Avian and Poultry Biology Reviews 12 (3), 2001

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Comparative studies of postnatal neurogenesis and learning: a critical review

Pamela Banta Lavenex1,3, Pierre Lavenex2,3 and Nicola S. Clayton1,3,4*
1Section of Neurobiology, Physiology and Behavior, University of California Davis, 1544 Newton Court, CA 95616, USA
2Department of Psychiatry, University of California Davis, 1544 Newton Court, CA 95616, USA
3Center for Neuroscience, University of California Davis, 1544 Newton Court, CA 95616, USA
4Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB3 3EB, UK

ABSTRACT

In this review we summarize studies of adult neurogenesis, from original descriptive accounts to more recent work aimed at identifying factors that influence neurogenesis as well as its possible function. Much of the recent work has focused on the relationship between neurogenesis and learning: we therefore present critical analyses of specific experiments and the conclusions that can be drawn from them.We describe two avian models, song learning and food caching, and argue that because these models have a high degree of ethological validity they are particularly well-suited for investigating the fate and specific functions of adult-born neurons.We also describework on neurogenesis in juveniles and how that has contributed to our understanding of the relationship between neurogenesis and learning, but caution against drawing inferences regarding the function of adult neurogenesis from these studies in juveniles because the cellular and functional mechanisms underlying juvenile and adult neurogenesis are likely distinct.We critically review several experiments investigating mammalian postnatal neurogenesis, and describe how particular flaws in the assumptions underlying their experimental design may render some of their results misleading.We suggest that by increasing the ethological validity of the mammalian models, it may be possible to strengthen the conclusions that can be drawn from such investigations.We conclude that there is inadequate empirical evidence linking either the phenomenon of adult neurogenesiswith a specific role in learning, or learning-associated paradigms with an increase in or enhancement of adult neurogenesis, and indeed, substantial evidence counter to these hypotheses.

Keywords: Adult neurogenesis, hippocampus, vocal control nuclei, song learning, food caching, memory, birds, mammals

Effects of selection for exponential growth rate at different ages on reproduction in chickens

C. L. Kerr1, R. H. Hammerstedt2 and G. F. Barbato1*

1Department Poultry Science, The Pennsylvania State University, PA 16802, USA
2Intercollege Graduate Program in Genetics, Department Biochemistry and Molecular Biology, The Pennsylvania State University, PA 16802, USA

ABSTRACT

This study evaluated the correlated responses between selection for early developmental growth (essential for commercial acceptance and profitability of meat-type chickens) and reproductive traits (essential to chick production). A double, divergent selection experiment for growth rate to different ages suggests that traditional concepts of the negative correlation between growth and reproduction are due to cumulative genetic effects influencing growth during the linear portion of the growth curve, not ``growth'' per se. Eight generations of divergent selection for exponential growth rate (EGR) from 0 to 14 days (EGR14) of age or 0 to 42 days of age (EGR42) resulted in a four-fold difference in EGR14 and an eight-fold difference in EGR42 between the divergently selected lines. Correlated traits contributing to reproductionincluded: percentage hen-day eggproduction (HDP), fertility and hatchability, and both age (AFE) and weight (WFE) at first egg. Hens from the line selected for fast EGR42 (42Hline)were significantlyheavier thanthose fromthe line selected for slowEGR42 (42L line) and came into production 31days earlier. Fertility diminished rapidly in the line selected for slow EGR14 while HDP was unchanged. TheAFE andWFE of both EGR14 selected lines were not different. Further, the average values forAFE,WFE of the EGR14 lines were intermediate to the mean values for the EGR42 lines, suggesting a critical period of development between 14 and 42 days of age influencing these traits and the onset of sexualmaturation.

Keywords: Genetics, selection, growth, sexual maturity, fertility