Naturally occurring histological findings and Alzheimer's-like pathology in the brain of aging African green monkeys (Chlorocebus sabaeus).

Nonhuman primates (NHPs) are important to study the pathophysiology of neurodegenerative disease and evaluate therapies targeting the central nervous system (CNS). Understanding the age-associated incidence of natural CNS pathology in a given NHP species is critical to assess the safety of potential treatments for neurodegenerative disorders like Alzheimer's disease (AD). We describe background and age-related neuropathology in the St. Kitts African green monkey (AGM), a recognized translational model for neurodegenerative research, additionally defining the age progression of AD-associated neuropathology in this species. Seventy-one AGM brains were examined, representing age groups of 3-6 years (n = 20), 7-9 years (n = 20), 10-15 years (n = 20), and >15 years (n = 11). A subset of brains (n = 31) was assessed immunohistochemically for AD-related pathology, including expressions of Aß, tau, and GFAP. Age-related microscopic findings included hemosiderosis, spheroid formation, neuronal lipofuscinosis and neuromelanosis, white matter and neuropil vacuolation, astrocytosis, and focal microgliosis. Non-age-related findings included perivascular ceroid-laden macrophages, meningeal melanosis, and vascular mineralization. Immunohistochemistry revealed 4G8-immunopositive Aß plaques and vascular deposits in the prefrontal, frontal, cingulate, and temporal cortices of nine animals over 15 years of age, with associated increase in GFAP expression. In 12 animals, 11 over the age of 10 years, phosphorylated tau CP13-immunoreactive neurons, neuropil, and oligodendrocyte-like cells were seen in the prefrontal, frontal, cingulate, orbital, temporal, and entorhinal cortices as well as the hippocampus; no neurofibrillary tangles were observed. AD-related pathology showed an age-related development in cognitive-associated areas in the AGM, highlighting the value of the AGM as a natural model for these neurodegenerative diseases.

Dysregulated claudin-5 cycling in the inner retina causes retinal pigment epithelial cell atrophy.

Age-related macular degeneration (AMD) is the leading cause of central retinal vision loss worldwide, with an estimated 1 in 10 people over the age of 55 showing early signs of the condition. There are currently no forms of therapy available for the end stage of dry AMD, geographic atrophy (GA). Here, we show that the inner blood-retina barrier (iBRB) is highly dynamic and may play a contributory role in GA development. We have discovered that the gene CLDN5, which encodes claudin-5, a tight junction protein abundantly expressed at the iBRB, is regulated by BMAL1 and the circadian clock. Persistent suppression of claudin-5 expression in mice exposed to a cholesterol-enriched diet induced striking retinal pigment epithelium (RPE) cell atrophy, and persistent targeted suppression of claudin-5 in the macular region of nonhuman primates induced RPE cell atrophy. Moreover, fundus fluorescein angiography in human and nonhuman primate subjects showed increased retinal vascular permeability in the evening compared with the morning. These findings implicate an inner retina-derived component in the early pathophysiological changes observed in AMD, and we suggest that restoring the integrity of the iBRB may represent a novel therapeutic target for the prevention and treatment of GA secondary to dry AMD.

Characterization of glucose-stimulated insulin release protocols in african green monkeys (Chlorocebus aethiops).

BACKGROUND: Management of diabetes remains a major health and economic challenge, demanding test systems in which to develop new therapies. These studies assessed different methodologies for determining glucose tolerance in green monkeys. METHODS: Twenty-eight African green monkeys between 4 and 24 years old underwent single or repeat intravenous glucose tolerance testing (IVGTT), oral glucose tolerance testing (OGTT), and/or graded glucose infusion testing. RESULTS: Geriatric monkeys exhibited glucose intolerance with impaired glucose-stimulated insulin secretion following IVGTT. Repeat IVGTT and OGTT assessments were inconsistent. Monkeys with low glucose-stimulated insulin secretion after graded glucose infusion exhibited elevated blood glucose levels. CONCLUSION: IVGTT and graded glucose infusion protocols revealed differences in glucose tolerance among green monkeys at single time points, including age-dependent differences suggestive of shifts in pancreatic beta-cell functional capacity, but care should be applied to study design and the interpretation of data in the setting of longitudinal studies.

Variations in the stimulus salience of cocaine reward influences drug-associated contextual memory.

Drugs of abuse act as reinforcers because they influence learning and memory processes resulting in long-term memory of drug reward. We have previously shown that mice conditioned by fixed daily dose of cocaine (Fix-C) or daily escalating doses of cocaine (Esc-C) resulted in short- and long-term persistence of drug memory, respectively, suggesting different mechanisms in acquisition of cocaine memory. The present study was undertaken to investigate the differential contribution of N-methyl-D-aspartate receptor (NMDAR) subunits in the formation of Fix-C and Esc-C memory in C57BL/6J mice. Training by Esc-C resulted in marked elevation in hippocampal expression of Grin2b mRNA and NR2B protein levels compared with training by Fix-C. The NR2B-containing NMDAR antagonist ifenprodil had similar attenuating effects on acquisition and reconsolidation of Fix-C and Esc-C memory. However, the NMDAR antagonist MK-801 had differential effects: (1) higher doses of MK-801 were required for post-retrieval disruption of reconsolidation of Esc-C memory than Fix-C memory; and (2) pre-retrieval MK-801 inhibited extinction of Fix-C memory but it had no effect on Esc-C memory. In addition, blockade of NMDAR downstream signaling pathways also showed differential regulation of Fix-C and Esc-C memory. Inhibition of neuronal nitric oxide synthase attenuated acquisition and disrupted reconsolidation of Fix-C but not Esc-C memory. In contrast, the mitogen-activating extracellular kinase inhibitor SL327 attenuated reconsolidation of Esc-C but not Fix-C memory. These results suggest that NMDAR downstream signaling molecules associated with consolidation and reconsolidation of cocaine-associated memory may vary upon changes in the salience of cocaine reward during conditioning.

The strength of aversive and appetitive associations and maladaptive behaviors.

Certain maladaptive behaviors are thought to be acquired through classical Pavlovian conditioning. Exaggerated fear response, which can develop through Pavlovian conditioning, is associated with acquired anxiety disorders such as post-traumatic stress disorders (PTSDs). Inflated reward-seeking behavior, which develops through Pavlovian conditioning, underlies some types of addictive behavior (e.g., addiction to drugs, food, and gambling). These maladaptive behaviors are dependent on associative learning and the development of long-term memory (LTM). In animal models, an aversive reinforcer (fear conditioning) encodes an aversive contextual and cued LTM. On the other hand, an appetitive reinforcer results in conditioned place preference (CPP) that encodes an appetitive contextual LTM. The literature on weak and strong associative learning pertaining to the development of aversive and appetitive LTM is relatively scarce; thus, this review is particularly focused on the strength of associative learning. The strength of associative learning is dependent on the valence of the reinforcer and the salience of the conditioned stimulus that ultimately sways the strength of the memory trace. Our studies suggest that labile (weak) aversive and appetitive LTM may share similar signaling pathways, whereas stable (strong) aversive and appetitive LTM is mediated through different pathways. In addition, we provide some evidence suggesting that extinction of aversive fear memory and appetitive drug memory is likely to be mediated through different signaling molecules. We put forward the importance of studies aimed to investigate the molecular mechanisms underlying the development of weak and strong memories (aversive and appetitive), which would ultimately help in the development of targeted pharmacotherapies for the management of maladaptive behaviors that arise from classical Pavlovian conditioning.

Sodium butyrate-induced histone acetylation strengthens the expression of cocaine-associated contextual memory.

The conditioned place preference (CPP) paradigm entails Pavlovian conditioning and allows evaluating the acquisition and extinction of drug-associated memory. Epigenetic regulation of chromatin structure by acetylation and deacetylation of histone proteins is critical for formation of long-term memory (LTM). We have recently shown that a single administration of the histone deacetylase (HDAC) inhibitor sodium butyrate (NaB) facilitated extinction of fear-associated memory in mice. Using the CPP paradigm, the present study investigated the effect of NaB on cocaine-associated memory. C57B/6 mice were conditioned by either fixed daily doses of cocaine (5mg/kg×4 and 15mg/kg×4days) or an escalating schedule (3, 6, 12 and 24mg/kg). Acute administration of NaB (1.2g/kg) prior to conditioning by fixed doses of cocaine increased the expression and impaired the extinction of place preference compared to control subjects. Subjects that were conditioned by 15mg/kg×4 cocaine and received a single injection of NaB following the first or the second CPP test showed impaired extinction compared to control mice that received saline instead of NaB. Subjects that were conditioned by escalating schedule of cocaine and subsequently received repeated injections of NaB during daily reexposure to nonreinforced context showed either enhancement or no effect on place preference. Acute administration of NaB (1.2g/kg) to naïve mice resulted in marked increase in acetylation of histone H3 lysine 14 (H3K14) and histone H4 lysine 8 (H4K8) in hippocampus but not amygdala. Results suggest that regardless of the scheduling of either cocaine or NaB administration, NaB-induced histone hyperacetylation in the hippocampus may strengthen cocaine-associated contextual memory.

Nitric oxide (NO) signaling as a potential therapeutic modality against psychostimulants.

Abuse of psychostimulants presents a significant health and social problem worldwide. Traditionally, the dopaminergic system has received much attention for its role in the development and manifestation of addictive behavior. The identification of the close interaction between the dopaminergic and glutamatergic pathway and by extension the nitric oxide (NO) signaling pathway (the nitrergic system) have provided a broader scope on the mechanisms underlying the development of addictive behavior following exposure to cocaine and methamphetamine. NO signaling is associated with the acquisition and maintenance of several behavioral phenotypes induced by cocaine and methamphetamine (METH), as well as in METH-induced dopaminergic depletion. Because it appears that NO signaling influences response to reward, memory formation, and free radical-induced neurotoxicity, pharmacotherapies targeting NO signaling pathway may prove beneficial in the treatment of psychostimulants abuse.

The effect of phosphodiesterase inhibitors on the extinction of cocaine-induced conditioned place preference in mice.

Several phosphodiesterase inhibitors (PDEis) improve cognition, suggesting that an increase in brain cAMP and cGMP facilitates learning and memory. Since extinction of drug-seeking behavior requires associative learning, consolidation and formation of new memory, the present study investigated the efficacy of three different PDEis in the extinction of cocaine-induced conditioned place preference (CPP) in B6129S mice. Mice were conditioned by escalating doses of cocaine which was resistant to extinction by free exploration. Immediately following each extinction session mice received (a) saline/vehicle, (b) rolipram (PDE4 inhibitor), (c) BAY-73-6691 (PDE9 inhibitor) or (d) papaverine (PDE10A inhibitor). Mice that received saline/vehicle during extinction training showed no reduction in CPP for >10 days. BAY-73-6691 (a) dose-dependently increased cGMP in hippocampus and amygdala, (b) significantly facilitated extinction and (c) diminished the reinstatement of cocaine CPP. Rolipram, which selectively increased brain cAMP levels, and papaverine which caused increases in both cAMP and cGMP levels, had no significant effect on the extinction of cocaine CPP. The results suggest that increase in hippocampal and amygdalar cGMP levels via blockade of PDE9 has a prominent role in the consolidation of extinction learning.

Clinical chemistry and hematology values in a Caribbean population of African green monkeys.

BACKGROUND: Hematology and clinical chemistry (HCC) reference values are critical in veterinary practice and in vivo pre-clinical research, enabling detection of health abnormalities, response to therapeutic intervention or adverse toxicological effects, as well as monitoring of clinical management. METHODS: In this report, reference ranges for 46 HCC parameters were characterized in 331 wild-caught and colony-bred African green monkeys. Effects of sex, weight and duration of captivity were determined by one-way analysis of variance. RESULTS: Significant sex differences were observed for several HCC parameters. Significant differences were also observed for select HCC variables between newly caught animals and those held in captivity for 1-12 months or longer. CONCLUSIONS: Comparison of this data with other non-human primate species and humans highlights similarities and disparities between species. Potential causes of interpopulation variability and relevance to the use of the African green monkey as a non-human primate model are discussed.