The dorsocaudal neostriatum of the domestic chick: a structure serving higher associative functions

Neural correlates of cognitively controlled vocalizations in a corvid songbird

The neuronal basis of the songbird's song system is well understood. However, little is known about the neuronal correlates of the executive control of songbird vocalizations. Here, we record single-unit activity from the pallial endbrain region "nidopallium caudolaterale" (NCL) of crows that vocalize to the presentation of a visual go-cue but refrain from vocalizing during trials without a go-cue. We find that the preparatory activity of single vocalization-correlated neurons, but also of the entire population of NCL neurons, before vocal onset predicts whether or not the crows will produce an instructed vocalization. Fluctuations in baseline neuronal activity prior to the go-cue influence the premotor activity of such vocalization-correlated neurons and seemingly bias the crows' decision to vocalize. Neuronal response modulation significantly differs between volitional and task-unrelated vocalizations. This suggests that the NCL can take control over the vocal motor network during the production of volitional vocalizations in a corvid songbird.

A comparative analysis of the dopaminergic innervation of the executive caudal nidopallium in pigeon, chicken, zebra finch, and carrion crow

Despite the long, separate evolutionary history of birds and mammals, both lineages developed a rich behavioral repertoire of remarkably similar executive control generated by distinctly different brains. The seat for executive functioning in birds is the nidopallium caudolaterale (NCL) and the mammalian equivalent is known as the prefrontal cortex (PFC). Both are densely innervated by dopaminergic fibers, and are an integration center of sensory input and motor output. Whereas the variation of the PFC has been well documented in different mammalian orders, we know very little about the NCL across the avian clade. In order to investigate whether this structure adheres to species-specific variations, this study aimed to describe the trajectory of the NCL in pigeon, chicken, carrion crow and zebra finch. We employed immunohistochemistry to map dopaminergic innervation, and executed a Gallyas stain to visualize the dorsal arcopallial tract that runs between the NCL and the arcopallium. Our analysis showed that whereas the trajectory of the NCL in the chicken is highly comparable to the pigeon, the two Passeriformes show a strikingly different pattern. In both carrion crow and zebra finch, we identified four different subareas of high dopaminergic innervation that span the entire caudal forebrain. Based on their sensory input, motor output, and involvement in dopamine-related cognitive control of the delineated areas here, we propose that at least three morphologically different subareas constitute the NCL in these songbirds. Thus, our study shows that comparable to the PFC in mammals, the NCL in birds varies considerably across species.

Mapping the Neural Substrates of Recent and Remote Visual Imprinting Memory in the Chick Brain

Social attachment formed by filial imprinting in newborn chicks undergoes a process of memory consolidation that involves rearrangement of its neural storage substrates. In the first 3 h after imprinting it depends on the integrity of the intermediate medial mesopallium (IMM) and beyond that time on unidentified memory storage structures dubbed S’. To search for the S’ memory system in the chick brain, we mapped and compared patterns of activity induced by retrieval of filial attachment memory before and after this critical transition. Chicks were trained in the visual imprinting task, and their memory was reactivated by imprinting stimulus either 1 h (recent memory retrieval) or 24 h (remote memory retrieval) after the completion of training. Patterns of brain activity were mapped by in situ hybridization to mRNA of an immediate early gene c-fos. We also mapped c-fos expression induced by the first presentation of the imprinting stimulus. Memory retrieval triggered massive c-fos expression in the chick brain both 1 and 24 h after the end of training. These activity patterns mostly coincided with the c-fos expression induced by the first presentation of imprinting stimulus. However, in the hippocampus c-fos induction was observed only after the first exposure to imprinting stimulus but not after memory retrieval. In the IMM, medio-rostral nidopallium/mesopallium, and hyperpallium densocellulare c-fos activation was induced by retrieval of only the remote but not of the recent memory. These c-fos mapping data point to the candidate brain structures for systems reorganization of imprinting memory in chicks.

Differential developmental changes in cortical representations of auditory-vocal stimuli in songbirds

Procedural skill learning requires iterative comparisons between feedback of self-generated motor output and a goal sensorimotor pattern. In juvenile songbirds, neural representations of both self-generated behaviors (each bird's own immature song) and the goal motor pattern (each bird's adult tutor song) are essential for vocal learning, yet little is known about how these behaviorally relevant stimuli are encoded. We made extracellular recordings during song playback in anesthetized juvenile and adult zebra finches ( Taeniopygia guttata) in adjacent cortical regions RA (robust nucleus of the arcopallium), AId (dorsal intermediate arcopallium), and RA cup, each of which is well situated to integrate auditory-vocal information: RA is a motor cortical region that drives vocal output, AId is an adjoining cortical region whose projections converge with basal ganglia loops for song learning in the dorsal thalamus, and RA cup surrounds RA and receives inputs from primary and secondary auditory cortex. We found strong developmental differences in neural selectivity within RA, but not in AId or RA cup. Juvenile RA neurons were broadly responsive to multiple songs but preferred juvenile over adult vocal sounds; in addition, spiking responses lacked consistent temporal patterning. By adulthood, RA neurons responded most strongly to each bird's own song with precisely timed spiking activity. In contrast, we observed a complete lack of song responsivity in both juvenile and adult AId, even though this region receives song-responsive inputs. A surprisingly large proportion of sites in RA cup of both juveniles and adults did not respond to song playback, and responsive sites showed little evidence of song selectivity. NEW & NOTEWORTHY Motor skill learning entails changes in selectivity for behaviorally relevant stimuli across cortical regions, yet the neural representation of these stimuli remains understudied. We investigated how information important for vocal learning in zebra finches is represented in regions analogous to infragranular layers of motor and auditory cortices during vs. after the developmentally regulated learning period. The results provide insight into how neurons in higher level stages of cortical processing represent stimuli important for motor skill learning.

Early-Life Adversity Induces Epigenetically Regulated Changes in Hippocampal Dopaminergic Molecular Pathways

Early-life adversity (ELA) represents a major risk factor for the development of behavioral dysfunctions and mental disorders later in life. On the other hand, dependent on type, time point, and duration, ELA exposure can also induce adaptations, which result in better stress coping and resilience later in life. Guided by the hypothesis that chronic exposure to ELA results in dysfunctional brain and behavior, whereas short exposure to ELA may result in resilience, the behavioral and neurobiological consequences of long-term separation stress (LTSS) and short-term separation stress (STSS) were compared in a mouse model for ELA. In line with our hypothesis, we found that LTSS induced depressive-like behavior, whereas STSS reduced depressive-like behavioral symptoms. We then tested the hypothesis that the opposite behavioral outcomes of the two stress paradigms may be mediated by functional, epigenetically regulated changes of dopaminergic modulation in the hippocampal formation. We found that STSS exposure elevated dopamine receptor D1 (DRD1) gene expression and decreased gene expression of its downstream modulator DARPP-32 (32-kDa dopamine- and cAMP-regulated phosphoprotein), which was paralleled by decreased H3 acetylation at its gene promoter region. In contrast, LTSS elevated DARPP-32 gene expression, which was not paralleled by changes in histone acetylation and DRD1 gene expression. These findings indicate that short- and long-term neonatal exposure to ELA induces changes in dopaminergic molecular pathways, some of which are epigenetically regulated and which either alleviate or aggravate depressive-like symptoms later in life.

Cortical inter-hemispheric circuits for multimodal vocal learning in songbirds

Vocal learning in songbirds and humans is strongly influenced by social interactions based on sensory inputs from several modalities. Songbird vocal learning is mediated by cortico-basal ganglia circuits that include the SHELL region of lateral magnocellular nucleus of the anterior nidopallium (LMAN), but little is known concerning neural pathways that could integrate multimodal sensory information with SHELL circuitry. In addition, cortical pathways that mediate the precise coordination between hemispheres required for song production have been little studied. In order to identify candidate mechanisms for multimodal sensory integration and bilateral coordination for vocal learning in zebra finches, we investigated the anatomical organization of two regions that receive input from SHELL: the dorsal caudolateral nidopallium (dNCL_SHELL ) and a region within the ventral arcopallium (Av). Anterograde and retrograde tracing experiments revealed a topographically organized inter-hemispheric circuit: SHELL and dNCL_SHELL , as well as adjacent nidopallial areas, send axonal projections to ipsilateral Av; Av in turn projects to contralateral SHELL, dNCL_SHELL , and regions of nidopallium adjacent to each. Av on each side also projects directly to contralateral Av. dNCL_SHELL and Av each integrate inputs from ipsilateral SHELL with inputs from sensory regions in surrounding nidopallium, suggesting that they function to integrate multimodal sensory information with song-related responses within LMAN-SHELL during vocal learning. Av projections share this integrated information from the ipsilateral hemisphere with contralateral sensory and song-learning regions. Our results suggest that the inter-hemispheric pathway through Av may function to integrate multimodal sensory feedback with vocal-learning circuitry and coordinate bilateral vocal behavior.

Role of sound stimulation in reprogramming brain connectivity

Sensory stimulation has a critical role to play in the development of an individual. Environmental factors tend to modify the inputs received by the sensory pathway. The developing brain is most vulnerable to these alterations and interacts with the environment to modify its neural circuitry. In addition to other sensory stimuli, auditory stimulation can also act as external stimuli to provide enrichment during the perinatal period. There is evidence that suggests that enriched environment in the form of auditory stimulation can play a substantial role in modulating plasticity during the prenatal period. This review focuses on the emerging role of prenatal auditory stimulation in the development of higher brain functions such as learning and memory in birds and mammals. The molecular mechanisms of various changes in the hippocampus following sound stimulation to effect neurogenesis, learning and memory are described. Sound stimulation can also modify neural connectivity in the early postnatal life to enhance higher cognitive function or even repair the secondary damages in various neurological and psychiatric disorders. Thus, it becomes imperative to examine in detail the possible ameliorating effects of prenatal sound stimulation in existing animal models of various psychiatric disorders, such as autism.

Prenatal loud music and noise: differential impact on physiological arousal, hippocampal synaptogenesis and spatial behavior in one day-old chicks

Prenatal auditory stimulation in chicks with species-specific sound and music at 65 dB facilitates spatial orientation and learning and is associated with significant morphological and biochemical changes in the hippocampus and brainstem auditory nuclei. Increased noradrenaline level due to physiological arousal is suggested as a possible mediator for the observed beneficial effects following patterned and rhythmic sound exposure. However, studies regarding the effects of prenatal high decibel sound (110 dB; music and noise) exposure on the plasma noradrenaline level, synaptic protein expression in the hippocampus and spatial behavior of neonatal chicks remained unexplored. Here, we report that high decibel music stimulation moderately increases plasma noradrenaline level and positively modulates spatial orientation, learning and memory of one day-old chicks. In contrast, noise at the same sound pressure level results in excessive increase of plasma noradrenaline level and impairs the spatial behavior. Further, to assess the changes at the molecular level, we have quantified the expression of functional synapse markers: synaptophysin and PSD-95 in the hippocampus. Compared to the controls, both proteins show significantly increased expressions in the music stimulated group but decrease in expressions in the noise group. We propose that the differential increase of plasma noradrenaline level and altered expression of synaptic proteins in the hippocampus are responsible for the observed behavioral consequences following prenatal 110 dB music and noise stimulation.

Effect of prenatal loud music and noise on total number of neurons and glia, neuronal nuclear area and volume of chick brainstem auditory nuclei, field L and hippocampus: a stereological investigation

The present study explores whether prenatal patterned and unpatterned sound of high sound pressure level (110 dB) has any differential effect on the morphology of brainstem auditory nuclei, field L (auditory cortex analog) and hippocampus in chicks (Gallus domesticus). The total number of neurons and glia, mean neuronal nuclear area and total volume of the brainstem auditory nuclei, field L and hippocampus of post-hatch day 1 chicks were determined in serial, cresyl violet-stained sections, using stereology software. All regions studied showed a significantly increased total volume with increase in total neuron number and mean neuronal nuclear area in the patterned music stimulated group as compared to control. Contrastingly the unpatterned noise stimulated group showed an attenuated volume with reduction in the total neuron number. The mean neuronal nuclear area was significantly reduced in the auditory nuclei and hippocampus but increased in the field L. Glial cell number was significantly increased in both experimental groups, being highest in the noise group. The brainstem auditory nuclei and field L showed an increase in glia to neuron ratio in the experimental groups as compared to control. In the hippocampus the ratio remained unaltered between control and music groups, but was higher in the noise group. It is thus evident that though the sound pressure level in both experimental groups was the same there were differential changes in the morphological parameters of the brain regions studied, indicating that the characteristics of the sound had a role in mediating these effects.

Birdsong: is it music to their ears?

Since the time of Darwin, biologists have wondered whether birdsong and music may serve similar purposes or have the same evolutionary precursors. Most attempts to compare song with music have focused on the qualities of the sounds themselves, such as melody and rhythm. Song is a signal, however, and as such its meaning is tied inextricably to the response of the receiver. Imaging studies in humans have revealed that hearing music induces neural responses in the mesolimbic reward pathway. In this study, we tested whether the homologous pathway responds in songbirds exposed to conspecific song. We played male song to laboratory-housed white-throated sparrows, and immunolabeled the immediate early gene product Egr-1 in each region of the reward pathway that has a clear or putative homologue in humans. We found that the responses, and how well they mirrored those of humans listening to music, depended on sex and endocrine state. In females with breeding-typical plasma levels of estradiol, all of the regions of the mesolimbic reward pathway that respond to music in humans responded to song. In males, we saw responses in the amygdala but not the nucleus accumbens – similar to the pattern reported in humans listening to unpleasant music. The shared responses in the evolutionarily ancient mesolimbic reward system suggest that birdsong and music engage the same neuroaffective mechanisms in the intended listeners.

Afferents from vocal motor and respiratory effectors are recruited during vocal production in juvenile songbirds

Learned behaviors require coordination of diverse sensory inputs with motivational and motor systems. Although mechanisms underlying vocal learning in songbirds have focused primarily on auditory inputs, it is likely that sensory inputs from vocal effectors also provide essential feedback. We investigated the role of somatosensory and respiratory inputs from vocal effectors of juvenile zebra finches (Taeniopygia guttata) during the stage of sensorimotor integration when they are learning to imitate a previously memorized tutor song. We report that song production induced expression of the immediate early gene product Fos in trigeminal regions that receive hypoglossal afferents from the tongue and syrinx (the main vocal organ). Furthermore, unilateral lesion of hypoglossal afferents greatly diminished singing-induced Fos expression on the side ipsilateral to the lesion, but not on the intact control side. In addition, unilateral lesion of the vagus reduced Fos expression in the ipsilateral nucleus of the solitary tract in singing birds. Lesion of the hypoglossal nerve to the syrinx greatly disrupted vocal behavior, whereas lesion of the hypoglossal nerve to the tongue exerted no obvious disruption and lesions of the vagus caused some alterations to song behavior. These results provide the first functional evidence that somatosensory and respiratory feedback from peripheral effectors is activated during vocal production and conveyed to brainstem regions. Such feedback is likely to play an important role in vocal learning during sensorimotor integration in juvenile birds and in maintaining stereotyped vocal behavior in adults.

Localized brain activation related to the strength of auditory learning in a parrot

Parrots and songbirds learn their vocalizations from a conspecific tutor, much like human infants acquire spoken language. Parrots can learn human words and it has been suggested that they can use them to communicate with humans. The caudomedial pallium in the parrot brain is homologous with that of songbirds, and analogous to the human auditory association cortex, involved in speech processing. Here we investigated neuronal activation, measured as expression of the protein product of the immediate early gene ZENK, in relation to auditory learning in the budgerigar (Melopsittacus undulatus), a parrot. Budgerigar males successfully learned to discriminate two Japanese words spoken by another male conspecific. Re-exposure to the two discriminanda led to increased neuronal activation in the caudomedial pallium, but not in the hippocampus, compared to untrained birds that were exposed to the same words, or were not exposed to words. Neuronal activation in the caudomedial pallium of the experimental birds was correlated significantly and positively with the percentage of correct responses in the discrimination task. These results suggest that in a parrot, the caudomedial pallium is involved in auditory learning. Thus, in parrots, songbirds and humans, analogous brain regions may contain the neural substrate for auditory learning and memory.

Food for song: expression of c-Fos and ZENK in the zebra finch song nuclei during food aversion learning

BACKGROUND

Specialized neural pathways, the song system, are required for acquiring, producing, and perceiving learned avian vocalizations. Birds that do not learn to produce their vocalizations lack telencephalic song system components. It is not known whether the song system forebrain regions are exclusively evolved for song or whether they also process information not related to song that might reflect their 'evolutionary history'.

METHODOLOGY/PRINCIPAL FINDINGS

To address this question we monitored the induction of two immediate-early genes (IEGs) c-Fos and ZENK in various regions of the song system in zebra finches (Taeniopygia guttata) in response to an aversive food learning paradigm; this involves the association of a food item with a noxious stimulus that affects the oropharyngeal-esophageal cavity and tongue, causing subsequent avoidance of that food item. The motor response results in beak and head movements but not vocalizations. IEGs have been extensively used to map neuro-molecular correlates of song motor production and auditory processing. As previously reported, neurons in two pallial vocal motor regions, HVC and RA, expressed IEGs after singing. Surprisingly, c-Fos was induced equivalently also after food aversion learning in the absence of singing. The density of c-Fos positive neurons was significantly higher than that of birds in control conditions. This was not the case in two other pallial song nuclei important for vocal plasticity, LMAN and Area X, although singing did induce IEGs in these structures, as reported previously.

CONCLUSIONS/SIGNIFICANCE

Our results are consistent with the possibility that some of the song nuclei may participate in non-vocal learning and the populations of neurons involved in the two tasks show partial overlap. These findings underscore the previously advanced notion that the specialized forebrain pre-motor nuclei controlling song evolved from circuits involved in behaviors related to feeding.

Hippocampal memory consolidation during sleep: a comparison of mammals and birds

The transition from wakefulness to sleep is marked by pronounced changes in brain activity. The brain rhythms that characterize the two main types of mammalian sleep, slow-wave sleep (SWS) and rapid eye movement (REM) sleep, are thought to be involved in the functions of sleep. In particular, recent theories suggest that the synchronous slow-oscillation of neocortical neuronal membrane potentials, the defining feature of SWS, is involved in processing information acquired during wakefulness. According to the Standard Model of memory consolidation, during wakefulness the hippocampus receives input from neocortical regions involved in the initial encoding of an experience and binds this information into a coherent memory trace that is then transferred to the neocortex during SWS where it is stored and integrated within preexisting memory traces. Evidence suggests that this process selectively involves direct connections from the hippocampus to the prefrontal cortex (PFC), a multimodal, high-order association region implicated in coordinating the storage and recall of remote memories in the neocortex. The slow-oscillation is thought to orchestrate the transfer of information from the hippocampus by temporally coupling hippocampal sharp-wave/ripples (SWRs) and thalamocortical spindles. SWRs are synchronous bursts of hippocampal activity, during which waking neuronal firing patterns are reactivated in the hippocampus and neocortex in a coordinated manner. Thalamocortical spindles are brief 7-14 Hz oscillations that may facilitate the encoding of information reactivated during SWRs. By temporally coupling the readout of information from the hippocampus with conditions conducive to encoding in the neocortex, the slow-oscillation is thought to mediate the transfer of information from the hippocampus to the neocortex. Although several lines of evidence are consistent with this function for mammalian SWS, it is unclear whether SWS serves a similar function in birds, the only taxonomic group other than mammals to exhibit SWS and REM sleep. Based on our review of research on avian sleep, neuroanatomy, and memory, although involved in some forms of memory consolidation, avian sleep does not appear to be involved in transferring hippocampal memories to other brain regions. Despite exhibiting the slow-oscillation, SWRs and spindles have not been found in birds. Moreover, although birds independently evolved a brain region--the caudolateral nidopallium (NCL)--involved in performing high-order cognitive functions similar to those performed by the PFC, direct connections between the NCL and hippocampus have not been found in birds, and evidence for the transfer of information from the hippocampus to the NCL or other extra-hippocampal regions is lacking. Although based on the absence of evidence for various traits, collectively, these findings suggest that unlike mammalian SWS, avian SWS may not be involved in transferring memories from the hippocampus. Furthermore, it suggests that the slow-oscillation, the defining feature of mammalian and avian SWS, may serve a more general function independent of that related to coordinating the transfer of information from the hippocampus to the PFC in mammals. Given that SWS is homeostatically regulated (a process intimately related to the slow-oscillation) in mammals and birds, functional hypotheses linked to this process may apply to both taxonomic groups.

Conjunction of vocal production and perception regulates expression of the immediate early gene ZENK in a novel cortical region of songbirds

The cortical nucleus LMAN (lateral magnocellular nucleus of the anterior nidopallium) provides the output of a basal ganglia pathway that is necessary for acquisition of learned vocal behavior during development in songbirds. LMAN is composed of two subregions, a core and a surrounding shell, that give rise to independent pathways that traverse the forebrain in parallel. The LMAN(shell) pathway forms a recurrent loop that includes a cortical region, the dorsal region of the caudolateral nidopallium (dNCL), hitherto unknown to be involved with learned vocal behavior. Here we show that vocal production strongly induces the IEG product ZENK in dNCL of zebra finches. Hearing tutor song while singing is more effective at inducing expression in dNCL of juvenile birds during the auditory-motor integration stage of vocal learning than is hearing conspecific song. In contrast, hearing conspecific song is relatively more effective at inducing expression in adult birds, regardless of whether they are producing song. Furthermore, ZENK+ neurons in dNCL include projection neurons that are part of the LMAN(shell) recurrent loop and a high proportion of dNCL projection neurons express ZENK in singing juvenile birds that hear tutor song. Thus juvenile birds that are actively refining their vocal pattern to imitate a tutor song show high levels of ZENK induction in dNCL neurons when they are singing while hearing the song of their tutor and low levels when they hear a novel conspecific. This pattern indicates that dNCL is a novel brain region involved with vocal learning and that its function is developmentally regulated.

Parallel pathways for vocal learning in basal ganglia of songbirds

The cortical nucleus LMAN provides the output of a basal ganglia pathway that is necessary for vocal learning in juvenile songbirds. The shell subregion of LMAN gives rise to recurrent loops that may subserve specific learning-related functions. We report here that lesions within the LMAN_shell pathway cause no immediate disruption of vocal behavior, but prevent the development of stable vocal sequences as well as the ability to imitate vocal sounds.

Prenatal auditory stimulation alters the levels of CREB mRNA, p-CREB and BDNF expression in chick hippocampus

Prenatal auditory stimulation influences the development of the chick auditory pathway and the hippocampus showing an increase in various morphological parameters as well as expression of calcium-binding proteins. Calcium regulates the activity of cyclic adenosine monophosphate-response element binding (CREB) protein. CREB is known to play a role in development, undergo phosphorylation with neural activity as well as regulate transcription of BDNF. BDNF is important for the survival of neurons and regulates synaptic strength. Hence in the present study, we have evaluated the levels of CREB mRNA and protein along with p-CREB protein as well as BDNF mRNA and protein levels in the chick hippocampus at embryonic days (E) 12, E16, E20 and post-hatch day (PH) 1 following activation by prenatal auditory stimulation. Fertilized eggs were exposed to species-specific sound or sitar music (frequency range: 100-6300Hz) at 65dB levels for 15min/h over 24h from E10 till hatching. The control chick hippocampus showed higher CREB mRNA and p-CREB protein in the early embryonic stages, which later decline whereas BDNF mRNA and BDNF protein levels increase until PH1. The CREB mRNA and p-CREB protein were significantly increased at E12, E16 and PH1 in the auditory stimulated groups as compared to control group. A significant increase in the level of BDNF mRNA was observed from E12 and the protein expression from E16 onwards in both auditory stimulated groups. Therefore, enhanced phosphorylation of CREB during development following prenatal sound stimulation may be responsible for cell survival. Increased levels of p-CREB again at PH1 may trigger synthesis of proteins necessary for synaptic plasticity. Further, the increased levels of BDNF may also help in regulating synaptic plasticity.

Effect of prenatal auditory stimulation on numerical synaptic density and mean synaptic height in the posthatch Day 1 chick hippocampus

Previous studies on prenatal auditory stimulation by species-specific sound or sitar music showed enhanced morphological and biochemical changes in chick hippocampus, which plays an important role in learning and memory. Changes in the efficiency of synapses, synaptic morphology and de novo synapse formation affects learning and memory. Therefore, in the present study, we set out to investigate the mean synaptic density and mean synaptic height at posthatch Day 1 in dorsal and ventral part of chick hippocampus following prenatal auditory stimulation. Fertilized 0 day eggs of domestic chick incubated under normal conditions were exposed to patterned sounds of species-specific and sitar music at 65 dB levels for 15 min/h round the clock (frequency range: 100-6300 Hz) from embryonic Day 10 till hatching. The synapses identified under transmission electron microscope were estimated for their numerical density by physical disector method and also the mean synaptic height calculated. Our results demonstrate a significant increase in mean synaptic density with no alterations in the mean synaptic height following both types of auditory stimulation in the dorsal as well as ventral part of the hippocampus. The observed increase in mean synaptic density suggests enhanced synaptic substrate to strengthen hippocampal function.

Localization of CB1 cannabinoid receptor mRNA in the brain of the chick (Gallus domesticus)

The cannabinoid receptor one (CB1) is prevalent in the brains of many species. Receptor binding, in situ hybridization and immunohistochemical surveys have described the distribution of this receptor in a limited number of species. The current study used in situ hybridization to examine the expression of CB1 mRNA in the chick brain, a non-mammalian vertebrate. The results were compared to the observed patterns of expression for CB1 mRNA, protein, and agonist binding that have been reported for other avian species and mammals. Importantly, since CB1 receptors are typically located on neuronal terminals, comparison of the somatic mRNA expression with previously reported descriptions of the location of functional receptors, allows speculation about the circuits that make use of these receptors. The expression pattern for CB1 mRNA appears to be highly conserved across species in key areas such as the cerebellum and portions of the forebrain. For example, high levels of expression were observed in the avian amygdala and hippocampus, areas which express high levels of CB1 in mammals. The avian substantia nigra and ventral tegmental area, however, showed specific labeling. This finding is in stark contrast to the high levels of receptor binding or CB1 protein, but not CB1 mRNA in these areas of the mammalian brain. Moderate labeling was also seen throughout the hyperpallium and mesopallium. Throughout the brain, a number of regions that are known to be involved in visual processing displayed high levels of expression. For example, the tectum also had strong mRNA expression within layers 9-11 of the stratum griseum et fibrosum superficale and stratum album centrale.

Effects of an imprinting procedure on cell proliferation in the chick brain

We report here studies on the effects of an imprinting procedure on cell proliferation in neonatal chicks in brain structures known to undergo plastic changes in imprinting. Proliferating cells were detected immunohistochemically on brain sections by incorporation of pre-training doses of 5-bromodeoxyuridine (BrdU) into DNA; numbers of new cells were counted in the intermediate medial mesopallium, the intermediate arcopallium, the medial part of the mesopallium and the nidopallium, the dorsocaudal nidopallium, the hippocampus, and the parahippocampal region 24 h and seven days after training. The intermediate medial mesopallium showed an increase in the number of BrdU-positive cells 24 h after training. However, at seven days post-training, the number of BrdU-containing cells decreased in the medial nidopallium and mesopallium, in the dorsocaudal nidopallium, and the right intermediate medial mesopallium. Thus, the imprinting procedure had differently directed transient and long-term influences on the genesis of new cells in the chick brain, inducing the appearance of a large number of cells in the parenchyma of the brain one day after training and decreases in the numbers of cells at later time points. This double effect may be associated with the fact that the imprinting procedure simultaneously initiates two brain processes involving the control of cell proliferation - one related to maturation of a species-specific functional system for tracking individuals of the same species and one related to remembering the characteristics of the actual parent.

Calbindin D-28K and parvalbumin expression in embryonic chick hippocampus is enhanced by prenatal auditory stimulation

Calcium-binding proteins (CaBPs) buffer excess of cytosolic Ca(2+), which accompanies neuronal activity following external stimuli. Prenatal auditory stimulation by species-specific sound and music influences early maturation of the auditory pathway and the behavioral responses in chicks. In this study, we determined the volume, total number of neurons, proportion of calbindin D-28K and parvalbumin-positive neurons along with their levels of expression in the developing chick hippocampus following prenatal auditory stimulation. Fertilized eggs of domestic chicks were exposed to sounds of either species-specific calls or sitar music at 65 dB for 15 min/h round the clock from embryonic day (E) 10 until hatching. Hippocampi of developmental stages (E12, E16 and E20) were examined. With an increase in embryonic age during normal development, the hippocampus showed an increase in its volume, total number of neurons as well as in the neuron proportions and levels of expression of calbindin D-28K and parvalbumin. A significant increase of volume at E20 was noted only in the music-stimulated group compared to that of their age-matched control (p<0.05). On the other hand, both auditory-stimulated groups showed a significant increase in the proportion of immunopositive neurons and the levels of expression of calbindin D-28K and parvalbumin as compared to the control at all developmental stages studied (p<0.003). The increase in proportions of CaBP neurons during development and in the sound-enriched groups suggests an activity-dependent increase in Ca(2+) influx. The enhanced expression of CaBPs may help in cell survival by preventing excitotoxic death of neurons during development and may also be involved in long-term potentiation.

Noradrenergic projections to the song control nucleus area X of the medial striatum in male zebra finches (Taeniopygia guttata)

There is considerable functional evidence implicating norepinephrine in modulating activity in the vocal control circuit of songbirds. However, our knowledge of noradrenergic inputs to the song system is incomplete. In this study, cholera toxin subunit B (CTB) injections into area X revealed projections from the noradrenergic nuclei locus coeruleus and subcoeruleus, and injections of biotinylated dextran amines into these noradrenergic nuclei labeled fibers in area X. The nonreciprocity of this connection was demonstrated by the absence of retrogradely labeled cells in area X following injections of CTB into the locus coeruleus. Additionally, we found novel inputs to area X from the nidopallium and arcopallium, the mesencephalic central gray, and the dorsolateralis anterior (DLL) and posterior (DLP) lateralis in the thalamus. Area X can be clearly distinguished from the surrounding medial striatum based on cytoarchitectural and chemical neuroanatomical criteria. We show here that neuromodulatory inputs to area X however, exhibit a considerable degree of overlap with the surrounding area. This finding suggests that regional specificity in neuromodulator action is most likely afforded by a specialization in receptor density and enzyme distribution rather than projections from the synthesizing nuclei. Our results extend current knowledge about noradrenergic projections to specialized nuclei of the song control circuit and provide neuroanatomical evidence for the functional action of norepinephrine-modulating context-dependent ZENK expression in area X. Furthermore, the novel projections to area X from telencephalic and thalamic areas could be new and interesting nodes in the striatopallidothalamic loop spanning the songbird brain.

Prenatal acoustic stimulation influences neuronal size and the expression of calcium-binding proteins (calbindin D-28K and parvalbumin) in chick hippocampus

Prenatal auditory enrichment by species-specific sounds and sitar music enhances the expression of immediate early genes, synaptic proteins and calcium binding proteins (CaBPs) as well as modifies the structural components of the brainstem auditory nuclei and auditory imprinting area in chicks. There is also facilitation of postnatal auditory preference of the chicks to maternal calls following both types of sound stimulation indicating prenatal perceptual learning. To examine whether the sound enrichment protocol also affects the areas related to learning and memory, we assessed morphological changes in the hippocampus at post-hatch day 1 of control and prenatally sound-stimulated chicks. Additionally, the proportions of neurons containing calbindin D-28K and parvalbumin immunoreactivity as well as their protein levels were determined. Fertilized eggs of domestic chick were incubated under normal conditions of temperature, humidity, forced draft of air as well as light and dark (12:12h) photoperiods. They were exposed to patterned sounds of species-specific and sitar music at 65 dB for 15 min per hour over a day/night cycle from day 10 of incubation till hatching. The hippocampal volume, neuronal nuclear size and total number of neurons showed a significant increase in the music-stimulated group as compared to the species-specific sound-stimulated and control groups. However, in both the auditory-stimulated groups the protein levels of calbindin and parvalbumin as well as the percentage of the immunopositive neurons were increased. The enhanced proportion of CaBPs in the sound-enriched groups suggests greater Ca(2+) influx, which may influence long-term potentiation and short-term memory.

The evolution of cerebrotypes in birds

Multivariate analyses of brain composition in mammals, amphibians and fish have revealed the evolution of 'cerebrotypes' that reflect specific niches and/or clades. Here, we present the first demonstration of similar cerebrotypes in birds. Using principal component analysis and hierarchical clustering methods to analyze a data set of 67 species, we demonstrate that five main cerebrotypes can be recognized. One type is dominated by galliforms and pigeons, among other species, that all share relatively large brainstems, but can be further differentiated by the proportional size of the cerebellum and telencephalic regions. The second cerebrotype contains a range of species that all share relatively large cerebellar and small nidopallial volumes. A third type is composed of two species, the tawny frogmouth (Podargus strigoides) and an owl, both of which share extremely large Wulst volumes. Parrots and passerines, the principal members of the fourth group, possess much larger nidopallial, mesopallial and striatopallidal proportions than the other groups. The fifth cerebrotype contains species such as raptors and waterfowl that are not found at the extremes for any of the brain regions and could therefore be classified as 'generalist' brains. Overall, the clustering of species does not directly reflect the phylogenetic relationships among species, but there is a tendency for species within an order to clump together. There may also be a weak relationship between cerebrotype and developmental differences, but two of the main clusters contained species with both altricial and precocial developmental patterns. As a whole, the groupings do agree with behavioral and ecological similarities among species. Most notably, species that share similarities in locomotor behavior, mode of prey capture or cognitive ability are clustered together. The relationship between cerebrotype and behavior/ecology in birds suggests that future comparative studies of brain-behavior relationships will benefit from adopting a multivariate approach.

The chicken immediate-early gene ZENK is expressed in the medio-rostral neostriatum/hyperstriatum ventrale, a brain region involved in acoustic imprinting, and is up-regulated after exposure to an auditory stimulus

The immediate-early gene zenk (an acronym for the avian orthologue of the mammalian genes zif-268, egr-1, ngfi-a and krox-24) has been extensively employed, in studies on oscine birds, as a marker of neuronal activity to reveal forebrain structures that are involved in the memory processes associated with the acquisition, perception and production of song. Audition-induced expression of this gene, in brain, has also recently been reported for the domestic chicken (Gallus gallus domesticus) and the Japanese quail (Coturnix coturnix japonica). Whilst the anatomical distribution of zenk expression was described for the quail, corresponding data for the chicken were not reported. We have, therefore, used in situ hybridisation to localise the mRNA that encodes the product of the zenk gene (which we call ZENK) within the brain of the 1-day-old chick. We demonstrate that this transcript is present in a number of forebrain structures including the medio-rostral neostriatum/hyperstriatum ventrale (MNH), a region that has been strongly implicated in auditory imprinting (which is a form of recognition memory), and Field L, the avian analog of the mammalian auditory cortex. Because of this pattern of gene expression, we have compared the level of the ZENK mRNA in chicks that have been subjected to a 30-min acoustic imprinting paradigm and in untrained controls. Our results reveal a significant increase (P< or =0.05) in the level of the ZENK mRNA in MNH and Field L, and in the two forebrain hemispheres; no increase was seen in the ectostriatum, which is a visual projection area. The data obtained implicate the immediate-early gene, zenk, in auditory imprinting, which is an established model of juvenile learning. In addition, our results indicate that the ZENK mRNA may be used as a molecular marker for MNH, a region that is difficult to anatomically and histochemically delineate.

Early socio-emotional experience induces expression of the immediate-early gene Arc/arg3.1 (activity-regulated cytoskeleton-associated protein/activity-regulated gene) in learning-relevant brain regions of the newborn chick

We have cloned a full-length complementary DNA from the chicken (Gallus gallus domesticus), which encodes a polypeptide that exhibits approximately 75% identity to the product of the mammalian gene Arc (activity-regulated cytoskeleton-associated protein), also known as arg3.1 (activity-regulated gene). Since this gene is an immediate-early gene that has been suggested to play a role in synaptic plasticity and learning and memory processes, its expression has been analyzed in a juvenile form of learning, namely, filial imprinting. Our results demonstrate that Arc/arg3.1 mRNA is detectable in the newborn chick brain, and that at this early age the level of this transcript can be altered by brief sensory/emotional experience. After postnatal exposure to a novel 30-min auditory imprinting stimulus, Arc/arg3.1 mRNA was found to be significantly increased in two higher associative areas, the mesopallium intermediomediale (P = 0.002) and the nidopallium dorso-caudale (P = 0.031), compared with naïve controls. The transcript level was also significantly elevated after imprinting in Area L pallii (P=0.045), which is analogous to the mammalian auditory cortex. In addition, increases were seen in the medio-rostral nidopallium/mesopallium (P = 0.054), which is presumed to be the analog of the mammalian prefrontal cortex, and the hyperpallium intercalatum (P = 0.054), but these did not quite reach significance. We discuss these data in the light of those obtained in an earlier study, in the same paradigm, for the avian immediate-early gene, zenk (an acronym for zif-268, egr-1, ngfi-a and krox-24, which are different names for the orthologous mammalian gene). We conclude that, although both the Arc/arg3.1 and zenk genes are induced by auditory imprinting, they are significantly up-regulated in different learning-relevant brain regions. It is, therefore, evident that they must be activated by different mechanisms.

Discriminative taste aversion learning: a learning task for older chickens

The study of learning and memory using the chicken model has relied on three learning paradigms, passive avoidance learning, imprinting and the pebble floor task. Passive avoidance learning and imprinting have been used predominantly in very young chickens and cannot be used to access learning and memory in older chickens. We have established a new behavioural learning paradigm, Discriminative Taste Aversion Learning (DTAL), that can be used with both young and older animals. The task requires chickens to discriminate between food crumbs dyed either red or yellow with one colour being associated with the aversive tasting substance, methylanthranilate. Learning can be tested at various times after the training session by presenting chickens with the coloured food crumbs without an aversive taste. Both chickens tested at 5 and 15 days post-hatch learned to avoid the aversive crumbs. Furthermore, the protein synthesis inhibitor anisomycin (30 mM; 10 microl per hemisphere) injected into the intermediate medial hyperstriatum ventrale 15 min pre-training or 45 min post-training blocked long-term memory for the DTAL task when tested 24 h later. Memory for the task was unaffected by anisomycin injection 120 min post-training or in control animals injected with saline at similar times. The timing of the cellular processes of protein synthesis needed for consolidation of the DTAL appears to be similar to those described for the other behavioural paradigms in young chickens.

Nonspatial and subdivision-specific working memory deficits after selective lesions of the avian prefrontal cortex

Association areas in the avian forebrain are shown to subserve higher cognitive functions, including working memory. One of these areas, the neostriatum caudolaterale (NCL) of pigeons, has been functionally compared with the mammalian prefrontal cortex (PFC) because of its prominent role in spatial delay and reversal tasks and its innervation by the dopaminergic system that modulates these functions. However, whereas the PFC maintains in working memory information of different domains, the essential role of the NCL in working memory has been demonstrated only for spatial tasks. To investigate whether the avian NCL is also crucial for nonspatial working memory functions, pigeons were tested in an object-related (color) delayed matching-to-sample (DMTS) task. Bilateral lesions were placed in the entire, dorsal, or ventral NCL to test for possible functional subdivisions that were proposed to exist on the basis of neurochemical and behavioral data. Pigeons with total, dorsal, and ventral NCL lesions showed significant deficits in their DMTS performance, whereas controls were not impaired. Thus, the avian NCL is critically involved in nonspatial working memory processes. Recovery from performance deficits was observed in animals with ventral or total NCL lesions, whereas animals with dorsal NCL lesions showed no improvement. Ventral NCL may mediate perseverative behavior, whereas dorsal NCL might be involved in active working memory. Differences in the connections of these subdivisions with striatal areas and other association areas in the frontomedial forebrain underline functional differences. The data indicate a possible segregation of functions in the avian NCL.

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.

Electrophysiological and morphological properties of cell types in the chick neostriatum caudolaterale

The neostriatum caudolaterale, in the chick also referred to as dorsocaudal neostriatal complex, is a polymodal associative area in the forebrain of birds that is involved in sensorimotor integration and memory processes. We have used whole-cell patch-clamp recordings in chick brain slices to characterize the principal cell types of the neostriatum caudolaterale. Electrophysiological properties distinguished four classes of neurons. The morphological characteristics of these classes were examined by intracellular injection of Lucifer Yellow. Type I neurons characteristically fired a brief burst of action potentials. Morphologically, type I neurons had large somata and thick dendrites with many spines. Type II neurons were characterized by a repetitive firing pattern with conspicuous frequency adaptation. Type II neurons also had large somata and thick dendrites with many spines. There was no clear morphological distinction between type I and type II neurons. Type III neurons showed high-frequency firing with little accommodation and a prominent time-dependent inward rectification. They had thin, sparsely spiny dendrites and extensive local axonal arborizations. Electrophysiological and morphological properties indicated them as being interneurons. Type IV neurons had a longer action potential duration, a larger input resistance, and a longer membrane time constant than the other classes. Type IV neurons had small somata and short dendrites with few spines. The long axon collaterals of neurons in all spiny cell classes (types I, II, IV) followed similar patterns, suggesting that neurons from all these types can contribute to the projections of the neostriatum caudolaterale to sensory, limbic and motor areas. The electrophysiological and anatomical characterization of the major classes of neurons in the caudal forebrain of the chick provides a framework for the investigation of sensorimotor integration and learning at the cellular level in birds.

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.

Transferring an inborn auditory perceptual predisposition with interspecies brain transplants

Inborn species' perceptual preferences are thought to serve as important guides for neonatal learning in most species of higher vertebrates. Although much work has been carried out on experiential contributions to the expression of such preferences, their neural and developmental correlates remain largely unexplored. Here we use embryonic neural transplants between two bird species, the Japanese quail and the domestic chicken, to demonstrate that an inborn auditory perceptual predisposition is transferable between species. The transfer of the perceptual preference was dissociated from changes to the vocalizations of the resulting animals (called chimeras), suggesting that experiential differences in auditory self-stimulation cannot explain the perceptual change. A preliminary localization of the effective brain region for the behavioral transfer by using a naturally occurring species-cell marker revealed that it is not contained within the major avian auditory pathways. To our knowledge, this is the first demonstration that abstract aspects of auditory perception can be transferred between species with transplants of the central nervous system.

God's organism? The chick as a model system for memory studies

The young chick is a powerful model system in which to study the biochemical and morphological processes underlying memory formation. Training chicks on a one trial passive avoidance task results in a molecular cascade in a specific brain region, the intermediate medial hyperstriatum ventrale. This cascade is initiated by glutamate release and engages a series of synaptic transients including increased calcium flux, up-regulation of NMDA-glutamate receptors, membrane protein phosphorylations, and the retrograde messenger NO. Expression of immediate early genes c-fos and c-jun precedes the synthesis, glycosylation, and redistribution, >4 hr downstream, of a number of synaptic membrane proteins, notably NCAM and L1. Other membrane proteins required in the early phase of memory formation include the amyloid precursor protein (APP) and apolipoprotein E. There are concomitant increases in dendritic spine number and changes in synaptic structure. Nonsynaptic factors, including corticosterone and BDNF, can modulate retention of the avoidance response, enhancing the salience of otherwise weakly retained memory. These results are discussed in relation to general concepts of memory formation and the spatio-temporal distribution of the putative memory trace.

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.