Pushpa S. Kalra - US grants

Evidence suggests that a complex hypothalamic neural circuitry may control pituitary LH secretion. We propose to test the hypothesis that an array of locally derived inhibitory and excitatory regulatory neuropeptides may participate in sustaining episodic LHRH-LH secretion in male rats. Further, inappropriate function of one or more of these neurochemical signals on a long-term basis, as in hyperprolactinemia or during aging, may result in subnormal function of the LHRH-LH axis. In this context, our focus will be on two inhibitory (endogenous opioid peptides (EOP), and Neuropeptide K) and two excitatory (Neuropeptide Y and Galanin) neuropeptides. Experiments are designed to decipher how they may act to modify the LHRH-LH axis, whether activation of corticotropin releasing hormone or EOP is involved and to delineate the relationship between gonadal steroids and the output of these neuropeptides. For EOP involvement, we will extend our ongoing studies to identify the factors responsible for imparting increased feedback sensitivity towards gonadal steroids. For the other three peptides, newer studies are proposed in young, old and hyperprl rats to assess their effects on hypothalamic LHRH output, on pituitary LH release alone and in conjunction with LHRH, to understand the effects of castration and gonadal steroid replacement (time course, strength and duration characteristics) on the output of each of these peptides and to identify the hypothalamic site(s) most affected by these manipulations. We will employ cellular and molecular biology techniques combined with RIA for measurement of LH and neuropeptides in samples obtained via chronic intrajugular cannulae, push-pull cannula technique and in vitro hypothalamic and dispersed pituitary cell perfusions. It is hoped that the outcome of these studies will enhance our understanding of the mode of action, physiological arrangements and interactions with gonadal steroids of these neuropeptides within the hypothalamic circuitry that controls the LHRH-LH axis in young, hyperprl and aged rats.

Neuropeptide Y (NPY) has recently been identified in diverse sites in the rat brain. Our studies show that NPY stimulates feeding in rats. The major objectives of this proposal are to understand further where and how NPY acts in the brain to modulate feeding and drinking behavior. Experiments are designed to determine a dose response effect of NPY, identify the specific central sites of NPY action and elucidate the interplay between NPY and adrenergic neurons. The major techniques are: intraventricular and intracerebral injection or infusion of NPY, adrenalectomy, hypophysectomy and use of pharmacologic drugs which block neurotransmitter synthesis or adrenergic receptors. It is hoped that these investigations will further our understanding of the central control of ingestive behavior in rats.

Obesity, a multivariate disease, can occur with or without accompanying hyperphagia. There is a growing sense of alarm that a large percentage of eating disorders and obesity may be environmental in origin. Among the environmental factors, neurotoxins and certain neural injury producing infections have drawn considerable attention and concern in recent years. This proposal focuses on the neurochemical basis of obesity produced experimentally by neurotoxins. Our long-term objectives are to understand the operative function of the brain circuitry involved in the development of obesity caused by neurotoxin-induced neural injury. Within the hypothalamus an interconnected network of neuropeptides including Neuropeptide Y, galanin and opioids, evokes normal feeding in the rat. We propose to test the hypothesis that obesity produced by three specific neurotoxins known to inflict varied cellular damage is either due to the increased secretion of one or more of these excitatory neuropeptides or due to an increase in receptor sensitivity in the hypothalamic paraventricular nucleus - perifornical (PVN-PF) area. The following neurotoxins will be employed: Ibotenic acid to selectively destroy cell bodies in the ventromedial hypothalamus; colchicine to block axonal transport in the ventromedial nucleus; 6-hydroxydopamine to damage the ascending ventral catecholaminergic bundle in the mid-brain. Secretion of neuropeptide Y, galanin and opioids will be measured in vivo by the push- pull cannula technique and in vitro in short-term cultures of the PVN-PF, and synthesis will be assessed by quantitation of mRNA and peptide contents will be measured in various hypothalamic sites. The second possibility of increase in receptor sensitivity will be assessed by quantitation of food intake after the intracerebroventricular injection of agonists and antagonists or immunoneutralization of neuropeptides. Neuropeptide receptor affinity and number in membranes from microdissected hypothalamic sites will be measured. It is anticipated that elucidating the patterns of neuropeptidergic signalling associated with neurotoxin- induced obesity will shed light on the etiology of idiopathic obesity.

Cytokines, the integral arm of bidirectional communication between the immune and central nervous systems, are also constitutive components of the hypothalamus where they may act as interneuronal signals. Our results indicate the existence of a communication link between the cytokine, Interleukin-1 (IL-1) and certain neuropeptides in the hypothalamus suggesting that the neuroendocrine and behavioral effects of cytokines may be mediated by these neuropeptides. We will test the hypothesis that the effects of cytokines on luteinizing hormone-releasing hormone (inhibition) and on corticotropin-releasing hormone (stimulation) are mediated by cytokine-induced upregulation of hypothalamic tachykinins and down- regulation of neuropeptide Y (NPY); furthermore we suggest that steroids restrain, whereas steroid deficiency, produced by peripheral action of cytokines, accentuates these central cytokine-neuropeptide interactions. This two-part hypothesis will be tested in 5 specific aims: Aim 1 is to identify the effective cytokines and demonstrate specificity of action in evoking cytokine-induced CRH and LHRH responses. In Aim 2 we will utilize antagonists to identify the tachykinin receptor subtypes and document tachykinin involvement in mediating the IL-1beta-induced neuroendocrine responses. Additionally, we will analyze the 3 species of preprotachykinin mRNAs in order to evaluate translational activation by IL-1beta. Aim 3 is to determine the effects of a chronic increase in central IL-1beta on tachykinin release in vivo and on gene expression. Aim 4 is to examine the effects of increases in peripheral cytokines on these hypothalamic interactions with the assumption that peripheral endotoxin stimulated IL- 1beta production in the hypothalamus, in turn, upregulates the central tachykinins. In accordance with the second part of our hypothesis, these proposed studies will be conducted in intact, castrated and testosterone- replaced male rats to decipher the role of gonadal steroids in modulating these hypothalamic interactions. Finally, in Aim 5 we plan to investigate the second putative aspect of cytokine action, viz. down-regulation of the excitatory peptide NPY. The acute and long-term effects of IL-1beta on NPY release in vivo and on gene expression in varied gonadal steroid environments will be studied. To accomplish these goals, release rates of the tachykinins, IL-1beta and NPY will be measured in vivo via the push- pull cannula and in vitro with short term hypothalamic cultures. To evaluate synthesis of the three classes of peptides, specific mRNA species will be quantitated by solution hybridization/RNase protection assay and the mRNAs localized in the hypothalamus by in situ hybridization; specificity of action will be demonstrated with specific tachykinin and IL-1beta receptor antagonists. The results of our investigations should establish (a) the intermediary role of the nociceptive tachykinins and of NPY in the hypothalamus and (b) the protective role of steroids underlying the neuroendocrine effects of cytokines. Because the cytokines, tachykinins and NPY are widely distributed in the brain, we envision that the knowledge of cytokine-neuropeptide interaction gained from these studies will aid in deciphering the devastating progression of neurodegeneration caused by inappropriate expression of cytokines in the brain due to chronic inflammatory diseases.

Obesity is a multivariate disease which has reached epidemic proportions. The neurochemical basis of excessive body weight (BW) gain due to a positive imbalance in energy intake over expenditure, is virtually unknown.. Excessive BW gain may result either from hyperphagia due to impaired signaling in the interconnected appetite regulating network (ARN) in the hypothalamus or it may be of dietary origin, with our without hyperphagia. The objectives of this proposal are to identify the neurochemical disruptions and rearrangements (plasticity) at various loci in the ARN and leptin feedback that underlie excessive BW gain. In Aim 1, to test the hypothesis that up-regulation of the daily pattern of orexigenic signaling in the ARN is responsible for hyperphagia, we will assess (a) synthesis (gene expression and levels of NPY, GAL, and AGRP) in well characterized and novel hypothalamic sites; (b) activity (food-intake in response to administration of these peptides and antagonists); and (c) receptor gene expression in novel hypothalamic sites. Aim 2 will test the hypothesis that alteration of the tonic restraint exercised by central anorexigenic signals (CART and the melanocortin, alphaMSH) contributes to hyperphagia. Aim 3 will test the hypothesis that leptin signaling is altered during hyperphagia by analyzing changes in the daily pattern of leptin gene expression in adipocytes, plasma leptin levels and leptin receptor mRNA in discrete hypothalamic sites and the response to leptin administration. To test these three interrelated hypotheses, we propose to employ a rat model of hyperphagia produced by destruction of the paraventricular nucleus, the target site of action of orexigenic and anorexigenic peptides originating in the arcuate nucleus of the hypothalamus. Finally, in Aim 4, we propose to determine whether similar mechanisms operate in diet-induced obesity. Since the development of effective therapeutic strategies for humans requires a complete understanding of the impairment in neurochemical loci, this proposal to elucidate the neurochemical etiology of hyperphagia and excessive BW gain in rodents models is designed to meet this goal.