Quantitative changes in the normal and apoptotic thymocytes of pigs treated with anabolic doses of the β2 adrenergic agonist clenbuterol

Key signalling factors and pathways in the molecular determination of skeletal muscle phenotype

The molecular basis and control of the biochemical and biophysical properties of skeletal muscle, regarded as muscle phenotype, are examined in terms of fibre number, fibre size and fibre types. A host of external factors or stimuli, such as ligand binding and contractile activity, are transduced in muscle into signalling pathways that lead to protein modifications and changes in gene expression which ultimately result in the establishment of the specified phenotype. In skeletal muscle, the key signalling cascades include the Ras-extracellular signal regulated kinase-mitogen activated protein kinase (Erk-MAPK), the phosphatidylinositol 3'-kinase (PI3K)-Akt1, p38 MAPK, and calcineurin pathways. The molecular effects of external factors on these pathways revealed complex interactions and functional overlap. A major challenge in the manipulation of muscle of farm animals lies in the identification of regulatory and target genes that could effect defined and desirable changes in muscle quality and quantity. To this end, recent advances in functional genomics that involve the use of micro-array technology and proteomics are increasingly breaking new ground in furthering our understanding of the molecular determinants of muscle phenotype.

The role of the sympathetic nervous system in the thymus in health and disease

The existence of a network of immunoneuroendocrine interactions that results in the reciprocal modulation of the classical functions of each system is well established at present. Most of the evidence derives from studies on secondary lymphoid organs, such as the spleen and lymph nodes. In this article, several aspects relevant to understand the role of the sympathetic nervous system in the establishment of these interactions in the thymus are discussed. At present, the sympathetic innervation of the thymus, the expression of adrenergic receptors in thymic cells, particularly of β-adrenergic receptors, and the effect of sympathetic neurotransmitters, although mainly derived from in vitro or pharmacological studies, seem to be relatively well studied. However, other aspects, such as the relevance that immune-sympathetic interactions at the thymic level may have for certain diseases, specially autoimmune or other diseases that primarily involve the activation of the immune system, as well as how the integration of sympathetic and hormonal signals at local levels may affect thymic functions, certainly deserve further investigation.

Beta2 adrenergic agonist, clenbuterol, enhances working memory performance in aging animals

Previous studies using a mixed beta1 and beta2 adrenergic antagonist, propanolol, have indicated that beta adrenoceptors have little effect on the cognitive functioning of the prefrontal cortex. However, recent studies have suggested that endogenous stimulation of beta1 adrenoceptors impairs working memory in both rats and monkeys. Since propanolol has no effect on cognition, we hypothesized that activation of beta2 adrenoceptors might improve performance in a working memory task. We tested this hypothesis by observing the effects of the beta2 agonist, clenbuterol, on spatial working memory performance. Clenbuterol was either infused directly into the prefrontal cortex (rats) or administered systemically (monkeys). Results demonstrated that clenbuterol improved performance in many young and aged rats and monkeys who performed poorly under control conditions. Actions at beta2 adrenoceptors were confirmed by challenging the clenbuterol response with the beta2 adrenergic antagonist, ICI 118,551. The effects of clenbuterol were not universal and depended on the cognitive status of the animal: the drug moderately improved only a subset of animals with working memory impairment.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Beta2-agonist clenbuterol induced changes in the distribution of white blood cells in rats

Clenbuterol [CLE: 4-amino-alpha(t-butyl-amino)methyl-3,5-dichlorobenzyl alcohol] is well known as a potent beta2-adrenergic agonist and non-steroidal anabolic drug, and thus it is generally used for sports doping and asthma therapy. Although the functions of immune cells such as white blood cells (WBCs) have shown to be modulated through beta2-adrenoceptors, the effects of CLE on immune-responsive systems have not been elucidated systematically. Therefore, the effects of CLE on the number of WBCs were studied in rats. Male adult rats were divided into CLE-administered group and the control group to compare the number of total WBCs, neutrophils, monocytes, lymphocytes, eosinophils, and basophils. The administration (dose = 1.0 mg . kg(-1) body weight . day(-1), s.c.) of CLE was maintained for 30 days. CLE did not change the number of total WBCs during the experimental period. However, CLE increased significantly the number of neutrophils and monocytes, while CLE decreased drastically the number of lymphocytes and eosinophils. There was no significant change in the number of basophils between both groups. These results suggest that the administration of CLE induces drastic redistribution of WBCs in circulation without changing the number of total WBCs, and these responses of WBCs during the administration of CLE are sustained for at least 30 days.