Applying genetic selection pressure to an outbred population of albino rats, we have derived lines that show consistently high versus low pain phenotype in the neuroma model of neuropathic pain. Trait segregation developed rapidly, replicating earlier observations using this methodology. The resulting novel selection lines, designated nHA and nLA, share a common genetic background but have dramatically contrasting neuropathic pain behavior. In addition to confirming that the pain trait selected is heritable (estimated realized heritability h(2)=0.31), we have refreshed the availability of this research resource, namely animals of uniform genetic background but with contrasting pain phenotype. Crossing nHA rats with animals of the high (recessive) line from the earlier selection program (HA) yielded offspring almost uniformly high in pain phenotype. This complementation analysis indicates that the same gene(s) was selected in both selection programs, attesting to its unique salience in determining pain phenotype in the neuroma model.
Sodium-deficient adult rats prefer NaCl to other monochloride salts (e.g., Denton, 1991; Schulkin, 1991). However, it is not known when or how this specificity develops. Our experiments charted the development of the ionic specificity of sodium appetite aroused by sodium depletion or intracerebroventricular injection of renin. We compared intake of 3% NaCl to three other monochlorides, potassium (K), ammonium (NH4), and lithium (Li), and calcium chloride (CaCl2) at various ages between 72 hr postnatal and weaning. This revealed a biphasic developmental scheme: The adult pattern of discrimination between the salts emerges between 3 and 18 days of age. Subsequently, the preference for Na over the other salts increases into adulthood.
The ontogeny of calcium ingestion and preference was examined in parathyroidectomized (PTX) rats. Sucklings were tested by means of oral infusion. Four-day-old neonatal rats increased ingestion of CaCl2 after PTX but the effect was not specific to calcium because intake of MgCl2 was also increased. After 6 days of age the increase was more specific to calcium. The response increased in potency until 20 days of age. Weanlings were tested by measuring intakes from two burets, one with CaCl2 and one with MgCl2. Twenty-six-day-old weanlings showed a mild preference for CaCl2, but by 30 days of age the preference for calcium was similar to that reported for adult rats.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.