Bruce Scharf

Antidepressant-induced neurogenesis in the hippocampus of adult nonhuman primates

New neurons are generated in the adult hippocampus of many species including rodents, monkeys, and humans. Conditions associated with major depression, such as social stress, suppress hippocampal neurogenesis in rodents and primates. In contrast, all classes of antidepressants stimulate neuronal generation, and the behavioral effects of these medications are abolished when neurogenesis is blocked. These findings generated the hypothesis that induction of neurogenesis is a necessary component in the mechanism of action of antidepressant treatments. To date, the effects of antidepressants on newborn neurons have been reported only in rodents and tree shrews. This study examines whether neurogenesis is increased in nonhuman primates after antidepressant treatment. Adult monkeys received repeated electroconvulsive shock (ECS), which is the animal analog of electroconvulsive therapy (ECT), the most effective short-term antidepressant. Compared with control conditions, ECS robustly increased precursor cell proliferation in the subgranular zone (SGZ) of the dentate gyrus in the monkey hippocampus. A majority of these precursors differentiated into neurons or endothelial cells, while a few matured into glial cells. The ECS-mediated induction of cell proliferation and neurogenesis was accompanied by increased immunoreactivity for the neuroprotective gene product BCL2 (B cell chronic lymphocytic lymphoma 2) in the SGZ. The ECS interventions were not accompanied by increased hippocampal cell death or injury. This study demonstrates that ECS is capable of inducing neurogenesis in the nonhuman primate hippocampus and supports the possibility that antidepressant interventions produce similar alterations in the human brain.

Variable foraging demand rearing: sustained elevations in cisternal cerebrospinal fluid corticotropin-releasing factor concentrations in adult primates

BACKGROUND The authors previously reported elevated cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations in juvenile primates nursed by mothers undergoing experimentally imposed unpredictable foraging conditions in comparison to normally reared controls. The purpose of the present study was to determine if these changes would endure into young adulthood. METHODS Cisternal CSF samples were obtained from those unpredictably reared young adult primates who had been previously studied as juveniles and age-matched ad libitum normally reared controls. Samples were assayed for CSF CRF. RESULTS Concentrations of CSF CRF were significantly elevated in the unpredictably reared sample in comparison to the ad libitum-reared control group. A significant positive correlation was noted between juvenile and young adult CSF CRF values within the unpredictably reared cohort. CONCLUSIONS Disturbances of maternal-infant attachment processes have an enduring impact on primate CRF function into young adulthood. The CRF elevations following unpredictable maternal foraging conditions appear traitlike in nature.

Differing concentrations of corticotropin-releasing factor and oxytocin in the cerebrospinal fluid of bonnet and pigtail macaques

The two neuropeptides corticotropin-releasing-factor (CRF) and oxytocin (OT) may produce opposing behavioral effects - elevations of the former have been associated with anxiety and social vigilance and reductions of the latter with reduced social affiliation. We sought to test the hypothesis that, within the primate macaque genus, the more gregarious, affiliative, and affectively stable bonnet species (Macaca radiata) would exhibit lower cerebrospinal fluid (CSF) CRF and higher CSF OT concentrations in comparison to its close relative, the temperamentally volatile and socially distant pigtail (Macaca nemestrina). Cisternal CSF samples were obtained from young adult male and female pigtail and bonnet macaques, and CRF and OT concentrations were measured by radioimmunoassay. Pigtail macaques exhibited significantly higher concentrations of CSF CRF and significant lower concentrations of CSF OT than bonnet macaques. Results were not attributable to age or sex differences in group composition. When included together in a multiple regression, CRF and OT showed a multiple R of 0.76, accounting for more than half of the species variance. Although species differences in the bioeffectiveness of these peptides may possibly confound the observed biobehavioral relationships, in the absence of any existing data to that effect, the current findings appear in accordance with the hypothesis and consistent with previously reported species-typical behaviors observed in these macaques.

Growth hormone response to clonidine in adversely reared young adult primates: relationship to serial cerebrospinal fluid corticotropin-releasing factor concentrations

A reduction of the growth hormone (GH) response to the alpha(2) adrenergic agonist clonidine is a neuroendocrine abnormality observed with reasonable consistency among human patients with mood and anxiety disorders. In previous primate studies, in comparison to predictably reared controls, monkeys exposed as infants to maternal variable foraging demand (VFD) rearing exhibited persistent elevations of cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF), as well as other biological disturbances. As CRF has been demonstrated to inhibit GH release, the authors hypothesized that within VFD-reared subjects, animals with relatively high CRF concentrations would exhibit relatively diminished GH responses to clonidine. The current study examined the relationship between the GH response to clonidine in VFD-reared adult primates in relation to a range of both juvenile and follow-up CSF CRF concentrations. Nine bonnet macaques (Macaca radiata) were given ascending dosages of clonidine under ketamine anesthesia. Plasma samples for GH-like immunoreactivity were obtained throughout the session. A significant positive correlation was noted between juvenile CSF CRF concentrations and the levels of the neuropeptide observed in young adults. The mean of the serial CSF CRF concentrations exhibited a significant inverse relationship towards the GH response to clonidine in young adulthood, with relatively high CSF CRF associated with relatively attenuated GH responses to clonidine. These data raise the possibility that a reduced GH response to clonidine may inversely reflect trait-like increases of central nervous system (CNS) CRF activity.

PNC-28, a p53-derived peptide that is cytotoxic to cancer cells, blocks pancreatic cancer cell growth in vivo†

PNC‐28 is a p53 peptide from its mdm‐2‐binding domain (residues 17–26), which contains the penetratin sequence enabling cell penetration on its carboxyl terminal end. We have found that this peptide induces necrosis, but not apoptosis, of a variety of human tumor cell lines, including several with homozygous deletion of p53, and a ras‐transformed rat acinar pancreatic carcinoma cell line, BMRPA1. Tuc3. On the other hand, PNC‐28 has no effect on untransformed cells, such as rat pancreatic acinar cells, BMRPA1, and human breast epithelial cells and no effect on the differentiation of human stem cells. In this study, we now test PNC‐28 in vivo for its ability to block the growth of BMRPA1. Tuc3 cells. When administered over a 2‐week period in the peritoneal cavities of nude mice containing simultaneously transplanted tumors, PNC‐28 causes complete destruction of these tumors. When delivered concurrently with tumor explantation at a remote site, PNC‐28 causes a complete blockade of any tumor growth during its 2‐week period of administration and 2 weeks posttreatment, followed by weak tumor growth that plateaus at low tumor sizes compared with tumor growth in the presence of a control peptide. When administered after tumor growth has occurred at a site remote from the tumor, PNC‐28 causes a decrease in tumor size followed by a slow increase in tumor growth that is significantly slower than growth in the presence of control peptide. These results suggest that PNC‐28 may be effective in treating cancers especially if delivered directly to the tumor.

Effects of LY354740, a novel glutamatergic metabotropic agonist, on nonhuman primate hypothalamic-pituitary-adrenal axis and noradrenergic function.

The search for novel anxiolytics and antidepressants has focused on compounds with the potential to reduce excessive hypothalamic-pituitary-adrenal (HPA) axis activity. L-glutamate, an excitatory neurotransmitter ubiquitously present within the central nervous system, conceivably plays an important role in activating the neural sites involved in stress modulation. Deactivation of the HPA axis by glutamatergic neurotransmission modulation may represent a novel therapeutic approach. Accordingly, the acute intravenous effects of the novel metabotropic (mGlu2/3) agonist LY354740 were tested on bonnet macaques (Macaca radiata) undergoing acute infusions of yohimbine, a noradrenergic stimulant. Dependent measures were the magnitude of the increase of plasma cortisol and plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) customarily elicited by yohimbine. Next, the effects of 6 weeks of chronic oral administration of LY354740 on baseline (postcapture) plasma cortisol and MHPG levels in comparison to the identical measure in untreated controls were assessed. Subjects chronically treated with LY354740 received yohimbine infusions which were compared to yohimbine infusions and saline infusions in non-LY354740-treated subjects. Preliminary evidence supports the view that acute LY354740 infusion resulted in a marked diminution of yohimbine-induced stress response, as manifest by a substantial attenuation of cortisol and MHPG response observed in comparison to the saline-treated yohimbine condition. Chronic oral administration of LY354740 led to postcapture baseline cortisol levels which were markedly reduced (approximately 50 percent) in comparison to untreated control subjects; however, there were no significant parallel differences in MHPG levels. Yohimbine infusions elicited an increase in cortisol and MHPG levels in both LY354740-treated and non-LY354740-treated subjects, in comparison to declines in cortisol values observed following vehicle infusions (group X time interaction; P<.0001). Chronic LY354740-treated subjects failed to achieve cortisol levels comparable in range to those of untreated subjects primarily because of their low baseline cortisol levels. In contrast, despite equivalent baselines, yohimbine-induced MHPG values were increased overall in the chronically treated group compared to the saline and yohimbine-alone groups. Thus, LY354740 markedly reduced the acute corticoid and noradrenergic response elicited by yohimbine infusion. Chronic administration of LY354740 appears to present a safe and effective mechanism to markedly down-modulate the HPA axis while retaining noradrenergic responsivity.

Lethargy, ulcers, bronchopneumonia and death in two aged female bonnet macaques presumed to be caused by Cercopithicine herpes virus I

Over the course of 4 weeks, two female aged bonnet macaque (Macaca radiata) group‐housed females died after the dominant male was removed from the group and the newly dominant male persistently chased, caught and bred all females in the pen. The two aged affected females were observed exhibiting lethargy, dyspnea, with widespread necroulcerative lesions in and around the mouth, muzzle and bridge of their noses. Extensive ulcerative glossitis, necrotic bronchopneumonia with intra‐nuclear inclusions and the absence of other evidence is highly suggestive that death was caused by an alphaherpes virus commonly known as herpes B virus. Herpes B virus is a potentially zoonotic disease periodically shed by macaques, which is structurally related to herpes simplex viruses I and II of humans. The emergence of fatal B virus to primates in this pen may have been associated with the combination of age and stress in the affected individuals.

Left Ventricular Systolic and Diastolic Function in Healthy Adult Bonnet Macaques (Macaca radiata)

Objectives: Macaques are used in cardiovascular and metabolic research. We determined echocardiographic-derived reference values of left ventricular (LV) systolic and diastolic function in healthy adult bonnet macaques (Macaca radiata). Methods: Transthoracic echocardiography was performed during ketamine sedation in 83 (67% female) healthy monkeys (age 7–26 years). Results: Technically adequate studies were obtained in all subjects and required 10.1 ± 1.3 min of scanning time. Age correlated inversely with the following Doppler indices: E (r = –0.44, p < 0.001), E/A (r = –0.26, p = 0.02), E′ (r = –0.45, p < 0.001, E′/A′ (r = –0.44, p < 0.001), E/E′ (r –0.25, p = 0.03), S′ (r = –0.33, p = 0.003), Vp (r = –0.26, p = 0.049). LV mass was more strongly correlated with crown rump length (r = 0.72, p < 0.001) and body surface area (r = 0.70, p < 0.001) than with body mass index (r = 0.47, p < 0.001) and weight (r = 0.63, p < 0.001). Conclusions: This study demonstrates echocardiography is feasible for characterizing LV function. Age-related changes in Doppler indices in primates are similar to those in humans. LV mass is more closely related to fat-free mass indices. We provide reference values for LV systolic and diastolic function in adult bonnet macaques across the captive life span.

Effects of Acute Confinement Stress-induced Hypothalamic-pituitary Adrenal Axis Activation and Concomitant Peripheral and Central Transforming Growth Factor-β1 Measures in Nonhuman Primates:

Transforming growth factor-β1 (TGF-β1) is a multifunctional cytokine with anti-inflammatory, immunosuppressive, and neuroprotective properties. The hypothalamic-pituitary-adrenal axis and immune system exert bidirectional influences on each other, via cortisol and TGF-β1, but the exact nature of the interaction is not well characterized. The current study examined the effects, in bonnet macaques (Macaca radiata), of two consecutive acute confinement stress periods in an unfamiliar room while mildly restrained, first without and then with dexamethasone pretreatment (0.01 mg/kg intramuscular). Preceding the confinement studies, a non-stress control condition obtained contemporaneous levels of cortisol and TGF-β1 in both plasma and cerebrospinal fluid to match the confinement stress studies. Subjects were reared under either normative or variable foraging demand conditions. Since there were no rearing effects at baseline or for any of the conditions tested—either for cortisol or TGF-β—the study analyses were conducted on the combined rearing groups. The stress condition increased both plasma and cerebrospinal fluid cortisol levels whereas dexamethasone pretreatment decreased cortisol concentrations to below baseline levels despite stress. The stress condition decreased TGF-β1 concentrations only in cerebrospinal fluid but not in serum. Together, the data suggested that stress-induced reductions of a centrally active neuroprotective cytokine occur in the face of hypothalamic-pituitary-adrenal axis activation, potentially facilitating glucocortoid-induced neurotoxicity. Stress-induced reductions of neuroprotective cytokines prompt exploration of protective measures against glucocorticoid-induced neurotoxicity.