Search

Following neonatal hypoxia-ischemia (HI) serotonin (5-hydroxytryptamine, 5-HT) levels are decreased in the brain. The regulation of brain 5-HT is dependent on the serotonin transporter (SERT) localised at the neuronal pre-synaptic cell membrane. However SERT can also traffic away from the cell membrane into the cytosol and, after injury, may contribute to the cell's inability to maintain 5-HT levels. Whether this occurs after neonatal HI brain injury is not known. In addition, there is contradictory evidence that glial cells may also contribute to the clearance of 5-HT in the brain. Using a postnatal day 3 (P3) HI rat pup model (right carotid ligation+30 min 6% O(2)), we found, in both control and P3 HI animals, that SERT is retained on the cell membrane and is not internalised in the cytosol. In addition, SERT was only detected on neurons. We found no evidence of SERT co-localisation on microglia or astrocytes. We conclude that neuronal SERT is the primary regulator of synaptic 5-HT availability in the intact and P3 HI-injured neonatal brain. Furthermore, since concomitant reductions in 5-HT, SERT and serotonergic neurons occur after neonatal HI, it is plausible that the decrease in brain 5-HT is a consequence of SERT being lost as neurons degenerate as opposed to remaining neurons internalising SERT or clearance by glial cells.

Neuronal losses are observed in the brain after neonatal hypoxia-ischemia (HI) however few studies have examined the effects of HI on specific neuronal phenotypes and their possible contribution to behavioural outcomes. In the present study we examined whether postnatal day 3 (P3) HI alters numbers of corticotropin-releasing factor (CRF) and neuropeptide-Y (NPY) neurons in the paraventricular nucleus of the hypothalamus (PVN), the bed nucleus of the stria terminalis (BNST) and the amygdala, 1 (P10) and 6 (P45) weeks after P3 HI. A significant reduction in the number of CRF-positive neurons in the PVN, central nucleus of the amygdala (CeA) and BNST ipsilateral to the carotid ligation 1 and 6 weeks after P3 HI was observed. There was also a significant reduction in the number of NPY-positive neurons in the PVN, amygdala and BNST ipsilateral to the carotid ligation 1 week after P3 HI. However after 6 weeks, only the number of PVN NPY-positive neurons decreased significantly. At 6 weeks post-insult, the number of CeA CRF-positive neurons was inversely associated with locomotor activity and exploratory behaviour in an open field. In contrast, no significant correlations between neuronal counts and early neurodevelopment tests performed on P10 were observed. Thus after P3 HI persistent losses of CRF- and NPY-positive neurons occur and the loss of CeA CRF neurons may provide a central anatomical mechanism underlying neurobehavioural deficits observed 6 weeks after P3 HI. © 2010 Elsevier B.V. All rights reserved.

In a preterm hypoxia-ischemia model in the post-natal day 3 rat, we characterized how the expression of purine ionotropic P2X(4) receptors change in the brain post-insult. After hypoxia-ischemia, P2X(4) receptor expression increased significantly and was associated with a late increase in ionised calcium binding adapter molecule-1 protein expression indicative of microglia cell activation. Minocycline, a potent inhibitor of microglia, attenuated the hypoxia-ischemia-induced increase in P2X(4) receptor expression. We postulate that P2X(4) receptor-positive microglia may represent a population of secondary injury-induced activated microglia. Future studies will determine whether this population contributes to the progression of injury in the immature brain.