Rae Silver - US grants

DESCRIPTION (Adapted from applicant's abstract): In many vertebrates, an increase in plasma gonadal steroids is detectable soon after the start of courtship or sexual behavior. In the course of studies aimed at understanding how environmental and behavioral stimuli produced changes in the brain that result, in turn, in altered endocrine secretions, we noted the appearance of GnRH-positive mast cells in the medial habenula. The mast cells were present in animals which were sacrificed 2 hours after the start of courtship, were few in animals housed in isolation, and were virtually absent in castrates. Brain mast cells are a widespread phenomenon. Their occurrence was documented in a variety of species when methods to detect biogenic amines first became widely available in the 1970's. While peripheral mast cells have been widely studied, especially in relation to allergy, the possible function of brain mast cells has been little explored. The first aim of this proposal is to delineate the context(s) (e.g. stress, response to novelty, sexual behavior) in which changes occur in number and state of activation of brain mast cells in the medial habenula. Our studies will be specific changes in mast cell number. The habenula is a conservative structure known to serve as link between forebrain and midbrain structures. The second broad goal of the research is to understand the normal physiological function of mast cells in the medial habenula. To this end, we will delineate behavioral function(s) of the medial habenula, and of its efferents and afferents. The overall hypothesis to be tested is that brain mast cells represent a novel signaling system, operating at the interface of the neural, endocrine and the immune systems.

DESCRIPTION (provided by applicant): The number of brain mast cells increases under specific social, stressful, and disease states. Also important, is the discovery that brain mast cells can cross the BBB. Although mast cells are best known for their role in mediating allergic reactions, it has become increasingly evident that they also play a protective role in defense against bacterial infection. Mast cells are heterogeneous, and their mediator content is dependent on their microenvironment, suggesting that brain mast cells should be studied as a unique population - as distinct from those in the periphery. The present application proposes to develop a mouse model which will be used in understanding the phenomenology and functional consequences of mast cells in the brain. Pilot data indicate that mast cell deficient animals lack a complete Acute Phase Response (APR) to bacterial infection. To examine the involvement of mast cells in mounting an immune response, we explore 2 social/behavioral/endocrine conditions in which the brain mast cell population is augmented: a cohabitation paradigm and a stress paradigm. Next, we test the hypothesis that prior exposure (which increases brain mast cell numbers) results in altered response to challenge of the immune system in mast cell rich brain loci. Specifically, we ask whether the mast cell number, activation state is augmented when their numbers in the brain are elevated. To test the hypothesis that brain mast cells have immunological consequences, we determine if increased mast cell numbers results in altered T cell surveillance in mast cell rich brain regions. We propose to test these hypotheses in mast cell deficient mice, in their wild type littermates and in mast cell reconstituted animals. This application will determine whether mast cells play a role in mounting an immune response in the brain.

Mast cells are complex immune cells containing many mediators, though they are best known for their role in allergies (produce histamine) and peripheral inflammation (swelling and redness after a bug bite). Surprisingly, mast cells are found in the brain, and the number of brain mast cells increase under specific normal and pathological conditions. Their location in the brain, near blood vessels, suggests that mast cells are poised to regulate behavioral and physiological responses, including body temperature regulation. Pilot work suggests that blocking mast cell activation can alter the elevated temperature response caused by a pathogen entering the body. We have generated mast cell deficient mice to explore the necessity of these cells for a physiologically appropriate immune response. Experiments involve injecting lipopolysaccharide (a piece of a bacteria cell) and measuring the resulting responses (i.e. body temperature, locomotor activity). This injection acts as a stimulus for mounting the immune system, causing a fever in normal mice, just like the reaction to bacteria. Three experimental groups will be studied: normal, mast cell deficient, and age matched adult deficient mice in which the mast cells have been reconstituted. The mast cell deficient mice are predicted to show little to no temperature change following injection of bacterial cell wall, while the response should be restored to normal in the reconstituted animals. Follow-up studies will explore how mast cells contribute to fever. The discovery that mast cells participate in thermoregulation would represent a revolutionizing instance of immune cells impacting physiology and behavior. In addition, the contribution of mast cells in the brain could change the current thinking that the brain is an immune-privileged site and further support the notion that non-neuronal cells in the brain contribute to the control of behavior. This project willprovide unique training opportunities for undergraduate and graduate students in the lab.

[unreadable] DESCRIPTION (provided by applicant): In the decades since the suprachiasmatic nucleus (SON) was first discovered as the brain clock, its function, cellular elements, and network organization have set the standard for understanding brain function at behavioral, physiological and molecular levels through analysis of cells, tissue and organisms. It was initially thought that the SCN was constituted of a uniform population of oscillators, sending out a coherent signal to the body. It is now clear that the brain clock is constituted of a functionally heterogeneous "circadian clock cells" that can be organized into distinct oscillating networks. Furthermore, there are oscillators and oscillating tissues in numerous organs. The hamster is the subject of choice as it has very precise daily rhythms, significant photoperiodic responses and a wealth of background studies indicating a) clock gene and protein expression in distinct SCN cells reveal the presence of "non-oscillating "gate" cells as well as oscillator cells (based on clock gene expression and electrical rhythmicity), b) on evidence that some intra-SCN cells are "slave oscillators" dependent on the eye, and c) on afferent and efferent connections of neurons of SCN sub-regions to each known brain target sites. The proposed research will characterize SCN activity to assess the consequence of network plasticity on central and peripheral oscillator responses. The first aim focuses on the SCN, characterizing network plasticity. The experiments entail examination of the phase of oscillating and non-oscillating cells of the SCN, under various experimental photic conditions, using molecular markers of circadian phase (clock genes) and neural activation (FOS) (Aim 1). The next focus is on rhythmic extra-SCN sites, examining rhythmicity induced in brain and peripheral target tissues (Aims 2 and 3). (Aim 4) proposes to use mathematical modeling to provide testable hypotheses and to conceptualize the results of the physiological studies. The hypothesis is that we will be able to delineate the relationship between activity of specific intra-SCN networks and brain target sites thereby addressing the long-sought explanation for SCN heterogeneity. [unreadable] [unreadable] [unreadable]