Neural growth : with special emphasis on adult neurogenesis and the effect of antiepileptic drugs

Neurons were for a long time thought to not renew themselves. In the 1960ies the phenomenon of neurogenesis was discovered, but it was not until 1998 that neurogenesis was demonstrated in humans. In this thesis neurogenesis was studied using a unique genetic mouse model (mceph/mceph), with postnatal epilepsy and excessive brain growth, due to a truncated Kv1.1 subunit. The model was used to learn more about how a channelopathy can disturb hippocampal neurogenesis, leading to hyperplasia, and how this can be treated. First, the expression and trafficking of the truncated potassium ion channel Kv1.1 was described to reveal its molecular nature. It was shown that the defective Kv1.1 does not form functional channels and moreover has the potential to render other potassium channel subunits non-functional. Even though lack of Kv1.1 is enough for excessive hippocampal growth, the defect Kv1.1 peptide worsens the epileptic condition by blocking additional Kv1 subunits. Cells have previously been shown to be enlarged in the hippocampus of this mouse. In this thesis a doubling in number of neurons and astrocytes was demonstrated by stereology. The increase in number of neurons was due to increased neurogenesis and altered apoptosis. To identify transcripts involved in the overgrowth of the mceph/mceph hippocampus a genome-wide screen for transcripts expressed at different levels in mceph/mceph versus wild type was performed. The following genes, involved in regulation of cell number, were verified as differentially regulated in mceph/mceph; NPY, Penk, Fjx1 and Vgf. Previously it was shown that oral treatment with the antiepileptic drug CBZ protect mceph/mceph mice from developing enlarged hippocampus.

This thesis shows that all hippocampal regions studied were protected from overgrowth and that the number of both neurons and astrocytes were normalized despite ongoing severe seizures. Transcripts potentially involved in the protection against the hippocampal overgrowth and hyperplasia were identified based on different expression levels in a microarray analysis. Verified genes include Mlc1, Sstr4, ApoD, Ndn, Aatk and Rgs2. These transcripts have a proposed function in proliferation, differentiation and/or apoptosis. Finally, an analysis of the effect of AEDs in utero, with focus on the head size of the newborn, was conducted on a large population-based Swedish cohort. This study revealed that the use of CBZ and VPA is increasing despite reports of malformations and growth retardations of the baby. Furthermore, CBZ and VPA monotherapy significantly reduced the head circumference (HC) and AED polytherapy increase the rate of small HC (> 2 SD). The implications of a smaller head on the development of the child is uncertain but should be explored. CBZ mono ] and polytherapy significantly reduced gestational age (GA) and there was a tendency for clonazepam and gabapentin monotherapy to reduce GA. The relevance of the reduced pregnancy duration is not clear but indicates a need for further studies in order to optimize treatment regimes for epileptic pregnant women.

List of scientific papers

I. Persson AS, Klement G, Almgren M, Sahlholm K, Nilsson J, Petersson S, Arhem P, Schalling M, Lavebratt C (2005). "A truncated Kv1.1 protein in the brain of the megencephaly mouse: expression and interaction." BMC Neurosci 6: 65
https://pubmed.ncbi.nlm.nih.gov/16305740

II. Almgren M, Persson AS, Fenghua C, Witgen BM, Schalling M, Nyengaard JR, Lavebratt C (2007). "Lack of potassium channel induces proliferation and survival causing increased neurogenesis and two-fold hippocampus enlargement." Hippocampus 17(4): 292-304
https://pubmed.ncbi.nlm.nih.gov/17315199

III. Almgren M, Persson B, Lavebratt C (2008). "Carbamazepine protects against neuronal hyperplasia and abnormal gene expression in the megencephaly mouse." Neurobiology of Disease (Submitted)

IV. Almgren M, Källén B, Lavebratt C (2008). "Population ]based study of antiepileptic drug exposure in utero ] influence on head circumference in newborns." Epilepsia (Submitted)