Kv2.1 expression in giant reticular neurons of the postnatal mouse brain.

Previous experiments charted the development of behavioral arousal in postnatal mice. From Postnatal Day 3 (P3) to Postnatal Day 6 (P6) mice (a) become significantly more active, "arousable"; and (b) in large reticular neurons, nucleus gigantocellularis (NGC), patch clamp recordings reveal a significantly increased ability to fire high frequency trains of action potentials as are associated with elevated cortical arousal. These action potential trains depend on delayed rectifiers such as Kv2.1. Here we report tracking the development of expression of a delayed rectifier, Kv2.1 in NGC neurons crucial for initiating CNS arousal. In tissue sections, light microscope immunohistochemistry revealed that expression of Kv2.1 in NGC neurons is greater at day P6 than at P3. Electron microscope immunohistochemistry revealed Kv2.1 labeling on the plasmalemmal surface of soma and dendrites, greater on P6 than P3. In brainstem reticular neuron cell culture, Kv2.1 immunocytochemistry increased monotonically from Days-In-Vitro 3-10, paralleling the ability of such neurons to fire action potential trains. The increase of Kv2.1 expression from P3 to P6, perhaps in conjunction with other delayed rectifier currents, could permit the ability to fire action potential trains in NGC neurons. Further work with genetically identified NGC neurons is indicated.

Tissue plasminogen activator in the amygdala is critical for stress-induced anxiety-like behavior.

Although neuronal stress circuits have been identified, little is known about the mechanisms that underlie the stress-induced neuronal plasticity leading to fear and anxiety. Here we found that the serine protease tissue-plasminogen activator (tPA) was upregulated in the central and medial amygdala by acute restraint stress, where it promoted stress-related neuronal remodeling and was subsequently inhibited by plasminogen activator inhibitor-1 (PAI-1). These events preceded stress-induced increases in anxiety-like behavior of mice. Mice in which the tPA gene has been disrupted did not show anxiety after up to three weeks of daily restraint and showed attenuated neuronal remodeling as well as a maladaptive hormonal response. These studies support the idea that tPA is critical for the development of anxiety-like behavior after stress.

Sexual Motivation in the Female and Its Opposition by Stress.

A well worked-out motivational system in laboratory animals produces estrogen-dependent female sex behavior. Here, we review (a) the logical definition of sexual motivation and (b) the basic neuronal and molecular mechanisms that allow the behavior to occur. Importantly, reproductive mechanisms in the female can be inhibited by stress. This is interesting because, in terms of the specificity of neuroendocrine dynamics in space and time, the two families of phenomena, sex and stress, are the opposite of each other. We cover papers that document stress effects on the underlying processes of reproductive endocrinology in the female. Not all of the mechanisms for such inhibition have been clearly laid out. Finally, as a current topic of investigation, this system offers several avenues for new investigation which we briefly characterize.

Regulation of neurotransmitter release by synapsin III.

Synapsin III is the most recently identified member of the synapsin family, a group of synaptic vesicle proteins that play essential roles in neurotransmitter release and neurite outgrowth. Here, through the generation and analysis of synapsin III knock-out mice, we demonstrate that synapsin III regulates neurotransmitter release in a manner that is distinct from that of synapsin I or synapsin II. In mice lacking synapsin III, the size of the recycling pool of synaptic vesicles was increased, and synaptic depression was reduced. The number of vesicles that fuse per action potential was similar between synapsin III knock-out and wild-type mice, and there was no change in the quantal content of EPSCs; however, IPSCs were greatly reduced in synapsin III-deficient neurons. The density and distribution of synaptic vesicles in presynaptic terminals did not appear to be different in synapsin III knock-out mice in comparison to wild-type littermates. In addition to the changes in neurotransmitter release, we observed a specific delay in axon outgrowth in cultured hippocampal neurons from synapsin III knock-out mice. Our data indicate that synapsin III plays unique roles both in early axon outgrowth and in the regulation of synaptic vesicle trafficking.

Studies of hormone action in the hippocampal formation: possible relevance to depression and diabetes.

OBJECTIVES: The goal is to review the plasticity and vulnerability of the hippocampus, a brain structure involved in episodic, declarative, contextual and spatial learning and memory, as well as its being a component in the control of autonomic and vegetative functions such as ACTH secretion. It discusses its possible role in the regulation of glucose homeostasis, and the need of hippocampal neurons for glucose because of their high metabolic activity. The hippocampus is also vulnerable to damage by stroke and head trauma and susceptible to damage during aging and repeated stress, and is sensitive to the effects of diabetes. METHODS: A summary of recent work in the author's laboratory and related work in the field using citations of literature based, in part, on Medline searches. CONCLUSIONS: In addition to its vulnerability, the hippocampus is also a plastic and adaptable brain region that is capable of considerable structural reorganization, including remodeling of dendrites and neurogenesis of dentate gyrus granule neurons in response to repeated stress. Animal models of Type 1 diabetes show accelerated remodeling of dendrites, and Type 2 diabetes remains to be studied in this regard. This is relevant to major depressive illness, in which a progressive atrophy of the hippocampal formation is reported and is accompanied by impairment of cognitive function in those subjects with hippocampal shrinkage. Therefore, hippocampal atrophy in depression, as well as in diabetes, may reflect either damage or plasticity involving structural reorganization that is potentially treatable.

Stress and hippocampal plasticity: implications for the pathophysiology of affective disorders.

The hippocampal formation, a structure involved in declarative, spatial and contextual memory, is a particularly sensitive and vulnerable brain region to stress and stress hormones. The hippocampus shows a considerable degree of structural plasticity in the adult brain. Stress suppresses neurogenesis of dentate gyrus granule neurons, and repeated stress causes atrophy of dendrites in the CA3 region. In addition, ovarian steroids regulate synapse formation during the estrous cycle of female rats. All three forms of structural remodeling of the hippocampus are mediated by hormones working in concert with excitatory amino acids (EAA) and N-methyl-D-aspartate (NMDA) receptors. EAA and NMDA receptors are also involved in neuronal death that is caused in pyramidal neurons by seizures and by ischemia and prolonged psychosocial stress. In the human hippocampus, magnetic resonance imaging studies have shown that there is a selective atrophy in recurrent depressive illness, accompanied by deficits in memory performance. Hippocampal atrophy may be a feature of affective disorders that is not treated by all medications. From a therapeutic standpoint, it is essential to distinguish between permanent damage and reversible atrophy in order to develop treatment strategies to either prevent or reverse deficits. In addition, remodeling of brain cells may occur in other brain regions. Possible treatments are discussed. Copyright 2001 John Wiley & Sons, Ltd.

Previous history of chronic stress changes the transcriptional response to glucocorticoid challenge in the dentate gyrus region of the male rat hippocampus.

Chronic stress is a risk factor for several neuropsychiatric diseases, such as depression and psychosis. In response to stress glucocorticoids (GCs) are secreted that bind to mineralocorticoid and glucocorticoid receptors, ligand-activated transcription factors that regulate the transcription of gene networks in the brain necessary for coping with stress, recovery, and adaptation. Chronic stress particularly affects the dentate gyrus (DG) subregion of the hippocampus, causing several functional and morphological changes with consequences for learning and memory, which are likely adaptive but at the same time make DG neurons more vulnerable to subsequent challenges. The aim of this study was to investigate the transcriptional response of DG neurons to a GC challenge in male rats previously exposed to chronic restraint stress (CRS). An intriguing finding of the current study was that having a history of CRS had profound consequences for the subsequent response to acute GC challenge, differentially affecting the expression of several hundreds of genes in the DG compared with challenged nonstressed control animals. This enduring effect of previous stress exposure suggests that epigenetic processes may be involved. In line with this, CRS indeed affected the expression of several genes involved in chromatin structure and epigenetic processes, including Asf1, Ash1l, Hist1h3f, and Tp63. The data presented here indicate that CRS alters the transcriptional response to a subsequent GC injection. We propose that this altered transcriptional potential forms part of the molecular mechanism underlying the enhanced vulnerability for stress-related disorders like depression caused by chronic stress.

Rapid and reversible changes in intrahippocampal connectivity during the course of hibernation in European hamsters.

The hippocampal formation is a highly plastic brain structure that undergoes structural remodeling in response to internal and external challenges such as metabolic imbalance and repeated stress. We investigated whether the extreme alterations in metabolic status that occur during the course of hibernation in European hamsters cause structural changes in the dendritic arborizations of the CA3 pyramidal neurons and their main excitatory afferents, the mossy fiber terminals (MFT), that originate in the dentate gyrus. We report that apical, but not basal, dendritic trees of Golgi-impregnated CA3 principal neurons are significantly shorter, less branched, and less spiny in hypothermic hamsters compared with active animals. After the induction of arousal from torpor, within 2 h, the apical dendritic lengths, branching patterns, and spine density estimations returned to levels found in active, euthermic hamsters. The ultrastructure of MFT in hibernating hamsters showed a significant reduction in synaptic vesicle density and in the percentage of MFT area covered by spine profiles. Awakened hamsters showed restoration of MFT morphology to that seen in active animals. MFT of torpid animals also showed a significant increase in the percentage area of mitochondrial profiles that remained higher 3 h after induced arousal from hibernation compared with euthermic controls. Thus, the torpid/awakening cycle of the hibernating European hamster causes a rapid and reversible morphological reorganization of intrahippocampal subregions involved in information processing. The reported reductions in morphological connectivity between the dentate gyrus and the CA3 subregions could underlie the cessation of exploratory activity and spatial navigation skills during hibernation.

Estrogen alters hippocampal dendritic spine shape and enhances synaptic protein immunoreactivity and spatial memory in female mice.

Estrogen (E) treatment induces axospinous synapses in rat hippocampus in vivo and in cultured hippocampal neurons in vitro. To better explore the molecular mechanisms underlying this phenomenon, we have established a mouse model for E action in the hippocampus by using Golgi impregnation to examine hippocampal dendritic spine morphology, radioimmunocytochemistry (RICC) and silver-enhanced immunocytochemistry to examine expression levels of synaptic protein markers, and hippocampal-dependent object-placement memory as a behavioral readout for the actions of E. In ovariectomized mice of several strains and F(1) hybrids, the total dendritic spine density on neurons in the CA1 region was not enhanced by E treatment, a finding that differs from that in the female rat. E treatment of ovariectomized C57BL/6J mice, however, caused an increase in the number of spines with mushroom shapes. By RICC and silver-enhanced immunocytochemistry, we found that the immunoreactivity of postsynaptic markers (PSD95 and spinophilin) and a presynaptic marker (syntaxin) were enhanced by E treatment throughout all fields of the dorsal hippocampus. In the object-placement tests, E treatment enhanced performance of object placement, a spatial episodic memory task. Taken together, the morphology and RICC results suggest a previously uncharacterized role of E in synaptic structural plasticity that may be interpreted as a facilitation of the spine-maturation process and may be associated with enhancement of hippocampal-dependent memory.

Receptores para glucocorticoides y concentración de corticosterona en cerebro / Glucocorticoid receptors and corticosterone concentration in brain

El presente trabajo de investigación, presentado con el título completo de "Correlación entre receptores para glucocorticoides y concentración de corticosterona en regiones cerebrales: Sus implicancias para el estudio del estrés", fue desarrollado por las Dras. Ana María Magariños y Mónica Ferrini y el Dr. Alejandro F. de Nicola en el Laboratorio de Bioquímica Neuroendócrina del Instituto de Biológia y Medicina Experimental, cocn el apoyo de la Fundación Raquel Guedikian de Estudios sobre el Estrés. En él se analiza la concentración de corticosterona (CORT) en varias regiones cerebrales de rata y su correlación con el contenido de receptores para glucocorticoides (GC). Los resultados son importantes para localizar los sitios de acción hormonal en el cerebro durante los estados de hiperfunción adrenal, típico del estrés

In vitro uptake of 18-hydroxycorticosterone by regions of the central nervous system

Estudiamos la unión específica de la 18-hidroxicorticosterona (18-OH-B) a fracciones nucleares y citoplasmáticas de células provenientes de bulbo, protuberancia, amígdala, pituitaria anterior, hipotálamo, hipocampo, área preóptica y pulmón de animales adrenalectomizados, después de incubar los tejidos con el ligando radiactivo. Encontramos que 18-OH-B tiene una mayor unión específica a núcleos obtenidos de bulbo y protuberancia; este perfil difiere de observaciones previas en las que otros corticosteroide íntimamente relacionados, como la corticosterona y la aldosterona, se encuentran principalmente concentrados en el sistema límbico