Neocortical Development in Brain of Young Children-A Stereological Study.

The early postnatal development of neuron and glia numbers is poorly documented in human brain. Therefore we estimated using design-based stereological methods the regional volumes of neocortex and the numbers of neocortical neurons and glial cells for 10 children (4 girls and 6 boys), ranging from neonate to 3 years of age. The 10 infants had a mean of 20.7 × 109 neocortical neurons (range 18.0-24.8 × 109) estimated with a coefficient of variation (CV) = 0.11; this range is similar to adult neuron numbers. The glia populations were 10.5 × 109 oligodendrocytes (range 5.0-16.0 × 109; CV = 0.40); 5.3 × 109 astrocytes (range 2.7-8.3 × 109, CV = 0.39); and 0.32 × 109 microglia (range 0.15-0.43 × 109, CV = 0.31). Thus, the estimated mean composite number of neocortical neuron and glial cells was 36.8 × 109 (range 26.8-48.3 × 109, CV = 0.21), of which approximately one-half were glial cells. There was a significant linear increase in oligodendrocyte and astrocyte numbers during the first 3 years of life, but no change in the total number of neurons. This is in line with our expectation that the total number of neocortical neurons is already determined in mid-fetal life.

Differential expression of parvalbumin in neonatal phencyclidine-treated rats and socially isolated rats.

Decreased parvalbumin expression is a hallmark of the pathophysiology of schizophrenia and has been associated with abnormal cognitive processing and decreased network specificity. It is not known whether this decrease is due to reduced expression of the parvalbumin protein or degeneration of parvalbumin-positive interneurons (PV(+) interneurons). In this study, we examined PV(+) expression in two rat models of cognitive dysfunction in schizophrenia: the environmental social isolation (SI) and pharmacological neonatal phencyclidine (neoPCP) models. Using a stereological method, the optical fractionator, we counted neurons, PV(+) interneurons, and glial cells in the medial prefrontal cortex (mPFC) and hippocampus (HPC). In addition, we quantified the mRNA level of parvalbumin in the mPFC. There was a statistically significant reduction in the number of PV(+) interneurons (p = 0.021) and glial cells (p = 0.024) in the mPFC of neonatal phencyclidine rats, but not in SI rats. We observed no alterations in the total number of neurons, hippocampal PV(+) interneurons, parvalbumin mRNA expression or volume of the mPFC or HPC in the two models. Thus, as the total number of neurons remains unchanged following phencyclidine (PCP) treatment, we suggest that the decreased number of counted PV(+) interneurons represents a reduced parvalbumin protein expression below immunohistochemical detection limit rather than a true cell loss. Furthermore, these results indicate that the effect of neonatal PCP treatment is not limited to neuronal populations.

Untreated Patients Dying With AIDS Have Loss of Neocortical Neurons and Glia Cells.

Untreated human immunodeficiency virus (HIV) depletes its host CD4 cells, ultimately leading to acquired immunodeficiency syndrome (AIDS). In brain, the HIV confines itself to astrocytes and microglia, the resident brain macrophages, but does not infect oligodendrocytes and neurons. Nonetheless, cognitive symptoms associated with HIV and AIDS are attributed to loss of axons and white matter damage. We used design-based stereology to estimate the numbers of neocortical neurons and glial cells (astrocytes, oligodendrocytes, and microglia), in a series of 12 patients dying with AIDS before the era of retroviral treatments, and in 13 age-matched control brains. Relative to the control material, there was a 19% loss of neocortical neuron (p = 0.04) and a 29% reduction of oligodendrocytes (p = 0.003) in the patients with AIDS, whereas astrocyte and microglia numbers did not differ between patients and controls. Furthermore, we saw a 17% reduction in mean hemispheric volume in the AIDS group (p = 0.0015), which was driven by neocortical and white matter loss (p < 0.05), while the archicortex, subcortical gray matter, and ventricular volumes were within normal limits. Our results confirm previous reports of neuronal loss in AIDS. The new finding of oligodendrocyte loss supports the proposal that HIV in the brain provokes demyelination and axonal dysfunction and suggests that remyelination treatment strategies may be beneficial to patients suffering from HIV-associated neurocognitive deficits.

Adrenomedullin and glucagon-like peptide-1 have additive effects on food intake in mice.

Adrenomedullin (ADM) is a vasoactive peptide expressed in several peripheral organs and known primarily for its beneficial vasoactive effects. However, ADM is also known to inhibit insulin secretion, and central administration of ADM has been shown to elicit anorexigenic effects. Here, we investigated if peripheral co-administration of ADM and glucagon-like peptide 1 (GLP-1) could subdue the hypoglycaemic effects of ADM while enhancing its anorectic properties. The effects of mono- and combination therapy of ADM and GLP-1 on appetite regulation and glucose homeostasis were assessed acutely in male NMRI mice for 12 h, while effects on glucose homeostasis were assessed by oral glucose tolerance tests (OGTT). While the monotherapy with GLP-1 and ADM resulted in modest anorexigenic effects, co-administration of the two peptides led to a marked additive reduction in food intake. Moreover, while OGTT-evoked blood glucose-excursions were significantly increased by ADM monotherapy, co-administration of ADM with a lower dose of GLP-1 normalized glucose excursions. In conclusion, we demonstrate additive anorectic effects of ADM and GLP-1, and that GLP-1 co-administration prevents ADM-induced impairment of glucose tolerance, suggesting that ADM could be potential anti-obesity target when combined with GLP-1 agonist therapy.

Metabolic and gut microbiome changes following GLP-1 or dual GLP-1/GLP-2 receptor agonist treatment in diet-induced obese mice.

Enteroendocrine L-cell derived peptide hormones, notably glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2), have become important targets in the treatment of type 2 diabetes, obesity and intestinal diseases. As gut microbial imbalances and maladaptive host responses have been implicated in the pathology of obesity and diabetes, this study aimed to determine the effects of pharmacologically stimulated GLP-1 and GLP-2 receptor function on the gut microbiome composition in diet-induced obese (DIO) mice. DIO mice received treatment with a selective GLP-1 receptor agonist (liraglutide, 0.2 mg/kg, BID) or dual GLP-1/GLP-2 receptor agonist (GUB09-145, 0.04 mg/kg, BID) for 4 weeks. Both compounds suppressed caloric intake, promoted a marked weight loss, improved glucose tolerance and reduced plasma cholesterol levels. 16S rDNA sequencing and deep-sequencing shotgun metagenomics was applied for comprehensive within-subject profiling of changes in gut microbiome signatures. Compared to baseline, DIO mice assumed phylogenetically similar gut bacterial compositional changes following liraglutide and GUB09-145 treatment, characterized by discrete shifts in low-abundant species and related bacterial metabolic pathways. The microbiome alterations may potentially associate to the converging biological actions of GLP-1 and GLP-2 receptor signaling on caloric intake, glucose metabolism and lipid handling.

Quantitative whole-brain 3D imaging of tyrosine hydroxylase-labeled neuron architecture in the mouse MPTP model of Parkinson's disease.

Parkinson's disease (PD) is a basal ganglia movement disorder characterized by progressive degeneration of the nigrostriatal dopaminergic system. Immunohistochemical methods have been widely used for characterization of dopaminergic neuronal injury in animal models of PD, including the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model. However, conventional immunohistochemical techniques applied to tissue sections have inherent limitations with respect to loss of 3D resolution, yielding insufficient information on the architecture of the dopaminergic system. To provide a more comprehensive and non-biased map of MPTP-induced changes in central dopaminergic pathways, we used iDISCO immunolabeling, light-sheet fluorescence microscopy (LSFM) and deep-learning computational methods for whole-brain three-dimensional visualization and automated quantitation of tyrosine hydroxylase (TH)-positive neurons in the adult mouse brain. Mice terminated 7 days after acute MPTP administration demonstrated widespread alterations in TH expression. Compared to vehicle controls, MPTP-dosed mice showed a significant loss of TH-positive neurons in the substantia nigra pars compacta and ventral tegmental area. Also, MPTP dosing reduced overall TH signal intensity in basal ganglia nuclei, i.e. the substantia nigra, caudate-putamen, globus pallidus and subthalamic nucleus. In contrast, increased TH signal intensity was predominantly observed in limbic regions, including several subdivisions of the amygdala and hypothalamus. In conclusion, mouse whole-brain 3D imaging is ideal for unbiased automated counting and densitometric analysis of TH-positive cells. The LSFM-deep learning pipeline tracked brain-wide changes in catecholaminergic pathways in the MPTP mouse model of PD, and may be applied for preclinical characterization of compounds targeting dopaminergic neurotransmission.

Guanylin and uroguanylin mRNA expression is increased following Roux-en-Y gastric bypass, but guanylins do not play a significant role in body weight regulation and glycemic control.

AIM: To determine whether intestinal expression of guanylate cyclase activator 2A (GUCA2A) and guanylate cyclase activator 2B (GUCA2B) genes is regulated in obese humans following Roux-en-Y gastric bypass (RYGB), and to evaluate the corresponding guanylin (GN) and uroguanylin (UGN) peptides for potentially contributing to the beneficial metabolic effects of RYGB. METHODS: Enteroendocrine cells were harvested peri- and post-RYGB, and GUCA2A/GUCA2B mRNA expression was compared. GN, UGN and their prohormones (proGN, proUGN) were administered subcutaneously in normal-weight mice to evaluate effects on food intake and glucose regulation. The effect of pro-UGN or UGN overexpression, using adeno-associated virus (AAV) vectors, was assessed in diet-induced obese (DIO) mice. Intracerebroventricular administration of GN and UGN was performed in rats for assessment of putative centrally mediated effects on food intake. GN and UGN, as well as their prohormones, were evaluated for effects on glucose-stimulated insulin secretion (GSIS) in rat pancreatic islets and perfused rat pancreas. RESULTS: GUCA2A and GUCA2B mRNA expression was significantly upregulated in enteroendocrine cells after RYGB. Peripheral administration of guanylins or prohormones did not influence food intake, oral glucose tolerance, and GSIS. Central administration of GN and UGN did not affect food intake in rats. Chronic AVV-mediated overexpression of UGN and proUGN had no effect on body weight or glucose homeostasis in DIO mice. CONCLUSION: GN and UGN, as well as their prohormones, do not seem to play a significant role in body weight regulation and glycemic control, suggesting that guanylin-family peptides do not show promise as targets for the treatment of obesity or diabetes.

Application of the Physical Disector Principle for Quantification of Dopaminergic Neuronal Loss in a Rat 6-Hydroxydopamine Nigral Lesion Model of Parkinson's Disease.

Stereological analysis is the optimal tool for quantitative assessment of brain morphological and cellular changes induced by neurotoxic lesions or treatment interventions. Stereological methods based on random sampling techniques yield unbiased estimates of particle counts within a defined volume, thereby providing a true quantitative estimate of the target cell population. Neurodegenerative diseases involve loss of specific neuron types, such as the midbrain tyrosine hydroxylase-positive dopamine neurons in Parkinson's disease and in animal models of nigrostriatal degeneration. Therefore, we applied an established automated physical disector principle in a fractionator design for efficient stereological quantitative analysis of tyrosine hydroxylase (TH)-positive dopamine neurons in the substantia nigra pars compacta of hemiparkinsonian rats with unilateral 6-hydroxydopamine (6-OHDA) lesions. We obtained reliable estimates of dopamine neuron numbers, and established the relationship between behavioral asymmetry and dopamine neuron loss on the lesioned side. In conclusion, the automated physical disector principle provided a useful and efficient tool for unbiased estimation of TH-positive neurons in rat midbrain, and should prove valuable for investigating neuroprotective strategies in 6-OHDA model of parkinsonism, while generalizing to other immunohistochemically-defined cell populations.

Long-Term Treatment with Liraglutide, a Glucagon-Like Peptide-1 (GLP-1) Receptor Agonist, Has No Effect on ß-Amyloid Plaque Load in Two Transgenic APP/PS1 Mouse Models of Alzheimer's Disease.

One of the major histopathological hallmarks of Alzheimer's disease (AD) is cerebral deposits of extracellular ß-amyloid peptides. Preclinical studies have pointed to glucagon-like peptide 1 (GLP-1) receptors as a potential novel target in the treatment of AD. GLP-1 receptor agonists, including exendin-4 and liraglutide, have been shown to promote plaque-lowering and mnemonic effects of in a number of experimental models of AD. Transgenic mouse models carrying genetic mutations of amyloid protein precursor (APP) and presenilin-1 (PS1) are commonly used to assess the pharmacodynamics of potential amyloidosis-lowering and pro-cognitive compounds. In this study, effects of long-term liraglutide treatment were therefore determined in two double APP/PS1 transgenic mouse models of Alzheimer's disease carrying different clinical APP/PS1 mutations, i.e. the 'London' (hAPPLon/PS1A246E) and 'Swedish' mutation variant (hAPPSwe/PS1ΔE9) of APP, with co-expression of distinct PS1 variants. Liraglutide was administered in 5 month-old hAPPLon/PS1A246E mice for 3 months (100 or 500 ng/kg/day, s.c.), or 7 month-old hAPPSwe/PS1ΔE9 mice for 5 months (500 ng/kg/day, s.c.). In both models, regional plaque load was quantified throughout the brain using stereological methods. Vehicle-dosed hAPPSwe/PS1ΔE9 mice exhibited considerably higher cerebral plaque load than hAPPLon/PS1A246E control mice. Compared to vehicle-dosed transgenic controls, liraglutide treatment had no effect on the plaque levels in hAPPLon/PS1A246E and hAPPSwe/PS1ΔE9 mice. In conclusion, long-term liraglutide treatment exhibited no effect on cerebral plaque load in two transgenic mouse models of low- and high-grade amyloidosis, which suggests differential sensitivity to long-term liraglutide treatment in various transgenic mouse models mimicking distinct pathological hallmarks of AD.

Characterization of liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, in rat partial and full nigral 6-hydroxydopamine lesion models of Parkinson's disease.

Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, have been demonstrated to promote neuroprotection in the rat 6-hydroxydopamine (6-OHDA) neurotoxin model of Parkinson's disease (PD), a neurodegenerative disorder characterized by progressive nigrostriatal dopaminergic neuron loss. In this report, we characterized the effect of a long-acting GLP-1 receptor agonist, liraglutide (500µg/kg/day, s.c.) in the context of a partial or advanced (full) 6-OHDA induced nigral lesion in the rat. Rats received a low (3µg, partial lesion) or high (13.5µg, full lesion) 6-OHDA dose stereotaxically injected into the right medial forebrain bundle (n=17-20 rats per experimental group). Six weeks after induction of a partial nigral dopaminergic lesion, vehicle or liraglutide was administered for four weeks. In the full lesion model, vehicle dosing or liraglutide treatment was applied for a total of six weeks starting three weeks pre-lesion, or administered for three weeks starting on the lesion day. Quantitative stereology was applied to assess the total number of midbrain tyrosine hydroxylase (TH) positive dopaminergic neurons. As compared to vehicle controls, liraglutide had no effect on the rotational responsiveness to d-amphetamine or apomorphine, respectively. In correspondence, while numbers of TH-positive nigral neurons were significantly reduced in the lesion side (partial lesion ≈55%; full lesion ≈90%) liraglutide administration had no influence dopaminergic neuronal loss in either PD model setting. In conclusion, liraglutide showed no neuroprotective effects in the context of moderate or substantial midbrain dopaminergic neuronal loss and associated functional motor deficits in the rat 6-OHDA lesion model of PD.

The GLP-1 receptor agonist liraglutide reduces pathology-specific tau phosphorylation and improves motor function in a transgenic hTauP301L mouse model of tauopathy.

In addition to a prominent role in glycemic control, glucagon-like peptide 1 (GLP-1) receptor agonists exhibit neuroprotective properties. There is mounting experimental evidence that GLP-1 receptor agonists, including liraglutide, may enhance synaptic plasticity, counteract cognitive deficits and ameliorate neurodegenerative features in preclinical models of Alzheimer's disease (AD), predominantly in the context of ß-amyloid toxicity. Here we characterized the effects of liraglutide in a transgenic mutant tau (hTauP301L) mouse tauopathy model, which develops age-dependent pathology-specific neuronal tau phosphorylation and neurofibrillary tangle formation with progressively compromised motor function (limb clasping). Liraglutide (500 µg/kg/day, s.c., q.d., n=18) or vehicle (n=18) was administered to hTauP301L mice for 6 months from the age of three months. Vehicle-dosed wild-type FVB/N mice served as normal control (n=17). The onset and severity of hind limb clasping was markedly different in liraglutide and vehicle-dosed transgenic mice. Clasping behavior was observed in 61% of vehicle-dosed hTauP301L mice with a 55% survival rate in 9-month old transgenic mice. In contrast, liraglutide treatment reduced the clasping rate to 39% of hTauP301L mice, and fully prevented clasping-associated lethality resulting in a survival rate of 89%. Stereological analyses demonstrated that hTauP301L mice exhibited hindbrain-dominant neuronal accumulation of phosphorylated tau closely correlated to the severity of clasping behavior. In correspondence, liraglutide treatment significantly reduced neuronal phospho-tau load by 61.9±10.2% (p<0.001) in hTauP301L mice, as compared to vehicle-dosed controls. In conclusion, liraglutide significantly reduced tau pathology in a transgenic mouse tauopathy model.

A Hamster Model of Diet-Induced Obesity for Preclinical Evaluation of Anti-Obesity, Anti-Diabetic and Lipid Modulating Agents.

AIM: Unlike rats and mice, hamsters develop hypercholesterolemia, and hypertriglyceridemia when fed a cholesterol-rich diet. Because hyperlipidemia is a hallmark of human obesity, we aimed to develop and characterize a novel diet-induced obesity (DIO) and hypercholesterolemia Golden Syrian hamster model. METHODS AND RESULTS: Hamsters fed a highly palatable fat- and sugar-rich diet (HPFS) for 12 weeks showed significant body weight gain, body fat accumulation and impaired glucose tolerance. Cholesterol supplementation to the diet evoked additional hypercholesterolemia. Chronic treatment with the GLP-1 analogue, liraglutide (0.2 mg/kg, SC, BID, 27 days), normalized body weight and glucose tolerance, and lowered blood lipids in the DIO-hamster. The dipeptidyl peptidase-4 (DPP-4) inhibitor, linagliptin (3.0 mg/kg, PO, QD) also improved glucose tolerance. Treatment with peptide YY3-36 (PYY3-36, 1.0 mg/kg/day) or neuromedin U (NMU, 1.5 mg/kg/day), continuously infused via a subcutaneous osmotic minipump for 14 days, reduced body weight and energy intake and changed food preference from HPFS diet towards chow. Co-treatment with liraglutide and PYY3-36 evoked a pronounced synergistic decrease in body weight and food intake with no lower plateau established. Treatment with the cholesterol uptake inhibitor ezetimibe (10 mg/kg, PO, QD) for 14 days lowered plasma total cholesterol with a more marked reduction of LDL levels, as compared to HDL, indicating additional sensitivity to cholesterol modulating drugs in the hyperlipidemic DIO-hamster. In conclusion, the features of combined obesity, impaired glucose tolerance and hypercholesterolemia in the DIO-hamster make this animal model useful for preclinical evaluation of novel anti-obesity, anti-diabetic and lipid modulating agents.

The GLP-1 Receptor Agonist Liraglutide Improves Memory Function and Increases Hippocampal CA1 Neuronal Numbers in a Senescence-Accelerated Mouse Model of Alzheimer's Disease.

Recent studies indicate that glucagon-like peptide 1 (GLP-1) receptor agonists, currently used in the management of type 2 diabetes, exhibit neurotrophic and neuroprotective effects in amyloid-ß (Aß) toxicity models of Alzheimer's disease (AD). We investigated the potential pro-cognitive and neuroprotective effects of the once-daily GLP-1 receptor agonist liraglutide in senescence-accelerated mouse prone 8 (SAMP8) mice, a model of age-related sporadic AD not dominated by amyloid plaques. Six-month-old SAMP8 mice received liraglutide (100 or 500 µg/kg/day, s.c.) or vehicle once daily for 4 months. Vehicle-dosed age-matched 50% back-crossed as well as untreated young (4-month-old) SAMP8 mice were used as control groups for normal memory function. Vehicle-dosed 10-month-old SAMP8 mice showed significant learning and memory retention deficits in an active-avoidance T-maze, as compared to both control groups. Also, 10-month-old SAMP8 mice displayed no immunohistological signatures of amyloid-ß plaques or hyperphosphorylated tau, indicating the onset of cognitive deficits prior to deposition of amyloid plaques and neurofibrillary tangles in this AD model. Liraglutide significantly increased memory retention and total hippocampal CA1 pyramidal neuron numbers in SAMP8 mice, as compared to age-matched vehicle-dosed SAMP8 mice. In conclusion, liraglutide delayed or partially halted the progressive decline in memory function associated with hippocampal neuronal loss in a mouse model of pathological aging with characteristics of neurobehavioral and neuropathological impairments observed in early-stage sporadic AD.

Stereological estimation of total cell numbers in the human cerebral and cerebellar cortex.

Our knowledge of the relationship between brain structure and cognitive function is still limited. Human brains and individual cortical areas vary considerably in size and shape. Studies of brain cell numbers have historically been based on biased methods, which did not always result in correct estimates and were often very time-consuming. Within the last 20-30 years, it has become possible to rely on more advanced and unbiased methods. These methods have provided us with information about fetal brain development, differences in cell numbers between men and women, the effect of age on selected brain cell populations, and disease-related changes associated with a loss of function. In that this article concerns normal brain rather than brain disorders, it focuses on normal brain development in humans and age related changes in terms of cell numbers. For comparative purposes a few examples of neocortical neuron number in other mammals are also presented.

Effect of age on neocortical brain cells in 90+ year old human females--a cell counting study.

An increasing number of people are living past the age of 100 years, but little is known about what differentiates centenarians from the rest of the population. In this study, brains from female subjects in 3 different age groups, 65-75 years (n = 8), 76-85 years (n = 8), and 94-105 years (n = 7), were examined to estimate the total number of neocortical neurons, astrocytes, oligodendrocytes, and microglia. There was no statistically significant difference in the mean number of neocortical neurons between the 3 groups: 17.9 × 10(9) (CV = SD/mean = 0.15) in the youngest group, 18.1 × 10(9) (CV = 0.22) in the second group, and 16.32 × 10(9) (CV = 0.24) in the oldest group. However, there was a significant difference in the total number of neocortical glial cells between the youngest (41.0 × 10(9)) and oldest (29.0 × 10(9)) age groups (p = 0.013). The significance was probably driven by a significant difference in the total number of neocortical oligodendrocytes that differed significantly between the youngest (27.5 × 10(9)) and oldest (18.1. × 10(9), p = 0.006) age groups. In conclusion, very old individuals have brain neuron numbers comparable with younger individuals, which may be encouraging for those who live into the "fourth age" and may contribute to the longevity of this exceptional group of people.

Application of stereological methods to estimate post-mortem brain surface area using 3T MRI.

The Cavalieri and Vertical Sections methods of design based stereology were applied in combination with 3 tesla (i.e. 3T) Magnetic Resonance Imaging (MRI) to estimate cortical and subcortical volume, area of the pial surface, area of the grey-white matter boundary, and thickness of the cerebral cortex. The material comprises eight human cadaveric cerebri which had been separated into sixteen cerebral hemisphere specimens prior to embedding in agar gel. The results from MRI were compared with corresponding 'gold standard' values subsequently obtained by application of the same methodology using physical sectioning of the specimens. 95% agreement intervals revealed poor agreement between MR imaging and physical sectioning, specially for pial surface and thickness, as well as cerebral cortex and subcortex volumes. On average, pial surface area was estimated to be almost half the extent using MRI compared to physical sectioning (i.e. 45%, p<0.05) and the average thickness of the cerebral cortex was calculated to be much greater (by 60.9%) on the MR images compared to the physical sections (3.7mm versus 2.3mm, p<0.001). The main cause of the discrepancies is that the resolution of the MR images is not sufficient to always allow reliable depiction of the cerebral sulci on 2D image sections. Accurate application of manual stereological methods for measuring the cortical surface area thus requires higher resolution MR imaging than is typically applied at 3T.

Socially isolated rats exhibit changes in dopamine homeostasis pertinent to schizophrenia.

Post-weaning social isolation of rats produces an array of behavioral and neurochemical changes indicative of altered dopamine function. It has therefore been suggested that post-weaning social isolation mimics some aspects of schizophrenia. Here we replicate and extent these findings to include an investigation of prefrontal cortical dopamine dynamics using in vivo microdialysis. Social isolation for 12 weeks after weaning caused increased locomotor activity in response to novelty and amphetamine challenge. In vivo microdialysis experiments revealed that while social isolation did not change basal dopamine levels in the nucleus accumbens, it did cause a significant reduction of basal dopamine release in the prefrontal cortex. In addition, social isolation lead to a significantly larger dopamine response to an amphetamine challenge, in both the nucleus accumbens and the prefrontal cortex compared to group housed controls. Taken together, these results indicate that post-weaning social isolation alters dopaminergic function with changes resembling subcortical hyperdopaminergia and prefrontal hypodopaminergia similar to what has been observed in schizophrenic patients.

Pharmacological characterization of social isolation-induced hyperactivity.

RATIONALE: Social isolation (SI) of rats directly after weaning is a non-pharmacological, non-lesion animal model based on the neurodevelopmental hypothesis of schizophrenia. The model causes several neurobiological and behavioral alterations consistent with observations in schizophrenia. OBJECTIVES: In the present study, we evaluated if isolated rats display both a pre-pulse inhibition (PPI) deficit and hyperactivity. Furthermore, the sensitivity of SI hyperactivity to antipsychotic was evaluated. METHODS: Rats were socially isolated or group-housed for 12 weeks starting on postnatal day 25. In one batch of animals, the PPI and hyperactivity response were repeatedly compared. Furthermore, we investigated the robustness of the SI-induced hyperactivity by testing close to 50 batches of socially isolated or group-housed rats and tested the sensitivity of the assay to first- and second-generation antipsychotics, haloperidol, olanzapine, and risperidone, as well as the group II selective metabotrobic glutamate receptor agonist (LY404039). RESULTS: Socially isolated rats showed a minor PPI deficit and a robust increase in hyperactivity compared with controls. Furthermore, SI-induced hyperactivity was selectively reversed by all antipsychotics, as well as the potential new antipsychotic, LY404039. CONCLUSION: SI-induced hyperactivity was more pronounced and robust, as compared with SI-induced PPI deficits. Furthermore, SI-induced hyperactivity might be predictive for antipsychotic efficacy, as current treatment was effective in the model. Finally, using LY404039, a compound in development against schizophrenia, we have shown that the hyperactivity assay is sensitive to potential novel mechanisms of action. Thus, SI-induced hyperactivity might be a robust and novel in vivo screening assay of antipsychotic efficacy.

Stereological brain volume changes in post-weaned socially isolated rats.

Rearing rats in isolation after weaning is an environmental manipulation that leads to behavioural and neurochemical alterations that resemble what is seen in schizophrenia. The model is neurodevelopmental in origin and has been used as an animal model of schizophrenia. However, only a few studies have evaluated the neuroanatomical changes in this animal model in comparison to changes seen in schizophrenia. In this study, we applied stereological volume estimates to evaluate the total brain, the ventricular system, and the pyramidal and granular cell layers of the hippocampus in male and female Lister Hooded rats isolated from postnatal day 25 for 15 weeks. We observed the expected gender differences in total brain volume with males having larger brains than females. Further, we found that isolated males had significantly smaller brains than group-housed controls and larger lateral ventricles than controls. However, this was not seen in female rats. Isolated males had a significant smaller hippocampus, dentate gyrus and CA2/3 where isolated females had a significant smaller CA1 compared to controls. Thus, our results indicate that long-term isolation of male rats leads to neuroanatomical changes corresponding to those seen in schizophrenia.

Increased dopaminergic activity in socially isolated rats: an electrophysiological study.

The development of animal models mimicking symptoms associated with schizophrenia has been a critical step in understanding the neurobiological mechanisms underlying the disease. Long-term social isolation from weaning in rodents, a model based on the neurodevelopmental hypothesis of schizophrenia, has been suggested to mimic some of the deficits seen in schizophrenic patients. We confirm in the present study that socially isolated rats display an increase in both spontaneous and d-amphetamine-induced locomotor activity, as well as deficits in sensorimotor gating as assessed in a pre-pulse inhibition paradigm. In addition, in vivo electrophysiological studies revealed changes in dopaminergic cell firing activity in the ventral tegmental area of isolated rats when compared to group-housed controls. These alterations include an increase in the number of spontaneously active dopaminergic neurons, and a change of firing activity towards a more irregular and bursting firing pattern. Taken together, our findings suggest that the behavioral phenotype induced by social isolation may be driven by an overactive dopamine system.