The response of the newborn rat to injury. I. Vascular and humoral aspects

Intravital microscopy for the study of mouse microcirculation in anti-inflammatory drug research: Focus on the mesentery and cremaster preparations

Intravital microscopy is an extremely useful tool used as a qualitative and quantitative way of observing leukocyte-endothelial cell interactions in-vivo. This present article reviews the methods of the technique of intravital microscopy, in particular focussing on the mesentery and cremaster preparations. It focuses on how to actually carry out the experiments required to directly observe and localize the changes in the function of the microcirculation. Where necessary the reader is asked to refer to a selection of highly acclaimed publications, which should enable the reader to truly appreciate, and if necessary perform, the technique of intravital microscopy.

Role of adrenal medulla in development of sexual dimorphism in inflammation

Many inflammatory diseases show a female predilection in adults, but not prepubertally. Because sex differences in the inflammatory response in the adult rat are mediated, in part, by sexual dimorphism in adrenal medullary function, we investigated the contribution of the adrenal medulla to the ontogeny of sexual dimorphism in inflammation. Whilst there was no sex difference in the magnitude of the plasma extravasation (PE) induced by the potent inflammatory mediator bradykinin (BK) in prepubertal rats, in adult rats BK-induced PE was markedly greater in males. Also, adult male rats, gonadectomized prior to puberty, had a lower magnitude of BK-induced PE than did adult male controls, whilst adult females gonadectomized prepubertally had higher BK-induced PE than did controls. In rats gonadectomized after puberty, the magnitude of BK-induced PE in adult males was not affected, whilst in females it resulted in significantly higher BK-induced PE, similar to the effect of prepubertal gonadectomy. When tested prepubertally, adrenal denervation increased the magnitude of BK-induced PE in females, but not in males. In contrast, in both males and females tested as adults, but castrated prepubertally, and in gonad-intact adult females, adrenal denervation significantly increased the magnitude of BK-induced PE. Adrenal denervation in prepubertal females given adult levels of 17beta-oestradiol produced a marked enhancement in the denervation-induced increase in magnitude of BK-induced PE compared to females not exposed prematurely to sex hormones. These studies suggest that an adrenal medulla-dependent inhibition of BK-induced PE is present in female but not male rats, and is enhanced by oestrogen but suppressed by testosterone.

Long-term effects of short-lasting early local inflammatory insult

We examined the long-term effects of a short-lasting (approximately 24 h) inflammatory insult generated by injections of 0.25% carrageenan (1 microl/g) into the hindpaws of newborn (P0) rat pups. At P60 animals which experienced this early inflammatory insult showed significant alterations in the withdrawal responses to noxious stimulation of the affected paws. Furthermore, in the absence of ongoing inflammation, the withdrawal latencies to heat stimulation and withdrawal thresholds to mechanical stimulation were increased by such experience. In the presence of ongoing CFA-induced inflammation, however, the same early experience decreased these parameters of response to noxious stimulation. These data suggest that early inflammatory insult may differentially affect the aspects of nociceptive circuitry involved in transient pain sensitivity and in inflammation-induced hyperalgesia.

Constitutional factors and the local and general responses to injury

The different constitutional factors which may affect the response to injury and the problems which must be considered in evaluating any injury model are discussed. Species, age, sex, nutrition and the presence of disease are discussed in relation to an injury model based on hind limb ischaemia, with reference to the extensive literature.

Inflammatory mechanisms in the newborn

Both the vascular and cellular aspects of inflammation were studied in rats aged from 6 hours to 2 months. The onset of a vascular permeability reaction was found to vary according to the age of rat and type of permeability agent injected. Induction of acute inflammations (turpentine pleurisy, 48/80 and dextran-induced foot oedema) in new born rats revealed a marked reduction of exudate/oedema formation compared with adult rats. These observations were related to a lack of histamine and 5-HT-mediated increased vascular permeability during the inflammatory reactions of newborn rats. Qualitative differences were observed between the acute inflammatory pleural cell exudates of newborn and adult rats after intra-pleural injection of dextran. In contrast to adults, polymorphs were observed to dominate the newborn reaction, and the peak accumulation of these cells was delayed. The mononuclear cells of 4-day lesions induced by sub-cutaneous implantation of glass coverslips showed a higher rate of mitosis in newborn animals, compared with adults. Ultrastructural studies of the mononuclear cells of peritoneal exudates induced by carrageenan indicated that those of newborn rats contained fewer lysosomes than adults. The Golgi apparatus of newborn mononuclear cells was observed to be poorly-developed compared with adult mononuclear cells.

The response of the newborn rat to intraleural dextran: vascular and cellular aspects

The development of hind paw oedema, in response to dextran injected in to the pleural cavity of rats, has been shown to differ with the age of rat studied. It was found that newborn rats were less responsive than adults, with respect to oedema formation induced by dextran. Attempts to suppress the dextran-indu.ced foot oedema using mepyramine and cyproheptadine, were successful only in rats from the adult age group. A semiquantitative analysis was made of the inflammatory cellular exudate produced by the intrapleural injection of dextran into rats of different ages. In contrast to the reaction of adult rats, it was found that accumulation of polymorphs in the pleura of newborn animals was delayed. The polymorph was the dominant cell type found in exudates induced either by intrapleural saline or dextran, in rats from the 6-hour age group. This contrasted strikingly with comparable exudates induced in adult rats, whose major cell type was the mononuclear cell (after saline), and the polymorph, followed by the mononuclear cell (after dextran). Fewer cells were observed in the reaction of 6-hour-old rats, compared with 7-day-old animals following intrapleural injection of the same volume of a 6-percent solution of dextran.

The response of the newborn rat to injury. II. Histopathological aspects and mononuclear cell turnover

Histopathological investigations of skin lesions induced by subcutaneous implantation of glass coverslips were carried out in rats between birth and adulthood. Differences were found between the cellular reactions of newborn and adult rats to this irritant. An increased number of cells was found in the skin lesions of newborn rats, compared with adults. Uptake of a 30-min. pulse of tritiated thymidine by mononuclear cells was found to be higher in newborn skin lesions than in those of adult rats. The reverse was observed for the mononuclear cells adherent to implanted glass coverslips. Giant cells were less evident on coverslips removed from the skin of newborn rats.

The mast cells of the newborn rat diaphragm and their response to histamine liberators

The mast cell population of rat diaphragm was estimated between birth and adulthood and found to rise with an increase in the age of rat studied. Degranulation of these cells was observed in rats from all age groups, following treatment with compound 48/80 and dextran. The association of mast cells with the blood vessel wall in adult rat diaphragm was not observed in the comparable tissues of newborn rats. These findings are discussed in relationship to the poor vascular permeability reactions exhibited by newborn and young rats.