[Biological and neural bases of partner preferences in rodents: models to understand human pair bonds]. / Bases biológicas y neurales de las preferencias de pareja en roedores: modelos para entender los vínculos afectivos en humanos.

AIM: To analyse the biological and neural bases of partner preference formation in rodents as models to understand human pair bonding. DEVELOPMENT: Rodents are social individuals, capable of forming short- or long-lasting partner preferences that develop slowly by stimuli like cohabitation, or rapidly by stimuli like sex and stress. Dopamine, corticosteroids, oxytocin, vasopressin, and opioids form the neurochemical substrate for pair bonding in areas like the nucleus accumbens, the prefrontal cortex, the piriform cortex, the medial preoptic area, the ventral tegmental area and the medial amygdala, among others. Additional areas may participate depending on the nature of the conditioned stimuli by which and individual recognizes a preferred partner. CONCLUSIONS: Animal models help us understand that the capacity of an individual to display long-lasting and selective preferences depends on neural bases, selected throughout evolution. The challenge in neuroscience is to use this knowledge to create new solutions for mental problems associated with the incapacity of an individual to display a social bond, keep one, or cope with the disruption of a consolidated one.

Equilibrium analysis of ethidium binding to DNA containing base mismatches and branches.

In the processes of DNA replication, recombination, and repair, duplex DNA can transiently form branched structures, such as Holliday junctions, as well as base pair mismatches and bulges. These stages have altered ligand and protein binding properties from normal double helical DNA. A variety of ligands have been reported to interact more tightly at branches and bulges than to normal duplex sites. The stoichiometry, structural basis, and thermodynamics of this effect have not been determined. We have investigated the binding of the intercalator, ethidium bromide, to several DNA constructs including base mismatches, bulges, and three- and four-arm branched structures, using chemical footprinting, titration calorimetry, and fluorescence lifetime measurements. Two classes of binding sites are detected in three- and four-arm junctions in our high ionic strength conditions: one class is characterized by a small number of ligands (2-4 per DNA), with high binding affinity (K > 10(5)), and the second by a larger number of sites (10-12 per DNA) with lower affinity (K approximately 10(4)). By use of appropriate control experiments, the former appear to be associated with sites at or near the branch point or mismatch, while the latter are consistent with binding to the normal duplex DNA region(s) of the molecule. Titration calorimetry indicates an enthalpy of -10 to -13 kcal/mol for binding of ethidium to a mismatch or three- and four-arm branch point. The tight binding class is associated with a fluorescence lifetime of 12-16 ns, distinct from that of free ethidium (ca. 2 ns) and the longer lifetime observed for ethidium intercalated in duplex DNA (22-26 ns).

Ordered restriction maps of Saccharomyces cerevisiae chromosomes constructed by optical mapping.

A light microscope-based technique for rapidly constructing ordered physical maps of chromosomes has been developed. Restriction enzyme digestion of elongated individual DNA molecules (about 0.2 to 1.0 megabases in size) was imaged by fluorescence microscopy after fixation in agarose gel. The size of the resulting individual restriction fragments was determined by relative fluorescence intensity and apparent molecular contour length. Ordered restriction maps were then created from genomic DNA without reliance on cloned or amplified sequences for hybridization or analytical gel electrophoresis. Initial application of optical mapping is described for Saccharomyces cerevisiae chromosomes.