To understand their migratory environmental history and habitat use in Mexican waters, 31 striped mullet Mugil cephalus and 40 white mullet M. curema (family Mugilidae) were collected from three habitats (Tamiahua Lagoon, and Cazones and Tecolutla estuaries, Veracruz) in the western Gulf of Mexico. Sr:Ca ratios in otoliths of mullets were measured from the primordium to the otolith edge with an electron probe microanalyzer. Mullets were aged by counting the otolith annuli. The patterns in mullet otolith Sr:Ca ratio differed among habitats and between species, indicating that habitat use and migratory behavior differed between species. Variability in otolith Sr:Ca ratios was consistent with that of the environment inhabited by the mullets. They showed a more diverse euryhaline preference than the simple catadromous behavior expected. The Sr:Ca ratios in the core region of the otolith indicated that mullets can spawn in both offshore waters and nearshore brackish waters, or that spawning may occur in offshore waters and that onshore currents/winds carry the fertilized eggs into onshore waters where salinities are lower. Peak Sr:Ca ratios corresponded to otolith annulus deposition, which validated the difference in timing of seaward spawning migration between striped mullet (winter) and white mullet (spring).

Con el objeto de entender la historia migratoria y el uso del hábitat de dos mugílidos de importancia comercial en México, se recolectaron 31 ejemplares de la lisa Mugil cephalus y 40 de la lebrancha M. curema de tres zonas geográficas distintas (la laguna de Tamiahua y los estuarios de Cazones y Tecolutla, Veracruz) del oeste del golfo de México. Se midió la proporción de Sr:Ca en los otolitos sagita desde el primordio hasta el margen del otolito con un microanalizador de electrones. La edad de los ejemplares fue determinada contando los anillos de crecimiento en el otolito. Los patrones de Sr:Ca fueron diferentes entre zonas geográficas y especies, lo que indica que el uso del hábitat y el comportamiento migratorio es distinto entre las dos especies. La variabilidad de la proporción de Sr:Ca en los otolitos fue consistente con el ambiente en el que habitan estas especies. Estos mugílidos muestran una preferencia eurihalina más que simplemente un comportamiento catádromo. La proporción de Sr:Ca en el núcleo de los otolitos indicó que estos mugílidos pueden desovar tanto en aguas marinas como en ambientes salobres o que posiblemente desoven en ambientes marinos y los huevos sean transportados a ambientes costeros salobres. Los valores máximos de la proporción de Sr:Ca correspondieron a la depositación del anillo anual, lo que valida las diferencias en la migración reproductiva al mar que realiza M. cephalus en invierno y M. curema en primavera.

Agmatine has neuroprotective effects on retinal ganglion cells (RGCs) as well as cortical and spinal neurons. It protects RGCs from oxidative stress even when it is not present at the time of injury. As agmatine has high affinity for various cellular receptors, we assessed protective mechanisms of agmatine using transformed RGCs (RGC-5 cell line). Differentiated RGC-5 cells were pretreated with 100 μM agmatine and consecutively exposed to 1.0 mM hydrogen peroxide (H2O2). Cell viability was determined by measuring lactate dehydrogenase (LDH), and the effects of selective alpha 2-adrenergic receptor antagonist yohimbine (0-500 nM) and N-methyl-D-aspartic acid (NMDA) receptor agonist NMDA (0-100 µM) were evaluated. Agmatine’s protective effect was compared to a selective NMDA receptor antagonist MK-801. After a 16-h exposure to H2O2, the LDH assay showed cell loss greater than 50%, which was reduced to about 30% when agmatine was pretreated before injury. Yohimbine almost completely inhibited agmatine’s protective effect, but NMDA did not. In addition, MK-801 (0-100 µM) did not significantly attenuate the H2O2-induced cytotoxicity. Our results suggest that neuroprotective effects of agmatine on RGCs under oxidative stress may be mainly attributed to the alpha 2-adrenergic receptor signaling pathway.