Autoradiographic analysis of serotonin 5-HT1A receptor binding in the human brain postmortem: effects of age and alcohol

Ginkgo biloba: A Leaf of Hope in the Fight against Alzheimer's Dementia: Clinical Trial Systematic Review

Alzheimer's disease (AD) is a stealthy and progressive neurological disorder that is a leading cause of dementia in the global elderly population, imposing a significant burden on both the elderly and society. Currently, the condition is treated with medications that alleviate symptoms. Nonetheless, these drugs may not consistently produce the desired results and can cause serious side effects. Hence, there is a vigorous pursuit of alternative options to enhance the quality of life for patients. Ginkgo biloba (GB), an herb with historical use in traditional medicine, contains bioactive compounds such as terpenoids (Ginkgolides A, B, and C), polyphenols, organic acids, and flavonoids (quercetin, kaempferol, and isorhamnetin). These compounds are associated with anti-inflammatory, antioxidant, and neuroprotective properties, making them valuable for cognitive health. A systematic search across three databases using specific keywords-GB in AD and dementia-yielded 1702 documents, leading to the selection of 15 clinical trials for synthesis. In eleven studies, GB extract/EGb 761® was shown to improve cognitive function, neuropsychiatric symptoms, and functional abilities in both dementia types. In four studies, however, there were no significant differences between the GB-treated and placebo groups. Significant improvements were observed in scores obtained from the Mini-Mental State Examination (MMSE), Short Cognitive Performance Test (SKT), and Neuropsychiatric Inventory (NPI). While the majority of synthesized clinical trials show that Ginkgo biloba has promising potential for the treatment of these conditions, more research is needed to determine optimal dosages, effective delivery methods, and appropriate pharmaceutical formulations. Furthermore, a thorough assessment of adverse effects, exploration of long-term use implications, and investigation into potential drug interactions are critical aspects that must be carefully evaluated in future studies.

The role of brain serotonin signaling in excessive alcohol consumption and withdrawal: A call for more research in females

Alcohol Use Disorder (AUD) is a leading cause of death and disability worldwide, but current treatments are insufficient in fully addressing the symptoms that often lead to relapses in alcohol consumption. The brain's serotonin system has been implicated in AUD for decades and is a major regulator of stress-related behaviors associated with increased alcohol consumption. This review will discuss the current literature on the association between neurobiological adaptations in serotonin systems and AUD in humans as well as the effectiveness of serotonin receptor manipulations on alcohol-related behaviors like consumption and withdrawal. We will further discuss how these findings in humans relate to findings in animal models, including a comparison of systemic pharmacological manipulations modulating alcohol consumption. We next provide a detailed overview of brain region-specific roles for serotonin and serotonin receptor signaling in alcohol-related behaviors in preclinical animal models, highlighting the complexity of forming a cohesive model of serotonin function in AUD and providing possible avenues for more effective therapeutic intervention. Throughout the review, we discuss what is known about sex differences in the sequelae of AUD and the role of serotonin in these sequelae. We stress a critical need for additional studies in women and female animals so that we may build a clearer path to elucidating sex-specific serotonergic mechanisms and develop better treatments.

Promising new pharmacological targets for depression: The search for efficacy

Pharmacological treatment of major depressive disorder (MDD) still relies on the use of serotonergic drugs, despite their limited efficacy. A few mechanistically new drugs have been developed in recent years, but many fail in clinical trials. Several hypotheses have been proposed to explain MDD pathophysiology, indicating that physiological processes such as neuroplasticity, circadian rhythms, and metabolism are potential targets. Here, we review the current state of pharmacological treatments for MDD, as well as the preclinical and clinical evidence for an antidepressant effect of molecules that target non-serotonergic systems. We offer some insights into the challenges facing the development of new antidepressant drugs, and the prospect of finding more effectiveness for each target discussed.

Activation of 5-HT1A Receptors Normalizes the Overexpression of Presynaptic 5-HT1A Receptors and Alleviates Diabetic Neuropathic Pain

Neuropathic pain is a well-documented phenomenon in experimental and clinical diabetes; however, current treatment is unsatisfactory. Serotoninergic-containing neurons are key components of the descending autoinhibitory pathway, and a decrease in their activity may contribute at least in part to diabetic neuropathic pain (DNP). A streptozotocin (STZ)-treated rat was used as a model for type 1 diabetes mellitus (T1DM). Pain transmission was evaluated using well-established nociceptive-based techniques, including the Hargreaves apparatus, cold plate and dynamic plantar aesthesiometer. Using qRT-PCR, Western blotting, immunohistochemistry, and HPLC-based techniques, we also measured in the central nervous system and peripheral nervous system of diabetic animals the expression and localization of 5-HT1A receptors (5-HT1AR), levels of key enzymes involved in the synthesis and degradation of tryptophan and 5-HT, including tryptophan hydroxylase-2 (Tph-2), tryptophan 2,3-dioxygenase (Tdo), indoleamine 2,3-dioxygenase 1 (Ido1) and Ido2. Moreover, spinal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA, a metabolite of 5-HT) and quinolinic acid (QA, a metabolite of tryptophan) were also quantified. Diabetic rats developed thermal hyperalgesia and cold/mechanical allodynia, and these behavioral abnormalities appear to be associated with the upregulation in the levels of expression of critical molecules related to the serotoninergic nervous system, including presynaptic 5-HT1AR and the enzymes Tph-2, Tdo, Ido1 and Ido2. Interestingly, the level of postsynaptic 5-HT1AR remains unaltered in STZ-induced T1DM. Chronic treatment of diabetic animals with 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), a selective 5-HT1AR agonist, downregulated the upregulation of neuronal presynaptic 5-HT1AR, increased spinal release of 5-HT (↑ 5-HIAA/5-HT) and reduced the concentration of QA, decreased mRNA expression of Tdo, Ido1 and Ido2, arrested neuronal degeneration and ameliorated pain-related behavior as exemplified by thermal hyperalgesia and cold/mechanical allodynia. These data show that 8-OH-DPAT alleviates DNP and other components of the serotoninergic system, including the ratio of 5-HIAA/5-HT and 5-HT1AR, and could be a useful therapeutic agent for managing DNP.

High-resolution and high-sensitivity PET for quantitative molecular imaging of the monoaminergic nuclei: A GATE simulation study

PURPOSE

Quantitative in vivo molecular imaging of fine brain structures requires high-spatial resolution and high-sensitivity. Positron emission tomography (PET) is an attractive candidate to introduce molecular imaging into standard clinical care due to its highly targeted and versatile imaging capabilities based on the radiotracer being used. However, PET suffers from relatively poor spatial resolution compared to other clinical imaging modalities, which limits its ability to accurately quantify radiotracer uptake in brain regions and nuclei smaller than 3 mm in diameter. Here we introduce a new practical and cost-effective high-resolution and high-sensitivity brain-dedicated PET scanner, using our depth-encoding Prism-PET detector modules arranged in a conformal decagon geometry, to substantially reduce the partial volume effect and enable accurate radiotracer uptake quantification in small subcortical nuclei.

METHODS

Two Prism-PET brain scanner setups were proposed based on our 4-to-1 and 9-to-1 coupling of scintillators to readout pixels using1.5 × 1.5 × 20 $1.5 \times 1.5 \times 20$  mm3 and0.987 × 0.987 × 20 $0.987 \times 0.987 \times 20$  mm3 crystal columns, respectively. Monte Carlo simulations of our Prism-PET scanners, Siemens Biograph Vision, and United Imaging EXPLORER were performed using Geant4 application for tomographic emission (GATE). National Electrical Manufacturers Association (NEMA) standard was followed for the evaluation of spatial resolution, sensitivity, and count-rate performance. An ultra-micro hot spot phantom was simulated for assessing image quality. A modified Zubal brain phantom was utilized for radiotracer imaging simulations of 5-HT1A receptors, which are abundant in the raphe nuclei (RN), and norepinephrine transporters, which are highly concentrated in the bilateral locus coeruleus (LC).

RESULTS

The Prism-PET brain scanner with 1.5 mm crystals is superior to that with 1 mm crystals as the former offers better depth-of-interaction (DOI) resolution, which is key to realizing compact and conformal PET scanner geometries. We achieved uniform 1.3 mm full-width-at-half-maximum (FWHM) spatial resolutions across the entire transaxial field-of-view (FOV), a NEMA sensitivity of 52.1 kcps/MBq, and a peak noise equivalent count rate (NECR) of 957.8 kcps at 25.2 kBq/mL using 450-650 keV energy window. Hot spot phantom results demonstrate that our scanner can resolve regions as small as 1.35 mm in diameter at both center and 10 cm away from the center of the transaixal FOV. Both 5-HT1A receptor and norepinephrine transporter brain simulations prove that our Prism-PET scanner enables accurate quantification of radiotracer uptake in small brain regions, with a 1.8-fold and 2.6-fold improvement in the dorsal RN as well as a 3.2-fold and 4.4-fold improvement in the bilateral LC compared to the Biograph Vision and EXPLORER, respectively.

CONCLUSIONS

Based on our simulation results, the proposed high-resolution and high-sensitivity Prism-PET brain scanner is a promising cost-effective candidate to achieve quantitative molecular neuroimaging of small but important brain regions with PET clinically viable.

Prolonged ethanol exposure modulates constitutive internalization and recycling of 5-HT1A receptors

Alcohol exposure alters the signaling of the serotoninergic system, which is involved in alcohol consumption, reward, and dependence. In particular, dysregulation of serotonin receptor type 1A (5-HT1AR) is associated with alcohol intake and withdrawal-induced anxiety-like behavior in rodents. However, how ethanol regulates 5-HT1AR activity and cell surface availability remains elusive. Using neuroblastoma 2a cells stably expressing human 5-HT1ARs tagged with hemagglutinin at the N-terminus, we found that prolonged ethanol exposure (18 h) reduced the basal surface levels of 5-HT1ARs in a concentration-dependent manner. This reduction is attributed to both enhanced receptor internalization and attenuated receptor recycling. Moreover, constitutive 5-HT1AR internalization in ethanol naïve cells was blocked by concanavalin A (ConA) but not nystatin, suggesting clathrin-dependent 5-HT1AR internalization. In contrast, constitutive 5-HT1AR internalization in ethanol-treated cells was blocked by nystatin but not by ConA, indicating that constitutive 5-HT1AR internalization switched from a clathrin- to a caveolin-dependent pathway. Dynasore, an inhibitor of dynamin, blocked 5-HT1AR internalization in both vehicle- and ethanol-treated cells. Furthermore, ethanol exposure enhanced the activity of dynamin I via dephosphorylation and reduced myosin Va levels, which may contribute to increased internalization and reduced recycling of 5-HT1ARs, respectively. Our findings suggest that prolonged ethanol exposure not only alters the endocytic trafficking of 5-HT1ARs but also the mechanism by which constitutive 5-HT1AR internalization occurs.

Interaction effect of serum serotonin level and age on the 12-week pharmacotherapeutic response in patients with depressive disorders

Despite the recognized antidepressant role of serotonin (5-hydroxytryptamine [5-HT]) signaling pathways in the central nervous system, the association between baseline peripheral 5-HT level and the antidepressant treatment response in clinical studies remains debatable. We investigated the interaction effects of baseline serum 5-HT level and age on the 12-week remission in outpatients with depressive disorders who received stepwise antidepressant treatment. Baseline serum serotonin levels were measured and the age of 1094 patients recorded. The patients received initial antidepressant monotherapy; then, patients with an insufficient response or who experienced uncomfortable side effects received alternative treatments every 3 weeks (3, 6, and 9 weeks). Subsequently, 12-week remission, defined as a Hamilton Depression Rating Scale (HAMD) score of ≤ 7, was evaluated. Individual and interaction effects of serum 5-HT level (as a binary [low vs. high, based on the median value of 72.6 ng/mL] or continuous variable) and age (as a binary [< 60 vs. ≥ 60 years] or continuous variable) on the 12-week remission rate were analyzed using logistic regression models after adjusting for relevant covariates. High 5-HT (≥ 72.6 ng/mL) and age ≥ 60 years were associated with the highest 12-week remission rates and a significant multiplicative interaction effect. The interaction effect of the two variables on the 12-week remission rate was significant even when analyzed as a continuous variable. Our study suggests that the association between baseline serum 5-HT level and 12-week antidepressant treatment outcomes differs according to patient age.

Use and abuse of dissociative and psychedelic drugs in adolescence

Adolescence is a period of profound developmental changes, which run the gamut from behavioral and neural to physiological and hormonal. It is also a time at which there is an increased propensity to engage in risk-taking and impulsive behaviors like drug use. This review examines the human and preclinical literature on adolescent drug use and its consequences, with a focus on dissociatives (PCP, ketamine, DXM), classic psychedelics (LSD, psilocybin), and MDMA. It is the case for all the substances reviewed here that very little is known about their effects in adolescent populations. An emerging aspect of the literature is that dissociatives and MDMA produce mixed reinforcing and aversive effects and that the balance between reinforcement and aversion may differ between adolescents and adults, with consequences for drug use and addiction. However, many studies have failed to directly compare adults and adolescents, which precludes definitive conclusions about these consequences. Other important areas that are largely unexplored are sex differences during adolescence and the long-term consequences of adolescent use of these substances. We provide suggestions for future work to address the gaps we identified in the literature. Given the widespread use of these drugs among adolescent users, and the potential for therapeutic use, this work will be crucial to understanding abuse potential and consequences of use in this developmental stage.

Effects of chronic exposure to low doses of Δ9- tetrahydrocannabinol in adolescence and adulthood on serotonin/norepinephrine neurotransmission and emotional behaviors

BACKGROUND

Chronic exposure to the Δ9-tetrahydrocannabinol (THC), the main cannabis pharmacological component, during adolescence has been shown to be associated with an increased risk of depression and suicidality in humans.

AIMS

Little is known about the impact of the long-term effects of chronic exposure to low doses of THC in adolescent compared to adult rodents.

METHODS

THC (1mg/kg i.p., once a day) or vehicle was administered for 20 days in both adolescent (post-natal day, PND 30-50) and young adult rats (PND 50-70). After a long washout period (20 days), several behavioral paradigms and electrophysiological recordings of serotonin (5-HT) and norepinephrine (NE) neurons were carried out.

RESULTS

Adolescent THC exposure resulted in depressive lbehaviors: a significant decrease in latency to first immobility in the forced swim test, increased anhedonia in the sucrose preference test. Decrease entries in the open arm were observed in the elevated plus maze after adolescent and adult exposure, indicating anxiousphenotype. A significant reduction in dorsal raphe serotonergic neural activity without changing locus coeruleus noradrenergic neural activity was found in THC adolescent and adult exposure.

CONCLUSIONS

Altogether, these findings suggest that low doses of chronic THC exposure during the developmental period and adulthood could result in increased vulnerability of the 5-HT system and anxiety symptoms; however, depressive phenotypes occur only after adolescent, but not adult exposure, underscoring the higher vulnerability of young ages to the mental effects of cannabis.

Examining the underpinnings of loudness dependence of auditory evoked potentials with positron emission tomography

Loudness dependence of auditory evoked potentials (LDAEP) has long been considered to reflect central basal serotonin transmission. However, the relationship between LDAEP and individual serotonin receptors and transporters has not been fully explored in humans and may involve other neurotransmitter systems. To examine LDAEP's relationship with the serotonin system, we performed PET using serotonin-1A (5-HT_1A) imaging via [¹¹C]CUMI-101 and serotonin transporter (5-HTT) imaging via [¹¹C]DASB on a mixed sample of healthy controls (n ​= ​4: 4 females, 0 males), patients with unipolar (MDD, n ​= ​11: 4 females, 7 males) and bipolar depression (BD, n ​= ​8: 4 females, 4 males). On these same participants, we also performed electroencephalography (EEG) within a week of PET scanning, using 1000 ​Hz tones of varying intensity to evoke LDAEP. We then evaluated the relationship between LDAEP and 5-HT_1A or 5-HTT binding in both the raphe (5-HT_1A)/midbrain (5-HTT) areas and in the temporal cortex. We found that LDAEP was significantly correlated with 5-HT_1A positively and with 5-HTT negatively in the temporal cortex (p ​< ​0.05), but not correlated with either in midbrain or raphe. In males only, exploratory analysis showed multiple regions in which LDAEP significantly correlated with 5-HT_1A throughout the brain; we did not find this with 5-HTT. This multimodal study partially validates preclinical models of a serotonergic influence on LDAEP. Replication in larger samples is necessary to further clarify our understanding of the role of serotonin in perception of auditory tones.

Function and Mechanism of Myelin Regulation in Alcohol Abuse and Alcoholism

Excessive alcohol use has adverse effects on the central nervous system (CNS) and can lead to alcohol use disorders (AUDs). Recent studies have suggested that myelin reductions may directly contribute to CNS dysfunctions associated with AUDs. Myelin consists of compact lipid membranes wrapped around axons to provide electrical insulation and trophic support. Regulation of myelin is considered as a new form of neural plasticity due to its profound impacts on the computation of neural networks. In this review, the authors first discuss experimental evidence showing how alcohol exposure causes demyelination in different brain regions, often accompanied by deficits in cognition and emotion. Next, they discuss postulated molecular and cellular mechanisms underlying alcohol's impact on myelin. It is clear that more extensive investigations are needed in this important but underexplored research field in order to gain a better understanding of the myelin-behavior relationship and to develop new treatment strategies for AUDs.

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Serotonin receptors and suicide, major depression, alcohol use disorder and reported early life adversity

Serotonin neurotransmitter deficits are reported in suicide, major depressive disorder (MDD) and alcohol use disorder (AUD). To compare pathophysiology in these disorders, we mapped brain serotonin transporter (SERT), 5-HT1A, and 5-HT2A receptor binding throughout prefrontal cortex and in anterior cingulate cortex postmortem. Cases and controls died suddenly minimizing agonal effects and had a postmortem interval ≤24 h to avoid compromised brain integrity. Neuropathology and toxicology confirmed absence of neuropathology and psychotropic medications. For most subjects (167 of 232), a DSM-IV Axis I diagnosis was made by psychological autopsy. Autoradiography was performed in right hemisphere coronal sections at a pre-genual level. Linear model analyses included sex and age with group and Brodmann area as interaction terms. SERT binding was lower in suicides (p = 0.004) independent of sex (females < males, p < 0.0001), however, the lower SERT binding was dependent on MDD diagnosis (p = 0.014). Higher SERT binding was associated with diagnosis of alcoholism (p = 0.012). 5-HT1A binding was greater in suicides (p < 0.001), independent of MDD (p = 0.168). Alcoholism was associated with higher 5-HT1A binding (p < 0.001) but only in suicides (p < 0.001). 5-HT2A binding was greater in suicides (p < 0.001) only when including MDD (p = 0.117) and alcoholism (p = 0.148) in the model. Reported childhood adversity was associated with higher SERT and 5-HT1A binding (p = 0.004) in nonsuicides and higher 5-HT2A binding (p < 0.001). Low SERT and more 5-HT1A and 5-HT2A binding in the neocortex in depressed suicides is dependent on Axis I diagnosis and reported childhood adversity. Findings in alcoholism differed from those in depression and suicide indicating a distinct serotonin system pathophysiology.

Does the 5-HT1A rs6295 polymorphism influence the safety and efficacy of citalopram therapy in the oldest old?

Major depressive disorder (MDD) in older people is a relatively common, yet hard to treat problem. In this study, we aimed to establish if a single nucleotide polymorphism in the 5-HT_1A receptor gene (rs6295) determines antidepressant response in patients aged > 80 years (the oldest old) with MDD. Nineteen patients aged at least 80 years with a new diagnosis of MDD were monitored for response to citalopram 20 mg daily over 4 weeks and genotyped for the rs6295 allele. Both a frequentist and Bayesian analysis was performed on the data. Bayesian analysis answered the clinically relevant question: 'What is the probability that an older patient would enter remission after commencing selective serotonin reuptake inhibitor (SSRI) treatment, conditional on their rs6295 genotype?' Individuals with a CC (cytosine-cytosine) genotype showed a significant improvement in their Geriatric Depression Score (p = 0.020) and cognition (p = 0.035) compared with other genotypes. From a Bayesian perspective, we updated reports of antidepressant efficacy in older people with our data and calculated that the 4-week relative risk of entering remission, given a CC genotype, is 1.9 [95% highest-density interval (HDI) 0.7-3.5], compared with 0.52 (95% HDI 0.1-1.0) for the CG (cytosine-guanine) genotype. The sample size of n = 19 is too small to draw any firm conclusions, however, the data suggest a trend indicative of a relationship between the rs6295 genotype and response to citalopram in older patients, which requires further investigation.

Monoaminergic Modulation of Motor Cortex Function

Elaboration of appropriate responses to behavioral situations rests on the ability of selecting appropriate motor outcomes in accordance to specific environmental inputs. To this end, the primary motor cortex (M1) is a key structure for the control of voluntary movements and motor skills learning. Subcortical loops regulate the activity of the motor cortex and thus contribute to the selection of appropriate motor plans. Monoamines are key mediators of arousal, attention and motivation. Their firing pattern enables a direct encoding of different states thus promoting or repressing the selection of actions adapted to the behavioral context. Monoaminergic modulation of motor systems has been extensively studied in subcortical circuits. Despite evidence of converging projections of multiple neurotransmitters systems in the motor cortex pointing to a direct modulation of local circuits, their contribution to the execution and learning of motor skills is still poorly understood. Monoaminergic dysregulation leads to impaired plasticity and motor function in several neurological and psychiatric conditions, thus it is critical to better understand how monoamines modulate neural activity in the motor cortex. This review aims to provide an update of our current understanding on the monoaminergic modulation of the motor cortex with an emphasis on motor skill learning and execution under physiological conditions.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

Different stress-related gene expression in depression and suicide

OBJECTIVE

Suicide occurs in some, but not all depressed patients. So far, it remains unknown whether the studied stress-related candidate genes change in depression, suicide or both. The prefrontal cortex (PFC) is involved in, among other things, impulse control and inhibitory behavior and plays an important role in both suicide and depression.

METHODS

We have employed qPCR to study 124 anterior cingulate cortex (ACC) and dorsolateral PFC (DLPFC) brain samples, obtained from two brain banks, from: i) young depressed patients (average age 43 years) who committed suicide (MDD-S) and depressed patients who died from causes other than suicide (MDD-NS) and from ii) elderly depressed patients (average age 75 years) who did not commit suicide (DEP). Both cohorts were individually matched with non-psychiatric non-suicide control subjects. We determined the transcript levels of hypothalamic-pituitary-adrenal axis-regulating molecules (corticotropin-releasing hormone (CRH), CRH receptors, CRH binding protein, mineralocorticoid receptor/glucocorticoid receptor), transcription factors that regulate CRH expression, CRH-stimulating cytokines, chaperone proteins, retinoid signaling, brain-derived neurotrophic factor and tropomyosin-related kinase B, cytochrome proteins, nitric oxide synthase (NOS) and monoamines.

RESULTS

In the MDD-S group, expression levels of CRH and neuronal NOS-interacting DHHC domain-containing protein with dendritic mRNA (NIDD) were increased. Other changes were only present in the DEP group, i.e. decreased NIDD, and increased and 5-hydroxytryptamine receptor 1A (5-HT1A) expression levels. Changes were found to be more pronounced in the anterior cingulate cortex than in the dorsolateral PFC.

CONCLUSION

Depressed patients who committed suicide have different gene expression patterns than depressed patients who died of causes other than suicide.

The role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect

Depression is a serious global illness, becoming more and more common in developed countries. Because of specific symptoms it is considered as a leading cause of disability all over the world with a high death factor due to suicides. There are many antidepressants used in the therapy, but still more than 30% of patients do not respond to the treatment. The heterogeneous nature of the illness and its complex, unclear aetiology may be responsible for these difficulties. Next to the main monoaminergic hypothesis of depression there are also many other approaches connected with the pathophysiology of the disease, including hypothalamic-pituitary-adrenal axis dysregulation, dopaminergic, cholinergic, glutamatergic or GABA-ergic neurotransmission. Nevertheless, it can be unambiguously stated that serotonergic, noradrenergic and dopaminergic systems are precisely connected with pathogenesis of depression, and should be therefore considered as valuable targets in patients' treatment. Bearing that in mind, this review presents the role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect.

Antidepressants and the adolescent brain

Major unipolar depression is a significant global health problem, with the highest incident risk being during adolescence. A depressive illness during this period is associated with negative long-term consequences including suicide, additional psychiatric comorbidity, interpersonal relationship problems, poor educational performance and poor employment attainment well into adult life. Despite previous safety concerns, selective serotonin reuptake inhibitors (SSRIs) remain a key component of the treatment of moderate to severe depression episodes in adolescents. The impact of SSRIs on the developing adolescent brain, however, remains unclear. In this review we first consider what is currently known about the developing brain during adolescence and how these development processes may be affected by a depressive illness. We then review our understanding of the action of SSRIs, their effects on the brain and how these may differ between adults and adolescents. We conclude that there is currently little evidence to indicate that the human adolescent brain is at developmental risk from SSRIs. Furthermore, there is no clear-cut evidence to support the concerns of marked suicidal adverse side effects accruing in depressed adolescents being treated with SSRIs. Neither, however, is there irrefutable evidence to dismiss all such concerns. This makes SSRI prescribing a matter of medical judgement, ensuring the benefits outweigh the risks for the individual patients, as with so much in therapeutics. Overall, SSRIs show clinical benefits that we judge to outweigh the risks to neurodevelopment and are an important therapeutic choice in the treatment of moderate to severe adolescent depression.

Dietary DHA during development affects depression-like behaviors and biomarkers that emerge after puberty in adolescent rats

DHA is an important omega-3 PUFA that confers neurodevelopmental benefits. Sufficient omega-3 PUFA intake has been associated with improved mood-associated measures in adult humans and rodents, but it is unknown whether DHA specifically influences these benefits. Furthermore, the extent to which development and puberty interact with the maternal diet and the offspring diet to affect mood-related behaviors in adolescence is poorly understood. We sought to address these questions by 1) feeding pregnant rats with diets sufficient or deficient in DHA during gestation and lactation; 2) weaning their male offspring to diets that were sufficient or deficient in DHA; and 3) assessing depression-related behaviors (forced swim test), plasma biomarkers [brain-derived neurotrophic factor (BDNF), serotonin, and melatonin], and brain biomarkers (BDNF) in the offspring before and after puberty. No dietary effects were detected when the offspring were evaluated before puberty. In contrast, after puberty depressive-like behavior and its associated biomarkers were worse in DHA-deficient offspring compared with animals with sufficient levels of DHA. The findings reported here suggest that maintaining sufficient DHA levels throughout development (both pre- and postweaning) may increase resiliency to emotional stressors and decrease susceptibility to mood disorders that commonly arise during adolescence.

Alterations of 5-HT1A receptor-induced G-protein functional activation and relationship to memory deficits in patients with pharmacoresistant temporal lobe epilepsy

The 5-hydroxytryptamine-1A (5-HT1A) receptors are known to be involved in the inhibition of seizures in epilepsy. Moreover, studies propose a role for the 5-HT1A receptor in memory function; it is believed that the higher density of this receptor in the hippocampus plays an important role in its regulation. Positron emission tomography (PET) studies in patients with mesial temporal lobe epilepsy (mTLE) have demonstrated that a decrease in 5-HT1A receptor binding in temporal regions may play a role in memory impairment. The evidences lead us to speculate whether this decrease in receptor binding is associated with a reduced receptor number or if the functionality of the 5-HT1A receptor-induced G-protein activation and/or the second messenger cascade is modified. The purpose of the present study is to determine 5-HT1A receptor-induced G-protein functional activation by 8-OH-DPAT-stimulated [(35)S]GTPγS binding assay in hippocampal tissue of surgical patients with mTLE. We correlate functional activity with epilepsy history and neuropsychological assessment of memory. We found that maximum functional activation stimulation values (Emax) of [(35)S]GTPγS binding were significantly increased in mTLE group when compared to autopsy samples. Furthermore, significant correlations were found: (1) positive coefficients between the Emax with the age of patient and frequency of seizures; (2) negative coefficients between the Emax and working memory, immediate recall and delayed recall memory tasks. Our data suggest that the epileptic hippocampus of patients with mTLE presents an increase in 5-HT1A receptor-induced G-protein functional activation, and that this altered activity is related to age and seizure frequency, as well as to memory consolidation deficit.

Transitions in the transcriptome of the serotonergic and dopaminergic systems in the human brain during adolescence

Adolescence is a period of profound neurophysiological, behavioral, cognitive and psychological changes, but not much is known about the underlying molecular neural mechanisms. The aim of this study was to systematically analyze expression levels of the genes forming serotonergic and dopaminergic synapses during adolescence. We analyzed the mRNA expression profiles of genes that code for all components of serotonergic and dopaminergic synapses, in 16 brain areas from human and non-human primates from public domain databases, to detect genes whose expression changes during adolescence. Two serotonin receptors, HTR1E and HTR1B had expression levels that exhibit a sharp transition in the prefrontal cortex in adolescence, but we found no similar transition in the dopaminergic system. A similar but smoother rise in expression levels is observed in HTR4 and HTR5A, and in HTR1E and HTR1B in three other expression datasets published. An earlier rise is observed in HTR1A, and a smooth and significant rise with age is observed in the expression of HTR1E in microarray measurements in macaque monkeys. The expression of HTR1E and HTR1B is correlated across subjects within each age group, suggesting that they are controlled by common mechanisms. These results point to HTR1E and HTR1B as major candidate genes involved in adolescence maturation processes, and to their operation through common control mechanisms. The maturation profiles may also involve several other 5-HT receptors, including the genes HTR5A, HTR4 and HTR1A.

5-HT(1A) [corrected] receptors in mood and anxiety: recent insights into autoreceptor versus heteroreceptor function

RATIONALE

Serotonin (5-HT) neurotransmission is intimately linked to anxiety and depression and a diverse body of evidence supports the involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT(1A)) subtype, in both disorders.

OBJECTIVES

In this review, we examine the function of 5-HT(1A) receptor subpopulations and re-interpret our understanding of their role in mental illness in light of new data, separating both spatial (autoreceptor versus heteroreceptor) and the temporal (developmental versus adult) roles of the endogenous 5-HT(1A) receptors, emphasizing their distinct actions in mediating anxiety and depression-like behaviors.

RESULTS

It is difficult to unambiguously distinguish the effects of different populations of the 5-HT(1A) receptors with traditional genetic animal models and pharmacological approaches. However, with the advent of novel genetic systems and subpopulation-selective pharmacological agents, direct evidence for the distinct roles of these populations in governing emotion-related behavior is emerging.

CONCLUSIONS

There is strong and growing evidence for a functional dissociation between auto- and heteroreceptor populations in mediating anxiety and depressive-like behaviors, respectively. Furthermore, while it is well established that 5-HT(1A) receptors act developmentally to establish normal anxiety-like behaviors, the developmental role of 5-HT(1A) heteroreceptors is less clear, and the specific mechanisms underlying the developmental role of each subpopulation are likely to be key elements determining mood control in adult subjects.

Neuronal control of breathing: sex and stress hormones

There is a growing public awareness that hormones can have a significant impact on most biological systems, including the control of breathing. This review will focus on the actions of two broad classes of hormones on the neuronal control of breathing: sex hormones and stress hormones. The majority of these hormones are steroids; a striking feature is that both groups are derived from cholesterol. Stress hormones also include many peptides which are produced primarily within the paraventricular nucleus of the hypothalamus (PVN) and secreted into the brain or into the circulatory system. In this article we will first review and discuss the role of sex hormones in respiratory control throughout life, emphasizing how natural fluctuations in hormones are reflected in ventilatory metrics and how disruption of their endogenous cycle can predispose to respiratory disease. These effects may be mediated directly by sex hormone receptors or indirectly by neurotransmitter systems. Next, we will discuss the origins of hypothalamic stress hormones and their relationship with the respiratory control system. This relationship is 2-fold: (i) via direct anatomical connections to brainstem respiratory control centers, and (ii) via steroid hormones released from the adrenal gland in response to signals from the pituitary gland. Finally, the impact of stress on the development of neural circuits involved in breathing is evaluated in animal models, and the consequences of early stress on respiratory health and disease is discussed.

5-HT1A sex based differences in Bmax, in vivo KD, and BPND in the nonhuman primate

Serotonin (5-HT) dysfunction has been implicated in neuropsychiatric illnesses and may play a pivotal role in the differential prevalence of depression between the sexes. Previous PET studies have revealed sex-based differences in 5-HT1A binding potential (BPND). The binding potential is a function of the radioligand-receptor affinity (1/KDapp), and receptor density (Bmax). In this work, we use a multiple-injection (MI) PET protocol and the 5-HT1A receptor antagonist, [(18)F]mefway, to compare sex-based differences of in vivo affinity, Bmax, and BPND in rhesus monkeys.

METHODS

PET [(18)F]mefway studies were performed on 17 (6m, 11f) rhesus monkeys using a 3-injection protocol that included partial saturation injections of mefway. Compartmental modeling was performed using a model to account for non-tracer doses of mefway for the estimation of KDapp and Bmax. BPND estimates were also acquired from the first injection (high specific activity [(18)F]mefway, 90-minute duration) for comparison using the cerebellum (CB) as a reference region. Regions of interest were selected in 5-HT1A binding regions of the hippocampus (Hp), dorsal anterior cingulate cortex (dACC), amygdala (Am), and raphe nuclei (RN).

RESULTS

Female subjects displayed significantly (*p<0.05) lower KDapp in the Hp (-32%), Am (-38%), and RN (-37%). Only the Hp displayed significant differences in Bmax with females having a Bmax of -29% compared to males. Male subjects demonstrated significantly lower BPND measurements in the Am (14%) and RN (29%).

CONCLUSION

These results suggest that the higher BPND values found in females are the result of lower [(18)F]mefway KDapp. Although a more experimentally complex measurement, separate assay of KDapp and Bmax provides a more sensitive measure than BPND to identify the underlying differences between females and males in 5-HT1A function.

Biological basis of suicide and suicidal behavior

OBJECTIVE

Suicide is a major public health concern as each year 30000 people die by suicide in the USA alone. In the teenage population, it is the second leading cause of death. There have been extensive studies of psychosocial factors associated with suicide and suicidal behavior. However, very little is known about the neurobiology of suicide. Recent research has provided some understanding of the neurobiology of suicide, which is the topic of this review.

METHODS

Neurobiology of suicide has been studied using peripheral tissues such as platelets, lymphocytes, and cerebrospinal fluid obtained from suicidal patients or from the postmortem brains of suicide victims.

RESULTS

These studies have provided encouraging information with regard to the neurobiology of suicide. They show an abnormality of the serotonergic mechanism, such as increased serotonin receptor subtypes and decreased serotonin metabolites (e.g. 5-hydroxyindoleacetic acid). These studies also suggest abnormalities of receptor-linked signaling mechanisms such as phosphoinositide and adenylyl cyclase. Other biological systems that appear to be dysregulated in suicide involve the hypothalamic-pituitary-adrenal axis, and neurotrophins and neurotrophin receptors. More recently, several studies have also indicated abnormalities of neuroimmune functions in suicide.

CONCLUSIONS

Some encouraging information emerged from the present review, primarily related to some of the neurobiological mechanisms mentioned above. It is hoped that neurobiological studies may eventually result in the identification of appropriate biomarkers for suicidal behavior as well as appropriate therapeutic targets for its treatment.

Lower anxiogenic effects of serotonin agonists are associated with lower activation of amygdala and lateral orbital cortex in adolescent male rats

There has been controversy over use of selective serotonin reuptake inhibitors (SSRIs) to treat affective disorders in children and adolescents due to clinical reports of increased risk for suicidal ideation and behavior during treatment, and animal studies showing changes in adult anxiety- and depressive-like behaviors after repeated treatment during adolescence. However, the acute effect of serotonergic drugs on affective behavior during adolescence is poorly understood. We investigated serotonergic modulation of anxiety-like behavior in adolescent (PN28-32) and adult (PN67-73) male rats using the SSRI fluoxetine, the 5-HT(1A) agonist 8-OH DPAT, and the 5-HT₂ agonist mCPP. Acute treatment with fluoxetine (10 mg/kg, i.p.) produced greater anxiogenic effects in adults than adolescents in the light/dark (LD) test for anxiety-like behavior, but fluoxetine (2.5, 5, and 10 mg/kg, i.p.) increased extracellular serotonin in the medial prefrontal cortex similarly in both ages. Adults were also more sensitive to the anxiogenic effects of 8-OH DPAT (0.25 and 0.5 mg/kg, i.p.), but not mCPP (0.5 and 1 mg/kg, i.p.), in the LD test. Fluoxetine (10 mg/kg) stimulated greater increases in c-Fos expression across the extended amygdala in adults than in adolescents, and 8-OH DPAT (0.5 mg/kg) produced greater increases in c-Fos in the lateral orbital cortex and central nucleus of the amygdala in adults. These data show that lower anxiogenic effects of acute SSRIs in adolescents are associated with lesser activation of cortical and amygdala brain regions. This immaturity could contribute to the different profile of behavioral effects observed in adolescents and adults treated with SSRIs.

Neuroimaging over the course of Parkinson's disease: from early detection of the at-risk patient to improving pharmacotherapy of later-stage disease

Brain imaging of striatal dopamine terminal degeneration serves an important role in the clinical management of Parkinson's disease (PD). Imaging biomarkers for interrogating dopaminergic systems are used for clarifying diagnosis when only subtle motor symptoms are present. However, motor dysfunction is not the earliest symptom of PD. There is increasing interest in identifying premotor PD patients, particularly because potential disease-modifying therapies are developed and the clinical imperative becomes early and accurate diagnosis. On the other end of the spectrum of the disease course, during later stages of PD, significant clinical challenges like levo-dopa-induced dyskinesias and medication on-off phenomenon become more prevalent. In this instance, better understanding of altered PD motor pathways suggests the potential utility of novel treatments targeting neuronal systems that are impacted by degenerating dopamine neurons and chronic dopamine replacement treatment. Molecular neuroimaging serves unique roles in both very early PD and later-stage disease, in the former, potentially pushing back the time of diagnosis, and in the latter, elucidating pathology relevant to new drug development.

Effects of the antidepressant fluoxetine on the subcellular localization of 5-HT1A receptors and SERT

Serotonin (5-HT) 5-HT(1A) autoreceptors (5-HT(1A)autoR) and the plasmalemmal 5-HT transporter (SERT) are key elements in the regulation of central 5-HT function and its responsiveness to antidepressant drugs. Previous immuno-electron microscopic studies in rats have demonstrated an internalization of 5-HT(1A)autoR upon acute administration of the selective agonist 8-OH-DPAT or the selective serotonin reuptake inhibitor antidepressant fluoxetine. Interestingly, it was subsequently shown in cats as well as in humans that this internalization is detectable by positron emission tomography (PET) imaging with the 5-HT(1A) radioligand [(18)F]MPPF. Further immunocytochemical studies also revealed that, after chronic fluoxetine treatment, the 5-HT(1A)autoR, although present in normal density on the plasma membrane of 5-HT cell bodies and dendrites, do not internalize when challenged with 8-OH-DPAT. Resensitization requires several weeks after discontinuation of the chronic fluoxetine treatment. In contrast, the SERT internalizes in both the cell bodies and axon terminals of 5-HT neurons after chronic but not acute fluoxetine treatment. Moreover, the total amount of SERT immunoreactivity is then reduced, suggesting that SERT is not only internalized, but also degraded in the course of the treatment. Ongoing and future investigations prompted by these finding are briefly outlined by way of conclusion.

Developmental risk I: depression and the developing brain

This article discusses recent findings on the neurobiology of pediatric depression as well as the interplay between genetic and environmental factors in determining the risk for the disorder. Utilizing data from both animal and human studies, the authors focus on the evolving understanding of the developmental neurobiology of emotional regulation, cognitive function and social behavior as it applies to the risk and clinical course of depression. Treatment implications and directions for future research are also discussed.

Effects of maternal L-tryptophan depletion and corticosterone administration on neurobehavioral adjustments in mouse dams and their adolescent and adult daughters

Major depressive disorder (MDD), a pathology characterized by mood and neurovegetative disturbances, depends on a multi-factorial contribution of individual predisposition (e.g., diminished serotonergic transmission) and environmental factors (e.g., neonatal abuse or neglect). Despite its female-biased prevalence, MDD basic research has mainly focused on male rodents. Most of present models of depression are also devalued due to the fact that they typically address only one of the aforementioned pathogenetic factors. In this paper we first describe the basic principles behind mouse model development and evaluation and then articulate that current models of depression are intrinsically devalued due to poor construct and/or external validity. We then report a first attempt to overcome this limitation through the design of a mouse model in which the genetic and the environmental components of early risk factors for depression are mimicked together. Environmental stress is mimicked through the supplementation of corticosterone in the maternal drinking water while biological predisposition is mimicked through maternal access to an L-tryptophan (the serotonin precursor) deficient diet during the first week of lactation. CD1 dams and their offspring exposed to the L-tryptophan deficient diet (T) and to corticosterone (80mg/l; C) were compared to animal facility reared (AFR) subjects. T and C mice served as intermediate reference groups. Adolescent TC offspring, compared to AFR mice, showed decreased time spent floating in the forced-swim test and increased time spent in the open sectors of an elevated 0-maze. Adult TC offspring showed reduced preference for novelty, decreased breakpoints in the progressive ratio operant procedure and major alterations in central BDNF levels and altered HPA regulation. The route of administration and the possibility to control the independent variables predisposing to depressive-like symptoms disclose novel avenues towards the development of animal models with increased external and construct validity. Furthermore, the observation that, compared to adult subjects, adolescent mice display an opposite profile suggests that peri-pubertal developmental processes may interact with neonatal predispositions to calibrate the adult abnormal phenotype.

Age-dependent effects of initial exposure to nicotine on serotonin neurons

Adolescence is a critical vulnerable period during which exposure to nicotine greatly enhances the possibility to develop drug addiction. Growing evidence suggests that serotonergic (5-HT) neurotransmission may contribute to the initiation and maintenance of addictive behavior. As the dorsal raphe (DR) and median raphe (MnR) nuclei are the primary 5-HT source to the forebrain, the current study tested the hypothesis that there are age-dependent effects of acute nicotine administration on activation of 5-HT neurons within these regions. Both adolescent (Postnatal day 30) and adult (Postnatal day 70) male Sprague-Dawley rats received subcutaneous injection of either saline or nicotine (0.2, 0.4, or 0.8 mg/kg). Subsequently, the number of 5-HT cells that were double-labeled for Fos and tryptophan hydroxylase was counted in seven subregions within the DR and the entire MnR. The results show that acute nicotine injection induces Fos expression in 5-HT neurons in a region-specific manner. In addition, adolescents show broader regional activations at either a lower (0.2 mg/kg) and a higher (0.8 mg/kg) dose of nicotine, displaying a unique U-shape response curve across doses. In contrast, 5-HT cells with activated Fos expression were restricted to fewer regions in adults, and the patterns of expression were more consistent across doses. The results reveal dose-dependent effects of nicotine during adolescence with apparent sensitization at different ends of the dosage spectrum examined compared to adults. These data indicate that initial exposure to nicotine may have unique effects in adolescence on the ascending 5-HT system, with the potential for consequences on the affective-motivational qualities of the drug and the subsequent propensity for repeated use.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

What can post-mortem studies tell us about the pathoetiology of suicide?

Suicide is a major public health concern; however, its neurobiology is unclear. Post-mortem brain tissue obtained from suicide victims and normal controls offers a useful method for studying the neurobiology of suicide. Despite several limitations, these studies have offered important leads in the neurobiology of suicide. In this article, we discuss some important findings resulting from these studies, focusing on serotonergic mechanisms, signal transduction systems, neuroendocrine studies and immune function abnormalities in suicide. These studies suggest that abnormalities of certain receptor subtypes, components of signaling systems such as protein kinase C and protein kinase A, transcription factors such as cyclic AMP response element-binding protein and neurotrophins may play an important role in the pathophysiology of suicide. These studies also suggest abnormalities of hypothalamic-pituitary-adrenal axis system components, feedback mechanisms and cytokines, which are chemical mediators of the immune functions. Post-mortem brain tissue offers an opportunity for future studies, such as genetic and epigenetic studies.

Decreased expression of Freud-1/CC2D1A, a transcriptional repressor of the 5-HT1A receptor, in the prefrontal cortex of subjects with major depression

Serotonin1A (5-HT(1A)) receptors are reported altered in the brain of subjects with major depressive disorder (MDD). Recent studies have identified transcriptional regulators of the 5-HT(1A) receptor and have documented gender-specific alterations in 5-HT(1A) transcription factor and 5-HT(1A) receptors in female MDD subjects. The 5' repressor element under dual repression binding protein-1 (Freud-1) is a calcium-regulated repressor that negatively regulates the 5-HT(1A) receptor gene. This study documented the cellular expression of Freud-1 in the human prefrontal cortex (PFC) and quantified Freud-1 protein in the PFC of MDD and control subjects as well as in the PFC of rhesus monkeys chronically treated with fluoxetine. Freud-1 immunoreactivity was present in neurons and glia and was co-localized with 5-HT(1A) receptors. Freud-1 protein level was significantly decreased in the PFC of male MDD subjects (37%, p=0.02) relative to gender-matched control subjects. Freud-1 protein was also reduced in the PFC of female MDD subjects (36%, p=0.18) but was not statistically significant. When the data was combined across genders and analysed by age, the decrease in Freud-1 protein level was greater in the younger MDD subjects (48%, p=0.01) relative to age-matched controls as opposed to older depressed subjects. Similarly, 5-HT(1A) receptor protein was significantly reduced in the PFC of the younger MDD subjects (48%, p=0.01) relative to age-matched controls. Adult male rhesus monkeys administered fluoxetine daily for 39 wk revealed no significant change in cortical Freud-1 or 5-HT(1A) receptor proteins compared to vehicle-treated control monkeys. Reduced protein expression of Freud-1 in MDD subjects may reflect dysregulation of this transcription factor, which may contribute to the altered regulation of 5-HT(1A) receptors observed in subjects with MDD. These data may also suggest that reductions in Freud-1 protein expression in the PFC may be associated with early onset of MDD.

Higher serotonin 1A binding in a second major depression cohort: modeling and reference region considerations

BACKGROUND

Serotonin 1A receptors (5-HT(1A)) are implicated in major depressive disorder (MDD). We previously reported higher 5-HT(1A) binding potential (BP(F)) in antidepressant naive MDD subjects compared with control subjects, while other studies report lower BP(ND). Discrepancies can be related to differences in study population or methodology. We sought to replicate our findings in a novel cohort and determine whether choice of reference region and outcome measure could explain discrepancies.

METHODS

Nine new control subjects and 22 new not recently medicated (NRM) MDD subjects underwent positron emission tomography. BP(F) and BP(ND) were determined using a metabolite and free fraction corrected arterial input function. BP(ND) was also determined using cerebellar gray matter (CGM) and cerebellar white matter (CWM) reference regions as input functions.

RESULTS

BP(F) was higher in the new NRM cohort (p = .037) compared with new control subjects, comparable to the previous cohort (p = .04). Cohorts were combined to examine the reference region and outcome measure. BP(F) was higher in the NRM compared with control subjects (p = .0001). Neither BP(ND) using CWM (p = .86) nor volume of distribution (V(T)) (p = .374) differed between groups. When CGM was used, the NRM group had lower 5-HT(1A) BP(ND) compared with control subjects (p = .03); CGM V(T) was higher in NRM compared with control subjects (p = .007).

CONCLUSIONS

Choice of reference region and outcome measure can produce different 5-HT(1A) findings. Higher 5-HT(1A) BP(F) in MDD was found with the method with fewest assumptions about nonspecific binding and a reference region without receptors.

Early-life blockade of 5-HT(1A) receptors alters adult anxiety behavior and benzodiazepine sensitivity

BACKGROUND

Early-life stress may affect 5-HT(1A) receptor circuitry, which could result in increased anxiety in later life. An increased anxiety phenotype in 5-HT(1A) receptor KO mice (1AKO) mice has been ascribed to 5-HT(1A) receptor absence during the early postnatal period. Thus, subtle and transient serotonergic changes during the early postnatal period may lead to an increased risk for developing stress-related disorders during adulthood.

METHODS

Wildtype and 1AKO mice on a Swiss-Webster (SW) background were treated during the early postnatal period with vehicle or the 5-HT(1A) receptor antagonist WAY-100,635.

RESULTS

Pharmacologic 5-HT(1A) receptor blockade during the early postnatal period induced long-lasting effects on anxiety and benzodiazepine sensitivity in adolescent and adult mice on a Swiss-Webster background and resembles the SW 1AKO phenotype. Furthermore, WAY-100,635-treated mice had increased cortical gamma-aminobutyric acid-A receptor (GABA(A)R) alpha(1) and alpha(3) subunit levels and increased hippocampal GABA(A)R alpha(2) subunit levels.

CONCLUSIONS

Absence of 5-HT(1A)R signaling during early stages of brain maturation predisposes an organism to affective dysfunction later in life. Because early-life treatment with WAY-100,635 in Swiss-Webster mice reduced diazepam sensitivity and increased GABA(A)R alpha subunit levels in the prefrontal cortex and hippocampus, our data suggest a putative link between early-life disruption of the serotonergic system and the emergence of increased anxiety and decreased benzodiazepine responsivity at adult age. Moreover, early-life 5-HT(1A) receptor functionality appears to be essential for the development of normal GABA(A)R functionality. This study may have clinical implications for psychoactive drug use during pregnancy and for the pharmacogenetic background of benzodiazepine sensitivity.

Gender, personality, and serotonin-2A receptor binding in healthy subjects

The vulnerability to mood disorders, impulsive-aggression, eating disorders, and suicidal behavior varies greatly with gender, and may reflect gender differences in central serotonergic function. We investigated the relationships of gender, mood, impulsivity, aggression and temperament to 5HT(2A) receptor binding in 21 healthy subjects using [18F]altanserin and PET neuroimaging. Binding potentials in pre-defined regions-of-interest (ROI) were calculated using the Logan graphical method, corrected for partial volume effects, and compared by gender with age co-varied. SPM analysis was used for voxel level comparisons. Altanserin binding (BP(P)) was greater in male than female subjects in the following nine ROIs: hippocampus (HIP) and Lt. HIP, lateral orbital frontal cortex (LOF) and Lt. LOF, left medial frontal cortex (Lt. MFC), left medial temporal cortex (Lt. MTC), left occipital cortex (Lt. OCC), thalamus (THL) and Lt. THL. Differences in Lt. HIP and Lt. MTL remained significant after Bonferroni correction. Gender differences were noted in the co-variation of psychological traits with BP(P) values in specific ROIs. Among males alone, aggression was negatively correlated with BP(P) values in Lt. LOF and Lt. MFC, and Suspiciousness positively correlated in LOF, Lt. LOF and Lt. MFC. Among female subjects alone, Negativism was positively correlated with BP(P) values in HIP, and Verbal Hostility in Lt. HIP. Altanserin binding in Lt. MTC was positively correlated with Persistence, with no significant gender effect. Gender differences in 5HT(2A) receptor function in specific ROIs may mediate expression of psychological characteristics such as aggression, suspiciousness and negativism. Future studies of 5HT(2A) receptor function and its relationship to behavior should control for gender.

Receptor mapping: architecture of the human cerebral cortex

PURPOSE OF REVIEW

Cytoarchitectonical brain mapping is of growing interest as a powerful tool for localization of activated brain regions in functional neuroimaging. Mapping of neurotransmitter receptors can provide novel molecular and functionally relevant information to the available cytoarchitectonical brain maps, because receptors are key molecules of neurotransmission. This review highlights the relation between cytoarchitectonical parcellations and the regionally inhomogeneous distribution of receptors. It will demonstrate the potential of receptor mapping for novel and functionally relevant insights into the regional organization of the human cortex.

RECENT FINDINGS

Mapping of a single receptor type can already reveal borders of functionally and cytoarchitectonically distinct cortical regions. The combined mapping of various receptors in each cortical area (receptor fingerprint) represents the balance between different neurotransmitter systems and often reveals hitherto unknown parcellations. Different brain regions are identified as parts of distinct functional systems.

SUMMARY

Receptor mapping of the human brain, particularly multireceptor mapping, provides a novel and multimodal view of its anatomical, functional and molecular organization. It reveals organizational principles of the segregation of cortical and subcortical structures. It improves our understanding of the brain's architecture beyond the limits of cytoarchitectonics and serves as a basis for clinical and pharmacological studies of brain diseases.

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Antagonist but not agonist labeling of serotonin-1A receptors is decreased in major depressive disorder

Serotonin-1A receptors may play a role in the pathophysiology of depression and suicide. In postmortem brain tissue, agonist binding to serotonin-1A receptors is reportedly increased or unchanged in depression or suicide, while neuroimaging studies report a decrease in antagonist binding to these receptors in subjects with depression. In this study, both agonist and antagonist radioligand binding to serotonin-1A receptors were examined in postmortem orbitofrontal cortex from subjects with major depressive disorder (MDD). Brain tissue was collected at autopsy from 11 subjects with MDD and 11 age- and gender-matched normal control subjects. Two depressed subjects had a recent psychoactive substance use disorder. Six subjects with MDD had a prescription for an antidepressant drug in the last month of life, and, of these six, postmortem bloods from only two subjects tested positive for an antidepressant drug. There was no significant difference between cohorts for age, postmortem interval or tissue pH. The receptor agonist [3H]8-OH-DPAT or the antagonist [3H]MPPF were used to autoradiographically label serotonin-1A receptors in frozen sections from cytoarchitectonically-defined left rostral orbitofrontal cortex (area 47). There was no significant difference between depressed and control subjects in agonist binding to serotonin-1A receptors. However, antagonist binding was significantly decreased in outer layers of orbitofrontal cortex in MDD. This observation in postmortem tissue confirms reports using an antagonist radioligand in living subjects with depression. Decreased antagonist binding to serotonin-1A receptors in outer layers of orbitofrontal cortex suggests diminished receptor signaling and may be linked to corresponding neuronal changes detected previously in these depressed subjects.

Decreased brain docosahexaenoic acid content produces neurobiological effects associated with depression: Interactions with reproductive status in female rats

Decreased tissue levels of docosahexaenoic acid (DHA; 22:6n-3) are implicated in the etiologies of non-puerperal and postpartum depression. With the aim of determining neurobiological sequelae of decreased brain DHA content, this study examined the effects of a loss of brain DHA content and concurrent reproductive status in adult female Long-Evans rats. An alpha-linolenic acid-deficient diet and breeding protocols were used to produce virgin and parous female rats with cortical phospholipid DHA levels 23-26% lower than virgin and parous rats fed a control diet containing adequate alpha-linolenic acid. Parous dams were tested/euthanized at weaning (postnatal day 20) of the second litter; virgin females, during diestrus. Decreased brain DHA was associated with decreased hippocampal BDNF gene expression and increased relative corticosterone response to an intense stressor, regardless of reproductive status. In virgin females with decreased brain DHA, serotonin content and turnover in frontal cortex were decreased compared to virgin females with normal brain DHA. In parous dams with decreased brain DHA, the density of 5-HT(1A) receptors in the hippocampus was increased, corticosterone response to an intense stressor was increased, and the latency to immobility in the forced swim test was decreased compared to parous dams with normal DHA. These findings demonstrate neurobiological alterations attributable to decreased brain DHA or an interaction of parous status and brain DHA level. Furthermore, the data are consistent with findings in depressed humans, and thus support a role for DHA as a factor in the etiologies of depressive illnesses, particularly postpartum depression.

Sex differences in the neurotoxic effects of adenosine A1 receptor antagonism during ethanol withdrawal: reversal with an A1 receptor agonist or an NMDA receptor antagonist

BACKGROUND

Neuronal adaptations that occur during chronic ethanol (EtOH) exposure have been observed to sensitize the brain to excitotoxic insult during withdrawal. The adenosine receptor system warrants further examination in this regard, as recent evidence has implicated adenosine receptor involvement in the behavioral effects of both EtOH exposure and withdrawal.

METHODS

The current studies examined effects of adenosine A(1) receptor manipulation on neuronal injury in EtOH-naive and EtOH-withdrawn male and female rat hippocampal slice cultures. EtOH-naive and EtOH pretreated (43.1 to 26.9 mM from days 5 to 15 DIV) cultures were exposed to the A(1) receptor agonist 2-Chloro-N(6)-cyclopentyladenosine (CCPA; 10 nM), the A(1) receptor antagonist 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX;10 nM), or the N-methyl-D-aspartate (NMDA) receptor antagonist D,L,-2-amino-5-phosphovalerate (APV; 20 microM) at 15 days in vitro (DIV). Cytotoxicity was measured in the primary neuronal layers of the dentate gyrus, CA3 and CA1 hippocampal regions by quantification of propidium iodide (PI) fluorescence after 24 hours. Immunohistochemical analysis of A(1) receptor abundance was conducted in EtOH-naive and EtOH pretreated slice cultures at 15 DIV.

RESULTS

Twenty-four hour exposure to DPCPX in EtOH-naive slice cultures did not produced neurotoxicity in any region of slice cultures. Though withdrawal from 10 day EtOH exposure produced no toxicity in either male or female slice cultures, exposure to DPCPX during 24 hours of EtOH withdrawal produced a marked increase in PI uptake in all hippocampal culture subregions in female cultures (to approximately 160% of control values). A significant effect for sex was observed in the CA1 region such that toxicity in females cultures exposed to the A(1) antagonist during withdrawal was greater than that observed in male cultures. These effects of DPCPX in EtOH withdrawn female and male slices were prevented by co-exposure to either the A(1) agonist CCPA or the NMDA receptor antagonist APV for 24 hours. No differences in the abundance of A(1) receptors were observed in male and female EtOH-naive or EtOH pretreated cultures.

CONCLUSIONS

The current findings suggest that the female hippocampus possesses an innate sensitivity to effects of EtOH exposure and withdrawal on neuronal excitability that is independent of hormonal influences. Further, this sex difference is not related to effects of EtOH exposure on A(1) receptor abundance, but likely reflects increased NMDA receptor-mediated signaling downstream of A(1) inhibition in females.

The serotonin-1A receptor distribution in healthy men and women measured by PET and [carbonyl-11C]WAY-100635

PURPOSE

The higher prevalence rates of depression and anxiety disorders in women compared to men have been associated with sexual dimorphisms in the serotonergic system. The present positron emission tomography (PET) study investigated the influence of sex on the major inhibitory serotonergic receptor subtype, the serotonin-1A (5-HT(1A)) receptor.

METHODS

Sixteen healthy women and 16 healthy men were measured using PET and the highly specific radioligand [carbonyl-(11)C]WAY-100635. Effects of age or gonadal hormones were excluded by restricting the inclusion criteria to young adults and by controlling for menstrual cycle phase. The 5-HT(1A) receptor BP(ND) was quantified using (1) the 'gold standard' manual delineation approach with ten regions of interest (ROIs) and (2) a newly developed delineation method using a PET template normalized to the Montreal Neurologic Institute space with 45 ROIs based on automated anatomical labeling.

RESULTS

The 5-HT(1A) receptor BP(ND) was found equally distributed in men and women applying both the manual delineation method and the automated delineation approach. Women had lower mean BP(ND) values in every region investigated, with a borderline significant sex difference in the hypothalamus (p = 0.012, uncorrected). There was a high intersubject variability of the 5-HT(1A) receptor BP(ND) within both sexes compared to the small mean differences between men and women.

CONCLUSIONS

To conclude, when measured in the follicular phase, women do not differ from men in the 5-HT(1A) receptor binding. To explain the higher prevalence of affective disorders in women, further studies are needed to evaluate the relationship between hormonal status and the 5-HT(1A) receptor expression.