Abundance and location of DARPP-32 in striato-tegmental circuits of domestic chicks

Early cellular and synaptic changes in dopaminoceptive forebrain regions of juvenile mice following gestational exposure to valproate

Gestational exposure of mice to valproic acid (VPA) is one currently used experimental model for the investigation of typical failure symptoms associated with autism spectrum disorder (ASD). In the present study we hypothesized that the reduction of dopaminergic source neurons of the VTA, followed by perturbed growth of the mesotelencephalic dopamine pathway (MT), should also modify pattern formation in the dopaminoceptive target regions (particularly its mesoaccumbens/mesolimbic portion). Here, we investigated VPA-evoked cellular morphological (apoptosis-frequency detected by Caspase-3, abundance of Ca-binding proteins, CaBP), as well as synaptic proteomic (western blotting) changes, in selected dopaminoceptive subpallial, as compared to pallial, regions of mice, born to mothers treated with 500 mg/kg VPA on day 13.5 of pregnancy. We observed a surge of apoptosis on VPA treatment in nearly all investigated subpallial and pallial regions; with a non-significant trend of similar increase the nucleus accumbens (NAc) at P7, the age at which the MT pathway reduction has been reported (also supplemented by current findings). Of the CaBPs, calretinin (CR) expression was decreased in pallial regions, most prominently in retrosplenial cortex, but not in the subpallium of P7 mice. Calbindin-D 28K (CB) was selectively reduced in the caudate-putamen (CPu) of VPA exposed animals at P7 but no longer at P60, pointing to a potency of repairment. The VPA-associated overall increase in apoptosis at P7 did not correlate with the abundance and distribution of CaBPs, except in CPu, in which the marked drop of CB was negatively correlated with increased apoptosis. Abundance of parvalbumin (PV) at P60 showed no significant response to VPA treatment in any of the observed regions we did not find colocalization of apoptotic (Casp3+) cells with CaBP-immunoreactive neurons. The proteomic findings suggest reduction of tyrosine hydroxylase in the crude synaptosome fraction of NAc, but not in the CPu, without simultaneous decrease of the synaptic protein, synaptophysin, indicating selective impairment of dopaminergic synapses. The morpho-functional changes found in forebrain regions of VPA-exposed mice may signify dendritic and synaptic reorganization in dopaminergic target regions, with potential translational value to similar impairments in the pathogenesis of human ASD.

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

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

Regional chemoarchitecture of the brain of lungfishes based on calbindin D-28K and calretinin immunohistochemistry

Lungfishes are the closest living relatives of land vertebrates, and their neuroanatomical organization is particularly relevant for deducing the neural traits that have been conserved, modified, or lost with the transition from fishes to land vertebrates. The immunohistochemical localization of calbindin (CB) and calretinin (CR) provides a powerful method for discerning segregated neuronal populations, fiber tracts, and neuropils and is here applied to the brains of Neoceratodus and Protopterus, representing the two extant orders of lungfishes. The results showed abundant cells containing these proteins in pallial and subpallial telencephalic regions, with particular distinct distribution in the basal ganglia, amygdaloid complex, and septum. Similarly, the distribution of CB and CR containing cells supports the division of the hypothalamus of lungfishes into neuromeric regions, as in tetrapods. The dense concentrations of CB and CR positive cells and fibers highlight the extent of the thalamus. As in other vertebrates, the optic tectum is characterized by numerous CB positive cells and fibers and smaller numbers of CR cells. The so-called cerebellar nucleus contains abundant CB and CR cells with long ascending axons, which raises the possibility that it could be homologized to the secondary gustatory nucleus of other vertebrates. The corpus of the cerebellum is devoid of CB and CR and cells positive for both proteins are found in the cerebellar auricles and the octavolateralis nuclei. Comparison with other vertebrates reveals that lungfishes share most of their features of calcium binding protein distribution with amphibians, particularly with salamanders.

Immunohistochemical Localization of DARPP-32 in the Brain of Two Lungfishes: Further Assessment of Its Relationship with the Dopaminergic System

The distribution of DARPP-32 (a phosphoprotein related to the dopamine D1 receptor) has been widely used as a means to clarify the brain regions with dopaminoceptive cells, primarily in representative species of tetrapods. The relationship between dopaminergic and dopaminoceptive elements is frequently analyzed using the catecholamine marker tyrosine hydroxylase (TH). In the present study, by means of combined immunohistochemistry, we have analyzed these relationships in lungfishes, the only group of sarcopterygian fishes represented by 6 extant species that are the phylogenetically closest living relatives of tetrapods. We used the Australian lungfish Neoceratodus forsteri and the African lungfish Protopterus dolloi. The DARPP-32 antibody yields a distinct and consistent pattern of neuronal staining in brain areas that, in general, coincide with areas that are densely innervated by TH-immunoreactive fibers. The striatum, thalamus, optic tectum, and torus semicircularis contain intensely DARPP-32-immunoreactive cell bodies and fibers. Cells are also located in the olfactory bulbs, amygdaloid complex, lateral septum, pallidum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, rostral rhombencephalic reticular formation, superior raphe nucleus, octavolateral area, solitary tract nucleus, and spinal cord. Remarkably, DARPP-32-immunoreactive fibers originating in the striatum reach the region of the dopaminergic cells in the mesencephalic tegmentum and represent a well-established striatonigral pathway in lungfishes. Double immunolabeling reveals that DARPP-32 is present in neurons that most likely receive TH input, but it is absent from the catecholaminergic neurons themselves, with the only exception of a few cells in the suprachiasmatic nucleus of Neoceratodus and the solitary tract nucleus of Protopterus. In addition, some species differences exist in the localization of DARPP-32 cells in the pallium, lateral amygdala, thalamus, prethalamus, and octavolateral area. In general, the present study demonstrates that the distribution pattern of DARPP-32, and its relationship with TH, is largely comparable to those reported for tetrapods, highlighting a shared situation among all sarcopterygians.

Rapid Effects of an Aggressive Interaction on Dehydroepiandrosterone, Testosterone and Oestradiol Levels in the Male Song Sparrow Brain: a Seasonal Comparison

Across vertebrates, aggression is robustly expressed during the breeding season when circulating testosterone is elevated, and testosterone activates aggression either directly or after aromatisation into 17β-oestradiol (E2 ) in the brain. In some species, such as the song sparrow, aggressive behaviour is also expressed at high levels during the nonbreeding season, when circulating testosterone is non-detectable. At this time, the androgen precursor dehydroepiandrosterone (DHEA) is metabolised within the brain into testosterone and/or E2 to promote aggression. In the present study, we used captive male song sparrows to test the hypothesis that an acute agonistic interaction during the nonbreeding season, but not during the breeding season, would alter steroid levels in the brain. Nonbreeding and breeding subjects were exposed to either a laboratory simulated territorial intrusion (L-STI) or an empty cage for only 5 min. Immediately afterwards, the brain was rapidly collected and flash frozen. The Palkovits punch technique was used to microdissect specific brain regions implicated in aggressive behaviour. Solid phase extraction followed by radioimmunoassay was used to quantify DHEA, testosterone and E2 in punches. Overall, levels of DHEA, testosterone and E2 were higher in brain tissue than in plasma. Local testosterone and E2 levels in the preoptic area, anterior hypothalamus and nucleus taeniae of the amygdala were significantly higher in the breeding season than the nonbreeding season and were not affected by the L-STI. Unexpectedly, subjects that were dominant in the L-STI had lower levels of DHEA in the anterior hypothalamus and medial striatum in both seasons and lower levels of DHEA in the nucleus taeniae of the amygdala in the breeding season only. Taken together, these data suggest that local levels of DHEA in the brain are very rapidly modulated by social interactions in a context and region-specific pattern.

Antipsychotics activate mTORC1-dependent translation to enhance neuronal morphological complexity

Although antipsychotic drugs can reduce psychotic behavior within a few hours, full efficacy is not achieved for several weeks, implying that there may be rapid, short-term changes in neuronal function, which are consolidated into long-lasting changes. We showed that the antipsychotic drug haloperidol, a dopamine receptor type 2 (D₂R) antagonist, stimulated the kinase Akt to activate the mRNA translation pathway mediated by the mammalian target of rapamycin complex 1 (mTORC1). In primary striatal D₂R-positive neurons, haloperidol-mediated activation of mTORC1 resulted in increased phosphorylation of ribosomal protein S6 (S6) and eukaryotic translation initiation factor 4E-binding protein (4E-BP). Proteomic mass spectrometry revealed marked changes in the pattern of protein synthesis after acute exposure of cultured striatal neurons to haloperidol, including increased abundance of cytoskeletal proteins and proteins associated with translation machinery. These proteomic changes coincided with increased morphological complexity of neurons that was diminished by inhibition of downstream effectors of mTORC1, suggesting that mTORC1-dependent translation enhances neuronal complexity in response to haloperidol. In vivo, we observed rapid morphological changes with a concomitant increase in the abundance of cytoskeletal proteins in cortical neurons of haloperidol-injected mice. These results suggest a mechanism for both the acute and long-term actions of antipsychotics.

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.

Neuro-economics in chicks: foraging choices based on amount, delay and cost

Studies on the foraging choices are reviewed, with an emphasis on the neural representations of elementary factors of food (i.e., amount, delay and consumption time) in the avian brain. Domestic chicks serve as an ideal animal model in this respect, as they quickly associate cue colors with subsequently supplied food rewards, and their choices are quantitatively linked with the rewards. When a pair of such color cues was simultaneously presented, the trained chicks reliably made choices according to the profitability of food associated with each color. Two forebrain regions are involved in distinct aspects of choices; i.e., nucleus accumbens-medial striatum (Ac-MSt) and arcopallium intermedium (AI), an association area in the lateral forebrain. Localized lesions of Ac-MSt enhanced delay aversion, and the ablated chicks made impulsive choices of immediate reward more frequently than sham controls. On the other hand, lesions of AI enhanced consumption-time aversion, and the ablated chicks shifted their choices toward easily consumable reward with their impulsiveness unchanged; delay and consumption time are thus doubly dissociated. Furthermore, chicks showed distinct patterns of risk-sensitive choices depending on the factor that varied at trials. Risk aversion occurred when food amount varied, whereas consistent risk sensitivity was not found when the delay varied; amount and delay were not interchangeable. Choices are thus deviated from those predicted as optima. Instead, factors such as amount, delay and consumption time could be separately represented and processed to yield economically sub-optimal choices.

Localized lesions of arcopallium intermedium of the lateral forebrain caused a handling-cost aversion in the domestic chick performing a binary choice task

Behavioral effects of handling cost (time and/or energetic cost for food consumption) on choice were examined using domestic chicks trained in operant task reinforced by delayed food rewards. When scattered sesame was delivered in more demanding conditions, a colored cue bead associated with six grains ('large' and 'costly' reward) was chosen progressively less frequently against another bead associated with one grain ('small' and 'not costly' reward). The choice thus proved to be highly sensitive to the anticipated handling cost. Excitotoxic lesion of the bilateral arcopallium intermedium also selectively reduced the choice of the six grains, while leaving actual cost investment (number of pecks and handling time) unaltered. No significant changes occurred in choices between one grain of sesame ('small' and 'not costly' reward) and one grain of barley (or a ball composed of six sesame grains glued by starch; 'large' and 'not costly' reward), indicating that choice based on anticipated food amount was not impaired. On the other hand, lesion of the ventral striatum did not change the choice ratio in any trial types. Operant peck latencies somewhat depended on food rewards, but were not affected by lesions of the arcopallium or the ventral striatum. The arcopallium could contribute to foraging behaviors by enabling chicks to overcome the handling cost, thus gaining more beneficial food. Furthermore, the present results indicate doubly dissociated functional roles of the ventral striatum and the arcopallium, the former in the cost of traveling for food and the latter in the cost of handling food, respectively.

Neural correlates of the proximity and quantity of anticipated food rewards in the ventral striatum of domestic chicks

To identify the neuro-cognitive substrates of valuation and choice, we analysed the neural correlates of anticipated food rewards in the ventral striatum of freely behaving chicks. One-week-old chicks were trained in a color-discrimination task using four color cues (red, yellow, green and blue), each of which was associated with a different food reward. Choosing a red bead was immediately rewarded with a large amount of food, choosing a yellow bead resulted in an immediate-small food reward, and choosing a green bead resulted in a late-large food reward. We selected chicks that consistently chose a large and immediate food reward (red over yellow, and red over green), with the proximity of the food valued higher than the size of the food reward (yellow over green). Of the 47 neurons recorded from the ventral striatum of these chicks, 20 neurons selectively showed cue-period responses to cues associated with food rewards. Five of these 20 neurons responded differentially during the cue period according to the expected delay to reward, and were thus assumed to code for the proximity of the reward. Additionally, three other neurons responded to the quantity of the reward. Furthermore, in the post-operant delay period, many of these 20 neurons showed reward-related activities that were linked to the proximity or presence of the food reward. We therefore propose that impulsive choice and behavioral perseveration observed after lesions of the ventral striatum could be due to impaired anticipation of rewards in the cue and delay periods, respectively.

Localized lesions of ventral striatum, but not arcopallium, enhanced impulsiveness in choices based on anticipated spatial proximity of food rewards in domestic chicks

The effects of bilateral chemical lesions of the ventral striatum (nucleus accumbens and the surrounding areas in the medial striatum) and arcopallium (major descending area of the avian telencephalon) were examined in 1-2-weeks old domestic chicks. Using a Y-maze, we analyzed the lesion effects on the choices that subject chicks made in two tasks with identical economical consequences, i.e., a small-and-close food reward vs. a large-and-distant food reward. In task 1, red, yellow, and green beads were associated with a feeder placed at various distances from the chicks; chicks thus anticipated the spatial proximity of food by the bead's color, whereas the quantity of the food was fixed. In task 2, red and yellow flags on the feeders were associated with various amount of food; the chicks thus anticipated the quantity of food by the flag's color, whereas the proximity of the reward could be directly visually determined. In task 1, bilateral lesions of the ventral striatum (but not the arcopallium) enhanced the impulsiveness of the chicks' choices, suggesting that choices based on the anticipated proximity were selectively changed. In task 2, similar lesions of the ventral striatum did not change choices. In both experiments, motor functions of the chicks remained unchanged, suggesting that the lesions did not affect the foraging efficiency, i.e., objective values of food. Neural correlates of anticipated food rewards in the ventral striatum (but not those in the arcopallium) could allow chicks to invest appropriate amount of work-cost in approaching distant food resources.