ABSTRACT
The function of adult neurogenesis in the rodent brain remains unclear. Ablation of adult born neurons has yielded conflicting results about emotional and cognitive impairments. One hypothesis is that adult neurogenesis in the hippocampus enables spatial pattern separation, allowing animals to distinguish between similar stimuli. We investigated whether spatial pattern separation and other putative hippocampal functions of adult neurogenesis were altered in a novel genetic model of neurogenesis ablation in the rat. In rats engineered to express thymidine kinase (TK) from a promoter of the rat glial fibrillary acidic protein (GFAP), ganciclovir treatment reduced new neurons by 98%. GFAP-TK rats showed no significant difference from controls in spatial pattern separation on the radial maze, spatial learning in the water maze, contextual or cued fear conditioning. Meta-analysis of all published studies found no significant effects for ablation of adult neurogenesis on spatial memory, cue conditioning or ethological measures of anxiety. An effect on contextual freezing was significant at a threshold of 5% (P = 0.04), but not at a threshold corrected for multiple testing. The meta-analysis revealed remarkably high levels of heterogeneity among studies of hippocampal function. The source of this heterogeneity remains unclear and poses a challenge for studies of the function of adult neurogenesis.
Subject(s)
Cognitive Dysfunction/genetics , Hippocampus/physiology , Neurogenesis/genetics , Neurons/metabolism , Thymidine Kinase/genetics , Animals , Anxiety/physiopathology , Cognitive Dysfunction/pathology , Conditioning, Psychological , Fear/physiology , Glial Fibrillary Acidic Protein/genetics , Glial Fibrillary Acidic Protein/metabolism , Hippocampus/metabolism , Maze Learning/physiology , Memory/physiology , Pharmacogenetics , Rats , Thymidine Kinase/metabolismABSTRACT
The past few decades have seen the field of genetic engineering evolve at a rapid pace, with neuroscientists now equipped with a wide range of tools for the manipulation of an animal's genome in order to study brain function. However, the number of species to which these technologies have been applied, namely the fruit fly, C. elegans, zebrafish and mouse, remains relatively few. This review will discuss the variety of approaches to genetic modification that have been developed in such traditional 'genetic systems', and highlight the progress that has been made to translate these technologies to alternative species such as rats, monkeys and birds, where certain neurobiological questions may be better studied.
Subject(s)
Genetic Engineering/methods , Neurosciences/methods , Animals , Models, BiologicalABSTRACT
The majority of inhibitory neurotransmission in the brain is mediated by the gamma-aminobutyric acid (GABA) type A (GABA(A)) receptor. The anticonvulsant loreclezole largely acts by potentiating GABA(A) receptors containing beta2 and beta3 subunits. We used a genetically modified mouse containing a loreclezole-insensitive beta2 subunit (beta2N265S) to determine the role of this subunit in mediating the sedative and anticonvulsive effects of loreclezole. Sedation was assessed by measuring spontaneous locomotor activity and beam walking performance, and anticonvulsant efficacy was determined by pentylenetetrazole (PTZ) and amygdala kindling-induced seizures. The beta2N265S mice did not exhibit loreclezole-mediated sedation as shown by normal locomotor activity and beam walking performance. However, loreclezole also failed to provide significant protection against PTZ-induced seizures in the beta2N265S mice. Reduced efficacy against amygdala-kindled seizures, both acutely and over a 13-day chronic dosing study, was also observed in beta2N265S mice. These results suggest that the majority of the sedative effects and a significant proportion of the anticonvulsant efficacy of loreclezole are mediated via beta2-containing GABA(A) receptors.
