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L A Dokas

Publications and source records attributed to L A Dokas.

30 records · Page 2Linked to original sources
PubMed1984

Alteration of hippocampal B50 phosphorylation after adrenalectomy.

Adrenalectomy alters endogenous phosphorylation of the presynaptic protein, B50, in the hippocampus. Three and four days following adrenalectomy decreases are seen, relative to control values, in the in vitro phosphorylation of B50 when a synaptic plasma membrane fraction from the hippocampus is incubated with [gamma-32P]ATP. At four days post-adrenalectomy, the percent decrease in B50 phosphorylation is -49.8 +/- 6.8%. No alteration is seen in the level of B50 phosphorylation when comparing hippocampal membrane preparations from sham-operated and intact animals. Fourteen days following adrenalectomy, hippocampal B50 phosphorylation was restored to normal levels. Hypophysectomy did not alter the degree of in vitro B50 phosphorylation, but the effect of adrenalectomy occurred in hypophysectomized rats. Following adrenalectomy, no differences are seen in the phosphorylation of any hippocampal cytosolic proteins. Changes in B50 phosphorylation seen in hypothalamic synaptic plasma membranes are likely due to the effects of sham-operation. The results indicate that a transient neurochemical or neuroendocrine event following adrenalectomy modulates in vivo the degree of B50 phosphorylation in hippocampal synaptic membranes.

Adrenal Glands↗
PubMed1983

Somatostatin and analogs inhibit endogenous synaptic plasma membrane protein phosphorylation in vitro.

The addition of somatostatin to hippocampal synaptic plasma membrane (SPM) preparations in vitro decreased subsequent phosphorylation of specific protein bands. 10(-4)M somatostatin inhibited the phosphorylation of protein bands with apparent molecular weights between 10 000 and 20 000 daltons and, to a lesser extent, 48 000 daltons (B-50) and 52 000. Increasingly greater degrees of inhibition were seen in response to somatostatin-28 and [D-Trp8]somatostatin. Inhibition of B-50 protein phosphorylation in the presence of [D-Trp8]somatostatin was most prominent in SPM preparations from the hippocampus and amygdala, with lesser degrees of inhibition seen in the cortex and hypothalamus. Addition of [D-Trp8]somatostatin to an ammonium sulfate-precipitated fraction (ASP 55-80) from cortex only slightly inhibited endogenous B-50 phosphorylation. The injection of [D-Trp8] somatostatin intracerebroventricularly into rats did not induce excessive grooming behavior but resulted in barrel rotation. These results suggest that somatostatin and congeners affect SPM protein phosphorylation in a manner different from that of ACTH, presumably involving membrane sites that bind somatostatin.

Adrenocorticotropic Hormone↗
PubMed1983

Analysis of brain and pituitary RNA metabolism: a review of recent methodologies.

Recent characterization of brain and pituitary RNA metabolism is reviewed. Relative to other tissues, the brain transcribes more of the unique, single-copy DNA. This transcriptional diversity reflects the inherent heterogeneity in organization and development of the brain. The end product of transcriptional regulation in the brain is a population of functional cytoplasmic mRNAs with multiple components, differing in complexity and abundance. Analysis of nuclear and cytoplasmic RNA provides evidence that both brain-specific synthesis and processing may determine the final mRNA population. Both polyadenylated and non-polyadenylated RNA classes contribute significantly to the total brain polysomal mRNA fraction. Characterizations of individual species of mRNA from both brain and pituitary are described. One possible transcriptional modulator in both the pituitary and brain is the presence of steroid hormone at responsive sites. Functional consequences of steroid accumulation within the brain may be (1) interactions with neurotransmitter, especially catecholamine, metabolism and function, (2) developmental interactions with neuronal systems, and (3) differentiation of glial cell function. The pleiotropic nature of steroid hormone effects (both transcriptional and non-transcriptional) within one brain region is considered by examining the biochemical effects of glucocorticoids in the hippocampus.

Animals↗
PubMed1982

Properties of CRF from normal and Brattleboro rat median eminence.

Most of the corticotrophin-releasing factor (CRF) activity of normal rat median eminence (ME) extract binds to a neurophysin affinity column. The bound material contains the large and small factors, which we have previously demonstrated to be required together for full activity. Most of the CRF activity of Brattleboro rat ME extract, which contains as much CRF activity as the ME extract of a normal rat, does not bind to a neurophysin affinity column. The CRF activity of Brattleboro rat ME extract resides entirely in a large molecule as determined by Sephadex G-25 chromatography. The different properties of Brattleboro and normal rat CRF suggest that the CRF activity in the Brattleboro rat may result from a substance which is different from that in a normal rat.

Animals↗
PubMed1981

Uridine metabolism in the goldfish retina during optic nerve regeneration: whole retina studies.

Accumulation of radioactivity from [3H]uridine in incubations of whole goldfish retinas is increased in the ipsilateral retina during a period of regeneration that follows unilateral optic nerve crush. Brief incubations to investigate the nature of enhanced labeling of the acid-soluble fraction showed a peak uptake 4 days following crush, with a gradual decrease to control levels by 21 days following crush. That nucleoside uptake may not mediate the effect is supported by the observation that the rate of uptake of 5'-deoxyadenosine, a nonmetabolizable nucleoside analog, is the same in post-crush (PC) and normal (N) retinal incubations. Following brief incubations of PC and N retinas with [3H]uridine, there is enhanced labeling in PC retinas relative to N retinas of recovered UMP, UDP, UTP, and uridine nucleotide sugars, whereas recovery of labeled uridine itself is slightly decreased. The results suggest that the increased accumulation of radioactivity in PC retinas following incubation with uridine reflects an increase in the activities of retinal uridine kinase and uridine nucleotide kinases.

Animals↗
PubMed1981

Uridine metabolism in the goldfish retina during optic nerve regeneration: cell-free preparations.

The activities of uridine kinase (EC 2.7.1.48), uridine monophosphate (UMP) kinase (EC 2.7.1.3.14), and uridine diphosphate (UDP) kinase (EC 2.7.4.6) were measured in retinal high-speed supernatant fractions following unilateral optic nerve crush in the goldfish. The enzyme activities followed a similar time course, with initial increases 2-3 days following nerve crush, peak activity at 4 days, and a gradual return to basal levels by day 21. The magnitude of the stimulation on day 4 was about 35% in each case. Activities of two enzymes of intermediary metabolism, pyruvate kinase (EC 2.7.1.40) and lactic dehydrogenase (EC 1.1.1.27), were not altered, indicating that the coordinate increases in nucleoside and nucleotide kinase activities were specific responses to the nerve injury. The increased labeling could not be explained by altered phosphohydrolytic activities. The nature of the enhancement was further studied in UDP kinase, the most active of the kinases examined. Neither low-molecular-weight components nor substrate availability could account for the observed increase in UDP kinase in the 4 day post-crush retinas. The Km for UDP was unaltered, and a mixing experiment did not support the possibility that stimulatory or inhibitory factors played a role. The enhancement of UDP kinase activity was blocked by injection of actinomycin D following nerve crush. The results suggest that the observed increases in enzymes of uridine metabolism result from their increased formation following nerve crush.

Animals↗
PubMed1971

Adenosine 3',5'-monophosphate increases capacity for RNA synthesis in rat liver nuclei.

Liver nuclei isolated from rats injected with adenosine 3', 5'-monophosphate exhibit an increased capacity for RNA synthesis compared with nuclei from control animals. This effect, which is highly specific for the cyclic nucleotide. can be observed within 1 hour after injection in both unoperated and adrenalectomized rats. These findings suggest that induction of enzyme synthesis mediated by way of adenosine 3', 5'-monophosphate may be controlled, at least in part, at the level of gene transcription.

Adenine Nucleotides↗
PubMedDate not supplied

Characteristics of [D-Trp8]-somatostatin-sensitive B50 phosphorylation.

Inhibition of the phosphorylation of the synaptic plasma membrane (SPM) protein B50 by [D-Trp8]-somatostatin in vitro is time-dependent. Increasing the time of incubation of hippocampal synaptic plasma membranes with the peptide from 15 sec to 30 min prior to addition of 7.5 microM [gamma-32P]ATP results in a complete reduction of B50 phosphorylation. Incubation of synaptic plasma membranes for 30 min in the absence of peptide does not alter basal B50 phosphorylation. Neither ACTH nor beta-endorphin produces similar effects--inhibition of B50 phosphorylation by ACTH is maximal at 15 sec and beta-endorphin produces only a small inhibition, even after 30 min. [D-Trp8]-somatostatin is not activating a membrane-bound protease, since maximal inhibition of B50 phosphorylation by the peptide is seen in the presence of leupeptin or bacitracin. Hippocampal synaptic plasma membranes contain protein phosphatase activity. Assays of B50 phosphorylation in synaptic plasma membranes done under conditions that favor either net phosphorylation or dephosphorylation are consistent with inhibition of protein phosphatase activity by [D-Trp8]-somatostatin. This evidence suggests that [D-Trp8]-somatostatin interacts with SPM binding sites in the hippocampus, which may alter the activity of an endogenous protein phosphatase to determine the degree of B50 phosphorylation.

Animals↗
PubMedDate not supplied

A comparison of the regulatory properties of striatal and cortical adenylate cyclase.

Biochemical properties of adenylate cyclase in striatal and cortical membranes have been analyzed in parallel with their regulation by cholinergic compounds. Striatal adenylate cyclase is more sensitive to forskolin, while the cortical enzyme is more stimulated by GTP. In the presence of GTP, more inhibition by acetylcholine is seen in the cortex than in the striatum. Acetylcholine inhibits striatal adenylate cyclase activity equally in the presence or absence of forskolin but has a diminished ability to inhibit forskolin-stimulated adenylate cyclase in the cortex. The greater sensitivity of cortical muscarinic receptor-coupled adenylate cyclase to EGTA and calcium indicates predominant involvement of the calcium/calmodulin-dependent subtype of the enzyme. The relative effectiveness of antagonists, demonstrating an order of potency of atropine > amitriptyline > pirenzepine > gallamine in reversing the inhibition of adenylate cyclase by acetylcholine for both brain regions, suggests predominantly m4 receptor-mediated responses. These results suggest an m4-type receptor may be coupled to subtypes of adenylate cyclase in the striatum and cortex which differ in their biochemical properties.

Acetylcholine↗