Molecular mechanisms involved in the subcortical plasticity induced by nitric oxide synthesis modulations

*H. MENDONCA, G. E. SARACENO2, A. A. SILVA1, F. CAPANI, C. A. SERFATY1, P. CAMPELLO-COSTA1

New Orleans

Congreso; Molecular mechanisms involved in the subcortical plasticity induced by nitric oxide synthesis modulations; 2012

The rat retinotectal (RT) system is a glutamatergic pathway that develops from diffuse projections to a precise pattern within the first two postnatal (P) weeks. This map is generated by correlated pre and postsynaptic activity, which requires retrograde signaling to inform the presynaptic terminal about target activity, leading to contact maintenance or elimination. Nitric oxide (NO) is a classical retrograde messenger in brain physiology, and its levels can be modulated by inhibitors or stimulators of its synthesis enzymes. It is known that the plasticity of excitatory synapses is dependent on differential expression of AMPA and NMDA receptors subunits, and modulated by GABAergic inputs. Moreover, NO has been described as an endogenous regulator of adenosine levels, which in turns, is involved in RT map development. Thus, we investigated the effect of NO modulation on RT development, on the expression of ionotropic glutamatergic receptors subunits, on GAD65, and A1 and A2a adenosine receptors in the superior colliculus (SC).Pigmented rats were intraperitonealy treated with NO synthase inhibitor (N ù-nitro-l-arginine 50mg/kg - NARG), stimulator (l-arginine 750mg/kg - LARG) or PBS from P9 to P12. At P13, we obtained serum samples for griess reaction, SC sections for NO fluorescence or immunohistochemistry (IHC), and SC samples for western blot (WB). For morphological analysis of RT projections, animals received HRP injection in the right eye at P12, and sections were processed for axon labeling in the SC at P13.Our results show that NARG treatment promoted a reduction of NO metabolites in serum in parallel to a decrease in SC NO fluorescence, while LARG promoted the opposite. Although the effects on NO generation were contrasting, both treatments promoted expansion of RT arbor. WB and IHC studies for ionotropic glutamatergic receptors subunits expression revealed that LARG promoted an increase of GluR2, whereas NARG treatment reduced it. We have shown as well that GluR1 is enhanced in NARG group. We also showed that NR1 expression were enhanced in LARG and decreased in NARG groups. Besides, NARG treatment promoted an increase in NR2b. Concerning the GABAergic system, we have found by WB that LARG treatment enhanced GAD65 expression and NARG reduced it. Moreover, NARG treated animals presented an increase in A1 receptor.So, LARG seems to induce system maturation, via increase in mature network markers as GluR2, NR1 and GAD65. This early maturation might stabilize projections that would be normally eliminated. Conversely, NARG seems to impair maturation by expression of the immature system markers GluR1, NR2b and A1, that prevents the refinement of RT map.