Effect of age on human brain serotonin (S-1) binding sites

Serotonin therapies for opioid-induced disordered swallow and respiratory depression

Opioids are well-known to cause respiratory depression, but despite clinical evidence of dysphagia, the effects of opioids on swallow excitability and motor pattern are unknown. We tested the effects of the clinically relevant opioid buprenorphine on pharyngeal swallow and respiratory drive in male and female rats. We also evaluated the utility of 5-HT1A agonists (8-OH-DPAT and buspirone) to improve swallowing and breathing following buprenorphine administration. Experiments were performed on 44 freely breathing Sprague-Dawley rats anesthetized with sodium pentobarbital. Bipolar fine wire electrodes were inserted into the mylohyoid, thyroarytenoid, posterior cricoarytenoid, thyropharyngeus, and diaphragm muscles to measure electromyographic (EMG) activity of swallowing and breathing. We evaluated the hypotheses that swallowing varies by stimulus, opioids depress swallowing and breathing, and that 5-HT1A agonists improve these depressions. Our results largely confirmed the following hypotheses: 1) swallow-related EMG activity was larger during swallows elicited by esophageal distension plus oral water infusion than by either stimulus alone. 2) Buprenorphine depressed swallow in both sexes, but females were more susceptible to total swallow suppression. 3) Female animals were also more vulnerable to opioid-induced respiratory depression. 4) 8-OH-DPAT rescued breathing following buprenorphine-induced respiratory arrest, and pretreatment with the partial 5-HT1A agonist buspirone prevented buprenorphine-induced respiratory arrest in female animals. 5) 8-OH-DPAT enhanced mylohyoid and thyropharyngeus EMG amplitude during swallow but did not restore excitability of the swallow pattern generator following total suppression by buprenorphine. Our results highlight sex-specific and behavior-specific effects of buprenorphine and provide preclinical evidence of a 5HT1A agonist for the treatment of respiratory depression and dysphagia.NEW & NOTEWORTHY This is the first study, to our knowledge, to evaluate sex-specific effects of opioid administration on pharyngeal swallow. We expand on a small but growing number of studies that report a lower threshold for opioid-induced respiratory depression in females compared with males, and we are the first to produce this effect with the partial μ-opioid-receptor agonist buprenorphine. This is the first demonstration, to our knowledge, that activation of 5-HT1A receptors can improve swallow and breathing outcomes following systemic buprenorphine administration.

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.

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.

Comparative neuropathology in aging primates: A perspective

While humans exhibit a significant degree of neuropathological changes associated with deficits in cognitive and memory functions during aging, non-human primates (NHP) present with more variable expressions of pathological alterations among individuals and species. As such, NHP with long life expectancy in captivity offer an opportunity to study brain senescence in the absence of the typical cellular pathology caused by age-related neurodegenerative illnesses commonly seen in humans. Age-related changes at neuronal population, single cell, and synaptic levels have been well documented in macaques and marmosets, while age-related and Alzheimer's disease-like neuropathology has been characterized in additional species including lemurs as well as great apes. We present a comparative overview of existing neuropathologic observations across the primate order, including classic age-related changes such as cell loss, amyloid deposition, amyloid angiopathy, and tau accumulation. We also review existing cellular and ultrastructural data on neuronal changes, such as dendritic attrition and spine alterations, synaptic loss and pathology, and axonal and myelin pathology, and discuss their repercussions on cellular and systems function and cognition.

Aging effect on head motion: A Machine Learning study on resting state fMRI data

BACKGROUND

Resting-state-fMRI is a technique used to explore the functional brain architecture in term of brain networks and their interactions. However, the robustness of Resting-state-fMRI analysis is negatively affected by physiological noise caused by subject head motion. The aim of our study was to provide new knowledge about the effect of normal aging on the head motion signals.

NEW METHOD

For the first time, we proposed a method for evaluating the most sensitive head motion parameters linked to subjects'aging. We enrolled 14-young(9females; mean-age = 28 ± 4.07) and 14-elderly(9females; mean-age = 66 ± 5.19) subjects. Along three axes(X,Y,Z), we extracted six motions parameters which reflected the head's movements to characterize translations(x,y,z) and rotations(angles phi,theta,psi). We performed:1)univariate analysis for comparing the groups and correlation to investigate the relationship between age and movement parameters; 2)Support-Vector-Machine, using bootstrap and calculating the feature importance.

RESULTS

Statistical analyses showed significant association between the aging and some motion's parameters(rotation psi; translations y and z). These results were also confirmed by multivariate analysis with Support-Vector-Machine that presented an AUC of 90 %.

COMPARISON TO EXISTING METHODS

The proposed method shows that normal aging produces significant increase in head motion parameters, highlighting the critical effect of motion on resting data analyses in particular considering psi, y and z movements. To our knowledge and at the present, this represents the first study investigating the accurate characterization of motion parameters in aging.

CONCLUSIONS

Our results have a high impact to improve healthy control recruitment and appropriately decreasing the risk of signal distortion, according to the age of enrolled subjects.

A genetic rat model of depression, Flinders sensitive line, has a lower density of 5-HT(1A) receptors, but a higher density of 5-HT(1B) receptors, compared to control rats

Deficiencies in brain serotonergic neurotransmission, which is in part associated with the alteration of brain serotonin (5-HT) receptors, have been proposed as part of a neurochemical imbalance in affective disorders, including depression. The drugs used for the treatment of these disorders generally act through and/or on the serotonergic system. Different animal models of depression have provided researchers with tools to obtain a better understanding of drug actions and possibilities to obtain insight into the neurochemical bases of these disorders. The measurements of the 5-HT(1A) and 5-HT(1B) receptor densities in a rat model of depression, Flinders sensitive line (FSL) rats, and comparisons with Sprague-Dawley (SPD) and Flinders resistant line (FRL) rats, are reported here. The receptor sites were quantified by autoradiography in more than 25 distinct brain regions known to have relatively large densities of respective sites. Some brain regions (e.g., dental gyrus, septal nucleus) were divided into several parts, according to previously known subdivisions, because of a substantial heterogeneity of these receptors. The densities in the FSL rats ("depressed" rats) were compared statistically to those in the SPD rats. In addition, comparisons were made to the densities in the FRL rats (rats not showing depressive symptoms). Comparisons were performed with the SPD and FRL rats because both of these strains have been used as control animals in studies of FSL rats. The results show that the densities of 5-HT(1A) receptors are not significantly different between the FSL and SPD rats, but they are significantly different from the FRL rats. 5-HT(1A) receptor density is significantly higher in the FRL rats than the SPD rats. The 5-HT(1B) receptors were significantly greater in the FSL rats than in either the SPD or FRL rats. In addition, the FRL rats have 5-HT(1B) receptor densities significantly lower in many brain regions than the SPD rats. The data presented here, in addition to previously reported differences in regional synthesis between these strains and the effect of acute citalopram on synthesis, suggest that SPD rats are likely a more appropriate control than FRL rats, when studies of FSL rats are performed with drugs acting directly or indirectly on, or through, the brain serotonergic system. However, comparisons, particularly of neurochemical and/or biological parameters in FRL rats, may reveal new insight into the alterations of 5-HT neurotransmission in this animal model of depression and possibly human depression, as well as the elevation of symptoms with treatments. The data also suggest that there could be a different fraction of 5-HT(1A) receptors in high and low affinity states in these strains, as well as the possibility of different intracellular signalling.

Drugs of abuse and the aging brain

Substance abuse among older adults has received little attention in the past, presumably because this population has traditionally accounted for only a small percentage of the drug abuse problem in the United States. The aging of the baby boomer generation (born 1946-1964), however, will soon swell the ranks of older adults and dramatically alter the demography of American society. Several observations suggest that this expansion will likely be accompanied by a precipitous increase in the abuse of drugs, including prescription medications and illicit substances, among older adults. While it is now evident that the brain changes continuously across life, how drugs of abuse interact with these age-related changes remains unclear. The dynamic nature of brain function, however, suggests that substance abuse during older age may augment the risks and require unique considerations for diagnosis and treatment. In addition to describing current and projected prevalence estimates of substance abuse among older adults, the present review discusses how aging affects brain systems involved in drug abuse, and explores the potential impact of drug abuse on the aging brain. Future directions for substance abuse research among older adults will also be considered.

Lack of serotonin1B receptor expression leads to age-related motor dysfunction, early onset of brain molecular aging and reduced longevity

Normal aging of the brain differs from pathological conditions and is associated with increased risk for psychiatric and neurological disorders. In addition to its role in the etiology and treatment of mood disorders, altered serotonin (5-HT) signaling is considered a contributing factor to aging; however, no causative role has been identified in aging. We hypothesized that a deregulation of the 5-HT system would reveal its contribution to age-related processes and investigated behavioral and molecular changes throughout adult life in mice lacking the regulatory presynaptic 5-HT(1B) receptor (5-HT(1B)R), a candidate gene for 5-HT-mediated age-related functions. We show that the lack of 5-HT(1B)R (Htr1b(KO) mice) induced an early age-related motor decline and resulted in decreased longevity. Analysis of life-long transcriptome changes revealed an early and global shift of the gene expression signature of aging in the brain of Htr1b(KO) mice. Moreover, molecular changes reached an apparent maximum effect at 18-months in Htr1b(KO) mice, corresponding to the onset of early death in that group. A comparative analysis with our previous characterization of aging in the human brain revealed a phylogenetic conservation of age-effect from mice to humans, and confirmed the early onset of molecular aging in Htr1b(KO) mice. Potential mechanisms appear independent of known central mechanisms (Bdnf, inflammation), but may include interactions with previously identified age-related systems (IGF-1, sirtuins). In summary, our findings suggest that the onset of age-related events can be influenced by altered 5-HT function, thus identifying 5-HT as a modulator of brain aging, and suggesting age-related consequences to chronic manipulation of 5-HT.

Serotonin 1A receptor binding and treatment response in late-life depression

Depression in late life carries an increased risk of dementia and brittle response to treatment. There is growing evidence to support a key role of the serotonin type 1A (5-HT(1A)) receptor as a regulator of treatment response, particularly the 5-HT(1A) autoreceptor in the dorsal raphe nucleus (DRN). We used [11C]WAY 100635 and positron emission tomography (PET) to test our hypothesis that 5-HT(1A) receptor binding in the DRN and prefrontal cortex is altered in elderly depressives and that these measures relate to treatment responsivity. We studied 17 elderly subjects with untreated (nonpsychotic, nonbipolar) major depression (four men, 13 women; mean age: 71.4+/-5.9) and 17 healthy control subjects (eight men, nine women; mean age: 70.0+/-6.7). Patients were subsequently treated with paroxetine as part of a clinical trial of maintenance therapies in geriatric depression. [11C]WAY 100635 PET imaging was acquired and binding potential (BP) values derived using compartmental modeling. We observed significantly diminished [11C]WAY 100635 binding in the DRN in depressed (BP = 2.31+/-0.90) relative to control (BP = 3.69+/-1.56) subjects (p = 0.0016). Further, the DRN BP was correlated with pretreatment Hamilton Depression Rating Scores (r = 0.60, p = 0.014) in the depressed cohort. A trend level correlation between DRN binding and time to remission (r = 0.52, p = 0.067) was observed in the 14 depressed patients for whom these data were available. Our finding of decreased [11C]WAY 100635 binding in the brainstem region of the DRN in elderly depressed patients supports evidence of altered 5-HT(1A) autoreceptor function in depression. Further, this work indicates that dysfunction in autoreceptor activity may play a central role in the mechanisms underlying treatment response to selective serotonin reuptake inhibitors in late-life depression.

Gender-specific aging effects on the serotonin 1A receptor

The effects of age on serotonergic function have been hypothesized to underlie age-related changes in mood and behaviors such as sleep and eating. Of particular interest is the serotonin type-1A (5-HT1A) receptor, due to its putative role in mediating the therapeutic efficacy of antidepressant treatment. Using positron emission tomography (PET) and [11C--carbonyl] WAY100635, we assessed 5-HT1A receptor binding in 21 healthy subjects (10 men, 11 women) ranging in age from 21 to 80 years. Regional binding potential values were generated using a reference tissue model and corrected for partial volume effects. We observed an inverse relationship between age and binding of [11C--carbonyl] WAY100635 to the 5-HT1A receptor in men, but not women. This finding is in accord with observations reported in the postmortem literature. Gender-specific effects of age on central serotonergic function may relate to differences between men and women in behavior, mood, and susceptibility to neuropsychiatric disease across the adult lifespan.

Neurohormonal responses to D-fenfluramine in healthy elderly subjects. A placebo-controlled study

Considering age-related changes in serotonin (5HT) function, we examined normative data of prolactin (PRL) and cortisol (CORT) responses to D-fenfluramine (D-FEN) in healthy elderly subjects. Twenty-three healthy male and female volunteers aged 60-86 participated in a single-blind, placebo-controlled, fixed-order, crossover-design challenge test. Two baseline PRL and CORT values and the responses of these hormones to 30 mg of oral D-FEN and placebo over a 4 h period were measured on two separate sessions. PRL and CORT responses were significantly greater following D-FEN than after placebo. Peak PRL responses (maximum change from baseline following D-FEN) were relatively robust compared to peak CORT responses. Peak PRL concentration was positively correlated with plasma D-nor-FEN concentration. Gender and aging had no effect on hormonal responses in the elderly. Although the weight adjusted dose used in this study was higher than the therapeutic dose of D-FEN, PRL responses were modest and only two participants experienced side effects. D-FEN is a safe serotonergic probe and PRL responsivity to D-FEN is a reliable index of central 5HT function in the elderly. An age-related decline in serotonergic function must be considered in determining the dose requirement for maximal hormonal responses to D-FEN challenge tests in the elderly.

Serotonin, cerebral blood flow, and cerebral metabolic rate in geriatric major depression and normal aging

While there is substantial evidence for abnormalities in serotonin (5-HT) neurotransmission in major depressive disorder (MDD), almost all of the findings derive from studies of young adults. Moreover, relatively little research has assessed brain 5-HT transmission in vivo. Neuroendocrine studies do not permit evaluation of a range of brain regions, but only the limited circuitry associated with hormone release. Data from autopsy studies are limited by the difficulties of assessment of the acute clinical picture before death, and by post-mortem artifacts. In vivo neuroimaging techniques overcome many of the methodological limitations of both these approaches. There is a large body of imaging data indicating regional cerebral blood flow (rCBF) and cerebral metabolic rate (rCMR) decrements both with aging and in patients with MDD. While the physiological bases for these phenomena are largely unknown, changes in brain 5-HT function may be involved. Neuroanatomical studies have revealed an intricate network of 5-HT-containing neurons within the cerebral microvasculature, with physiological evidence for serotonergic control of both rCBF and rCMR. Acute pharmacological challenges are available to probe brain 5-HT function. Such paradigms, using neuroendocrine responses as endpoints, have been of some utility in predicting outcome with antidepressant treatment. The role of 5-HT dysregulation in geriatric MDD takes on more importance given concerns regarding putative reduced efficacy of serotonin-specific reuptake inhibitors (SSRIs) in this population. If this is due to diminished responsivity of 5-HT systems, then the ability to identify antidepressant nonresponders via 5-HT challenge in combination with neuroimaging measures may have important clinical utility.

Corticosterone regulation of serotonin transporter and 5-HT1A receptor expression in the aging brain

Hypercortisolemia is often observed in patients suffering from major depression. As the serotonergic (5-hydroxytryptamine; 5-HT) system plays a major role in the etiology of depression, a loss of endocrine and neurotransmitter system interactions, including corticosterone regulation of 5-HT transporter (5-HTT) and 5-HT receptor expression, may underlie age-related deficits in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and correlate with an increased incidence of depression with advancing age. In this study, female Fischer 344 rats, ages 3, 13, and 18 months, were bilaterally adrenalectomized and supplemented for 3 weeks with corticosterone (0, 200, or 600 mg; LC, MC, or HC, respectively) containing 21 day sustained-release pellets implanted subcutaneously. Quantitative autoradiography of hippocampal and cortical regions using [3H]citalopram revealed a significant decrease in hippocampal 5-HTT binding in the 3-month HC treatment group compared to age-matched MC and LC groups; this loss was not present in the 13- or 18-month groups. Similarly, quantitative autoradiography using the radiolabeled 5-HT(1A) receptor agonist 8-hydroxy-2-(di-N-propylamino) tetralin demonstrated a significant decline in receptor density in 3- and 13-month MC and HC groups as compared to age-matched LC groups in the hippocampus. These hormone treatments (MC or HC), however, failed to alter hippocampal 5-HT(1A) binding site density in the 18-month groups as compared to the age-matched LC group. The 5-HT(2A) receptor was also evaluated using [3H]ketanserin and showed no age- or corticosterone-related changes in the cortex. Overall, an age-associated deficit in the regulation of the hippocampal serotonergic system by varied corticosterone treatment was revealed in the present study, which may underlie the increased incidence of depression and hypercortisolemia found with advancing age.

A neuroendocrine study of serotonin function in depressed stroke patients compared to non depressed stroke patients and healthy controls

OBJECTIVES

We employed a neuroendocrine challenge paradigm to study serotonergic abnormalities associated with poststroke depression.

METHOD

Twelve depressed stroke patients (major depression N= 5, minor depression N = 7), 8 nondepressed stroke patients and 12 healthy volunteers completed a single-blind, placebo-controlled, challenge tests. Baseline cortisol (CORT) and prolactin (PRL) values, and these hormonal responses to 30 mg of oral d-FEN and placebo over a 4 hour period were measured in the three groups.

RESULTS

There were intergroup differences for baseline adjusted PRL responses (change scores from baseline) to d-FEN (group effect F = 4.38, df = 2,29, p = 0.02) while these responses to placebo were comparable between groups (group effect F = 1.82, df = 2,29, p = 0.18). Peak PRL responses (post d-FEN maximal PRL change from baseline scores) in depressed stroke patients were significantly greater than in nondepressed patients (p = 0.005) but comparable to healthy normals (p = 0.47). However, these responses between major and minor depression were not significant (p = 0.34). There was a trend suggesting a negative correlation between peak PRL response and severity of depression (p = 0.056). Depressed patients were younger than the controls (p = 0.054). Also, the depressed group was more functionally impaired (p = 0.04) and more likely to have right-sided lesions (p = 0.009) compared with the nondepressed group. Differences in baseline adjusted PRL changes between depressed and nondepressed groups became non significant when the influence of laterality of lesions was covaried, whereas covariation of functional scores and age did not alter the significance. CORT responses did not show intergroup differences.

LIMITATIONS

The study group was small and was heterogenous in lesion characteristics, time since stroke and type of depression. A fixed-order design was used in the challenge test paradigm.

CONCLUSIONS

When laterality of stroke lesion was taken into account, depressed and nondepressed stroke patients did not differ in PRL responses to d-FEN.

Cellular electrophysiological effects of chronic fluoxetine and duloxetine administration on serotonergic responses in the aging hippocampus

The pharmacological and physiological effects of chronic administration of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor (SSRI) fluoxetine and the dual 5-HT/norepinephrine (NE) reuptake inhibitor duloxetine were compared on 5-HT-mediated electrophysiological responses recorded in the hippocampus of young (3-5 months) and old (17-20 months) female Fischer 344 rats. Fluoxetine, duloxetine, or vehicle (saline) was administered once daily for 14 days (10 mg/kg, i.p.) and extracellular recordings of spontaneously firing CA1 and CA3 pyramidal neurons were conducted 24 h following the last injection using microiontophoretic drug application techniques in a chloral hydrate anesthetized preparation. The recovery times (RT50 values; sec) following 5-HT application on pyramidal neurons were significantly increased in the young and old chronic fluoxetine (FLX) treated groups (73% and 104%, respectively; P < 0.05), but not chronic duloxetine- (DLX) or vehicle- (VEH) treated groups. Following prolonged application of duloxetine (5-10 min), the 5-HT RT50 values were significantly increased in the young FLX groups as compared to the age-matched DLX- and VEH-treated groups. In contrast, a significant decline in the time to recovery produced by 5-HT (52%) was observed in the old vs. young FLX-treated group following the second co-application of 5-HT with duloxetine. Within each drug treatment and age group, co-application of duloxetine and 5-HT did not alter the inhibitory responses (IT50 values; nC) produced by the application of 5-HT alone. These results demonstrate cellular adaptive changes in serotonergic neuronal function occur following repeated exposure to 5-HT reuptake inhibitors in an age-dependent manner.

Expression of brain Gi protein in the aging F344 rat following exposure to corticosterone

G protein expression has been shown to be modulated by circulating plasma corticosterone in young animals. A loss of G protein expression regulation by corticosterone in the elderly could explain declines in the function of G protein-coupled receptors and their effective signal transduction processes in the nervous system found in normal and pathological aging. In this study, adrenalectomized 3- and 18-months-old female Fischer 344 rats were exposed to low, moderate or high levels of plasma corticosterone to determine the effect of this hormone on Gi protein expression in the hippocampus and frontal cortex. Basal Gi protein expression, assessed by Western blot analysis, did not vary across age in either brain region. Hippocampal Gi protein levels increased following moderate and high corticosterone administration in the 3-months old animals (125%; P < 0.05) but not in the 18-months old animals. In contrast, in the frontal cortex, Gi protein expression increased significantly in the 18-months-old group (93%; P < 0.05) following exposure to high concentrations of corticosterone. These results suggest that steroid hormones, specifically corticosterone, may differentially modulate neurotransmitter-G protein coupling in an age-dependent manner.

Neurotransmission and the ontogeny of human brain

The early appearance of neurotransmitters in brain tissue refers to their regulative functions on the neuronal circuits. Many neurotransmitters have direct effects on neuronal outgrowth and differentiation during brain development, which precede their role in synaptic information coding. Both the neurotrophic and neurotoxic properties of excitatory amino acids (EAAs) have focused special interest on glutamatergic neurotransmission during brain development. Therefore, this work intends to review and discuss developmental alterations of the EAA neurotransmitter system in the human brain, their relation to human brain maturation and implications for pathological processes during early human brain development.

The somatosensory cortex of human: cytoarchitecture and regional distributions of receptor-binding sites

The aim of this study is to characterize the regional and laminar distribution patterns of various neurotransmitter binding sites in areas 3a, 3b, 1, and 2 of the human primary somatosensory cortex, and to compare these receptor-based "maps" with the cytoarchitectonic parcelation. Cryostat sections from a dorsomedial region of the postcentral gyrus close to the interhemispheric fissure and from a ventrolateral region close to the Sylvian fissure were examined. Neurotransmitter-binding sites were analyzed with quantitative in vitro receptor autoradiography. Different muscarinic-binding sites were labeled with [3H]pirenzepine and [3H]oxotremorine-M, noradrenergic-binding sites with [3H]prazosin, different serotoninergic-binding sites with [3H]5-hydroxytryptamine and [3H]ketanserine, glutamate-binding sites with l-[3H]glutamate, and GABA-binding sites with [3H]muscimol. Adjacent sections were stained with a modified Nissl method for cytoarchitectonic analysis. The binding sites either were preferentially localized in the superficial layers ([3H]5-hydroxytryptamine, [3H]prazosin, l-[3H]glutamate, [3H]muscimol, and [3H]pirenzepine) or were more homogeneously distributed with highest densities in layers III-V ([3H]oxotremorine-M and [3H]ketanserine). Changes in the distribution patterns of [3H]oxotremorine-M- and [3H]ketanserine-binding sites precisely matched the borders between areas 4/3a, 3b/1, and 1/2, as defined cytoarchitectonically. In addition, the autoradiographs showed that area 1 possibly consists of two subregions which cannot be distinguished cytoarchitectonically. The results demonstrate that the regional and laminar distribution patterns of some, but not all, transmitter-binding sites are precisely correlated with the cytoarchitectonic parcelation of the human primary somatosensory cortex. In addition, binding sites may reveal new borders not detectable in Nissl-stained sections. Finally, the human primary somatosensory cortex differs clearly from the primary motor cortex due to higher densities of l-[3H]glutamate-, [3H]muscimol-, [3H]pirenzepine-, [3H]oxotremorine-M-, and [3H]ketanserine-binding sites.

Apparent absence of aging and gender effects on serotonin 1A receptors in human neocortex and hippocampus

The effects of gender, aging and gender x age on the binding of the 5-HT1A receptor high-affinity agonist [3H]8-hydroxy-2(di-N-propylamino)tetralin ([3H]8-OH-DPAT), were evaluated and compared in tissues of human prefrontal, temporal, parietal, occipital cortex and hippocampus obtained from 21 autopsy subjects. The results revealed no variation with age or gender in either the [3H]8-OH-DPAT maximum binding capacity (Bmax) or dissociation constant (Kd) values. On the other hand, when separate correlations to subject ages were performed for men and women, aging effects on [3H]8-OH-DPAT Bmax and Kd were detected: in men, a significant age-dependent decrease in Kd values was observed in the occipital cortex; in women, the Bmax significantly decreased with aging in the parietal cortex and hippocampus, while increasing in occipito-cortical membranes. Overall, the present study reveals that, although neither gender nor aging 'per se' seem to modify the 5-HT1A receptor binding, gender may reveal region-specific aging effects, i.e. on receptor affinity in men and receptor density in women. Such findings should stimulate further investigation on the hypothesized existence of gender x age-related cross-connections between serotonergic system and hypothalamus-pituitary-gonadal circuits.

Effect of idebenone on in vivo serotonin release and serotonergic receptors in young and aged rats

The effect of idebenone on the serotonergic system was evaluated in the aging rat by measuring the kinetic constants of 3H-5HT and 3H-ketanserin binding sites in the cerebral cortex of rats at 3, 15 and 24 months of age following acute and subchronic administration of the drug. Idebenone displayed no in vitro affinity toward any population of serotonin receptors and did not modify their kinetic parameters after a single dose of 100 mg/kg, at any age tested. A subchronic treatment with the drug for 21 days at the dose of 30 mg/kg did not induce any relevant change in 3- and 15-month-old rats, whereas it significantly increased the density of both 3H-5HT and 3H-ketanserin binding sites in 24-month-old rats, where a lower number of receptors is detected as a consequence of aging. This effect was rather specific, since under the same experimental conditions no changes were detected in the density of cortical beta-adrenergic receptors in aged animals. In microdialysis studies, acute administration with idebenone did not affect 5HT and 5HIAA release at any age. Conversely, the pattern of serotonin metabolism was significantly modified in aged rats following repeated treatment with idebenone and was partially restored to a value similar to the one observed in young animals. These results suggest that idebenone, a putative neuroprotective agent which has been shown to improve brain metabolism in ischemic conditions, might also attenuate age-associated neuronal damage, acting probably on several neurotransmitter systems which undergo selective modification during aging.

Complex effects of age and gender on hypothermic, adrenocorticotrophic hormone and cortisol responses to ipsapirone challenge in normal subjects

The effects of a challenge dose of the 5-HT1A agonist, ipsapirone (0.3 mg per kg body weight), or placebo on body temperature and on adrenocorticotrophic hormone (ACTH) and cortisol release, were examined in 30 normal subjects (14 males, 19-74 years and 16 females, 22-69 years) using a randomized, double blind design. Irrespective of age or gender, ipsapirone induced a significant reduction in body temperature relative to placebo and a significant increase in ACTH and cortisol release. Maximal temperature reduction by ipsapirone was significantly blunted in older subjects and was inversely related to age. There was no gender difference in the hypothermic response to ipsapirone. ACTH and cortisol responses showed an opposite impact of aging in males and females. Whereas both responses diminished with age in male subjects, they increased with age in females. The cortisol response of older females was significantly larger than that of all the other subjects. Adverse effects of ipsapirone were also more marked in elderly females and were correlated with ACTH and cortisol responses. These findings should be taken into consideration in the use of ipsapirone and other 5-HT1A agonists as challenge procedures for studying central serotonergic function in depression and other disorders. Careful matching of control and experimental subjects is indicated so as to avoid spurious results which reflect the effects of age and gender rather than the pathophysiology of the disorders being investigated.

Effect of aging in human cortical pre- and postsynaptic serotonin binding sites

5-HT1A, 5-HT1D, 5-HT2 binding sites and affinity and 5-HT uptake sites were simultaneously determined in frontal cortex samples from 23 control subjects, aged 16-75 years. A significant reduction in the number of 5-HT1D and 5-HT2 binding sites was found with regard to age, together with a significant decrease in the 5-HT2 binding affinity. It is suggested that the total 5-HT1 age-related loss described in previous studies could be ascribed to the 5-HT2 subtype. Furthermore, aging does not seem to be associated with a reduced cortical serotonergic innervation, as indicated by the stability of the [3H]paroxetine-labeled 5-HT uptake sites.

Age-related behavioural, neurochemical and radioligand binding changes in the central 5-HT system of Sprague-Dawley rats

Mature (3-4 months) and aged (18-19 months) Sprague-Dawley (SD) rats were treated with 5-HT receptor agonists and drug-induced behaviours monitored. The 5-HT2/1C agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), induced wet dog shakes and back muscle contractions which were significantly increased in aged, compared to mature, rats, suggesting an age-related enhancement of 5-HT2 receptor function. In contrast, the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) induced forepaw treading, flat body posture, hypothermia and hyperactivity which were not significantly different in aged compared to mature rats. Levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus and frontal cortex were measured using high performance liquid chromatography with electrochemical detection. There were no age-related changes in hippocampal 5-HT or 5-HIAA. However both 5-HT and 5-HIAA were increased in the frontal cortex of aged SD rats. 8-OH-DPAT reduced 5-HIAA in both regions examined in mature rats, an effect which was attenuated in the aged rats, suggesting an age-related reduction in presynaptic 5-HT1A receptor function. DOI did not induce any changes in 5-HT or 5-HIAA in either of the regions examined. Radioligand binding studies with [3H] ketanserin showed there to be no significant age-related changes in cortical 5-HT2 receptor density or affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoaminergic and cholinergic synaptic markers in the nucleus basalis of meynert (nbM): Normal age-related changes and the effect of heart disease and Alzheimer's disease

Neurotransmitter markers for acetylcholine, serotonin (5-HT), and dopamine (DA) were measured in autopsied human nucleus basalis of Meynert (nbM) from nondemented individuals without heart disease (non-HD) (age range, 4-84 years; n = 77), nondemented individuals with heart disease (HD) (age range, 57-92 years; n = 23), and individuals with Alzheimer's disease (AD) (age range, 59-92 years; n = 22). No significant differences in any chemical marker were found between age-matched HD and non-HD individuals. The activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), and [3H]spiperone binding were regionally distributed within the nbM in control (non-HD) subjects less than 54 years of age. The activity of AChE, 5-[3H]HT binding, and the content of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT were regionally distributed in the nbM in non-HD, HD, and AD subjects more than 54 years of age. The binding of [3H]spiperone was regionally distributed in the nbM in HD and AD subjects more than 54 years of age, only. Activity of ChAT and AChE, content of 5-HT, 5-HIAA, and DA, binding of 5-[3H]HT, and the turnover number for DA (ratio of HVA/DA) all decreased with increasing age in the non-HD control population. The content of HVA, binding of [3H]spiperone, and the turnover number for 5-HT (ratio of 5-HIAA/5-HT) did not change with increasing age. Significant reductions in ChAT and AChE activities were found in AD nbM compared with postmortem interval- and age-matched HD and non-HD individuals. The reduction of 5-HT and 5-HIAA content and [3H]spiperone binding in individuals with AD of all ages suggests a loss of functional serotonergic innervation of the nbM. Dopaminergic synaptic markers were less affected in AD nbM, although turnover numbers for both DA and 5-HT were increased in AD. Receptor upregulation in response to presynaptic deficits did not occur for DA or 5-HT.

Aging reduces cardiovascular and sympathetic responses to NTS injections of serotonin in rats

Serotonergic mechanisms for baroreflex modulation could become altered with age. This possibility was explored by comparing cardiovascular and sympathetic effects elicited in 2-month- and 24-month-old rats by injecting serotonin (5-HT) directly into the nucleus tractus solitarius (NTS) which is the primary baroreflex relay station in the medulla. Ensuing decreases in mean pressure, heart rate, and renal nerve firing were significantly smaller in 24-month-old than in 2-month-old rats. By contrast, similar injections into the NTS of the vehicle alone were ineffective in both age groups. Postmortem examination of brain sections showed that NTS injection sites were equally distributed in both age groups, thereby indicating that the brain areas affected by 5-HT were identical regardless of age. Reduced sensitivity of peripheral myocardial beta-adrenergic and vascular alpha-adrenergic receptors was considered partly responsible because 5-HT injected into the NTS lowers blood pressure by decreasing sympathetic vasomotor tone and slows the heart by increasing vagal tone with reciprocal sympatho-inhibition. But since reduced adrenergic sensitivity would not account for the concurrent decrease in renal nerve firing, a more logical explanation is that the sensitivity of serotonergic mechanisms in the NTS for inhibiting blood pressure, heart rate, and renal nerve activity decreases with age.

Serotonergic measures in suicide brain: 5-HT1A binding sites in frontal cortex of suicide victims

The density of 5-HT1A binding using 3H-8-hydroxy-2-(di-n-propyl-amino) tetralin (8-OH-DPAT) as binding ligand, was studied in human frontal cortex of suicide victims and normal controls who died due to medical disease or accidentally. There was no difference in the maximum number of binding site (Bmax) or Kd (an inverse measure of affinity) of 5-HT1A receptor binding sites between normal controls and the entire group of suicide victims. However, nonviolent suicides had significantly higher Bmax (22-25%) compared to both controls and violent suicides. A negative correlation between age and Bmax of 5-HT1A binding sites was found in male controls but not in female controls or suicide victims. This relationship was less apparent among the male controls over age 60.

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

Quantitative autoradiographic analysis of serotonin 5-HT1A receptors in the human brain, using [3H]8-OH-DPAT as a ligand, reveals region-specific decreases in receptor labeling with age in several cortical and hippocampal regions and in the raphe nuclei. This is due to a change in receptor density (Bmax) with no apparent change in affinity (Kd) as affirmed by saturation binding analysis on representative cortical regions. The presence of alcohol is associated with decreased binding in several cortical gyri. Suicide, gender and postmortem delay had no effect on 8-OH-DPAT binding.

Serotonin, memory, and the aging brain

Serotonin is widely distributed throughout the central nervous system and is implicated in a variety of neural functions such as pain, feeding, sleep, sexual behavior, cardiac regulation and cognition. This paper is concerned with the last of these. Abnormalities of the serotonergic nervous system are well documented in pathologic studies of Alzheimer's disease and there is evidence suggesting that changes in this system occur in association with non-disease aging. Data on the role of serotonin in learning and memory and on the effects of aging on brain serotonin function are reviewed and discussed in relation to pharmacologic treatment strategies for the memory impairments associated with advancing age.

Aging and regenerative capacity of the rat serotonergic system. A morphological, neurochemical and behavioral analysis after transplantation of fetal raphe cells

Morphological dissimilarities between the brains of young (3 months) and aged (28 months and older) rats were demonstrated using serotonin-immunocytochemistry. A degeneration of the serotonergic system, noted as a decreased innervation and the appearance of enlarged or swollen varicosities, was observed particularly in the frontoparietal cortex, and the neostriatum of the aged rat brain. No direct relationship between this aberrant morphology and decrease in density of serotonin-innervation was found as we demonstrated a decline in fiber density without the appearance of aberrant serotonergic fibers in the hippocampus. HPLC analysis revealed that serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels in the frontoparietal cortex, hippocampus and raphe area were increased in the aged rat, while the 5-HT level in the caudate-putamen complex was not different from the young adult rat. The ratio 5-HIAA/5-HT, indicative of 5-HT turnover, appeared increased in the frontoparietal cortex, sensoric part, the caudate-putamen and the raphe area, while this ration in the frontoparietal cortex, motoric part and the hippocampus was not altered in the aged rat. Behavioral screening revealed a decrease spatial performance of aged males in a Morris Water-Maze task. To investigate whether the age of the host recipient was of influence on the regenerative capacity, a fetal raphe cell suspension of embryonic day E 15 was implanted in the caudate-putamen of young adult as well as aged rats. Neither differences in survival of the serotonergic cells nor in fiber outgrowth between both groups appeared five weeks after transplantation. Subsequently, transplantation of raphe cells in the hippocampus of young adult rats, after lesioning the hippocampal serotonergic innervation with 5,7-DHT, was performed to compare behavioral, morphological and neurochemical effects of the implants. It appeared that 11 months after transplantation the serotonergic innervation of the previously denervated hippocampus was greatly restored. There was a striking resemblance between the immunohistochemical and neurochemical data with respect to the increase in the amount of newly formed serotonergic fibers, the increase in uptake of [3H]-5-HT and in 5-HT and 5-HIAA levels. Also the behavior of lesioned and lesioned + transplanted males was rather similar to controls. In the behavioral tests we were mainly interested in hippocampal functioning, therefore orientation was of our prime interest. The other behavioral tests were only to confirm that the possible changes were linked to hypothalamic or extra-hypothalamic functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Autoradiographic analysis of age-dependent changes in serotonin 5-HT2 receptors of the human brain postmortem

Autoradiographic analysis of 5-HT2 receptors in the human brain, using [3H]ketanserin as a ligand, reveals region-specific changes in receptor labeling as a function of age. In the prefrontal cortex and hippocampal dentate gyrus of 12 normal subjects, label density decreases sharply with age over the 2nd and 3rd decades, reaches a minimum around age 50 and then starts to increase again in the 6th and 7th decades. Other brain regions studied, including frontoparietal and temporal cortex, basal ganglia and thalamus, did not show significant changes with age. Saturation binding experiments on prefrontal cortical samples from 23 normal subjects reveal that the decrease in label density is due to changes in receptor density (Bmax) with no apparent change in affinity (Kd). Sex, presence of alcohol and postmortem delay had no effect on ketanserin binding.

Effects of age and gender on CNS serotonergic responsivity in normal adults

The effects of age and gender on central nervous system (CNS) serotonergic responsivity were assessed with a neuroendocrine challenge test in 30 normal adults. Subjects greater than or equal to 30 years of age, compared with younger subjects, exhibited decreased prolactin secretion in response to a 60-mg oral dose of dl-fenfluramine hydrochloride, an indirect serotonin agonist. Furthermore, women had greater prolactin responses than men. As prolactin secretory capacity appears to be stable through midlife, the age-associated decrease in fenfluramine-induced prolactin release suggests a decline in CNS serotonergic responsivity. In contrast, the finding of greater prolactin release in women than in men probably reflects the effects of nonserotonergic modulatory influences at the level of the lactotroph. Age and gender effects must be considered in studies of the CNS serotonergic system.

Brain 5-HT1 binding sites in depressed suicides

5-HT1 and 5-HT1A binding sites were measured in brain tissue obtained at postmortem from 19 suicides, with definite evidence of depression, and 19 sex and age-matched controls. Thirteen of the depressed suicides had not been prescribed psychoactive drugs recently (drug-free suicides); six had been receiving antidepressant drugs, alone or in combination with other drugs (antidepressant-treated suicides). No significant differences were found in the number or affinity of 5-HT1 and 5-HT1A binding sites in frontal or temporal cortex between drug-free suicides and controls. The number of 5-HT1 sites was significantly lower (by 20%), affinity unaltered, in hippocampus and the affinity significantly lower (by 33%), number unaltered, in amygdala of drug-free suicides than controls. The number of 5-HT1 binding sites tended to be higher and the affinity lower in the antidepressant-treated compared to drug-free suicides, and significantly so in hippocampus. The present results, together with our previous studies, provide no evidence of altered cortical 5-HT markers in depressed suicides, but further emphasise abnormalities in the hippocampus.

Growth of brain tissue grafts is dependent upon host age

Growth of grafts of cortex cerebri, hippocampus, septum and cerebellum in oculo were significantly reduced in 16--17-month-old hosts as compared to growth in 3-month-old and 1.5-month-old rat hosts. (Host age is given as the age of the recipients at the time of grafting.) This growth difference was less pronounced in locus coeruleus grafts. The vascular network (as observed with laminin immunofluorescence) in cortex cerebri, hippocampus, cerebellum and septum grafts in 16--17-month-old hosts was abnormal with few thick-walled vessels in clusters as compared to the more 'normal' vascularization found in 1.5-month-old hosts with a high number of thin-walled blood vessels evenly distributed throughout the grafts. Grafts in the oldests hosts were markedly more gliotic than grafts in 1.5- and 3-month-old hosts as evaluated using immunofluorescence with antibodies against glial fibrillary acidic protein. Neurofilament immunoreactivity in the grafts seemed not to be influenced by host age. When a second cortex cerebri or hippocampus graft was placed into contact with a previously grafted locus coeruleus graft, the second graft grew less well in 16--17-month-old hosts as compared to 1.5-month-old hosts. When cortex cerebri was added to a previously grafted cortex cerebri graft, the second graft in both 16--17- and 3-month-old hosts grew to larger sizes than the corresponding single cortex grafts, although the growth differences between the two groups of hosts described above were still maintained. Thus, cortex grafts in 16--17-month-old hosts still have the ability to become trophically stimulated. The vascularization of the second graft in both groups was almost normalized and the gliotic reaction was less pronounced in the second grafts in both groups as compared to the single cortex grafts. In conclusion, the present results indicate that host age affects growth and morphology of intraocular single grafts from several brain regions. Using double grafts of cortex cerebri it was shown that grafts in 16-17-month-old hosts still had the capacity to become trophically stimulated. Data on brain transplants in older hosts are important in view of clinical possibilities to use transplantation strategies to counteract the symptoms of neurodegenerative diseases, which usually occur in old patients.

Identification of 5-hydroxytryptamine1D binding sites in human brain membranes

High-affinity, specific 3H-5-hydroxytryptamine (5-HT) binding was analyzed in membrane homogenates of human frontal cortex, caudate, and globus pallidus. 5-HT1A and 5-HT1C binding sites were pharmacologically blocked using 100 nM 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) and 100 nM mesulergine, respectively. The majority of 5-HT1 sites remained in each of the three brain regions under these conditions. The pattern of nucleotide interactions with these binding sites (GppNHp = GTP = GDP greater than GMP = adenine nucleotides) suggests a possible linkage to a G protein. RU 24969 competition studies confirmed the absence of 5-HT1B binding sites in human cortex, caudate, and globus pallidus. Drug interactions with putative 5-HT1D binding sites in bovine caudate membranes correlated significantly with their affinities for human membrane recognition sites labeled by 3H-5-HT in the presence of 100 nM 8-OH-DPAT + 100 nM mesulergine. We conclude that the majority of 3H-5-HT labeled recognition sites in human cortex, caudate, and globus pallidus represent 5-HT1D binding sites.

Aberrant morphology of serotonergic fibers in the forebrain of the aged rat

The morphological aspects and density of the serotonergic innervation in the forebrain of young (2 months) and aged (28-32 months) rats was studied employing immunocytochemistry with an antibody to serotonin. In the aged rats aberrant morphology of many of the preserved fibers was observed. The aberrant fibers were characterized by swollen varicosities and swollen intervaricose connections. They formed small networks. These findings were mainly restricted to the frontoparietal cortex and caudate putamen. In the same regions we observed a decrease in serotonergic innervation. There was no overall relation between aberrant morphology and decrease of serotonin-innervation as we observed a decrease in fiber density without morphological abnormalities in the hippocampus. It is suggested that the aberrant morphology may reflect the local degeneration of serotonergic forebrain afferents during the process of aging.

The neural basis of memory decline in aged monkeys

Nonhuman primates experience changes in behavior as they progress into old age. Visual recognition, spatial learning, habit formation, and visuospatial manipulation are impaired in aged rhesus monkeys relative to young controls. We have begun to study the possible neural substrate for these changes, focusing on brain areas that are known, from lesion studies, to be essential for the successful performance of specific tasks. Aged nonhuman primates develop senile plaques, most commonly in amygdala, hippocampus, and neocortex. Our preliminary data suggest that the density of plaques may be related to poor behavioral performance in some aged monkeys. However, behavioral decline begins before the appearance of significant numbers of senile plaques, suggesting that other factors may interfere with cognition. Numerous studies of several genera have shown that receptors for neurotransmitters decline in number between the adolescent years and old age. Our autoradiographic analyses of primate temporal neocortex demonstrate loss of muscarinic, nicotinic, dopaminergic and serotoninergic receptor binding sites between the ages of 2 and 22 years. Preliminary data indicate that markers for adenyl cyclase and phosphatidyl inositol second-messenger systems also are reduced in temporal cortex. Although these declines represent a potential substrate for behavioral changes, no studies have directly related a decrease in receptor number to deficits in learning and memory in aged primates. Other changes in the aging brain include loss of neurons, reduced neurochemical markers, and decreased content of neuronal ribonucleic acid (RNA). All of these decrements may be interrelated to some extent in that decreased RNA could result in changes in neurochemical markers and receptors and, eventually, in dysfunction and death of neurons. These observations underscore the importance of establishing a time course for age-associated neural abnormalities, examining regions of brain in which changes are most likely to occur, and studying their relationship to the progression of behavioral dysfunction. Detailed anatomical analyses of the distribution of in situ uptake/receptor binding sites and messenger RNA (mRNA) in aged nonhuman primates may clarify some of the factors that most likely contribute to behavioral changes in elderly humans.

Age-related changes in rat serotonergic and adrenergic systems and in receptor responsiveness to subchronic desipramine treatment

Noradrenergic (NA) and serotonergic (5-HT) receptor profiles were compared in the cerebral cortex of young adult (3 months old) and aged (24 months old) male Sprague Dawley rats. Beta and alpha-1 receptors were significantly decreased in 24 month old rats, whereas alpha-2 receptors remained unchanged. 5-HT-2 Postsynaptic receptors and 5-HT high affinity uptake were reduced in aged animals; on the other hand the number of 3H-imipramine (3H-IMI) recognition sites located on serotonin nerve terminals and labelled also by 3H-paroxetine (3H-PAR), were significantly higher in the cerebral cortex of old rats. The ratio 5-hydroxyindoleacetic acid (5-HIAA)/5-HT, an index of serotonin turn-over, increased in some brain areas of senescent rats. There were no age-related changes in the responsiveness of investigated binding sites to subchronic desipramine treatment; the density of beta-noradrenergic and 5-HT-2 serotonergic receptors and that of 3H-IMI binding sites was reduced both in young adult and aged rats.

Autoradiographic analysis of [3H]imipramine binding in the human brain postmortem: effects of age and alcohol

In vitro quantitative autoradiography of high-affinity [3H]imipramine binding sites was performed on 16 human brains postmortem. The densities of binding sites were highest in the hypothalamus. Next, in descending order, were the basal and lateral nuclei of the amygdala; substantia innominata; insular cortex; the central nucleus of the amygdala; the anterior nucleus of the thalamus; the head of the caudate nucleus; portions of the frontal, parietal, and temporal cortex; claustrum; the granular layer of the dentate gyrus; substantia nigra; the pyramidal layer of CA fields; globus pallidus; red nucleus; and white matter. Imipramine binding was found to increase with age in a region-specific manner. The presence of alcohol had a similar effect, which was most pronounced in the hippocampus. Sex and time from death to autopsy did not affect imipramine binding, in our sample.

Serotonin 5-HT2 receptor binding on blood platelets--a peripheral marker for depression?

Several methods of platelet membrane preparation and binding conditions were screened in order to optimize the labeling of serotonergic 5-HT2 receptors on previously frozen human platelet membranes with tritiated ketanserin. Under optimal conditions, 5-HT2 receptors in normal subjects (5 males, 7 females, age range 21 to 71) have a Kd of 1.5 +/- 0.2 nM and a Bmax of 33.9 +/- 5.3 fmole/mg protein. In a group of patients with major depressive disorder exactly matched for age and sex with the normal control group, we find a significant increase in receptor density, to 66.8 +/- 11.4 fmole/mg, with no significant change in the affinity (2.3 +/- 0.5 nM). Four weeks of treatment with antidepressant drugs result in a significant decrease of Bmax, down to control levels (29.4 +/- 3.9). Thus, ketanserin can be used to monitor changes in platelet serotonin 5-HT2 receptors which may be a relevant marker for the state of depression.

5-Hydroxytryptamine-sensitive [3H]imipramine binding of protein nature in the human brain. II. Effect of normal aging and dementia disorders

Recently, a high-affinity [3H]imipramine binding site of protein nature that appeared related to the 5-hydroxytryptamine (5-HT, serotonin) uptake mechanism was demonstrated in the rat brain. In a preceding paper a similar [3H]imipramine binding site of protein nature and displaceable by 5-HT was demonstrated in the human brain. Most previous [3H]imipramine binding studies of the human brain have used desipramine-sensitive binding, which appears to contain a significant amount of additional binding not related to 5-HT neurons. Therefore this study of the human brain in the normal aging, in Alzheimer's disease/senile dementia of Alzheimer type (AD/SDAT) and in multiinfarction dementia (MID) presents data on 5-HT-sensitive [3H]imipramine binding. The influence of normal aging (17-100 years) was studied in the frontal and cingulate cortices, in the putamen, caudate nucleus, amygdala and in the hippocampus. An age-related change in 5-HT-sensitive [3H]imipramine binding was only noted in the cingulate cortex with a 50% loss in Bmax over the adult age range. In contrast, desipramine-sensitive [3H]imipramine binding studied in the frontal cortex and in the putamen showed marked increases in Bmax with age which correlated with increases in Kd. It is suggested that these increases are related to an increased binding to lipophilic membrane components not related to 5-HT neurons. The 5-HT-sensitive [3H]imipramine binding (Bmax) was reduced to 60% of control in the cingulate cortex and to 50% in the putamen in AD/SDAT. In MID there was a 50% loss of [3H]imipramine binding sites (Bmax) in the putamen, but a 30% loss in the cingulate cortex did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal changes in serotonin receptors following prenatal alterations in serotonin levels: further evidence for functional fetal serotonin receptors

Recent work by ourselves and others has indicated that serotonin (5-HT) acts as a regulator of neuronal growth in fetal tissue, probably through an action on the high affinity 5-HT receptors known to be present. In order for our hypothesis to be correct, these receptors must be shown to be functional in fetal tissue. Furthermore, since 5-HT has a dual role in neuronal development, these receptors must be functional both in the region of the serotonergic cell body (brainstem) and in projection areas (forebrain). We have tested the functional status of fetal 5-HT receptors by testing their ability to adapt to changes in the level of 5-HT. Pregnant rats were treated with saline, p-chlorophenylalanine (a 5-HT depletor) or 5-methoxytryptamine (a 5-HT agonist) and the characteristics of the high affinity 5-HT receptors in the rat pups determined using a binding assay with [3H]5-HT. Our results show that both forebrain and brainstem receptors respond to alterations in transmitter level in a manner similar to adult brain. Thus, fetal 5-HT receptors are functional and capable of playing a role in neuronal development.