Autonomic Innervation of Pancreas in Egyptian Spiny Mouse (Acomys cahirinus, Desmarest)

The aim of the study was to obtain details of the morphology of the autonomic innervation of pancreas. Six adult Egyptian spiny mice (Acomys cahirinus, Desmarest) were studied for the presence and location of autonomic fibres and cells in the pancreas. The macromorphological investigations were performed using the thiocholine method adapted for this type of specimens. For processing tissues two histochemical techniques were used: thiocholine method on activity of AChE and the glyoxylic acid method for adrenergic structures. Cholinergic fibres and small autonomic ganglia were found among the secretory sections and along the pancreatic duct and both pancreaticoduodenal arteries, and its branches, reaching the Langerhans islets and forming around them a kind of net. From 24 to 40 AChE-positive ganglions in the whole exocrine part were observed. The highest density of cholinergic fibres was observed in the head of pancreas. Numerous adrenergic fibres that accompanied blood vessels as well as interlobular and intralobular ducts were found inside the exocrine parts of the pancreas. Neither adrenergic cells or adrenergic fibres were observed inside the pancreatic islets. Our results can be used in comparative anatomy studies of pancreas in mammals.

Regulation of the M current: transduction mechanism and role in ganglionic transmission

Slow excitatory postsynaptic potentials in sympathetic ganglia often involve suppression of a voltage-dependent potassium current termed the M current. This current is suppressed by the muscarinic action of acetylcholine, by peptides such as luteinizing hormone releasing hormone, and sometimes by α-adrenoceptor agonists. Activation of β-adrenoceptors sometimes produces weak potentiation. The voltage dependence of the M current is such that its suppression increases the excitability of ganglionic neurones. Since this sometimes leads to spontaneous discharge, activation of the slow excitatory postsynaptic potential mechanism (or modulation of M current) within a sympathetic ganglion produces effects that manifest in the autonomic outflow to the target organ. In frogs, M currents are present in the neurones of both paravertebral sympathetic ganglia and cardiac parasympathetic ganglia. Since the M current is suppressed by adrenaline in the parasympathetic ganglia and these ganglia often receive adrenergic fibres from sympathetic ganglia, this might reflect an important means of interaction between the two branches of the autonomic system. At the cellular level, M-current suppression is little affected by drugs that interfere with membrane phosphorylation–dephosphorylation processes. This observation is discussed in relationship to the current understanding of the transduction mechanism for agonist-induced M-current suppression.Key words: autonomic nerve, K+ channel, G protein, muscarinic mechanism, adrenergic mechanism.