Showing papers on "Temporal cortex published in 1974"

Effects of Ablating the Striate Cortex on a Successive Pattern Discrimination: Further Study of the Visual System in the Tree Shrew (Tupaia glis)

Abstract: Previous studies have shown that treeshrews without striate cortex can easily discriminate between two simple patterns presented simultaneously. It has been suggested that these animals cannot actually ''identify'' patterns without striate cortex, but simply detect differences between two stimuli by scanning. The present study showed that tree shrews with damage to striate cortex, including complete removal, can discriminate horizontal from vertical stripes when presented either simultaneously or successively. This result supports the view that tree shrews do have the capacity to identify patterns in the absence of striate cortex. The present study also showed that tree shrews can perform the same discrimination following damage to the temporal cortex. However, if the lesion included all of the striate cortex plus a large amount of temporal cortex, the animals failed to discriminate the orientation of stripes even when they were displayed simultaneously.

Physiological disposition and biotransformation of levo-methadone-1-3h in the dog

Abstract: A method with minimal sensitivity of 1 to 2 ng, previously developed for levo -methadone after small doses has been used to estimate this drug in selected anatomical areas of the central nervous system and the peripheral tissues of the dog. After a 2 mg/kg (free base) s.c. dose of levo -methadone-1- 3 H to the dog, peak levels of drug in plasma (143 ng/ml) and in different anatomical areas of the central nervous system (1270-2029 ng/g) occurred at two hours. Measurable quantities of drug persisted in different areas of the dog brain and peripheral tissues for at least three weeks. At the same time the concentrations in plasma were barely detectable at periods of one and three weeks after drug administration. High levels of methadone were observed in lung, liver, spleen, kidney, heart and intestine with somewhat lower concentrations in muscle and fat. The approximate half-life of levo -methadone in dog plasma after a 2 mg/kg s.c. dose was six to seven hours and that in temporal cortex, hypothalamus, cerebellum and caudate nucleus ranged between three and four hours. The mean percentages of free drug excreted in the urine and feces of dogs 96 hours after a single 2 mg/kg s.c. dose were 19.4%, conjugated acid-hydrolyzable metabolites, 5.4% and total radioactivity, 68.3%. The values of conjugated metabolites and total radioactivity in dogs given chronic injections of methadone were significantly lower than those in acute animals. levo -Methadone was extensively metabolized by: 1) N-dealkylation and cyclization to substituted pyrrolidine and pyrroline metabolites; 2) N-oxidation; 3) hydroxylation in the para position of the aromatic nucleus; 4) keto group reduction; 5) glucuronide conjugation of resultant hydroxyl groups; and 6) minor conversion to secondary and primary amines. Persistence of levo -methadone and a metabolite in selected anatomical areas of the central nervous system of the dog and the binding of the metabolite to a specific brain protein could conceivably lead to a biochemical alteration of the receptor site and result in a reduced ability of the drug to initiate a pharmacological response. Possible relevance of these observations to the phenomena of pharmacological tolerance and the protracted course of the withdrawal syndrome observed with methadone are described.