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Biomedical subjects

S Knapp

Publications and source records attributed to S Knapp.

At least 145 records · Page 8Linked to original sources
PubMed1979

Conformational influences on brain tryptophan hydroxylase by submicromolar calcium: opposite effects of equimolar lithium.

Tryptophan hydroxylase from rat midbrain, EGTA-pretreated and dialyzed, manifested allosteric properties with respect to its substrate tryptophan, cofactor tetrahydrobiopterin, and the calcium ion. Kinetic studies suggest two preferred enzyme conformations in the presence of low concentrations of the cosubstrates: a higher affinity form manifesting hyperbolic substrate kinetics, induced by submicromolar (0.4--0.8 microM) calcium in vitro and cocaine in vivo, and a lower affinity form exaggerating cooperativity with respect to substrate, induced by submicromolar (0.4 to 0.8 microM) lithium in vitro and lithium in vivo. Lithium's effect on serotonin biosynthesis may be due to its antagonism of the positive effector influence of calcium on tryptophan hydroxylase, either as a negative effector or by blocking the calcium site.

Animals↗
PubMed1976

Histologic and enzymatic studies of the mesolimbic and mesostriatal serotonergic pathways.

Selective lesions of the dorsal (B7), median (B8), or lateral (B9) raphe nuclei were made stereotaxically in male rats 4 weeks before sacrifice. The extent of damage to each raphe nucleus was quantified histologically by means of a simplified formaldehyde histochemical method for visualization of serotonin in cryostat sections. A detailed mapping of the distribution of the yellow-fluorescent raphe perikarya provided the basis for quantification. Tryptophan hydroxylase activity was measured in 6 forebrain regions from each animal, and the results were correlated with the per cent damage to each raphe nucleus. Tyrosine hydroxylase was also assayed in 5 of these regions; it was not significantly affected by any of the raphe lesions. Dorsal raphe lesions reduced tryptophan hydroxylase activity in the striatum, thalamus, cortex, and hypothalamus, but not in the septal nuclei or hippocampus. Damage to B8 resulted in decrements in this serotonergic enzyme in the septal nuclei, hippocampus, cortex, and hypothalamus, but not in the striatum or thalamus. Lesions of the scattered B9 cells had no significant effect on enzyme activity in any region examined. These data suggest that the dorsal and median raphe nuclei provide two distinct though perhaps overlapping serotonergic systems innervating different parts of the forebrain: a mesostriatal pathway originating in B7 and a mesolimbic system derived from B8. Behavioral studies on the animals, which are presented in a companion paper, indicated that damage to the median nucleus is responsible for many of the behavioral effects previously reported after combined lesions of both major raphe nuclei.

Animals↗
PubMed1976

A neurobiological model for the symmetrical prophylactic action of lithium in bipolar affective disorder.

By treating rats with lithium chloride or cocaine hydrochloride, or lithium chloride followed by cocaine hydrochloride, we have shown the antagonistic effects of these drugs on two mechanisms that may be involved in regulating serotonin 5-HT) synthesis in the striate cortex. Lithium chloride (5 to 10 meq/kg/day) stimulates the relative velocity of the active uptake of labelled tryptophan and proportionally enhances the conversion of labelled tryptophan to 5-HT in synaptosomally enriched preparations. With continued administration of lithium chloride, the activity of tryptophan hydroxylase from the median raphe and subsequently in lysed synaptosomal preparations from striate cortex is reduced; the substrate uptake remains enhanced, but the conversion of substrate to transmitter returns to control levels. In contrast, an injection of cocaine hydrochloride inhibits the high affinity uptake of tryptophan, reducing the conversion of the amino acid to 5-HT and resulting in an increase in the biosynthetic enzyme activity. However, administration of cocaine hydrochter three daily lithium chloride injections (10 meq/kg) results in no apparent effects on substrate uptake, conversion, or enzyme activity. We theorize that the effect of lithium was to push two regulatory parameters (the uptake of substrate and the enzyme activity) to their respective functional upper and lower limits, leaving the serotonergic neurons "buffered" against the "usual" effects of the stimulant drug, and offer this neurobiological model for consideration in relation to the clinical effects of lithium in the prophylaxis of both mania and depression in some patients.

Animals↗
PubMed1976

Coincidence of blockade of synaptosomal 5-hydroxytryptamine uptake and decrease in tryptophan hydroxylase activity: effects of fenfluramine.

A single injection of fenfluramine hydrochloride resulted in a short-term increase in striate synaptosomal conversion of tryptophan to serotonin (5-HT) in rat brain. In contrast, D- and L-amphetamine sulfate resulted in a short-term decrease of this index of 5-HT biosynthesis. None of the amphetamines studied altered the kinetics of synaptosomal uptake of L-[3-14C]-tryptophan measured in the same striate preparation. Within 4 hours after fenfluramine administration, 3H-5-HT uptake into synaptosomes was markedly decreased; it returned to control levels in 10 to 14 days. Intrasynaptosomal tryptophan hydroxylase activity dropped markedly within 4 hours of drug administration and remained depressed for 10 to 14 days, its return to control levels coinciding with that of 3H-5-HT uptake. Only 5-HT cell body enzyme prepared from the lateral midbrain (B9) demonstrated a reduction in activity comparable to that seen in the synaptosomes; very small decreases occurred in cell body enzyme prepared from whole midbrain (B7, B8, B9) or medial midbrain (B7, B8). Lateral midbrain tryptophan hydroxylase activity returned to control levels by 8 days. In vitro, fenfluramine (100 muM) affected none of these indices of central 5-HT synthesis except 3H-5-HT uptake, which it reduced, and synaptosomal 3H-5-HT release, which it facilitated. The effects of fenfluramine on 5-HT biosynthesis persisted longer than those of D-amphetamine, which lasted less than 24 hours. However, the fenfluramine effects were much shorter than those reported for p-chloroamphetamine, which persist for up to 3 months. These three amphetamines apparently affect the lateral midbrain raphe nuclei selectively.

Animals↗
PubMed1975

A model for the neurobiological mechanisms of action involved in lithium prophylaxis of bipolar affective disorder.

The effects of chronic administration of lithium chloride on the serotonin synthesizing apparatus in rat brain suggest a theoretical model that could explain how chronic treatment with lithium is prophylactic against both poles of affect in manic-depressive disorder. After three to five days of lithium chloride administration the Vmax of high affinity uptake of (14C) tryptophan into striate synaptosomes increased to 140% of control values, and tryptophan-to-serotonin conversion activity increased to about the same degree. These events were followed by an apparently compensatory decrease in the Vmax of midbrain activity cell body and striate nerve ending tryptophan hydroxylase activity. After 21 days of drug administration (14C)-tryptophan uptake remained above control levels, and soluble midbrain and solubilized striate synaptosomal enzyme activity remained below control levels, but synaptosomal conversion activity had returned to control levels. In vitro, drug concentrations from 10 to 53 mM did not affect the enzyme activity, but did enhance the uptake and conversion measures. Also, increasing tryptophan levels either by pre-incubation with L-tryptophan in vitro or by the administration of L-tryptophan (20 to 60 mg/kg) in vivo enhanced the uptake and conversion measures. The data suggest the possibility that lithium pushed two complementary adaptive mechanisms to their capacities, and the net result is restricted but balanced function of serotonergic transmission in the brain.

Affective Symptoms↗
PubMed1975

Effects of lithium chloride on parameters biosynthetic capacity for 5-hydroxytryptamin in rat brain.

Administration of lithium chloride to rats resulted in a biphasic, temporally related alteration in the brain's biosynthetic capacity for 5-hydroxytryptamine (5-HT). After 3 to 5 days of drug administration, the Vmax of the high affinity uptake of [14-C]tryptophan into striate nerve ending synaptosomes increased to 140% of control values. The stimulated uptake of radioactive precursor apparently resulted in an augmentation of tryptophan-to-5-HT conversion activity of the same magnitude in these synaptosomes. These events were succeeded by an apparently compensatory decrease in the Vmax of midbrain cell body and nerve-ending solubilized tryptophan-5-hydroxylase (EC 1.99.1.4). After 21 days of drug administration, [14-C]tryptophan uptake remained above control levels, but striate synaptosomal conversion activity had returned to control levels. In contrast, soluble midbrain and solubilized striate synaptosomal enzyme activity remained significantly below control values. In vitro lithium chloride at 10 or 53 mM had no effect on soluble tryptophan hydroxylase activity, but either concentration of lithium chloride significantly enhanced the uptake of [14-C]tryptophan into striate synaptosomes, and consequently also the synaptosomal conversion of tryptophan to 5-HT. Increasing tryptophan levels either by preincubation of synaptosomes with L-tryptophan or by administration of L-tryptophan loads (20-60 mg/kg) resulted in augmented [14-C]tryptophan uptake and conversion activity. The sequence of events that we observed after lithium treatment is consistent with receptor-mediated neuronal feedback regulation of tryptophan hydroxylase activity after stimulation of tryptophan uptake and conversion of 5-HT.

Animals↗
PubMed1975

Current research in the indoleamine hypothesis of affective disorders.

Lithium cloride (10 meq/kg/day) administered to rats for 3 days before pharmacological challenge with cocaine hydrochloride (100 mg/kg) antagonized the effects of the stimulant drug on complementary constituents of serotonin synthesis. This neurobiological antagonism, as well as lithium's antagonism of the behavioral effects of other drugs that can produce extreme moods in man, suggests that lithium may work against mania and depression by "buffering" the serotonergic system--that is, by pushing two adaptive processes respectively to their upper and lower limits, which returns the net synthesis of transmitter to a "normal" range and keeps it there.

Affective Symptoms↗