Eitan Friedman

Altered platelet protein kinase C activity in bipolar affective disorder, manic episode

Protein kinase C (PKC) activity and PKC translocation in response to serotonin were investigated in platelets obtained from bipolar affective disorder subjects before and during lithium treatment. Ratios of platelet membrane-bound to cytosolic PKC activities were elevated in the manic subjects. In addition, serotonin-elicited platelet PKC translocation was found to be enhanced in those subjects. Lithium treatment for up to 2 weeks resulted in a reduction in cytosolic and membrane-associated PKC activities and in an attenuated PKC translocation in response to serotonin. These preliminary results suggest that alteration in platelet PKC is associated with the manic phase of bipolar illness. The results also suggest that lithium treatment reduces the sensitivity of platelets to PKC translocation induced by activation of serotonin-2 receptors.

Evidence for a Distinct D1Like Dopamine Receptor that Couples to Activation of Phosphoinositide Metabolism in Brain

Abstract: Dopamine and the D1, receptor agonist SKF 38393 activate the phospholipase C‐rnediated hydrolysis of phosphoinositides in brain slices. This action is selectively inhibited by SCH‐23390, thus suggesting its mediation through the dopamine D1 receptor. To determine if the dopamine receptor that mediates Phosphoinositide hydrolysis is the adenylyl, cyclase‐linked D1 receptor or a different subtype of the dopamine D1 receptor, 20 benzazepine compounds that were previously characterized as selective dopamine D1 receptor agonists were tested for stimulation of Phosphoinositide hydrolysis in rat striatal slices and for activation of adenylyl cyclase in rat striatal membranes. The compounds displayed a range of potencies and efficacies in stimulating adenylyl cyclase or Phosphoinositide hydrolysis. Compounds such as SKF 81427 and SKF 38393 were as efficacious as dopamine in stimulating Phosphoinositide hydrolysis, whereas other compounds, including SKF 85174 and SKF 86284, although showing high efficacy in stimulating cyclic AMP, failed to stimulate inositol phosphate formation. There was no correlation between the potencies (r= 0.016; p < 0.95) or efficacies (r=−0.294; p < 0.24) of the tested compounds in stimulating cyclic AMP formation and phosphoinositide hydrolysis. These observations indicate that the D1‐like dopamine receptor that mediates phosphoinositide hydrolysis is pharmacologically distinct from the classic D1 receptor that is coupled to stimulation of cyclic AMP formation.

Enhanced Protein Kinase C Activity and Translocation in Bipolar Affective Disorder Brains

Protein kinase C (PKC) activity and its redistribution were determined in the frontal cortices of postmortem brains of bipolar affective disorder subjects and age-, sex-, and postmortem time-matched controls. Membrane and cytosolic PKC activity was determined by histone phosphorylation using [32P]-adenosine triphosphate as substrate. Specific PKC isozyme levels were assessed by Western blot analysis using antipeptide antibodies. Brain membrane-associated PKC activity was higher in bipolar vs. control tissue. An examination of the specific PKC isozymes in cortical homogenates revealed that cytosolic alpha- and membrane-associated gamma- and zeta PKC isozymes were elevated in cortices of bipolar affective disorder subjects, whereas cytosolic epsilon PKC was found to be reduced. In control brain slices, incubation with 1 mumol/L phorbol 12-myristate 13-acetate (PMA) caused an increase in membrane PKC activity, whereas cytosolic enzyme activity was decreased. This redistribution of the enzyme by PMA was markedly potentiated in brain slices of bipolar subjects. The results suggest that PKC-mediated phosphorylation is increased in brains of subjects with bipolar affective illness.

Spontaneous alternation behavior : an animal model for obsessive-compulsive disorder ?

This study entailed the adoption of a well-established behavioral paradigm, spontaneous alternation, as a possible animal model for some of the symptoms observed in obsessive-compulsive disorder (OCD) in humans. Food-deprived rats were run in a T-maze in which both a black and a white goal box were equally baited with a small amount of chocolate milk. Each rat was given 7 trials every other day during which it was placed in the start box and allowed to make a choice. The mean number of choices until an alternation occurred was recorded. After a stable baseline of spontaneous alternation was achieved the effects of manipulating the serotonergic system were tested. Both the nonselective 5-HT agonist 5-MeODMT (1.25 mg/kg) and the more selective 5-HT1A agonist 8-OH-DPAT (2 mg/kg) disrupted spontaneous alternation. A course of chronic treatment (2 x 5 mg/kg for 21 days) with the selective 5-HT uptake blocking agent fluoxetine had a protective effect on the 5-MeODMT-induced disruption of spontaneous alternation behavior. Serotonergic manipulations of spontaneous alternation may be a simple animal model for the perseverative symptoms or indecisiveness seen in people diagnosed with OCD.

Attenuated protein kinase C activity and translocation in Alzheimer's Disease brain

Protein kinase C (PKC) activity and its redistribution were determined in postmortem Alzheimers disease (AD) and age-matched control brains. Cytosolic and membrane-associated PKC activities were lower in frontal and temporal cortices and hippocampi of AD brains. Increased concentrations of phosphatidyl-L-serine, Ca2+ or phorbol 12-myristate, 13-acetate only weakly increased enzyme activity in AD tissues. Redistribution of cytosolic PKC to the membranous fraction was elicited in control brain slices by 162 nM PMA in the presence of K+ (65 mM). This redistribution of the enzyme was markedly reduced in AD brain slices. In contrast, the immunoreactivity of the alpha- and gamma-PKC isozymes were elevated in cortical tissue from AD subjects. No changes were noted in beta-PKC immunoreactivity. These results suggest that the reduced PKC activity and the attenuated translocation of the enzyme in AD brain tissue may be attributed to down regulation of PKC or to alteration in PKC protein. The increase in PKC immunoreactivity may be a reflection of an altered susceptibility to proteolysis or a compensatory response secondary to the loss in enzyme activity.

Effect of Age on Brain Cortical Protein Kinase C and Its Mediation of 5-Hydroxytryptamine Release

Abstract: The effects of age on the activity and translocation of protein kinase C (PKC) and on the facilitation of 5‐hydroxytryptamine (5‐HT, serotonin) release induced by PKC activation with the phorbol ester phorbol 12‐myristate 13‐acetate were investigated. The activities of cortical PKC and its translocation in response to K+ depolarization and phorbol ester stimulation were reduced during aging in Fischer‐344 rats. Parietal cortical brain slices from 6‐, 12‐, and 24‐month‐old animals were preloaded with [3H]5‐HT and release was evoked by 65 mM K+ or the calcium ionophore A23187. 5‐HT release induced by either K+ or A23187 was found to be reduced in 12‐ and 24‐month‐old as compared to 6‐month‐old animals. This decrease was not reversed by high extracellular Ca2+. Activation of PKC resulted in a facilitated transmitter release in tissue from 6‐ and 12‐month‐old animals but reduced [3H]5‐HT release in slices from 24‐month‐old animals. These responses were prevented by the putative PKC inhibitor 1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine (H‐7), but not by increasing extracellular or intracellular Ca2+. The results demonstrate an age‐related change (1) in brain PKC activity and translocation and (2) in a physiological response to PKC stimulation. These results may have implications for other PKC‐mediated functions that are altered during senescence.

Pre- and post-synaptic cholinergic dysfunction in aged rodent brain regions : new findings and an interpretative review

Age‐related impairment of dynamic aspects of central cholinergic neurotransmission has been indicated by many studies of aged rodents, but the regional distribution of cholinergic deficits and the relative contribution of presynaptic hypofunction and reduced acetylcholine release, loss of synaptic integrity or loss of muscarinic receptors remains unclear. This study therefore compared choline acetyltransferase activity (as a structural marker) and sodium‐dependent high affinity choline uptake (which reflects both ongoing cholinergic neuronal activity and structural integrity) in the hippocampus, cortex and striatum of male C57BL mice at 3–4, 10–12 or 28–32 months of age. To evaluate the relationship of changes in muscarinic receptors to presynaptic alterations, binding of the antagonist 3H‐quinuclidinyl benzilate was compared in membranes prepared from each of these brain regions. High affinity choline uptake was significantly reduced in all three brain regions by 28–32 months of age. This trend was already evident by 10–12 months of age, especially in hippocampus and cortex. By contrast, choline acetyltransferase activity was unchanged in striatum and actually increased in hippocampus and cortex of aged mice. Muscarinic binding was reduced significantly only in striatum and this effect was significant by 10–12 months of age. This decrease in antagonist binding was accompanied by a small but significant reduction in the relative proportion of high affinity agonist sites as defined by carbachol displacement.

Lithium inhibition of protein kinase C activation-induced serotonin release

The effect of lithium on protein kinase C (PKC) stimulation-induced serotonin and norepinephrine release facilitation was examined in [3H]5-HT and [3H]NE preloaded superfused rat brain slices. The facilitation of K+-evoked [3H]5-HT release elicited by the active phorbol esters PMA and PDBu was inhibited by 4 mM but not by 1 mM in vitro lithium. In experiments performed in cortical, hippocampal and hypothalamic slices obtained from animals treated for 3 weeks with lithium-containing diet, PMA-induced facilitation of K+-elicited [3H]5-HT release was found to be inhibited by the treatment (serum lithium <1 mEq/l). Basal [3H]5-HT efflux, which was enhanced by PMA in control animals, was also inhibited by lithium treatment. In parietal cortical slices, PMA elicited increase in K+-evoked [3H]NE release was prevented in slices taken from lithium-treated (3 weeks) animals. Lithium treatment did not affect the activity and distribution of protein kinase C in cortical tissue. However, 3 weeks of treatment reduced the PMA-induced translocation of the enzyme. These results suggest that lithium treatment interferes with serotonin and norepinephrine release facilitation which results from the stimulation of PKC by phorbol esters. These actions of the ion may be mediated by its ability to inhibit PMA induced PKC translocation.

Chronic fluoxetine or desmethylimipramine treatment alters 5-HT2 receptor mediated c-fos gene expression

These studies examined the effects of a 21-day treatment regime with either the tricyclic antidepressant, desmethylimipramine (DMI), or the selective 5-HT uptake inhibitor, fluoxetine, on 5-HT2 receptors in rat brain, as assessed by selective agonist-mediated c-fos gene expression. Chronic, but not acute, treatment with fluoxetine (10 mg/kg, i.p. for 21 days) resulted in supersensitization of the response to an acute challenge (4 mg/kg, i.p.) with the selective 5-HT2 agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI), both in frontal cortex and in hippocampus. Chronic treatment with DMI (10 mg/kg, i.p. for 21 days) resulted in a significant desensitization of the response to DOI. These findings are discussed in relation to the possible modes of action of these two clinically useful agents.

Failure To Thrive in the Elderly: Exploration of the Concept and Delineation of Psychiatric Components:

Findings from an exploratory study of the relationships between routine clinical laboratory tests and the clinical status of elderly patients living in a nursing home or congregate housing facility demonstrate that low albumin and anemia are associated with decreased survival and with self-care deficits, cognitive impairment, depression, and summary measures of the severity of medical illness. The interrelationships observed among these variables support the usefulness of the concept of failure to thrive. Although albumin can serve as a nutritional marker, findings on its relationship with sedimentation rate, triiodothyronine uptake, fasting plasma amino acids, and retinol-binding protein levels suggest that the low albumin related to failure to thrive is not a simple reflection of steady-state deficits in protein-calorie nutrition; it appears to be sensitive to more direct effects of disease and inflammation or to the interactions between nutrition and illness.