Pigeon Brain Research Articles

Dynamic temporal neural patterns based on multichannel LFPs Identify different brain states during anesthesia in pigeons: comparison of three anesthetics.

Anesthetic-induced brain activity study is crucial in avian cognitive-, consciousness-, and sleep-related research. However, the neurobiological mechanisms underlying the generation of brain rhythms and specific connectivity of birds during anesthesia are poorly understood. Although different kinds of anesthetics can be used to induce an anesthesia state, a comparison study of these drugs focusing on the neural pattern evolution during anesthesia is lacking. Here, we recorded local field potentials(LFPs) using a multi-channel micro-electrode array inserted into the nidopallium caudolateral (NCL) of adult pigeons (Columba livia) anesthetized with chloral hydrate, pelltobarbitalum natricum or urethane. Power spectral density (PSD) and functional connectivity analyses were used to measure the dynamic temporal neural patterns in NCL during anesthesia. Neural decoding analysis was adopted to calculate the probability of the pigeon's brain state and the kind of injected anesthetic. In the NCL during anesthesia, we found elevated power activity and functional connectivity at low-frequency bands and depressed power activity and connectivity at high-frequency bands. Decoding results based on the spectral and functional connectivity features indicated that the pigeon's brain states during anesthesia and the injected anesthetics can be effectively decoded. These findings provide an important foundation for future investigations on how different anesthetics induce the generation of specific neural patterns.

Parallel executive pallio-motor loops in the pigeon brain.

A core component of the avian pallial cognitive network is the multimodal nidopallium caudolaterale (NCL) that is considered to be analogous to the mammalian prefrontal cortex (PFC). The NCL plays a key role in a multitude of executive tasks such as working memory, decision-making during navigation, and extinction learning in complex learning environments. Like the PFC, the NCL is positioned at the transition from ascending sensory to descending motor systems. For the latter, it sends descending premotor projections to the intermediate arcopallium (AI) and the medial striatum (MSt). To gain detailed insight into the organization of these projections, we conducted several retrograde and anterograde tracing experiments. First, we tested whether NCL neurons projecting to AI (NCLarco neurons) and MSt (NCLMSt neurons) are constituted by a single neuronal population with bifurcating neurons, or whether they form two distinct populations. Here, we found two distinct projection patterns to both target areas that were associated with different morphologies. Second, we revealed a weak topographic projection toward the medial and lateral striatum and a strong topographic projection toward AI with clearly distinguishable sensory termination fields. Third, we investigated the relationship between the descending NCL pathways to the arcopallium with those from the hyperpallium apicale, which harbors a second major descending pathway of the avian pallium. We embed our findings within a system of parallel pallio-motor loops that carry information from separate sensory modalities to different subpallial systems. Our results also provide insights into the evolution of the avian motor system from which, possibly, the song system has emerged.

Can blood morphology, oxidative stress, and cholinesterase activity determine health status of pigeon Columba livia f. urbana?

Environmental studies in Northern Poland are example of the functioning of ecophysiological relationships under anthropogenic impact. The aim of our studies was to investigate sex-dependent effects on the alterations in the concentration of chemical elements in soil samples collected from habitats of feral pigeon Columba livia f. urbana from Northern Poland, as well as feathers, biomarkers of oxidative stress, antioxidant defense, and total cholinesterase activity in tissues (liver, kidney, brain). Concentration of Si, Zn, and Pb in feathers of pigeons was significant. The levels of Si and Zn were higher in feathers of females from non-polluted, while higher Pb levels were found only in females from polluted areas (p = 0.000). This was confirmed by MANOVA of biomarkers of antioxidant defense, elements concentration, and revealing the order of effects: tissue type > environment > sex. Erythrocytes of males living in polluted areas were more fragile to hemolytic agents resulting in a higher percentage of hemolyzed erythrocytes. The effects of polluted environment on the level of carbonyl derivatives of oxidatively modified proteins compared to the effects of sex were more pronounced in the case of kidney (p = 0.000) and hepatic tissues (p = 0.000). Polluted areas were associated with significant increase in SOD activity in the brain and hepatic tissues of pigeons (p = 0.000). Health status of feral pigeons is significantly different in conditions of environmental destabilization.

Quantitative functional imaging of the pigeon brain: implications for the evolution of avian powered flight.

The evolution of flight is a rare event in vertebrate history, and one that demands functional integration across multiple anatomical/physiological systems. The neuroanatomical basis for such integration and the role that brain evolution assumes in behavioural transformations remain poorly understood. We make progress by (i) generating a positron emission tomography (PET)-based map of brain activity for pigeons during rest and flight, (ii) using these maps in a functional analysis of the brain during flight, and (iii) interpreting these data within a macroevolutionary context shaped by non-avian dinosaurs. Although neural activity is generally conserved from rest to flight, we found significant increases in the cerebellum as a whole and optic flow pathways. Conserved activity suggests processing of self-movement and image stabilization are critical when a bird takes to the air, while increased visual and cerebellar activity reflects the importance of integrating multimodal sensory information for flight-related movements. A derived cerebellar capability likely arose at the base of maniraptoran dinosaurs, where volumetric expansion and possible folding directly preceded paravian flight. These data represent an important step toward establishing how the brain of modern birds supports their unique behavioural repertoire and provide novel insights into the neurobiology of the bird-like dinosaurs that first achieved powered flight.

Segmented spin-echo echo-planar imaging improves whole-brain BOLD functional MRI in awake pigeon brains.

Functional magnetic resonance imaging (fMRI) in awake small animals such as pigeons or songbirds opens a new window into the neural fundaments of cognitive behavior. However, high-field fMRI in the avian brain is challenging due to strong local magnetic field inhomogeneities caused by air cavities in the skull. A spoiled gradient-echo fMRI sequence has already been used to map the auditory network in songbirds, but due to susceptibility artifacts only 50% of the whole brain could be recorded. Since whole-brain fMRI coverage is vital to reveal whole-brain networks, an MRI sequence that is less susceptible to these artifacts was required. This was recently achieved in various bird species by using a rapid acquisition with relaxation enhancement (RARE) sequence. Weak blood oxygen level-dependent (BOLD) sensitivity, low temporal resolution, and heat caused by the long train of RF refocusing pulses are the main limits of RARE fMRI at high magnetic fields. To go beyond some of these limitations, we here describe the implementation of a two-segmented spin-echo echo-planar imaging (SE-EPI). The proposed sequence covers the whole brain of awake pigeons. The sequence was applied to investigate the auditory network in awake pigeons and assessed the relative merits of this method in comparison with the single-shot RARE sequence. At the same imaging resolution but with a volume acquisition of 3 s versus 4 s for RARE, the two-segmented SE-EPI provided twice the strength of BOLD activity compared with the single-shot RARE sequence, while the image signal-to-noise ratio (SNR) and in particular the temporal SNR were very similar for the two sequences. In addition, the activation patterns in two-segmented SE-EPI data are more symmetric and larger than single-shot RARE results. Two-segmented SE-EPI represents a valid alternative to the RARE sequence in avian fMRI research since it yields more than twice the BOLD sensitivity per unit of time with much less energy deposition and better temporal resolution, particularly for event-related experiments.

Regional Patterning of Adult Neurogenesis in the Homing Pigeon's Brain.

In the avian brain, adult neurogenesis has been reported in the telencephalon of several species, but the functional significance of this trait is still ambiguous. Homing pigeons (Columba livia f.d.) are well-known for their navigational skills. Their brains are functionally adapted to homing with, e.g., larger hippocampi. So far, no comprehensive mapping of adult neuro- and gliogenesis or studies of different developmental neuronal stages in the telencephalon of homing pigeons exists, although comprehensive analyses in various species surely will result in a higher understanding of the functional significance of adult neurogenesis. Here, adult, free flying homing pigeons were treated with 5-bromo-deoxyuridine (BrdU) to label adult newborn cells. Brains were dissected and immunohistochemically processed with several markers (GFAP, Sox2, S100ß, Tbr2, DCX, Prox1, Ki67, NeuN, Calbindin, Calretinin) to study different stages of adult neurogenesis in a quantitative and qualitative way. Therefore, immature and adult newborn neurons and glial cells were analyzed along the anterior–posterior axis. The analysis proved the existence of different neuronal maturation stages and showed that immature cells, migrating neurons and adult newborn neurons and glia were widely and regionally unequally distributed. Double- and triple-labelling with developmental markers allowed a stage classification of adult neurogenesis in the pigeon brain (1: continuity of stem cells/proliferation, 2: fate specification, 3: differentiation/maturation, 4: integration). The most adult newborn neurons and glia were found in the intercalated hyperpallium (HI) and the hippocampal formation (HF). The highest numbers of immature (DCX+) cells were detected in the nidopallium (N). Generally, the number of newborn glial cells exceeded the number of newborn neurons. Individual structures (e.g., HI, N, and HF) showed further variations along the anterior–posterior axis. Our qualitative classification and the distribution of maturing cells in the forebrain support the idea that there is a functional specialization, respectively, that there is a link between brain-structure and function, species-specific requirements and adult neurogenesis. The high number of immature neurons also suggests a high level of plasticity, which points to the ability for rapid adaption to environmental changes through additive mechanisms. Furthermore, we discuss a possible influence of adult neurogenesis on spatial cognition.

Age-related reduction of hemispheric asymmetry by pigeons: A behavioral and FDG-PET imaging investigation of visual discrimination.

Pigeons are long-lived and slowly aging animals that present a distinct opportunity to further our understanding of age-related brain changes. Generally, for pigeons, the left hemisphere contributes to discrimination of local information, whereas the right contributes to processing of global information. The function of each hemisphere may be examined by covering one eye, as the optic nerves decussate almost completely in birds, directing the majority of visual information to the contralateral hemisphere. Using this eye-capping technique, we investigated pigeons' ability to select grains from among grit while under binocular and monocular viewing conditions, across three different age groups. Prior to the grit-grain discrimination task, pigeons were injected with a radioactive tracer, which was taken up by the brain as the pigeons performed the task. Upon completion of the discrimination task, the pigeons' brains were imaged via [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) scans. This process allowed us to compare hemispheric activity during the discrimination task for each individual within each age group. The Very Old subjects showed significantly worse discrimination performance compared to the Adult and Old subjects, particularly when needing to search primarily with their right hemisphere. Furthermore, the Very Old subjects did not show differences in hemispheric activation when performing the task, whereas the left hemisphere was most active for the Adult and Old groups. To our knowledge, this is the first study to use FDG-PET imaging to evaluate whether the pigeon brain shows evidence of age-related reduction in hemispheric asymmetry during a visual discrimination task.

The functional architecture, receptive field characteristics, and representation of objects in the visual network of the pigeon brain.

We provide an extensive review of the pigeon visual system, focussing on the known cell types, receptive field characteristics, mechanisms of perception/visual attention, and projection profiles of neurons in the thalamofugal and tectofugal pathways. The similarities and differences with the primate visual system at each stage of the visual hierarchy are highlighted. We conclude with a discussion of object and face processing in birds, as well as the current state of knowledge in the search for face-selective neurons in the avian visual system.

Neurons in the pigeon nidopallium caudolaterale, but not the corticoidea dorsolateralis, display value and effort discounting activity

We recorded from single neurons in two areas of the pigeon brain while birds were required to peck a stimulus indicating either a high effort task or a low effort task would follow. Upon completion of the task the birds received the same reward. We found that activity in the nidopallium caudolaterale, an area equivalent to the mammalian prefrontal cortex, was modulated by the value of the reward that would be received based on how much effort was required to obtain it. Value coding was most prominent during the presentation of the stimulus indicating a high or low effort task, and in the delay period immediately prior to carrying out the effort task. In contrast, activity in the corticoidea dorsolateralis was not modulated by value, however, population firing patterns suggest that it may be involved in associating actions with outcomes. Our findings support the view that activity in the nidopallium caudolaterale reflects value of reward as a function of effort discounting and as such may serve functions similar to the mammalian anterior cingulate cortex.

A Fully Implantable Wireless Stimulation System for Pigeon Navigation.

Navigation of freely moving animals has been studied for potential application to emergency situations and hazardous environments. A fully implantable stimulation system for remote animal navigation was proposed and applied to living pigeons. The animal navigation system, consisting of an external controller and a neural stimulator, was designed based on the anatomy of the pigeons. Depth electrodes were fabricated based on the anatomy of target pigeon brain regions. The fabricated neural stimulators received data wirelessly from the external controller and generated biphasic current pulses with preset parameters of amplitude, duration, and rate. The average impedance of the fabricated electrodes was 12.0∠-13.05° kΩ at 1 kHz. The neural stimulator was implanted on the dorsal side, and the depth electrodes were inserted into the formatio reticularis medialis mesencephali (FRM). When successive current pulses with an amplitude of 400 μA, a rate of 58 Hz, and a duration of 80 μs were applied to the target regions at 0.85 s intervals, turning/circling behaviors were induced for 6.2 s. The feasibility of the proposed wireless stimulation system was demonstrated in vivo.

Dose-related impacts of imidacloprid oral intoxication on brain and liver of rock pigeon (Columba livia domestica), residues analysis in different organs

Available data regarding Imidacloprid (IMI) insecticide hazards to birds are still being scare. Our study aimed to investigate toxic impacts of IMI oral gavage by different dose levels on the brain and liver of Rock pigeon (Columba livia domestica). Forty mature male birds were divided equally into four groups. A control group (C) was orally dosed Mazola corn oil and other three groups; the low dose (LD), the medium dose (MD), and the high dose (HD) groups were orally dosed IMI in Mazola corn oil by three dose levels corresponding to 1/15th, 1/10th, 1/5th IMI oral LD50 respectively. IMI exposure induced a significant decrease in serum levels of glutathione (GSH), superoxide dismutase (SOD) enzyme activity. On the other hand; malondialdehyde (MDA) levels were elevated. The levels of serum total protein, albumin, globulin, and A/G ratio showed a non-significant changes in all IMI dosed groups except levels of total protein in the HD IMI dosed group showed a significant decrease compared to the C group. Serum levels of alanine aminotransferase (ALT), lactate dehydrogenase (LDH), uric acid, plasma tumor necrosis factor α (TNFα) and plasma acetylcholinesterase (AChEs) enzyme activities showed a significant dose related increase in all IMI exposed groups compared to the C group; except the levels of ALT, LDH, and uric acid showed a non significant decrease in the LD IMI dosed group only. Residues of IMI were detected in the pectoral muscles, liver, brain, and kidney of all dosed rock pigeon. Moreover; pectoral muscles were the highest tissue for IMI residues detection. This is the first study reports accumulation of IMI in tissues other than crop, liver, and kidney of rock pigeon including brain and muscles. Moreover, the examined brain and liver tissues of all IMI dosed groups showed dosed related alterations in their structural and ultra-structural morphology. It is concluded that IMI oral administration to pigeon induced oxidative stress and detrimental effects in brain and liver of exposed pigeons. Additionally; IMI bio-accumulated in different organs being muscles is the highest tissues for IMI residues, thus monitoring of IMI residues in food is very essential.

Visuospatial attention in the lateralised brain of pigeons \u2013 a matter of ontogenetic light experiences

The ontogenetic mechanisms leading to complementary hemispheric specialisations of the two brain halves are poorly understood. In pigeons, asymmetrical light stimulation during development triggers the left-hemispheric dominance for visuomotor control but light effects on right-hemispheric specialisations are largely unknown. We therefore tested adult pigeons with and without embryonic light experience in a visual search task in which the birds pecked peas regularly scattered on an area in front of them. Comparing the pecking pattern of both groups indicates that the embryonic light conditions differentially influence biased visuospatial attention under mono- and binocular seeing conditions. When one eye was occluded, dark-incubated pigeons peck only within the limits of the visual hemifield of the seeing eye. Light-exposed pigeons also peck into the contralateral field indicating enlarged monocular visual fields of both hemispheres. While dark-incubated birds evinced an attentional bias to the right halfspace when seeing with both eyes, embryonic light exposure shifted this to the left. Thus, embryonic light experience modifies processes regulating biased visuospatial attention of the adult birds depending on the seeing conditions during testing. These data support the impact of light onto the emergence of functional dominances in both hemispheres and point to the critical role of interhemispheric processes.

Age-Dependent Neurogenesis and Neuron Numbers within the Olfactory Bulb and Hippocampus of Homing Pigeons.

Many birds are supreme long-distance navigators that develop their navigational ability in the first months after fledgling but update the memorized environmental information needed for navigation also later in life. We studied the extent of juvenile and adult neurogenesis that could provide such age-related plasticity in brain regions known to mediate different mechanisms of pigeon homing: the olfactory bulb (OB), and the triangular area of the hippocampal formation (HP tr). Newly generated neurons (visualized by doublecortin, DCX) and mature neurons were counted stereologically in 35 pigeon brains ranging from 1 to 168 months of age. At the age of 1 month, both areas showed maximal proportions of DCX positive neurons, which rapidly declined during the first year of life. In the OB, the number of DCX-positive periglomerular neurons declined further over time, but the number of mature periglomerular cells appeared unchanged. In the hippocampus, the proportion of DCX-positive neurons showed a similar decline yet to a lesser extent. Remarkably, in the triangular area of the hippocampus, the oldest birds showed nearly twice the number of neurons as compared to young adult pigeons, suggesting that adult born neurons in these regions expanded the local circuitry even in aged birds. This increase might reflect navigational experience and, possibly, expanded spatial memory. On the other hand, the decrease of juvenile neurons in the aging OB without adding new circuitry might be related to the improved attachment to the loft characterizing adult and old pigeons.

Categories in the pigeon brain: A reverse engineering approach.

Pigeons are well known for their visual capabilities as well as their ability to categorize visual stimuli at both the basic and superordinate level. We adopt a reverse engineering approach to study categorization learning: Instead of training pigeons on predefined categories, we simply present stimuli and analyze neural output in search of categorical clustering on a solely neural level. We presented artificial stimuli, pictorial and grating stimuli, to pigeons without the need of any differential behavioral responding while recording from the nidopallium frontolaterale (NFL), a higher visual area in the avian brain. The pictorial stimuli differed in color and shape; the gratings differed in spatial frequency and amplitude. We computed representational dissimilarity matrices to reveal categorical clustering based on both neural data and pecking behavior. Based on neural output of the NFL, pictorial and grating stimuli were differentially represented in the brain. Pecking behavior showed a similar pattern, but to a lesser extent. A further subclustering within pictorial stimuli according to color and shape, and within gratings according to frequency and amplitude, was not present. Our study gives proof-of-concept that this reverse engineering approach-namely reading out categorical information from neural data--can be quite helpful in understanding the neural underpinnings of categorization learning.

Detection of Neospora caninum-DNA in brain tissues from pigeons in Changchun, Jilin (China)

Neospora caninum is an intracellular protozoan infecting many domestic and wild animals. The domestic chicken (Gallus domesticus) and the sparrow (Passer domesticus) are known as natural intermediate hosts of N. caninum, whereas the role of other birds such as pigeons is still unclear. In the present study, pigeon brain tissues collected in Jilin of China were screened by N. caninum specific-nested PCR to determine whether pigeons functioned as the natural intermediate hosts of N. caninum. The prevalences of N. caninum DNA and Toxoplasma gondii DNA among the brain samples were 30% (63/210) and 13.33% (28/210), respectively. One brain sample was co-infected with N. caninum and T. gondii in naturally infected pigeon. Of the 63 positive samples 42 could be assigned to the NC-PR genotype, 10 to the NC-1 genotypes and 5, 3 and 3 respectively to the each of the three new genotypes identified, indicating genetic polymorphism of N. caninum in pigeons in Jilin of China. The present study expanded the list of intermediate hosts of N. caninum to include pigeons which suggests that pigeons are involved in the transmission of the N. caninum.

Autophagy is upregulated in brain tissues of pigeons exposed to avermectin

Avermectin (AVM) is used in agriculture and veterinary medicine for the prevention of parasitic diseases; AVM is the active component of some insecticidal and nematicidal products. Residues of AVM drugs or their metabolites in livestock feces have toxic effects on non-target aquatic and terrestrial organisms. In this study, changes in the levels of autophagy related genes and ultrastructure in pigeon brain tissues after subchronic exposure to AVM for 30, 60 and 90 d were investigated. The decrease in the mRNA levels of TORC1 and TORC2 and increase in the mRNA levels of LC3, Beclin 1, Dynein, ATG5 and ATG4B and the increase in the protein levels of LC3, Beclin 1 and Dynein in a dose– and time-dependent manner in the pigeon brain were observed. The number of autophagic vacuoles in the cerebrum, cerebellum and optic lobe increased significantly with the concentration of AVM and the exposure time. We found that the changes in the levels of autophagy related genes and the ultrastructure in the cerebrum were more obvious than in the cerebellum and the optic lobe. The results suggest that AVM could induce autophagy in pigeon brain tissues. The information presented in this study is helpful for understanding the mechanism of AVM-induced autophagy in birds.

Mechanisms of object recognition: what we have learned from pigeons.

Behavioral studies of object recognition in pigeons have been conducted for 50 years, yielding a large body of data. Recent work has been directed toward synthesizing this evidence and understanding the visual, associative, and cognitive mechanisms that are involved. The outcome is that pigeons are likely to be the non-primate species for which the computational mechanisms of object recognition are best understood. Here, we review this research and suggest that a core set of mechanisms for object recognition might be present in all vertebrates, including pigeons and people, making pigeons an excellent candidate model to study the neural mechanisms of object recognition. Behavioral and computational evidence suggests that error-driven learning participates in object category learning by pigeons and people, and recent neuroscientific research suggests that the basal ganglia, which are homologous in these species, may implement error-driven learning of stimulus-response associations. Furthermore, learning of abstract category representations can be observed in pigeons and other vertebrates. Finally, there is evidence that feedforward visual processing, a central mechanism in models of object recognition in the primate ventral stream, plays a role in object recognition by pigeons. We also highlight differences between pigeons and people in object recognition abilities, and propose candidate adaptive specializations which may explain them, such as holistic face processing and rule-based category learning in primates. From a modern comparative perspective, such specializations are to be expected regardless of the model species under study. The fact that we have a good idea of which aspects of object recognition differ in people and pigeons should be seen as an advantage over other animal models. From this perspective, we suggest that there is much to learn about human object recognition from studying the “simple” brains of pigeons.

Isolation and molecular characterization of Toxoplasma gondii isolated from pigeons and stray cats in Lisbon, Portugal

Cats and pigeons are important factors in the epidemiology of Toxoplasma gondii as felids are the only definitive hosts that can excrete environmentally resistant oocysts, and pigeons share the same places of cats and humans constituting a good model and indicator of the ground field contamination. We aimed to study the virulence and genotypes of T. gondii isolated from pigeons and stray cats in Lisbon, Portugal. Fresh samples of brain from 41 pigeons and 164 cats revealing antibodies to T. gondii were inoculated in mice. Three isolates (one isolated from a cat and two isolated from pigeons) were virulent in the mouse model. Sag2-based genotyping of T. gondii was achieved in 70.7% (29/41) of samples isolated from pigeons (26 samples were type II, two were type III, and one strain was type I). From the cat brain samples, 50% (82/164) yielded Sag2 positive results, where 72 belonged to genotype II and 10 were no type III (it was not possible to discriminate between type I and II). Further genotyping was obtained by multiplex PCR of 5 microsatellites (TUB2, TgM-A, W35, B17, B18), allowing the identification of two recombinant strains that had been previously identified as type II by Sag2 amplification (one isolated from cat brain and the other from pigeon brain). This is the first evidence of recombinant strains circulating in Portugal and the first report of T. gondii genotyping from cats in this country. This study also highlights the importance of environmental contamination in the synanthropic cycle constituting a potential source of human infection.

Expression of vesicular glutamate transporter 3 mRNA in the brain and retina of the pigeon

Vesicular glutamate transporters (vGluTs), which accumulate glutamate into synaptic vesicles, are classified into three subtypes in mammalian brains: vGluT1, vGluT2, and vGluT3. VGluT3 is localized in non-glutamatergic neurons of the brain and retinal amacrine cells. In birds, the vGluT3 genome is found, but its distribution in the brain or retina is unknown. The present study was conducted to analyze vGluT3 cDNA sequence and elucidate its distribution in the pigeon brain and retina. The vGluT3 cDNA comprises 1761bp and showed 95% and 88% identity to the chicken and zebra finch vGluT3 cDNAs, respectively, and 74% identity to human vGluT3 cDNA. In situ hybridization revealed that the vGluT3 mRNA was expressed in neurons of the caudal linear nucleus (LC) of the brain and in amacrine cells of the inner nuclear layer of the retina. A combination of in situ hybridization and serotonin immunohistochemistry revealed three types of stained cells in LC and retina: vGluT3+/serotonin+, vGluT3+/serotonin−, and vGluT3−/serotonin+. The vGluT3+/serotonin+ cells were approximately 22% in LC and 16% in the retina. The present results suggest that the pigeon vGluT3 mRNA is comparable with the mammalian type.

Global DNA hypomethylation: A potential mechanism in King pigeon nerve tissue damage induced by avermectin

As an effective insecticidal and nematicidal agent, avermectin (AVM) has been widely used in agricultural production and stock farming areas. Subsequently, the residues of AVM or its active metabolites in animal manure pose a toxic threat to non-target organisms in the environment. As the most characteristic epigenetic phenomena, DNA methylation status is a useful biological signal for the toxicity assessment of environmental chemical toxicants. In this study, analyses of the overall level of genomic DNA methylation were performed, and the expression levels of DNA methyltransferases (DNMTs), as well as demethylase methyl-CpG-binding domain protein 2 (MBD2), in pigeon brain tissues after subchronic exposure (with a AVM concentration of 20mg/kg, 40mg/kg and 60mg/kg, respectively) to AVM for 30, 60 and 90days were investigated. Global DNA hypomethylation and down-regulation of DNMT mRNA expression occurred in a dose–time-dependent manner in pigeon brains. The expression level of MBD2, which functions as a demethylase, was significantly enhanced in a dose-dependent but not time-dependent manner. In addition, the elevated expression level of MBD2 had a more robust effect on genomic DNA hypomethylation compared to changes in DNMT expression. Taken together, these results suggested that subchronic dose exposures of AVM could affect the global DNA methylation status, and this mechanism is closely related to changes in the expression levels of DNMTs and MBD2.