Dawn Sadler

The cellular structure and lipid/protein composition of adipose tissue surrounding chronically stimulated lymph nodes in rats

To test the hypothesis that chronic immune stimulation of a peripheral lymph node induces the formation of additional mature adipocytes in adjacent adipose tissue, one popliteal lymph node of large male rats was stimulated by local injection of 10 µg or 20 µg lipopolysaccharide three times a week for 6 weeks. Adipocyte volumes in sites defined by their anatomical relations to the stimulated and homologous unstimulated popliteal lymph nodes were measured, plus adipocyte complement of the popliteal depot, and the lipid and protein content of adipocytes and adipose stroma. The higher dose of lipopolysaccharide doubled the mass of the locally stimulated lymph node and the surrounding adipose tissue enlarged by the appearance of additional mature adipocytes. Similar but smaller changes were observed in the popliteal adipose depot of the unstimulated leg and in a nodeless depot. The lipid content of the adipocytes decreased and that of the stroma increased dose‐dependently in all samples measured but the changes were consistently greater in the depot surrounding the stimulated lymph node. The protein content of both adipocytes and stroma increased in samples surrounding the stimulated node. We conclude that chronic immune stimulation of lymphoid tissues induces the formation of more adipocytes in the adjacent adipose tissue. These findings suggest a mechanism for the selective hypertrophy of lymphoid‐containing adipose depots in the HIV‐associated adipose redistribution syndrome.

Changes in adipocytes and dendritic cells in lymph node containing adipose depots during and after many weeks of mild inflammation

The time course and cellular basis for inflammation‐induced hypertrophy of adipose tissue were investigated over 20 weeks in mature male rats. Mild inflammation was induced by subcutaneous injection of 20 µg lipopolysaccharide into one hind‐leg three times/week for 4 or 8 weeks, followed by up to 12 weeks ‘rest’ without intervention. Mean volume and frequency of apoptosis (TUNEL assay) were measured in adipocytes isolated from sites defined by their anatomical relations to lymph nodes, plus numbers of CCL21‐stimulated lymph node‐derived and adipose tissue‐derived dendritic cells. Experimental inflammation increased dendritic cells and adipocyte apoptosis in the locally stimulated popliteal depot and the lymphoid tissue‐associated regions of the contralateral popliteal and mesentery and omentum. Responses declined slowly after inflammation ended, but all measurements from the locally stimulated popliteal depot, and the omentum, were still significantly different from controls after 12 weeks rest. The locally stimulated popliteal adipose tissue enlarged by 5% within 4 weeks and remained larger than the control. We conclude that prolonged inflammation induces permanent enlargement, greater adipocyte turnover and increased dendritic cell surveillance in the adjacent adipose tissue and the omentum. The experiment suggests a mechanism for selective hypertrophy of lymphoid tissue‐associated adipose tissue in chronic stress and inflammatory disorders, including impaired lymph drainage, Crohns disease and HIV‐associated lipodystrophy, and a link between evolutionary fitness, sexual selection and aesthetically pleasing body symmetry. It would be useful for further study of molecular mechanisms in inflammation‐induced local hypertrophy of adipose tissue and development of specific therapies that avoid interference with whole‐body lipid metabolism.

Progestin-induced changes in play behaviour of the prepubertal rat

The effects of neonatal exposure to medroxyprogesterone acetate on later play behaviour was studied. The experiments reported here indicate that animals of both sexes exposed to the hormone neonatally show lower levels of rough-and-tumble play in the prepubertal period. The effect is primarily one on play initiation: the organisation of play behaviour once initiated is not significantly affected, and the effect on play does not seem to be secondary to effects on some other behaviour. Several hypotheses are considered that might account for these findings.

Site-specific differences in the action of NRTI drugs on adipose tissue incubated in vitro with lymphoid cells, and their interaction with dietary lipids

Existing theories of the origin of HIV-related adipose tissue redistribution syndrome cannot adequately explain simultaneous hypertrophy of certain depots and atrophy of others, or its occasional occurrence in untreated HIV infection. These experiments explore the hypothesis that hypertrophy of lymphoid tissue-containing adipose depots arises from drug-induced disruption to local interactions between perinodal adipocytes and activated lymphoid cells. Guinea pigs were fed on plain or lipid-supplemented (10% suet, sunflower or fish oil) chow ad libitum or restricted, and the popliteal lymph nodes were activated by repeated injection of lipopolysaccharide. Explants of perinodal and other samples from popliteal, mesentery, omentum and nodeless perirenal and epididymal depots were incubated with lymphoid cells and zidovudine, didanosine, lamivudine or stavudine at physiological concentrations (0.1-1 microg/ml) or interleukin-10 and interleukin-6, and basal and maximum lipolysis was measured. All drugs increased lipolysis from perinodal adipocytes, especially mesenteric, though less than exogenous cytokines. Effects on adipocytes from non-perinodal sites and nodeless depots were minimal. The sunflower-oil diet enhanced, and the fish-oil and restricted diets reduced, these effects. We conclude that these NRTI antiretroviral drugs modulate the local interactions between perinodal adipocytes and activated lymphoid cells. Local interactions, and hence the selective hypertrophy of node-containing adipose depots, may be curtailed by dietary manipulation.

The effects of dietary lipids on adrenergically-stimulated lipolysis in perinodal adipose tissue following prolonged activation of a single lymph node

The effects of feeding beef suet (mostly saturated and monoenoic fatty acids), sunflower oil (rich in n-6 fatty acids) and fish oil (rich in n-3 fatty acids) on the response of mesenteric, omental, popliteal and perirenal adipocytes to experimentally-induced local inflammation were studied in adult guinea pigs. After 6 weeks on the experimental diets, the animals were fed standard chow, and lipopolysaccharide was injected unilaterally daily for 4 d to induce swelling of one popliteal lymph node. Basal lipolysis in the perinodal adipocytes of all depots studied was higher in the sunflower oil-fed animals than in the controls fed on standard chow, and lower in those fed on suet or fish oil. Dietary lipids altered rates of lipolysis during incubation with l0(-5) M noradrenaline in all samples studied from the locally-activated popliteal depot, but only in adipocytes within 5 mm of a large lymph node in the other depots. The fish-oil diet attenuated the spread of increased lipolysis within the locally-activated popliteal adipose tissue, and from this depot to other node-containing depots. These experiments show that n-6 polyunsaturated fatty acids promote and n-3 fatty acids suppress the spread of immune activation to adipocytes within and between depots, and alter the sensitivity of perinodal adipocytes to noradrenaline. Dietary effects are reduced or absent in adipocytes in sites remote from lymph nodes, and thus such samples do not adequately represent processes in perinodal adipose tissue. These results are consistent with the hypothesis that perinodal adipocytes interact with adjacent lymphoid cells during immune responses.

Scent-marking behaviour in response to conspecific odours by the rat, Rattus norvegicus

Abstract The scent-marking behaviour of male and female rats in response to conspecific odours was investigated in two experiments. The results of the first experiment indicated that exposure to conspecific odours generally led to an increase in marking rates. However, no sex differences were found, and large differences in marking responses according to the sex of the odour donor were only found for dioestrous females. These results do not suggest that the primary function of scent-marking in this species is sexual. In the second experiment, odour sources differed not only in the sex of the donor, but also in their relative familiarity to the animal being tested. This experiment showed that males marked more in response to odours from familiar (non-related) females. Females did not differ significantly on measures of marking but did display greater interest in odours from unfamiliar males. The results are discussed in relation to possible functions of marking in this species.

Modification of juvenile play and other social behaviour in the rat by neonatal progestins: Further studies

The effects of altering neonatal levels of progestins on the later development of social play behaviour was studied. Progestin levels were raised in experiment one by administering injections of either progesterone or medroxyprogesterone acetate. This indicated that exposure to either hormone led to reduced levels of social play in juvenile rats of both sexes, confirming earlier reports of lowered levels of play following medroxyprogesterone obtained via maternal milk. In Experiment 2, endogenous progestin levels were lowered by administration of the antiserum to progesterone. The prediction that this should result in raised levels of juvenile play was supported for males, but not for females. Females in Experiment 2 by contrast showed a decrease in play. Possible reasons for this sex difference in response to progesterone antiserum are discussed.

Dietary fatty acids influence the appearance of tumour necrosis factor-α receptors on adipocytes following an immune challenge

Rats were fed from weaning on chow supplemented with suet or sunflower oil (10 % (w/w) each). The appearance of receptors for tumour necrosis factor-alpha on perinodal adipocytes from the popliteal depot following a subcutaneous injection of bacterial lipopolysaccharide was examined. In rats fed on sunflower oil-supplemented chow receptors appeared at a time similar to that described in rats fed unsupplemented chow, but in rats fed on chow supplemented with suet receptor appearance was significantly delayed. The popliteal adipocytes were found to contain different proportions of fatty acids as assessed by GLC. These preliminary results suggest that the fatty acid component of the diet can, by influencing the triacylglycerol-fatty acids within adipocytes, directly alter the time course of an early inflammatory immune response.

Effects of modulating neonatal progestins and androgens on the development of play and other social behavior in the rat

Rough-and-tumble play is sexually dimorphic in many species of mammals. Effects of androgen exposure on this behavior have been well documented, although the possible role of other hormones is less well known. This paper reports experiments in a series designed to investigate effects of neonatal exposure to progestins on the development of juvenile play behavior in rats. Specifically, the effects of altering levels of progestins and androgens in combination on the subsequent development of play behavior was studied, in order to investigate further the mechanism of progestogenic effects. We have previously [L. I. A. Birke and D. Sadler (1984). Physiol. Behav. 33, 217-219] reported an apparently anomalous effect of lowering endogenous progesterone using the antiserum given postnatally; this was predicted to raise levels of juvenile play. The prediction was, however, supported only for males; treated females showed lower levels of play than controls. The present study was designed to investigate these effects further, and to test hypotheses about the mode of action of neonatal progestins. Using various combinations of neonatal progestins (progesterone or medroxy-progesterone acetate, MPA), and testosterone or the antiserum to testosterone, we analyzed the amounts of play and other social behavior shown by juvenile rats. The data support a hypothesis that the previously reported effects of progestin exposure on play result from weakly androgenic actions of the progestins, which presumably compete with other androgens in males. The cellular mechanisms involved are, however, unknown.

The effects of exercise and dietary restriction on the activities of hexokinase and phosphofructokinase in superficial, intra-abdominal and intermuscular adipose tissue of guinea-pigs

1. The activities per gram of adipose tissue of hexokinase and phosphofructokinase were higher in the centre two intermuscular adipose depots of guinea-pigs than in any of the seven superficial and intra-abdominal depots studied. 2. The capacity for glucose utilization was reduced following about 3 months of regular exercise in all adipose depots studied except in the popliteal depot. The proportion of lipid decreased, and that of protein increased, in this intermuscular depot following regular, strenuous exercise, but it did not enlarge disproportionately. 3. We suggest that certain intermuscular adipose depots may act as a local energy source for adjacent muscles. The anatomical relations of adipose tissue to muscle may be an integral part of its physiological function.