Degeneration of nigrostriatal dopaminergic system is the principal lesion in Parkinson’s disease. Because glial cell line-derived neurotrophic factor (GDNF) promotes survival of dopamine neurons in vitro and in vivo, intracranial delivery of GDNF has been attempted for Parkinson’s disease treatment but with variable success. For improving GDNF-based therapies, knowledge on physiological role of endogenous GDNF at the sites of its expression is important. However, due to limitations of existing genetic model systems, such knowledge is scarce. Here, we report that prevention of transcription of Gdnf 3’UTR in Gdnf endogenous locus yields GDNF hypermorphic mice with increased, but spatially unchanged GDNF expression, enabling analysis of postnatal GDNF function. We found that increased level of GDNF in the central nervous system increases the number of adult dopamine neurons in the substantia nigra pars compacta and the number of dopaminergic terminals in the dorsal striatum. At the functional level, GDNF levels increased striatal tissue dopamine levels and augmented striatal dopamine release and re-uptake. In a proteasome inhibitor lactacystin-induced model of Parkinson’s disease GDNF hypermorphic mice were protected from the reduction in striatal dopamine and failure of dopaminergic system function. Importantly, adverse phenotypic effects associated with spatially unregulated GDNF applications were not observed. Enhanced GDNF levels up-regulated striatal dopamine transporter activity by at least five fold resulting in enhanced susceptibility to 6-OHDA, a toxin transported into dopamine neurons by DAT. Further, we report how GDNF levels regulate kidney development and identify microRNAs miR-9, miR-96, miR-133, and miR-146a as negative regulators of GDNF expression via interaction with Gdnf 3’UTR in vitro. Our results reveal the role of GDNF in nigrostriatal dopamine system postnatal development and adult function, and highlight the importance of correct spatial expression of GDNF. Furthermore, our results suggest that 3’UTR targeting may constitute a useful tool in analyzing gene function.

SUMMARYIn a study using a heated chamber for induction of experimental febrile seizures (eFS) in rat pups, ictal activity was shown to be precipitated by a respiratory alkalosis (Schuchmann et al., 2006). In sharp contrast to this, in a recent review Dubé et al., (2007) suggest that the respiratory alkalosis is model specific, and that no increase in respiratory rate is observed in the widely used "hair dryer model" of eFS. The data in the present work, based on well-established techniques for measuring respiratory rates in rat pups, show a pronounced increase in the "hair dryer model" with values that are slightly higher than those recorded in the heated chamber model. Hence, a temperatureevoked increase in respiration is a common feature of these two models of eFS. KEY WORDS: Neonate rat, Hyperthermia, Hyperventilation, Epilepsy.Febrile seizures (FS) present the most common type of convulsive events in children (Stafstrom, 2002). "Simple FS" characterized by their brief duration of generalized cortical epileptiform are considered benign. However, the spectrum of fever-related epileptic syndromes includes a wide range of disease states, and some of them are associated with an increased risk of subsequent epilepsy (Berg et al., 1998;Shinnar, 1998). A major nonbenign category includes "complex FS" that have a prolonged duration or include partial (focal) seizure activity (Stafstrom, 2002). Although a number of susceptibility genes associated with fever-induced convulsions have been identified (Baulac et al., 2004), the neurophysiological mechanisms underlying these disease states have not been identified.In order to study the mechanisms and consequences of FS, animal models have been developed where an increase in body temperature is induced by elevating the ambient temperature (e.g., Holtzman et al., 1981;Baram et al., 1997). In one of the most widely used models (Baram et al., 1997;Dubé and Baram, 2005), rat pups at postnatal (P) days of about 10-11 are exposed to a stream of hot air from a hair dryer for 30 min, which leads to a very rapid increase in body temperature and to experimental FS (eFS) that commence within about 2-4 min (Dubé and Baram, 2005;Dubé et al., 2007). The total duration of the eFS in this model is set to about 22-24 min to mimic complex FS.In a recent study, we modified the above model in a manner in which the pups are placed in a heated chamber with an ambient temperature of about 48• C, and in which heat transfer is not heavily dependent on convection, as is the case with the hair dryer. The rise in body temperature is much slower, and eFS are seen with a delay of about 30 min from the start of the hyperthermia exposure (Schuchmann et al., 2006). A key finding in this work was that the eFS were preceded by a steady rise in the rate of respiration, up to 160% of the control level. This resulted in a respiratory alkalosis (net loss of CO 2 ) as demonstrated by an alkaline shift that was measured using a pH-selective electrode implanted in the cortex. Notably, several lines of evidence sug...

Parvalbumin‐positive interneurons (PV+) are a key component of inhibitory networks in the brain and are known to modulate memory and learning by shaping network activity. The mechanisms of PV+ neuron generation and maintenance are not fully understood, yet current evidence suggests that signalling via the glial cell line‐derived neurotrophic factor (GDNF) receptor GFRα1 positively modulates the migration and differentiation of PV+ interneurons in the cortex. Whether GDNF also regulates PV+ cells in the hippocampus is currently unknown. In this study, we utilized a Gdnf “hypermorph” mouse model where GDNF is overexpressed from the native gene locus, providing greatly increased spatial and temporal specificity of protein expression over established models of ectopic expression. Gdnfwt/hyper mice demonstrated impairments in long‐term memory performance in the Morris water maze test and an increase in inhibitory tone in the hippocampus measured electrophysiologically in acute brain slice preparations. Increased PV+ cell number was confirmed immunohistochemically in the hippocampus and in discrete cortical areas and an increase in epileptic seizure threshold was observed in vivo. The data consolidate prior evidence for the actions of GDNF as a regulator of PV+ cell development in the cortex and demonstrate functional effects upon network excitability via modulation of functional GABAergic signalling and under epileptic challenge.

The y-axis values in Fig 4M are incorrect. Please view the correct figure here.

No abstract