Biochemical evidence of selective nerve cell changes in the normal ageing human and rat brain

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.

Randomized Controlled Trial of a Decision Support Intervention About Cardiopulmonary Resuscitation for Hospitalized Patients Who Have a High Risk of Death

BACKGROUND

Many seriously ill hospitalized patients have cardiopulmonary resuscitation (CPR) as part of their care plan, but CPR is unlikely to achieve the goals of many seriously ill hospitalized patients.

OBJECTIVE

To determine if a multicomponent decision support intervention changes documented orders for CPR in the medical record, compared to usual care.

DESIGN

Open-label randomized controlled trial.

PATIENTS

Patients on internal medicine and neurology wards at two tertiary care teaching hospitals who had a 1-year mortality greater than 10% as predicted with a validated model and whose care plan included CPR, if needed.

INTERVENTION

Both the control and intervention groups received usual communication about CPR at the discretion of their care team. The intervention group participated in a values clarification exercise and watched a CPR video decision aid.

MAIN MEASURE

The primary outcome was the proportion of patients who had a no-CPR order at 14 days after enrollment.

KEY RESULTS

We recruited 200 patients between October 2017 and October 2018. Mean age was 77 years. There was no difference between the groups in no-CPR orders 14 days after enrollment (17/100 (17%) intervention vs 17/99 (17%) control, risk difference, - 0.2%) (95% confidence interval - 11 to 10%; p = 0.98). In addition, there were no differences between groups in decisional conflict summary score or satisfaction with decision-making. Patients in the intervention group had less conflict about understanding treatment options (decisional conflict knowledge subscale score mean (SD), 17.5 (26.5) intervention arm vs 40.4 (38.1) control; scale range 0-100 with lower scores reflecting less conflict).

CONCLUSIONS

Among seriously ill hospitalized patients who had CPR as part of their care plan, this decision support intervention did not increase the likelihood of no-CPR orders compared to usual care.

PRIMARY FUNDING SOURCE

Canadian Frailty Network, The Ottawa Hospital Academic Medical Organization.

Which demographic variables are necessary to correct in neuroimaging studies of serotonin transporter availability? A SPECT study with [¹²³I]ADAM

Previous studies have shown that many demographic variables influence serotonin transporter (SERT) availability as assessed by single photon emission computed tomography (SPECT). The aim of this study was to explore which demographic variables influenced the SERT availability most in a SPECT study with [(123)I]ADAM. Ninety-five healthy volunteers were recruited. Age, sex, smoking, alcohol intake, educational level, body mass index, seasonal change, and SERT availability were recorded and then analyzed by multivariate linear regression. Age was the only variable that was significantly associated with SERT availability (calculate: (midbrain-cerebellum)/cerebellum). Furthermore, the inverse correlation of age and SERT availability may be present only before the age of 47. Age should be a covariate in SERT-related neuroimaging analyses, particularly in participants under the age of 47 years.

Extrastriatal binding of [¹²³I]FP-CIT in the thalamus and pons: gender and age dependencies assessed in a European multicentre database of healthy controls

PURPOSE

Apart from binding to the dopamine transporter (DAT), [(123)I]FP-CIT shows moderate affinity for the serotonin transporter (SERT), allowing imaging of both monoamine transporters in a single imaging session in different brain areas. The aim of this study was to systematically evaluate extrastriatal binding (predominantly due to SERT) and its age and gender dependencies in a large cohort of healthy controls.

METHODS

SPECT data from 103 healthy controls with well-defined criteria of normality acquired at 13 different imaging centres were analysed for extrastriatal binding using volumes of interest analysis for the thalamus and the pons. Data were examined for gender and age effects as well as for potential influence of striatal DAT radiotracer binding.

RESULTS

Thalamic binding was significantly higher than pons binding. Partial correlations showed an influence of putaminal DAT binding on measured binding in the thalamus but not on the pons. Data showed high interindividual variation in extrastriatal binding. Significant gender effects with 31 % higher binding in women than in men were observed in the thalamus, but not in the pons. An age dependency with a decline per decade (±standard error) of 8.2 ± 1.3 % for the thalamus and 6.8 ± 2.9 % for the pons was shown.

CONCLUSION

The potential to evaluate extrastriatal predominant SERT binding in addition to the striatal DAT in a single imaging session was shown using a large database of [(123)I]FP-CIT scans in healthy controls. For both the thalamus and the pons, an age-related decline in radiotracer binding was observed. Gender effects were demonstrated for binding in the thalamus only. As a potential clinical application, the data could be used as a reference to estimate SERT occupancy in addition to nigrostriatal integrity when using [(123)I]FP-CIT for DAT imaging in patients treated with selective serotonin reuptake inhibitors.

Loss of functional GABA(A) receptors in the Alzheimer diseased brain

The cholinergic and glutamatergic neurotransmission systems are known to be severely disrupted in Alzheimer's disease (AD). GABAergic neurotransmission, in contrast, is generally thought to be well preserved. Evidence from animal models and human postmortem tissue suggest GABAergic remodeling in the AD brain. Nevertheless, there is no information on changes, if any, in the electrophysiological properties of human native GABA receptors as a consequence of AD. To gain such information, we have microtransplanted cell membranes, isolated from temporal cortices of control and AD brains, into Xenopus oocytes, and recorded the electrophysiological activity of the transplanted GABA receptors. We found an age-dependent reduction of GABA currents in the AD brain. This reduction was larger when the AD membranes were obtained from younger subjects. We also found that GABA currents from AD brains have a faster rate of desensitization than those from non-AD brains. Furthermore, GABA receptors from AD brains were slightly, but significantly, less sensitive to GABA than receptors from non-AD brains. The reduction of GABA currents in AD was associated with reductions of mRNA and protein of the principal GABA receptor subunits normally present in the temporal cortex. Pairwise analysis of the transcripts within control and AD groups and analyses of the proportion of GABA receptor subunits revealed down-regulation of α1 and γ2 subunits in AD. In contrast, the proportions of α2, β1, and γ1 transcripts were up-regulated in the AD brains. Our data support a functional remodeling of GABAergic neurotransmission in the human AD brain.

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.

In vivo muscarinic 2 receptor imaging in cognitively normal young and older volunteers

The precise effects of normal aging on the cholinergic system are unknown, as both in vitro and PET studies have shown conflicting results. In vivo determination of muscarinic receptor distribution and density has been hampered by both poor subtype selectivity and/or blood-brain barrier permeability of known ligands. Previous in vitro and in vivo work with the F-18 labeled muscarinic agonist, 3-(3- (3-[(18)F]Flouropropyl)thio)-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine ((18)FP-TZTP) suggested the use of (18)FP-TZTP to selectively quantify M2 receptors in humans. In this study, we used (18)FP-TZTP to infer M2 receptor avidity in the brains of 15 healthy younger subjects (mean age = 28.3 +/- 5.5 years) and 20 healthy older subjects (mean age = 62.1 +/- 7.7 years). Corrections for subject motion during the 120-min acquisition and partial voluming (PVC) were performed. A one-tissue compartment model was used to estimate the volumes of distribution (V(T)) of (18)FP-TZTP. Within both groups of subjects, volumes of distribution (K(1)/k(2)) in cortical, subcortical, and cerebellar areas were consistent with M2 receptor topography. Compared to younger subjects older subjects had significantly higher means and standard deviations for the volumes of distribution of (18)FP-TZTP throughout much of the cerebellum, cortex, and subcortex (Global Gray V(T) = 742 +/- 163 in older subjects and 645 +/- 74 in younger subjects, P < 0.03). Across all subjects (18)FP-TZTP, regional, and Global Gray distribution volumes were significantly correlated to age (Global Gray V(T,) r = 0.41, P < 0.01). A lower concentration of acetylcholine in the synapse of some older subjects is one possible explanation for the data.

Analysis of visual evoked potentials and background electroencephalographic activity in young and elderly subjects

OBJECTIVE

New techniques developed in this laboratory to overcome the loss of information involved in conventional evoked potential averaging are applied here to visual evoked potential (VEP) in young and elderly normal subjects.

METHODS

The techniques are based on statistical descriptions of the times and amplitudes of the electroencephalographic deflections recorded before (background) and after (evoked) a series of pattern reversal visual stimuli.

RESULTS

The elderly had a higher rate of background deflections at all electrode sites, but lower amplitudes at the occipital electrodes. The elderly had a lower rate of deflections during the period of evoked activity compared with the background period. The young had a higher degree of response deflection time locking and amplitude. The mean amplitude of the deflections recorded during the period of evoked activity was significantly greater in amplitude than the background deflections and greater than the amplitudes of the conventionally averaged VEP derived from the same data. Thus the lower amplitude VEPs seen in the elderly are due to their poor time locking and reduced amplification. Only 79% of the stimulus trials contributed deflections to the P1 response component in both young and elderly subjects and 63% to the N1. In young subjects, several of the new response parameters showed the presence of evoked response components that were not apparent in the conventionally averaged VEP derived from the same data.

CONCLUSIONS

The novel methods presented here provide a great deal of additional information that is unavailable when analyzing data using only conventional evoked potential averaging.

Age-related decline of serotonin transporters in living human brain of healthy males

There is growing interest in serotonin transporter (5-HTT) function in the human brain, since alteration in 5-HTT has been suggested in a variety of neurophychiatric disorders. Age-related decline in postsynaptic 5-HT receptors has been demonstrated in postmortem human studies and in vivo imaging studies, and has been assumed to be related to changes in mental function in the normal aging process. However, few studies have investigated the aging effect on 5-HTT in human brain in vivo, since the availability of suitable ligands has been limited. To investigate the aging effect on 5-HTT in living human brain, we performed positron emission tomography (PET) scans with a selective ligand for 5-HTT, [11C](+)McN5652. We examined 28 healthy male volunteers aged between 20 and 79 years. The uptake was quantified in the thalamus and midbrain by graphical analysis with the cerebellum as a reference tissue, and binding potential (BP) was used for the index of 5-HTT binding. There was a significant age-related decline in BP in the thalamus and midbrain. The decline in [11C](+)McN5652 binding was 9.6% per decade in the thalamus and 10.5% per decade in the midbrain.

Brain aging research at the close of the 20th century: from bench to bedside

Remarkable and continued growth in the field of brain aging research has been fueled by a confluence of factors. Developments in molecular biology, imaging, and genetics coupled with the imperative caused by the aging of the population has created fertile ground for improved understanding of the interaction between brain function and behavior. Aging changes in neurochemical systems may account for the spectrum of cognitive and behavioral states of successfully aged pen sons, but may also contribute to enhanced vulnerability to depressive or dementing illness. In particular, the refinement of in vivo imaging approaches to investigating the structure and function of the aging brain has provided the opportunity to strengthen our knowledge of the biological substrate of the aging brain and neuropsychiatrie disorders, and translate these into therapeutics.

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.

Age-related decline in central serotonin transporter availability with [(123)I]beta-CIT SPECT

Postmortem studies have provided limited and conflicting data regarding aging effects on the central serotonin transporter (SERT). The present study investigated the effect of age on SERT availability in the human brainstem and diencephalon with single photon emission computed tomography (SPECT) using the ligand [(123)I]2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane ([(123)I]beta-CIT). Healthy control subjects (n = 126) who ranged in age from 18 to 88 were injected with 6.0 +/- 0.8 (mean +/- SD) mCi [(123)I]beta-CIT and imaged 23.1 +/- 1.9 h later under equilibrium conditions. A ratio of specific to nondisplaceable brain uptake (i.e. , V(3)" = [brainstem-diencephalon -occipital]/occipital), a measure proportional to the binding potential (B(max)/K(D)), was derived. SERT availability (V(3)") showed a significant inverse correlation with age (r = -0.40, P < 0.0001). Linear regression analysis revealed that V(3)" declined by 29.5% over the age range 18 to 88, or approximately 4.2% per decade. These results demonstrate reductions in the availability of central SERT binding sites with age in living human subjects.

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.

Physostigmine challenge before and after chronic cholinergic blockade in elderly volunteers

BACKGROUND

As a test of possible muscarinic up-regulation, the cortisol response to intravenous (i.v.) physostigmine (an anticholinesterase) was measured in 9 elderly volunteers before and after chronic cholinergic blockade with the muscarinic cholinergic antagonist scopolamine.

METHODS

Each of the 9 elderly control subjects was given two physostigmine (0.5 mg i.v.) infusions separated by 21 doses of nightly scopolamine (1.2 mg p.o.). No scopolamine was administered the night before infusions, and glycopyrrolate (0.2 mg i.v.) was administered prior to physostigmine, to block its peripheral effects. Vital signs were monitored and blood samples were collected at six time points surrounding the physostigmine infusion (-10, +10, +20, +30, +50, and +70 min). Behavioral measures and cognitive tests were administered prior to and 30 min after the physostigmine.

RESULTS

The cortisol response to physostigmine was greater after the second (post-chronic scopolamine) infusion study compared to the first (p < .05) as measured by an area under the curve analysis of all time points. When individual time points were compared, the mean cortisol response was significantly increased after the second physostigmine infusion at the +50- and +70-min time points (p < .05). There were no significant changes in behavioral rating scales, cognitive tests, or vital signs between the two physostigmine infusion study days.

CONCLUSIONS

This study demonstrates increased hypothalamic-pituitary-adrenocortical axis responsivity to a central nervous system cholinergic stimulus after chronic muscarinic blockade in 9 elderly control subjects. It also gives further evidence to support previous suggestions of muscarinic plasticity, specifically postsynaptic up-regulation, in the aging brain following exposure to chronic anticholinergic treatment.

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.

Aging effects on the startle response and startle plasticity in Fischer F344 rats

The effects of aging on acoustic and airpuff startle reactivity, acoustic and airpuff startle habituation, acoustic and cross-modal (light-acoustic) prepulse inhibition (PPI), and fear-potentiated startle (FPS) were examined using 3- (Y: young), 11- (AD: adult), 17- (MA: middle-aged), and 22- (O: old) month-old Fischer F344 rats. AD rats had the highest acoustic startle reactivity with the Y and MA rats showing smaller and comparable startle levels. The O rats had diminished startle reactivity, with over a 65% reduction in responding. Airpuff startle reactivity was comparable in the Y and AD groups, while the MA and O groups had 40% and 80% reductions in airpuff startle respectively. There was an age-related increase in airpuff startle habituation. Acoustic and cross-modal PPI were reduced significantly in O rats when compared to other age groups. Finally, there were no effects of age on FPS. In summary, these studies suggest that in Fischer F344 rats, there are age-associated differences in startle reactivity, startle habituation, and PPI, but no aging effect on FPS.

Dietary docosahexaenoic acid increases cerebral acetylcholine levels and improves passive avoidance performance in stroke-prone spontaneously hypertensive rats

We have recently shown that inferior performance in passive avoidance task is accompanied with decreased hippocampal choline (Ch) in stroke-prone spontaneously hypertensive rats (SHRSP) compared with normotensive control Wistar-Kyoto rats (WKY). We also reported that dietary docosahexaenoic acid (DHA) suppresses the development of hypertension and stroke-related behavioral changes, resulting in the prolongation of the life span of SHRSP. In this study, we examined the effect of dietary DHA on the cerebral acetylcholine (ACh) levels and learning performance in passive avoidance tasks in SHRSP. The arachidonic acid decreased and the DHA increased in plasma lipids dose dependently with dietary DHA treatments, which decreased the systolic blood pressure in SHRSP. Dietary DHA significantly restored the significantly inferior learning performance in passive avoidance response observed in control SHRSP (DHA 0%). Furthermore, the hippocampal ACh levels were correlated positively with the total response latency in passive avoidance tasks. These results suggest that cholinergic dysfunction in the brain of control SHRSP is responsible, at least in part, for the impaired learning ability and the dietary DHA ameliorates this performance failure.

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.

Combined cholinergic and 5-HT2 receptor activation suppresses thalamocortical oscillations in aged rats

The present study investigated whether combined stimulation of the cholinergic system and 5-hydroxytryptamine (5-HT) subtype 2 receptors can suppress neocortical high-voltage spindles (HVSs) reflecting thalamocortical oscillations in aged rats. Cholinesterase inhibitors-tetrahydro-aminoacridine (THA: 1.0 and 3.0 mg/kg i.p.) and physostigmine (0.36 mg/kg i.p.)- and a 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI; 0.3 and 1.0 mg/kg SC)-suppressed HVSs in aged rats. A combination of subthreshold doses of THA (0.3 mg/kg i.p.) and DOI (0.1 mg/kg s.c.) suppressed HVSs more effectively than either drug alone. Furthermore, a 5-HT2 receptor antagonist, ketanserin (5.0 and 20.0 mg/kg s.c.), reduced the efficacy of THA (1.0 and 3.0 mg/kg i.p.) and physostigmine (0.12 and 0.36 mg/kg i.p.) in decreasing HVSs. THA and ketanserin slightly decreased, physostigmine tended to increase, and DOI significantly increased behavioral activity of the rats, demonstrating that the effects of the drugs on behavioral activity may be separated from their effects on generation of thalamocortical oscillations. The results suggest that activation of the cholinergic system and 5-HT2 receptors has additive effects in the suppression of thalamocortical oscillations in aged rats.

The effects of cholinergic drugs on rat neocortical high-voltage spindles in ketanserin-treated rats

To investigate the roles of the cholinergic system and 5-HT2 receptors in the modulation of thalamocortical oscillations, we studied the effects of systemic (s.c.) administration of anticholinesterases (physostigmine, tetrahydroaminoacridine) and muscarinic acetylcholine receptor agonists (pilocarpine, oxotremorine) on spontaneous thalamically generated rhythmic neocortical high-voltage spindles in adult rats pretreated with either saline or ketanserin, a 5-HT2 receptor antagonist. Ketanserin at 20.0 mg/kg increased the number of high-voltage spindles. In saline-treated rats, tetrahydroaminoacridine 3.0 and 9.0 mg/kg was able to decrease high-voltage spindles, whereas in ketanserin 20.0 mg/kg-treated rats only the highest dose of tetrahydroaminoacridine (9.0 mg/kg) decreased high-voltage spindles. Both doses of physostigmine, 0.12 and 0.36 mg/kg, decreased high-voltage spindles in both saline and ketanserin 20.0 mg/kg-treated rats. Lower doses of tetrahydroaminoacridine (1.0 mg/kg) and physostigmine (0.06 mg/kg) were ineffective in both saline- and ketanserin 20.0 mg/kg-treated rats. Pilocarpine 3.0 mg/kg and oxotremorine 0.1 and 0.9 mg/kg decreased high-voltage spindles in saline-treated rats. However, in rats treated with ketanserin 20.0 mg/kg, only the lower doses of pilocarpine (0.3 and 1.0 mg/kg) and oxotremorine (0.03 mg/kg) were able to decrease the high-voltage spindles. The results suggest that activation of the cholinergic system and activation of 5-HT2 receptors have additive effects in the suppression of thalamocortical oscillations and related neocortical high-voltage spindles in rats, thus maintaining effective information processing in thalamocortical networks.

Age-related decline in central cholinergic function demonstrated with scopolamine

Scopolamine hydrobromide was administered intravenously to 23 normal subjects (40-89 years) in doses of 0.1 mg, 0.25 mg, and 0.5 mg, in a double-blind. Placebo-controlled, random-order fashion. The effects of scopolamine, as compared to placebo, were assessed using a comprehensive cognitive test battery, as well as behavioral and physiological measures. Scopolamine produced the expected dose-dependent impairments in most of the cognitive functions assessed. Behavioral and physiological measures were also affected, but only minimally. More importantly, there was a significant overall correlation between age and scopolamine-impaired performances on psychomotor speed, short-term recall, visual tracking speed, visuo-motor coordination, and sequencing ability. There was, however, some inter-individual variability in this phenomenon. The results provide further evidence that cholinergically mediated cognitive functions show an increased sensitivity to scopolamine with age, albeit with heterogeneity that bears further investigation.

Suppression of neocortical high-voltage spindles by nicotinic acetylcholine and 5-HT2 receptor stimulation

To investigate the roles of the nicotinic acetylcholine receptor and the serotonin (5-hydroxytryptamine; 5-HT) subtype 2 receptor in the modulation of rat thalamocortical oscillations, the effects of systemic (s.c.) administration of nicotine, a nicotinic acetylcholine receptor agonist, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a 5-HT2 receptor agonist, on neocortical high-voltage spindle activity occurring during quiet waking-immobility behavior in aged (28 months of age) and adult (7 months of age) rats were studied. Nicotine 0.1 and 0.3 mg/kg alleviated the age-related increase of neocortical high-voltage spindles, whereas in adult rats only nicotine 0.3 mg/kg was effective. DOI 0.3, 1.0 and 2.0 mg/kg suppressed high-voltage spindles in both aged and adult rats. In aged rats, a combination of subthreshold doses of nicotine (0.03 mg/kg) and DOI (0.1 mg/kg) decreased neocortical high-voltage spindles, whereas in adult rats two different subthreshold dose combinations (nicotine 0.03 or 0.1 mg/kg+DOI 0.1 mg/kg) had no effect. p-Chlorophenylalanine (400 mg/kg/day i.p. for 3 consecutive days) treatment decreased brain serotonin concentration (> 80% reduction), but did not affect high-voltage spindles. However, in both aged and adult rats, p-chlorophenylalanine treatment blocked the decrease in high-voltage spindle activity produced by DOI 0.3 mg/kg, though not the decrease produced by higher doses of DOI (1.0 and 2.0 mg/kg). It is important that, in adult rats, p-chlorophenylalanine treatment was able to abolish the decrease in high-voltage spindle activity seen after a relatively high dose of nicotine (0.3 mg/kg). The results suggest that nicotinic acetylcholine and 5-HT2 receptors may act in concert to suppress neocortical high-voltage spindling in rats, and that intact brain serotonergic systems may be important for some of the therapeutic effects of nicotine.

In vivo quantification of cerebral muscarinic receptors in normal human aging using positron emission tomography and [11C]tropanyl benzilate

Regional cerebral muscarinic cholinergic receptor binding was quantified in normal young and elderly subjects employing the muscarinic antagonist radioligand [11C]tropanyl benzilate (TRB). Binding was determined by kinetic analyses of positron emission tomographic (PET) determinations of cerebral activity in conjunction with radial arterial blood sampling following intravenous radiotracer injection. A significant, but minor (8%), loss of frontal cortical receptors relative to whole brain average receptor density was found with advancing age. Parametric estimates of binding suggest small reductions in cerebral cortex binding as well as increases in brain stem and cerebellar binding underlying the observed pattern difference. However, these latter changes did not achieve statistical significance. We conclude that cerebral muscarinic receptor availability, as depicted by antagonist binding, does not undergo a major decline during normal aging of the adult human brain. The cerebral cortical cholinergic dysfunction in elderly subjects, suggested by prior clinical evidence, is not attributable to major loss of total muscarinic cholinoceptive capacity.

Cholinergic changes in the hippocampus of stroke-prone spontaneously hypertensive rats

BACKGROUND AND PURPOSE

We investigated age-related changes in the central cholinergic systems in stroke-prone spontaneously hypertensive rats (SHRSP) to examine whether the regional and progressive cholinergic changes occur and are correlated with behavioral changes in the passive avoidance task.

METHODS

Tissue levels of choline (Ch) and acetylcholine (ACh) were determined in the cerebral regions, including the hippocampus, of SHRSP (at two ages: 15 to 20 and 30 to 40 weeks) that had been tested in a passive avoidance task and were compared with those of age-matched controls, Wistar-Kyoto rats (WKY). With the use of in vivo microdialysis, high K+-stimulated release of hippocampal ACh, a functional parameter of the cholinergic system, was also determined in 15- to 20-week-old SHRSP.

RESULTS

We found that 15- to 20-week-old SHRSP demonstrated a markedly lower level of hippocampal Ch than age-matched WKY. The decrease in the Ch level in 15- to 20-week-old SHRSP was observed in all regions examined; however, in the hippocampus a significant difference from WKY was subsequently observed at the age of 30 to 40 weeks. The hippocampal ACh release was markedly decreased by repetitive stimulation with high K+ in 15- to 20-week-old SHRSP. Behavioral impairment in the passive avoidance task was observed in the two age groups of SHRSP, with significant and positive correlations between the hippocampal ACh levels and the response latency.

CONCLUSIONS

A decrease in hippocampal Ch level was observed in both 15- to 20-week-old and 30- to 40-week-old SHRSP, accompanied by performance failure in the passive avoidance task. The abnormal release of hippocampal ACh in response to the repetitive K+ stimulation was also noted in 15- to 20-week-old SHRSP. Thus, cholinergic dysfunction in the hippocampal system may be responsible for behavioral abnormality in the passive avoidance task in SHRSP.

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.

Cholinergic markers in aged cognitively impaired Long-Evans rats

Aged Long-Evans rats (24-25 months old) were classified into cognitively impaired or unimpaired subgroups based on their performances in the Morris Swim Maze task compared to young controls. Using quantitative in vitro receptor autoradiography, we investigated the status of various cholinergic markers in these two groups and in young adults (six months) animals. The apparent density of [3H]pirenzepine (muscarinic M1) sites was similar in the three groups of rats in various cortical areas, subfields of the hippocampus, medial septum and striatum. Similarly, choline acetyltransferase activity and the density of [3H]hemicholinium-3 (high-affinity choline uptake) and [3H]cytisine (nicotinic) binding sites were also unchanged in the brain regions studied between the aged cognitively impaired, unimpaired and young adult rats. In contrast, significant increases in [3H]AF-DX 384 (muscarinic M2) binding density were observed in various cortical areas and in the molecular layer of the dentate gyrus of aged cognitively impaired versus unimpaired rats and in few cortical regions of old as compared to young animals. Therefore, a selective alteration in the regulation of putative M2 receptor sites is apparent, particularly in the aged cognitively impaired rats. Increases in M2 binding sites could lead to a decrease in the capacity to release acetylcholine, as some of the M2 receptors are believed to act as negative autoreceptors. This could influence cognitive functions as selective M2 blockers have recently been reported to facilitate spatial memory in aged impaired rats [Doods et al. (1993) Life Sci. 52, 497-503: Quirion et al. (1995) J. Neurosci. 15, 1455-1462.

5HT2 receptors in cerebral cortex of migraineurs studied using PET and 18F-fluorosetoperone

Since the brain 5HT2 receptors might be implicated in migraine pathogenesis, we have used positron emission tomography and 18F-fluorosetoperone, a 5HT2 specific radioligand, to investigate in vivo the cortical 5HT2 receptors in migraine subjects. Nine migraineurs who had either migraine with and without aura (n = 5) or only migraine without aura (n = 4) were studied between attacks. Twelve unmedicated healthy subjects of similar mean age were used as controls. Brain radioactivity was measured after 18F-setoperone IV injection for 90 min. A decrease of the regional specific distribution volumes (SDV) of the ligand was observed both in migraineurs and in controls. The age adjusted group means of SDV did not differ between patients and controls for the whole and for the right or left frontal, temporal, parietal and occipital cortex. These results suggest that cortical 5HT2 receptors may be unaltered between attacks in migraine sufferers.

Expression of tyrosine hydroxylase in the aging, rodent olfactory system

Tyrosine hydroxylase (TH) mRNA, immunoreactivity, and activity were examined as a reflection of dopamine expression in juxtaglomerular neurons intrinsic to the olfactory bulbs of young (6-month-old), middle aged (18-month-old), and aged (25- to 29-month-old) rats and mice. TH expression was maintained at levels observed in young animals in the olfactory bulbs of aged animals from two mouse strains, C57Bl/6JNia and C57Bl/6NNia, and one rat strain, an F1 hybrid between F344 and Brown Norway strains. The parental F344 rat strain exhibited reductions in TH expression of about 20% in 26- to 29-month-old animals as compared to 6- and 18 month-old rats. However, there was significant inter-animal variability. Some aged F344 rats had TH levels that were similar and others had activity levels that were 50% of those in young and middle aged animals. Neither the general condition of the animals nor the presence of adrenal tumors predicted the individuals with reduced TH expression. Olfactory bulb size, estimated from protein content, did not differ between rats and mice of different ages. In addition, expression of olfactory marker protein, a protein found primarily in mature olfactory receptor neurons, also was unchanged indicating the maintenance of afferent innervation. These data suggest that, in contrast to other brain dopamine systems, the expression of the dopamine phenotype is maintained in the aging olfactory bulb.

Acetylcholine measurement of cerebrospinal fluid by in vivo microdialysis in freely moving rats

Acetylcholine (ACh) and choline (Ch) levels in rat cerebrospinal fluid (CSF) were determined by in vivo microdialysis (CSF microdialysis) in both halothane-anesthetized and freely-moving rats. The Ch/ACh ratio in CSF perfused with Ringer's solution (30 microliters/30 min) containing 10(-5) M physostigmine, a centrally active cholinesterase inhibitor, was significantly lower than that in unprocessed CSF due to significantly higher ACh levels in the former. The successive measurement on the 2nd and 7th day after the guide cannula implantation demonstrated the feasibility of the CSF microdialysis method for repetitive monitoring of CSF ACh and Ch levels in freely moving rats without extensive tissue damage. Intraperitoneal administration of physostigmine caused an increase in CSF ACh levels, whereas administration of neostigmine, which cannot penetrate into the blood brain barrier, did not. Furthermore, a centrally active acetylcholinergic M1-receptor agonist, AF102B, produced an increase in CSF ACh and Ch levels. Thus, the present study demonstrates that CSF microdialysis is a useful method for evaluating overall central cholinergic activity and investigating the pharmacological effects of various drugs that act via the central cholinergic system.

On the effect of ageing on the distribution of vasoactive intestinal polypeptide and calcitonin gene-related peptide in the rat brain

The distribution of calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) was investigated by the use of immunohistochemical techniques in the brain of young and aged rats. CGRP-like immunoreactivity (CGRP-LI) showed a significant decrease only in the amygdala, whereas a substantial age-dependent decrease in VIP-like immunoreactivity (VIP-LI) was observed in the cortex, amygdala, substantia nigra, hippocampus and suprachiasmatic nucleus.

Neurochemical profiles in cerebrospinal fluid of stroke-prone spontaneously hypertensive rats

The purpose of the present study was to evaluate stroke-prone spontaneously hypertensive rats (SHRSP) neurochemically by determining the cerebrospinal fluid (CSF) levels of acetylcholine (ACh), norepinephrine (NE) and serotonin (5-HT) as an index of central neuronal activity. The CSF ACh levels of 15- to 20-week-old SHRSP were significantly lower than those of age-matched Wistar Kyoto rats (WKY) both under the urethane/alpha-chloralose anesthesia and in freely moving conditions. The difference in the CSF ACh levels between SHRSP and WKY was more marked at 30-40 weeks. Sustained changes were not observed in the CSF NE and 5-HT levels. Thus, the progressive dysfunction in the central cholinergic system may characterize the pathophysiological state of this animal model with cerebral lesions caused by continuous high blood pressure.

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.

Aging and 3H-paroxetine binding in rat brain: effect of imipramine and tetrahydroacridine

3H-Paroxetine (PA) binding was studied in the frontal cortex (FC) and hippocampus (H) of 4 mos (young), 15 mos (adult) and 24 mos (aged) old Fischer 344 rats. Bmax (maximum number of binding sites) of PA binding was significantly higher in the H of adult rats compared with either young or old rats. There was no difference in Bmax between young and old rats. No change in Kd was observed in H and Kd or Bmax in FC with age. We also studied the effect of imipramine and tetrahydroacridine (THA) on PA binding in FC and H. Both drugs inhibited PA binding in FC and H but THA was 2000 times less potent than imipramine. There was no effect of age on IC50 values of imipramine and THA. These observations suggest that the number of 5-HT transporter sites in the hippocampus increases with brain maturity but then drops significantly during old age. This finding may have implications for age-related decrements in learning and memory, thought to be mediated by hippocampal structures.

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)

Oxytocin concentration changes in different rat brain areas but not in plasma during aging

The concentration of oxytocin was measured by radioimmunoassay in different brain areas, hypophysis, and plasma of male Wistar Kyoto rats during aging. Although no difference in the concentration of oxytocin in any of the above tissues among 2- and 6-month-old rats was found, in 12-month-old rats a 21% decrease was observed in both septum and hippocampus, but not in the hypothalamus, hypophysis, and plasma, when compared to values of 2- and 6-month-old rats. In 18-month-old rats, the decrease of septal and hippocampal oxytocin content was higher than that found in 12-month-old rats, but no change was found in the hypothalamus, neurohypophysis, and plasma. In 24-month-old rats, oxytocin content was similar to that found in 18-month-old rats in all tissues analyzed. The results suggest that aging induces an impairment of oxytocinergic transmission in the central nervous system but not in the neurohypophyseal system.

Age-related changes in transmitter glutamate and NMDA receptor/channels in the brain of senescence-accelerated mouse

The senescence-accelerated mouse (SAM-P/8) is known as a murine model of aging and memory dysfunction. In the hippocampus and cerebral cortex of P/8, the contents of glutamic acid and glutamine were significantly higher than those of normal strain R/1 during 2 and 14 months. High K(+)-evoked endogenous glutamic acid release from the slices of P/8 was increased in comparison with R/1 at 9 and 11 months. In addition, the Bmax of [3H]dizocilpine (MK-801, channel blocker for N-methyl-D-aspartic acid receptor/channel) binding in the cerebral cortex was age-dependently decreased in P/8 but not in R/1. These results suggest that synaptic dysfunctions in the glutamatergic system occur in the CNS of SAM-P/8.

Central anticholinergic hypersensitivity in aging

Although neurochemical reductions in cholinergic systems have been found to occur during aging, such changes do not necessarily translate to functional deficits. The cognitive deficits of normal aging have been attributed in part to hypocholinergic function, but anticholinergic hypersensitivity in the elderly has not been systematically documented. To test the cholinergic hypothesis of aging, we investigated the effects of scopolamine on memory and attention in healthy young and elderly subjects. Treatments included intramuscular glycopyrrolate (0.0044 mg/kg) and scopolamine (0.002, 0.004, and 0.007 mg/kg) in a randomized double-blind design. The test battery included the Selective Reminding Task (SRT), Digit Span, Paired Associates Learning (PAL), Symbol Digit Modalities Test (SDMT), and the Continuous Performance Task. Elderly controls were more impaired at lower scopolamine doses than were the young on SRT, PAL, and SDMT. These results demonstrate anticholinergic hypersensitivity and are consistent with decremental changes in cholinergic status during normal aging.

Effects of concurrent nicotinic antagonist and PCPA treatments on spatial and passive avoidance learning

The present study investigates the effects of concurrent manipulations of nicotinic cholinergic receptors (mecamylamine 10 mg/kg, i.p.) and serotonin neurons (PCPA, 400 mg on each of 4 days) on spatial navigation (water maze, WM) and passive avoidance (PA) performance. PCPA treatment had no effect on WM navigation or PA performance of intact rats, but greatly aggravated mecamylamine induced performance deficit. Either single or combined treatments with hexamethonium (5.0 mg/kg, s.c.) and PCPA had no effect on WM or PA performance. These findings may suggest that nicotinic cholinergic receptors are also importantly involved in the cholinergic-serotonergic regulation of cognitive functioning.

Aging of the serotonergic system in the rat forebrain: An immunocytochemical and neurochemical study

Age-related changes in both morphological and neurochemical parameters of indol- and catecholaminergic system in the rat brain were examined. A qualitative histochemical survey of the occurrence of aberrant serotonergic fibers in the aged rat brain suggests region-specificity in the process of degeneration. Forebrain areas, such as the caudate-putamen complex, globus pallidus, prefrontal and frontoparietal cortices were consistently affected, whereas serotonergic fibers were only infrequently affected in other areas like septal and amygdaloid nuclei. Neurochemical data similarly revealed regional differences. 5-Hydroxytryptamine levels were increased in the frontoparietal cortex, hippocampus, hypothalamus and the mesencephalic raphe region but remained unchanged in the caudate-putamen complex. 5-Hydroxyindolacetic acid levels were also enhanced in all these areas. Examination of brains of 12-, 18- and 24-month-old rats revealed that aberrant serotonergic fibers were already present at the age of 12 months and their incidence increase with age. There was no difference in the number of serotonergic cells in the dorsal raphe nucleus of young and aged rats. Aberrant tyrosine hydroxylase-immunoreactive fibers were observed only infrequently. Their occurrence showed no overlap with the areas containing aberrant serotonergic fibers. Neurochemical estimates of the levels of catecholamines in young versus aged rat brain areas similarly revealed regional and neurotransmitter specific differences to occur during the process of aging.

Free radicals, lipid peroxidation, SOD activity, neurotransmitters and choline acetyltransferase activity in the aged rat brain

The mechanism of aging is suggested to be related to oxygen free radicals. Free radicals, lipid peroxidation and SOD activity have been reported to be increased in the aged brain. A Japanese herbal medicine, Sho-saiko-to-go-keishi-ka-shakuyaku-to (TJ-960), which has scavenging activities against hydroxyl radicals, superoxide, 1,1-diphenyl-2-picrylhydrazyl radicals, carbon-centered radicals and alpha-tocopheroxyl radicals, decreased carbon-centered radicals and thiobarbituric acid reactive substances (TBARS) levels in the aged rat brain after a 3-week oral administration of 5% TJ-960 solution. TJ-960 elevated superoxide dismutase (SOD) activity in the cytosol fraction of the hippocampus and hypothalamus of aged rats. It decreased norepinephrine and 5-hydroxytryptamine (5-HT) levels in the hypothalamus and increased the 5-HT level in the cerebellum. TJ-960 treatment increased choline acetyltransferase activity in aged rats. As herbal medicines do not generally have harmful side effects, antioxidant TJ-960 appears to be a suitable prophylactic agent against some neuronal symptoms of aging.

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.

Neurotransmitters in neocortex of aged rhesus monkeys

The effects of aging on levels of neurotransmitters were determined in two regions of the cerebral cortex in rhesus monkeys (Macaca mulatta). Choline acetyltransferase (ChAT) activity as well as somatostatin, neuropeptide Y, and substance P immunoreactivities were analyzed in the right caudal cingulate gyrus and in the left and right inferior occipital poles in five age groups: 4-6 years; 8-11 years; 20-25 years; 26-29 years; and 31-34 years. Neuroactive amino acids and markers for monoamine transmitters were analyzed only in the youngest (4-6 years) and oldest (31-34 years) animals. Across the five age groups studied. ChAT activity as well as somatostatin and neuropeptide Y immunoreactivities were significantly decreased bilaterally in occipital poles of the 31- to 34-year-old group. There were no significant age-related differences in substance P immunoreactivity. In 4-6-year-old vs. 31-34-year-old monkeys, levels of amino acid neurotransmitters were unchanged. However, there were significant reductions in norepinephrine, serotonin and its metabolites, kynurenine, and 4-hydroxyphenyllactic acid in occipital poles of the 31- to 34-year-old monkeys. No significant neurochemical changes were detected in the cingulate cortex. These findings demonstrate that aged nonhuman primates show reductions in cortical markers for a variety of neurotransmitters, including acetylcholine, somatostatin, neuropeptide Y, norepinephrine, and serotonin but that these changes do not occur uniformly in the neocortex.

Pharmacological consequences of cholinergic plus serotonergic manipulations

The present study investigated pharmacological consequences of combined cholinergic and serotonergic blockade. Raphe medianus (RM) lesions (5,7-DHT) had no effect on spatial learning, but augmented scopolamine 0.8 mg/kg induced learning deficit. Pilocarpine (4 mg/kg) could reverse scopolamine (0.8 mg/kg), but not scopolamine (0.8 mg/kg) + RM lesion induced spatial learning impairment. However, a higher dose of pilocarpine could restore spatial learning deficit induced by scopolamine (0.8 mg/kg) and RM lesions. These findings support the important role of cholinergic-serotonergic interaction in the regulation of spatial learning and suggests that the combined cholinergic-serotonergic deficit in patient's with Alzheimer's disease may have an impact on therapeutic approaches which seek to normalize AD related cognitive impairments.

Loss of NMDA, but not GABA-A, binding in the brains of aged rats and monkeys

In this quantitative neurochemical study we investigated age-related changes in the GABAergic, glutamatergic, and cholinergic neurotransmitter systems in rats and rhesus monkeys. Sixteen young (5 months) and 20 aged (24 months) rats and seven "young" (4-9 years), six "adult" (20-25 years), and five "aged" (29-34 years) monkeys were studied. NMDA-displaceable 1-[3H]glutamate binding was significantly decreased in many neocortical and subcortical regions examined in aged rats and monkeys. The level of choline acetyltransferase (ChAT) activity and [3H]muscimol binding were unchanged in aged animals.

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.