Electroshock afterdischarges are related to neuronal oscillability: neuronal models of Aplysia.

Identifiable giant neurons of Aplysia explored intracellularly behave differently at the offset of an intracellular electroshock (IES) or after a synaptic 'tetanization', according to their functional type: neurons of the stable type depolarize and fire at the offset of the IES, anodal or cathodal, thus eliciting an afterdischarge (AD). The threshold of this AD is lowered if the neuron is destabilized, i.e. converted from the stable to an oscillatory type (for instance by decalcification). Neurons normally of the tonic type are more sensitive to an IES, eliciting a longer afterdischarge than the stable neurons. Extracellular electroshock (EES) anodal or cathodal, applied directly on desheathed somata of Helix give long-lasting afterdischarges at the offset. In addition, EES stimulating presynaptic terminals or axons leads to a high frequency synaptic input on remote neurons. At the offset of this input either prolonged synaptic afterdischarges or postsynaptic rebounds of the membrane potential sustaining bursts of decreasing amplitude denote apparent oscillatory properties of the synaptically activated neuron. Finally, any conversion by convulsants of tonic neurons to oscillators highly facilitates the elicitation of afterdischarges of axons simultaneous to paroxysmal depolarization shifts of the homologous somata. These results indicate that afterdischarge elicitation is highly facilitated (low threshold) in normal oscillatory neurons and/or chemically destabilized neurons.

Pancreas divisum: magnetic resonance cholangiopancreatography findings.

Pancreas divisum is a common congenital abnormality of the pancreas that results from the lack of fusion between the dorsal and ventral pancreatic ducts during foetal development. In these cases, the dorsal duct becomes the main pancreatic duct and drains most of the pancreas. Pancreas divisum is mainly asymptomatic, but the prevalence of pancreas divisum is higher in patients with chronic abdominal pain and idiopathic pancreatitis. A study of 20 patients with pancreas divisum (12 men and eight women; aged 19-77 years; mean age 39 years) and who underwent magnetic resonance cholangiopancreatography (MRCP), was performed. In our series, pancreas divisum was clinically manifested as unexplained episodes of abdominal pain (mean duration 3.2 years) (60 percent), mild pancreatitis (30 percent) or incidentally (ten percent). MRCP demonstrated non-communicating dorsal and ventral ducts, independent drainage sites, a dominant dorsal pancreatic duct, and a small cystic dilatation of the dorsal duct at minor papilla (santorinocoele). In this pictorial essay, we review the most common MRCP features of pancreas divisum.

[Increase in birefringence and hypoexcitability of unmyelinated nerve by volatile anesthetics]. / Augmentation de biréfringence et hypoexcitabilité du nerf amyélinique par les anesthésiques volatils

Increase in total positive birefringence, or decrease in negative birefringence of an unmyelinated nerve by volatile anesthetics occur simultaneously during the decrease of the action potential, and suggest axomembrane molecular reorganization possibly concerning the phospholipid layer.

Decrease in magnetic anisotropy of external segments of the retinal rods after a total photolysis.

The magnetic anisotropy of a polymembrane cell, such as the external segment of the frog retinal rod, is defined as the difference between the axial magnetic susceptibility (chiar), chia - chir = deltachi of the segment. After the total photolysis of the rhodopsin in situ, deltachi decreases a significantly by 20%. This decrease in magnetic anisotrophy should involve a subtle molecular disorder, mostly due to an alteration of the rhodopsin molecule.

Hypothermic decrease in microtubule density and birefringence in unimyelinated axons.

The density of microtubules, T.D. (number of tubules/unit area) is highest in small crab nerve axons. After cooling of the nerve at 0 degrees C, the tubule density tends to zero (T.D. 2% of the normothermic value). Once the cooled nerves are returned in normothermia, the reconstitution of the microtubules is evidenced (T.D. = 90% of the initial normothermic value). Therefore cooling "depolymerizes" the tubules, whereas rewarming leads to their "repolymerization." These results definitely improve the interpretation of the birefringence decrease by cooling: as tubules and filaments contribute to the positive fraction of the total positive birefringence, their depolymerization by cooling explains to a large extent the decrease in total birefringence.