Synapses In Cortex Research Articles

Increased number of excitatory synapsis and decreased number of inhibitory synapsis in the prefrontal cortex in autism.

Previous studies in autism spectrum disorder demonstrated an increased number of excitatory pyramidal cells and a decreased number of inhibitory parvalbumin+ chandelier interneurons in the prefrontal cortex of postmortem brains. How these changes in cellular composition affect the overall abundance of excitatory and inhibitory synapses in the cortex is not known. Herein, we quantified the number of excitatory and inhibitory synapses in the prefrontal cortex of 10 postmortem autism spectrum disorder brains and 10 control cases. To identify excitatory synapses, we used VGlut1 as a marker of the presynaptic component and postsynaptic density protein-95 as marker of the postsynaptic component. To identify inhibitory synapses, we used the vesicular gamma-aminobutyric acid transporter as a marker of the presynaptic component and gephyrin as a marker of the postsynaptic component. We used Puncta Analyzer to quantify the number of co-localized pre- and postsynaptic synaptic components in each area of interest. We found an increase in the number of excitatory synapses in upper cortical layers and a decrease in inhibitory synapses in all cortical layers in autism spectrum disorder brains compared with control cases. The alteration in the number of excitatory and inhibitory synapses could lead to neuronal dysfunction and disturbed network connectivity in the prefrontal cortex in autism spectrum disorder.

Changes in Behavior and Neural Dynamics across Adolescent Development.

Adolescence is an important developmental period, during which substantial changes occur in brain function and behavior. Several aspects of executive function, including response inhibition, improve during this period. Correspondingly, structural imaging studies have documented consistent decreases in cortical and subcortical gray matter volume, and postmortem histologic studies have found substantial (∼40%) decreases in excitatory synapses in prefrontal cortex. Recent computational modeling work suggests that the change in synaptic density underlie improvements in task performance. These models also predict changes in neural dynamics related to the depth of attractor basins, where deeper basins can underlie better task performance. In this study, we analyzed task-related neural dynamics in a large cohort of longitudinally followed subjects (male and female) spanning early to late adolescence. We found that age correlated positively with behavioral performance in the Eriksen Flanker task. Older subjects were also characterized by deeper attractor basins around task related evoked EEG potentials during specific cognitive operations. Thus, consistent with computational models examining the effects of excitatory synaptic pruning, older adolescents showed stronger attractor dynamics during task performance.SIGNIFICANCE STATEMENT There are well-documented changes in brain and behavior during adolescent development. However, there are few mechanistic theories that link changes in the brain to changes in behavior. Here, we tested a hypothesis, put forward on the basis of computational modeling, that pruning of excitatory synapses in cortex during adolescence changes neural dynamics. We found, consistent with the hypothesis, that variability around event-related potentials shows faster decay dynamics in older adolescent subjects. The faster decay dynamics are consistent with the hypothesis that synaptic pruning during adolescent development leads to stronger attractor basins in task-related neural activity.

Pruning recurrent neural networks replicates adolescent changes in working memory and reinforcement learning

Adolescent development is characterized by an improvement in multiple cognitive processes. While performance on cognitive operations improves during this period, the ability to learn new skills quickly, for example, a new language, decreases. During this time, there is substantial pruning of excitatory synapses in cortex and specifically in prefrontal cortex. We have trained a series of recurrent neural networks to solve a working memory task and a reinforcement learning (RL) task. Performance on both of these tasks is known to improve during adolescence. After training, we pruned the networks by removing weak synapses. Pruning was done incrementally, and the networks were retrained during pruning. We found that pruned networks trained on the working memory task were more resistant to distraction. The pruned RL networks were able to produce more accurate value estimates and also make optimal choices more consistently. Both results are consistent with developmental improvements on these tasks. Pruned networks, however, learned some, but not all, new problems more slowly. Thus, improvements in task performance can come at the cost of flexibility. Our results show that overproduction and subsequent pruning of synapses is a computationally advantageous approach to building a competent brain.

Variation in early life maternal care predicts later long range frontal cortex synapse development in mice

Empirical and theoretical work suggests that early postnatal experience may inform later developing synaptic connectivity to adapt the brain to its environment. We hypothesized that early maternal experience may program the development of synaptic density on long range frontal cortex projections. To test this idea, we used maternal separation (MS) to generate environmental variability and examined how MS affected 1) maternal care and 2) synapse density on virally-labeled long range axons of offspring reared in MS or control conditions. We found that MS and variation in maternal care predicted bouton density on dorsal frontal cortex axons that terminated in the basolateral amygdala (BLA) and dorsomedial striatum (DMS) with more, fragmented care associated with higher density. The effects of maternal care on these distinct axonal projections of the frontal cortex were manifest at different ages. Maternal care measures were correlated with frontal cortex → BLA bouton density at mid-adolescence postnatal (P) day 35 and frontal cortex → DMS bouton density in adulthood (P85). Meanwhile, we found no evidence that MS or maternal care affected bouton density on ascending orbitofrontal cortex (OFC) or BLA axons that terminated in the dorsal frontal cortices. Our data show that variation in early experience can alter development in a circuit-specific and age-dependent manner that may be relevant to understanding the effects of early life adversity.

Functional Territories of Human Dentate Nucleus.

Anatomical connections link the cerebellar cortex with multiple sensory, motor, association, and paralimbic cerebral areas. The majority of fibers that exit cerebellar cortex synapse in dentate nuclei (DN) before reaching extracerebellar structures such as cerebral cortex, but the functional neuroanatomy of human DN remains largely unmapped. Neuroimaging research has redefined broad categories of functional division in the human brain showing that primary processing, attentional (task positive) processing, and default-mode (task negative) processing are three central poles of neural macroscale functional organization. This broad spectrum of human neural processing categories is represented not only in the cerebral cortex, but also in the thalamus, striatum, and cerebellar cortex. Whether functional organization in DN obeys a similar set of macroscale divisions, and whether DN are yet another compartment of representation of a broad spectrum of human neural processing categories, remains unknown. Here, we show for the first time that human DN are optimally divided into three functional territories as indexed by high spatio-temporal resolution resting-state MRI in 77 healthy humans, and that these three distinct territories contribute uniquely to default-mode, salience-motor, and visual cerebral cortical networks. Our findings provide a systems neuroscience substrate for cerebellar output to influence multiple broad categories of neural control.

Developmental Trajectories of Auditory Cortex Synaptic Structures and Gap-Prepulse Inhibition of Acoustic Startle Between Early Adolescence and Young Adulthood in Mice.

Cortical excitatory and inhibitory synapses are disrupted in schizophrenia, the symptoms of which often emerge during adolescence, when cortical excitatory synapses undergo pruning. In auditory cortex, a brain region implicated in schizophrenia, little is known about the development of excitatory and inhibitory synapses between early adolescence and young adulthood, and how these changes impact auditory cortex function. We used immunohistochemistry and quantitative fluorescence microscopy to quantify dendritic spines and GAD65-expressing inhibitory boutons in auditory cortex of early adolescent, late adolescent, and young adult mice. Numbers of spines decreased between early adolescence and young adulthood, during which time responses increased in an auditory cortex-dependent sensory task, silent gap-prepulse inhibition of the acoustic startle reflex (gap-PPI). Within-bouton GAD65 protein and GAD65-expressing bouton numbers decreased between late adolescence and young adulthood, a delay in onset relative to spine and gap-PPI changes. In mice lacking the spine protein kalirin, there were no significant changes in spine number, within-bouton GAD65 protein, or gap-PPI between adolescence and young adulthood. These results illustrate developmental changes in auditory cortex spines, inhibitory boutons, and auditory cortex function between adolescence and young adulthood, and provide insights into how disrupted adolescent neurodevelopment could contribute to auditory cortex synapse pathology and auditory impairments.

Differential Proteomics Data Integration Reveals Anxiety-associated Molecular and Cellular Mechanisms in Cingulate Cortex Synapses.

Introduction The wide spectrum of neuropsychiatric conditions collectively known as 'anxiety disorders” are highly comorbid with depression and are the most common psychiatric conditions encountered in the general population. Despite considerable advances in understanding symptomatology, the functional mechanisms of anxiety-related behaviour remain poorly understood. Methods & Objectives Using the CADITM platform, we carried out an analytical integration of quantitative differential proteomics data obtained from cingulate cortex (CC) synaptosomes of high and low-anxiety (HAB/LAB) mice to enable the detailed identification of the mechanisms that, at least in part, underlie the HAB phenotype. Results The synaptic environment in the CC of HAB animals is dominated by the stabilization and enlargement of existing excitatory dendritic spines, increased high-frequency stimulation of excitatory glutamatergic synapses, enhanced control over the modulation of synaptic strength and relatively weakened inhibitory GABAergic control together with increased spontaneous synaptic activity in non-glutamatergic network members. This is coupled with increased oxidative phosphorylation, enhanced fatty acid oxidation and ATP production in synaptic mitochondria. While ketone bodies appear to be the main energy source for ATP synthesis, glucose/lactate metabolism is mainly used to maintain NADH/FADH2 homeostasis. The effects of increased oxidative and ionic stress appear simultaneously and synergistically controlled through at least seven different mechanisms without involving the glutathione-associated network. Conclusions In high-anxiety trait animals, cingulate cortex activity is characterized by low de novo synaptic spine generation, over-activation of excitatory networks, long-term potentiation (LTP) maintenance, significant neurotransmission imbalances and structural as well as metabolic adaptations to persistent mitochondrial Ca2+ loading and oxidative stress.

Abstract W MP41: Potentiation of Gaba-Mediated Synaptic Inhibition in the Recovery Phase: A Novel Therapeutic Target for Stroke

Background: Stroke is a major cause of disability yet pharmacotherapy targeting the recovery phase is lacking. Cortical circuit reorganization adjacent to the stroke site promotes recovery, thus elucidating mechanisms that promote this plasticity could lead to new therapeutics. Tonic neuronal inhibition, mediated by extrasynaptic GABA A receptors,inhibits post-stroke recovery. However, effects of phasic (synaptic) GABA signaling - which promotes plasticity during development - are unknown. Here we use a combined approach of i) array tomography to determine the composition of GABA synapses in the post-stroke mouse brain, ii) electrophysiology to determine whether stroke leads to functional changes in GABA-mediated phasic inhibition, and (iii) treatment with zolpidem, an FDA-approved GABA agonist, to modulate recovery. Results: We found, using array tomography, a 1.7-fold increase in the number of GABAergic synapses containing the α1 receptor subunit in layer 5 of the peri-infarct cortex (synapse number/μm 3 : 0.039±0.006 (control) vs 0.064±0.006 (stroke); P<0.01), but not in layer 2/3. There was an associated increase in spontaneous inhibitory post-synaptic currents (sIPSC) specific to layer 5 pyramidal neurons (sIPSC charge (fC): -403±27.8 (control) vs -724±166 (stroke); p=0.03). This effect was transient, occurring during the onset of functional recovery. To test whether the increased phasic inhibitory GABAergic signaling promotes stroke recovery, we treated animals with zolpidem, an agonist with high affinity for α1 subunit-containing GABA A receptors. Low dose zolpidem increased GABA A phasic signaling in layer 5 pyramidal cells and notably increased the rate and extent of behavioral recovery without altering infarct size. Conclusions: These data provide the first evidence that enhanced GABA A -mediated synaptic activity during the recovery phase improves stroke outcome. These data identify modulation of phasic GABA signaling as a novel therapeutic strategy for stroke, indicate zolpidem as a potential drug to improve recovery, and underscore the necessity to distinguish the role of tonic and phasic GABA inhibition in stroke recovery.

Binocular form deprivation influences the visual cortex.

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors are considered to play a crucial role in synaptic plasticity in the developing visual cortex. In this study, we established a rat model of binocular form deprivation by suturing the rat binocular eyelids before eye-opening at postnatal day 14. During development, the decay time of excitatory postsynaptic currents mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors of normal rats became longer after eye-opening; however, the decay time did not change significantly in binocular form deprivation rats. The peak value in the normal group became gradually larger with age, but there was no significant change in the binocular form deprivation group. These findings indicate that binocular form deprivation influences the properties of excitatory postsynaptic currents mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in the rat visual cortex around the end of the critical period, indicating that form stimulation is associated with the experience-dependent modification of neuronal synapses in the visual cortex.

Enriched environment increases the total number of CNPase positive cells in the corpus callosum of middle-aged rats.

It had been reported that enriched environment was beneficial for the brain cognition, neurons and synapses in cortex and hippocampus. With diffusion tensor imaging (DTI), several studies recently found the trained-induced larger corpus callosum. However, the effect of enriched environment on the oligodendrocytes in corpus callosum has not been explored with the unbiased stereological methods. In current study, the effect of enriched environment on the total number of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) positive cells in middle-aged rat corpus callosum was investigated by means of immunohistochemical techniques and the unbiased stereological methods. We found that, when compared to standard rats, the spatial learning capacity of enriched-environment rats was significantly increased. The total number of the CNPase positive cells in the corpus callosum of enriched-environment middle-aged rats was significantly increased when compared to standard rats. The present study provided, to the best of our knowledge, the first evidence of environmental enrichment-induced increases in the total number of CNPase positive cells in the corpus callosum of middle-aged rats.

Phase-specific remodeling of synapses in the S1 cortex of neuropathic pain mice and its association with astrocytic Ca2+ signaling

Phase-specific remodeling of synapses in the S1 cortex of neuropathic pain mice and its association with astrocytic Ca2+ signaling

Serotonin as a mediator of cross-modal cortical reorganization.

When one type of sensory system is disrupted, other intact remaining sensory function can be improved. Although this form of plasticity, cross-modal plasticity, is widely known, the molecular and cellular mechanisms underlying it are poorly understood. In a recent study, we demonstrated that visual deprivation increases extracellular serotonin in the juvenile rat barrel cortex and resulted in facilitation of synaptic delivery of AMPA-type glutamate receptors (AMPARs) at layer4-2/3 synapses in the barrel cortex via the activation of serotonin 5HT2A/2C receptors and ERK. This caused sharpening of functional whisker-barrel map at layer2/3 of the barrel cortex. Thus, sensory dysfunction of one modality leads to improvement of remaining modalities by the refinement of cortical organization through serotonin signaling-mediated facilitation of synaptic AMPARs delivery.

T-SNARE and v-SNARE in the GABAergic and glutamatergic synapses of the rat cerebellar cortex

Using light microscope immunohistochemistry, the distributions of the t-SNARE, SNAP-25 and syntaxin-1a, and v-SNARE, VAMP-2 (or synaptobrevin-2), have been analyzed in the rat cerebellar cortex and compared with those of GAD-65/67, marker of GABAergic neurons, and vGLUT-1 and vGLUT-2, markers of glutamatergic neurons. SNAP-25 immunoreactivity was detected throughout the cortex, highly diffused in the neuropil. In the molecular and Purkinje layers, the immunoreactivity surrounded dendrite trunks of the Purkinje neurons, and bodies of stellate, basket and Purkinje neurons, which appeared all immunonegative. In the granular layer, the immunoreactivity was less diffuse and formed small grains localized within the protoplasmic islands of Held (synaptic glomeruli). Immunoreactivity was also observed in the white matter. The distribution of syntaxin-1a immunoreactivity appeared superimposable to that of SNAP-25. VAMP-2 immunoreactivity was observed in small dots finely dispersed in the neuropil of the molecular/Purkinje layer; a moderate labelling of the Purkinje neuron bodies was also observed. In the granular layer, VAMP-2 immunoreactivity formed larger deposits, presumably corresponding to mossy fibre terminals. Experiments of double labelling immunohistochemistry revealed no co-localization between t-SNARE (SNAP-25) or v-SNARE (VAMP-2) and GAD-65/67. On the contrary, co-localization between SNAP-25 and VAMP-2, on one side, and v-GLUT-1 or vGLUT-2, on the other side, was frequently revealed. Briefly, in the molecular layer, v-GLUT-1 and vGLUT-2-positive terminals only partly displayed also SNAP-25 immunoreactivity; whereas in the granular layer, all v-GLUT-1 and vGLUT-2-positive terminals displayed this co-localization. The results of this study indicate that t-SNARE and v-SNARE largely characterize the glutamatergic synapses in the rat cerebellar cortex. The same proteins are lacking in the GABAergic synapses.

P1-121: Generation and characterization of neuron-specific mitochondrial targeted DsRed2 transgenic mouse model to image synapse modification in Alzheimer's disease

Memory loss is the earliest symptom of Alzheimer's disease (AD) patients. Its underline mechanism is related to synapses' reduction and elimination. However, the detailed correlation between synapses' modification in AD is unclear now especially in vital status. In order to decipher the mechanism of synapse change in AD, we have been generating and characterizing a fluorescent-protein-reporter transgenic mouse. We use thy-1 as promoter to drive dsRed2 expression in a neuron specific pattern. DsRed is a red fluorescent protein with 20%–30% homologous sequence with GFP. Its strong expression in cells is simultaneously with lower auto-fluorescent signals from the background. It also can penetrate tissues deeper. Due to these advantages, we selected DsRed2, a genetic variant of DsRed, which is human codon- optimized for compatible expression in mammalian cells as reporter gene. Our previous in vitro results indicated that the fluorescent protein can show the internal structure of cells more accurately when targeted to the subcellular compartments. In this in vivo study, a mitochondrial targeting sequence (mt) is fused to the 5'-end of DsRed2 to direct the protein expression exclusively in the mitochondria of cells. We cloned the whole fragment of mtDsRed2 into the XhoI site in Thy-1 promoter by T4 ligation. The right clones was validated by restriction enzyme digestion and sequencing. We also transfected NSC-34 cells by this construct and the results showed the codons are in-frame. Then we utilized zygote-injection-based transgenic approaches to generate the transgenic mouse. Until now we obtained five founders which show strong and right size bands for transgene by genotyping. We are going to observe the formation and plasticity of synapse in vivo by two-photon fluorescent microscopy with this mouse. These data will show the normal status of synapses in cortex. Then, we are going to cross this mouse with inducible APP transgenic mouse to clarify the synapses change in AD. This study will disclose the mechanism of memory loss in AD, which will supply meaningful information to discover and/or invent novel method(s) for diagnosis and interferences of AD in early stage.

Metabotropic glutamate receptors mGluR4 and mGluR8 regulate transmission in the lateral olfactory tract–piriform cortex synapse

The piriform cortex (PC) is the primary terminal zone of projections from the olfactory bulb, termed the lateral olfactory tract (LOT). The PC plays a critical role in processing of olfactory stimuli and is also a highly seizure prone area thought to be involved in some forms of temporal lobe epilepsy. Pharmacological and immunohistochemical studies provide evidence for the localization of various metabotropic glutamate receptors (GluRs) in the PC. We employed whole-cell patch clamp recordings from PC pyramidal cells to determine the roles of group III mGluRs in modulating synaptic transmission at the LOT–PC synapse. The group III mGluR agonist, l-AP4, induced a concentration-dependent inhibition of synaptic transmission at the LOT–PC synapse at concentrations that activate mGluR4 and mGluR8, but not mGluR7 or other mGluR subtypes (EC 50 = 473 nM). In addition, the selective mGluR8 agonist, DCPG (300 nM), also suppressed synaptic transmission at the LOT synapse. Furthermore, the inhibitory actions of l-AP4 and Z-cyclopentyl-AP4, a selective mGluR4 agonist, were potentiated by the mGluR4 positive allosteric modulator, PHCCC (30 μM). The high potency of l-AP4, combined with the observed effects of DCPG and PHCCC, suggests that both mGluR4 and mGluR8 play a role in the l-AP4-induced inhibition of synaptic transmission at the LOT–PC synapse.

T1468 Stimulation of the Medial Thalamus-Anterior Cingulate Cortex Synapses Is Important for Learning and Triggering Pain Memories in Visceral Hypersensitive States

T1468 Stimulation of the Medial Thalamus-Anterior Cingulate Cortex Synapses Is Important for Learning and Triggering Pain Memories in Visceral Hypersensitive States

Track study in hypoxia ischemia brain damage on developing of cerebral cortex synapse on newborn rats

目的 追踪研究缺氧缺血性脑损伤对新生大鼠发育期间大脑皮质突触发育的影响.方法取7 d龄Wistar仔鼠,随机分成实验组和假手术组(对照组).采用形态学和形态计量学的方法对生后7 d到2月(成年)分8个时段对额叶皮质的发育,进行长期跟踪研究.结果实验组6h～7 d各组神经元胞质内出现空泡,线粒体肿胀、嵴模糊;核不规则、皱缩甚至溶解.脑损伤后仔鼠额叶皮质神经元[C24h:(142.0±17.3)个,E24h:(106±28.2)个,C2w:(142.5±19.23)个,E2w:(126.0±24.5)个]及神经纤维的密度(C6h:20.2±2.1,E6h:14.9±1.92,C24h:20.4±2.6,E24h:11.4±2.4)显著降低(P＜0.05,P＜0.01).突触的形态计量学参数表面积密度(Sv)和面数密度(NA)降低,突触后膜致密层变薄(P＜0.05,P＜0.01).结论缺氧缺血性脑损伤对新生大鼠发育期间大脑皮质中突触的质量,神经元及神经纤维密度的影响,是影响智力发育的重要因素。

Serial pathways from primate prefrontal cortex to autonomic areas may influence emotional expression

BackgroundExperiencing emotions engages high-order orbitofrontal and medial prefrontal areas, and expressing emotions involves low-level autonomic structures and peripheral organs. How is information from the cortex transmitted to the periphery? We used two parallel approaches to map simultaneously multiple pathways to determine if hypothalamic autonomic centres are a key link for orbitofrontal areas and medial prefrontal areas, which have been associated with emotional processes, as well as low-level spinal and brainstem autonomic structures. The latter innervate peripheral autonomic organs, whose activity is markedly increased during emotional arousal.ResultsWe first determined if pathways linking the orbitofrontal cortex with the hypothalamus overlapped with projection neurons directed to the intermediolateral column of the spinal cord, with the aid of neural tracers injected in these disparate structures. We found that axons from orbitofrontal and medial prefrontal cortices converged in the hypothalamus with neurons projecting to brainstem and spinal autonomic centers, linking the highest with the lowest levels of the neuraxis. Using a parallel approach, we injected bidirectional tracers in the lateral hypothalamic area, an autonomic center, to label simultaneously cortical pathways leading to the hypothalamus, as well as hypothalamic axons projecting to low-level brainstem and spinal autonomic centers. We found densely distributed projection neurons in medial prefrontal and orbitofrontal cortices leading to the hypothalamus, as well as hypothalamic axonal terminations in several brainstem structures and the intermediolateral column of the spinal cord, which innervate peripheral autonomic organs. We then provided direct evidence that axons from medial prefrontal cortex synapse with hypothalamic neurons, terminating as large boutons, comparable in size to the highly efficient thalamocortical system. The interlinked orbitofrontal, medial prefrontal areas and hypothalamic autonomic centers were also connected with the amygdala.ConclusionsDescending pathways from orbitofrontal and medial prefrontal cortices, which are also linked with the amygdala, provide the means for speedy influence of the prefrontal cortex on the autonomic system, in processes underlying appreciation and expression of emotions.

Plasticity at hippocampal to prefrontal cortex synapses: Dual roles in working memory and consolidation

Plasticity at hippocampal to prefrontal cortex synapses: Dual roles in working memory and consolidation

Dopamine Terminals in the Rat Prefrontal Cortex Synapse on Pyramidal Cells that Project to the Nucleus Accumbens

Afferents to the prefrontal cortex (PFC) from dopamine neurons in the ventral tegmental area have been implicated in working memory processes and in the pathogenesis of schizophrenia. Previous anatomical investigations have demonstrated that dopamine terminals synapse on dendritic spines and shafts of pyramidal cells in the PFC. Moreover, neurochemical and physiological studies suggest that dopamine modulates the activity of PFC neurons that project to the nucleus accumbens. However, whether this modulation involves direct synaptic input to cortico-accumbens projection neurons has not been determined. To address this question, retrograde transport of an attenuated strain of pseudorabies virus (PRV) from the nucleus accumbens was combined with immunoperoxidase labeling of tyrosine hydroxylase (TH) to identify dopamine terminals in the PFC. At survival times <48 hr, extensive dendritic distribution of immunogold labeling for PRV was observed in cortico-accumbens neurons. However, evidence consistent with trans-synaptic passage of PRV within this timeframe was observed only rarely. When examined at the electron microscopic level, immunogold labeling for PRV was localized to neuronal somata, proximal and distal dendrites, and dendritic spines. Some of these dendritic processes received symmetric synaptic input from TH-immunoreactive terminals. These data represent the first demonstration of dopamine synaptic contacts onto an identified population of pyramidal cells in the PFC. The findings have important implications for understanding how dopamine modulates cortical outflow to limbic regions in normal brain and pathological states such as schizophrenia.