Behavioral and neurochemical correlates of morphine and hypoxia interactions

Dopamine, acetylcholine, and glutamate interactions in aging. Behavioral and neurochemical correlates

Aging, hypoxia, and thiamin deficiency diminish motor performance. Similar alterations of ACh, DA, and glutamate metabolism accompany hypoxia, thiamin deficiency, and aging. Both aging and hypoxia reduce ACh release and stimulate DA and glutamate release. Presynaptic enhancement of DA and glutamate release may be important in the production of cell damage that may contribute, in part, to age-related deficits in motor as well as cognitive function. The decline in ACh release may be important in the production of the cognitive deficits. An understanding of the interactions of neurotransmitters in hypoxia and thiamin deficiency aids our understanding of normal aging and increases the possibility of developing better treatments for the multiple neurotransmitter deficiencies that accompany many metabolic, age-related, and chronic degenerative disorders.

Effect of age on behavioral and enzymatic changes during thiamin deficiency

Open field behavior and whole brain enzymatic activities were determined during thiamin deficiency in two strains of young, as well as in aged mice. In young CD-1 mice, thiamin deficiency reduced total distance traveled and vertical movements after 7 days and the decline was more than 50% by day 9. The behavioral deficit was highly correlated to decreases in 2-oxoglutarate dehydrogenase activity (KGDH). The open field behavior of Balb/c mice was about 40% less than in CD-1 mice and responded in a qualitatively different manner to thiamin deficiency. The activity of the Balb/c mice increased and then decreased with thiamin deficiency. The activity of 3 month old mice peaked on day 6 (126% of initial score), whereas 10 and 30 month mice showed a much greater increase (about 175% of initial scores), but on day 7. Although the activity of the thiamin dependent enzyme transketolase (TK) was affected similarly at all ages, the activity of KGDH in the aged brain was more sensitive to thiamin deficiency than in the young; KGDH activity declined 41%, 57% or 74% at 3, 10, or 30 months, respectively. Thus, the current mouse model is an attractive one to study the interaction of thiamin deficiency with aging.

Locomotor activity as a predictor of times and dosages for studies of nicotine's neurochemical actions

Nicotine's action on the central nervous system is complex and likely involves an interaction of neurotransmitters. To determine the time after administration of nicotine and dosage for neurochemical studies, locomotor activity of CD-1 mice was determined at 5 min intervals between 0-60 min. A low nicotine dosage (0.05 mg/kg) did not alter activity 5-15 min after drug injection, but increased activity 28% at 15-25 min post-injection. A high dosage (0.8 mg/kg) reduced total distance 62% and rearing 87% at 5-15 min; at 15-25 minutes total distance declined 56% and rearing 69%; all measures returned to control values after 30 minutes; rearing then increased at 40 min after nicotine. Pretreatment (15 min before nicotine) with mecamylamine (1.0 mg/kg), but not hexamethonium (1.0 mg/kg), prevented the depressant effect of nicotine. Dopamine (DA) and its metabolites as well as acetylcholine (ACh) synthesis were measured at the point of nicotine's maximal depressant action. Striatal levels of dihydroxyphenylacetic acid (DOPAC) were increased and ACh utilization was reduced in striatum (-25%) and cortex (-24%) 10 min after nicotine (0.8 mg/kg). Mecamylamine, while preventing the depressant effect of nicotine on locomotor activity, did not alter its effects on DA metabolism. These results demonstrate that the behavioral outcome of acute nicotine treatment is time and dose-dependent. Nicotine's depressant action appears not to be due to altered DA but may be related to changes in carbohydrate and acetylcholine metabolism.