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T J Bartness

Publications and source records attributed to T J Bartness.

At least 19 recordsLinked to original sources
PubMed2003

Brainstem melanocortin 3/4 receptor stimulation increases uncoupling protein gene expression in brown fat.

Central administration of melanocortin 3 and 4 receptor (MC3/4-R) agonists increases energy expenditure, with the hypothalamus commonly held as the primary site of action. It is also clear, however, that MC4-R are expressed in caudal brainstem structures of relevance to the control of energy expenditure. Three experiments investigated whether hindbrain MC-R contribute to the energy expenditure effects of central MC3/4-R agonist treatments; in each, we examined the effect of fourth intracerebroventricular (i.c.v.) administration of a MC3/4-R agonist, MTII (three injections, each separated by 12 h), on uncoupling protein 1 (UCP-1) gene expression in brown adipose tissue (BAT). First, we compared the effects of fourth and third i.c.v. administration of MTII and found that the hindbrain and forebrain treatments were equally effective at elevating UCP-1 mRNA expression in BAT compared with the respective vehicle-treated group results. A second experiment demonstrated that the fourth i.c.v. MTII-induced rise in UCP-1 expression was mediated by sympathetic outflow to BAT by showing that this response was abolished by surgical denervation of BAT. In the third experiment, we showed that chronic decerebrate rats, like their neurologically intact controls, elevated UCP-1 mRNA expression in response to fourth i.c.v. MTII administration. Taken together, the results indicate that: 1) there is an independent caudal brainstem MC3/4-R trigger for a sympathetically stimulated elevation in BAT UCP-1 gene expression, and 2) the MTII-induced rise in UCP-1 expression can be mediated by circuitry intrinsic to the caudal brainstem and spinal cord.

Adipose Tissue, Brown↗
PubMed2002

Sympathoadrenal system differentially affects photoperiodic changes in humoral immunity of Siberian hamsters (Phodopus sungorus).

Siberian hamsters (Phodopus sungorus) rely on photoperiod as a primary cue to coordinate seasonally appropriate changes in physiology and behaviour. Among these seasonal changes is reduced immune function in short 'winter-like' days, compared to long 'summer-like' days. Previous evidence suggests that immune function is regulated, in part, by the sympathoadrenal system. The precise role of the sympathoadrenal system in regulating photoperiodic changes in immune function, however, remains unspecified. The goal of the present study was to examine the differential contributions of direct sympathetic innervation of immune target tissue, as well as adrenal medullary catecholamines, to photoperiodic changes in immune function in male Siberian hamsters. In Experiment 1, hamsters underwent either bilateral surgical removal of the adrenal medulla (ADMEDx), or sham surgeries, and were maintained in long (LD 16 : 8) or short days (LD 8 : 16). In Experiment 2, hamsters received either surgical denervation of the spleen, or sham surgeries, and were then housed in long or short days. Serum anti-KLH IgG concentrations and splenic norepinephrine (NE) content were determined in both experiments. Short-day hamsters had reduced humoral immunity compared to long-day hamsters. ADMEDx reduced immune function, but only in long-day hamsters. In contrast, splenic denervation reduced humoral immunity, but only in short-day hamsters. Splenic NE content was increased in short days and by ADMEDx. NE content was markedly reduced in denervated hamsters compared to sham-operated hamsters. Collectively, these results suggest that the sympathoadrenal system is associated with photoperiodic changes in immune function.

Adrenal Glands↗
PubMed2002

Metabolic signals, hormones and neuropeptides involved in control of energy balance and reproductive success in hamsters.

In the 'postgenome era', most research on the neuroendocrine control of energy homeostasis has focused on hormonal and neuropeptide control of food intake (i.e. the amount of food eaten) in rats and mice. The amount of food consumed is influenced by both the motivation to procure food and the consummatory act of ingestion. In some species, the rate of food intake remains relatively constant, while survival is maintained via changes in food procurement, external storage and internal expenditure. For example, in hamsters, metabolic signals, peripheral hormones and central neuropeptides influence hunger motivation, food hoarding and changes in energy expenditure without necessarily influencing the amount of food ingested. A similar suite of metabolic signals, hormones and neuropeptides is involved in optimizing reproductive success under fluctuating energetic conditions. Reproductive processes are inhibited or delayed when energy expenditure outstrips energy intake and mobilization from storage. Estrous cyclicity in Syrian hamsters is sensitive to the availability of oxidizable glucose, but the presence of central glucose alone is not sufficient for normal estrous cycles. Food deprivation-induced anestrus does not depend upon food deprivation-induced increases in concentrations of adrenal hormones such as glucocorticoids. If hormones such as insulin and leptin play a role, they might do so by modulating the availability of glucose detected at extra-hypothalamic sites, instead of or in addition to direct effects on the mechanisms that control gonadotropin releasing hormone secretion. Despite our ability to measure and manipulate gene transcription, understanding of fuel homeostasis requires examination of indirect effects of hormones and neuropeptides on peripheral metabolism, attention to the motivational as well as consummatory aspects of ingestion, and the study of behaviour in a natural or seminatural context.

Animals↗
PubMed2001

Novel method for localized, functional sympathetic nervous system denervation of peripheral tissue using guanethidine.

A simple technique for local chemical sympathectomy of peripheral tissues is described using guanethidine. Multiple microinjections of guanethidine were made into inguinal or epididymal white adipose tissue (IWAT and EWAT) pads or spleens of hamsters. Guanethidine virtually abolished the sympathetic innervation of both EWAT and IWAT, as measured by the absence of significant norepinephrine (NE) tissue content two weeks later and as suggested by the two-fold increase in IWAT mass characteristic of surgically induced WAT denervation. These measures were not affected in the contralateral pads given equivolumetric injections of saline. Guanethidine injections into the spleen lead to a functional sympathectomy, as indicated by significant depletions of NE content. Because guanethidine treatment did not decrease body mass, induce ptosis, or spread to closely associated adjacent tissue (contralateral EWAT pad), no chemical-induced malaise or global sympathetic denervation was suggested. Guanethidine was more effective than two other local sympathectomy treatments, injections of the sympathetic neurotoxin anti-dopamine-beta-hydroxylase saporin or surgical denervation, in decreasing IWAT NE content and increasing IWAT pad mass. Collectively, these results suggest that locally applied, chemical sympathectomy with guanethidine provides an effective, restricted method for sympathectomizing WAT, spleen and likely other peripheral tissues.

Adipose Tissue↗
PubMed2001

Neurochemical phenotype of sympathetic nervous system outflow from brain to white fat.

The sympathetic innervation of white adipose tissue (WAT) appears to be a dominant mechanism triggering lipolysis. The purpose of this study was to determine the neurochemical phenotype of neurons comprising the sympathetic outflow from brain to WAT. This was accomplished by injecting Siberian hamster WAT with a viral retrograde transneuronal tract tracer, the pseudorabies virus (PRV), in combination with immunocytochemical characterization of several neurotransmitters or their synthetic enzymes in the brain. Catecholaminergic (tyrosine hydroxylase [TH] and dopamine-beta-hydroxylase [DBH] immunoreactivity) and peptidergic (arginine vasopressin [AVP] and oxytocin [OXY] immunoreactivity) neurons were part of this outflow, but the percentage of double-labeled cells was small, consistent with previous studies. Brainstem PRV + TH- or PRV + DBH-labeled cells were in previously identified noradrenergic areas (A5, A6, and subcoeruleus, rostroventrolateral medulla [RVL], some reticular nuclei). Forebrain double labeling was greatest in the paraventricular (TH, AVP, OXY) and suprachiasmatic (AVP) nuclei, both implicated in the central control of lipolysis. Differences between the PRV double labeling reported here for WAT versus that of other sympathetic peripheral targets were PRV + DBH in A5 and RVL, and PRV + TH in RVL and in the lateral paragigantocellular and lateral reticular nuclei. Collectively, these results begin to identify the neurochemical identity of the sympathetic outflow from brain to WAT.

Adipose Tissue↗
PubMed2001

Effects of foraging effort on body fat and food hoarding in Siberian hamsters.

Food hoard size varies inversely with body fat levels in Siberian hamsters. If food hoarding only increases when body fat decreases, then hamsters foraging for their food should only increase food hoarding when foraging efforts decrease body fat ("lipostatic hypothesis"); however, if food hoarding increases whenever there is an energy flux away from fat storage, then it should increase regardless of significant body fat decreases ("metabolic hypothesis"). Female Siberian hamsters (Phodopus sungorus) earned food pellets after completion of a programmed number of wheel revolutions (Immobilized Wheel [free access to food], Free Wheel [wheel active, free food], and 10, 50, 100, and 200 revolutions/pellet). Hamsters were killed after 19 days and inguinal, retroperitoneal, and parametrial white adipose tissue (WAT) pads (IWAT, RWAT, and PWAT, respectively) were harvested and carcass composition determined. Food hoard size increased fourfold with the availability of running wheels alone (Free Wheel), increased threefold with low foraging levels (10 and 50 revolutions/pellet), but was nearly abolished at the highest foraging level (200 revolutions/pellet). Surplus food (earned, not eaten or hoarded) was significantly greatest at the lowest level of foraging. As foraging effort increased, PWAT mass decreased the most (<10 revolutions/pellet), while RWAT and IWAT mass only were decreased at the highest foraging effort. Carcass lipid content only was significantly decreased at the highest foraging effort, yet food hoarding was nearly abolished at that level. Collectively, these results demonstrate that body fat levels and food hoarding can be uncoupled with increases in foraging effort. J. Exp. Zool. 289:162-171, 2001.

Adipose Tissue↗
PubMed2001

The regulation of total body fat: lessons learned from lipectomy studies.

Surgical removal of body fat (partial lipectomy) is a means of directly reducing fat such that metabolic and behavioral responses can be readily attributed to the lipid deficit. If total body fat is regulated, then lipectomy should trigger compensatory increases in nonexcised white adipose tissue (WAT) mass and/or regrowth at excision sites. Many species, including laboratory rats and mice, show lipectomy-induced compensatory recovery of body fat. Those animals exhibiting naturally occurring annual adiposity cycles, such as ground squirrels and hamsters, do so most impressively reaching seasonally appropriate body fat levels indistinguishable from controls. Reparation of the lipid deficit occurs without an increase in food intake, and generally through enlargement of non-excised WAT mass, rather than regrowth of excised WAT. A body fat regulatory system involving humoral and sensory neural inputs to the brain as well as sympathetic neural outputs from brain to adipose tissue is presented. Collectively, the lipectomy model appears useful for testing mechanisms controlling adiposity, or individual depot growth, and offers insight into how lipid stores fluctuate naturally.

Adipose Tissue↗
PubMed2001

The biology of white adipocyte proliferation.

Expanded adipose tissue mass increases the risk for many clinical conditions including diabetes, hypertension, coronary atherosclerotic heart disease, and some forms of cancer. Therefore, it is imperative that we understand the mechanisms by which fat pads expand. The enlargement of fat cells during the development of obesity has been previously hypothesized to be a triggering factor for the proliferation of new fat cells. There is now a preponderance of evidence that adipose tissue is a source of growth factors such as IGF-I, IGF binding proteins, TNF alpha, angiotensin II, and MCSF that are capable of stimulating proliferation. The relative importance of these autocrine/paracrine factors in the normal control of preadipocyte proliferation is unknown. In addition, the proliferative response of preadipocytes to the paracrine milieu is undoubtedly modulated by neural inputs to fat tissue and/or serum factors. Together, these multiple regulatory controls orchestrate overall and region-specific adipose tissue cellularity responses associated with the development of hyperplastic obesity. Both in vivo and in vitro studies are needed to understand the complex, interacting physiological mechanisms by which growth of this important organ is regulated.

Adipocytes↗
PubMed2001

CNS sympathetic outflow neurons to white fat that express MEL receptors may mediate seasonal adiposity.

Many animals show seasonal changes in adiposity that are triggered by changes in the photoperiod. For example, in short "winterlike" days, the nocturnal duration of pineal melatonin (MEL) secretion increases ultimately resulting in body fat decreases by Siberian hamsters. These decreases in body fat are mediated through increases in the sympathetic drive on white adipose tissue (WAT). The central nervous system (CNS) origins of the sympathetic outflow from brain to WAT include the suprachiasmatic nucleus (SCN), an area necessary for the reception of season-encoded MEL signals in Siberian hamsters. Therefore, we tested whether SCN neurons that are part of the sympathetic outflow to WAT also express MEL receptors (MEL(1a)). This was accomplished by labeling the sympathetic outflow from brain to WAT using a transsynaptic retrograde tract tracer, the pseudorabies virus (PRV), injected into inguinal WAT combined with labeling of brain MEL(1a) receptors using in situ hybridization. We found PRV-labeled neurons that also expressed MEL(1a)-receptor mRNA in several brain regions including the SCN. Thus the increased duration of MEL secretion in short days may increase MEL(1a)-receptor stimulation that, in turn, increases the sympathetic drive on WAT, thereby increasing lipolysis and decreasing adiposity.

Adipose Tissue↗
PubMed2001

Direct innervation of white fat and adrenal medullary catecholamines mediate photoperiodic changes in body fat.

Seasonal adjustments in Siberian hamster adiposity are triggered by day length changes [i.e., short "winter-like" days (SDs) elicit body fat decreases vs. long "summer-like" days (LDs)]. These and other white adipose tissue (WAT) mass decreases traditionally have been ascribed to lipolysis triggered by sympathetically mediated, adrenal medullary released epinephrine; however, recent evidence suggests that direct sympathetic innervation of WAT also is important. Therefore, the contributions of WAT sympathetic innervation and adrenal medullary catecholamines to SD-induced decreases in adiposity were tested. Siberian hamsters were surgically bilaterally adrenal demedullated (ADMEDx) or sham ADMEDx, and all had one inguinal WAT (IWAT) pad sympathectomized via locally injected guanethidine, with the contralateral pad serving as a within-animal innervated control. One-half of the hamsters remained in LDs; the remainder was transferred to SDs. Guanethidine and ADMEDx abolished IWAT norepinephrine and adrenal epinephrine contents, respectively. Although sympathetic denervation or ADMEDx alone did not block SD-induced decreases in IWAT mass, their combination did. These results suggest that both adrenal catecholamines and the sympathetic innervation of WAT interact to decrease SD-induced decreased adiposity.

Adipose Tissue↗
PubMed2001

SCN efferents to peripheral tissues: implications for biological rhythms.

The suprachiasmatic nucleus (SCN) is the principal generator of circadian rhythms and is part of an entrainment system that synchronizes the animal with its environment. Here, we review the possible communication of timing information from the SCN to peripheral tissues involved in regulating fundamental physiological functions as revealed using a viral, transneuronal tract tracer, the pseudorabies virus (PRV). The sympathetic nervous system innervation of the pineal gland and the sympathetic outflow from brain to white adipose tissue were the first demonstrations of SCN-peripheral tissue connections. The inclusion of the SCN as part of these and other circuits was the result of lengthened postviral injection times compared with those used previously. Subsequently, the SCN has been found to be part of the sympathetic outflow from the brain to brown adipose tissue, thyroid gland, kidney, bladder, spleen, adrenal medulla, and perhaps the adrenal cortex. The SCN also is involved in the parasympathetic nervous system innervation of the thyroid, liver, pancreas, and submandibular gland. Individual SCN neurons appear connected to more than one autonomic circuit involving both sympathetic and parasympathetic innervation of a single tissue, or sympathetic innervation of two different peripheral tissues. Collectively, the results of these PRV studies require an expansion of the traditional roles of the SCN to include the autonomic innervation of peripheral tissues and perhaps the modulation of neuroendocrine systems traditionally thought to be controlled solely by hypothalamic stimulating/inhibiting factors.

Animals↗
PubMed2001

North American Association for the Study of Obesity annual meeting.

The annual meeting of the North American Association for the Study of Obesity was held in Long Beach, CA, USA with approximately 1500 attendees, including basic and clinical obesity/food intake researchers and local and regional physicians. The meeting highlighted a clear trend toward pharmacological approaches directed at the brain control of obesity/food intake/energy expenditure as well as combinations of therapies, eg, drug and dietary, two drugs, drug and behavioral change. The magnitude of the body weight losses in the human studies was typically 5 to 15% of starting weight, which was recognized as unsatisfactory. Examples of new developments included attempts to block receptors of accepted neuropeptides involved in food intake and energy expenditure, such as the neuropeptide Y (NPY) 5 receptor, documentation of the ability of current drugs used to treat other disorders that also decrease body weight/food intake, such as the antidepressant drug bupropion SR and the anti-epileptic agent topiramate, as well as development of new peptide receptor agonists, such as A-200, a modified human recombinant leptin preparation. Recognition of dietary supplements and over-the-counter medications as potential obesity promoting triggers, such as melatonin were also presented.

Journal Article↗
PubMed2000

Short-day increases in aggression are inversely related to circulating testosterone concentrations in male Siberian hamsters (Phodopus sungorus).

Many nontropical rodent species display seasonal changes in both physiology and behavior that occur primarily in response to changes in photoperiod. Short-day reductions in reproduction are due, in part, to reductions in gonadal steroid hormones. In addition, gonadal steroids, primarily testosterone (T), have been implicated in aggression in many mammalian species. Some species, however, display increased aggression in short days despite basal circulating concentrations of T. The goal of the present studies was to test the effects of photoperiod on aggression in male Siberian hamsters (Phodopus sungorus) and to determine the role of T in mediating photoperiodic changes in aggression. In Experiment 1, hamsters were housed in long and short days for either 10 or 20 weeks and aggression was determined using a resident-intruder model. Hamsters housed in short days for 10 weeks underwent gonadal regression and displayed increased aggression compared to long-day-housed animals. Prolonged maintenance in short days (i.e., 20 weeks), however, led to gonadal recrudescence and reduced aggression. In Experiment 2, hamsters were housed in long and short days for 10 weeks. Half of the short-day-housed animals were implanted with capsules containing T whereas the remaining animals received empty capsules. In addition, half of the long-day-housed animals were castrated whereas the remaining animals received sham surgeries. Short-day control hamsters displayed increased aggression compared to either castrated or intact long-day-housed animals. Short-day-housed T treated hamsters, however, did not differ in aggression from long-day-housed animals. Collectively, these results confirm previous findings of increased aggression in short-day-housed hamsters and suggest that short-day-induced increases in aggression are inversely related to gonadal steroid hormones.

Aggression↗
PubMed2000

Photoperiod and gender affect adipose tissue growth and cellularity in juvenile Syrian hamsters.

Adult Syrian hamsters are reproductively active and at their annual body and lipid mass nadirs in long 'summer-like' days (LDs), whereas they are reproductively quiescent and at their annual body and lipid mass peaks in short 'winter-like' days (SDs). Because hamsters are born in the SDs of fall in the wild, the development of the reproductive system of juvenile Syrian hamsters exposed to SDs has been studied in the laboratory, but not the development of body and lipid mass. Therefore, we tested the effect of SDs on white adipose tissue (WAT) growth and cellularity (fat cell number, FCN; fat cell volume, FCV) in 3-15-week-old male and female Syrian hamsters. SDs increased body fat in both genders. This effect was partially independent of the decline in gonadal steroids because gonadal regression was only beginning in males (Week 11) and females (Week 15) when carcass lipid content was significantly increased in males, and nearly so in females. This SD-induced increased adiposity was reflected in few regional differences in WAT growth, and then only in males (increased mesenteric and inguinal WAT masses). SDs increased FCV for all non-gonadal WAT and increased FCN only in retroperitoneal WAT. SDs blunted the LD-induced increased FCV and FCN of parametrial and epididymal WAT, respectively. For nearly all conditions and pads, FCV peaked first, followed by increased FCN, the latter accounting for nearly all WAT growth. These data appear to support the view that adipocyte proliferation is stimulated once a 'critical' FCV is reached.

Adipocytes↗
PubMed2000

Catecholaminergic enzymes, vasopressin and oxytocin distribution in Siberian hamster brain.

Siberian hamsters exhibit marked seasonal changes in physiology and behavior that are triggered by the daylength and that can be mimicked in the laboratory by changing the photoperiod, making them a convenient and popular species for the study of regulatory biology. Because no atlas of neurotransmitter distribution exists for this species, the purpose of the present study was to map the distribution of cell bodies containing catecholaminergic synthetic enzymes (tyrosine hydroxylase and dopamine-beta-hydroxylase) and several neurotransmitters (arginine vasopressin and oxytocin) in Siberian hamster brain using immunocytochemistry. The distributions of these catecholaminergic synthetic enzymes and neurotransmitters largely were similar to those for Syrian hamsters with some notable differences. There were novel groups of neurotransmitter- or synthetic enzyme-immunoreactive neurons such as tyrosine hydroxylase-immunoreactive cells in the bed nucleus of the stria terminalis, dopamine-beta-hydroxylase-immunoreactive cells in the motor trigeminal, hypoglossal, and paraabducens nuclei, and arginine vasopressin- and oxytocin-immunoreactive cells within the nucleus of the diagonal band, dorsal hypothalamic area, and arcuate nucleus compared with Syrian hamsters. This is the first description of the distribution of cell bodies for some commonly studied catecholaminergic synthetic enzymes and peptides in Siberian hamsters.

Animals↗
PubMed2000

Co-expression of melatonin (MEL1a) receptor and arginine vasopressin mRNAs in the Siberian hamster suprachiasmatic nucleus.

Durational melatonin signals, cued by the photoperiod and generated by the pineal gland, are processed in the brain to induce seasonally appropriate physiological and behavioural adaptations. The melatonin receptor subtype MEL1a (also known as mt1) appears to regulate seasonal responses. Single label in situ hybridization for MEL1a receptor mRNA revealed labelled cells in several brain regions of Siberian hamsters, including the suprachiasmatic nucleus, the paraventricular nucleus of the thalamus, and the reuniens nucleus of the thalamus. To characterize suprachiasmatic nucleus cells containing MEL1a receptor mRNA, we used 35S-labelled cRNA probes for MEL1a receptor mRNA in combination with digoxigenin-labelled cRNA probes for vasopressin, somatostatin, or orphan retinoid Z receptor beta (RZRbeta; a putative nuclear melatonin receptor). Cells in the suprachiasmatic nucleus that contained MEL1a receptor mRNA also contained mRNAs for vasopressin and RZRbeta, but not for somatostatin. These data suggest that suprachiasmatic nucleus vasopressin cells may respond to melatonin signals, raising the possibility that suprachiasmatic nucleus vasopressin output mediates some of the effects of melatonin on seasonal or circadian responses.

Animals↗
PubMed1999

Control of reproductive and energetic status by environmental cues in a desert rodent, Shaw's jird.

The photoperiod is the controller of reproductive cycles in temperate climates for most mammalian species. Several nonphotoperiodic cues appear to control reproductive status at lower latitudes. We tested the roles of the photoperiod or water availability on the reproductive status of the desert-dwelling Shaw's jird (Meriones shawi) trapped from a moderately temperate climate (approximately 30 degrees N in Egypt). Males and females were transported to the laboratory and, in Experiment 1, were housed in either the longest (LDs) or shortest (SDs) photoperiod that occurs naturally at this latitude (14 h light, 10 h dark, and 10 h light, 14 h dark, respectively). In Experiment 2, LD-housed male jirds were subjected to a water availability schedule that inhibits reproductive status in a closely related species (Meriones unguiculatus). Specifically, one group had no free water, but had lettuce available once a week for 24 h (control jirds received free water for 10-60 min/day). Neither photoperiod nor free-water deprivation affected reproductive status of male or female jirds. That is, neither testes mass nor spermatogenetic activity (males), nor uterine mass nor folliculogenesis (females) were affected by either condition. In addition, photoperiod did not affect body or white adipose tissue (WAT) masses, although SDs decreased carcass lipid in males. Free-water deprivation decreased body and WAT pad masses, and all carcass components. Collectively, these results suggest that changes in day length or water availability alone do not affect reproductive status in Shaw's jird.

Adaptation, Physiological↗