Faculty Bibliography

In a cortical P2 fraction, [14C]gamma-aminobutyric acid ([14C]GABA), [14C]glycine, [14C]taurine, and [14C]glutamic and [14C]aspartic acids are transported by four separate high-affinity transport systems with L-glutamic acid and L-aspartic acid transported by a common system. GABA transport in cortical synaptosomal tissue occurs by one high-affinity system, with no second, low-affinity, transport system detectable. Only one high-affinity system is observed for the transport of aspartic/glutamic acids; as with GABA transport, no low-affinity transport is detectable. In the uptake of taurine and glycine (cerebral cortex and pons-medulla-spinal cord) both high- and low-affinity transport processes could be detected. The high-affinity GABA and high-affinity taurine transport classes exhibit some overlap, with the GABA transport system being more specific and having a much higher Vmax value. High-affinity GABA transport exhibits no overlap with either the high-affinity glycine or the high-affinity aspartic/glutamic acid transport class, and in fact they demonstrate somewhat negative correlations in inhibition profiles. The inhibition profiles of high-affinity cortical glycine transport and those of high-affinity cortical taurine and aspartic/glutamic acid transport also show no significant positive relationship. The inhibition profiles of high-affinity glycine transport in the cerebral cortex and in the pons-medulla-spinal cord show a significant positive correlation with each other; however, high-affinity glycine uptake in the pons-medulla-spinal cord is more specific than that in the cerebral cortex. The inhibition profile of high-affinity taurine transport exhibits a nonsignificant negative correlation with that of the aspartic/glutamic acid transport class

K+-equilibrium potential was determined in brain cortex slices of rat by measuring 86Rb+ distribution between the extra- and intracellular space. The ratio of internal to external Rb+ concentration was 39 +/- 1.8, corresponding to a resting membrane potential of 93.8 mV. Li+ (1-126 mM) decreased the membrane potential in both cortex slices and synaptosomes in a concentration-dependent manner. The presence of 1 mM Li+ was enough to cause a slight but distinct depolarization. During incubation in Li+-containing medium slices took up K+; however, for depolarization the presence of extracellular Li+ seemed to be necessary

In a continuing study of proteolysis of CNS proteins by CNS enzymes, neurofilament proteins (210 K, 155 K, 70 K) and desmin were separated, and the breakdown of individual proteins by purified brain cathepsin D was measured and compared to breakdown by plasma thrombin. With both cathepsin D and thrombin, the rate of breakdown of the 70 K protein was the highest, followed by the 155 K, and that of the 210 K was the lowest. With each substrate cathepsin D breakdown was the highest at pH 3; small but significant breakdown could be seen at pH 6. The pattern of intermediate breakdown products depended on pH, with greater amounts of fragments detected at higher pH, and the patterns with the two enzymes were different. We showed that differences exist in cleavage sites and breakdown rates of the neurofilament proteins. The capacity of the cathepsin D present in the tissue to hydrolyze these substrates was high, even at pH close to neutral, and was greatly in excess of that needed for physiological neurofilament turnover

The effects of lithium (Li) on brain and plasma levels of concurrently administered haloperidol (HAL) were investigated. One group of guinea pigs (n = 12) was also treated with HAL for 11 days, but Li was added during the last 5 days of treatment. At the end of treatment, the HAL + Li group had significantly higher brain and plasma levels of HAL than the group treated with HAL alone. The correlation coefficient between plasma and brain HAL (0.97) indicated that plasma levels of HAL determine brain levels of this drug

We previously found a decrease in protein synthesis in brain during development, which was much greater as measured in brain slices than in brain in vivo. In the present work such changes in brain were compared to those in other organs. With measurement of incorporation of flooding doses of [14C]valine into proteins of organs, the highest synthesis rate in the adult animal in vivo was found in liver (2.2%) followed by kidney (1.8%), spleen (1.6%), lung (1.0%), heart (0.7%), brain (0.6%) and muscle (0.5%). In immature animals the synthesis rate was highest in spleen (2.6%) followed by liver (2.4%), kidney (1.7%), lung (1.6%), brain (1.5%), heart (1.1%), and muscle (0.9%). Protein synthesis in slices from each tissue proceeded at lower rates than in vivo, especially in adults. The tissue affected the most by the preparation of the slices was muscle

Presynaptic nerve terminals when depolarized are sensitive to morphological and functional alteration by horseradish peroxidase. Mouse brain slices, 0.1 mm, depolarized by a K(+)-HEPES buffer and exposed to horseradish peroxidase exhibited alterations in both synaptic vesicle membrane structure and in high-affinity [(14)C]?-aminobutyric acid uptake. The post stimulatory retrieval of synaptic vesicles from the nerve terminal plasma membrane in the presence of horseradish peroxidase resulted in a decrease in the synaptic vesicle population with a concurrent increase in non-synaptic vesicle membrane structures. High-affinity [(14)C]?-aminobutyric acid uptake into 0.1-mm slices of mouse cerebral cortex and ponsmedulla-spinal cord was inhibited by 31% and 24%, respectively, after incubation for 60 min in K(+)-HEPES buffer containing horseradish peroxidase. Superoxide dismutase protected both the synaptic vesicle membrane and the high-affinity uptake system from the deleterious effects of horseradish peroxidase, pointing to the possible involvement of superoxide anion radicals in the horseradish peroxidase-related effects. These horseradish peroxidase induced alterations appear to be directed towards the exposed synaptic vesicle membrane, since non-stimulated brain slices exposed to horseradish peroxidase do not exhibit a reduction in either high- or low-affinity [(14)C]?-aminobutyric acid uptake. Low-affinity uptake of [(14)C]?-aminobutyric acid and [(14)C]?-aminoisobutyric acid into cortical slices was not affected after incubation in K(+)-HEPES with horseradish peroxidase. Low-affinity uptake, however, is reduced by the high-K(+)/Na(+)-free stimulatory incubation prior to uptake. It appears, thus, that high- and low-affinity uptake are distinct and different systems, with the high-affinity transport system structurally associated with synaptic vesicle membrane

Effects of caffeine on monoamine systems in the mouse brain were studied in three lines of experiments. First, concentrations of 10(-7) M to 10(-2) M of caffeine were tested for their potency in inhibiting the carriers involved in the neuronal uptake of dopamine, norepinephrine, and serotonin. The IC50 of caffeine in inhibiting the first two carriers was approximately 10(-2) M, and that in inhibiting the serotonin was 2 x 10(-3) M. Second, concentrations of 10(-5) M to 10(-3) M of caffeine were tested for their potency in affecting the in vitro KC1-induced release of [3H]dopamine from dopamine terminals in the striatum and from norepinephrine terminals in the hypothalamus, and the release of [3H]serotonin from serotonin terminals in the striatum. Little or no effect was observed. Third, caffeine was administered for 3 weeks to mice via their drinking water at 73, 123, and 162 mg/kg per day. No changes were found in their D2-dopaminergic, 5-HT2-serotonergic, or alpha 1-adrenergic receptors in the striatum or cerebral cortex as compared with animals on normal drinking water. All these neurochemical results are consonant with the interpretation of behavioral studies suggesting that caffeine is an only mildly stimulatory drug that should not be grouped with other psycho-stimulant drugs such as amphetamine and cocaine that do affect monoamine systems in the brain

Tyrosine hydroxylase (TH) activity data obtained from hypothalamic tissue samples of highly inbred mouse strains with known differences in their mesencephalic TH activity (BALB/cJ, C57BL/6ByJ, CXBI/ByJ), F1 hybrids and F2 generations were subjected to quantitative genetic analysis. No differences were observed between C57BL/6ByJ and CXBI/ByJ strains, but highly significant differences were found in hypothalamic TH activity between BALB/cJ and C57BL/6ByJ strains. Segregating genetic factors could not be detected in the replicate (C57BL/6ByJ X CXBI/ByJ) F2 generations, while the presence of segregating genetic units was indicated in the (C57BL/6ByJ X BALB/cJ)F2 population. Estimation of minimum number of genes and Elston's non-parametric one-locus test reveal that more genes are responsible for strain differences of TH activity in the hypothalamus compared to the dopaminergic areas of the mesotelencephalon. The results indicate that the heterogeneity of the catecholamine neuronal populations and terminal fields in the hypothalamus is reflected by the complex nature of the genetic control of TH activity in this brain region

An apparent inverse relationship between smoking and Parkinson's disease prompted an investigation of the effect of chronic nicotine administration on dopaminergic and serotonergic receptors in rat brain. Nicotine, 0.8 mg/kg, was injected once daily, five times per week, for 6 weeks. In nucleus accumbens the Kd for [3H]domperidone was increased 2-4-fold, and the Bmax was increased 1.5-2-fold. No changes were observed in the binding of [3H]domperidone in caudate-putamen or in that of [3H]ketanserin in frontal cortex. It is concluded that chronic nicotine administration may have a suppressant effect on central nervous system release of dopamine that in pre-parkinsonian persons causes an aversion to the effects of smoking

Rats with unilateral 6-hydroxydopamine lesions of the substantia nigra became briefly sedated and hypothermic after the acute injection of nicotine s.c. (0.4 or 0.8 mg/kg free base). When nicotine was repeated 5 days per week there was rapid tolerance for the sedation and slower tolerance for the hypothermia and the lesioned animals began to rotate ipsiversively after each injection. Stereotypic behavior was also noted. Rats injected with nicotine 5 days per week and nigrally lesioned on the 24th day rotated promptly on their first postoperative injection of nicotine. The nicotinic antagonist, mecamylamine (1.0 mg/kg i.p.), completely blocked the induced rotation. The appearance of rotation did not seem to depend on tolerance to sedation. The direction of rotation indicated enhancement of activity in the intact nigrostriatal system. However, 10 min after the acute injection of 0.8 mg/kg nicotine no change was found in the ratios of dopamine to its metabolites DOPAC and homovanillic acid in the substantia nigra, caudate-putamen, nucleus accumbens, olfactory tubercle, frontal cortex, or ventral tegmental area. Rats given 0.4 or 0.8 mg/kg nicotine 5 days per week and either lesioned prior to nicotine or lesioned during the third week rotated during the sixth week without any sign of tolerance. One day after the 30th injection in intact or lesioned rats the ratios of dopamine to its metabolites did not differ from those in saline controls on either the right or left side of any of the regions examined. There was no evidence of a change in dopamine metabolism after an acute challenge with nicotine or of a sustained change after repeated injection. The possibility remains that repeated nicotine modifies the dopaminergic response to nicotine without causing a sustained change in metabolism