The effects of prenatal choline availability on Pavlovian conditioning were assessed in adult male rats (3–4 mo). Neither supplementation nor deprivation of prenatal choline affected the acquisition and extinction of simple Pavlovian conditioned excitation, or the acquisition and retardation of conditioned inhibition. However, prenatal choline availability significantly altered the contextual control of these learned behaviors. Both control and choline-deprived rats exhibited context specificity of conditioned excitation as exhibited by a loss in responding when tested in an alternate context after conditioning; in contrast, choline-supplemented rats showed no such effect. When switched to a different context following extinction, however, both choline-supplemented and control rats showed substantial contextual control of responding, whereas choline-deficient rats did not. These data support the view that configural associations that rely on hippocampal function are selectively sensitive to prenatal manipulations of dietary choline during prenatal development.
To provide context for the diversification of archosaurs--the group that includes crocodilians, dinosaurs, and birds--we generated draft genomes of three crocodilians: Alligator mississippiensis (the American alligator), Crocodylus porosus (the saltwater crocodile), and Gavialis gangeticus (the Indian gharial). We observed an exceptionally slow rate of genome evolution within crocodilians at all levels, including nucleotide substitutions, indels, transposable element content and movement, gene family evolution, and chromosomal synteny. When placed within the context of related taxa including birds and turtles, this suggests that the common ancestor of all of these taxa also exhibited slow genome evolution and that the comparatively rapid evolution is derived in birds. The data also provided the opportunity to analyze heterozygosity in crocodilians, which indicates a likely reduction in population size for all three taxa through the Pleistocene. Finally, these data combined with newly published bird genomes allowed us to reconstruct the partial genome of the common ancestor of archosaurs, thereby providing a tool to investigate the genetic starting material of crocodilians, birds, and dinosaurs.
Our laboratory has discovered that alterations in choline availability to the developing rat fetus lead to long-term changes in spatial and temporal memory function across the lifespan and associated changes in the septo-hippocamal system. The current study was undertaken to determine if performance on an attention task, believed to be relatively independent of septo-hippocampal function, was modified by changes in choline availability prior to birth. A sustained attention task was developed for mice that includes all the features of the 2-choice signal-detection procedure initially applied to rats (McGaughy & Sarter, 1995). Prenatal choline deficiency significantly impaired the ability of adult mice to sustain attention to a brief visual cue throughout a session as evidenced by decreased "Hits" and increased "Omissions" during the second-half of trials. In contrast, prenatal choline supplementation enhanced the ability of mice to detect visual cues but did not alter their ability to maintain attention throughout a session. These data support the view that the effects of alterations in choline availability on brain anatomy, physiology, and function likely extend beyond the septo-hippocampal system that modulates spatial memory. In the case of the sustained attention task, this likely includes cholinergic projections from the basal forebrain to neocortex.
