Specific neurotrophic factors support the survival of cortical projection neurons at distinct stages of development.

Repair of specific neuronal circuitry in the neocortex may be possible via neural precursor transplantation or manipulation of endogenous precursors in situ. These approaches will almost certainly require a detailed understanding of the mechanisms that control survival and differentiation of specific neuronal lineages. Such analysis has been hampered by the overwhelming diversity of neuronal types intermixed in neocortex and the inability to isolate individual lineages. To elucidate stage-specific controls over the survival of individual lineages of cortical neurons, we purified immature callosal projection neurons (CPN) at distinct stages of development from embryonic and postnatal mouse cortex by retrograde fluorescence labeling, followed by fluorescence-activated cell sorting. Purified CPN survive well in culture, acquire stage-specific projection neuron morphologies, and express appropriate neurotransmitters and growth factor receptors. Purified CPN are dependent on exogenous trophic support for survival in a stage-specific manner. Survival of postnatal day 2 (P2) to P3 and P6-P7 CPN is promoted by overlapping but distinct sets of neurotrophic factors, whereas embryonic day 19 CPN show less specificity of dependence on peptide factors. These studies demonstrate for the first time the stage-specific control by peptide growth factors over the survival of a specific cortical neuronal lineage. Such information may be critical for the future goal of directed differentiation of transplanted or endogenous precursors toward cellular repair of complex cortical circuitry.

Neuroprotection by complement (C1) inhibitor in mouse transient brain ischemia.

The authors investigated the effect of the C1 inhibitor (C1-INH), the only known inhibitor of complement C1, in a murine model of transient focal ischemia. Ischemia was induced by intraluminal occlusion of the middle cerebral artery. After 2 hours, reperfusion was produced by removing the nylon monofilament occluding the artery. The effect of 15 U C1-INH (intravenously) was evaluated in terms of general and focal neurologic deficits, ischemic volume, neutral red staining (to identify the brain areas subject to ischemic damage), and glial fibrillary acidic protein immunoreactivity (to show astrocytic response). Forty-eight hours after ischemia, C1-INH significantly improved general and focal deficits by 36% and 54%, respectively, and significantly reduced infarct volume (CI-INH, 6.69% +/- 2.93%; saline, 24.24% +/- 8.24%) of total brain. Neutral red staining further showed the strong protective effect of C1-INH in cortex, hippocampus, and striatum. Astrocyte activation induced by ischemia was not affected by C1-INH. These findings show that C1-INH displayed a potent neuroprotective action by effectively reducing ischemia-reperfusion injury.

Impaired central stress-induced release of noradrenaline in rats with heart failure: a microdialysis study.

Sympathetic hyperactivity in rats with heart failure is associated with increased extracellular noradrenaline in the hypothalamic paraventricular nucleus at rest. However, it is unknown how this nucleus responds to stressful stimuli. In the present study we therefore examined the basal and stress-induced release of noradrenaline in the paraventricular nucleus of conscious Sprague-Dawley rats with heart failure measured by in vivo microdialysis. Basal noradrenaline concentration in the paraventricular nucleus of rats with heart failure was more than double that in sham-operated controls. Immobilization stress decreases noradrenaline levels in the paraventricular nucleus of rats with heart failure to 57% of baseline, while it increased in sham-operated controls to 228%. However, serum corticosterone was similarly elevated at 30 and 90 min post-stress in both experimental groups. We have shown that heart failure causes an impairment of the central noradrenergic system's response to acute sympatho-excitation but does not affect the hypothalamo-pituitary-adrenocortical response.

Differentiation of transplanted neural precursors varies regionally in adults striatum.

In the current experiments, we address the emerging hypothesis that transplanted neural precursor cells can respond to local microenvironmental signals in the post-developmental brain and exhibit patterns of differentiation that depend critically on specific location within the brain. HiB5 precursor cells were transplanted into adult mouse cortex, corpus callosum, and multiple positions in striatum, and assessed for differentiation by morphology and immunocytochemistry. Our results indicate that the likelihood of both neuronal and glial differentiation of transplanted precursors depends on proximity to the medial striatum or subventricular zone of the adult host, supporting the concept that microenvironmental signals can critically affect the differentiation fate of neural precursors, and suggesting the potential to manipulate such signals in the adult brain.

Regulation of cAMP-dissociation kinetics in lactating rat mammary gland.

The cAMP-dissociation kinetics of rat mammary gland cytosols are dependent upon the temperature of cAMP association. Dissociation rates (measured at pH 6.5, 24 degrees C) were biphasic (k = 0.08-0.23 min-1 and k = 0.02 min-1) and monophasic (k-1 = 0.02 min-1) after 0 degrees C and 24 degrees C association, respectively. The temperature-dependent change from an initial fast rate to an initial slow rate was observed at all concentrations of cAMP tested from 1 to 1000 nM. When the slow-dissociating site was associated with non-radioactive 8-bromo-cAMP, the dissociation rates of [3H]-cAMP from the remaining dissociating site was slow (k = 0.02 min-1) and fast (k = 0.05 min-1) at 24 degrees C and 0 degrees C associating rate can be converted to the slow-dissociating rate by warming. When 0.2 M sodium thiocyanate was added to the association mixture at 24 degrees C, biphasic dissociation rates of k = 0.23 min-1 and k = 0.02 min-1 were observed, suggesting that the chaotropic salt blocks the interconversion of rates. The data are consistent with the model for cAMP-dependent protein kinase which exhibits two binding sites with different affinities. The type II enzyme from mammary gland cytosol exhibits in addition the phenomenon of temperature-dependent interconversion of the two binding affinities.

Effect of MgATP on cAMP-dissociation kinetics of lactating rat mammary gland.

Mammary gland cytosols exhibit temperature-dependent interconversion of cAMP-dissociation rates from low to high affinity (k-1 = 0.14 min-1 at 0 degree C to k-1 = 0.02 min-1 at 24 degrees association). This interconversion corresponds to a change from a site 2 to a site 1 cAMP-dissociation rate for the type II cAMP-dependent protein kinase in mammary gland cytosols. This report presents data which indicates a requirement for MgATP in the temperature-dependent interconversion of cAMP-dissociation rates. The effect of MgATP on the generation of the high affinity state was observed at 24 degrees C but not 0 degree C association. The effect of MgATP was not mimicked by equimolar MgAMP-PNP, but did require an intact type II protein kinase holoenzyme which can undergo autophosphorylation of its regulatory subunit. The effect of MgATP was reproduced with partially purified preparations of beef heart type II protein kinase. These results suggest that MgATP may act through autophosphorylation of the type II holoenzyme. The data suggest a novel role of MgATP in the regulation of cAMP binding to cAMP-dependent protein kinase II.

cAMP-dependent protein kinase II interactions with nuclei derived from rat mammary tumor.

cAMP-dependent protein kinase from bovine heart exhibited significant interactions with nuclei from rat mammary tumors. These enzyme-nuclear interactions occurred when the intact holoenzyme was preincubated with 10 nM cAMP, 1 mM MgATP at 24 degrees C to produce high-affinity monophasic cAMP-dissociation kinetics. The enzyme-nuclear interactions are correlated with the loss of cAMP and PO4 from the purified enzyme. The data indicate that the high affinity cAMP-dependent protein kinase II exhibits significant nuclear interaction which may be related to cAMP function in rat mammary tumors.