Modulation of arachidonate turnover in cerebral phospholipids

Effects of phospholipase A2 inhibitors on the antidepressant-induced axonal regeneration of noradrenergic locus coeruleus neurons

In previous experiments, we have shown that antidepressants such as desipramine (DMI) can induce axonal regeneration of noradrenergic locus coeruleus neurons. In this article, we suggest that phospholipase A2 is involved in the molecular mechanism of the antidepressant-induced regeneration of brain noradrenergic axons. The effects of the PLA2 inhibitors, mepacrine (MEP) or 4-bromphenacyl bromide (BPB), upon the DMI-induced regeneration of noradrenergic axons in the rat cerebral cortex were assessed by either histofluorescence or immunohistochemistry using an antibody to dopamine-beta-hydroxylase. Symmetrical sites of the frontal cortex in both hemispheres were pretreated with 6-hydroxydopamine (6-OHDA). Then, the same cortical site of one hemisphere was infused with DMI by means of osmotic minipumps for more than 2 weeks, while the corresponding cortical site of the other hemisphere was infused with DMI plus MEP or BPB. It was found that the PLA2 inhibitors could attenuate the DMI-induced regeneration of noradrenergic axons. Thus, if axonal retraction or degeneration of brain noradrenergic neurons is involved in the pathogenesis of clinical depression, elucidating the malfunction of the PLA2 systems may provide substantial evidence to aid in our understanding of the cause of depression at the molecular level.

Interactions of phospholipids and free fatty acids with antidepressant recognition binding sites in rat brain

The lipid microenvironment of cell membranes has been shown to regulate both neurotransmitter and hormone receptors. Preincubation of cortical synaptosomal membranes of rat brain with phospholipase A2 (PLA2) increases the number of [3H]imipramine ([3H]IMI) high affinity binding sites without altering Kd (Bmax control: 2.53 +/- 0.28 pmol/mg protein vs Bmax PLA2: 3.66 +/- 0.26 pmol/mg protein). The displacement curves of [3H]IMI binding in synaptosomal membranes with other tricyclic antidepressants are not affected by the presence of PLA2. The effect of PLA2 was prevented by incubation with EGTA (2 x 10(-3)) or bovine serum albumin (BSA; 1:1). In addition, end products of catalytic activity of PLA2 such as unsaturated fatty acids (arachidonic or oleic acids) mimicked the effect of PLA2. These effects were entirely prevented by preincubation with BSA. The in vitro addition of the acidic phospholipid phosphatidylserine isolated from bovine brain (BC-PS) produced a similar increase in Bmax. This action was also blocked by addition of BSA. On the other hand, palmitic acid, a saturated fatty acid, and lysophosphatidylserine (lysoPS) or lysophosphatidylethanolamine (lysoPE) failed to modify [3H]IMI binding sites. The chronic administration of tricyclic antidepressant (AD) resulted in a 25% decrease in [3H]IMI binding sites in synaptosomal membranes. Preincubation of these AD-treated membranes with PLA2 did not alter [3H]IMI binding, whereas the addition of unsaturated free fatty acids (FFA) produced a greater increase in the density of [3H]IMI binding sites in comparison with control membranes. Taken together, these findings suggest that unsaturated free fatty acids could play an important role in the regulation of the number of [3H]IMI high affinity binding sites in the mammalian brain.

Arecoline-stimulated brain incorporation of intravenously administered fatty acids in unanesthetized rats

Brain incorporation of [1-14C]arachidonate ([14C]AA; 170 microCi/kg), [1-14C]docosahexaenoate ([14C]DA; 100 microCi/kg), or [9,10-3H]palmitate ([3H]PA; 6.4 mCi/kg) infused intravenously for 5 min was examined in the awake rat following systemic administration of the cholinomimetic arecoline (15 mg/kg i.p.). The rat was killed 15 min after infusion, and the brain was removed, frozen, and prepared for biochemical analysis and autoradiography. Brain radioactivity, normalized for plasma exposure, was increased by 41 and 45% in arecoline-treated rats given [14C]AA and [14C]DA, respectively. Pretreatment with atropine prevented the increase in fatty acid incorporation. Arecoline treatment had no effect on brain incorporation of [3H]PA. Quantitative autoradiography indicated regionally selective increases in brain [14C]AA and [14C]DA incorporation in response to arecoline. The results suggest that intravenously administered radiolabeled fatty acids can be used to study neurotransmitter-stimulated brain lipid metabolism in vivo.