Differential Stimulation of Noradrenaline Release by Reversal of the Na+/Ca2+ Exchanger and Depolarization in Chromaffin Cells

We compared the effectiveness of Ca²⁺ entering by Na⁺/Ca²⁺ exchange with that of Ca²⁺ entering by channels produced by membrane depolarization with K⁺ in inducing catecholamine release from bovine adrenal chromaffin cells. The Ca²⁺ influx through the Na⁺/Ca²⁺ exchanger was promoted by reversing the normal inward gradient of Na⁺ by preincubating the cells with ouabain to increase the intracellular Na⁺ and then removing Na⁺ from the external medium. In this way we were able to increase the cytosolic free Ca²⁺ concentration ([Ca²⁺]_c) by Na⁺/Ca²⁺ exchange to 325 ± 14 nM, which was similar to the rise in [Ca²⁺]_c observed upon depolarization with 35 mM K⁺ of cells not treated with ouabain. After incubating the cells with ouabain, K⁺ depolarization raised the [Ca²⁺]_c to 398 ± 31 nM, and the recovery of [Ca²⁺]_c to resting levels was significantly slower. Reversal of the Na⁺ gradient caused an −6-fold increase in the release of noradrenaline or adrenaline, whereas K⁺ depolarization induced a 12-fold increase in noradrenaline release but only a 9-fold increase in adrenaline release. The ratio of noradrenaline to adrenaline release was 1.24 ± 0.23 upon reversal of the Na⁺/Ca²⁺ exchange, whereas it was 1.83 ± 0.19 for K⁺ depolarization. Reversal of the Na⁺/Ca²⁺ exchange appeared to be as efficient as membrane depolarization in inducing adrenaline release, in that the relation of [Ca²⁺]_c to adrenaline release was the same in both cases. In contrast, we found that for the same average [Ca²⁺]_c, the Ca²⁺ influx through voltage-gated channels was much more efficient than the Ca²⁺ entering through the Na⁺/Ca²⁺ exchanger in inducing noradrenaline release from chromaffin ceils. This greater effectiveness of membrane depolarization in stimulating noradrenaline release suggests that there is a pool of noradrenaline vesicles which is more accessible to Ca²⁺ entering through voltage-gated Ca²⁺ channels than to Ca²⁺ entering through the Na⁺/Ca²⁺ exchanger, whereas the adrenaline vesicles do not distinguish between the source of Ca²⁺.     

Comparative studies on antidepressant action of alprazolam in different animal models

Alprazolam, a new benzodiazepine from triazolobenzodiazepine group, produced anxiolytic action in the conflict test with potency similar to that of diazepam. The myorelaxant activity of the drug was relatively weak. Unlike desipramine, alprazolam failed to reduce the immobility of rats in the forced swim test and was unable to prevent clonidine-induced hypothermia. Alprazolam, unlike desipramine, failed also to potentiate behavioral effect of noradrenaline injected into the hippocampus. Alprazolam after acute but not chronic administration antagonized the synchronizing effect of clonidine on EEG pattern. On the other hand, alprazolam similarly to tricyclic antidepressants, prevented the suppression of dominance behavior by clonidine in rats competing for food. The results indicate that alprazolam acts only weakly upon noradrenergic mechanisms related to depression and to antidepressant action of drugs.     

Periodic lateralized epileptiform discharges: etiology, clinical aspects, seizures, and evolution in 130 patients.

The purpose of this study was to analyze the clinical aspects in 130 patients presenting periodic lateralized epileptiform discharges (PLEDs) in their EEG and to compare these results with those found in the literature. Etiology, neurologic deficit, seizure occurrence, and evolution were studied in each patient by historical review. The recordings were obtained on 8- or 16-channel EEGs with electrode placement according to the International 10-20 System. Recordings containing PLEDs were selected. PLEDs were defined as repetitive periodic, focal, or hemispheric epileptiform discharges (spikes, spike and waves, polyspikes, sharp waves) usually recurring every 1 to 2 seconds. The statistical study was carried out via the chi(2) test using the computer program SPSS. The main etiology found in this group of patients was stroke (61 of 130 patients). Other processes found were brain infections, tumors, hematomas, and several other entities grouped together as miscellaneous (anoxic encephalopathy, subarachnoid hemorrhage, craniocerebral trauma, Creutzfeldt-Jacob disease, migraine, multiple sclerosis, and aminophylline intoxication). Half of these patients (65 of 130) developed seizures, mostly partial motor seizures. No significant relation between etiology and seizures was found (chi(2) = 2.81, P = 0.4222). Seizures recurred in 14 of 130 patients during a follow-up of 14.5 months. PLEDs were not recorded in any EEG at the time of seizure recurrence. PLEDs constitute a distinctive but uncommon EEG phenomenon of repetitive, periodic, and stereotyped lateralized complexes. In agreement with the literature, PLEDs were associated with an acute process and occurred early during the course of the illness in all patients studied and were usually associated with structural lesions, with stroke being the main etiology. Traditionally, seizures occur with PLEDs but it is also accepted that they can exist in patients who never develop epileptic activity, either clinically or electrically, as demonstrated in 50% of the patients studied. No significant association between seizures and any etiology could be found. It was not demonstrated that the occurrence of seizures may influence the outcome in any way.     

Office-based anaesthesia for vitreoretinal surgery

The objectives of this study were to consider the effectiveness of local anaesthesia (LA) for office-based vitreoretinal (VR) surgery, the requirement to supplement the anaesthetic blockade, the demographic pattern of the sample and the acceptance of LA by patients. This prospective observational audit involved 111 patients that had undergone 128 VR procedures. Assessment data included: patient’s information, details of type of anaesthetic, and pain during surgery. A clinical audit was also carried out with telephone survey to establish the postoperative use of analgesics, the frequency of nausea, emesis, and insomnia. Results suggest that VR surgery can be carried out effectively and safely with LA, in an office-based surgery, provided that experienced surgeons exist. We noted a high degree of patient acceptance, a reasonable level of postoperative pain and a low frequency of nausea and vomits.     

Altered tachykinergic influence on gastric mechanical activity in mdx mice

This study investigated whether alterations in gastric activity in dystrophic mdx mouse can be attributed to dysfunctions of tachykinins. Endoluminal pressure was recorded and the expression of neuronal nitric oxide synthase (nNOS), NK1 and NK2 neurokinin receptors was investigated by immunohistochemistry. SR48968, NK2 receptor antagonist, but not SR140333, NK1 receptor antagonist, decreased the tone only in mdx gastric preparations. In the presence of N(omega)-nitro-l-arginine methyl ester (l-NAME), inhibitor of NOS, SR48968 reduced the tone also in normal stomach. [Sar(9), Met(O(2))(11)]-SP, agonist of NK1 receptors, caused tetrodotoxin-sensitive relaxations, antagonized by SR140333 or l-NAME, with no difference in the potency or efficacy between normal and mdx preparations. [beta-Ala(8)]-NKA(4-10), an NK2 receptor agonist, induced SR48968-sensitive contractions in both types of preparations, although the maximal response of mdx tissues was significantly lower than normal preparations. Immunohistochemistry demonstrated a consistent reduction of nNOS and NK2 receptor expression in mdx stomach smooth muscle cells and no change in nNOS and NK1 receptor expression in neurones. In conclusion, in mdx stomach the activation of NK2 receptors plays a role in the development of the tone, associated with a reduced NO production by muscular nNOS. The hypo-responsiveness to NK2 receptors could depend on the reduced expression of these receptors.