Synaptic communication is a dynamic process that is key to the regulation of neuronal excitability and information processing in the brain. To date, however, the molecular signals controlling synaptic dynamics have been poorly understood. Membrane-derived bioactive phospholipids are potential candidates to control short-term tuning of synaptic signaling, a plastic event essential for information processing at both the cellular and neuronal network levels in the brain. Here, we showed that phospholipids affect excitatory and inhibitory neurotransmission by different degrees, loci, and mechanisms of action. Signaling triggered by lysophosphatidic acid (LPA) evoked rapid and reversible depression of excitatory and inhibitory postsynaptic currents. At excitatory synapses, LPA-induced depression depended on LPA₁/G_αi/o-protein/phospholipase C/myosin light chain kinase cascade at the presynaptic site. LPA increased myosin light chain phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. At inhibitory synapses, postsynaptic LPA signaling led to dephosphorylation, and internalization of the GABA_Aγ2 subunit through the LPA₁/G_α12/13-protein/RhoA/Rho kinase/calcineurin pathway. However, LPA-induced depression of GABAergic transmission was correlated with an endocytosis-independent reduction of GABA_A receptors, possibly by GABA_Aγ2 dephosphorylation and subsequent increased lateral diffusion. Furthermore, endogenous LPA signaling, mainly via LPA₁, mediated activity-dependent inhibitory depression in a model of experimental synaptic plasticity. Finally, LPA signaling, most likely restraining the excitatory drive incoming to motoneurons, regulated performance of motor output commands, a basic brain processing task. We propose that lysophospholipids serve as potential local messengers that tune synaptic strength to precedent activity of the neuron. Neuronal networks are modules of synaptic connectivity that underlie all brain functions, from simple reflexes to complex cognitive processes. Synaptic plasticity allows these networks to adapt to changing external and internal environments. Membrane-derived bioactive phospholipids are potential candidates to control short-term synaptic plasticity. We demonstrate that lysophosphatidic acid (LPA), an important intermediary in lipid metabolism, depresses the main excitatory and inhibitory synaptic systems by different mechanisms. LPA depresses inhibitory synaptic transmission by reducing the number of postsynaptic receptors at inhibitory synapses; whereas it depresses excitatory synaptic transmission by decreasing the size of the ready-to-use synaptic vesicle pool at excitatory terminals. Finally, we demonstrate that LPA signaling contributes to the performance of motor output commands in adult animals. Our data documents that synaptic strength and neuronal activity are modulated by products of membrane phospholipid metabolism, which suggests that bioactive phospholipids are candidates in coupling brain function to the metabolic status of the organism.

Rho-associated kinase (ROCK) regulates neural cell migration, proliferation and survival, dendritic spine morphology, and axon guidance and regeneration. There is, however, little information about whether ROCK modulates the electrical activity and information processing of neuronal circuits. At neonatal stage, ROCKα is expressed in hypoglossal motoneurons (HMNs) and in their afferent inputs, whereas ROCKβ is found in synaptic terminals on HMNs, but not in their somata. Inhibition of endogenous ROCK activity in neonatal rat brainstem slices failed to modulate intrinsic excitability of HMNs, but strongly attenuated the strength of their glutamatergic and GABAergic synaptic inputs. The mechanism acts presynaptically to reduce evoked neurotransmitter release. ROCK inhibition increased myosin light chain (MLC) phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. Functional and ultrastructural changes induced by ROCK inhibition were fully prevented/reverted by MLC kinase (MLCK) inhibition. Furthermore, ROCK inhibition drastically reduced the phosphorylated form of p21-associated kinase (PAK), which directly inhibits MLCK. We conclude that endogenous ROCK activity is necessary for the normal performance of motor output commands, because it maintains afferent synaptic strength, by stabilizing the size of the readily releasable pool of synaptic vesicles. The mechanism of action involves a tonic inhibition of MLCK, presumably through PAK phosphorylation. This mechanism might be present in adults since unilateral microinjection of ROCK or MLCK inhibitors into the hypoglossal nucleus reduced or increased, respectively, whole XIIth nerve activity.

The molecular signaling that underpins synapse loss in neuropathological conditions remains unknown. Concomitant upregulation of the neuronal nitric oxide (NO) synthase (nNOS) in neurodegenerative processes places NO at the center of attention. We found thatde novonNOS expression was sufficient to induce synapse loss from motoneurons at adult and neonatal stages. In brainstem slices obtained from neonatal animals, this effect required prolonged activation of the soluble guanylyl cyclase (sGC)/protein kinase G (PKG) pathway and RhoA/Rho kinase (ROCK) signaling. Synapse elimination involved paracrine/retrograde action of NO. Furthermore, before bouton detachment, NO increased synapse myosin light chain phosphorylation (p-MLC), which is known to trigger actomyosin contraction and neurite retraction. NO-induced MLC phosphorylation was dependent on cGMP/PKG-ROCK signaling. In adulthood, motor nerve injury induced NO/cGMP-dependent synaptic stripping, strongly affecting ROCK-expressing synapses, and increased the percentage of p-MLC-expressing inputs before synapse destabilization. We propose that this molecular cascade could trigger synapse loss underlying early cognitive/motor deficits in several neuropathological states.

Disruption in membrane excitability contributes to malfunction and differential vulnerability of specific neuronal subpopulations in a number of neurological diseases. The adaptor protein p11, and background potassium channel TASK1, have overlapping distributions in the CNS. Here, we report that the transcription factor Sp1 controls p11 expression, which impacts on excitability by hampering functional expression of TASK1. In the SOD1-G93A mouse model of ALS, Sp1-p11-TASK1 dysregulation contributes to increased excitability and vulnerability of motor neurons. Interference with either Sp1 or p11 is neuroprotective, delaying neuron loss and prolonging lifespan in this model. Nitrosative stress, a potential factor in human neurodegeneration, stimulated Sp1 expression and human p11 promoter activity, at least in part, through a Sp1-binding site. Disruption of Sp1 or p11 also has neuroprotective effects in a traumatic model of motor neuron degeneration. Together our work suggests the Sp1-p11-TASK1 pathway is a potential target for treatment of degeneration of motor neurons.

The aim of the present work was to improve our knowledge on the mechanisms underlying the beneficial or deleterious effects on testicular function of the so-called Mediterranean and Western diet by analyzing glutamyl aminopeptidase (GluAP), gamma glutamyl transpeptidase (GGT) and dipeptidyl peptidase IV (DPP IV) activities in testis, as enzymes involved in testicular function. Male Wistar rats (6 months old) were fed for 24 weeks with three different diets: standard (S), an S diet supplemented with virgin-olive-oil (20%) (VOO), or a S diet enriched with butter (20%) plus cholesterol (0.1%) (Bch). At the end of the experimental period, plasma lipid profiled (total triglycerides, total cholesterol and cholesterol fractions (HDL, LDL and VDL)) were measured. Enzymatic activities were determined by fluorimetric methods in soluble (sol) and membrane-bound (mb) fractions of testicular tissue using arylamide derivatives as substrates. Results indicated an increase in plasmatic triglycerides, total cholesterol, LDL and VLDL in Bch. A significant increase of mb GluAP and GGT activities was also found in this diet in comparison with the other two diets. Furthermore, significant and positive correlations were established between these activities and plasma triglycerides and/or total cholesterol. These results support a role for testicular GluAP and GGT activities in the effects of saturated fat (Western diet) on testicular functions. In contrast, VOO increased sol DPP IV activity in comparison with the other two diets, which support a role for this activity in the effects of monounsaturated fat (Mediterranean diet) on testicular function. The present results strongly support the influence of fatty acids and cholesterol on testicular GluAP and GGT activities and also provide support that the reported beneficial influence of the Mediterranean diet in male fertility may be mediated in part by an increase of testicular sol DPP IV activity.