Manganese-enhanced magnetic resonance imaging (MEMRI) exploits the biophysical similarity of Ca2+ and Mn2+ to map the brain's activity in vivo. However, to what extent different Ca2+ channels ...contribute to the enhanced signal that MEMRI provides and how Mn2+ dynamics influence Mn2+ brain accumulation after systemic administration of MnCl2 are not yet fully understood. Here, we demonstrate that mice lacking the L-type Ca2+ channel 1.2 (Cav1.2) in the CNS show approximately 50% less increase in MEMRI contrast after repeated systemic MnCl2 injections, as compared to control mice. In contrast, genetic deletion of L-type Ca2+ channel 1.3 (Cav1.3) did not reduce signal. Brain structure- or cell type-specific deletion of Cav1.2 in combination with voxel-wise MEMRI analysis revealed a preferential accumulation of Mn2+ in projection terminals, which was confirmed by local MnCl2 administration to defined brain areas.
Taken together, we provide unequivocal evidence that Cav1.2 represents an important channel for neuronal Mn2+ influx after systemic injections. We also show that after neuronal uptake, Mn2+ preferentially accumulates in projection terminals.
Display omitted
•Cav1.2 is an important entrance point for Mn2+ into neurons.•Mn2+ entering neurons via Cav1.2 preferentially accumulates in projection terminals.•This suggests MEMRI as a tool for the identification of activated neuronal circuits.
Highlights • Chronic elevations in corticosterone (CORT) modulate endocannabinoid levels. • CORT-induced changes in endocannabinoids are mediated by CRH signaling. • Chronic overexpression of CRH ...modulates endocannabinoids similar to chronic CORT.
Key points
Ongoing, moderate noise exposure does not instantly damage the auditory system but may cause lasting deficits, such as elevated thresholds and accelerated ageing of the auditory system.
...The neuromodulatory peptide urocortin‐3 (UCN3) is involved in the body's recovery from a stress response, and is also expressed in the cochlea and the auditory brainstem.
Lack of UCN3 facilitates age‐induced hearing loss and causes permanently elevated auditory thresholds following a single 2 h noise exposure at moderate intensities.
Outer hair cell function in mice lacking UCN3 is unaffected, so that the observed auditory deficits are most likely due to inner hair cell function or central mechanisms.
Highly specific, rather than ubiquitous, expression of UCN3 in the brain renders it a promising candidate for designing drugs to ameliorate stress‐related auditory deficits, including recovery from acoustic trauma.
Environmental acoustic noise is omnipresent in our modern society, with sound levels that are considered non‐damaging still causing long‐lasting or permanent changes in the auditory system. The small neuromodulatory peptide urocortin‐3 (UCN3) is the endogenous ligand for corticotropin‐releasing factor receptor type 2 and together they are known to play an important role in stress recovery. UCN3 expression has been observed in the auditory brainstem, but its role remains unclear. Here we describe the detailed distribution of UCN3 expression in the murine auditory brainstem and provide evidence that UCN3 is expressed in the synaptic region of inner hair cells in the cochlea. We also show that mice with deficient UCN3 signalling experience premature ageing of the auditory system starting at an age of 4.7 months with significantly elevated thresholds of auditory brainstem responses (ABRs) compared to age‐matched wild‐type mice. Following a single, 2 h exposure to moderate (84 or 94 dB SPL) noise, UCN3‐deficient mice exhibited significantly larger shifts in ABR thresholds combined with maladaptive recovery. In wild‐type mice, the same noise exposure did not cause lasting changes to auditory thresholds. The presence of UCN3‐expressing neurons throughout the auditory brainstem and the predisposition to hearing loss caused by preventing its normal expression suggests UCN3 as an important neuromodulatory peptide in the auditory system's response to loud sounds.
Key points
Ongoing, moderate noise exposure does not instantly damage the auditory system but may cause lasting deficits, such as elevated thresholds and accelerated ageing of the auditory system.
The neuromodulatory peptide urocortin‐3 (UCN3) is involved in the body's recovery from a stress response, and is also expressed in the cochlea and the auditory brainstem.
Lack of UCN3 facilitates age‐induced hearing loss and causes permanently elevated auditory thresholds following a single 2 h noise exposure at moderate intensities.
Outer hair cell function in mice lacking UCN3 is unaffected, so that the observed auditory deficits are most likely due to inner hair cell function or central mechanisms.
Highly specific, rather than ubiquitous, expression of UCN3 in the brain renders it a promising candidate for designing drugs to ameliorate stress‐related auditory deficits, including recovery from acoustic trauma.
Abstract
It has been shown previously (Sotnikov
et al
.,
) that mice selectively inbred for high anxiety‐related behavior (
HAB
) vs. low anxiety‐related behavior in the elevated plus maze ...differentially respond to trimethylthiazoline (
TMT
), a synthetic fox fecal odor. However, less is known about whether environmental factors can rescue these extreme phenotypes. Here, we found that an enriched environment (
EE
) provided during early adolescence induced anxiolytic effects in
HAB
(
HAB
‐
EE
) mice, rescuing their strong avoidance behavior induced by
TMT
. In a series of experiments, the contribution of maternal, juvenile and adolescent behavior to the anxiolytic effects elicited by
EE
was investigated. At the molecular level, using
c‐fos
expression mapping, we found that the activity of the medial and basolateral amygdala was significantly reduced in
HAB
‐
EE
mice after
TMT
exposure. We further analysed the expression of
C
rhr1
, as its amount in the amygdala has been reported to be important for the regulation of anxiety‐related behavior after
EE
. Indeed,
in situ
hybridisation indicated significantly decreased
C
rhr1
expression in the basolateral and central amygdala of
HAB
‐
EE
mice. To further test the involvement of
C
rhr1
in
TMT
‐induced avoidance, we exposed conditional glutamatergic‐specific
C
rhr1
‐knockout mice to the odor. The behavioral response of
C
rhr1
‐knockout mice mimicked that of
HAB
‐
EE
mice, and
c‐fos
expression in the amygdala after
TMT
exposure was significantly lower compared with controls, thereby further supporting a critical involvement of
C
rhr1
in environmentally‐induced anxiolysis. Altogether, our results indicate that EE can rescue strong avoidance of
TMT
by
HAB
mice with
C
rhr1
expression in the amygdala being critically involved.
Autodigestion of the pancreas by its own prematurely activated digestive proteases is thought to be an important event in the onset of acute pancreatitis. The mechanism responsible for the ...intrapancreatic activation of digestive zymogens is unknown, but a recent hypothesis predicts that a redistribution of lysosomal cathepsin B (CTSB) into a zymogen-containing subcellular compartment triggers this event. To test this hypothesis, we used CTSB-deficient mice in which the ctsb gene had been deleted by targeted disruption. After induction of experimental secretagogue-induced pancreatitis, the trypsin activity in the pancreas of ctsb(-/-) animals was more than 80% lower than in ctsb(+/+) animals. Pancreatic damage as indicated by serum activities of amylase and lipase, or by the extent of acinar tissue necrosis, was 50% lower in ctsb(-/-) animals. These experiments provide the first conclusive evidence to our knowledge that cathepsin B plays a role in intrapancreatic trypsinogen activation and the onset of acute pancreatitis.
The ability of many drugs of abuse, including cocaine, to mediate reinforcement and drug-seeking behaviors is in part mediated by the corticotropin-releasing hormone (CRH) system, in which CRH exerts ...its effects partly via the CRH receptor subtype 1 (CRHR1) in extra-hypothalamic areas. In fact, CRHR1 expressed in regions of the mesolimbic dopamine (DA) system have been demonstrated to modify cocaine-induced DA release and alter cocaine-mediated behaviors. Here we examined the role of neuronal selectivity of CRHR1 within the mesolimbic system on cocaine-induced behaviors. First we used a transgenic mouse line expressing GFP under the control of the Crhr1 promoter for double fluorescence immunohistochemistry to demonstrate the cellular location of CRHR1 in both dopaminergic and D1 dopaminoceptive neurons. We then studied cocaine sensitization, self-administration, and reinstatement in inducible CRHR1 knockouts using the CreERT2/loxP in either dopamine transporter (DAT)-containing neurons (DAT-Crhr1) or dopamine receptor 1 (D1)-containing neurons (D1-Crhr1). For sensitization testing, mice received five daily injections of cocaine (15 mg/kg IP). For self-administration, mice received eight daily 2 h cocaine (0.5 mg/kg per infusion) self-administration sessions followed by extinction and reinstatement testing. There were no differences in the acute or sensitized locomotor response to cocaine in DAT-Crhr1 or D1-Crhr1 mice and their respective controls. Furthermore, both DAT-Crhr1 and D1-Crhr1 mice reliably self-administered cocaine at the level of controls. However, DAT-Crhr1 mice demonstrated a significant increase in cue-induced reinstatement relative to controls, whereas D1-Crhr1 mice demonstrated a significant decrease in cue-induced reinstatement relative to controls. These data demonstrate the involvement of CRHR1 in cue-induced reinstatement following cocaine self-administration, and implicate a bi-directional role of CRHR1 for cocaine craving.
TNF-alpha-induced apoptosis is thought to involve mediators from acidic vesicles. Cathepsin B (cat B), a lysosomal cysteine protease, has recently been implicated in apoptosis. To determine whether ...cat B contributes to TNF-alpha-induced apoptosis, we exposed mouse hepatocytes to the cytokine in vitro and in vivo. Isolated hepatocytes treated with TNF-alpha in the presence of the transcription inhibitor actinomycin D (AcD) accumulated cat B in their cytosol. Further experiments using cell-free systems indicated that caspase-8 caused release of active cat B from purified lysosomes and that cat B, in turn, increased cytosol-induced release of cytochrome c from mitochondria. Consistent with these observations, the ability of TNF-alpha/AcD to induce mitochondrial release of cytochrome c, caspase activation, and apoptosis of isolated hepatocytes was markedly diminished in cells from CatB(-/-) mice. Deletion of the CatB gene resulted in diminished liver injury and enhanced survival after treatment in vivo with TNF-alpha and an adenovirus construct expressing the IkappaB superrepressor. Collectively, these observations suggest that caspase-mediated release of cat B from lysosomes enhances mitochondrial release of cytochrome c and subsequent caspase activation in TNF-alpha-treated hepatocytes.
PDF
