Neuroscience
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Comparative Study
Acute hypoxia and programmed cell death in developing CNS: Differential vulnerability of chick optic tectum layers.
The chick optic tectum displays an alternating pattern of cellular and plexiform layers and at embryonic day (ED) 12 there are mainly four cellular layers: transient cell compartment 3 (TCC3), compartment "h-i-j"(C"h-i-j"), stratum griseum centrale (SGC) and subventricular zone (SvZ). In the present work we characterized the programmed cell death (PCD) of these layers and their vulnerability to acute hypoxia at ED12, and also identified the main cellular type involved in hypoxic cell death. The colocalization of three independent markers of cell degeneration: pyknotic nuclei by Hoechst staining, fragmented DNA by TdT-mediated dUTP nick-end labeling (TUNEL), and presence of active caspase-3 by immunofluorescence, was analyzed in embryos that developed in normoxic conditions (control embryos) and embryos that were subjected to hypoxia (8% O(2)/92% N(2)) for 60 min (hypoxic embryos), followed by 0-12 h of normoxic recovery. ⋯ In addition, the significant colocalization between the neuron specific nuclear protein (NeuN) and TUNEL signal showed that hypoxia affected primarily neurons. In conclusion, our findings demonstrate that in the chick optic tectum at ED12, PCD is layer dependent and that acute hypoxia causes a transient increase in neuronal death in a delayed fashion, which is also layer dependent. The morphological features of the neuronal death process at the light microscope level resembled apoptosis.
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Osmoprotective genes are tonicity-activated genes involved in cellular osmoadaptation to hypertonicity and considered to be regulated by a specific transcription factor called tonicity-responsive enhancer-binding protein (TonEBP). In the brain we had previously established that TonEBP was expressed and tonicity-induced in neurons only. Here we have compared in various brain regions of rats subjected to systemic hypertonicity, the cellular expression of TonEBP through immunocytochemistry and the cellular expression of osmoprotective genes, namely aldose reductase (AR), sodium-dependent myo-inositol transporter (SMIT), betaine/GABA transporter (BGT1) and taurine transporter (TauT), by in situ hybridization using non-radioactive digoxigenin-labeled riboprobes. ⋯ The present work reveals large discrepancies between the cellular distribution of the tonicity-induced expression of osmoprotective genes and that of their regulatory transactivator TonEBP. Depending on the cell subsets and the osmoprotective genes, TonEBP may appear insufficient or conversely unnecessary for the tonicity-induced activation of an osmoprotective gene. Altogether our results show that brain cells, even from the same class, activate distinct osmoprotective genes through distinct activation processes to adapt to hypertonicity.
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Activation of D1-like (D1, D5) or D2-like (D1, D3, D4) dopamine receptors in the nucleus accumbens shell is sufficient to reinstate cocaine-seeking behavior in rats. The goal of these experiments was to assess whether cooperative activation of D1-like and D2-like dopamine receptors in the accumbens shell is required to promote cocaine reinstatement. Rats were initially trained to self-administer cocaine (0.25 mg, i.v.) using a fixed-ratio schedule of reinforcement for approximately 21 days. ⋯ Similarly, administration of the selective D1/5 dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) (1.0 microg) into the nucleus accumbens shell prior to quinpirole (3.0 microg) blocked reinstatement of drug-seeking behavior elicited by this D2/3 dopamine receptor agonist. Moreover, intra-accumbal shell co-administration of subthreshold doses of quinpirole (1.5 microg) and SKF-81297 (0.1 microg) promoted cocaine-seeking behavior. Collectively, these results indicate that cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is necessary to reinstate cocaine seeking in rats.