Effects of gamma-aminobutyric acid on skate retinal horizontal cells: evidence for an electrogenic uptake mechanism.

In the retinae of many vertebrates, there are classes of horizontal cell that probably utilize gamma-aminobutyric acid (GABA) as a neurotransmitter. As with other amino acid transmitter agents, the postsynaptic action of GABA is thought to be terminated by uptake into neurons and glia surrounding the release site. The present study examined whether an uptake system for GABA could be detected in isolated skate horizontal cells by means of electrophysiological methods. Pressure ejection of GABA onto voltage-clamped horizontal cells produced an inward current that showed no sign of desensitization regardless of the GABA concentration. The dose-response relationship followed simple Michaelis-Menten kinetics, with a half-maximal response elicited at approximately 110 microM. Nipecotic acid produced a similar current and reduced the responses to GABA when introduced in the bath solution prior to the GABA pulse. On the other hand, application of 500 microM muscimol or 1 mM baclofen, GABAA and GABAB receptor agonists, respectively, were completely without effect. The GABA-induced current was not blocked by superfusion with 500 microM bicuculline, 500 microM picrotoxin, or 500 microM phaclofen. However, the responses to GABA were abolished when the cells were superfused in Ringer's solution in which choline or lithium had been substituted for sodium, and were reduced when the extracellular chloride concentration was decreased from 266 mM to 16 mM. Current-voltage data showed a maximal response to GABA when the cells were held at or below their resting potential. At more depolarized levels, the inward current became progressively smaller until, near +50 mV, it could no longer be detected; over the range tested (-90 to +50 mV), the response never reversed into an outward current. These findings suggest that the GABA-induced currents in skate horizontal cells are mediated by an electrogenic uptake mechanism.     

Comparison of muscular pulmonary arteries in low and high altitude hamsters and rats

Measurements were made of the ratio of medial area to total arterial area in the muscular pulmonary arteries of a fossorial species, the hamster, and a non-fossorial control, the rat. It was found that the medial area was less in hamsters than in rats. In addition, chronic hypoxic exposure resulted in further medial thickening in rats, while the hamster was unaffected. The hamster has previously been shown to have a blunted hypoxic pulmonary pressor response, and the present data indicate that this relative unresponsiveness is associated with less pulmonary vascular smooth muscle. In addition, the insensitivity to hypoxia of the pulmonary vasculature and a lack of vascular luminal narrowing may tend to minimize increases in pulmonary vascular resistance during chronic hypoxia in the hamster, and thus be beneficial adaptations for a burrowing species.     

Flesinoxan pretreatment differentially affects corticosterone, prolactin and behavioural responses to a flesinoxan challenge

To determine whether alterations in 5-HT_1A receptor mediated responses induced by a single injection with a selective 5-HT_1A receptor agonist is a transient effect, or whether the (de)sensitisation is more persistent, rats were pretreated with the selective and full 5-HT_1A receptor agonist, flesinoxan (3 mg/kg SC once daily) for either 1 day or 1 week. Twenty-four hour after the last pretreatment injection, rats were challenged with flesinoxan (3 mg/kg SC), and the effects on plasma corticosterone and prolactin levels, lower lip retraction and behaviour in the shock-probe burying test were determined. Several 5-HT_1A receptor mediated responses were modified differentially following the flesinoxan pretreatment. However, all changes induced by a single flesinoxan injection remained present upon repeated flesinoxan administration. The differential changes in the responses to flesinoxan cannot easily be explained by differences in pre-or postsynaptically 5-HT_1A mediated responses. The prolactin response to flesinoxan, which is thought to be mediated postsynaptically, was enhanced, whereas the corticosterone response to flesinoxan, which is also mediated postsynaptically, was attenuated. The presynaptically mediated lower lip retraction response was attenuated as well, whereas the behavioural effects of flesinoxan remained relatively unaffected following repeated flesinoxan administration. Upon prolonged flesinoxan pretreatment, the changes induced by a single flesinoxan injection remained present or increased further. Although repeated flesinoxan administration (1 day and 1 week) resulted in 20% lower plasma flesinoxan concentrations, this effect could not explain the neuroendocrine and behavioural findings. Received: 15 November 1996/Final version: 29 November 1996     

Inhibition of bleomycin lung toxicity by N-acetyl cysteine in the rat

N-acetyl cysteine (NAC) has recently been shown to have antioxidant properties, and since bleomycin produces pulmonary damage via free oxygen radical toxicity, the possible protective effect of NAC on bleomycin lung toxicity was investigated. Rats received saline (n = 7), NAC (n = 6), bleomycin (n = 7) or bleomycin and NAC (n = 6) by direct intratracheal injection. Seven days later the animals were killed and the lungs processed for histology or morphometry. All rats treated with bleomycin only had typical changes of bleomycin lung toxicity whereas the animals treated with bleomycin and NAC had minimal pathology. The control animals had normal lungs. These results were confirmed by morphometry which demonstrated significantly higher volume densities (p less than .01) of alveolar wall and free alveolar cells in the bleomycin group compared to the other 3 groups. It is concluded that NAC inhibits bleomycin lung toxicity when administered by direct intratracheal injection.     

The effect of various types of gastrostomy on the lower esophageal sphincter

Previous studies have demonstrated a cause and effect relationship between standard Stamm gastrostomy (SG) and subsequent gastroesophageal reflux (GER). To further investigate this clinical problem, three additional types of gastrostomy were evaluated in regard to their influence on the lower esophageal high pressure zone (LEHPZ). Twenty-three male cats were entered in the study weighing 2.6 to 3.6 kg. Baseline manometric studies of the LEHPZ were determined after ketamine anesthesia. In group I (n = 9), Witzel gastrostomy was performed over a 12 Fr catheter without fixation of the stomach to the anterior abdominal wall. In group II (n = 7), percutaneous gastrostomy was performed without fixation of the stomach to the anterior abdominal wall. In group III (n = 7), percutaneous gastrostomy was performed but the stomach was firmly fixed to the abdominal wall. LEHPZ pressures were then repeated 2 weeks postoperatively. Mean preoperative LEHPZ pressure for group I was 16.2 +/- 3.72 mmHg, group II was 16.5 +/- 6.91 mmHg, and group III was 18.3 +/- 5.59 mmHg. Mean postoperative pressure for group 1 was 14.7 +/- 4.26 mmHg, group II was 16.5 +/- 5.77 mmHg, and group III was 10.8 +/- 3.97 mmHg. LEHPZ pressure was similar preoperatively and postoperatively in groups I and II but was significantly decreased postoperatively (P less than .01) in group III. Contrast studies demonstrated maintenance of the angle of His in group 1 and II and alteration of the angle of His in group III. Gastrostomy associated with fixation of the stomach to the anterior abdominal wall results in decreased LEHPZ pressures. This predisposes the subject to GER.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tracheobronchopathia Osteochondroplastica

Summary: The clinical, pathological and physiological features of two patients suffering from tracheobronchopathia osteochondroplastica (TO) are described. Unequivocal evidence of extrapul-monary airways obstruction was not able to be obtained by lung function testing, despite extensive central airway involvement in both patients. TO is a rare condition of which there is only one other clinical report from this country. As the bronchoscopic appearance may closely resemble that of endobronchial neoplasm, TO should be remembered in the differential diagnosis of patients with haemoptysis.     

The effects of selective serotonin reuptake inhibitors on extracellular 5-HT levels in the hippocampus of 5-HT(1B) receptor knockout mice

The effects of two selective serotonin reuptake inhibitors on 5-hydroxy-tryptamine (5-HT) in the hippocampus were studied in wildtype and in 5-HT(1B) receptor knockout mice using in vivo microdialysis. Basal 5-HT levels in the hippocampus were not different between the two genotypes. The functional absence of 5-HT(1B) receptors was examined in the knockout mice by local infusion of the 5-HT(1B) receptor agonist, 1,4-Dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl)-5H-pyrrolo[3,2-b]pyridin-5-one (CP93129) into the hippocampus. CP93129 (1 microM) decreased 5-HT levels in wildtype mice, but not in 5-HT(1B) knockout mice. Systemic administration of the selective 5-HT reuptake inhibitor paroxetine (5 mg/kg, i.p.) increased extracellular 5-HT levels. The increase of 5-HT in 5-HT(1B) knockout mice was almost twofold higher than in wildtype mice. Systemic administration of selective 5-HT reuptake inhibitors stimulates both terminal 5-HT(1B) autoreceptors and somatodendritic 5-HT(1A) autoreceptors. Therefore, the selective 5-HT reuptake inhibitor, fluvoxamine, was applied locally into the hippocampus to investigate the role of the terminal 5-HT(1B) autoreceptors. Local administration of 0.3 microM fluvoxamine resulted in comparable increases in extracellular 5-HT in both genotypes, whereas 1.0 microM fluvoxamine produced a twofold greater increase in 5-HT levels in 5-HT(1B) knockout as compared to wildtype mice. In conclusion, the differences in hippocampal 5-HT output between wildtype and 5-HT(1B) knockout mice after local or systemic administration of selective 5-HT reuptake inhibitors show that 5-HT(1B) autoreceptors play a significant role in the inhibition of 5-HT release at serotonergic nerve terminals. In addition, the different dose-response to fluvoxamine suggests that 5-HT(1B) knockout mice have possible adaptations of 5-HT transporters in order to compensate for the loss of the terminal 5-HT(1B) autoreceptor.     

Pathways of proximal tubular cell death in bismuth nephrotoxicity

Colloidal bismuth subcitrate (CBS), a drug for treatment of peptic ulcers, has been reported in the literature to be nephrotoxic in humans when taken in high overdoses. To investigate the mechanism of bismuth nephropathy, we developed an animal model by feeding rats single doses of CBS containing 3.0 mmol Bi/kg body weight. Terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling assay, immunostaining for active caspase-3, and electron microscopy showed that proximal tubular epithelial cells die by necrosis and not by apoptosis within 3 h after CBS administration. Exposure of the renal epithelial cell lines NRK-52E and LLC-PK1 to Bi(3+) in citrate buffer served as an in vitro model of bismuth nephropathy. NRK-52E cells exposed to 100 microM Bi(3+) or more died by necrosis, as was demonstrated by nuclear staining with Hoechst 33258 and flow cytometry using Alexa(488)-labeled Annexin-V and the vital nuclear dye TOPRO-3. Bismuth-induced cell death of NRK-52E cells was not prevented by the caspase-3 inhibitor z-VAD-fmk, whereas this inhibitor did prevent cisplatinum-induced apoptosis. Mitochondrial dysfunction and induction of free radicals were shown not to be involved in bismuth nephrotoxicity. The early time point of damage induction in vitro as well as in vivo and the early displacement of N-cadherin, as found in previous studies, suggest that bismuth induces cell death by destabilizing the cell membrane. In conclusion, we showed that high overdose of bismuth induced cell death by necrosis in vivo as well as in vitro, possibly by destabilization of the cell membrane.