Changes of brain activity in the aged SAMP mouse

Application of Animal Models in Diabetic Cardiomyopathy

Diabetic heart disease is a growing and important public health risk. Apart from the risk of coronary artery disease or hypertension, diabetes mellitus (DM) is a well-known risk factor for heart failure in the form of diabetic cardiomyopathy (DiaCM). Currently, DiaCM is defined as myocardial dysfunction in patients with DM in the absence of coronary artery disease and hypertension. The underlying pathomechanism of DiaCM is partially understood, but accumulating evidence suggests that metabolic derangements, oxidative stress, increased myocardial fibrosis and hypertrophy, inflammation, enhanced apoptosis, impaired intracellular calcium handling, activation of the renin-angiotensin-aldosterone system, mitochondrial dysfunction, and dysregulation of microRNAs, among other factors, are involved. Numerous animal models have been used to investigate the pathomechanisms of DiaCM. Despite some limitations, animal models for DiaCM have greatly advanced our understanding of pathomechanisms and have helped in the development of successful disease management strategies. In this review, we summarize the current pathomechanisms of DiaCM and provide animal models for DiaCM according to its pathomechanisms, which may contribute to broadening our understanding of the underlying mechanisms and facilitating the identification of possible new therapeutic targets.

Heart failure with preserved ejection fraction: present status and future directions

The clinical importance of heart failure with preserved ejection fraction (HFpEF) has recently become apparent. HFpEF refers to heart failure (HF) symptoms with normal or near-normal cardiac function on echocardiography. Common clinical features of HFpEF include diastolic dysfunction, reduced compliance, and ventricular hypokinesia. HFpEF differs from the better-known HF with reduced ejection fraction (HFrEF). Despite having a "preserved ejection fraction," patients with HFpEF have symptoms such as shortness of breath, excessive tiredness, and limited exercise capability. Furthermore, the mortality rate and cumulative survival rate are as severe in HFpEF as they are in HFrEF. While beta-blockers and renin-angiotensin-aldosterone system modulators can improve the survival rate in HFrEF, no known therapeutic agents show similar effectiveness in HFpEF. Researchers have examined molecular events in the development of HFpEF using small and middle-sized animal models. This review discusses HFpEF with regard to etiology and clinical features and introduces the use of mouse and other animal models of human HFpEF.

Functional magnetic resonance imaging and the brain: A brief review

Functional magnetic resonance imaging (fMRI) is employed in many behavior analysis studies, with blood oxygen level dependent- (BOLD-) contrast imaging being the main method used to generate images. The use of BOLD-contrast imaging in fMRI has been refined over the years, for example, the inclusion of a spin echo pulse and increased magnetic strength were shown to produce better recorded images. Taking careful precautions to control variables during measurement, comparisons between different specimen groups can be illustrated by fMRI imaging using both quantitative and qualitative methods. Differences have been observed in comparisons of active and resting, developing and aging, and defective and damaged brains in various studies. However, cognitive studies using fMRI still face a number of challenges in interpretation that can only be overcome by imaging large numbers of samples. Furthermore, fMRI studies of brain cancer, lesions and other brain pathologies of both humans and animals are still to be explored.

Age-dependent loss of cholinergic neurons in learning and memory-related brain regions and impaired learning in SAMP8 mice with trigeminal nerve damage

The tooth belongs to the trigeminal sensory pathway. Dental damage has been associated with impairments in the central nervous system that may be mediated by injury to the trigeminal nerve. In the present study, we investigated the effects of damage to the inferior alveolar nerve, an important peripheral nerve in the trigeminal sensory pathway, on learning and memory behaviors and structural changes in related brain regions, in a mouse model of Alzheimer's disease. Inferior alveolar nerve transection or sham surgery was performed in middle-aged (4-month-old) or elderly (7-month-old) senescence-accelerated mouse prone 8 (SAMP8) mice. When the middle-aged mice reached 8 months (middle-aged group 1) or 11 months (middle-aged group 2), and the elderly group reached 11 months, step-down passive avoidance and Y-maze tests of learning and memory were performed, and the cholinergic system was examined in the hippocampus (Nissl staining and acetylcholinesterase histochemistry) and basal forebrain (choline acetyltransferase immunohistochemistry). In the elderly group, animals that underwent nerve transection had fewer pyramidal neurons in the hippocampal CA1 and CA3 regions, fewer cholinergic fibers in the CA1 and dentate gyrus, and fewer cholinergic neurons in the medial septal nucleus and vertical limb of the diagonal band, compared with sham-operated animals, as well as showing impairments in learning and memory. Conversely, no significant differences in histology or behavior were observed between middle-aged group 1 or group 2 transected mice and age-matched sham-operated mice. The present findings suggest that trigeminal nerve damage in old age, but not middle age, can induce degeneration of the septal-hippocampal cholinergic system and loss of hippocampal pyramidal neurons, and ultimately impair learning ability. Our results highlight the importance of active treatment of trigeminal nerve damage in elderly patients and those with Alzheimer's disease, and indicate that tooth extraction should be avoided in these populations.

Permanent deficits in brain functions caused by long-term ketamine treatment in mice

Ketamine, an injectable anesthetic, is also a popular recreational drug used by young adults worldwide. Ketamine is a non-competitive antagonist of N-methyl-d-aspartate receptor, which plays important roles in synaptic plasticity and neuronal learning. Most previous studies have examined the immediate and short-term effects of ketamine, which include learning and cognitive deficits plus impairment of working memory, whereas little is known about the long-term effects of repeated ketamine injections of common or usual recreational doses. Therefore, we aimed to evaluate the deficits in brain functions with behavioral tests, including wire hang, hot plate and water maze tests, plus examine prefrontal cortex apoptotic markers, including Bax, Bcl-2 and caspase-3, in mice treated with 6 months of daily ketamine administration. In our study, following 6 months of ketamine injection, mice showed significant deterioration in neuromuscular strength and nociception 4 hours post-dose, but learning and working memory were not affected nor was there significant apoptosis in the prefrontal cortex. Our research revealed the important clinical finding that long-term ketamine abuse with usual recreational doses can detrimentally affect neuromuscular strength and nociception as part of measurable, stable and persistent deficits in brain function.

MRI in small brains displaying extensive plasticity

Manganese-enhanced magnetic resonance imaging (ME-MRI), blood oxygen-level-dependent functional MRI (BOLD fMRI) and diffusion tensor imaging (DTI) can now be applied to animal species as small as mice or songbirds. These techniques confirmed previous findings but are also beginning to reveal new phenomena that were difficult or impossible to study previously. These imaging techniques will lead to major technical and conceptual advances in systems neurosciences. We illustrate these new developments with studies of the song control and auditory systems in songbirds, a spatially organized neuronal circuitry that mediates the acquisition, production and perception of complex learned vocalizations. This neural system is an outstanding model for studying vocal learning, brain steroid hormone action, brain plasticity and lateralization of brain function.

Damage to the nigrostriatal system in the MPTP-treated SAMP8 mouse

Application of aged animals to studies of Parkinson's disease (PD) will be beneficial to improve the understanding of its pathogenesis. The senescence-accelerated mouse prone8 (SAMP8) mouse has an early onset of senility and a short life span, characterized by learning and memory impairment, and affective disturbance in the aging process. There is no animal currently being used as a PD model that exhibits these characteristics. Application of the SAMP8 mouse to PD research may have several merits. For the first time, we have investigated damage of the nigrostriatal system in the SAMP8 mouse induced by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Male SAMP8 mice (12 weeks) were treated with four subcutaneous injections of MPTP (20mg/kg at 2h intervals): spontaneous activity decreased significantly after the third injection, and recovered 48h after the first injection. In MPTP-SAMP8 mice, the tyrosine hydroxylase (TH)-positive neuronal loss at 6h (7.06%), 24h (12.79%), 3 days (22.49%), and 8 days (42.39%), while striatal dopamine (DA) levels decreased at 6h by 79.09%, at 24h by 80.33%, at 3 days by 83.86%, and at 8 days by 80.14%. These results indicated that there were marked decreases in striatal DA levels and a loss of dopaminergic neurons in the substantia nigra, with the behavior change following shortly thereafter, in MPTP-SAMP8 mice. On the basis of the current findings, the SAMP8 mouse is also vulnerable to neurotoxic effects of MPTP. These data suggest that the SAMP8 mouse may be utilized in PD research.

Cell death in the Purkinje cells of the cerebellum of senescence accelerated mouse (SAMP(8))

The cerebella of SAMP(8) (accelerated aging mouse) and SAMR(1) controls were analyzed by Western Blotting of tyrosine hydroxylase and choline acetyltransferase, as well as by TUNEL and histological silver staining. Both tyrosine hydroxylase and choline acetyltransferase levels were higher in SAMR(1) than in SAMP(8). There was also an age-related decrease in enzyme levels in SAMP(8), with the reduction of tyrosine hydroxylase being more apparent. Concomitantly, there was an age-related increase of apoptosis in the medial neocerebellum and the vermis as revealed by TUNEL, with changes being significant in the SAMP(8) strain. Histologically, some Purkinje cells appeared to disappear during aging. Taken together, the data suggests that the aging SAMP(8) strain displays differential Purkinje cell death in the medial cerebellum and that some of the dying cells are likely to be catecholaminergic.