In adult mammals, learning, memory, and restoration of sensorimotor lost functions imply synaptic reorganization that requires diffusible messengers-mediated communication between presynaptic and postsynaptic structures. A candidate molecule to accomplish this function is the gaseous intercellular messenger nitric oxide (NO), which is involved in synaptogenesis and projection refinement during development; however, the role of NO in synaptic reorganization processes in adulthood remains to be established. In this work, we tested the hypothesis that this free radical is a mediator in the adult mammal CNS synaptic remodeling processes using a model of hypoglossal axonal injury recently developed by us. Axonal injury-induced disconnection of motoneurons from myocytes produces withdrawal of synaptic inputs to motoneurons and concomitant upregulation of the neuronal isoform of NO synthase (NOS-I). After recovery of the neuromuscular function, synaptic coverage is reestablished and NOS-I is downregulated. We also report, by using functional and morphological approaches, that chronic inhibition of the NO/cGMP pathway prevents synaptic withdrawal evoked by axon injury, despite the persistent muscle disconnection. After successful withdrawal of synaptic boutons, inhibition of NO synthesis, but not of cGMP, accelerated the recovery of synaptic coverage, although neuromuscular disconnection was maintained. Furthermore, protein S-nitrosylation was upregulated after nerve injury, and this effect was reversed by NOS-I inhibition. Our results suggest that during synaptic remodeling in the adult CNS, NO acts as a signal for synaptic detachment and inhibits synapse formation by cGMP-dependent and probably S-nitrosylation-mediated mechanisms, respectively. We also suggest a feasible role of NO in neurological disorders coursing with NOS-I upregulation.

The tetrapeptide sequence His-Phe-Arg-Trp, derived from melanocyte-stimulating hormone (alphaMSH) and its analogs, causes a decrease in food intake and elevates energy utilization upon binding to the melanocortin-4 receptor (MC4R). To utilize this sequence as an effective agent for treating obesity, we improved its metabolic stability and intestinal permeability by synthesizing a library of backbone cyclic peptidomimetic derivatives. One analog, peptide 1 (BL3020-1), was selected according to its selectivity in activating the MC4R, its favorable transcellular penetration through enterocytes and its enhanced intestinal metabolic stability. This peptide was detected in the brain following oral administration to rats. A single oral dose of 0.5 mg/kg in mice led to reduced food consumption (up to 48% vs the control group) that lasted for 5 h. Repetitive once daily oral dosing (0.5 mg/kg/day) for 12 days reduced weight gain. Backbone cyclization was shown to produce a potential drug lead for treating obesity.

Glutamate-induced excitotoxicity, the most common pathological mechanism leading to neuronal death, may occur even with normal levels of glutamate if it coincides with a persistent enhancement of neuronal excitability. Neurons expressing nitric oxide (NO) synthase (NOS-I), which is upregulated in many human chronic neurodegenerative diseases, are highly susceptible to neurodegeneration. We hypothesized that chronic production of NO in damaged neurons may increase their intrinsic excitability via modulation of resting or "leak" K ϩ currents. Peripheral XIIth nerve injury in adult rats induced de novo NOS-I expression and an increased incidence of lowthreshold motor units, the latter being prevented by chronic inhibition of the neuronal NO/cGMP pathway. Accordingly, sustained synthesis of NO maintained an enhanced basal activity in injured motoneurons that was slowly reverted (over the course of 2-3 h) by NOS-I inhibitors. In slice preparations, persistent, but not acute, activation of the NO/cGMP pathway evoked a robust augment in motoneuron excitability independent of synaptic activity. Furthermore, chronic activation of the NO/cGMP pathway fully suppressed TWIK-related acid-sensitive K ϩ (TASK) currents through a protein kinase G (PKG)-dependent mechanism. Finally, we found evidence for the involvement of this long-term mechanism in regulating membrane excitability of motoneurons, because their pH-sensitive currents were drastically reduced by nerve injury. This NO/cGMP/PKG-mediated modulation of TASK conductances might represent a new pathological mechanism that leads to hyperexcitability and sensitizes neurons to excitotoxic damage. It could explain why de novo expression of NOS-I and/or its overexpression makes them susceptible to neurodegeneration under pathological conditions.

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.