Differential effects of norepinephrine on phosphatidylinositol 4,5-bisphosphate stimulated hydrolysis in brains of mice genetically selected for differences in ethanol sensitivity

The opposite effects of acute and chronic alcohol on lipopolysaccharide-induced inflammation are linked to IRAK-M in human monocytes

Impaired host defense after alcohol use is linked to altered cytokine production, however, acute and chronic alcohol differently modulate monocyte/macrophage activation. We hypothesized that in human monocytes, acute alcohol induces hyporesponsiveness to LPS, resulting in decreased TNF-alpha, whereas chronic alcohol increases TNF-alpha by sensitization to LPS. We found that acute alcohol increased IL-1R-associated kinase-monocyte (IRAK-M), a negative regulator of IRAK-1, in human monocytes. This was associated with decreased IkappaB alpha kinase activity, NFkappaB DNA binding, and NFkappaB-driven reporter activity after LPS stimulation. In contrast, chronic alcohol decreased IRAK-M expression but increased IRAK-1 and IKK kinase activities, NFkappaB DNA binding, and NFkappaB-reporter activity. Inhibition of IRAK-M in acute alcohol-exposed monocytes using small interfering RNA restored the LPS-induced TNF-alpha production whereas over-expression of IRAK-M in chronic alcohol macrophages prevented the increase in TNF-alpha production. Addition of inhibitors of alcohol metabolism did not alter LPS signaling and TNF-alpha production during chronic alcohol exposure. IRAK-1 activation induces MAPKs that play an important role in TNF-alpha induction. We determined that acute alcohol decreased but chronic alcohol increased activation of ERK in monocytes and ERK inhibitor, PD98059, prevented the chronic alcohol-induced increase in TNF-alpha. In summary, inhibition of LPS-induced NFkappaB and ERK activation by acute alcohol leads to hyporesponsiveness of monocytes to LPS due to increased IRAK-M. In contrast, chronic alcohol sensitizes monocytes to LPS through decreased IRAK-M expression and activation of NFkappaB and ERK kinases. Our data indicate that IRAK-M is a central player in the opposite regulation of LPS signaling by different lengths of alcohol exposure in monocytes.

Differences in norepinephrine clearance in cerebellar slices from low-alcohol-sensitive and high-alcohol-sensitive rats

High-alcohol-sensitive (HAS) and low-alcohol-sensitive (LAS) rats were bred for sensitivity and insensitivity, respectively, to the sedative/hypnotic effects of ethanol. These rats also display differential sensitivity to the depressant effects of locally applied ethanol on cerebellar Purkinje neurons in vivo. We have found that LAS animals exhibit a greater influence of endogenous beta-adrenergic activity on neuronal responses to gamma-aminobutyric acid (GABA) and ethanol than do HAS animals. In the current study, we investigated the possibility that the regulation of synaptic norepinephrine levels by norepinephrine transporters could contribute to a differential beta-adrenergic influence on GABA and ethanol sensitivity between HAS and LAS rats. We locally applied norepinephrine from a glass micropipette into the various layers of cerebellar brain slices prepared from LAS and HAS rats, and recorded the levels of norepinephrine clearance by using Nafion-coated carbon-fiber microelectrodes. Norepinephrine clearance was significantly faster by approximately 64% in the Purkinje cell layer of HAS rats. No differences in norepinephrine clearance were found in the molecular or the granule layer between LAS and HAS rats. The catecholamine uptake inhibitor nomifensine reduced norepinephrine clearance in both rat lines. These findings support the hypothesis that regulation of synaptic norepinephrine levels by norepinephrine transporter activity in the Purkinje cell layer may contribute to the differential sensitivity of Purkinje neurons to ethanol and GABA in LAS and HAS rats.

Characterization of neurotensin-stimulated phosphoinositide hydrolysis in brain regions of long sleep and short sleep mice

Previous studies have shown that long sleep (LS) and short sleep (SS) mice, which were selectively bred for differences in brain sensitivity to ethanol, differ in neurotensin (NT) receptor densities in specific brain regions. The present study was designed to determine whether these receptor differences mediate differences in the effects of NT on the phosphoinositide (PI) second messenger system in four brain regions from LS and SS mice. Baseline and NT- or carbachol-stimulated PI hydrolysis were Ca(2+)-dependent. Stimulation of PI hydrolysis by NT or carbachol was region specific; NT effect was approximately equal in ventral midbrain (VMB) and entorhinal cortex (EC) with slightly less stimulation in nucleus accumbens (NA) and no effect in the cerebellum (CE). Carbachol-enhanced PI hydrolysis was greatest in the VMB followed by EC and NA with no stimulation in the CE. There were no between line (LS vs. SS) differences in carbachol effects, but stimulation by NT was greater in EC and NA from LS than from SS mice. Ethanol enhanced NT-stimulated, but not carbachol-stimulated, PI metabolism in SS and LS NA brain slices. Results with levocabastine, an inhibitor of low-affinity NT receptor (NTL) binding, suggest that NT may stimulate PI hydrolysis via NTL, as well as high-affinity receptors.