Colocalization of immediate early genes in catecholamine cells after song exposure in female zebra finches (Taeniopygia guttata).

The physiological state of animals in many taxonomic groups can be modified via social interactions including simply receiving communication signals from conspecifics. Here, we explore whether the catecholaminergic system of female songbirds responds during social interactions that are limited to song reception. We measured the protein product of an immediate early gene (ZENK) within three catecholaminergic brain regions in song-exposed (n = 11) and silence-exposed (n = 6) female zebra finches (Taeniopygia guttata). ZENK-ir induction was quantified in catecholamine cells as well as within cells of unknown phenotypes in three brain regions that synthesize catecholamines, the ventral tegmental area, the periaqueductal gray and the locus coeruleus (LoC). Our results reveal that there are no significant differences in the overall number of cells expressing ZENK between song- and silence-exposed females. However, when we limited our measurements to catecholamine-containing cells, we noticed a greater number of catecholamine-containing cells expressing ZENK within the LoC in the song-exposed females compared to silence-exposed females. Furthermore, we measured five behaviors during the song- and silence-exposed period, as behavioral differences between these groups may account for differences in the coinduction of ZENK and TH-ir. Our results reveal that there were no statistically significant differences in the five measured behaviors between song- and silence-exposed females. Our study demonstrates that noradrenergic cells within the LoC are involved in the neural architecture underlying sound perception and that cells within the catecholaminergic system are modulated by social interactions, particularly the reception of signals used in animal communication.

Effect of Concomitant Benzodiazepine Use on Efficacy and Safety of Esketamine Nasal Spray in Patients with Major Depressive Disorder and Acute Suicidal Ideation or Behavior: Pooled Randomized, Controlled Trials.

PURPOSE: The impact of benzodiazepines on the efficacy and safety of esketamine as a rapid-acting antidepressant remains unclear. MATERIALS AND METHODS: Data from two identically designed, randomized double-blind studies were pooled and analyzed on a post-hoc basis. In both studies, adults with major depressive disorder with acute suicidal ideation or behavior were randomized to placebo or esketamine 84 mg nasal spray twice-weekly for 4 weeks, each with comprehensive standard-of-care (initial hospitalization and newly initiated or optimized oral antidepressant[s]). Efficacy and safety were analyzed in two groups based on whether patients used concomitant benzodiazepines, which were prohibited within 8 hours before and 4 hours after the first dose of esketamine and within 8 hours of the primary efficacy assessment at 24 hours. The primary efficacy endpoint - change from baseline to 24 hours post-first dose in Montgomery-Asberg Depression Rating Scale (MADRS) total score - was analyzed using ANCOVA. RESULTS: Most patients (309/451, 68.5%) used concomitant benzodiazepines. Greater decrease in MADRS total score was observed with esketamine (mean [SD]: -16.1 [11.73]) versus placebo (-12.6 [10.56]) at 24 hours (least-squares mean difference: -3.7, 95% CI: -5.76, -1.59). The differences between the esketamine and placebo groups were clinically meaningful, irrespective of benzodiazepine use (benzodiazepine: -4.3 [-6.63, -1.89]; no benzodiazepine: -3.1 [-6.62, 0.45]). Among patients taking esketamine, change in MADRS total score was not significantly different between patients taking benzodiazepines (-15.8 [11.27]) versus those not taking benzodiazepines (-16.8 [12.82]) (least-squares mean difference: 1.1, [-2.24, 4.45]). Among esketamine-treated patients, the incidence of sedation was higher with benzodiazepine use, whereas dissociation was similar. CONCLUSION: Benzodiazepines do not meaningfully affect the rapid-acting antidepressant effect of esketamine at 24 hours post-first dose among patients with MDD and acute suicidal ideation or behavior.

Single units in the pigeon brain integrate reward amount and time-to-reward in an impulsive choice task.

BACKGROUND: Animals prefer small over large rewards when the delays preceding large rewards exceed an individual tolerance limit. Such impulsive choice behavior occurs even in situations in which alternative strategies would yield more optimal outcomes. Behavioral research has shown that an animal's choice is guided by the alternative rewards' subjective values, which are a function of reward amount and time-to-reward. Despite increasing knowledge about the pharmacology and anatomy underlying impulsivity, it is still unknown how the brain combines reward amount and time-to-reward information to represent subjective reward value. RESULTS: We trained pigeons to choose between small, immediate rewards and large rewards delivered after gradually increasing delays. Single-cell recordings in the avian Nidopallium caudolaterale, the presumed functional analog of the mammalian prefrontal cortex, revealed that neural delay activation decreased with increasing delay length but also covaried with the expected reward amount. This integrated neural response was modulated by reward amount and delay, as predicted by a hyperbolical equation, of subjective reward value derived from behavioral studies. Furthermore, the neural activation pattern reflected the current reward preference and the time point of the shift from large to small rewards. CONCLUSIONS: The reported activity was modulated by the temporal devaluation of the anticipated reward in addition to reward amount. Our findings contribute to the understanding of neuropathologies such as drug addiction, pathological gambling, frontal lobe syndrome, and attention-deficit disorders, which are characterized by inappropriate temporal discounting and increased impulsiveness.

Stimulation of dopamine D1 receptors in the avian fronto-striatal system adjusts daily cognitive fluctuations.

Several studies have shown that the level of dopaminergic transmission and D1 receptor signaling is crucial for working memory (WM) in the prefrontal cortex (PFC) of mammals. Thus, hyper- or hypostimulation of prefrontal D1 receptors are pathophysiological findings often involved in cognitive and WM impairments. These observations can be mimicked by supranormal stimulation or inhibition with D1 receptor agonists or D1 antagonists, respectively. As a consequence, it is assumed that there is a normal range of dopamine function in prefrontal cortex that can be described as an inverted U-shaped relationship between dopamine transmission, i.e. D1 receptor stimulation, and intact WM. If this is true, short-term fluctuations of cognitive performance might be described as small-scale adjustments along the tip of the inverted U-curve and should depend on D1 receptor stimulation. We tested this hypothesis in pigeons performing a delayed-matching-to-sample task (DMTS), a classic paradigm to test WM. We applied the D1 agonist SKF81297 and the D1 antagonist SCH23390 into the nidopallium caudolaterale (NCL), the avian functional analogue of the PFC, and simultaneously in the medial striatum (MSt), by in vivo microdialysis while the animals performed the task. Animals showed daily fluctuations in WM performance. While the D1 agonist was able to improve or to decrease performance during low or strong performance periods, respectively, performance did not differ from control with the D1 antagonist. This study shows that D1 receptors seem to calibrate differentially prefronto-striatal functions based on individual low or high performance states.

Catecholaminergic cell groups and vocal communication in male songbirds.

Birdsong is a species-typical vocal signal that facilitates reproduction and deters competitors. Song production is regulated by a clearly defined and specialized neural circuitry in which high concentrations of catecholamines are present. The nuclei within the song control circuit receive projections from catecholaminergic cell populations involved in attention, arousal and motivation, including periaqueductal gray (PAG), ventral tegmental area (VTA), locus coeruleus (LoC) and sub coeruleus (SC). Here, we examine whether catecholamine-containing neurons in these regions exhibit the immediate early gene, ZENK, during spontaneous, undirected song production in male zebra finches (Taeniopygia guttata). Males were assigned to "singing" or "silent" groups based on the total duration of spontaneous, undirected song produced within a 30 min period. We quantified the number of cells expressing both ZENK-ir and tyrosine hydroxylase (TH)-ir within the VTA, PAG, LoC and SC. The number of cells expressing co-localized ZENK and TH-ir was significantly elevated within the PAG in males that were singing compared to silent males. The number of cells expressing ZENK-ir alone was also elevated in the VTA and SC in singing males compared to silent males. Although ZENK expression is elevated in singing birds it does not positively correlate with the amount of singing produced. It is therefore likely that catecholaminergic PAG neurons are involved in motivational or attentional components of vocal expression rather than vocal motor output. Overall, our study is consistent with the hypothesis that PAG catecholamine-containing neurons as well as VTA and SC neurons play a role in vocal communication of male songbirds.

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.

Visual responses and afferent connections of the n. ventrolateralis thalami (VLT) in the pigeon (Columba livia).

The nucleus ventrolateralis thalami (VLT) in pigeons receives direct retinal and forebrain projections and has reciprocal connections with the optic tectum. Although VLT is a component of the avian visual system, no study directly examined its connections or its cellular response characteristics. We, therefore, recorded from single units in the pigeon's VLT while visually stimulating the ipsi- and/or contralateral eye. In addition, tracing experiments were conducted to investigate its afferent connections. Electrophysiologically, we discovered three types of neurons, two of which were probably activated via a top-down telencephalotectal system (latencies > 100 ms). Type I neurons responded to uni- and bilateral and type II neurons exclusively to bilateral stimulation. Type III neurons were probably activated by retinal or retinotectal input (latencies < 27 ms) and responded to contra- and bilateral stimulation. Retrograde tracer injections into the VLT revealed an ipsilateral forebrain input from the visual Wulst, from subregions of the arcopallium, and bilateral afferents from the optic tectum. Most intriguing was the direct connection between the VLTs of both hemispheres. We suggest that the avian VLT is part of a system that integrates visuomotor processes which are controlled by both forebrain hemispheres and that VLT contributes to descending tectomotor mechanisms.

Asymmetrical modes of visual bottom-up and top-down integration in the thalamic nucleus rotundus of pigeons.

The aim of this study was to separate bottom-up and top-down influences within cerebral asymmetries. This was studied in the lateralized visual system of pigeons by recording from single units of the left and right diencephalic nucleus rotundus of the tectofugal pathway while visually stimulating the ipsilateral and/or contralateral eye. Analyses of response latencies revealed rotundal neurons with short and/or late response components. Cells with short latencies very likely represent bottom-up neurons participating in the ascending retinotectorotundal system. Because lidocaine injections into the visual Wulst produced a significant reduction of late response components only, neurons with long latencies were probably activated via a top-down telencephalotectorotundal system. The distribution and response characteristics of bottom-up and top-down neurons provided insight into several asymmetries of ascending and descending pathways. Asymmetries of the ascending retinotectorotundal system (bottom-up) were characterized by longer periods of tonic activation in the left and shorter response latencies in the right rotundus. Left-right differences in these responses probably facilitate faster access to visual input to the right hemisphere and a prolonged processing of this input in the left. The descending telencephalotectorotundal system (top-down) revealed a completely different lateralized organization. This system was characterized by long latency responses that exclusively derived from the left hemisphere, regardless of whether recordings took place in the left or the right rotundus. We assume that asymmetrical modes of visual processing within both hemispheres of the ascending tectofugal system are ultimately directed to left hemispheric forebrain mechanisms that subsequently generate executive control over sensory and motor structures.

Working memory neurons in pigeons.

Working memory, the ability to temporarily store and manipulate currently relevant information, is required for most cognitive faculties. In humans and other mammals, the prefrontal cortex (PFC) provides the underlying neural network for these processes. Within the PFC, working memory neurons display sustained elevated activity while holding active an internal representation of the relevant stimulus during its physical absence or retaining a motor plan for the forthcoming response. Working memory, however, is not a hallmark of higher vertebrates endowed with a neocortex. Birds also master complex cognitive problems invoking working memory, but they lack a laminated neocortex. Behavioral studies in pigeons show that the neostriatum caudolaterale (NCL) plays a central role in executive functions, such as working memory and response control. For neurons in the NCL of pigeons, we show activity changes during the delay of a working memory task, which were similar to those observed in PFC neurons and were related to the successful holding of information in memory and to the subsequent behavior. Thus, although the anatomical and morphological structure of the neuronal substrate in birds is radically different from the mammalian neocortical architecture, the neuronal mechanisms evolved to master equivalent cognitive demands seem to be very similar.

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.

Neural correlates of a default response in a delayed go/no-go task.

Working memory, the ability to temporarily retain task-relevant information across a delay, is frequently investigated using delayed matching-to-sample (DMTS) or delayed Go/No-Go tasks (DGNG). In DMTS tasks, sample cues instruct the animal which type of response has to be executed at the end of a delay. Typically, performance decreases with increasing delay duration, indicating that working memory fades across a delay. However, no such performance decrease has been found when the sample cues exist of present vs. absent stimuli, suggesting that pigeons do not rely on working memory, but seem to respond by default in those trials. We trained 3 pigeons in a DGNG task and found a similar default response pattern: The diverging slopes of the retention functions on correct Go and No-Go trials suggested that pigeons by default omitted their response following No-Go stimuli, but actively retained task-relevant information across the delay for successful responses on Go trials. We conducted single-cell recordings in the avian nidopallium caudolaterale, a structure comparable to the mammalian prefrontal cortex. On Go trials, many neurons displayed sustained elevated activity during the delay preceding the response, replicating previous findings and suggesting that task-relevant information was neurally represented and maintained across the delay. However, the same units did not show enhanced delay activity preceding correct response suppressions in No-Go trials. This activation-inactivation pattern presumably constitutes a neural correlate of the default response strategy observed in the DGNG task.

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.

Embryonic light stimulation induces different asymmetries in visuoperceptual and visuomotor pathways of pigeons.

In birds, visual object discrimination performance is lateralized with a dominance of the right eye/left hemisphere. This asymmetry is induced by embryonic light stimulation. However, visually guided behavior, even during simple object distinction tasks, is composed of different behavioral and neural modules. Therefore, the aim of the present study was to test whether all neural subsystems involved in visual discriminations are lateralized in a similar way after prehatch visual stimulation. To examine this question, two behavioral paradigms were used which reveal complementary aspects of visually guided behavior. The first was the grain-grit discrimination task in which no left-right differences in the number of pecks, but significant differences in the number of grains can be found. Therefore, grain-grit discrimination reveals visuoperceptual performance but not visuomotor speed. The contrary seems to be the case for a successive pattern discrimination with a VR32 schedule. Here, the hemispheres do not differ with respect to discrimination accuracy but with regard to the number of pecks emitted. Thus, successive pattern discrimination with lean VR schedules reveals hemispheric differences in visuomotor speed without testing visuoperceptual performance. Using these two paradigms a group of light and a group of dark incubated pigeons were tested. The results show that dark incubated birds evinced no asymmetry in any measure while light incubated ones were right-eye dominant in both variables. However, light incubation induced a visual left hemispheric dominance by modulating two different processes, a left-hemispheric increase of visuoperceptual processes; and a right-hemispheric decrease for visuomotor speed. Taken together these data show that embryonic light stimulation elicits visual lateralization by differently modulating visuoperceptual and visuomotor systems in both hemispheres.

Effects of monocular viewing on orientation in an arena at the release site and homing performance in pigeons.

Orientation and homing performance of pigeons with the left or right eye occluded were assessed in an arena at the release site and during the subsequent homing flight. Three release sites near Pisa, Italy, were used. Compared to binocular controls, monocular birds showed a bias in orientation towards the side of the viewing eye. In the arena, this bias was considerable and the mean deviation corresponded to the angle of the optical axis, suggesting a systematic error in visual representation during directional orientation. During flight after leaving the arena the directional bias decreased and the homeward orientation increased. While there was a slight lateralization of overall homing performance in favour of the right eye, there was no lateralization in directional orientation in the arena or at vanishing. Our results show that navigational mechanisms in either brain hemisphere profit from information obtained before take off and while flying over the release site. The existence and degree of lateralization is discussed in comparison to other studies that investigated homing under monocular viewing conditions.

Differential increase of extracellular dopamine and serotonin in the 'prefrontal cortex' and striatum of pigeons during working memory.

Monoamines, such as dopamine (DA) and serotonin (5-HT), play a central role in the modulation of cognitive processes at the forebrain level. Experimental and clinical studies based on dopaminergic pathology, depletion or medication indicate that DA, in particular, is involved in working memory (WM). However, it is unclear whether DA is indeed related to WM, whether its function is specific to the prefrontal cortex (PFC), and whether other modulators, such as 5-HT, might have similar functions. Therefore, the aims of this study were threefold. First, we analysed whether increased prefrontal DA release is related to WM in general or only to its short-term memory component. Second, we examined whether the DA release during cognitive tasks is specific to prefrontal areas or also occurs in the striatum. Third, we analysed whether prefrontal or striatal 5-HT release accompanies working and short-term memory. We approached these questions by using in vivo microdialysis to analyse the extracellular DA and 5-HT release in the pigeons' 'PFC' and striatum during matching-to-sample tasks with or without a delay. Here, we show that DA has no unitary function but is differentially released during working as well as short-term memory in the pigeons' 'prefrontal' cortex. Striatal DA shows an increased efflux only during WM that involves a delay component. WM is also accompanied by a 'prefrontal' but not a striatal release of 5-HT, whose efflux pattern is thus partly different to that of DA. Our findings thus show a triple dissociation between transmitters, structures and tasks within the avian 'prefronto'-striatal system.

Neural architecture of choice behaviour in a concurrent interval schedule.

Concurrent interval schedules are classic experimental paradigms that are traditionally employed in psychological research on choice behaviour. To analyse the neural basis of choice in a concurrent fixed interval schedule, pigeons were trained to peck on two response keys. Responses were differentially rewarded in key specific short or long time intervals (SI vs. LI). Using tetrodotoxin, we reversibly blocked the neostriatum caudolaterale (NCL, the avian functional equivalent of the prefrontal cortex), avian caudate-putamen and nucleus accumbens to examine their contribution. A detailed analysis of baseline choice behaviour revealed that response distribution and key affinity were determined by cued or time-related expectancy for rewards on the SI key. The pigeons' response frequency increased on the SI key and decreased on the LI key with increasing temporal proximity to the SI reward and pigeons switched to the LI key after reward delivery. Pecking bursts on the LI key were negatively correlated with bursts on the SI key. Neostriatum caudolaterale inactivation did not affect pecking activity per se but interfered with reward-related temporal modulation of pecking frequency, switching pattern and coupling of LI to SI pecks. Blockade of caudate-putamen resulted in a complete behavioural halt, while inactivation of nucleus accumbens diminished operant behaviour without affecting consummatory responses. These data suggest that the NCL is tuned via indirect striato-pallial projections to integrate cued or time-related reward expectancy into a response selection process in order to set, maintain or shift goals. The NCL possibly feeds forward the resulting motor commands to the caudate-putamen for execution.