Isolation versus grouped housing in rats: Differential effects of low doses of heroin in the place preference paradigm

Male Long Evans rats were reared from weaning (21–23 days) either in isolation or in groups of four for 40 days. Animals were then individually introduced to a testing apparatus consisting of two distinct chambers. A modified place preference paradigm was used consisting of 3 phases: (1) An habituation phase (4 days) during which rats were allowed free access to the entire test apparatus for 15 min. periods daily; (2) A conditioning phase (4 days) during which rats were confined to their non-preferred side for 15 minutes each day immediately following subcutaneous injection of 0, 20, 40 and 80 μg/kg of heroin HCl; (3) A test phase (1 day) during which rats were again allowed free access to the testing chamber following injection of vehicle. The difference in time spent on the conditioned side during habituation and test periods was determined. The group-reared rats showed similar effects for all doses of heroin whereas the same magnitude of drug effect was attained only at the highest dose used in the isolated rats. This differential sensitivity to heroin in the place preference paradigm is discussed in terms of the modification of behavioral effects of opiates by environmental influences.     

SIRT1 regulates nuclear number and domain size in skeletal muscle fibers

Skeletal muscle fibers are giant multinucleated cells wherein individual nuclei govern the protein synthesis in a finite volume of cytoplasm; this is termed the myonuclear domain (MND). The factors that control MND size remain to be defined. In the present study, we studied the contribution of the NAD⁺‐dependent deacetylase, sirtuin 1 (SIRT1), to the regulation of nuclear number and MND size. For this, we isolated myofibers from mice with tissue‐specific inactivation (mKO) or inducible overexpression (imOX) of SIRT1 and analyzed the 3D organisation of myonuclei. In imOX mice, the number of nuclei was increased whilst the average MND size was decreased as compared to littermate controls. Our findings were the opposite in mKO mice. Muscle stem cell (satellite cell) numbers were reduced in mKO muscles, a possible explanation for the lower density of myonuclei in these mice; however, no change was observed in imOX mice, suggesting that other factors might also be involved, such as the functional regulation of stem cells/muscle precursors. Interestingly, however, the changes in the MND volume did not impact the force‐generating capacity of muscle fibers. Taken together, our results demonstrate that SIRT1 is a key regulator of MND sizes, although the underlying molecular mechanisms and the cause‐effect relationship between MND and muscle function remain to be fully defined.     

Parasympathetic and sympathetic postganglionic synapses in ureterovesical autonomic pathways

Summary Histochemical techniques for acetylcholinesterase and catecholamine show that ureterovesical ganglia of both cat and dog contain dense intraganglionic cholinergic and adrenergic plexuses. Ramifications of both plexuses surround most cholinergic and adrenergic ganglion cell bodies as pericellular synaptic plexuses. Similar pericellular plexuses exist around extraganglionic cholinergic and adrenergic ganglion cells. Both adrenergic and cholinergic synaptic fibers persist in denervated pregnaglionic nerve-free specimens, indicating that cholinergic synaptic fibers are postganglionic parasympathetic in nature. The presence of adrenergic (postganglionic sympathetic) and postganglionic parasympathetic synapses around cell bodies in ureterovesical ganglia provides a morphologic basis for the sympathoinhibitory and muscarinic parasympatho-excitatory phenomena described in these ganglia.