A single glucose transporter configuration in normal primate brain endothelium: comparison with resected human brain.

Cellular distribution of the Glut1 glucose transporter in normal primate brains was analyzed by immunogold electron microscopy. Two configurations of endothelial Glut1 glucose transporter (high and low density capillaries) have been found in resections of traumatically injured and epileptogenic human brain; the objective of the present study was to ascertain whether these same 2 capillary populations, expressing high and low glucose transporter densities, were the common configuration in normal brain. The relative numbers of Glut1 glucose transporter-associated gold particles on luminal and abluminal endothelial cell membranes were determined within the cerebral cortex of several normal, nonhuman primates. Low Glut1 densities were seen in brain endothelia of both the rhesus and squirrel monkey cortex, with slightly greater quantities of Glut1 in vervet monkey cortices. The Glut1 transporter was most highly expressed in the baboon cortex, approaching the concentrations seen in human brains. In the rhesus, squirrel, and vervet monkeys, Glut1 concentrations were greater on the abluminal than luminal capillary membranes. In contrast, mean luminal membrane Glut1 concentrations were greater in baboons, resembling the distribution seen in the human brain. Brain regional differences in transporter concentration were seen in comparing membrane densities in the baboon cortex (approximately 15 Glut1-gold particles per micrometer), hippocampus (approximately 12 Glut1 gold particles per micrometer), cerebellum (approximately 6 Glut1-gold particles per micrometer), and retinal microvasculature (approximately 20 Glut1-gold particles per micrometer). We conclude that a single, uniform Glut1 distribution characterizes brain capillaries of normal nonhuman primates, and hypothesize that the presence of high and low density glucose transporter endothelial cells (seen in human traumatic injury and seizure resections) represents a pathologic response to brain insult.

Effects of large neutral amino acid concentrations on 6-[F-18]Fluoro-L-DOPA kinetics.

6-[F-18]Fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) has been used to measure the central dopaminergic function in many species, including humans and monkeys. For transport across the blood brain barrier (BBB), FDOPA competes with plasma large neutral amino acids (LNAA). In this article we evaluate the effects of normal physiological LNAA concentration variation on BBB transport (K1) and the FDOPA uptake measurement, Ki. We also investigate a method for reducing the dependency of FDOPA quantitation on LNAA. Adult vervet monkeys (Cercopithecus aethiops sabaeus, n = 19) were fasted overnight before FDOPA positron emission tomography scans. Blood samples were drawn for LNAA determination, metabolite analysis, and compartmental modeling. The estimated K1 and Ki were both negatively correlated with LNAA concentrations (r2 = 0.51 and 0.62, respectively). Using an adjustment to K1 and Ki based on these correlations, the LNAA dependency was reduced (SD of the data for K1 was reduced by 33%, for Ki by 40%). Experiments with amino acid loading on an additional six animals indicate that BBB transport can be described using Michaelis-Menten kinetics. Results show a clear dependence of FDOPA uptake on plasma LNAA concentrations, which can be removed to increase the precision of FDOPA quantitation.

Recovery of striatal dopamine function after acute amphetamine- and methamphetamine-induced neurotoxicity in the vervet monkey.

In six vervet monkeys, presynaptic striatal dopamine function was assessed longitudinally by [18F]fluoro-L-DOPA (FDOPA)-positron emission tomography (PET) after administration (2 x 2 mg/kg, i.m., 4 h apart) of either amphetamine (Amp), n = 3, or methamphetamine (MeAmp), n = 3. At 1-2 weeks postdrug, both Amp and MeAmp exposure effected similar decreases (60-70%) in the FDOPA influx rate constant (FDOPA Ki), an index of striatal dopamine synthesis capacity. Subsequent studies in these subjects showed that FDOPA Ki values were decreased by 45-67% at 3-6 weeks, by 25% at 10-12 weeks and by 16% in one Amp-treated subject at 32 weeks. Biochemical analysis showed that striatal dopamine concentrations were decreased by 75% at 3-4 weeks and by 55% at 10-12 weeks. These results indicate that in vervet monkey striatum, an acute Amp or MeAmp drug dosage produces extensive striatal dopamine system neurotoxicity. However, these effects were reversible; observed time-dependent recovery in both FDOPA Ki and dopamine concentrations indicates that neurochemical plasticity remains active in the adult primate striatum. At 3-4 and 10-12 weeks postdrug, the concurrent characterization of the striatal FDOPA Ki and dopamine concentrations for individual subjects showed that Ki decreases between 24 and 67% corresponded to dopamine depletions of 55-85%. These relatively larger postdrug decrements in steady-state striatal dopamine concentrations suggest that compensatory increases in dopamine synthesis capacity develop in the partially lesioned striatum. In contrast to the dopamine depletion in striatum, substantia nigra concentrations remained unchanged from referent values at both 3-4 and 10-12 weeks postdrug. Thus, the integrity of the substantia nigra could not be inferred from decreases in the striatal FDOPA Ki parameter. This disparity between striatum and substantia nigra reactivity to systemic administration of amphetamines suggests that each has unique dopamine system regulatory mechanisms.

Ethological and 6-[18F]fluoro-L-DOPA-PET profiles of long-term vulnerability to chronic amphetamine.

A chronic 10-day amphetamine (Amp) protocol was used to induce significant long-term decrements of the striatal [18F]fluoro-L-DOPA influx rate constant (FDOPA Ki) in the vervet monkey. Longitudinal FDOPA-positron emission tomography (PET) assessment in Amp-treated subjects subsequently revealed a gradual recovery of striatal dopamine function: FDOPA Ki values were decreased by approximately 70% at 1 month, approximately 45% at 6 months, approximately 20% at 12 months and were similar to pre-Amp values at 24 months. Motoric and social behavioral measures were obtained on all subjects within a species-typical group setting. Behavioral observations were conducted during both basal and stressor-challenge conditions, the latter being created by placing a potential intruder-animal in an individual cage adjacent to the subject's group enclosure. During basal conditions, post-Amp stereotypies were present at 2 weeks and locomotor behaviors were increased throughout 1 month; both alterations occurred while FDOPA Ki values were significantly decreased. Social behaviors were also significantly affected; affiliative behavior was decreased up to 6 months while aggressive behavior was increased for 12 months. However, a different pattern of behavioral changes emerged under stressor-challenge conditions. Motoric and social changes were of greater magnitude and persisted longer than in basal settings while aggressive behavior remained elevated at 24 months. These results indicate that chronic Amp-induced decreases in FDOPA Ki values and behavioral alterations are reversible. Changes in striatal dopamine function as indexed with FDOPA-PET are not correlated with post-Amp alterations in behaviors and moreover, expression of those behaviors is context-dependent.

Mitochondrial content of choroid plexus epithelium.

The objective of the present study was to examine the apparent work capacity of one of the two separate membrane systems (the blood-cerebrospinal fluid barrier) that isolate the mammalian brain extracellular fluid (and cerebrospinal fluid, CSF) from plasma. Digitized analyses of electron-microscopic images provided estimates of mitochondrial volumes, which were expressed as a percentage of the cell cytoplasm. We recorded a high mitochondrial content of 12-15% in the cuboidal epithelium of primate choroid plexus, which was consistent in vervet, rhesus, and squirrel monkeys, as well as in baboons. Similarly high mitochondrial contents were observed in the rabbit, rat, and mouse choroid plexus. It has been postulated that the high mitochondrial content of brain endothelium is associated with maintaining the ionic gradients within the central nervous system. We observed that the mitochondrial content of the choroid plexus (where CSF is produced) was slightly higher than in (prior measurements of) the blood-brain barrier (BBB). In addition, surface areas at the apical borders of the choroid plexus epithelia (where the Na+K+ATPase activity has been localized) were increased 7- to 13-fold over the basal borders, in the primate species examined. The observation of high mitochondrial volumes in choroid plexus cells is consistent with the suggestion that increased mitochondrial densities seen in choroidal epithelia and BBB capillaries provide a metabolic work capability for both secretory activities and maintaining ionic gradients across blood-CSF barriers.

Longitudinal behavioral and 6-[18F]fluoro-L-DOPA-PET assessment in MPTP-hemiparkinsonian monkeys.

Biochemical and behavioral criteria were established to determine the long-term stability of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced unilateral striatal dopamine deficiency in the vervet monkey. At time points over a 12-month period, post-MPTP striatal dopamine synthesis capacity was indexed with 6-[18F]fluoro-L-DOPA (FDOPA)-positron emission tomography. For the MPTP-treated subjects (n = 4), an intrasubject FDOPA influx rate constant (Ki) ratio method of right (lesioned) striatum/left (unlesioned) striatum values was used to assess changes in striatal activity. Striatal FDOPA Ki ratios differed less than 5% between studies conducted at 1-2, 5-7, and 9-11 months post-MPTP; these results indicated a stable MPTP-induced striatal lesion over this time period. At the 5-7 and 9-11 month time points, behavioral indices of the MPTP-induced deficits were obtained within a species-typical group setting. For three of the four subjects, persistent decrements in motoric, affiliative, and vigilance behavior were observed while the frequency of aggression toward group members was increased. At the 9-11 month time point, one subject showed a 30% improvement in the social measures, indicative of a partial recovery from the MPTP-induced behavioral decrements although its striatal FDOPAKi ratio remained unchanged. Thus, behavioral and noninvasive biochemical methods can provide complementary indices to assess individual differences in sensitivity to MPTP-induced deficits. Both types of data are required to determine lesion stability and, subsequently, the efficacy of interventions designed to restore normal function in this primate Parkinsonian model.

6-[18F]fluoro-L-DOPA-PET studies show partial reversibility of long-term effects of chronic amphetamine in monkeys.

The acute and long-term effects of chronic amphetamine administration on the striatal dopamine system in monkeys were assessed with 6-[18F]fluoro-L-DOPA (FDOPA) and positron emission tomography (PET). Vervet monkeys (Cerecopithecus aethiops) were administered amphetamine doses, i.m., that increased from 4 mg/kg/d to 18 mg/kg/d over a 10 day period. Post-amphetamine FDOPA-PET scans at 1-2, 3-4, and 6 week time points in individual subjects showed persistent decrements in dopamine synthesis capacity as reflected by FDOPA influx rate constant (Ki) values being approximately 30% that of pre-drug assessment. In other animals that were administered the same drug regimen, biochemical analysis of striatal regions at 1-2 weeks post-drug indicated that dopamine concentrations were decreased by approximately 95% throughout caudate and putamen regions, while the homovanillic acid/dopamine level ratio was increased 3-10-fold. Post-drug FDOPA-PET Ki values remained consistently low up to 6 weeks; however, at the 5-6 month time point, relative increases in FDOPA-Ki values (approximately 53% of pre-drug values) were observed for all subjects, indicative of partial recovery of striatal dopamine synthesis capacity. These results demonstrate that FDOPA-PET can reveal temporal activity changes within the striatal dopamine system of individual subjects. The apparent, partial reversibility of amphetamine's neurotoxic effects suggests a plasticity of dopaminergic function that may include regeneration of dopaminergic terminals and compensatory increases in residual dopamine synthesis rates. The persistence of the partial decrement in dopamine synthesis capacity, however, may indicate a long term component of amphetamine's toxic effects.

Developmental changes in brain metabolism in sedated rhesus macaques and vervet monkeys revealed by positron emission tomography.

The present positron emission tomography study used 2-deoxy-2[18F]fluoro-D-glucose to examine age-related changes in local cerebral metabolic rates for glucose (LCMRglc) in sedated rhesus macaques and vervet monkeys. Nineteen vervet monkeys were scanned in a cross-sectional design, which consisted of three age groups (birth to 59 d, 60-179 d, 180 d to adult) that captured the developmental period of greatest synaptic density within the second group. Two rhesus and two vervet monkeys were also examined longitudinally. Subjects were sedated throughout the procedure with a combination of ketamine and midazolam. Longitudinal and cross-sectional analyses of 20 brain regions indicated lowest LCMRglc in rhesus and vervet monkeys < 2 months of age (about 60% of adult levels). These metabolic rates more than doubled to approximately 155% of adult levels after the second postnatal month, coincident with transient synaptic overproduction and increased sociobehavioral activity. LCMRglc remained high until 6 months postnatally, coincident with continued dendritic growth and the emerging sociobehavioral independence of the young monkey. After 6 months, LCMRglc decreased gradually to adult levels. Thus, the period between 2 and 6 months is a time of peak metabolic activity, which coincides with increased histologic and behavioral activity in the developing monkey.

Menstrual cycle and social behavior in vervet monkeys.

We assessed the relationship between social behavior and the menstrual cycle in 11 adult female vervet monkeys (Cercopithecus aethiops sabaeus) living in an established, stable social group. The findings indicated that fluctuations in ovarian steroids are accompanied by behavioral changes in vervet monkeys. A significant increase in aggressive action, avoidance of social overtures, and retreats from threat occurred during the late luteal phase. However, the social environment can greatly affect behavior independent of the phase of the menstrual cycle. The 10 nondominant (or subordinate) individuals not only exhibited behavioral changes across their own menstrual cycles, but also were responsive to the dominant female's cycle. During the dominant female's late luteal phase, subordinate females significantly increased aggression and decreased social activity. Some of behavioral patterns in female vervet monkeys are therefore relatively independent of direct hormonal modulation and support the contention of the dominant female as the driving force for behavioral changes related to aggression and social interaction. The differential effect of hormones and social status and other environmental factors on behavior has not been critically evaluated in human studies of the premenstrual syndrome. The present study suggests that it is important to assess which behavioral patterns in women are hormonally mediated and which are dependent on the environment.

Individual differences in basal cisternal cerebrospinal fluid 5-HIAA and HVA in monkeys. The effects of gender, age, physical characteristics, and matrilineal influences.

We examined the effects of gender, age, weight, length, body shape (ectomorphy), and matrilineal influences on cisternal cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA) and homovanillic acid (HVA) in 78 socially living adult and adolescent vervet monkeys. CSF 5-HIAA and the 5-HIAA:HVA ratio were higher (by 27% and 18%, respectively) in females. In both sexes, CSF 5-HIAA and the 5-HIAA:HVA ratio increased with age. Neither weight nor length were independently related to CSF 5-HIAA or HVA; however, shape correlated with CSF 5-HIAA and HVA in males (higher in thin, long subjects). Male offspring had CSF 5-HIAA concentrations and 5-HIAA:HVA ratios that were significantly closer to their mothers than did age-matched, maternally unrelated males. Repeated measures of CSF 5-HIAA and HVA in another 22 males living in unvarying settings showed that individual differences in these measures persisted over time. The data underscore the impact of gender, age, and matrilineal relationships on individual differences in CSF monoamine metabolites and highlight the importance of controlling for age and gender in neuropharmacological investigations of clinical populations.

Plasma catecholamines and social behavior in male vervet monkeys (Cercopithecus aethiops sabaeus).

Many investigations in humans indicate that epinephrine, norepinephrine and their ratio may correlate with such traits as social competence, academic achievement, and aggression. However, the socioeconomic, dietary, and environmental confounds accompanying most human studies complicate their interpretation. Social status, aggression, and other social behaviors can be reliably assessed in nonhuman primates under conditions controlling for crucial environmental factors. If interpretation of human studies is correct, dominant and subordinate male vervet monkeys should exhibit distinctive patterns of catecholamine secretion. To test this possibility, seventeen adult male monkeys living in six stable social groups were observed for 6 months. Based on their success in agonistic events, subjects were categorized as dominant or subordinate. Alpha scores were calculated from empirically derived factors to provide a noncategorical measure of dominant behavioral style. Plasma epinephrine and norepinephrine samples obtained from anesthetized subjects did not differ between dominant and subordinate males. Alpha scores, however, distinguished high from low norepinephrine/epinephrine ratio groups. These findings are consistent with studies in humans linking high epinephrine, low norepinephrine, and social competence.

Fenfluramine effects on serotonergic measures in vervet monkeys.

Chronic fenfluramine treatment reduced whole blood serotonin and CSF 5-hydroxyindoleacetic acid, but increased aggressive and locomotor behavior, in adult male vervet monkeys (Cercopithecus aethiops sabaeus). Following a drug-free washout period to monitor the drug recovery course, we initiated a second period of fenfluramine treatment in the same animals. When whole blood serotonin concentrations were reduced by about 40% from predrug baseline levels, we examined 11 cortical and subcortical brain regions for their content of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, norepinephrine, and dopamine. We observed correspondence between the reduction in whole blood serotonin and the reduction in brain 5-hydroxytryptamine. Similarly, there was a correspondence between the reduced 5-hydroxyindoleacetic acid levels observed in CSF and brain. No alterations were noted in the concentrations of norepinephrine or dopamine. These observations suggest that the behavioral effects observed in monkeys after chronic fenfluramine treatment result from reduced central serotonin.

Serotonergic mechanisms promote dominance acquisition in adult male vervet monkeys.

In a counter-balanced, cross-over study, we examined the contributions of serotonergic systems to the acquisition of social dominance in adult male vervet monkeys. Subjects were members of 12 social groups, each containing 3 adult males, at least 3 adult females, and their offspring. Animals were observed in 5 intervals including a first baseline, a first experimental, a second baseline, a second experimental, and a third baseline period. At the end of the first baseline period, the dominant male was removed from each group. In each group, one of the two remaining subordinate males was selected at random for treatment and during the first experimental period, 6 of the 12 treated males received drugs that enhanced serotonergic activity (3 were given tryptophan 40 mg/kg/day and 3 fluoxetine 2 mg/kg/day). The other 6 treated males received drugs that reduced serotonergic function (3 were given fenfluramine 2 mg/kg/day and 3 cyproheptadine 60 micrograms/kg/day). At the end of the first experimental period, the original dominant male was returned to his group and the second baseline period began. In all instances, the originally dominant male regained his dominant position. The second experimental period began with the dominant male again being removed and, the 12 treated males were given the treatment they had not received in the first experimental period. At the start of the third 12-week baseline period, the original dominant male was returned to his group and resumed his dominant status. When the 12 treated subjects received tryptophan or fluoxetine, they became dominant in all instances. When they received fenfluramine or cyproheptadine, their vehicle-treated cage mates became dominant. The sequence of the behavioral changes shown by the treated males as they acquired dominance status paralleled those seen in naturalistic conditions. These observations support the distinction between dominance and aggression and strongly suggest that when hierarchical relationships are uncertain, serotonergic mechanisms may mediate the behaviors which permit a male to attain high dominance status.

The complex relationship between behavioral attributes, social status, and whole blood serotonin in male Macaca fascicularis.

Among group-housed male Cercopithecus aethiops, dominant animals have higher concentrations of whole bood serotonin (WBS) than their subordinate counterparts. In contrast, there appears to be no relationship between social status and WBS in Macaca nemestrina. We report here the relationship between social status and WBS among 29 male Macaca fascicularis housed in groups of five. Membership in these groups was disrupted periodically (20 times in 26 months) with a reorganization manipulation. Concentrations of WBS were assessed just prior to the 20th (final) social reorganization and at 1, 2, and 5 weeks following that reorganization. Correlations between these repeated samples were high, indicating considerable intraindividual stability in WBS. Overall, there were no persistent differences in WBS between clearly dominant (ranked 1 or 2) and subordinate (ranked 3, 4, or 5) monkeys, despite the substantial behavioral differences between such animals and the stability of social status across time. A multivariate analysis indicated that WBS was best predicted by a model that included a positive relationship with the interaction between rate of grooming and social status (P < 0.002), a negative relationship with extreme aggressiveness (P = 0.03), and a positive relationship with time spent alone (P < 0.04). Further analysis of the social status by grooming rate interaction revealed that WBS was higher in dominants than subordinates, but only if the dominants also initiated grooming frequently. These differences in the relationship WBS and social status in C. aethiops and M. fascicularis may reflect differences in the behavioral dynamics underlying the dominance hierarchies in small groups of these two species.

Comparison of ketamine, physical restraint, halothane and pentobarbital: lack of influence on serotonergic measures in monkeys and rats.

The consequences of the use of ketamine for immobilization have been examined on the concentration of whole blood serotonin, concentrations of neurotransmitters and metabolites in CSF and brain, and specific binding of ligands related to neurotransmitters in brain. Vervet monkeys (Cercopithecus aethiops sabaeus) were examined under conditions which compared ketamine with physical restraint and with halothane. It was found that ketamine, used acutely in monkeys for restraint, had no influence on the concentration of serotonin in whole blood or the concentration of 5-hydroxyindoleacetic acid or homovanillic acid in the CSF. In rats, untreated animals were compared with those treated with ketamine alone, or in conjunction with pentobarbital. Treatment with ketamine had no influence on the specific binding of ketanserin, imipramine, prazosin or dihydroalprenolol in brain of rat, nor any influence on the concentrations of serotonin, 5-hydroxyindoleacetic acid, norepinephrine, epinephrine, dopamine, or dihydroxyphenylacetic acid in brain. A moderately increased concentration of homovanillic acid was observed in several areas of the brain of the rat after ketamine alone or paired with pentobarbital.

Vervet monkey (Cercopithecus aethiops sabaeus) whole blood serotonin level is determined by platelet uptake sites.

Whole blood serotonin levels in adult male vervet monkeys living in social groups are sensitive to the animals' social environment. The mechanisms that translate different behavioral and environmental cues into altered whole blood serotonin levels are unknown. In this study, we have measured platelet number, size, serotonin content, and serotonin uptake, as well as the serum concentrations of tryptophan, Mg+2 and Ca+2. Results showed that whole blood serotonin levels, platelet serotonin content, and the serotonin uptake parameter Vmax were stable within animals on repeated sampling. The whole blood serotonin level was highly positively associated with platelet serotonin content, and the platelet serotonin content was highly positively associated with Vmax. These findings suggested that whole blood serotonin levels were a function of the number of platelet uptake sites.

Similarity of 5-HT2 receptor sites in dominant and subordinate vervet monkeys.

Pharmacological studies using serotonergic agents have revealed status-linked behavioral effects in dominant and subordinate vervet monkeys. A possible explanation for the greater drug response observed in dominant animals is that there is a CNS difference between dominant and subordinate animals. Such differences could exist at the level of serotonin receptor sites, membrane responsiveness, or interaction with other neurotransmitters. We have examined the specific 3H-ketanserin binding in various regions of vervet monkey brain to evaluate the hypothesis that dominant and subordinate vervet monkeys differ in CNS 5-HT2 receptor sites. No differences were found in the number or affinity of 3H-ketanserin binding sites between dominant and subordinate animals. Further, no differences were found in the displacement of 3H-ketanserin binding by the serotonin agonist quipazine. These results suggest the conclusion that differences at 5-HT2 binding sites do not account for status-linked differences in behavioral drug response in vervet monkeys and that other or additional mechanisms must underlie status-related drug response differences.

Differential behavioral effects of tryptophan and 5-hydroxytryptophan in vervet monkeys: influence of catecholaminergic systems.

In previous studies tryptophan and 5-hydroxy-tryptophan (5-HTP) treatments produced opposite effects on aggression and vigilance and differing effects on eating and locomoting in vervet monkeys. This study examined the effects of the serotonin reuptake inhibitor fluoxetine, and the catecholamine reuptake inhibitor desmethylimipramine (DMI) on tryptophan and 5-HTP induced behavioral changes. Thirty-two adult males from 16 different social groups were studied. Tryptophan (10, 20, and 40 mg/kg/day) produced dose-dependent reductions in aggression, vigilance, and locomotion and increases in eating. In contrast, 5-HTP (20, 40, and 80 mg/kg/day) increased aggression and vigilance and did not affect locomotion or eating. Fluoxetine (0.5, 1.0, and 2.0 mg/kg/day) produced effects identical to tryptophan while DMI (1.5, 3.0, and 6.0 mg/kg/day) resulted in dose-dependent increases in aggression, vigilance, and locomotion, and decrements in eating. When combined with tryptophan, fluoxetine augmented and DMI diminished the effects of tryptophan on all behaviors. Fluoxetine decreased and DMI increased the effects of 5-HTP on aggression and vigilance. Thus concurrent DMI enhanced and concurrent fluoxetine reduced the differences between 5-HTP and tryptophan. These results suggest that 5-HTP's effects on catecholaminergic systems may underlie the differing behavioral effects of tryptophan and 5-HTP on behavior in a species closely related to humans.