Reliability of spike and burst firing in thalamocortical relay cells.

The reliability and precision of the timing of spikes in a spike train is an important aspect of neuronal coding. We investigated reliability in thalamocortical relay (TCR) cells in the acute slice and also in a Morris-Lecar model with several extensions. A frozen Gaussian noise current, superimposed on a DC current, was injected into the TCR cell soma. The neuron responded with spike trains that showed trial-to-trial variability, due to amongst others slow changes in its internal state and the experimental setup. The DC current allowed to bring the neuron in different states, characterized by a well defined membrane voltage (between -80 and -50 mV) and by a specific firing regime that on depolarization gradually shifted from a predominantly bursting regime to a tonic spiking regime. The filtered frozen white noise generated a spike pattern output with a broad spike interval distribution. The coincidence factor and the Hunter and Milton measure were used as reliability measures of the output spike train. In the experimental TCR cell as well as the Morris-Lecar model cell the reliability depends on the shape (steepness) of the current input versus spike frequency output curve. The model also allowed to study the contribution of three relevant ionic membrane currents to reliability: a T-type calcium current, a cation selective h-current and a calcium dependent potassium current in order to allow bursting, investigate the consequences of a more complex current-frequency relation and produce realistic firing rates. The reliability of the output of the TCR cell increases with depolarization. In hyperpolarized states bursts are more reliable than single spikes. The analytically derived relations were capable to predict several of the experimentally recorded spike features.

[Computerized tomographic diagnosis of hepatocarcinoma after injection of lipiodol into the hepatic artery]. / Diagnostic scanographique des hépatocarcinomes après injection de lipiodol dans l'artère hépatique.

Iodized oil (lipiodol) injected into the hepatic artery is selectively retained by hepatocarcinomas, as demonstrated by computerized tomography (CT) performed one week after the injection. The value of this technique for the diagnosis of hepatocarcinoma was assessed in a retrospective study of 45 patients. In 39 per cent of the cases intrahepatic tumoral extension was determined by the iodized oil which showed tumoral nodules that had not been detected by conventional methods, such as ultrasonography and CT alone. The lesions revealed by the iodized oil were small nodules around the main tumour. The combined iodized oil-CT technique plays an important role in the choice of treatment, especially when surgical excision is contemplated. It might also contribute to an early diagnosis of hepatocarcinoma in patients at risk, as illustrated by four of our cases where conventional morphological examinations had been negative.

[Emergency colonoscopy in lower intestinal occlusion]. / La coloscopie en urgence au cours des occlusions intestinales basses.

From March 1980 to June 1983, 23 patients presenting with clinical and or radiological manifestations of colonic obstruction and with uncertainty as to medical/surgical possibilities of management, underwent emergency colonoscopy in the intensive care unit of our Digestive Disease Department. The investigations were conducted without preparation (enema) or premedication, using an ordinary colonoscope. The endoscopic examination led to correct diagnosis in 21 patients out of 23 (91.3 p. 100). The main causes of occlusion were: colonic or rectal cancer (11 cases), Ogilvie's syndrome (6 cases), volvulus of the sigmoid colon (3 cases). Endoscopy contributed to treatment in eight patients with good results in six. It was unsatisfactory in two cases of volvulus of the sigmoid colon which recurred. In two instances complications occurred which were attributable to the method: one pneumoperitoneum without frank perforation and a transtumoral perforation in a case of sigmoid cancer, discovered at laparotomy. No septic complication or mortality resulted from endoscopy. Colonoscopy under normal conditions should not be advocated systematically, but can be used as a method of investigation and possibly of therapy in selected cases of colonic obstruction admitted into intensive care units.

Role of cholinergic mechanisms in the response to secretin of isolated canine pancreas.

The effects of carbamylcholine (CCH, 100 mug per hr) and of atropine (0.25, 1.0, and 10.0 mg per hr) on the response of the exocrine pancreas to secretin (0.1, 0.5, and 5.0 clinic units per hr) were studied using the isolated canine pancreas perfused with whole heparin-treated blood. CCH induced a sharp decrease in D50 (dose of secretin which elicits half the calculated maximal response) but no increase in maximal response to secretin. Experiments performed under different haemodynamic conditions show that this potentiating effect (synergism) is partly due to vasomotor modifications and chiefly to the action of CCH on the receptor of secretin. Although this work indicates that cholinergic tone is not necessary for secretin-induced hydrelatic response to occur, it evidences that this cholinergic tone plays a major role in modulating the pancreatic response to submaximal doses of secretin. It has also been found that large doses of atropine (10 mg per hr) were necessary to achieve a complete inhibition of enzymatic response to CCH. Even at these high doses, however, enzymatic response to secretin and cholecystokinin-pancreozymin were not significantly inhibited.