Monoaminergic innervation of the macaque extended amygdala

Neuroanatomical basis of 5-HT1A receptor agonism in disruption of maternal behavior in rats

The acute activation of serotonin 1 A (5-HT1A) receptors appears to disrupt maternal behavior in rats; however, the underlying neuroanatomical mechanisms remain poorly understood. We employed two approaches to investigate the role of 5-HT1A receptors in maternal behavior to address this knowledge gap. First, we used real-time polymerase chain reaction (PCR) to analyze 5-HT1A receptor mRNA expression in female rats at different reproductive stages. We identified stage- and region-specific expression patterns, including temporary increases in the nucleus accumbens (NAc), ventral tegmental area (VTA), and dorsal raphe nucleus (DRN), as well as a temporary decrease in the medial prefrontal cortex (mPFC), amygdala, hippocampus, and ventromedial hypothalamic nucleus (VMH) during the perinatal, early, and middle postpartum periods. These findings suggest that coordinated 5-HT1A activity across these brain regions is critical for normal maternal behavior. Second, we used c-Fos immunohistochemistry to elucidate the central mechanisms underlying the effects of the acute and repeated administration of 8-OH-DPAT (a 5-HT1A receptor agonist, 1.0 mg/kg, sc.) on maternal behavior. Acute 8-OH-DPAT administration disrupted maternal behaviors, including pup retrieval, pup licking, nest building and hovering over pups, while simultaneously increased c-Fos expression in the mPFC, ventral bed nucleus of the stria terminalis (vBNST), NAc shell, lateral septum (LS), and medial amygdala (MeA). Disruptions in pup retrieval, pup licking and nest building persisted following five days of repeated 8-OH-DPAT treatment, whereas hovering over pups showed substantial recovery, returning to near-normal levels. Concurrently, c-Fos expression increased in the vBNST but decreased in the mPFC, MeA, and DRN. These results suggest that acute and repeated 8-OH-DPAT administration disrupts maternal behavior via distinct presynaptic and postsynaptic 5-HT1A receptor mechanisms. This study highlights the complex regulatory role of 5-HT1A receptor activity in maternal care and provides insights into the neuroanatomical and neurochemical mechanisms underlying maternal behavior.

Anatomical and neurochemical organization of the serotonergic system in the mammalian brain and in particular the involvement of the dorsal raphe nucleus in relation to neurological diseases

The brainstem is a neglected brain area in neurodegenerative diseases, including Alzheimer's and Parkinson's disease, frontotemporal lobar degeneration and autonomic dysfunction. In Depression, several observations have been made in relation to changes in one particular the Dorsal Raphe Nucleus (DRN) which also points toward as key area in various age-related and neurodevelopmental diseases. The DRN is further thought to be related to stress regulated processes and cognitive events. It is involved in neurodegeneration, e.g., amyloid plaques, neurofibrillary tangles, and impaired synaptic transmission in Alzheimer's disease as shown in our autopsy findings. The DRN is a phylogenetically old brain area, with projections that reach out to a large number of regions and nuclei of the central nervous system, particularly in the forebrain. These ascending projections contain multiple neurotransmitters. One of the main reasons for the past and current interest in the DRN is its involvement in depression, and its main transmitter serotonin. The DRN also points toward the increased importance and focus of the brainstem as key area in various age-related and neurodevelopmental diseases. This review describes the morphology, ascending projections and the complex neurotransmitter nature of the DRN, stressing its role as a key research target into the neural bases of depression.

A comparison of cell density and serotonergic innervation of the amygdala among four macaque species

The genus Macaca is an ideal model for investigating the biological basis of primate social behavior from an evolutionary perspective. A significant amount of behavioral diversity has been reported among the macaque species, but little is known about the neural substrates that support this variation. The present study compared neural cell density and serotonergic innervation of the amygdala among four macaque species using histological and immunohistochemical methods. The species examined included rhesus (Macaca mulatta), Japanese (M. fuscata), pigtailed (M. nemestrina), and moor macaques (M. maura). We anticipated that the more aggressive rhesus and Japanese macaques would have lower serotonergic innervation within the amygdala compared to the more affiliative pigtailed and moor macaques. In contrast to our prediction, pigtailed macaques had higher serotonergic innervation than Japanese and moor macaques in the basal and central amygdala nuclei when controlling for neuron density. Our analysis of neural cell populations revealed that Japanese macaques possess significantly higher neuron and glia densities relative to the other three species, however we observed no glia-to-neuron ratio differences among species. The results of this study revealed serotonergic innervation and cell density differences among closely related macaque species, which may play a role in modulating subtle differences in emotional processing and species-typical social styles.

Serotonergic innervation of the human amygdala and evolutionary implications

OBJECTIVES

The serotonergic system is involved in the regulation of socio-emotional behavior and heavily innervates the amygdala, a key structure of social brain circuitry. We quantified serotonergic axon density of the four major nuclei of the amygdala in humans, and examined our results in light of previously published data sets in chimpanzees and bonobos.

MATERIALS AND METHODS

Formalin-fixed postmortem tissue sections of the amygdala from six humans were stained for serotonin transporter (SERT) utilizing immunohistochemistry. SERT-immunoreactive (ir) axon fiber density in the lateral, basal, accessory basal, and central nuclei of the amygdala was quantified using unbiased stereology. Nonparametric statistical analyses were employed to examine differences in SERT-ir axon density between amygdaloid nuclei within humans, as well as differences between humans and previously published data in chimpanzees and bonobos.

RESULTS

Humans displayed a unique pattern of serotonergic innervation of the amygdala, and SERT-ir axon density was significantly greater in the central nucleus compared to the lateral nucleus. SERT-ir axon density was significantly greater in humans compared to chimpanzees in the basal, accessory basal, and central nuclei. SERT-ir axon density was greater in humans compared to bonobos in the accessory basal and central nuclei.

CONCLUSIONS

The human pattern of SERT-ir axon distribution in the amygdala complements the redistribution of neurons in the amygdala in human evolution. The present findings suggest that differential serotonergic modulation of cognitive and autonomic pathways in the amygdala in humans, bonobos, and chimpanzees may contribute to species-level differences in social behavior.

Cyto- and Myelo-Architecture of the Amygdaloid Complex of the Common Marmoset Monkey (Callithrix jacchus)

The amygdaloid complex (AC) is a heterogeneous aggregate of nuclei located in the rostromedial region of the temporal lobe. In addition to being partly connected among themselves, the AC nuclei are strongly interconnected with the cerebral cortex, striatum, basal forebrain, hypothalamus and brainstem. Animal and human functional studies have established that the AC is a central hub of the neuronal networks supporting emotional responsivity, particularly its negative/aversive components. Dysfunction of AC circuits in humans has been implicated in anxiety, depression, schizophrenia and bipolar disorder. The small New-World marmoset monkey (Callithrix jacchus) has recently become a key model for neuroscience research. However, the nuclear and fiber tract organization of marmoset AC has not been examined in detail. Thus, the extent to which it can be compared to the AC of Old-World (human and macaque) primates is yet unclear. Here, using Nissl and acetylcholinesterase (AChE) histochemical stains as a reference, we analyzed the cytoarchitecture and nuclear parcellation of the marmoset AC. In addition, given the increasing relevance of tractographic localization for high-resolution in vivo imaging studies in non-human primates, we also identified the myelin fiber tracts present within and around the AC as revealed by the Gallyas method. The present study provides a detailed atlas of marmoset AC. Moreover, it reveals that, despite phylogenetic distance and brain size differences, every nucleus and myelinated axon bundle described in human and macaque studies can be confidently recognized in marmosets.

Connectivity between the central nucleus of the amygdala and the bed nucleus of the stria terminalis in the non-human primate: neuronal tract tracing and developmental neuroimaging studies

The lateral division of the bed nucleus of the stria terminalis (BSTL) and central nucleus of the amygdala (Ce) form the two poles of the 'central extended amygdala', a theorized subcortical macrostructure important in threat-related processing. Our previous work in nonhuman primates, and humans, demonstrating strong resting fMRI connectivity between the Ce and BSTL regions, provides evidence for the integrated activity of these structures. To further understand the anatomical substrates that underlie this coordinated function, and to investigate the integrity of the central extended amygdala early in life, we examined the intrinsic connectivity between the Ce and BSTL in non-human primates using ex vivo neuronal tract tracing, and in vivo diffusion-weighted imaging and resting fMRI techniques. The tracing studies revealed that BSTL receives strong input from Ce; however, the reciprocal pathway is less robust, implying that the primate Ce is a major modulator of BSTL function. The sublenticular extended amygdala (SLEAc) is strongly and reciprocally connected to both Ce and BSTL, potentially allowing the SLEAc to modulate information flow between the two structures. Longitudinal early-life structural imaging in a separate cohort of monkeys revealed that extended amygdala white matter pathways are in place as early as 3 weeks of age. Interestingly, resting functional connectivity between Ce and BSTL regions increases in coherence from 3 to 7 weeks of age. Taken together, these findings demonstrate a time period during which information flow between Ce and BSTL undergoes postnatal developmental changes likely via direct Ce → BSTL and/or Ce ↔ SLEAc ↔ BSTL projections.

Whole-brain mapping of afferent projections to the bed nucleus of the stria terminalis in tree shrews

The bed nucleus of the stria terminalis (BST) plays an important role in integrating and relaying input information to other brain regions in response to stress. The cytoarchitecture of the BST in tree shrews (Tupaia belangeri chinensis) has been comprehensively described in our previous publications. However, the inputs to the BST have not been described in previous reports. The aim of the present study was to investigate the sources of afferent projections to the BST throughout the brain of tree shrews using the retrograde tracer Fluoro-Gold (FG). The present results provide the first detailed whole-brain mapping of BST-projecting neurons in the tree shrew brain. The BST was densely innervated by the prefrontal cortex, entorhinal cortex, ventral subiculum, amygdala, ventral tegmental area, and parabrachial nucleus. Moreover, moderate projections to the BST originated from the medial preoptic area, supramammillary nucleus, paraventricular thalamic nucleus, pedunculopontine tegmental nucleus, dorsal raphe nucleus, locus coeruleus, and nucleus of the solitary tract. Afferent projections to the BST are identified in the ventral pallidum, nucleus of the diagonal band, ventral posteromedial thalamic nucleus, posterior complex of the thalamus, interfascicular nucleus, retrorubral field, rhabdoid nucleus, intermediate reticular nucleus, and parvicellular reticular nucleus. In addition, the different densities of BST-projecting neurons in various regions were analyzed in the tree shrew brains. In summary, whole-brain mapping of direct inputs to the BST is delineated in tree shrews. These brain circuits are implicated in the regulation of numerous physiological and behavioral processes including stress, reward, food intake, and arousal.

Pattern of distribution of serotonergic fibers to the amygdala and extended amygdala in the rat

As is well recognized, serotonergic (5-HT) fibers distribute widely throughout the forebrain, including the amygdala. Although a few reports have examined the 5-HT innervation of select nuclei of the amygdala in the rat, no previous report has described overall 5-HT projections to the amygdala in the rat. Using immunostaining for the serotonin transporter, SERT, we describe the complete pattern of distribution of 5-HT fibers to the amygdala (proper) and to the extended amygdala in the rat. Based on its ontogenetic origins, the amygdala was subdivided into two major parts, pallial and subpallial components, with the pallial component further divided into superficial and deep nuclei (Olucha-Bordonau et al. 2015). SERT⁺ fibers were shown to distributed moderately to densely to the deep and cortical pallial nuclei, but, by contrast, lightly to the subpallial nuclei. Specifically, 1) of the deep pallial nuclei, the lateral, basolateral, and basomedial nuclei contained a very dense concentration of 5-HT fibers; 2) of the cortical pallial nuclei, the anterior cortical and amygdala-cortical transition zone rostrally and the posteromedial and posterolateral nuclei caudally contained a moderate concentration of 5-HT fibers; and 3) of the subpallial nuclei, the anterior nuclei and the rostral part of the medial (Me) nuclei contained a moderate concentration of 5-HT fibers, whereas caudal regions of Me as well as the central nuclei and the intercalated nuclei contained a sparse/light concentration of 5-HT fibers. With regard to the extended amygdala (primarily the bed nucleus of stria terminalis; BST), on the whole, the BST contained moderate numbers of 5-HT fibers, spread fairly uniformly throughout BST. The findings are discussed with respect to a critical serotonergic influence on the amygdala, particularly on the basal complex, and on the extended amygdala in the control of states of fear and anxiety. J. Comp. Neurol. 525:116-139, 2017. © 2016 Wiley Periodicals, Inc.

Distinct effect of 5-HT1A and 5-HT2A receptors in the medial nucleus of the amygdala on tonic immobility behavior

The tonic immobility (TI) response is an innate fear behavior associated with intensely dangerous situations, exhibited by many species of invertebrate and vertebrate animals. In humans, it is possible that TI predicts the severity of posttraumatic stress disorder symptoms. This behavioral response is initiated and sustained by the stimulation of various groups of neurons distributed in the telencephalon, diencephalon and brainstem. Previous research has found the highest Fos-IR in the posteroventral part of the medial nucleus of the amygdala (MEA) during TI behavior; however, the neurotransmission of this amygdaloid region involved in the modulation of this innate fear behavior still needs to be clarified. Considering that a major drug class used for the treatment of psychopathology is based on serotonin (5-HT) neurotransmission, we investigated the effects of serotonergic receptor activation in the MEA on the duration of TI. The results indicate that the activation of the 5HT1A receptors or the blocking of the 5HT2 receptors of the MEA can promote a reduction in fear and/or anxiety, consequently decreasing TI duration in guinea pigs. In contrast, blocking the 5HT1A receptors or activating the 5HT2 receptors in this amygdalar region increased the TI duration, suggesting an increase in fear and/or anxiety. These alterations do not appear to be due to a modification of spontaneous motor activity, which might non-specifically affect TI duration. Thus, these results suggest a distinct role of the 5HT receptors in the MEA in innate fear modulation.

Differential serotonergic innervation of the amygdala in bonobos and chimpanzees

Humans' closest living relatives are bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), yet these great ape species differ considerably from each other in terms of social behavior. Bonobos are more tolerant of conspecifics in competitive contexts and often use sexual behavior to mediate social interactions. Chimpanzees more frequently employ aggression during conflicts and actively patrol territories between communities. Regulation of emotional responses is facilitated by the amygdala, which also modulates social decision-making, memory and attention. Amygdala responsiveness is further regulated by the neurotransmitter serotonin. We hypothesized that the amygdala of bonobos and chimpanzees would differ in its neuroanatomical organization and serotonergic innervation. We measured volumes of regions and the length density of serotonin transporter-containing axons in the whole amygdala and its lateral, basal, accessory basal and central nuclei. Results showed that accessory basal nucleus volume was larger in chimpanzees than in bonobos. Of particular note, the amygdala of bonobos had more than twice the density of serotonergic axons than chimpanzees, with the most pronounced differences in the basal and central nuclei. These findings suggest that variation in serotonergic innervation of the amygdala may contribute to mediating the remarkable differences in social behavior exhibited by bonobos and chimpanzees.

Distribution of dopamine transporter immunoreactive fibers in the human amygdaloid complex

The nuclei of the human amygdaloid complex can be distinguished from each other on the basis of their cytoarchitecture, chemistry and connections, all of which process the information needed for the different functions (ranging from attention to memory and emotion) of the amygdala. This complex receives dopaminergic input that exerts modulatory effects over its intrinsic network and is critical for reward-related learning and fear conditioning. To determine the specific distribution of the dopaminergic input through the different nuclei and nuclear subdivisions of this structure we used stereological tools to quantify the fibers containing the dopamine transporter (used to signal the dopaminergic phenotype) in post-mortem samples from control individuals. Dopaminergic axons targeted every nucleus of the amygdaloid complex, and the density of dopamine transporter-containing axons varied considerably among its nuclear groups. The central group showed the greatest density of dopamine transporter-positive fibers, more than double the density of the basolateral group, the second most densely innervated structure. The dopamine transporter-positive innervation is very scant in the corticomedial group. The density of dopamine transporter-positive fibers did not vary among the nuclei of the basolateral group - i.e. basal, lateral and accessory basal nuclei - although there were significant density gradients among the subdivisions of these nuclei. These detailed quantitative data on dopamine transporter-positive innervation in the human amygdaloid complex can offer a useful reference in future studies aimed at analysing putative dysfunctions of this system in diseases involving brain dopamine, such as certain anxiety disorders, Parkinson's disease and schizophrenia.

The role of the dorsal raphé nucleus in reward-seeking behavior

Pharmacological experiments have shown that the modulation of brain serotonin levels has a strong impact on value-based decision making. Anatomical and physiological evidence also revealed that the dorsal raphé nucleus (DRN), a major source of serotonin, and the dopamine system receive common inputs from brain regions associated with appetitive and aversive information processing. The serotonin and dopamine systems also have reciprocal functional influences on each other. However, the specific mechanism by which serotonin affects value-based decision making is not clear. To understand the information carried by the DRN for reward-seeking behavior, we measured single neuron activity in the primate DRN during the performance of saccade tasks to obtain different amounts of a reward. We found that DRN neuronal activity was characterized by tonic modulation that was altered by the expected and received reward value. Consistent reward-dependent modulation across different task periods suggested that DRN activity kept track of the reward value throughout a trial. The DRN was also characterized by modulation of its activity in the opposite direction by different neuronal subgroups, one firing strongly for the prediction and receipt of large rewards, with the other firing strongly for small rewards. Conversely, putative dopamine neurons showed positive phasic responses to reward-indicating cues and the receipt of an unexpected reward amount, which supports the reward prediction error signal hypothesis of dopamine. I suggest that the tonic reward monitoring signal of the DRN, possibly together with its interaction with the dopamine system, reports a continuous level of motivation throughout the performance of a task. Such a signal may provide "reward context" information to the targets of DRN projections, where it may be integrated further with incoming motivationally salient information.

The influence of serotonin on fear learning

Learning of associations between aversive stimuli and predictive cues is the basis of Pavlovian fear conditioning and is driven by a mismatch between expectation and outcome. To investigate whether serotonin modulates the formation of such aversive cue-outcome associations, we used functional magnetic resonance imaging (fMRI) and dietary tryptophan depletion to reduce brain serotonin (5-HT) levels in healthy human subjects. In a Pavlovian fear conditioning paradigm, 5-HT depleted subjects compared to a non-depleted control group exhibited attenuated autonomic responses to cues indicating the upcoming of an aversive event. These results were closely paralleled by reduced aversive learning signals in the amygdala and the orbitofrontal cortex, two prominent structures of the neural fear circuit. In agreement with current theories of serotonin as a motivational opponent system to dopamine in fear learning, our data provide first empirical evidence for a role of serotonin in representing formally derived learning signals for aversive events.

Evidence for coordinated functional activity within the extended amygdala of non-human and human primates

Neuroanatomists posit that the central nucleus of the amygdala (Ce) and bed nucleus of the stria terminalis (BST) comprise two major nodes of a macrostructural forebrain entity termed the extended amygdala. The extended amygdala is thought to play a critical role in adaptive motivational behavior and is implicated in the pathophysiology of maladaptive fear and anxiety. Resting functional connectivity of the Ce was examined in 107 young anesthetized rhesus monkeys and 105 young humans using standard resting-state functional magnetic resonance imaging (fMRI) methods to assess temporal correlations across the brain. The data expand the neuroanatomical concept of the extended amygdala by finding, in both species, highly significant functional coupling between the Ce and the BST. These results support the use of in vivo functional imaging methods in nonhuman and human primates to probe the functional anatomy of major brain networks such as the extended amygdala.

Understanding behavioral effects of early life stress using the reactive scope and allostatic load models

The mechanisms through which early life stress leads to psychopathology are thought to involve allostatic load, the "wear and tear" an organism is subjected to as a consequence of sustained elevated levels of glucocorticoids caused by repeated/prolonged stress activations. The allostatic load model described this phenomenon, but has been criticized as inadequate to explain alterations associated with early adverse experience in some systems, including behavior, which cannot be entirely explained from an energy balance perspective. The reactive scope model has been more recently proposed and focuses less on energy balance and more on dynamic ranges of physiological and behavioral mediators. In this review we examine the mechanisms underlying the behavioral consequences of early life stress in the context of both these models. We focus on adverse experiences that involve mother-infant relationship disruption, and dissect those mechanisms involving maternal care as a regulator of development of neural circuits that control emotional and social behaviors in the offspring. We also discuss the evolutionary purpose of the plasticity in behavioral development, which has a clear adaptive value in a changing environment.

Phasic and sustained fear are pharmacologically dissociable in rats

Previous findings suggest differences in the neuroanatomical substrates of short- (seconds) vs longer-duration (minutes) fear responses. We now report that phasic and sustained fear can also be differentiated pharmacologically, based on their response to several treatments that either are or are not clinically effective anxiolytics. For these experiments, short- or long-duration clicker stimuli were paired with footshock. Acoustic startle amplitude was later measured in the absence of the clicker, or within seconds (phasic fear) or minutes (sustained fear) of its onset. Before testing, rats received a single injection of vehicle, the benzodiazepine chlordiazepoxide, the 5HT(1A) agonist and dopamine D2 antagonist buspirone, the selective serotonin reuptake inhibitor fluoxetine, or a 3-week treatment with either vehicle or fluoxetine. Chlordiazepoxide blocked sustained, but not phasic startle increases. Acute buspirone, which is not anxiolytic in human beings, did not affect sustained startle increases, but did disrupt phasic increases. Chronic fluoxetine blocked sustained startle increases and unreliably reduced phasic increases; acute fluoxetine affected neither. The results indicate that phasic and sustained fear responses can be pharmacologically dissociated, further validating this distinction, and suggest that sustained startle increases may be especially useful as anxiety models and anxiolytic screens.

Distribution of 5-HT2A receptor immunoreactivity in the rat amygdaloid complex and colocalization with γ-aminobutyric acid

The 5-HT2A receptor (5-HT2Ar) is located in a variety of excitatory and inhibitory neurons in many regions of the central nervous system and is a major target for atypical antipsychotic drugs. In the present study, an immunoperoxidase experiment was used to investigate the distribution of 5-HT2Ar immunoreactivity in the rat amygdaloid complex. In the basolateral amygdala, the colocalization of 5-HT2Ar with inhibitory transmitter γ-aminobutyric acid (GABA) was studied using double-immunofluorescence confocal microscopy. The staining pattern obtained was colchicine-sensitive. In fact, pretreatment with colchicine increased the number of 5-HT2Ar-immunoreactive somata. Accordingly, with the exception of the intercalated nuclei, the amygdaloid complex of colchicine-injected rats exhibited a high density of 5-HT2Ar-IR somata. Morphological analyses indicated that 5-HT2Ar was located on both excitatory and inhibitory neurons in the rat amygdaloid complex. In addition, double-immunofluorescence observations revealed that the great majority of GABA-immunoreactive neurons in the basolateral amygdala exhibited 5-HT2Ar immunoreactivity (66.3%-70.6% depending on the nucleus). These data help to clarify the complex role of the 5-HT2Ar in the amygdaloid complex suggesting that this receptor can regulate amygdaloid activity by acting on different neuronal populations.

Coding of task reward value in the dorsal raphe nucleus

The dorsal raphe nucleus and its serotonin-releasing neurons are thought to regulate motivation and reward-seeking. These neurons are known to be active during motivated behavior, but the underlying principles that govern their activity are unknown. Here we show that a group of dorsal raphe neurons encode behavioral tasks in a systematic manner, tracking progress toward upcoming rewards. We analyzed dorsal raphe neuron activity recorded while animals performed two reward-oriented saccade tasks. There was a strong correlation between the tonic activity level of a neuron during behavioral tasks and its encoding of reward-related cues and outcomes. Neurons that were tonically excited during the task predominantly carried positive reward signals. Neurons that were tonically inhibited during the task predominantly carried negative reward signals. Neurons that did not change their tonic activity levels during the task had weak reward signals with no tendency for a positive or negative direction. This form of correlated task and reward coding accounted for the majority of systematic variation in dorsal raphe response patterns in our tasks. A smaller component of neural activity reflected detection of reward delivery. Our data suggest that the dorsal raphe nucleus encodes participation in a behavioral task in terms of its future motivational outcomes.

Cognitive impact of genetic variation of the serotonin transporter in primates is associated with differences in brain morphology rather than serotonin neurotransmission

A powerful convergence of genetics, neuroimaging and epidemiological research has identified the biological pathways mediating individual differences in complex behavioral processes and the related risk for disease. Orthologous genetic variation in non-human primates (NHPs) represents a unique opportunity to characterize the detailed molecular and cellular mechanisms that bias behaviorally and clinically relevant brain function. We report that a rhesus macaque orthologue of a common polymorphism of the serotonin transporter gene (rh5-HTTLPR) has strikingly similar effects on behavior and brain morphology to those in humans. Specifically, the rh5-HTTLPR (S)hort allele broadly affects cognitive choice behavior and brain morphology without observably affecting the 5-hydroxytryptamine (5-HT) transporter or 5-HT(1A) concentrations in vivo. Collectively, our findings indicate that 5-HTTLPR-associated behavioral effects reflect genotype-dependent biases in cortical development rather than static differences in serotonergic signaling mechanisms. Moreover, these data highlight the vast potential of NHP models in advancing our understanding of human genetic variation affecting behavior and neuropsychiatric disease liability.

Effect of tryptophan hydroxylase-2 gene variants on amygdalar and hippocampal volumes

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of serotonin (5-HT). Genetic variations in human TPH2, a newly identified isoform of TPH, have been shown to impact on enzymatic activity of TPH and to be associated with emotion-related personality traits and mood/anxiety disorders. Identification of an intermediate phenotype that bridges the relationship between genes and behavior may be of great importance in the further clarification of how hTPH2 contributes to emotional regulation. Previous studies have shown that a polymorphism in the upstream regulatory region of hTPH2 (SNP G-703T, rs4570625) correlates functional MRI response of the amygdala. In this study, we examined the effect of this genotype on amygdalar and hippocampal volumes in 208 mentally healthy individuals. To measure volumes of amygdala and hippocampus, gray matter regions of interest were outlined manually on three-dimensional MRI data obtained using a 1.5-T scanner. Additionally, personality traits were evaluated using the Temperament and Character Inventory (TCI). Those subjects with T allele carriers were associated with significantly smaller volumes in bilateral amygdala and hippocampus and higher reward dependence than those with G allele homozygotes. These results suggest that amygdalar and hippocampal volumes assessed using MRI may be a useful intermediate phenotype that will uncover the biological pathway linking 5-HT synthesis and emotional behaviors and affective disorders.

The response of neurons in the bed nucleus of the stria terminalis to serotonin: implications for anxiety

Substantial evidence has suggested that the activity of the bed nucleus of the stria terminalis (BNST) mediates many forms of anxiety-like behavior in human and non-human animals. These data have led many investigators to suggest that abnormal processing within this nucleus may underlie anxiety disorders in humans, and effective anxiety treatments may restore normal BNST functioning. Currently some of the most effective treatments for anxiety disorders are drugs that modulate serotonin (5-HT) systems, and several decades of research have suggested that the activation of 5-HT can modulate anxiety-like behavior. Despite these facts, relatively few studies have examined how activity within the BNST is modulated by 5-HT. Here we review our own investigations using in vitro whole-cell patch-clamp electrophysiological methods on brain sections containing the BNST to determine the response of BNST neurons to exogenous 5-HT application. Our data suggest that the response of BNST neurons to 5-HT is complex, displaying both inhibitory and excitatory components, which are mediated by 5-HT(1A), 5-HT(2A), 5-HT(2C) and 5-HT(7) receptors. Moreover, we have shown that the selective activation of the inhibitory response to 5-HT reduces anxiety-like behavior, and we describe data suggesting that the activation of the excitatory response to 5-HT may be anxiogenic. We propose that in the normal state, the function of 5-HT is to dampen activity within the BNST (and consequent anxiety-like behavior) during exposure to threatening stimuli; however, we suggest that changes in the balance of the function of BNST 5-HT receptor subtypes could alter the response of BNST neurons to favor excitation and produce a pathological state of increased anxiety.

Heterogeneous dopamine populations project to specific subregions of the primate amygdala

Amygdala dysfunction has been reported among patients with various psychiatric disorders, and dopamine is critical to the amygdala's ability to mediate fear conditioning. Recent work indicates that the midbrain dopaminergic neurons have heterogeneous receptor and membrane channel profiles, as well as differential physiologic responses to discrete stimuli. To begin understanding how dopamine affects amygdala physiology and pathology in higher primates, we mapped the inputs from the midbrain dopaminergic neurons to various amygdala nuclei in the monkey using retrograde and anterograde tracing techniques, and single and double immunofluorescence histochemistry for tracer and tyrosine hydroxylase, a dopamine marker. Our results show that the primate amygdala as a whole receives broad input, mostly from the dorsal tier of the substantia nigra, pars compacta, and the A8-retrorubral field. Input from the A10-ventral tegmental area, while present, was less prominent. These results differ from data in the rat, where the midline A10-ventral tegmental area is a major source of dopamine to the amygdala "mesolimbic" pathway. Both the "amygdala proper" and the "extended amygdala" receive the majority of their input from the dorsal tier of the substantia nigra and A8-retrorubral field, but the extended amygdala receives additional modest input from the ventral tier. In addition, the "extended amygdala" structures have a denser input than the "amygdala proper," with the exception of the lateral core of the central nucleus, which receives no input. Our anterograde studies confirm these findings, and revealed fine, diffuse terminal fibers in the amygdala proper, but a denser network of fibers in the extended amygdala outside the lateral core of the central nucleus. These results indicate that the entire extent of the dorsal tier beyond the A10-ventral tegmental area may regulate the amygdala in primates, and subsequently serve as a source of dysfunction in primate psychopathology.

Bi-directional modulation of bed nucleus of stria terminalis neurons by 5-HT: molecular expression and functional properties of excitatory 5-HT receptor subtypes

Activation of neurons in the anterolateral bed nucleus of the stria terminalis (BNST(ALG)) plays an important role in mediating the behavioral response to stressful and anxiogenic stimuli. Application of 5-HT elicits complex postsynaptic responses in BNST(ALG) neurons, which includes (1) membrane hyperpolarization (5-HT(Hyp)), (2) hyperpolarization followed by depolarization (5-HT(Hyp-Dep)), (3) depolarization (5-HT(Dep)) or (4) no response (5-HT(NR)). We have shown that the inhibitory response is mediated by activation of postsynaptic 5-HT(1A) receptors. Here, we used a combination of in vitro whole-cell patch-clamp recording and single cell reverse transcriptase polymerase chain reaction (RT-PCR) to determine the pharmacological properties and molecular profile of 5-HT receptor subtypes mediating the excitatory response to 5-HT in BNST(ALG) neurons. We show that the depolarizing component of both the 5-HT(Hyp/Dep) and the 5-HT(Dep) response was mediated by activation of 5-HT(2A), 5-HT(2C) and/or 5-HT(7) receptors. Single cell RT-PCR data revealed that 5-HT(7) receptors (46%) and 5-HT(1A) receptors (41%) are the most prevalent receptor subtypes expressed in BNST(ALG) neurons. Moreover, 5-HT receptor subtypes are differentially expressed in type I-III BNST(ALG) neurons. Hence, 5-HT(2C) receptors are almost exclusively expressed by type III neurons, whereas 5-HT(7) receptors are expressed by type I and II neurons, but not type III neurons. Conversely, 5-HT(2A) receptors are found predominantly in type II neurons. Finally, bi-directional modulation of individual neurons occurs only in type I and II neurons. Significantly the distribution of 5-HT receptor subtypes in BNST(ALG) neurons predicted the observed expression pattern of 5-HT responses determined pharmacologically. Together, these results suggest that 5-HT can differentially modulate the excitability of type I-III neurons, and further suggest that bi-directional modulation of BNST(ALG) neurons occurs primarily through an interplay between 5-HT(1A) and 5-HT(7) receptors. Hence, modulation of 5-HT(7) receptor activity in the BNST(ALG) may offer a novel avenue for the design of anxiolytic medications.

Serotonin transporter availability in the amygdala and bed nucleus of the stria terminalis predicts anxious temperament and brain glucose metabolic activity

The serotonin transporter (5-HTT) plays a critical role in regulating serotonergic neurotransmission and is implicated in the pathophysiology of anxiety and affective disorders. Positron emission tomography scans using [(11)C]DASB [(11)C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile] to measure 5-HTT availability (an index of receptor density and binding) were performed in 34 rhesus monkeys in which the relationship between regional brain glucose metabolism and anxious temperament was previously established. 5-HTT availability in the amygdalohippocampal area and bed nucleus of the stria terminalis correlated positively with individual differences in a behavioral and neuroendocrine composite of anxious temperament. 5-HTT availability also correlated positively with stress-induced metabolic activity within these regions. Collectively, these findings suggest that serotonergic modulation of neuronal excitability in the neural circuitry associated with anxiety mediates the developmental risk for affect-related psychopathology.

Subcellular localization of the antidepressant-sensitive norepinephrine transporter

BACKGROUND

Reuptake of synaptic norepinephrine (NE) via the antidepressant-sensitive NE transporter (NET) supports efficient noradrenergic signaling and presynaptic NE homeostasis. Limited, and somewhat contradictory, information currently describes the axonal transport and localization of NET in neurons.

RESULTS

We elucidate NET localization in brain and superior cervical ganglion (SCG) neurons, aided by a new NET monoclonal antibody, subcellular immunoisolation techniques and quantitative immunofluorescence approaches. We present evidence that axonal NET extensively colocalizes with syntaxin 1A, and to a limited degree with SCAMP2 and synaptophysin. Intracellular NET in SCG axons and boutons also quantitatively segregates from the vesicular monoamine transporter 2 (VMAT2), findings corroborated by organelle isolation studies. At the surface of SCG boutons, NET resides in both lipid raft and non-lipid raft subdomains and colocalizes with syntaxin 1A.

CONCLUSION

Our findings support the hypothesis that SCG NET is segregated prior to transport from the cell body from proteins comprising large dense core vesicles. Once localized to presynaptic boutons, NET does not recycle via VMAT2-positive, small dense core vesicles. Finally, once NET reaches presynaptic plasma membranes, the transporter localizes to syntaxin 1A-rich plasma membrane domains, with a portion found in cholera toxin-demarcated lipid rafts. Our findings indicate that activity-dependent insertion of NET into the SCG plasma membrane derives from vesicles distinct from those that deliver NE. Moreover, NET is localized in presynaptic membranes in a manner that can take advantage of regulatory processes targeting lipid raft subdomains.

Amygdala projections to central amygdaloid nucleus subdivisions and transition zones in the primate

In rats and primates, the central nucleus of the amygdala (CeN) is most known for its role in responses to fear stimuli. Recent evidence also shows that the CeN is required for directing attention and behaviors when the salience of competing stimuli is in flux. To examine how information flows through this key output region of the primate amygdala, we first placed small injections of retrograde tracers into the subdivisions of the central nucleus in Old world primates, and examined inputs from specific amygdaloid nuclei. The amygdalostriatal area and interstitial nucleus of the posterior limb of the anterior commissure (IPAC) were distinguished from the CeN using histochemical markers, and projections to these regions were also described. As expected, the basal nucleus and accessory basal nucleus are the main afferent connections of the central nucleus and transition zones. The medial subdivision of the central nucleus (CeM) receives a significantly stronger input from all regions compared to the lateral core subdivision (CeLcn). The corticoamygdaloid transition zone (a zone of confluence of the medial parvicellular basal nucleus, paralaminar nucleus, and the sulcal periamygdaloid cortex) provides the main input to the CeLcn. The IPAC and amygdalostriatal area can be divided in medial and lateral subregions, and receive input from the basal and accessory basal nucleus, with differential inputs according to subdivision. The piriform cortex and lateral nucleus, two important sensory interfaces, send projections to the transition zones. In sum, the CeM receives broad inputs from the entire amygdala, whereas the CeLcn receives more restricted inputs from the relatively undifferentiated corticoamygdaloid transition region. Like the CeN, the transition zones receive most of their input from the basal nucleus and accessory basal nucleus, however, inputs from the piriform cortex and lateral nucleus, and a lack of input from the parvicellular accessory basal nucleus, are distinguishing afferent features.

The comparative distributions of the monoamine transporters in the rodent, monkey, and human amygdala

The monoamines in the amygdala modulate multiple aspects of emotional processing in the mammalian brain, and organic or pharmacological dysregulation of these systems can result in affective pathologies. Knowledge of the normal distribution of these neurotransmitters, therefore, is central to our understanding of both the normal processes regulated by the amygdala and the pathological conditions associated with monoaminergic dysregulation. The monoaminergic transporters have proven to be accurate and reliable markers of the distributions of their substrates. The purpose of this review was twofold: First, to briefly recount the functional relevance of dopamine, serotonin, and norepinephrine transmission in the amygdala, and second, to describe and compare the distributions of the monoamine transporters in the rodent, monkey, and human brain. The transporters were found to be heterogeneously distributed in the amygdala. The dopamine transporter (DAT) is consistently found to be extremely sparsely distributed, however the various accounts of its subregional topography are inconsistent, making any cross-species comparisons difficult. The serotonin transporter (SERT) had the greatest overall degree of labeling of the three markers, and was characterized by substantial inter-species variability in its relative distribution. The norepinephrine transporter (NET) was shown to possess an intermediate level of labeling, and like the SERT, its distribution is not consistent across the three species. The results of these comparisons indicate that caution should be exercised when using animal models to investigate the complex processes modulated by the monoamines in the amygdala, as their relative contributions to these functions may differ across species.

The dorsal raphe nucleus—From silver stainings to a role in depression

Over a hundred years ago, Santiago Ramón y Cajal used a new staining method developed by Camillo Golgi to visualize, among many other structures, what we today call the dorsal raphe nucleus (DRN) of the midbrain. Over the years, the DRN has emerged as a multifunctional and multitransmitter nucleus, which modulates or influences many CNS processes. It is a phylogenetically old brain area, whose projections reach out to a large number of regions and nuclei of the CNS, particularly in the forebrain. Several DRN-related discoveries are tightly connected with important events in the history of neuroscience, for example the invention of new histological methods, the discovery of new neurotransmitter systems and the link between neurotransmitter function and mood disorders. One of the main reasons for the wide current interest in the DRN is the nucleus' involvement in depression. This involvement is particularly attributable to the main transmitter of the DRN, serotonin. Starting with a historical perspective, this essay describes the morphology, ascending projections and multitransmitter nature of the DRN, and stresses its role as a key target for depression research.

Amygdala-prefrontal disconnection in borderline personality disorder

Abnormal fronto-amygdala circuitry has been implicated in impulsive aggression, a core symptom of borderline personality disorder (BPD). We examined relative glucose metabolic rate (rGMR) at rest and after m-CPP (meta-chloropiperazine) with (18)fluorodeoxyglucose (FDG) with positron emission tomography (PET) in 26 impulsive aggressive (IED)-BPD patients and 24 controls. Brain edges/amygdala were visually traced on MRI scans co-registered to PET scans; rGMR was obtained for ventral and dorsal regions of the amygdala and Brodmann areas within the prefrontal cortex (PFC). Correlation coefficients were calculated between rGMR for dorsal/ventral amygdala regions and PFC. Additionally, amygdala volumes and rGMR were examined in BPD and controls. Correlations PFC/amygdala Placebo: Controls showed significant positive correlations between right orbitofrontal (OFC) and ventral, but not dorsal, amygdala. Patients showed only weak correlations between amygdala and the anterior PFC, with no distinction between dorsal and ventral amygdala. Correlations PFC/amygdala: m-CPP response: Controls showed positive correlations between OFC and amygdala regions, whereas patients showed positive correlations between dorsolateral PFC and amygdala. Group differences between interregional correlational matrices were highly significant. Amygdala volume/metabolism: No group differences were found for amygdala volume, or metabolism in the placebo condition or in response to meta-chloropiperazine (m-CPP). We demonstrated a tight coupling of metabolic activity between right OFC and ventral amygdala in healthy subjects with dorsoventral differences in amygdala circuitry, not present in IED-BPD. We demonstrated no significant differences in amygdala volumes or metabolism between BPD patients and controls.

Puberty, hormones, and sex differences in alcohol abuse and dependence

Sex differences in patterns of drinking and rates of alcohol abuse and dependence begin to emerge during the transition from late puberty to young adulthood. Increases in pubertal hormones, including gonadal and stress hormones, are a prominent developmental feature of adolescence and could contribute to the progression of sex differences in alcohol drinking patterns during puberty. This paper reviews experimental and correlational studies of gonadal and stress-related hormone changes and their effects on alcohol drinking and other associated actions of alcohol. Mechanisms are suggested by which reproductive hormones and stress-related hormones may modulate neural circuits within the brain reward system to produce sex differences in alcohol drinking patterns and vulnerability to alcohol abuse and dependence which become apparent during the late pubertal period.

Distribution of serotonin transporter labeled fibers in amygdaloid subregions: implications for mood disorders

BACKGROUND

The serotonin transporter 5-HTT mediates responses to serotonin reuptake inhibitors (SSRIs), a mainstay treatment in mood disorders. The amygdala, a key emotional processing center, has functional abnormalities in mood disorders, which resolve following successful SSRI treatment. To better understand the effects of SSRIs in mood disorders, we examined the distribution of 5-HTT labeled fibers relative to specific nuclear groups in the amygdala.

METHODS

Immunocytochemical techniques were used to chart 5-HTT labeled fibers in the amygdala in coronal sections through the brain of six adult Macaques. Nissl staining was used to define nuclear groups in the amygdala.

RESULTS

The serotonin transporter 5-HTT is distributed heterogeneously in the primate amygdala, with the lateral subdivision of the central nucleus, intercalated cell islands, amygdalohippocampal area, and the paralaminar nucleus showing the heaviest concentrations.

CONCLUSIONS

5HTT-labeled fibers are very densely concentrated in output regions of the amygdala. High concentrations of 5-HTT-positive fibers in the central nucleus indicate that tight regulation of serotonin is critical in modulating fear responses mediated by this nucleus. High concentrations of 5-HTT-labeled fibers in the intercalated islands and parvicellular basal nucleus/paralaminar nucleus, which contain immature -appearing neurons, suggest a potential trophic role for serotonin in these subregions.

Serotonergic modulation of the limbic system

The limbic system is composed of cortical as well as subcortical structures, which are intimately interconnected. The resulting macrostructure is responsible for the generation and expression of motivational and affective states. Especially high levels of serotonin are found in limbic forebrain structures. Serotonin projections to these structures, which arise from serotonergic cell body groups in the midbrain, form a dense plexus of axonal processes. In many areas of the limbic system, serotonergic neurotransmission can best be described as paracrine or volume transmission, and thus serotonin is believed to play a neuromodulatory role in the brain. Serotonergic projections to limbic structures, arising primarily from the dorsal and median raphe nuclei, compose two distinct serotonergic systems differing in their topographic organization, electrophysiological characteristics, morphology, as well as sensitivity to neurotoxins and perhaps psychoactive or therapeutic agents. These differences may be extremely important in understanding the role of these two serotonergic systems in normal brain function and in mental illness. Central serotonergic neurons or receptors are targets for a variety of therapeutic agents used in the treatment of disorders of the limbic system.

Norepinephrine modulates glutamatergic transmission in the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) and its adrenergic input are key components in stress-induced reinstatement and maintenance of drug use. Intra-BNST injections of either beta-adrenergic receptor (beta-AR) antagonists or alpha2-adrenergic receptor (alpha2-AR) agonists can inhibit footshock-induced reinstatement and maintenance of cocaine- and morphine-seeking. Using electrophysiological recording methods in an in vitro slice preparation from C57/Bl6j adult male mouse BNST, we have examined the effects of adrenergic receptor activation on excitatory synaptic transmission in the lateral dorsal supracommissural BNST (dBNST) and subcommissural BNST (vBNST). Alpha2-AR activation via UK-14,304 (10 microM) results in a decrease in excitatory transmission in both dBNST and vBNST, an effect predominantly dependent upon the alpha2A-AR subtype. Beta-AR activation via isoproterenol (1 microM) results in an increase in excitatory transmission in dBNST, but not in vBNST. Consistent with the work with receptor subtype specific agonists, application of the endogenous ligand norepinephrine (NE, 100 microM) elicits two distinct effects on glutamatergic transmission. In dBNST, NE elicits an increase in transmission (62% of dBNST NE experiments) or a decrease in transmission (38% of dBNST NE experiments). In vBNST, NE elicits a decrease in transmission in 100% of the experiments. In dBNST, the NE-induced increase in synaptic transmission is blocked by beta1/beta2- and beta2-, but not beta1-specific antagonists. In addition, this increase is also reduced by the alpha2-AR antagonist yohimbine and is absent in the alpha2A-AR knockout mouse. In vBNST, the NE-induced decrease in synaptic transmission is markedly reduced in the alpha2A-AR knockout mouse. Further experiments demonstrate that the actions of NE on glutamatergic transmission can be correlated with beta-AR function.

Serotonin fibre densities in subcortical areas: differential effects of isolated rearing and methamphetamine

Serotoninergic neurons interact with dopaminergic cells on all levels and are physiologically affected by both isolated rearing (IR) and a single early methamphetamine (MA) injection. We therefore checked for anatomical effects of both interventions by immunohistochemically staining serotonin fibres and assessing fibre densities in the caudate-putamen (CPu), nucleus accumbens (NAc) and amygdala of Mongolian gerbils. IR led to significantly increased 5-HT fibre densities in the dorsal part of the CPu and in the central and basolateral amygdala. No effects were seen in the ventral CPu, in the NAc and in the lateral amygdala. The early MA injection resulted in a denser 5-HT innervation in the dorsomedial and ventromedial CPu, in the NAc shell of animals reared in an enriched environment and in the NAc core of both rearing conditions, leaving the lateral CPu and the amygdala unaffected. Thus, the single pharmacological versus the environmental challenge exerts an almost complementary effect on the 5-HT innervation in different areas of the brain, which demonstrates that systemic interactions, e.g. with dopaminergic and glutamatergic afferents, must be taken into account when the seemingly uniform 5-HT projections are investigated.

Detecting subsecond dopamine release with fast-scan cyclic voltammetry in vivo

BACKGROUND

Dopamine is a potent neuromodulator in the brain, influencing a variety of motivated behaviors and involved in several neurologic diseases. Measurements of extracellular dopamine in the brains of experimental animals have traditionally focused on a tonic timescale (minutes to hours). However, dopamine concentrations are now known to fluctuate on a phasic timescale (subseconds to seconds).

APPROACH

Fast-scan cyclic voltammetry provides analytical chemical measurements of phasic dopamine signals in the rat brain.

CONTENT

Procedural aspects of the technique are discussed, with regard to appropriate use and in comparison with other methods. Finally, examples of data collected using fast-scan cyclic voltammetry are summarized, including naturally occurring dopamine transients and signals arising from electrical stimulation of dopamine neurons.

SUMMARY

Fast-scan cyclic voltammetry offers real-time measurements of changes in extracellular dopamine concentrations in vivo. With its subsecond time resolution, micrometer-dimension spatial resolution, and chemical selectivity, it is the most suitable technique currently available to measure transient concentration changes of dopamine.

Dorsal and ventral distribution of excitable and synaptic properties of neurons of the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) is a structure uniquely positioned to integrate stress information and regulate both stress and reward systems. Consistent with this arrangement, evidence suggests that the BNST, and in particular the noradrenergic input to this structure, is a key component of affective responses to drugs of abuse. We have utilized an in vitro slice preparation from adult mice to determine synaptic and membrane properties of these cells, focusing on the dorsal and ventral subdivisions of the anterolateral BNST (dBNST and vBNST) because of the differential noradrenergic input to these two regions. We find that while resting membrane potential and input resistance are comparable between these subdivisions, excitable properties, including a low-threshold spike (LTS) likely mediated by T-type calcium channels and an Ih-dependent potential, are differentially distributed. Inhibitory and excitatory postsynaptic potentials (IPSPs and EPSPs, respectively) are readily evoked in both dBNST and vBNST. The fast IPSP is predominantly GABAA-receptor mediated and is partially blocked by the AMPA/kainate-receptor antagonist CNQX. In the presence of the GABAA-receptor antagonist picrotoxin, cells in dBNST but not vBNST are more depolarized and have a higher input resistance, suggesting tonic GABAergic inhibition of these cells. The EPSPs elicited in BNST are monosynaptic, exhibit paired pulse facilitation, and contain both an AMPA- and an N-methyl-d-aspartate (NMDA) receptor-mediated component. These data support the hypothesis that neurons of the dorsal and ventral BNST differentially integrate synaptic input, which is likely of behavioral significance. The data also suggest mechanisms by which information may flow through stress and reward circuits.

Defining the caudal ventral striatum in primates: cellular and histochemical features

Afferents from the amygdala help to define the ventral striatum and mediate goal-directed behaviors. In addition to well known inputs to the classic ventral striatum, the amygdala also projects to the caudoventral striatum and amygdalostriatal area. We examined whether the primate caudoventral striatum and amygdalostriatal area can be considered part of the "ventral" striatum based on cellular and histochemical features found in the classic rostral ventral striatum. We used several histochemical stains, including calbindin-D28k, a marker of the shell compartment, acetylcholinesterase, substance P, tyrosine hydroxylase, and Bcl-2, a marker of immature neurons, to examine this question. Our results indicate that the lateral amygdalostriatal area and caudoventral striatum are "striatal like" based on intermediate to high acetylcholinesterase and tyrosine hydroxylase levels. The lateral amygdalostriatal area is chemically similar to the shell, whereas the caudoventral striatum more closely resembles the striatum outside the shell. In contrast, the medial amygdalostriatal area is more related to the central amygdaloid nucleus than to the striatum. Bcl-2 immunoreactivity is associated with granular islands and medium-sized cells in the vicinity of the ventral striatum both rostrally and caudally. Together, the caudal ventral striatum has a histochemical and cellular organization similar to that of the rostral ventral striatum, consistent with their common innervation by the amygdala and other ventral structures. In addition, Bcl-2 is expressed in and near both poles of the ventral striatum, suggesting that these areas maintain a heightened capacity for growth and plasticity compared with other striatal sectors.

A comparison of anti-biotin and biotinylated anti-avidin double-bridge and biotinylated tyramide immunohistochemical amplification

Often it is difficult to detect very small amounts of antigen with conventional immunohistochemical techniques. We evaluate three amplification techniques involving anti-biotin or anti-avidin double-bridges or biotinylated tyramide amplification to enhance the sensitivity of serotonin transporter immunohistochemistry. For the anti-biotin double-bridge, after the secondary antibody, the sections were incubated in anti-biotin antibody followed by a second incubation in the secondary antibody and then avidin-biotin-peroxidase complex (ABC). For the biotinylated anti-avidin technique, after the ABC, sections were incubated in biotinylated anti-avidin, followed by another incubation in ABC. For the biotinylated tyramide technique, after the ABC step, sections were incubated in biotinylated tyramide and hydrogen peroxide, followed by another incubation in ABC. The anti-biotin double-bridge also resulted in a large increase in the number of stained fibers and the intensity of labeling with no increase in background. A biotinylated anti-avidin double-bridge also produced significant signal amplification but significant background. The biotinylated tyramide technique resulted in an even larger increase in the number of labeled fibers and an intensity of their staining with a moderate amount of background staining. However, this advantage was not present at high dilutions of primary antibody. Thus, the anti-biotin double-bridge is likely to be useful in immunohistochemistry and immunofluorescence as well as other situations where increased sensitivity and low background from biotin markers is needed. The biotinylated tyramide technique may also be useful where some degree of background labeling is acceptable.