Immunohistochemical evidence for the presence of synaptic connections of nitrergic neurons in the rat rostral migratory stream

Effect of microwave radiation on adult neurogenesis and behavior of prenatally exposed rats

Postnatal neurogenesis appears to be highly sensitive to environmental factors, including microwave electromagnetic radiation (MWR). Here, we investigated the impact of MWR during intrauterine development on juvenile and adult neurogenesis in the rostral migratory stream (RMS) and the dentate gyrus of the hippocampus in the rat brain, as well as its effect on animal behavior. Female rats were exposed to MWR at a frequency of 2.45 GHz for 2 hours daily throughout pregnancy. The offspring of irradiated mothers survived to either juvenile age or adulthood. The brains of the rats were subjected to morphological analysis, assessing cell proliferation and death in both neurogenic regions. In the RMS, the differentiation of nitrergic neurons was also investigated. The effect of MWR on behavior was evaluated in rats surviving to adulthood. Prenatal MWR exposure caused significant changes in the number of proliferating and dying cells, depending on the age of the animals and the observed neurogenic region. In addition, MWR attenuated the maturation of nitrergic neurons in the RMS in both juvenile and adult rats. Morphological alterations in neurogenesis were accompanied by changes in animals' behavior. Affected neurogenesis and changes in animal behavior suggest a high sensitivity of the developing brain to MWR.

Melatonin mitigates hippocampal and cognitive impairments caused by prenatal irradiation

Formation of new neurons and glial cells in the brain is taking place in mammals not only during prenatal embryogenesis but also during adult life. As an enhancer of oxidative stress, ionizing radiation represents a potent inhibitor of neurogenesis and gliogenesis in the brain. It is known that the pineal hormone melatonin is a potent free radical scavenger and counteracts inflammation and apoptosis in brain injuries. The aim of our study was to establish the effects of melatonin on cells in the hippocampus and selected forms of behaviour in prenatally irradiated rats. The male progeny of irradiated (1 Gy of gamma rays; n = 38) and sham-irradiated mothers (n = 19), aged 3 weeks or 2 months, were used in the experiment. Melatonin was administered daily in drinking water (4 mg/kg b. w.) to a subset of animals from each age group. Prenatal irradiation markedly suppressed proliferative activity in the dentate gyrus in both age groups. Melatonin significantly increased the number of proliferative BrdU-positive cells in hilus of young irradiated animals, and the number of mature NeuN-positive neurons in hilus and granular cell layer of the dentate gyrus in these rats and in CA1 region of adult irradiated rats. Moreover, melatonin significantly improved the spatial memory impaired by irradiation, assessed in Morris water maze. A significant correlation between the number of proliferative cells and cognitive performances was found, too. Our study indicates that melatonin may decrease the loss of hippocampal neurons in the CA1 region and improve cognitive abilities after irradiation.

On the existence of mechanoreceptors within the neurovascular unit of the mammalian brain

We describe a set of perivascular interneurons (PINs) with series of fibro-vesicular complexes (FVCs) throughout the gray matter of the adult rabbit and rat brains. PIN-FVCs are ubiquitous throughout the brain vasculature as detected in Golgi-impregnated specimens. Most PINs are small, aspiny cells with short or long (> 1 mm) axons that split and travel along arterial blood vessels. Upon ramification, axons form FVCs around the arising vascular branches; then, paired axons run parallel to the vessel wall until another ramification ensues, and a new FVC is formed. Cytologically, FVCs consist of clusters of perivascular bulbs (PVBs) encircling the precapillary and capillary wall surrounded by end-feet and the extracellular matrix of endothelial cells and pericytes. A PVB contains mitochondria, multivesicular bodies, and granules with a membranous core, similar to Meissner corpuscles and other mechanoreceptors. Some PVBs form asymmetrical, axo-spinous synapses with presumptive adjacent neurons. PINs appear to correspond to the type 1 nNOS-positive neurons whose FVCs co-label with markers of sensory fiber-terminals surrounded by astrocytic end-feet. The PIN is conserved in adult cats and rhesus monkey specimens. The location, ubiquity throughout the vasculature of the mammalian brain, and cytological organization of the PIN-FVCs suggests that it is a sensory receptor intrinsic to the mammalian neurovascular unit that corresponds to an afferent limb of the sensorimotor feed-back mechanism controlling local blood flow.

Roles of Gasotransmitters in Synaptic Plasticity and Neuropsychiatric Conditions

Synaptic plasticity is important for maintaining normal neuronal activity and proper neuronal functioning in the nervous system. It is crucial for regulating synaptic transmission or electrical signal transduction to neuronal networks, for sharing essential information among neurons, and for maintaining homeostasis in the body. Moreover, changes in synaptic or neural plasticity are associated with many neuropsychiatric conditions, such as schizophrenia (SCZ), bipolar disorder (BP), major depressive disorder (MDD), and Alzheimer's disease (AD). The improper maintenance of neural plasticity causes incorrect neurotransmitter transmission, which can also cause neuropsychiatric conditions. Gas neurotransmitters (gasotransmitters), such as hydrogen sulfide (H2S), nitric oxide (NO), and carbon monoxide (CO), play roles in maintaining synaptic plasticity and in helping to restore such plasticity in the neuronal architecture in the central nervous system (CNS). Indeed, the upregulation or downregulation of these gasotransmitters may cause neuropsychiatric conditions, and their amelioration may restore synaptic plasticity and proper neuronal functioning and thereby improve such conditions. Understanding the specific molecular mechanisms underpinning these effects can help identify ways to treat these neuropsychiatric conditions.

Secretagogin-dependent matrix metalloprotease-2 release from neurons regulates neuroblast migration

The rostral migratory stream (RMS) is viewed as a glia-enriched conduit of forward-migrating neuroblasts in which chemorepulsive signals control the pace of forward migration. Here we demonstrate the existence of a scaffold of neurons that receive synaptic inputs within the rat, mouse, and human fetal RMS equivalents. These neurons express secretagogin, a Ca²⁺-sensor protein, to execute an annexin V-dependent externalization of matrix metalloprotease-2 (MMP-2) for reconfiguring the extracellular matrix locally. Mouse genetics combined with pharmacological probing in vivo and in vitro demonstrate that MMP-2 externalization occurs on demand and that its loss slows neuroblast migration. Loss of function is particularly remarkable upon injury to the olfactory bulb. Cumulatively, we identify a signaling cascade that provokes structural remodeling of the RMS through recruitment of MMP-2 by a previously unrecognized neuronal constituent. Given the life-long presence of secretagogin-containing neurons in human, this mechanism might be exploited for therapeutic benefit in rescue strategies.

Role of nitric oxide and related molecules in schizophrenia pathogenesis: biochemical, genetic and clinical aspects

Currently, schizophrenia is considered a multifactorial disease. Over the past 50 years, many investigators have considered the role of toxic free radicals in the etiology of schizophrenia. This is an area of active research which is still evolving. Here, we review the recent data and current concepts on the roles of nitric oxide (NO) and related molecules in the pathogenesis of schizophrenia. NO is involved in storage, uptake and release of mediators and neurotransmitters, including glutamate, acetylcholine, noradrenaline, GABA, taurine and glycine. In addition, NO diffuses across cell membranes and activates its own extrasynaptic receptors. Further, NO is involved in peroxidation and reactive oxidative stress. Investigations reveal significant disturbances in NO levels in the brain structures (cerebellum, hypothalamus, hippocampus, striatum) and fluids of subjects with schizophrenia. Given the roles of NO in central nervous system development, these changes may result in neurodevelopmental changes associated with schizophrenia. We describe here the recent literature on NOS gene polymorphisms on schizophrenia, which all point to consistent results. We also discuss how NO may be a new target for the therapy of mental disorders. Currently there have been 2 randomized double-blind placebo-controlled trials of L-lysine as an NOS inhibitor in the CNS.

Structural variation and interactions among astrocytes of the rostral migratory stream and olfactory bulb: II. Golgi and electron microscopic study of the adult rat

Cytological characteristics of a cell sharing structure of both an astrocyte and a neuron, previously termed amphomorphic cell (AC), were defined here in adult rat rostral migratory stream (RMS). The AC perikaryon corresponds to that of the B1 cell of the adult mouse subventricular zone (SVZ)-RMS. The AC and its processes are confined to the RMS. Each AC originates four sets of processes that overlap with those from its homologues and adjacent neural and stromal elements. ACs interact between them via reciprocal sets of processes: those directed caudally bear spheroidal vesicles (SVP) and form gap junctions with pleomorphic vesicles (PVs) associated with the anterior set from the adjacent AC. Large asymmetric synapses, a set of them arising from the anterior olfactory nucleus, converge on each SV. The interlacing processes of the AC, together with a set of perikaryal out-growths form the glial cuff surrounding migrating neuroblasts described earlier. Small asymmetrical and symmetrical synapses terminate in subsets of differentiated A-cells, termed here A1, in the bulbar part of the RMS. Both AC- and A1-cells form electrical synapses between them and with their homologues. The strategic, wide-spread distribution between the neuropil and blood vessels of the AC, its processes, and migrating neuroblasts, suggests that the AC might mediate between both endogenous inductors and neurotransmitters, influencing the adult-born neurons it had previously originated.

Diverse effect of different odor stimuli on behavior and Fos protein production in the olfactory system neurogenic region of adult rats

Previously it has been demonstrated that processes of postnatal neurogenesis in the olfactory system neurogenic region-the subventricular zone (SVZ), rostral migratory stream (RMS), and olfactory bulb (OB) can be significantly altered by different factors of an environment. However, the mechanisms involved in regulation of neurogenesis by exogenous factors in the olfactory system remain unclear. The purpose of the present study was to contribute to the understanding of these mechanisms by immunohistochemical assessment of Fos protein induction in areas of adult neurogenesis. To evaluate the coordinate activation of Fos production in neurons of the olfactory system neurogenic region, a brief exposure to artificial odor (eau de Cologne) or naturalistic odor (cat odor) has been used in alert rats. Our results revealed that the effects of these odors are easily distinguishable at both the behavioral and the morphological level. Cat odor induced greater changes in anxiety level, and produced typical pattern of Fos activation in the accessory olfactory bulb (AOB), a brain region associated with defensive behavior. An important finding is, that next to distinct Fos expression in the OB and the AOB, Fos positive cells have been found also within the SVZ/RMS of the odor stimulated rats. Interestingly, Fos expression in the RMS was detected only after exposure to artificial odor stimulus. These results provide new evidence that some SVZ/RMS cells have complete prerequisites necessary for the Fos signal transduction cascade.