Huntington’s disease is an inherited neurodegenerative disease characterized by the degeneration of the cerebral cortex, thalamus, and striatum. The loss of neurons in the cerebral cortex and the thalamus may affect the synaptic circuitry in the striatum as these regions send glutamatergic projections (corticospinal & thalamostriatal) to neurons in the striatum. Prior studies have suggested the detrimental impact that the mutant Huntingtin protein (mHTT) may have on corticostriatal afferents, but less is known thalamic inputs to the dorsal striatum. In this study, we report a 50% reduction in thalamostriatal axospinous synapse density and significant reductions in dendritic spine volume at the ultrastructural level using electron microscopy. Additionally, dystrophic alterations to mitochondria size and morphology were also found. At the microcircuit level, we report a reduction in the spatial abundance of thalamostriatal axon terminals at the rostral, middle, and caudal levels of the dorsolateral striatum while an inverse distribution was observed for mHTT, suggesting a novel topographic distribution of thalamostriatal projections and mHTT along the rostral-caudal axis of the dorsolateral striatum. These findings are novel in the Q175 HD mouse model and supports the theory of an excitatory: inhibitory imbalance contributing to structural synaptic changes in the dorsal striatum. Further studies of the corticostriatal projections will determine the global extent of this imbalance.

The present study was undertaken to investigate the origin of cocaine- and amphetamine-regulated transcript (CART) peptide immunoreactive (irCART) fibers observed in the nucleus of the solitary tract (NTS) and assess the role of CART peptide on phenylephrine (PE)-induced baroreflex. Immunohistochemical and retrograde tract-tracing studies showed that some of the irCART fibers observed in the NTS may have their cell bodies in the nodose ganglia. In urethane-anesthetized rats, intracisternal or bilateral intra-NTS microinjection of the CART peptide fragment 55-102 (0.1-3 nmol), referred to herein as CARTp, consistently and dose dependently attenuated PE-induced bradycardia. CARTp, in the doses used here, caused no significant changes of resting blood pressure or heart rate. Bilateral intra-NTS injections of CART antibody (1:500) potentiated PE-induced bradycardia. Injections of saline, normal rabbit serum, or concomitant injection of CARTp and CART antiserum into the NTS caused no significant changes of PE-induced baroreflex. The result suggests that endogenously released CARTp from primary afferents or exogenously administered CARTp modulates PE-induced baroreflex.

The murine model has been used to investigate the role of cardiac sensory axons in various disease states. However, the distribution and morphological structures of cardiac nociceptive axons in normal murine tissues have not yet been well characterized. In this study, whole-mount atria from FVB mice were processed with calcitonin gene-related peptide (CGRP) and substance P (SP) primary antibodies followed by secondary antibodies, and then examined using confocal microscopy. We found: 1) Large CGRP-IR axon bundles entered the atria with the major veins, and these large bundles bifurcated into small bundles and single axons that formed terminal end-nets and free endings in the epicardium. Varicose CGRP-IR axons had close contacts with muscle fibers, and some CGRP-IR axons formed varicosities around principle neurons (PNs) within intrinsic cardiac ganglia (ICGs). 2) SP-IR axons also were found in the same regions of the atria, attached to veins, and within cardiac ganglia. Similar to CGRP-IR axons, these SP-IR axons formed terminal end-nets and free endings in the atrial epicardium and myocardium. Within ICGs, SP-IR axons formed varicose endings around PNs. However, SP-IR nerve fibers were less abundant than CGRP-IR fibers in the atria. 3) None of the PNs were CGRP-IR or SP-IR. 4) CGRP-IR and SP-IR often colocalized in terminal varicosities around PNs. Collectively, our data document the distribution pattern and morphology of CGRP-IR and SP-IR axons and terminals in different regions of the atria. This knowledge provides useful information for CGRP-IR and SP-IR axons that can be referred to in future studies of pathological remodeling.

Baroreflex control of heart rate (HR) is impaired in human diabetes mellitus and in large experimental models. However, baroreflex impairment in diabetic mouse models and diabetes-induced remodeling of baroreflex circuitry are not well studied. We examined the impairment of baroreflex control of heart rate (HR) and assessed structural remodeling of cardiac ganglia in the streptozotocin (STZ)-induced diabetic mouse model. FVB mice were either injected with vehicle or STZ. Group 1: mice were anesthetized and the femoral artery and vein were catheterized at the 30th day after vehicle or STZ injection. On the second day after surgery, baroreflex-mediated HR responses to sodium nitroprusside (SNP) and phenylephrine (PE)-induced mean arterial blood pressure (MABP) changes were measured in conscious mice. Group 2: Fluoro-Gold was administered (i.p.) to label cardiac ganglia in each mouse at the 25th day after vehicle or STZ injection. After another five days, animals were perfused and cardiac ganglia were examined using confocal microscopy. Compared with control, we found in STZ mice: 1) the HR decreased, but MABP did not. 2) The PE-induced increases of MABP were decreased. 3) Baroreflex bradycardia was attenuated in the rapid MABP ascending phase but the steady-state ΔHR/ΔMABP was not different at all PE doses. 4) SNP-induced MABP decreases were not different. 5) Baroreflex tachycardia was attenuated. 6) The sizes of cardiac ganglia and ganglionic principal neurons were decreased. 7) The ratio of nucleus/cell body of cardiac ganglionic neurons was increased. We conclude that baroreflex control of HR is impaired in conscious STZ mice. In addition, diabetes may induce a significant structural remodeling of cardiac ganglia. Such an anatomical change of cardiac ganglia may provide new information for the understanding of diabetes-induced remodeling of the multiple components within the baroreflex circuitry.

Baroreflex control of heart rate (HR) is impaired in human type 1 diabetes mellitus. The goal of this study is to use a transgenic mouse model of type 1 diabetes (OVE26) to assess the diabetes-induced baroreflex impairment in the conscious state. OVE26 transgenic mice (which develop hyperglycemia within the first three weeks after birth due to the specific damage of beta cells) and normal control mice (FVB) 5-6 months of age were anesthetized, and the left femoral artery and both veins were catheterized. On the second day after surgery, baroreflex-mediated HR responses to arterial blood pressure (ABP) changes that were induced by separate microinfusion of phenylephrine (PE) and sodium nitroprusside (SNP) at different doses (0.03-0.4 μg/min) were measured in the conscious state. Compared with FVB control, we found that in OVE26 diabetic mice 1) mean ABP (MABP) and HR were decreased (p < 0.05). 2) PE-induced MABP increases were comparable to those in FVB mice (p > 0.05). 3) Baroreflex-mediated bradycardia was attenuated (p < 0.05). 4) SNP-induced MABP decreases was reduced (p < 0.05). 5) Baroreflex-mediated tachycardia was attenuated (p < 0.05). Since baroreflex control of HR in conscious OVE26 mice is impaired in a similar fashion to human diabetes mellitus, we suggest that OVE26 mice may provide a useful model to study the neural mechanisms of diabetes-induced baroreflex impairment.

Intrinsic cardiac neurons are core elements of a complex neural network that serves as an important integrative center for regulation of cardiac function. Although mouse models are used frequently in cardiovascular research, very little is known about mouse intrinsic cardiac neurons. Accordingly, we have dissociated neurons from adult mouse heart, maintained these cells in culture, and defined their basic phenotypic properties. Neurons in culture were primarily unipolar, and 89% had prominent neurite outgrowth after 3 days (longest neurite length of 258 ± 20 μm, n = 140). Many neurites formed close appositions with other neurons and nonneuronal cells. Neurite outgrowth was drastically reduced when neurons were kept in culture with a majority of nonneural cells eliminated. This finding suggests that nonneuronal cells release molecules that support neurite outgrowth. All neurons in coculture showed immunoreactivity for a full complement of cholinergic markers, but about 21% also stained for tyrosine hydroxylase, as observed previously in sections of intrinsic cardiac ganglia from mice and humans. Whole cell patch-clamp recordings demonstrated that these neurons have voltage-activated sodium current that is blocked by tetrodotoxin and that neurons exhibit phasic or accommodating patterns of action potential firing during a depolarizing current pulse. Several neurons exhibited a fast inward current mediated by nicotinic ACh receptors. Collectively, this work shows that neurons from adult mouse heart can be maintained in culture and exhibit appropriate phenotypic properties. Accordingly, these cultures provide a viable model for evaluating the physiology, pharmacology, and trophic factor sensitivity of adult mouse cardiac parasympathetic neurons.

Effects of substance P (SP) and selective tachykinin agonists on neurotransmission at guinea-pig intracardiac ganglia were studied in vitro. Voltage responses of neurons to superfused tachykinins and nerve stimulation were measured using intracellular microelectrodes. Predominant effects of SP (1 μM) were to cause slow depolarization and enable synaptic transmission at low intensities of nerve stimulation. Augmented response to nerve stimulation occurred with 29 of 40 intracardiac neurons (approx. 73%). SP inhibited synaptic transmission at 23% of intracardiac neurons but also caused slow depolarization. Activation of NK3 receptors with 100 nM [MePhe 7]neurokinin B caused slow depolarization, enhanced the response of many intracardiac neurons to low intensity nerve stimulation or local application of acetylcholine, and triggered action potentials independent of other stimuli in 6 of 42 neurons. The NK1 agonist [Sar 9,Met(O2)11]SP had similar actions but was less effective and did not trigger action potentials independently. Neither selective agonist inhibited cholinergic neurotransmission. We conclude that SP can function as a positive or negative neuromodulator at intracardiac ganglion cells, which could be either efferent neurons or interneurons. Potentiation occurs primarily through NK3 receptors and may enable neuronal responses with less preganglionic nerve activity. Inhibition of neurotransmission by SP is most likely explained by the known blocking action of this peptide at ganglionic nicotine receptors.

The objective of the study was to determine if chronic interruption of all extrinsic nerve inputs to the heart alters cholinergic-mediated responses within the intrinsic cardiac nervous system (ICN). Extracardiac nerve inputs to the ICN were surgically interrupted (ICN decentralized). Three weeks later, the intrinsic cardiac right atrial ganglionated plexus (RAGP) was removed and intrinsic cardiac neuronal responses were evaluated electrophysiologically. Cholinergic receptor abundance was evaluated using autoradiography. In sham controls and chronic decentralized ICN ganglia, neuronal postsynaptic responses were mediated by acetylcholine, acting at nicotinic and muscarinic receptors. Muscarine- but not nicotine-mediated synaptic responses that were enhanced after chronic ICN decentralization. After chronic decentralization, muscarine facilitation of orthodromic neuronal activation increased. Receptor autoradiography demonstrated that nicotinic and muscarinic receptor density associated with the RAGP was unaffected by decentralization and that muscarinic receptors were tenfold more abundant than nicotinic receptors in the right atrial ganglia in each group. After chronic decentralization of the ICN, intrinsic cardiac neurons remain viable and responsive to cholinergic synaptic inputs. Enhanced muscarinic responsiveness of intrinsic cardiac neurons occurs without changes in receptor abundance.

No description available.

No description available.