Distinct activation of monoaminergic pathways in chick brain in relation to auditory imprinting and stressful situations: a microdialysis study

Dopamine Modulation of Motor and Sensory Cortical Plasticity among Vertebrates

Goal-directed learning is a key contributor to evolutionary fitness in animals. The neural mechanisms that mediate learning often involve the neuromodulator dopamine. In higher order cortical regions, most of what is known about dopamine's role is derived from brain regions involved in motivation and decision-making, while significantly less is known about dopamine's potential role in motor and/or sensory brain regions to guide performance. Research on rodents and primates represents over 95% of publications in the field, while little beyond basic anatomy is known in other vertebrate groups. This significantly limits our general understanding of how dopamine signaling systems have evolved as organisms adapt to their environments. This review takes a pan-vertebrate view of the literature on the role of dopamine in motor/sensory cortical regions, highlighting, when available, research on non-mammalian vertebrates. We provide a broad perspective on dopamine function and emphasize that dopamine-induced plasticity mechanisms are widespread across all cortical systems and associated with motor and sensory adaptations. The available evidence illustrates that there is a strong anatomical basis-dopamine fibers and receptor distributions-to hypothesize that pallial dopamine effects are widespread among vertebrates. Continued research progress in non-mammalian species will be crucial to further our understanding of how the dopamine system evolved to shape the diverse array of brain structures and behaviors among the vertebrate lineage.

Frequent Visits to an Outdoor Range and Lower Areas of an Aviary System Is Related to Curiosity in Commercial Free-Range Laying Hens

Individual hen preferences to spend time at particular locations within a free-range aviary system and relationships with temperament is relatively unknown. Hens (n = 769) from three commercial flocks were monitored with Radio Frequency Identification technology to determine time spent on the range, upper and lower aviary tiers, and nest boxes. Prior depopulation, novel arena (NA) and novel object (NO) tests assessed exploration and fearfulness. During early life; more time on the lower tier was associated with more lines crossed in the NA test (p < 0.05). No other evidence suggested preference during early life was related to fear or curiosity. More time on the range and lower tier were associated with heavier pre-ranging body weight and gain (p = 0.0001). Over the hens' whole life; time spent on range and lower tier was associated with approaching the NO (p < 0.01). More time spent on the upper tier was associated with less time near the NO and fewer lines crossed in NA (p < 0.01). The relationships during early and whole life use of space and some potential indicators of fearfulness were inconsistent and therefore, no strong, valid, and reliable indicators of hen fearfulness such as freezing were identified.

Carbon Dioxide and Nitrogen Infused Compressed Air Foam for Depopulation of Caged Laying Hens

Simple Summary

Compressed air, detergent, and water make up compressed air foam. Our laboratory has previously reported that compressed air foam may be an effective method for mass depopulation of caged layer hens. Gases, such as carbon dioxide and nitrogen, have also been used for poultry euthanasia and depopulation. The objective of this study was to produce compressed air foam infused with carbon dioxide or nitrogen to compare its efficacy against foam with air and gas inhalation methods (carbon dioxide or nitrogen) for depopulation of caged laying hens. The study showed that a carbon dioxide-air mixture or 100% nitrogen can replace air to make compressed air foam. However, the foam with carbon dioxide had poor foam quality compared to the foam with air or nitrogen. The physiological stress response of hens subjected to foam treatments with and without gas infusion did not differ significantly. Hens exposed to foam with nitrogen died earlier as compared to methods such as foam with air and carbon dioxide. The authors conclude that infusion of nitrogen into compressed air foam results in better foam quality and shortened time to death as compared to the addition of carbon dioxide.

Abstract

Depopulation of infected poultry flocks is a key strategy to control and contain reportable diseases. Water-based foam, carbon dioxide inhalation, and ventilation shutdown are depopulation methods available to the poultry industry. Unfortunately, these methods have limited usage in caged layer hen operations. Personnel safety and welfare of birds are equally important factors to consider during emergency depopulation procedures. We have previously reported that compressed air foam (CAF) is an alternative method for depopulation of caged layer hens. We hypothesized that infusion of gases, such as carbon dioxide (CO₂) and nitrogen (N₂), into the CAF would reduce physiological stress and shorten time to cessation of movement. The study had six treatments, namely a negative control, CO₂ inhalation, N₂ inhalation, CAF with air (CAF Air), CAF with 50% CO₂ (CAF CO₂), and CAF with 100% N₂ (CAF N₂). Four spent hens were randomly assigned to one of these treatments on each of the eight replication days. A total of 192 spent hens were used in this study. Serum corticosterone and serotonin levels were measured and compared between treatments. Time to cessation of movement of spent hens was determined using accelerometers. The addition of CO₂ in CAF significantly reduced the foam quality while the addition of N₂ did not. The corticosterone and serotonin levels of spent hens subjected to foam (CAF, CAF CO₂, CAF N₂) and gas inhalation (CO₂, N₂) treatments did not differ significantly. The time to cessation of movement of spent hens in the CAF N₂ treatment was significantly shorter than CAF and CAF CO₂ treatments but longer than the gas inhalation treatments. These data suggest that the addition of N₂ is advantageous in terms of shortening time to death and improved foam quality as compared to the CAF CO₂ treatment.

Central administration of neuropeptide Y differentially regulates monoamines and corticosterone in heat-exposed fed and fasted chicks

Recently, we demonstrated that brain neuropeptide Y (NPY) mRNA expression was increased in heat exposed chicks. However, the functions of brain NPY during heat stress are unknown. This study was conducted to investigate whether centrally administered NPY affects food intake, rectal temperature, monoamines, stress hormones and plasma metabolites in chicks under high ambient temperatures (HT). Five or six-day-old chicks were centrally injected with 0, 188 or 375pmol of NPY and exposed to either HT (35±1°C) or a control thermoneutral temperature (CT; 30±1°C) for 3h whilst fed or fasted. NPY increased food intake under both CT and HT. NPY reduced rectal temperature 1 and 2h after central administration under CT, but not under HT. Interestingly, NPY decreased brain serotonin and norepinephrine concentrations in fed chicks, but increased concentrations of brain dopamine and its metabolites in fasted and fed chicks, respectively. Plasma epinephrine was decreased by NPY in fed chicks, but plasma concentrations of norepinephrine and epinephrine were increased significantly by NPY in fasted-heat exposed chicks. Furthermore, NPY significantly reduced plasma corticosterone concentrations in fasted chicks. Plasma glucose and triacylglycerol were increased by NPY in fed chicks, but triacylglycerol declined in fasted NPY-injected chicks. In conclusion, brain NPY may attenuate the reduction of food intake during heat stress and the increased brain NPY might be a potential regulator of the monoamines and corticosterone to modulate stress response in heat-exposed chicks.

Relationships between range access as monitored by radio frequency identification technology, fearfulness, and plumage damage in free-range laying hens

Severe feather-pecking (SFP), a particularly injurious behaviour in laying hens (Gallus gallus domesticus), is thought to be negatively correlated with range use in free-range systems. In turn, range use is thought to be inversely associated with fearfulness, where fearful birds may be less likely to venture outside. However, very few experiments have investigated the proposed association between range use and fearfulness. This experiment investigated associations between range use (time spent outside), fearfulness, plumage damage, and BW. Two pens of 50 ISA Brown laying hens (n=100) were fitted with radio frequency identification (RFID) transponders (contained within silicone leg rings) at 26 weeks of age. Data were then collected over 13 days. A total of 95% of birds accessed the outdoor run more than once per day. Birds spent an average duration of 6.1 h outside each day over 11 visits per bird per day (51.5 min per visit). The top 15 and bottom 15 range users (n=30), as determined by the total time spent on the range over 13 days, were selected for study. These birds were tonic immobility (TI) tested at the end of the trial and were feather-scored and weighed after TI testing. Birds with longer TI durations spent less time outside (P=0.01). Plumage damage was not associated with range use (P=0.68). The small group sizes used in this experiment may have been conducive to the high numbers of birds utilising the outdoor range area. The RFID technology collected a large amount of data on range access in the tagged birds, and provides a potential means for quantitatively assessing range access in laying hens. The present findings indicate a negative association between fearfulness and range use. However, the proposed negative association between plumage damage and range use was not supported. The relationships between range use, fearfulness, and SFP warrant further research.

Changes in brain monoamine metabolism of neonatal chicks under two different acute stress conditions

1. The purpose of the present study was to clarify brain monoamine metabolism during two different conditions of acute stress by quantifying changes in the brain of neonatal chicks exposed to either restraint with isolation, or fasting stress. 2. Under restraint with isolation-induced stress, dopaminergic metabolism was clearly stimulated. 3. During fasting stress, dopaminergic activity, serotonergic and norepinephrinergic metabolisms were stimulated. 4. It was concluded that brain monoamine metabolism of chicks is differentially affected by stressors.

The avian subpallium: new insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

The subpallial region of the avian telencephalon contains neural systems whose functions are critical to the survival of individual vertebrates and their species. The subpallial neural structures can be grouped into five major functional systems, namely the dorsal somatomotor basal ganglia; ventral viscerolimbic basal ganglia; subpallial extended amygdala including the central and medial extended amygdala and bed nuclei of the stria terminalis; basal telencephalic cholinergic and non-cholinergic corticopetal systems; and septum. The paper provides an overview of the major developmental, neuroanatomical and functional characteristics of the first four of these neural systems, all of which belong to the lateral telencephalic wall. The review particularly focuses on new findings that have emerged since the identity, extent and terminology for the regions were considered by the Avian Brain Nomenclature Forum. New terminology is introduced as appropriate based on the new findings. The paper also addresses regional similarities and differences between birds and mammals, and notes areas where gaps in knowledge occur for birds.

The experience-dependent maturation of prefronto-limbic circuits and the origin of developmental psychopathology: implications for the pathogenesis and therapy of behavioural disorders

The maturation of prefronto-limbic neuronal pathways that mediate essential affective and social regulatory functions is experience dependent. Immediately after birth the infant's affective experiences, especially those embedded in the relationship with the primary caregiver, trigger the reorganization and adaptive fine-tuning of synaptic circuits. Research in humans and in animal models supports the hypothesis that socio-emotional deprivation and emotional trauma during early childhood may leave 'scars' in prefronto-limbic function, brain regions that are essential for emotional behaviour, learning, and memory. The focus of this review is to point out that mechanisms involved in structuring and optimizing neural circuits during brain development might also be used in moulding personality and behaviour during psychotherapy in the adult brain.

The impact of perinatal stress on the functional maturation of prefronto-cortical synaptic circuits: implications for the pathophysiology of ADHD?

Enriched as well as impoverished or adverse perinatal environment plays an essential role in the development and refinement of neuronal pathways, which are the neural substrate of intellectual capacity and socioemotional competence. Perinatal experience and learning events continuously interact with the adaptive shaping of excitatory, inhibitory, and neuromodulatory synaptic as well as the endocrine stress systems, including the neuronal corticotropin-releasing factor (CRF) pathways. Adverse environments, such as stress and emotional deprivation can not only delay experience-dependent maturation of these pathways, but also induce permanent changes in prefronto-cortical wiring patterns. We assume that such dysfunctional connections are the neuronal basis for the development of psychosocially induced mental disorders during later life. The aim of this review is to focus on the impact of perinatal stress on the neuronal and synaptic reorganization during brain development and possible implications for the etiology and therapy of mental disorders such as ADHD.

Intracerebroventricular injection of L-proline and D-proline induces sedative and hypnotic effects by different mechanisms under an acute stressful condition in chicks

The central effects of L-proline, D-proline and trans-4-hydroxy-L-proline were investigated by using the acute stressful model with neonatal chicks in Experiment 1. Sedative and hypnotic effects were induced by all compounds, while plasma corticosterone release under isolation stress was only attenuated by L-proline. To clarify the mechanism by which L-proline and D-proline induce sedative and hypnotic effects, the contribution of the strychnine-sensitive glycine receptor (glycine receptor) and N-methyl-D-aspartate glutamate receptor (NMDA receptor) were further investigated. In Experiments 2-3, the glycine receptor antagonist strychnine was co-injected intracerebroventricular (i.c.v.) with L-proline or D-proline. The suppression of isolation-induced stress behavior by D-proline was attenuated by strychnine. However, the suppression of stress behavior by L-proline was not attenuated. In Experiment 4, the NMDA receptor antagonist (+)-MK-801 was co-injected i.c.v. with L-proline. The suppression of stress behavior by L-proline was attenuated by (+)-MK-801. These results indicate that L-proline and D-proline differentially induce sedative and hypnotic effects through NMDA and glycine receptors, respectively.

Effects of genetic group selection against mortality on behavior and peripheral serotonin in domestic laying hens with trimmed and intact beaks

Severe feather pecking is a maladaptive behavior in laying hens that may result in cannibalism and ultimately death of the victims. Selection methods in which the genetic effect of an animal on the survival of its group members is taken into account, i.e. 'group selection', have been shown to be very effective in reducing mortality due to feather pecking and cannibalism in laying hens. It has been suggested that fearfulness and serotonergic functioning are involved in the causation and development of feather pecking. We investigated effects of selection based on survivability in non-beak trimmed groups on fear-related behavior and peripheral 5-HT concentration and uptake in hens with trimmed or intact beaks, in a 2 x 2 factorial arrangement. Hens from the second generation of the low mortality line showed less fear-related behavior than control line hens. In addition, they displayed higher whole blood 5-HT concentrations and a lower platelet 5-HT uptake, indicating differences in functional activity of the 5-HT system. Beak trimming resulted in lowered levels of fear, and in a reduction of feather damage. Hens with trimmed and intact beaks did, however, not differ in peripheral 5-HT. The results imply that fearfulness and 5-HT activity are related to feather pecking without distinguishing between cause and effect. However, given that selection altered fear-related behaviors and peripheral 5-HT concentration and uptake, whereas beak trimming affected fearfulness and feather damage, but not 5-HT parameters, we suggest that peripheral 5-HT activity might reflect the predisposition to develop severe feather pecking under adverse conditions in laying hens.

Consequences of different housing conditions on brain morphology in laying hens

The aim of this study was to analyze the impact of physical and social stress on the avian forebrain morphology. Therefore, we used laying hens kept in different housing systems from puberty (approximately 16 weeks old) until the age of 48 weeks: battery cages, small littered ground pen, and free range system. Cell body sizes and catecholaminergic and serotonergic innervation patterns were investigated in brain areas expected to be sensitive to differences in environmental stimulation: hippocampal substructures and the nidopallium caudolaterale (NCL), a functional analogue of the prefrontal cortex. Our analysis shows both structures differing in the affected morphological parameters. Compared to battery cage hens, hens in the free range system developed larger cells in the dorsomedial hippocampus. Only these animals exhibited an asymmetry in the tyrosine hydroxylase density with more fibres in the left dorsomedial hippocampus. We assume that the higher spatial complexity of the free range system is the driving force of these changes. In contrast, in the NCL the housing systems affected only the serotonergic innervation pattern with highest fibre densities in free range hens. Moreover hens of the free range system displayed the worst plumage condition, which most likely is caused by feather pecking causing an altered serotonergic innervation pattern. Considering the remarkable differences between the three housing conditions, their effects on hippocampal structures and the NCL were surprisingly mild. This observation suggests that the adult brain of laying hens displays limited sensitivity to differences in social and physical environment induced post-puberty, which warrants further studies.

Pharmacological characterisation of the electrically evoked release of monoamines from chicken brainin vitro

1. A study was conducted to develop an in vitro model for examining the basal and electrical-stimulation-induced release of [3H]monoamines from chicken hyperstriatal neurones in order to demonstrate the presence of presynaptic autoreceptors for the three main monoamine transmitters: noradrenaline, dopamine and 5-HT. 2. Two sets of experiments were carried out: the first was to evaluate the effect of calcium and tetrodotoxin (TTX, sodium channel conductance inhibitor) in order to demonstrate that evoked release of monoamines was a consequence of exocytotic processes; the second to investigate the effect of selective agonists and antagonists on neurotransmitter release. 3. Ross and Cobb broiler chickens of either sex (approximately 7 to 8 weeks old) were used. Slices of hyperstriatal tissue were preincubated with [3H]noradrenaline, [3H]dopamine or [3H]5-hydroxytryptamine (5-HT), washed, perfused and electrically stimulated at three time points (S1, S2 and S3) which released [3H]noradrenaline, [3H]dopamine and [3H]5-HT, as determined by scintillation spectrometry. 4. When calcium was removed from, or TTX added to, the superfusion medium prior to and including the second period of electrical stimulation (S2) the evoked releases of [3H]noradrenaline, [3H]dopamine and [3H]5-HT at S2 were abolished. 5. In the presence of the selective alpha2-adrenoceptor agonist UK 14304 during the S2 period, the S2/S1 ratio was lower than the control ratio due to a reduction in the stimulated release of [3H]noradrenaline. The selective alpha2-adrenoceptor antagonist RX 821002 blocked the UK 14304-induced reduction of evoked release and the S2/S1 ratio was similar to the control ratio. 6. The D2-like receptor agonist quinpirole reduced the S2/S1 ratio for [3H]dopamine release, an effect blocked by the antagonist AJ 76. The 5-HT1B receptor agonist CP 94253 during S2 reduced the S2/S1 ratio due to a reduction in evoked [3H]5-HT. This effect was blocked by the 5-HT1B receptor antagonist GR 55562. 7. The results demonstrate, for the first time, the functional presence of presynaptic alpha2-adrenoceptors, presynaptic 5-HT1B autoreceptors and presynaptic D2-like autoreceptors in broiler chicken hyperstriatal neurones in vitro.

Early neonatal and postweaning social emotional deprivation interferes with the maturation of serotonergic and tyrosine hydroxylase-immunoreactive afferent fiber systems in the rodent nucleus accumbens, hippocampus and amygdala

The impact of early emotional experience on the development of serotonergic and dopaminergic fiber innervation of the nucleus accumbens, hippocampal formation and the amygdala was quantitatively investigated in the precocious rodent Octodon degus. Two animal groups were compared: 1) degus which were repeatedly separated from their parents during the first three postnatal weeks, after weaning they were individually reared in chronic social isolation and 2) controls which were reared undisturbed with their families. In the deprived animals 5-hydroxytryptamine-immunoreactive fiber densities were increased in the core region of the nucleus accumbens (up to 126%), in the central nucleus of the amygdala (up to 112%) and in the outer subregion of the dentate gyrus stratum moleculare (up to 149%), whereas decreased fiber densities were detected in the dentate subgranular layer (down to 86%) and in the stratum lacunosum of the hippocampal cornu ammonis region 1 (down to 86%). Tyrosine hydroxylase-immunoreactive fiber densities were increased in the core (up to 115%) and shell region (up to 113%) of the nucleus accumbens of deprived animals, whereas decreased fiber densities (down to 84%) were observed in the hilus of the dentate gyrus. In the stratum granulosum and subgranular layer the fiber densities increased up to 168% and 127% respectively. In summary, these results indicate that the postnatal establishment of the monoaminergic innervation of limbic areas is modulated in response to early emotional experience, and that this environmental morphological adaptation is highly region specific.

Effect of amount and frequency of head-only stunning currents on the electroencephalogram and somatosensory evoked potentials in broilers

The effectiveness of head-only electrical stunning of broilers, with a root mean square (RMS) current of 100 or 150mA delivered using either 50, 400 or 1500Hz sine wave alternating current (AC), was investigated. The changes occurring in the spontaneous electroencephalogram (EEG) were evaluated using Fast Fourier Transformations (FFT) to determine the impact of the amount and frequency of stunning current on total (2-30 Hz) and relative (13-30 Hz) power contents in the EEG. Induction of epileptiform activity and reduction in the EEG power contents to less than 10% of pre-stun levels from the end of epileptiform activity were used as indicators of effective stunning. The duration of unconsciousness and insensibility was determined on the basis of the return of EEG power contents. In addition, the changes occurring in somatosensory evoked potentials (SEPs) were subjectively evaluated to determine the impact of stunning treatments. The results of ANOVA (repeated measures) showed statistically significant effects of interactions between the current frequencies, amount of current and repeated measures on changes in EEG power contents (P < 0.001). Stunning broilers with 150 mA delivered using 50 Hz resulted in EEG changes that were indicative of more pronounced neuronal inhibition following epileptiform activity and also lasted longer than was the case when broilers were stunned with 150 mA delivered using 400 Hz. Stunning broilers with 100 mA delivered using 50 Hz resulted in changes very similar to those observed after stunning with 150 mA of 50 Hz, but which lasted for a relatively shorter time. However, these changes were more pronounced and lasted longer than did stunning with 100 mA delivered using 400 Hz. The effects of stunning broilers with 150 mA of 400 Hz were similar to those found after stunning with 100 mA of 50 Hz. By contrast, stunning broilers with 100 mA of 1500 Hz failed to fulfil the criteria set out in this study. Stunning of broilers with 150 mA of 1500 Hz induced epileptiform activity but failed to reduce EEG power contents to less than 10% of pre-stun levels. Therefore, the stunning of broilers with 100 or 150 mA of 1500 Hz may not be adequate to avoid pain and suffering during slaughter. Thus, minimum currents of 100, 150 and 200 mA should be delivered whilst using 50, 400 and 1500 Hz, respectively, to achieve effective electrical stunning in broilers. Severing of the carotid arteries in the neck following head-only electrical stunning, and high frequency (> 125 Hz) electrical water bath stunning of broilers should also become a statutory requirement to prevent the return of consciousness during bleeding.

Opiate modulation of monoamines in the chick forebrain: Possible role in emotional regulation?

Numerous studies have shown that the opiate system is crucially involved in emotionally guided behavior. In the present study, we focussed on the medio-rostral neostriatum/hyperstriatum ventrale (MNH) of the chick forebrain. This avian prefrontal cortex analogue is critically involved in auditory filial imprinting, a well-characterized juvenile emotional learning event. The high density of mu-opiate receptors expressed in the MNH led to the hypothesis that mu-opiate receptor-mediated processes may modulate the glutamatergic, dopaminergic, and/or serotonergic neurotransmission within the MNH and thereby have a critical impact on filial imprinting. Using microdialysis and pharmaco-behavioral approaches in young chicks, we demonstrated that: the systemic application of the mu-opiate receptor antagonist naloxone (5, 50 mg/kg) significantly increased extracellular levels of 5-HIAA and HVA; the systemic application of the specific mu-opiate receptor agonist DAGO (5 mg/kg) increased the levels of HVA and taurine, an effect that was antagonized by simultaneously applied naloxone (5 mg/kg); the local application of DAGO (1 mM) had no effects on 5-HIAA, HVA, glutamate, and taurine, however, the effects of systemically injected naloxone (5 mg/kg) were abolished by simultaneously applied DAGO (1 mM); the systemic application of naloxone (5 mg/kg) increased distress behavior (measured as the duration of distress vocalization during separation from the peer group). These results are in line with our hypothesis that the mu-opiate receptor-mediated modulation of serotonergic and dopaminergic neurotransmission alters the emotional and motivational status of the animal and thereby may play a modulatory role during filial imprinting in the newborn animal.

Haloperidol impairs auditory filial imprinting and modulates monoaminergic neurotransmission in an imprinting-relevant forebrain area of the domestic chick

In vivo microdialysis and behavioural studies in the domestic chick have shown that glutamatergic as well as monoaminergic neurotransmission in the medio-rostral neostriatum/hyperstriatum ventrale (MNH) is altered after auditory filial imprinting. In the present study, using pharmaco-behavioural and in vivo microdialysis approaches, the role of dopaminergic neurotransmission in this juvenile learning event was further evaluated. The results revealed that: (i) the systemic application of the potent dopamine receptor antagonist haloperidol (7.5 mg/kg) strongly impairs auditory filial imprinting; (ii) systemic haloperidol induces a tetrodotoxin-sensitive increase of extracellular levels of the dopamine metabolite, homovanillic acid, in the MNH, whereas the levels of glutamate, taurine and the serotonin metabolite, 5-hydroxyindole-3-acetic acid, remain unchanged; (iii) haloperidol (0.01, 0.1, 1 mm) infused locally into the MNH increases glutamate, taurine and 5- hydroxyindole-3-acetic acid levels in a dose-dependent manner, whereas homovanillic acid levels remain unchanged; (iv) systemic haloperidol infusion reinforces the N-methyl-d-aspartate receptor-mediated inhibitory modulation of the dopaminergic neurotransmission within the MNH. These results indicate that the modulation of dopaminergic function and its interaction with other neurotransmitter systems in a higher associative forebrain region of the juvenile avian brain displays similar neurochemical characteristics as the adult mammalian prefrontal cortex. Furthermore, we were able to show that the pharmacological manipulation of monoaminergic regulatory mechanisms interferes with learning and memory formation, events which in a similar fashion might occur in young or adult mammals.

Social stress differentially regulates neuroendocrine responses in laying hens: I. Genetic basis of dopamine responses under three different social conditions

Effects of genetic-environmental interactions on plasma dopamine (DA) concentrations were studied in White Leghorn chickens selected for both high (HGPS) or low (LGPS) group productivity and survivability resulting from cannibalism and flightiness. Plasma DA levels were measured from chickens in three social treatments: single-, two-, or ten-hen cages. The two-hen treatment consisted of paired chickens from three genetic lines: HGPS, LGPS and a commercial strain, Dekalb XL (DXL). In HGPS/DXL and LGPS/DXL pairs, the DXL hen was used as a standardized genetic competitor. The ten-hen treatment contained only hens from the same line, which is similar to the original selection condition. After 7 weeks housing in the social environments, LGPS hens in the ten-hen treatment had greater plasma DA concentrations than HGPS hens (P<0.05). Compared to levels in the ten-hen treatment from the same line, plasma DA concentrations in both HGPS and LGPS hens were significantly lower in the two-hen treatment (average mean, 0.09 vs. 0.15 ng/ml and 0.22 vs. 0.44 ng/ml, P<0.05, respectively), but significantly higher in the single-hen treatment (average mean, 0.44 vs. 0.15 ng/ml and 1.78 vs. 0.44 ng/ml, P<0.05 and P<0.01, respectively). In the single-hen treatment, LGPS hens had greater plasma DA levels than HGPS hens (P<0.05). The results provide evidence of genetically related differences in the regulation of chickens' plasma DA concentrations in response to social stress. These differences may magnify the behavioral and physiological differences observed in the lines under basal and challenged conditions. These results suggest that these chicken lines may provide a new model for investigating effects of DA on the control of behavioral, neural and endocrine responses to stress.

Temporal patterns of limbic monoamine and plasma corticosterone response during social stress

Dominant and subordinate males respond differently to the stress of social interaction. After an hour of social interaction, subordinate male Anolis carolinensis have elevated serotonergic activity in hippocampus, but dominant males do not. In other species, and using other stressors, the activation of hippocampal serotonergic activity is much more rapid than one hour. To elucidate early stress responsiveness, adult male A. carolinensis were divided into four groups: isolated controls, and pairs of males sampled after 10, 20 or 40 minutes of aggressive interaction. Development of dominant-subordinate relationships was determined by behavior and by the celerity of eyespot darkening. Serotonergic activity in the hippocampus, nucleus accumbens and amygdala was elevated rapidly and equally in both dominant and subordinate males, as were plasma corticosterone concentrations. Serotonergic activity remained elevated through 40 minutes in hippocampus and nucleus accumbens. Only subordinate males had elevated corticosterone levels at 40 minutes. Social status does not impede socially induced stress responses. Rather, rapid regulation of serotonergic stress responses appears to be a mediating factor in determining both behavioral output and social status. Temporal expressions of monoaminergic and endocrine stress responses are distinctive between males of dominant and subordinate social status. Such temporal patterns of transmitter and glucocorticoid activity may reflect neurocircuitry adaptations that result in behavior modified to fit social status.

A quantitative immuno-electron microscopic study of dopamine terminals in forebrain regions of the domestic chick involved in filial imprinting

The mediorostral neostriatum/hyperstriatum ventrale and neostriatum dorsocaudale of the domestic chick are crucially involved in filial imprinting and are major targets of mesotelencephalic dopaminergic projections. To better understand the functional role of dopamine in these forebrain regions, the ultrastructure of dopamine terminals was studied by serial section electron microscopy using immunohistochemical labeling with antibodies to tyrosine hydroxylase and dopamine. At light as well as electron microscopic level, dopamine and tyrosine hydroxylase-immunoreactive fibers were present at moderate densities in the mediorostral neostriatum/hyperstriatum ventrale and high densities in the neostriatum dorsocaudale. The frequency of tyrosine hydroxylase-immunoreactive profiles per unit area was significantly higher in the neostriatum dorsocaudale than in the mediorostral neostriatum/hyperstriatum ventrale. In both regions, tyrosine hydroxylase-immunoreactive terminals were relatively small, with mean areas of 0.55 microm(2) in the mediorostral neostriatum/hyperstriatum ventrale and 0.48 microm(2) in the neostriatum dorsocaudale. The majority of tyrosine hydroxylase-immunoreactive synapses were symmetrical (83% in the mediorostral neostriatum/hyperstriatum ventrale, 75% in the neostriatum dorsocaudale) as opposed to asymmetrical (17 and 25%, respectively), but there were also tyrosine hydroxylase-immunoreactive terminals which lacked clear synaptic specializations. The preferred targets of the synaptic tyrosine hydroxylase-immunoreactive terminals were dendritic shafts (64% in the mediorostral neostriatum/hyperstriatum ventrale, 63% in the neostriatum dorsocaudale) and less frequently dendritic spines (17 and 23%, respectively) or perikarya (19 and 14%, respectively). In both forebrain regions, immunoreactive terminals were often found in close apposition to unstained terminals making asymmetrical synapses. In conclusion, these results indicate that the ultrastructural features of dopamine terminals in the avian telencephalon are very similar to those described in mammals and that dopamine may exert its effects primarily by modulating excitatory inputs.

Role of adrenoceptor subtypes in memory consolidation

Noradrenaline release in areas within the forebrain occurs following activation of noradrenergic cells in the locus coeruleus (LoC). Release of noradrenaline by attentional/arousal/vigilance factors appears to be essential for learning and is responsible for the consolidation of memory. Noradrenaline can activate any of nine different adrenoceptor (AR) subtypes in the brain and selectivity of action may be achieved by the spatial location and relative density of the AR subtypes, by different affinities of the different subtypes and by temporal selectivity in terms of when the different ARs are activated in the memory formation process. This review examines the use of selective agonists and antagonists to determine the roles of the AR subtypes in the one-trial discriminated avoidance learning paradigm in the chick. A model is developed that integrates noradrenergic activity in basal ganglia (lobus parolfactorius (LPO)) and association cortex (intermediate medial hyperstriatum ventrale (IMHV)) leading to the consolidation of memory 30 min after training. There is evidence that beta(2)- and beta(3)-ARs are important in the association area but require input from alpha(2)-AR stimulated activity in the basal ganglia for consolidation. On the other hand, alpha(1)-AR activation in the IMHV is inhibitory and prevents consolidation. While there is no role for beta(1)-ARs in memory consolidation, they play a role in short-term memory (STM). The use of the precocial chick has clear advantages in having a temporally discrete learning task which allows for discrimination memory and whose development can be followed at discrete intervals after learning. These studies reveal clear roles for AR subtypes in the formation and consolidation of memory in the chick, which have allowed the development of a model that can now be tested in mammalian systems.

Functional aspects of dopamine metabolism in the putative prefrontal cortex analogue and striatum of pigeons (Columba livia)

Dopamine (DA) in mammalian associative structures, such as the prefrontal cortex (PFC), plays a prominent role in learning and memory processes, and its homeostasis differs from that of DA in the striatum, a sensorimotor region. The neostriatum caudolaterale (NCL) of birds resembles the mammalian PFC according to connectional, electrophysiological, and behavioral data. In the present study, DA regulation in the associative NCL and the striatal lobus parolfactorius (LPO) of pigeons was compared to uncover possible differences corresponding to those between mammalian PFC and striatum. Extracellular levels of DA and its metabolites (homovanillic acid [HVA], dihydroxyphenylacetic acid [DOPAC]) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) were investigated by in vivo microdialysis of urethane-anesthetized pigeons under basal conditions and after systemic administration of D-amphetamine. DA was reliably determined only in LPO dialysates, and DA metabolite levels were significantly higher in LPO than in NCL. The HVA/DOPAC ratio, indicating extracellular lifetime of DA, was more than twice as high in NCL than in LPO dialysates. After amphetamine, DA increased in LPO while still being undetectable in NCL, and DA metabolites decreased in both regions. 5-HIAA slightly decreased in NCL dialysates. Amphetamine effects were delayed in NCL compared with the striatum. In conclusion, effects of amphetamine on the pigeon's ascending monoamine systems resemble those found in mammals, suggesting similar regulatory properties. The neurochemical differences between NCL and LPO parallel those between associative regions, such as PFC and dorsal striatum in mammals. They may reflect weaker regulation of extracellular DA, favoring DAergic volume transmission, in associative than striatal forebrain regions.

Serotonergic innervation of the telencephalon in the domestic chick

The serotonergic system in the telencephalon of the domestic chick was investigated using an antibody specific to serotonin (5-HT). Most parts of the forebrain, such as the different subdivisions of the visual Wulst and the neostriatum, displayed a rather uniform, moderate to dense innervation of serotonergic (5-HT+) fibers. However, some highly distinct area-specific differences could be observed. Primary sensory areas such as the ectostriatum, layer L2 of field L, and the rostral part of the nucleus basalis displayed very few 5-HT+ fibers. In contrast, the dorsal part of the archistriatum intermedium, the nucleus taeniae, a medial part of the lobus parolfactorius and the dorsomedial part of the hippocampus displayed an extremely dense serotonergic innervation. In general, three different types of 5-HT+ axons could be distinguished. The most common was a fine, highly varicose type, whereas beaded axons, exhibiting larger varicosities, and a thick non-varicose type, exhibiting occasional swellings, were much sparser. In summary, these findings indicate that the serotonergic innervation of the avian telencephalon is extensive but site-specific, and is organized in a highly similar way to that in mammals. The high accumulation of 5-HT+ fibers in the dorsal part of the archistriatum intermedium points to a prominent role for 5-HT in fear behavior.

The dopaminergic innervation of the avian telencephalon

The present review provides an overview of the distribution of dopaminergic fibers and dopaminoceptive elements within the avian telencephalon, the possible interactions of dopamine (DA) with other biochemically identified systems as revealed by immunocytochemistry, and the involvement of DA in behavioral processes in birds. Primary sensory structures are largely devoid of dopaminergic fibers, DA receptors and the D1-related phosphoprotein DARPP-32, while all these dopaminergic markers gradually increase in density from the secondary sensory to the multimodal association and the limbic and motor output areas. Structures of the avian basal ganglia are most densely innervated but, in contrast to mammals, show a higher D2 than D1 receptor density. In most of the remaining telencephalon D1 receptors clearly outnumber D2 receptors. Dopaminergic fibers in the avian telencephalon often show a peculiar arrangement where fibers coil around the somata and proximal dendrites of neurons like baskets, probably providing them with a massive dopaminergic input. Basket-like innervation of DARPP-32-positive neurons seems to be most prominent in the multimodal association areas. Taken together, these anatomical findings indicate a specific role of DA in higher order learning and sensory-motor processes, while primary sensory processes are less affected. This conclusion is supported by behavioral findings which show that in birds, as in mammals, DA is specifically involved in sensory-motor integration, attention and arousal, learning and working memory. Thus, despite considerable differences in the anatomical organization of the avian and mammalian forebrain, the organization of the dopaminergic system and its behavioral functions are very similar in birds and mammals.

Effect of social experience on dopamine-stimulated adenylyl cyclase activity and G protein composition in chick forebrain

The stimulation of adenylyl cyclase (AC) by dopamine was investigated in membrane fractions of the forebrain areas mediorostral neostriatum/hyperstriatum ventrale (MNH) and lobus parolfactorius (LPO) of 8-day-old domestic chicks that had been raised under different social conditions: group A, socially isolated; group B, imprinted on an acoustic stimulus; group C, trained but nonimprinted; and group D, reared in small groups. Only in the brain of the socially experienced groups could cyclic AMP (cAMP) synthesis be stimulated by dopamine, but not in the socially isolated animals (group A). Ligand binding studies of dopamine D1- and D2-type receptors in membrane fractions did not reveal differences between socially experienced and isolated animals. Forskolin stimulation of total AC in MNH and LPO membrane fractions revealed a significantly enhanced AC stimulation in the socially reared but not in the imprinted group compared with isolated controls. Stimulation of AC by the G protein activator guanylylimidodiphosphate was significantly increased in the MNH and the LPO of socially reared chicks compared with isolated control animals. These results suggest that early postnatal social experience modulates the rate of cAMP synthesis and that these lasting changes are not due to changes of dopamine receptors but are related to increased AC activities and to increased sensitivity of Gs protein.

Single unit activity during a Go/NoGo task in the "prefrontal cortex" of pigeons

Single unit activity was recorded during a delayed auditory/visual Go/NoGo task from the neostriatum caudolaterale (NCL) of pigeons, a multimodal associative avian forebrain structure comparable to the prefrontal cortex (PFC). The animals were trained to mandibulate (to open their beak) during the Go period after which they received a drop of water as reward. Neuronal activity changes were observed during the delay period (DELAY) between auditory and visual stimulation, to the onset of the visual stimulus or to the delivery of the reward. In some neurons, responses were related to the behavioral significance of the stimulus such that the neuronal activity was statistically different between Go and NoGo trials. Moreover, some units anticipated the upcoming reward or changed their firing frequency in a correlated manner prior to beak movements. These neuronal activity patterns suggest that the NCL provides a neural network that participates in the integration and processing of external stimuli in order to generate goal directed behavior.

N-methyl-D-aspartate receptor-mediated modulation of monoaminergic metabolites and amino acids in the chick forebrain: an in vivo microdialysis and electrophysiology study

The associative avian forebrain region medio-rostral neostriatum/hyperstriatum ventrale (MNH) is involved in auditory filial imprinting and may be considered the avian analogue of the mammalian prefrontal cortex. In search of the neurochemical and physiological mechanisms which play a role in this learning process, we introduced microdialysis and a combined microdialysis/electrophysiological approach in domestic chicks a few days old. With this technique, we were able to follow changes of the extracellular levels of glutamate, taurine, 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin, and homovanillic acid (HVA), a metabolite of dopamine, and neuronal activity simultaneously in freely moving animals. We obtained first evidence of a modulatory interaction between glutamatergic and monoaminergic neurotransmission mediated by N-methyl-D-aspartate (NMDA) receptors. During local intracerebral infusion of 300 microM NMDA via reverse microdialysis, an increase of taurine and a decrease of 5-HIAA and HVA were detected, accompanied by enhanced extracellular spike rates. Glutamate was increased only during consecutive infusion of increasing NMDA concentrations, when higher (1 mM) NMDA concentrations were infused. The effects of NMDA were antagonized by D, L-2-amino-5-phosphonovaleric acid (1 mM). Infusion of high potassium induced similar changes in taurine, 5-HIAA, and HVA, as found during infusion of NMDA, but decreased extracellular spike rates, which indicates that different cellular mechanisms may underlie the observed neurochemical changes. Neither urethane anesthesia nor different delays between probe implantation and experiment influenced the neurochemical and electrophysiological results; however, changes of taurine were observed only in chronically implanted, awake animals. In summary, microdialysis in combination with electrophysiology provides a powerful tool to detect changes of neuronal activity and transmitter release in the avian brain, with which the role of transmitter interactions can be followed during and after different learning events.