Bcl-2 transgenic mice with increased number of neurons have a greater learning capacity

Development of a water-escape motivated version of the Stone T-maze for mice

Mice provide a highly valuable resource for investigating learning and memory processes; however, many of the established tasks for evaluating learning and memory were developed for rats. Behaviors of mice in these tasks appear to be driven by different motivational factors, and as a result, they often do not perform reliably on tasks involving rewards traditionally used for rats. Because of difficulties in measuring learning and memory in mice as well as the need to have a task that can reliably measure these behavioral processes, we have developed a mouse version of the Stone T-maze utilizing what appears to be the primary motivation of mice, escape to a safe location. Specifically, we have constructed a task that requires the mouse to wade through water to reach a dark and dry goal box. To escape this aversive environment, the Stone T-maze requires learning the correct sequence of 13 left and right turns to reach the goal box. Through a series of experiments examining a variety of protocols, it was found that mice will reliably perform this task. This task can be used to assess learning and memory without the potential performance confounds that can affect performance of mice in other tasks. We believe this task offers a valuable new tool for evaluating learning and memory in mice not previously available to researchers.

Central injection of caspase inhibitors facilitates the formation of freezing behavior in rats

We studied the effects of central administration of pancaspase inhibitor z-VAD-fmk and specific caspase 3 inhibitor z-DEVD-fmk on learning and memory in rats. The inhibitors selectively facilitated the formation of freezing behavior without modulating consolidation and retrieval of passive defense behavior in the model of conditioned freezing.

Interleukin-1beta and caspase-1: players in the regulation of age-related cognitive dysfunction

Scientific research on the unprecedented and growing number of older adults in the United States and other industrialized countries has focused much attention on the health consequences of aging. Over the last few decades, inflammation in the brain and its implication in the progression of aging and age-related cognitive dysfunction has been an area of increasing importance to neuroscientists and is now considered as one of the most interesting and promising topics for aging research. One of the critical aspects of inflammatory processes is that the activation of one upstream inflammatory molecule initiates a cascade of self-sustaining inflammatory events which leads to the activation of a number of different downstream functions. Recently, a great deal of attention has been given to the interplay between inflammatory and apoptotic processes and the regulation of these processes by the caspases. The caspase family of proteases can be divided into proapoptotic and pro-inflammatory members. The present review summarizes recent observations of the interactions between the inflammatory cytokine interleuldn-1 (IL-1) beta and the inflammatory/apoptotic caspase-1 and their involvement in age-related impairments in cognition. A comprehensive understanding of these mechanisms could potentially lead to the development of preventive or protective therapies that reduce or inhibit the cognitive decline associated with aging and age-related neurodegenerative disease.

Improvement of memory for context by inhibition of caspase-1 in aged rats

Impaired learning and memory is a common pathologic feature associated with numerous neurologic disorders. There is strong evidence that central inflammation contributes significantly to the progression of several neurodegenerative diseases as well as to the ageing process. For example, in aged rats an increase in interleukin-1beta (IL-1beta) is implicated in the decline of synaptic plasticity in the hippocampus and impaired performance on cognitive tasks such as contextual fear conditioning. IL-1beta is a proinflammatory cytokine initially synthesized in an inactive precursor form that is cleaved by caspase-1 to generate the biologically mature form. In the present study, cleavage of IL-1beta was chronically inhibited using a specific caspase-1 inhibitor (Ac-YVAD-CMK; 10 pmol) in both aged (22 month) and young (4 month) rats. Both groups received Ac-YVAD-CMK for 28 days intracerebroventricularly through a brain infusion cannula connected to an osmotic minipump. On day 20 the animals were trained in contextual fear conditioning, and memory for context was tested on day 22. Chronic infusion of a specific caspase-1 inhibitor in aged rats ameliorated age-related increases in hippocampal IL-1beta and improved memory for context.

Mutant and genetically modified mice as models for studying the relationship between aging and carcinogenesis

Increased interest is emerging in using mouse models to assess the genetics of aging and age-related diseases, including cancer. However, only limited information is available regarding the relationship between aging and spontaneous tumor development in genetically modified mice. Analysis of various transgenic and knockout rodent models with either a shortened or an extended life span, provides a unique opportunity to evaluate interactions of genes involved in the aging process and carcinogenesis. There are only a few models which show life span extension. Ames dwarf mutant mice, p66(-/-) knockout mice, alpha MUPA and MGMT transgenic mice live longer than wild-type strains. The incidence of spontaneous tumors in these mutant mice was usually similar to those in controls, whereas the latent period of tumor development was increased. Practically all models of accelerated aging showed increased incidence and shorter latency of tumors. This phenomenon has been observed in animals which display a phenotype that more closely resembles natural aging, and in animals which manifest only some features of the normal aging process. These observations are in agreement with an earlier established positive correlation between tumor incidence and the rate of tumor incidence increase associated with aging and the aging rate in a population. Thus, genetically modified animals are a valuable tool in unravelling mechanisms underlying aging and cancer. Systemic evaluation of newly generated models should include onco-gerontological studies.

Genetic deletion of angiotensin AT2 receptor leads to increased cell numbers in different brain structures of mice

Angiotensin II (Ang II) is a potent vasoactive peptide and displays growth factor-like properties. Different high-affinity Ang II receptor subtypes (AT1A, AT1B and AT2) have been cloned. They are expressed in various brain structures. Additionally, it has been assumed that Mas could interact directly or indirectly with the renin-angiotensin system. The AT1 receptor mediates pressor and mitogenic effects of Ang II, whereas physiological function and signaling mechanisms of the AT2 receptor remain poorly understood. Recent reports have shown that Ang II could mediate apoptosis through AT2 receptors. Since the AT1A, AT2 and Mas knockout mice provide new tools for uncovering potential actions of Ang II, the cell number in different brain structures of male adult wild-type mice and mice deficient for AT1A, AT2 or Mas was evaluated to get more insight into the role of Ang II in central nervous system development. In nearly all investigated brain structures (cortex, hippocampus, amygdala, thalamus), the cell number was significantly higher in AT2-deficient mice in comparison to wild-type mice. To the contrary, in AT1A-deficient mice the cell number was significantly less than in controls in the lateral geniculate and the medial amygdaloid nucleus. However, cell numbers were not changed in Mas-knockout mice compared to their wild-types. These results show the contrary effects of both angiotensin receptors on cell growth and represent the first demonstration of their action on neuronal cell development evidenced in the adult mouse brain.

DNA fragmentation factor 45 deficient mice exhibit enhanced spatial learning and memory compared to wild-type control mice

Programmed cell death or apoptosis is a highly regulated physiological process that is critical in development, particularly in the central nervous system. The DNA fragmentation factor 45 (DFF45 or ICAD) is a subunit of a heterodimeric DNase complex that is crucial for DNA fragmentation and normal apoptosis. To examine the neurobiological consequences of lacking DNA fragmentation and timely apoptosis during mouse development in vivo, we compared spatial learning behaviors in DFF45 mutant and wild-type control mice. We found that DFF45 mutant mice exhibit enhanced spatial learning and memory compared to wild-type mice. Moreover, both the granule cell density and total granule cell number in the hippocampal dentate gyrus region are higher in the DFF45 mutant brains than in the wild-type brains. We propose that the increase in granule cell number in the dentate region due to the DFF45 mutation changes the neuronal network underlying spatial learning and memory in DFF45 mutant mice.

Schizophrenia: pathophysiological mechanisms--a synthesis

A Nobel Symposium, 'Schizophrenia: Pathophysiological Mechanisms' was held in Stockholm, October 1-3, 1998. The topics ranged from etiology, genetics, neuropathology, neurotransmitter, brain imaging, to integrative aspects including cognition and language. The collective amount of information is already enormous and will rapidly increase with advances in molecular pathology, gene transcript profiling and non-invasive imaging techniques. Probably reflecting the complexity is the absence of a disease model that can accommodate the data and explain its roots. In the process of moving from simplistic mechanisms involving single or a few interacting neurotransmitters or circuits and turning to more complex interactive models, there is a need for improved data storage and retrieval. Stochastic search in chemical libraries for potential new drug candidates coupled with rational approaches in their final design may improve therapeutic efficacy.