Ribonuclease recruitment using a small molecule reduced c9ALS/FTD r(G4C2) repeat expansion in vitro and in vivo ALS models.

The most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD) is an expanded G4C2 RNA repeat [r(G4C2)exp] in chromosome 9 open reading frame 72 (C9orf72), which elicits pathology through several mechanisms. Here, we developed and characterized a small molecule for targeted degradation of r(G4C2)exp. The compound was able to selectively bind r(G4C2)exp's structure and to assemble an endogenous nuclease onto the target, provoking removal of the transcript by native RNA quality control mechanisms. In c9ALS patient­derived spinal neurons, the compound selectively degraded the mutant C9orf72 allele with limited off-targets and reduced quantities of toxic dipeptide repeat proteins (DPRs) translated from r(G4C2)exp. In vivo work in a rodent model showed that abundance of both the mutant allele harboring the repeat expansion and DPRs were selectively reduced by this compound. These results demonstrate that targeted small-molecule degradation of r(G4C2)exp is a strategy for mitigating c9ALS/FTD-associated pathologies and studying disease-associated pathways in preclinical models.

Proteinase-activated receptors in the nucleus of the solitary tract: evidence for glial-neural interactions in autonomic control of the stomach.

Bleeding head injury is associated with gastric stasis, a symptom of collapse of autonomic control of the gut described by Cushing around 1932. Recent work suggests that the proteinase thrombin, produced secondary to bleeding, may be the root cause. Results from our in vivo physiological studies show that fourth ventricular injection of PAR1 agonists, as well as thrombin itself, produced significant reductions in gastric transit in the awake rat. We expected that the PAR1 effect to inhibit gastric transit was the result of direct action on vagovagal reflex circuitry in the dorsal medulla. Surprisingly, our immunohistochemical studies demonstrated that PAR1 receptors are localized exclusively to the astrocytes and not the neurons in the nucleus of the solitary tract (NST; principal locus integrating visceral afferent input and part of the gastric vagovagal reflex control circuitry). Our in vitro calcium imaging studies of hindbrain slices revealed that PAR1 activation initially causes a dramatic increase in astrocytic calcium, followed seconds later by an increase in calcium signal in NST neurons. The neuronal effect, but not the astrocytic effect, of PAR1 activation was eliminated by glutamate receptor antagonism. TTX did not eliminate the effects of PAR1 activation on either glia or neurons. Thus, we propose that glia are the primary CNS sensors for PAR agonists and that the response of these glial cells drives the activity of adjacent (e.g., NST) neurons. These results show, for the first time, that changes in autonomic control can be directly signaled by glial detection of local chemical stimuli.

CXCR4 receptors in the dorsal medulla: implications for autonomic dysfunction.

The chemokine receptor, CXCR4, plays an essential role in guiding neural development of the CNS. Its natural agonist, CXCL12 [or stromal cell-derived factor-1 (SDF-1)], normally is derived from stromal cells, but is also produced by damaged and virus-infected neurons and glia. Pathologically, this receptor is critical to the proliferation of the HIV virus and initiation of metastatic cell growth in the brain. Anorexia, nausea and failed autonomic regulation of gastrointestinal (GI) function cause morbidity and contribute to the mortality associated with these disease states. Our previous work on the peripheral cytokine, tumor necrosis factor-alpha, demonstrated that similar morbidity factors involving GI dysfunction are attributable to agonist action on neural circuit elements of the dorsal vagal complex (DVC) of the hindbrain. The DVC includes vagal afferent terminations in the solitary nucleus, neurons in the solitary nucleus (NST) and area postrema, and visceral efferent motor neurons in the dorsal motor nucleus (DMN) that are responsible for the neural regulation of digestive functions from the oral cavity to the transverse colon. Immunohistochemical techniques demonstrate a dense concentration of CXCR4 receptors on neurons throughout the DVC and the hypoglossal nucleus. CXCR4-immunoreactivity is also intense on microglia within the DVC, though not on the astrocytes. Physiological studies show that nanoinjection of SDF-1 into the DVC produces a significant reduction in gastric motility in parallel with an elevation in the numbers of cFOS-activated neurons in the NST and DMN. These results suggest that this chemokine receptor may contribute to autonomically mediated pathophysiological events associated with CNS metastasis and infection.

Tumor necrosis factor potentiates central vagal afferent signaling by modulating ryanodine channels.

Disease processes such as infection, leukemia, and autoimmune disorders are often associated with nausea, emesis, and anorexia. A common denominator of these rather disparate states is the production of the early, proinflammatory cytokine tumor necrosis factor-alpha (TNF) in significant quantities. Recent studies have shown that TNF may act as a neuromodulator in the hindbrain to produce malaise by potentiating visceral afferent signaling at the central processes of the vagus nerve. However, the mechanism by which TNF produces this signal amplification is not known. Our time-lapse calcium imaging studies of individual central vagal afferent varicosities in the caudal brainstem slice preparation show that, although TNF has minimal direct effects to elevate terminal intracellular calcium levels, TNF does potentiate the terminal afferent responses to other stimuli through a ryanodine-based, calcium-induced calcium release mechanism. Such a scheme may explain how TNF sensitizes visceral as well as somatosensory primary afferents.

TNF alpha-p55 receptors: medullary brainstem immunocytochemical localization in normal and vagus nerve-transected rats.

Tumor necrosis factor alpha (TNF(alpha)) is a potent modulator of autonomic reflex mechanisms that control the stomach. Evidence suggests that TNF(alpha) action directly on vago-vagal reflex control circuits causes the autonomic misregulation of digestion manifested as gastrointestinal stasis, nausea, and emesis associated with illness. Neurophysiological studies indicated that TNF(alpha) may have effects on vagal afferents in the solitary nucleus, as well as neurons of the solitary nucleus (NST) and dorsal motor nucleus (DMN) of the vagus. The aim of this study was to determine the location of the TNFR1 receptor (p55) in the medulla using immunocytochemical methods. We devised a technique for localizing the p55 receptor using heat-induced antigen recovery in fixed tissue sections. This protocol allowed us to demonstrate that dense p55-immunoreactivity (p55-ir) is constitutively present on central (but not peripheral) vagal afferents in the solitary tract (ST) and nucleus; p55-ir is also present on afferents entering the spinal trigeminal nucleus. Unilateral supra-nodose vagotomy eliminated p55-ir from ipsilateral central vagal afferents. Virtually all neurons in the brainstem appeared to express p55-ir at a low level, i.e., just above background. However, vagotomy caused a dramatic up-regulation of p55-ir in vagal motor neurons. This increase in p55-ir in axotomized neurons may play a pivotal role in the connection between the occurrence of the injury and the initiation of apoptotic processes resulting in elimination of damaged neurons.

Co-localization of TRHR1 and LepRb receptors on neurons in the hindbrain of the rat.

We have reported a highly cooperative interaction between leptin and thyrotropin releasing hormone (TRH) in the hindbrain to generate thermogenic responses (Hermann et al., 2006) (Rogers et al., 2009). Identifying the locus in the hindbrain where leptin and TRH act synergistically to increase thermogenesis will be necessary before we can determine the mechanism(s) by which this interaction occurs. Here, we performed heat-induced epitope recovery techniques and in situ hybridization to determine if neurons or afferent fibers in the hindbrain possess both TRH type 1 receptor and long-form leptin receptor [TRHR1; LepRb, respectively]. LepRb receptors were highly expressed in the solitary nucleus [NST], dorsal motor nucleus of the vagus [DMN] and catecholaminergic neurons of the ventrolateral medulla [VLM]. All neurons that contained LepRb also contained TRHR1. Fibers in the NST and the raphe pallidus [RP] and obscurrus [RO] that possess LepRb receptors were phenotypically identified as glutamatergic type 2 fibers (vglut2). Fibers in the NST and RP that possess TRHR1 receptors were phenotypically identified as serotonergic [i.e., immunopositive for the serotonin transporter; SERT]. Co-localization of LepRb and TRHR1 was not observed on individual fibers in the hindbrain but these two fiber types co-mingle in these nuclei. These anatomical arrangements may provide a basis for the synergy between leptin and TRH to increase thermogenesis.

Serotonergic fiber sprouting to external anal sphincter motoneurons after spinal cord contusion.

The present study analyzed the anatomical plasticity of serotonergic immunoreactive projections to external anal sphincter (EAS) motoneurons, and the behavioral plasticity of EAS reflexes, penile erection, and locomotion in rats with spinal contusion injury (SCI) or complete spinal cord transection (TX). Electromyographic activity of the EAS, penile erection latency, and BBB locomotor score exhibited parallel recovery over the 6-week recovery period after contusion SCI. This pattern of recovery was not observed in TX animals. While locomotor scores demonstrated a small increase after TX, erectile and anorectal function remained at abnormal levels established immediately after injury. Serotonergic immunofluorescent (5-HT-IF) staining at the lesion site identified a small number of fibers spared after SCI that may provide a substrate for functional recovery. Pixel density measurements of 5-HT-IF in the vicinity of retrogradely labeled EAS and unlabeled pudendal motoneurons necessary for penile erection provide indirect evidence of serotonergic sprouting that parallels the observed functional recovery in animals with SCI. No 5-HT-IF was detected caudal to the injury site in TX animals. These studies indicate: (1) lumbosacral eliminative and reproductive reflexes provide a valid means of studying the mechanisms of post-SCI plasticity; (2) the similar recovery curves suggest similar return of descending control, perhaps through sprouting of descending serotonergic fibers; (3) the observed deficits after TX likely represent the permanent removal of descending inhibition and reflect reorganization of segmental circuitry.