Effects of d- and l-amphetamine on habituation and sensitization of the acoustic startle response in rats

In a series of 3 experiments the effects of 2, 4, 8, or 16 mg/kg d-amphetamine and 4, 8, 16, or 32 mg/kg l-amphetamine on acoustic startle amplitude in the rat were investigated. d-Amphetamine was 4--5 times as potent as l-amphetamine in augmenting startle amplitude. Startle potentiation was associated with vigorous stereotypies but the resultant cage movement could not account for the change in startle. Pretreatment with alpha-methyl-p-tyrosine (100 mg/kg, 1 hr before) had only a slight depressant effect on startle but essentially eliminated augmentation of startle by either d-amphetamine (8 mg/kg) or l-amphetamine (32 mg/kg). d-Amphetamine did not have a direct effect on startle but instead enhanced sensitization produced by the startle stimuli without altering sensitization produced by background white noise or habituation. The results suggest that startle sensitization is enhanced by increased availability of catecholamines and, by virtue of the different potencies of the d- and l-isomers, that dopamine and norepinephrine may affect startle differently.

Effects of 6-hydroxydopamine and alpha-methyl-para-tyrosine on the acoustic startle response in rats

The acoustic startle response was measured in rats after depletion of central catecholamines either chronically (through intraventricular injection of 6-hydroxydopamine) or acutely (through intraperitoneal injections of alpha-methyl-para-tyrosine). Chronic depletion resulted in an augmented startle response which could not be attributed to a failure of habituation or enhanced sensitization, while acute depletion depressed startle amplitude. The results were interpreted as evidence that catecholamines normally exert a facilitatory influence on the startle response and that the enhanced response seen in the chronically lesioned animal reflects the potentiation of the role of catecholamine-containing neurons through the development of denervation supersensitivity. This interpretation is consistent with other observations which suggest that catecholamines play a general role in modulating thresholds to aversive events.

Early inhibition of hepatic bilirubin conjugation after paracetamol (acetaminophen) administration in the rat

Administration of paracetamol (acetaminophen) 13.3 mmol kg-1 body weight to rats led 2 h later to an impaired capacity to conjugate an intravenous load of bilirubin, in the absence of biochemical signs of liver damage and before the reactive metabolite of the drug had become bound within the liver. In addition, paracetamol inhibited the excretion into the bile of conjugated bilirubin, although the plasma levels of the uncomjugated pigment only were elevated. This study provides additional evidence that hepatic glucuronide conjugation is impaired early after paracetamol overdose, and that this precedes the accumulation and binding of the hepatotoxic metabolite of the drug within the liver cells.

The chemistry of 2,1-benzisothiazoles. IX. The reaction of 3-chloro-substituted 2,1-benzisothiazoles with nucleophiles and the preparation of(2,1-Benzisothiazol-3-yl)acetic acid

3-Chloro-2,1-benzisothiazole (2; R = H, R? = Cl) and 3,5-dichloro-2,1- benzisothiazole (2;R,R? = Cl) react readily with nucleophiles, and yield 3-substituted products. Acid hydrolysis of one such product, ethyl (2,1-benzisothiazol-3-yl)cyanoacetate (2; R = H, R? = CH(CN)CO2Et),affords (2,1-benzisothiazol-3-yl)acetic acid (2; R = H, R? = CH2CO2H), an auxin analogue.

The chemistry of 2,1-benzisothiazoles. VIII. Tautomerism of 2,1-Benzisothiazolin-3-one and the preparation of N- and O-alkylated derivatives

Both N-alkyl and O-alkyl derivatives of 2,1-benzisothiazolin-3-one (1) have been prepared by unambiguous syntheses. Comparison of ultraviolet spectra indicates that (1) exists in the keto form rather than as its tautomer 2,1-benzisothiazol-3-ol (2). Alkylation of the anion of (1) yields N-alkylated products.

A method of direct chemical brain stimulation in behavioral studies using microiontophoresis

A method of microiontophoresis for direct chemical brain stimulation in chronic, awake animals for behavioral studies is described. Carbachol-induced drinking was employed to test the method. Fluid-filled micropipettes (tip diameters: 5-15 mu) were stereotaxically implanted in the region of the nucleus of the diagonal band. Up to 3 weeks after recovery, ions could be ejected directly into the brain of awake animals by passing a direct current through the pipette. Iontophoretic ejection of carbachol in doses as low as 0.05 mug elicited drinking. This effect could be blocked by intraperitoneal injection of 0.5 mg/kg scopolamine. Passage of choline ions produced no detectable effect. The microiontophoretic technique allows direct chemical brain stimulation in chronic, awake animals without major changes in tonicity or volume that can occur with crystalline or fluid implants through cannulae. Additionally, the technique allows precise localization, precise control of dosage, and minimal damage at the site of stimulation.

Emergency endoscopy after gastrointestinal haemorrhage in 50 patients with portal hypertension

Endoscopy was carried out in 50 patients with oesophageal varices within 24 hours of a major haematemesis or melaena. Sources of bleeding were identified in 42 of the cases and in only 19 patients was bleeding due to oesophageal varices. Bleeding from gastric varices was present in 11 patients, and a variety of acute and chronic lesions made up the remainder. In contrast with previous series haemorrhage from erosive gastric lesions was seen in only five patients and was no more common in 23 patients with alcoholic cirrhosis than in the group as a whole.

rates of N-methylation of 2-Methybenzotriazole, 2,1,3-Benzoxadiazole, 2,1,3-Benzothia(or Selena)diazole, 1,2,5-Oxadiazole and 1,2,5-Thiadiazole

The rates of quaternization of the title compounds with dimethyl sulphate are reported. The reactivity order is Se > NMe > S > O; benzofusion has only a small rate-diminishing effect.

Rates of N-methylation of N-methylpyrazole, isothiazole and isoxazole and their 2,1- and 1,2-benzologues

The rates of quaternization of N-methylpyrazole, isothiazole and isoxazole and of their 2,l- and 1,2-benzologues with methyl iodide in dimethyl sulphoxide and with dimethyl sulphate are reported. All compounds quaternized at 33� and a number of new compounds were isolated. The order of reactivity in each series is NMe > S > O. Benzofusion was shown to be rate-diminishing with one exception. 2,l-Benzisoxazole reacted faster than did isoxazole and the reason for this behaviour is discussed.