocal learning and memory. The robust nucleus of the arcopallium (RA) receives synaptic inputs from both the posterior and anterior pathways of the song control system in songbirds. Hence, RA plays an important role in the control of singing. RA receives dopaminergic (DArgic) inputs that increase the excitability of RA projection neurons (PNs). However, the effects of DA on excitatory synaptic transmission are yet to be deciphered. In this study, the effects of DA on the excitatory synaptic transmission of the PNs in the RA of adult male zebra finches were investigated using a whole-cell patch-clamp recording. We observed that DA decreased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and miniature excitatory postsynaptic currents (mEPSCs). The effects of DA were mimicked by the D1-like DA receptor (D1R) agonist, SKF-38393, but not the D2-like DA receptor (D2R) agonist, Quinpirole. Also, the effects of DA were blocked by D1R antagonist, SCH-23390, but not the D2R antagonist, Sulpiride. These results demonstrate that DA modulates excitatory synaptic transmission by acting on D1R in the RA of adult male zebra finches.

Auditory learning in an operant task with social reinforcement is dependent on neuroestrogen synthesis in the male songbird auditory cortex

Animals continually assess their environment for cues associated with threats, competitors, allies, mates or prey, and experience is crucial for those associations. The auditory cortex is important for these computations to enable valence assignment and associative learning. The caudomedial nidopallium (NCM) is part of the songbird auditory association cortex and it is implicated in juvenile song learning, song memorization, and song perception. Like human auditory cortex, NCM is a site of action of estradiol (E2) and is enriched with the enzyme aromatase (E2-synthase). However, it is unclear how E2 modulates auditory learning and perception in the vertebrate auditory cortex. In this study we employ a novel, auditory-dependent operant task governed by social reinforcement to test the hypothesis that neuro-E2 synthesis supports auditory learning in adult male zebra finches. We show that local suppression of aromatase activity in NCM disrupts auditory association learning. By contrast, post-learning performance is unaffected by either NCM aromatase blockade or NCM pharmacological inactivation, suggesting that NCM E2 production and even NCM itself are not required for post-learning auditory discrimination or memory retrieval. Therefore, neuroestrogen synthesis in auditory cortex supports the association between sounds and behaviorally relevant consequences.

Brain Distribution and Sexually Dimorphic Expression of Amylin in Different Reproductive Stages of the Zebra Finch (Taeniopygia guttata) Suggest Roles of the Neuropeptide in Song Learning and Social Behaviour.

The expression of the recently identified neuropeptide, amylin, is restricted in rodents to the postpartum preoptic area and may play a role in the control of parental behaviours and food intake. These processes are substantially different between bird and rodent parents as birds do not lactate but often show biparental care of the offspring. To establish the presence and role of amylin in the bird brain, in the present study, we investigated the distribution of amylin in brains of adult male and female zebra finches in three different reproductive stages (i.e. paired without young, incubating eggs or provisioning nestlings) and in unpaired control birds living in same sex flocks. Amylin mRNA was identified in the hypothalamus of zebra finch by RT-PCR, which was also used to produce probes for in situ hybridisation. Subsequently, in situ hybridisation histochemistry was performed in brain sections, and the labelling signal was quantified and compared between the groups. Amylin showed a much wider brain distribution than that of rodents. A strong and, in some regions, sexually dimorphic label was found in the striatum and several brain regions of the social behavioural network in both males and females. Many regions responsible for the learning of birdsong also contained amylin-positive neurons, and some regions showed sex differences reflecting the fact that vocalisation is sexually dimorphic in the zebra finch: only males sing. Area X (Ar.X), a striatal song centre present only in males, was labelled in paired but not unpaired male. Ar.X, another song centre, the lateral part of the magnocellular nucleus of the anterior nidopallium (lMAN) also contained amylin and had higher amylin label in paired, as opposed to unpaired birds. The wider distribution of amylin in birds as compared to rodents suggests a more general role of amylin in social or other behaviours in avian species than in mammals. Alternatively, parental care in birds may be a more complex behavioural trait involving a wider set of brain regions. The sex differences in song centres, and the changes with reproductive status suggest a participation of amylin in social behaviours and related changes in the singing of males.

Long-term Devocalization of Zebra Finches.

Songbirds, such as the zebra finch, are a popular animal model for studying the neural basis of vocal and complex skill learning. Adult male zebra finches produce courtship song toward females (referred to as 'directed song') and recording and analyzing sounds of directed song along with underlying neural activity is important for investigating behavioral and neural mechanisms of song production and learning. However, recording of directed song is easily contaminated by calls that are often as loud as directed songs and frequently produced by a female bird is presented in the same sound-recording chamber to elicit directed song. We developed a new surgical procedure to relatively easily and almost completely devocalize female zebra finches semi-permanently, without affecting other behaviors. This procedure enables researchers to record directed songs with almost no contamination by female calls. The procedure can also be used to devocalize male birds as well and, thus, has great potential for a variety of experimental purposes, such as long-term elimination of auditory feedback during singing in male birds.

The expression of DARPP-32 in adult male zebra finches (Taenopygia guttata).

Although the catecholaminergic circuitry in the zebra finch brain has been well studied, there is little information regarding the postsynaptic targets of dopamine. To answer this question, we looked at overall patterns of immunoreactivity for DARPP-32 (a dopamine and cAMP-regulated phosphoprotein, present mostly in dopaminoceptive neurons) in adult male zebra finches. Our results demonstrated that as in mammals and other avian species, DARPP-32 expression was highest in both medial and lateral striatum. Interestingly, a specific pattern of immunoreactivity was observed in the song control system, with 'core' song control regions, that is, LMANcore (lateral magnocellular nucleus of the anterior nidopallium), RA (nucleus robustus arcopallialis) and HVC being less immunoreactive for DARPP-32 than 'shell' areas such as LMANshell, RAcup, AId (intermediate arcopallium) and HVCshelf. Our results suggest that whereas dopamine may modulate the shell pathways at various levels of the AFP, dopaminergic modulation of the core pathway occurs mainly through Area X, a basal ganglia nucleus. Further, secondary sensory cortices including the perientopallial belt, Fields L1 and L3 had higher DARPP-32-immunoreactivity than primary sensory cortical areas such as the pallial basolateral nucleus, entopallium proper and Field L2, corresponding to somatosensory, visual and auditory systems, respectively. We also found DARPP-32-rich axon terminals surrounding dopaminergic neurons in the ventral tegmental area-substantia nigra complex which in turn project to the striatum, suggesting that there may be a reciprocal modulation between these regions. Overall, DARPP-32 expression appears to be higher in areas involved in integrating sensory information, which further supports the role of this protein as a molecular integrator of different signal processing pathways.

Cannabidiol improves vocal learning-dependent recovery from, and reduces magnitude of deficits following, damage to a cortical-like brain region in a songbird pre-clinical animal model

Cannabidiol (CBD), a non-euphorigenic compound derived from Cannabis, shows promise for improving recovery following cerebral ischemia and has recently been shown effective for the treatment of childhood seizures caused by Dravet and Lennox-Gastaut syndromes. Given evidence for activity to mitigate effects of CNS insult and dysfunction, we considered the possibility that CBD may also protect and improve functional recovery of a complex learned behavior. To test this hypothesis, we have applied a songbird, the adult male zebra finch, as a novel pre-clinical animal model. Their learned vocalizations were temporarily disrupted with bilateral microlesions of HVC (used as a proper name) a pre-vocal motor cortical-like brain region that drives song. These microlesions destroy about 10% of HVC, and temporarily impair song production, syntax and phonology for about seven days. Recovery requires sensorimotor learning as it depends upon auditory feedback. Four CBD doses (0, 1, 10 and 100 mg/kg) within three surgery conditions (microlesion, no-microlesion, sham-microlesion) were evaluated (n = 5–6). Birds were recorded over 20 days: three baseline; six pre-microlesion drug treatment days and; 11 post-microlesion treatment and recovery days. Results indicate 10 and 100 mg/kg CBD effectively reduced the time required to recover vocal phonology and syntax. In the case of phonology, the magnitude of microlesion-related disruptions were also reduced. These results suggest CBD holds promise to improve functional recovery of complex learned behaviors following brain injury, and represent establishment of an important new animal model to screen drugs for efficacy to improve vocal recovery.

Effects of Androgen Availability on the Activation of Neuroprotective Pathways Following Traumatic Brain Injury

Following traumatic brain injury (TBI), steroid hormones are neuroprotective. Specifically, estrogens decrease apoptotic signaling, neuroinflammation, oxidative stress, and have been shown to normalize glutamate concentrations. Furthermore, androgens also regulate neuroinflammation and mediate gliosis. However, the mechanisms underlying these influences are poorly understood. Cyclooxygenase (COX‐2) and prostaglandin E2 (PGE2) activation appear to be necessary for the injury induced upregulation of estrogen synthesis. This sex specific increase in estrogens promotes neuroprotection by increasing estrogen receptor‐α dependent decreases in neuroinflammation presumably by altering the activity of protein kinase A (PKA) or phosphoinositide‐3‐kinase (PI3K). While there is a considerable amount known about the role of estrogens in this pathway, very little is known about how androgens interact with estrogens to promote neuroprotection. The goal of this study was to further investigate the effect of androgens specifically, but also to identify if there are any interactions between androgens and estrogens on the activation of the COX‐2/PGE2 pathway. Prior to the concussive injury protocol, adult male and female zebra finches (Taeniopygia guttata) were implanted with androgens or an androgen antagonist (flutamide) and collected 1 week later. Activation of the COX‐2/PGE2 pathway was measured using analysis of quantitative polymerase chain reaction and immunohistochemistry. Preliminary data suggest that androgens are involved in estrogen mediated neuroprotection following injury and suggest a novel role for androgens following TBI.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Sensory feedback independent pre-song vocalizations correlate with time to song initiation.

The song of the adult male zebra finch is a well-studied example of a learned motor sequence. Song bouts begin with a variable number of introductory notes (INs) before actual song production. Previous studies have shown that INs progress from a variable initial state to a stereotyped final state before each song. This progression is thought to represent motor preparation, but the underlying mechanisms remain poorly understood. Here, we assessed the role of sensory feedback in the progression of INs to song. We found that the mean number of INs before song and the progression of INs to song were not affected by removal of two sensory feedback pathways (auditory or proprioceptive). In both feedback-intact and feedback-deprived birds, the presence of calls (other non-song vocalizations), just before the first IN, was correlated with fewer INs before song and an initial state closer to song. Finally, the initial IN state correlated with the time to song initiation. Overall, these results show that INs do not require real-time sensory feedback for progression to song. Rather, our results suggest that changes in IN features and their transition to song are controlled by internal neural processes, possibly involved in getting the brain ready to initiate a learned movement sequence.

Response properties of single neurons in higher level auditory cortex of adult songbirds.

The caudomedial nidopallium (NCM) is a higher level region of auditory cortex in songbirds that has been implicated in encoding learned vocalizations and mediating perception of complex sounds. We made cell-attached recordings in awake adult male zebra finches ( Taeniopygia guttata) to characterize responses of single NCM neurons to playback of tones and songs. Neurons fell into two broad classes: narrow fast-spiking cells and broad sparsely firing cells. Virtually all narrow-spiking cells responded to playback of pure tones, compared with approximately half of broad-spiking cells. In addition, narrow-spiking cells tended to have lower thresholds and faster, less variable spike onset latencies than did broad-spiking cells, as well as higher firing rates. Tonal responses of narrow-spiking cells also showed broader ranges for both frequency and amplitude compared with broad-spiking neurons and were more apt to have V-shaped tuning curves compared with broad-spiking neurons, which tended to have complex (discontinuous), columnar, or O-shaped frequency response areas. In response to playback of conspecific songs, narrow-spiking neurons showed high firing rates and low levels of selectivity whereas broad-spiking neurons responded sparsely and selectively. Broad-spiking neurons in which tones failed to evoke a response showed greater song selectivity compared with those with a clear tuning curve. These results are consistent with the idea that narrow-spiking neurons represent putative fast-spiking interneurons, which may provide a source of intrinsic inhibition that contributes to the more selective tuning in broad-spiking cells. NEW & NOTEWORTHY The response properties of neurons in higher level regions of auditory cortex in songbirds are of fundamental interest because processing in such regions is essential for vocal learning and plasticity and for auditory perception of complex sounds. Within a region of secondary auditory cortex, neurons with narrow spikes exhibited high firing rates to playback of both tones and multiple conspecific songs, whereas broad-spiking neurons responded sparsely and selectively to both tones and songs.

The Avian Basal Ganglia Are a Source of Rapid Behavioral Variation That Enables Vocal Motor Exploration.

The basal ganglia (BG) participate in aspects of reinforcement learning that require evaluation and selection of motor programs associated with improved performance. However, whether the BG additionally contribute to behavioral variation ("motor exploration") that forms the substrate for such learning remains unclear. In songbirds, a tractable system for studying BG-dependent skill learning, a role for the BG in generating exploratory variability, has been challenged by the finding that lesions of Area X, the song-specific component of the BG, have no lasting effects on several forms of vocal variability that have been studied. Here we demonstrate that lesions of Area X in adult male zebra finches (Taeniopygia gutatta) permanently eliminate rapid within-syllable variation in fundamental frequency (FF), which can act as motor exploration to enable reinforcement-driven song learning. In addition, we found that this within-syllable variation is elevated in juveniles and in adults singing alone, conditions that have been linked to enhanced song plasticity and elevated neural variability in Area X. Consistent with a model that variability is relayed from Area X, via its cortical target, the lateral magnocellular nucleus of the anterior nidopallium (LMAN), to influence song motor circuitry, we found that lesions of LMAN also eliminate within-syllable variability. Moreover, we found that electrical perturbation of LMAN can drive fluctuations in FF that mimic naturally occurring within-syllable variability. Together, these results demonstrate that the BG are a central source of rapid behavioral variation that can serve as motor exploration for vocal learning.SIGNIFICANCE STATEMENT Many complex motor skills, such as speech, are not innately programmed but are learned gradually through trial and error. Learning involves generating exploratory variability in action ("motor exploration") and evaluating subsequent performance to acquire motor programs that lead to improved performance. Although it is well established that the basal ganglia (BG) process signals relating to action evaluation and selection, whether and how the BG promote exploratory motor variability remain unclear. We investigated this question in songbirds, which learn to produce complex vocalizations through trial and error. In contrast with previous studies that did not find effects of BG lesions on vocal motor variability, we demonstrate that the BG are an essential source of rapid behavioral variation linked to vocal learning.

Pre-Bout Neural Activity Changes in Premotor Nucleus HVC Correlate with Successful Initiation of Learned Song Sequence.

Preparatory activity, characterized by gradual, longer timescale changes in neural activity, is present in a number of different brain areas before the onset of simple movements and is believed to be important for movement initiation. However, relatively little is known about such activity before initiation of naturally learned movement sequences. The song of an adult male zebra finch is a well studied example of a naturally learned movement sequence and previous studies have shown robust premotor activity immediately before song. Here, I characterize longer timescale changes in neural activity in adult male zebra finch premotor nucleus HVC before onset of song bouts. I show that interneurons and a subset of basal-ganglia-projecting neurons change their activity several hundred milliseconds before song bout onset. Interneurons increased their activity, whereas basal-ganglia-projecting neurons either increased or decreased their activity. Such changes in neural activity were larger, started earlier, and were more common specifically before song bouts that began with the short, repetitive, introductory notes (INs) characteristic of zebra finch song bouts. Further, stronger and earlier changes were also correlated with successful song sequence initiation. Finally, a small fraction of basal-ganglia-projecting neurons that increased their activity before song bout onset did not have song or IN-related activity, suggesting a specialized preparatory role for such neurons. Overall, these data suggest that pre-bout activity in HVC represents preparatory activity important for initiation of a naturally learned movement sequence.SIGNIFICANCE STATEMENT Changes in neuronal activity well before the onset of simple movements are thought to be important for movement initiation. However, a number of animal movements consist of sequences of simple movements and relatively little is known about neuronal activity before such movement sequences. Using adult zebra finch song, a well studied example of a movement sequence, I show here that neurons in premotor nucleus HVC change their activity hundreds of milliseconds before song bout onset. In most neurons, the presence of such changes correlated with successful song sequence initiation. My results show the presence of preparatory neural activity in HVC and suggest a role for HVC in sequence initiation in addition to its established role in song sequence timing.

Morphological characterization of HVC projection neurons in the zebra finch (Taeniopygia guttata).

Singing behavior in the adult male zebra finch is dependent upon the activity of a cortical region known as HVC (proper name). The vast majority of HVC projection neurons send primary axons to either the downstream premotor nucleus RA (robust nucleus of the arcopallium, or primary motor cortex) or Area X (basal ganglia), which play important roles in song production or song learning, respectively. In addition to these long-range outputs, HVC neurons also send local axon collaterals throughout that nucleus. Despite their implications for a range of circuit models, these local processes have never been completely reconstructed. Here, we use in vivo single-neuron Neurobiotin fills to examine 40 projection neurons across 31 birds with somatic positions distributed across HVC. We show that HVC(RA) and HVC(X) neurons have categorically distinct dendritic fields. Additionally, these cell classes send axon collaterals that are either restricted to a small portion of HVC ("local neurons") or broadly distributed throughout the entire nucleus ("broadcast neurons"). Overall, these processes within HVC offer a structural basis for significant local processing underlying behaviorally relevant population activity.

Familiar But Unexpected: Effects of Sound Context Statistics on Auditory Responses in the Songbird Forebrain.

Rapid discrimination of salient acoustic signals in the noisy natural environment may depend, not only on specific stimulus features, but also on previous experience that generates expectations about upcoming events. We studied the neural correlates of expectation in the songbird forebrain by using natural vocalizations as stimuli and manipulating the category and familiarity of context sounds. In our paradigm, we recorded bilaterally from auditory neurons in awake adult male zebra finches with multiple microelectrodes during repeated playback of a conspecific song, followed by further playback of this test song in different interleaved sequences with other conspecific or heterospecific songs. Significant enhancement in the auditory response to the test song was seen when its acoustic features differed from the statistical distribution of context song features, but not when it shared the same distribution. Enhancement was also seen when the time of occurrence of the test song was uncertain. These results show that auditory forebrain responses in awake animals in the passive hearing state are modulated dynamically by previous auditory experience and imply that the auditory system can identify the category of a sound based on the global features of the acoustic context. Furthermore, this probability-dependent enhancement in responses to surprising stimuli is independent of stimulus-specific adaptation, which tracks familiarity, suggesting that the two processes could coexist in auditory processing. These findings establish the songbird as a model system for studying these phenomena and contribute to our understanding of statistical learning and the origin of human ERP phenomena to unexpected stimuli.SIGNIFICANCE STATEMENT Traditional auditory neurophysiology has mapped acoustic features of sounds to the response properties of neurons; however, growing evidence suggests that neurons can also encode the probability of sounds. We recorded responses of songbird auditory neurons in a novel paradigm that presented a familiar test stimulus in a sequence with similar or dissimilar sounds. The responses encode, not only stimulus familiarity, but also the expectation for a class of sounds based on the recent statistics of varying sounds in the acoustic context. Our approach thus provides a model system that uses a controlled stimulus paradigm to understand the mechanisms by which top-down processes (expectation and memory) and bottom-up processes (based on stimulus features) interact in sensory coding.

Song Processing in the Zebra Finch Auditory Forebrain Reflects Asymmetric Sensitivity to Temporal and Spectral Structure.

Despite being commonly referenced throughout neuroscientific research on songbirds, reports of hemispheric specialization in the processing of song remain controversial. The notion of such asymmetries in songbirds is further complicated by evidence that both cerebral hemispheres in humans may be specialized for different aspects of speech perception. Some studies suggest that the auditory neural substrates in the left and right hemispheres of humans process temporal and spectral elements within speech sounds, respectively. To determine whether songbirds process their conspecific songs in such a complementary, bilateral manner, we performed functional magnetic resonance imaging (fMRI) on 15 isoflurane anesthetized adult male zebra finches (Taeniopygia guttata) while presenting them with (1) non-manipulated, (2) spectrally-filtered (reduced spectral structure), and (3) temporally-filtered (reduced temporal structure) conspecific song. Our results revealed sensitivity of both primary (Field L) and secondary (caudomedial nidopallium, NCM) auditory regions to changes in spectral and temporal structure of song. On the one hand, temporally-filtered song elicited a bilateral decrease in neural responses compared to the other stimulus types. On the other hand, spectrally filtered song elicited significantly greater responses in left Field L and NCM than temporally filtered or non-manipulated song while concurrently reducing the response relative to non-manipulated song in the right auditory forebrain. The latter hemispheric difference in sensitivity to manipulations of spectral structure in song, suggests that there is an asymmetry in spectral and temporal domain processing in the zebra finch auditory forebrain bearing some resemblance to what has been observed in human auditory cortex.

Context-specific habituation of the freezing response in newborn chicks.

Previous studies have found that in mature animals habituation is context-specific in some species but not in others. Given the mixed evidence present in the literature, we decided to explore whether habituation is context-specific in newborn chicks. The results showed that 3 days after hatching, chicks were capable of using global contextual information to rapidly habituate their freezing response to a series of sudden acoustic stimuli. Our study is the 1st to show context-specific habituation in this avian species, a result in agreement with those of previous findings in adult male zebra finches (Taeniopygia guttata). Furthermore, although our study does not intend to provide a systematic investigation of the ontogeny of habituation in this species, our findings show that a few days after hatching, juvenile chicks are capable of a sophisticated associative learning process that takes into account complex environmental information. (PsycINFO Database Record

HDAC3 Inhibitor RGFP966 Modulates Neuronal Memory for Vocal Communication Signals in a Songbird Model.

Epigenetic mechanisms that modify chromatin conformation have recently been under investigation for their contributions to learning and the formation of memory. For example, the role of enzymes involved in histone acetylation are studied in the formation of long-lasting memories because memory consolidation requires gene expression events that are facilitated by an open state of chromatin. We recently proposed that epigenetic events may control the entry of specific sensory features into long-term memory by enabling transcription-mediated neuronal plasticity in sensory brain areas. Histone deacetylases, like HDAC3, may thereby regulate the specific sensory information that is captured for entry into long-term memory stores (Phan and Bieszczad, 2016). To test this hypothesis, we used an HDAC3-selective inhibitor (RGFP966) to determine whether its application after an experience with a sound stimulus with unique acoustic features could contribute to the formation of a memory that would assist in mediating its later recognition. We gave adult male zebra finches limited exposure to unique conspecific songs (20 repetitions each, well below the normal threshold to form long-term memory), followed by treatment with RGFP966 or vehicle. In different groups, we either made multi-electrode recordings in the higher auditory area NCM (caudal medial nidopallidum), or determined expression of an immediate early gene, zenk (also identified as zif268, egr-1, ngfi-a and krox24), known to participate in neuronal memory in this system. We found that birds treated with RGFP966 showed neuronal memory after only limited exposure, while birds treated with vehicle did not. Strikingly, evidence of neuronal memory in NCM induced by HDAC3-inhibition was lateralized to the left-hemisphere, consistent with our finding that RGFP966-treatment also elevated zenk expression only in the left hemisphere. The present findings show feasibility for epigenetic mechanisms to control neural plasticity underlying the formation of specific memories for conspecific communication sounds. This is the first evidence in zebra finches that epigenetic mechanisms may contribute to gene expression events for memory of acoustically-rich sensory cues.

A fast and accurate zebra finch syllable detector.

The song of the adult male zebra finch is strikingly stereotyped. Efforts to understand motor output, pattern generation, and learning have taken advantage of this consistency by investigating the bird’s ability to modify specific parts of song under external cues, and by examining timing relationships between neural activity and vocal output. Such experiments require that precise moments during song be identified in real time as the bird sings. Various syllable-detection methods exist, but many require special hardware, software, and know-how, and details on their implementation and performance are scarce. We present an accurate, versatile, and fast syllable detector that can control hardware at precisely timed moments during zebra finch song. Many moments during song can be isolated and detected with false negative and false positive rates well under 1% and 0.005% respectively. The detector can run on a stock Mac Mini with triggering delay of less than a millisecond and a jitter of σ ≈ 2 milliseconds.

Central Administration of Indomethacin Mitigates the Injury-Induced Upregulation of Aromatase Expression and Estradiol Content in the Zebra Finch Brain.

Injury to the vertebrate brain causes neuroinflammation, characterized in part by increases in prostaglandins. In rodents and songbirds, brain injury also induces the transcription and translation of aromatase in reactive astrocytes around the site of damage. Interestingly, this induction is more rapid in female zebra finches relative to males. Induced aromatization is neuroprotective, as inhibition of aromatase and estrogen replacement, increases and decreases the extent of damage, respectively. Although the consequences of induced astrocytic aromatization are intensely studied, little is known about what factors induce aromatase. Inflammation is sufficient to induce astrocytic aromatase suggesting that the link between inflammation and aromatase expression may be causal. To test this hypothesis, adult male and female zebra finches received bilateral mechanical injuries through which either the cyclooxygenase (COX)-1/2 inhibitor indomethacin or vehicle was administered into contralateral hemispheres. Subjects were killed either 6 or 24 hours after injury. In both sexes, an enzyme immunoassay for prostaglandin E2 (PGE2) revealed that indomethacin decreased PGE2 relative to the contralateral hemisphere at both time points, suggesting that the dose and mode of administration used were successful in affecting neuroinflammation locally. Indomethacin reduced aromatase expression and 17β-estradiol (E2) content at 6 hours but not 24 hours following injury in females. However, in males, the inhibitory effect of indomethacin on aromatase and E2 was apparent at 24 but not 6 hours after treatment. These data suggest that COX activity, perhaps via consequent prostaglandin secretion, may induce aromatase expression and central E2, an effect that is detectable in temporally distinct patterns between sexes.