Neurons Of Intermediolateral Column Research Articles

Spinal neuromodulation mitigates myocardial ischemia-induced sympathoexcitation by suppressing the intermediolateral nucleus hyperactivity and spinal neural synchrony.

Myocardial ischemia disrupts the cardio-spinal neural network that controls the cardiac sympathetic preganglionic neurons, leading to sympathoexcitation and ventricular tachyarrhythmias (VTs). Spinal cord stimulation (SCS) is capable of suppressing the sympathoexcitation caused by myocardial ischemia. However, how SCS modulates the spinal neural network is not fully known. In this pre-clinical study, we investigated the impact of SCS on the spinal neural network in mitigating myocardial ischemia-induced sympathoexcitation and arrhythmogenicity. Ten Yorkshire pigs with left circumflex coronary artery (LCX) occlusion-induced chronic myocardial infarction (MI) were anesthetized and underwent laminectomy and a sternotomy at 4-5 weeks post-MI. The activation recovery interval (ARI) and dispersion of repolarization (DOR) were analyzed to evaluate the extent of sympathoexcitation and arrhythmogenicity during the left anterior descending coronary artery (LAD) ischemia. Extracellular in vivo and in situ spinal dorsal horn (DH) and intermediolateral column (IML) neural recordings were performed using a multichannel microelectrode array inserted at the T2-T3 segment of the spinal cord. SCS was performed for 30 min at 1 kHz, 0.03 ms, 90% motor threshold. LAD ischemia was induced pre- and 1 min post-SCS to investigate how SCS modulates spinal neural network processing of myocardial ischemia. DH and IML neural interactions, including neuronal synchrony as well as cardiac sympathoexcitation and arrhythmogenicity markers were evaluated during myocardial ischemia pre- vs. post-SCS. ARI shortening in the ischemic region and global DOR augmentation due to LAD ischemia was mitigated by SCS. Neural firing response of ischemia-sensitive neurons during LAD ischemia and reperfusion was blunted by SCS. Further, SCS showed a similar effect in suppressing the firing response of IML and DH neurons during LAD ischemia. SCS exhibited a similar suppressive impact on the mechanical, nociceptive and multimodal ischemia sensitive neurons. The LAD ischemia and reperfusion-induced augmentation in neuronal synchrony between DH-DH and DH-IML pairs of neurons were mitigated by the SCS. These results suggest that SCS is decreasing the sympathoexcitation and arrhythmogenicity by suppressing the interactions between the spinal DH and IML neurons and activity of IML preganglionic sympathetic neurons.

Melanocortin 4 Receptors Reciprocally Regulate Sympathetic and Parasympathetic Preganglionic Neurons

Melanocortin 4 receptors (MC4Rs) in the central nervous system are key regulators of energy and glucose homeostasis. Notably, obese patients with MC4R mutations are hyperinsulinemic and resistant to obesity-induced hypertension. Although these effects are probably dependent upon the activity of the autonomic nervous system, the cellular effects of MC4Rs on parasympathetic and sympathetic neurons remain undefined. Here, we show that MC4R agonists inhibit parasympathetic preganglionic neurons in the brainstem. In contrast, MC4R agonists activate sympathetic preganglionic neurons in the spinal cord. Deletion of MC4Rs in cholinergic neurons resulted in elevated levels of insulin. Furthermore, re-expression of MC4Rs specifically in cholinergic neurons (including sympathetic preganglionic neurons) restores obesity-associated hypertension in MC4R null mice. These findings provide a cellular correlate of the autonomic side effects associated with MC4R agonists and demonstrate a role for MC4Rs expressed in cholinergic neurons in the regulation of insulin levels and in the development of obesity-induced hypertension.

Heterogeneity of Membrane Properties in Sympathetic Preganglionic Neurons of Neonatal Mice: Evidence of Four Subpopulations in the Intermediolateral Nucleus

Spinal cord sympathetic preganglionic neurons (SPNs) integrate activity from descending and sensory systems to determine the final central output of the sympathetic nervous system. The intermediolateral column (IML) has the highest number and density of SPNs and, within this region, SPN somas are found in distinct clusters within thoracic and upper lumbar spinal segments. Whereas SPNs exhibit a rostrocaudal gradient of end-target projections, individual clusters contain SPNs with diverse functional roles. Here we explored diversity in the electrophysiological properties observed in Hb9-eGFP-identified SPNs in the IML of neonatal mice. Overall, mouse SPN intrinsic membrane properties were comparable with those seen in other species. A wide range of values was obtained for all measured properties (up to a 10-fold difference), suggesting that IML neurons are highly differentiated. Using linear regression we found strong correlations between many cellular properties, including input resistance, rheobase, time constant, action potential shape, and degree of spike accommodation. The best predictor of cell function was rheobase, which correlated well with firing frequency-injected current (f-I) slopes as well as other passive and active membrane properties. The range in rheobase suggests that IML neurons have a recruitment order with stronger synaptic drives required for maximal recruitment. Using cluster analysis, we identified at least four subpopulations of SPNs, including one with a long time constant, low rheobase, and high f-I gain. We thus propose that the IML contains populations of neurons that are differentiable by their membrane properties and hypothesize they represent diverse functional classes.

Lack of Neurotrophin-4 Causes Selective Structural and Chemical Deficits in Sympathetic Ganglia and Their Preganglionic Innervation

Neurotrophin-4 (NT-4) is perhaps the still most enigmatic member of the neurotrophin family. We show here that NT-4 is expressed in neurons of paravertebral and prevertebral sympathetic ganglia, i.e., the superior cervical (SCG), stellate (SG), and celiac (CG) ganglion. Mice deficient for NT-4 showed a significant reduction (20-30%) of preganglionic sympathetic neurons in the intermediolateral column (IML) of the thoracic spinal cord. In contrast, neuron numbers in the SCG, SG, and CG were unchanged. Numbers of axons in the thoracic sympathetic trunk (TST) connecting the SG with lower paravertebral ganglia were also reduced, whereas axon numbers in the cervical sympathetic trunk (CST) were unaltered. Axon losses in the TST were paralleled by losses of synaptic terminals on SG neurons visualized by electron microscopy. Furthermore, immunoreactivity for the synaptic vesicle antigen SV2 was clearly reduced in the SG and CG. Levels of catecholamines and tyrosine hydroxylase immunoreactivity were dramatically reduced in the SG and the CG but not in the SCG. Despite this severe phenotype in the sympathetic system, blood pressure levels were not reduced and displayed a pattern more typical of deficits in baroreceptor afferents. Numbers of IML neurons were unaltered at postnatal day 4, suggesting a postnatal requirement for their maintenance. In light of these and previous data, we hypothesize that NT-4 provided by postganglionic sympathetic neurons is required for establishing and/or maintaining synapses of IML neurons on postganglionic cells. Impairment of synaptic connectivity may consequently reduce impulse flow, causing a reduction in transmitter synthesis in postganglionic neurons.

Expression of neurotrophin receptors trkB and trkC and their ligands in rat adrenal gland and the intermediolateral column of the spinal cord.

Neurotrophins and their trk receptors constitute major classes of signaling molecules with important actions in the developing and adult nervous system. With regard to the sympathoadrenal cell lineage, which gives rise to sympathetic neurons and chromaffin cells, neurotrophin-3 (NT-3) and nerve growth factor (NGF) are thought to influence developing sympathetic neurons. Neurotrophin requirements of chromaffin cells of the adrenal medulla are less well understood than those for NGF. In order to provide the bases for understanding of putative functions of neurotrophins for the development and maintenance of chromaffin cells and their preganglionic innervation, in situ hybridization has been used to study the expression of brain-derived neurotrophic factor (BDNF) and NT-3, together with their cognate receptors trkB and trkC, in the adrenal gland and in the intermediolateral column (IML) of the spinal cord. BDNF is highly expressed in the embryonic adrenal cortex and later in cells of the cortical reticularis zone. Adrenal medullary chromaffin cells fail to express detectable levels of mRNAs for BDNF, NT-3, and their cognate receptors trkB and trkC. Neurons in the IML express BDNF and trkB, and low levels of NT-3 and trkC. Our data make it unlikely that BDNF and NT-3 serve as retrograde trophic factors for IML neurons but suggest roles of BDNF and NT-3 locally within the spinal cord and possibly for sensory nerves of the adrenal cortex.

Glial Cell Line-Derived Neurotrophic Factor Rescues Target-Deprived Sympathetic Spinal Cord Neurons But Requires Transforming Growth Factor-β as CofactorIn Vivo

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for several populations of CNS and peripheral neurons. Synthesis and storage of GDNF by the neuron-like adrenal medullary cells suggest roles in adrenal functions and/or in the maintenance of spinal cord neurons that innervate the adrenal medulla. We show that unilateral adrenomedullectomy causes degeneration of all sympathetic preganglionic neurons within the intermediolateral column (IML) of spinal cord segments T7-T10 that project to the adrenal medulla. In situ hybridization revealed that IML neurons express the glycosylphosphatidylinositol-linked alpha receptor 1 and c-Ret receptors, which are essential for GDNF signaling. IML neurons also display immunoreactivity for transforming growth factor-beta (TGF-beta) receptor II. Administration of GDNF (recombinant human, 1 microg) in Gelfoam implanted into the medullectomized adrenal gland rescued all Fluoro-Gold-labeled preganglionic neurons projecting to the adrenal medulla after four weeks. Cytochrome c applied as a control protein was not effective. The protective effect of GDNF was prevented by co-administration to the Gelfoam of neutralizing antibodies recognizing all three TGF-beta isoforms but not GDNF. This suggests that the presence of endogenous TGF-beta was essential for permitting a neurotrophic effect of GDNF. Our data indicate that GDNF has a capacity to protect a population of autonomic spinal cord neurons from target-deprived cell death. Furthermore, our results demonstrate for the first time that the previously reported requirement of TGF-beta for permitting trophic actions of GDNF in vitro (Kreiglstein et al., 1998) also applies to the in vivo situation.

Quantitative study of intermediolateral column cell counts in Machado-Joseph disease

The number of intermediolateral column (ILC) neurons in 6 alternating segments from the 2nd to 12th thoracic segment of the spinal cord were studied in 4 cases with Machado-Joseph disease (MJD), 3 cases with olivopontocerebellar atrophy (OPCA), a case with Shy-Drager syndrome (SDS), and 5 normal controls. We counted the number of ILC neurons with clearly defined nucleoli in 12 sections of each segment, each section 20 μm thick and taken at 100 μm intervals and then divided the 6 alternating segments into 3 groups, upper (Th2, 4), middle (Th6, 8) and lower (Th10, 12). In each of the three groups of normal control cases, the number of ILC neurons had decreased with aging. In all MJD cases, the number of ILC neurons had moderately decreased in comparison with age-matched controls. One of the MJD cases showed a marked decrease in the number of ILC neurons, as did the SDS case. The ILCs of the entire thoracic spinal cord in the MJD cases were moderately involved.

Phosphorylated high molecular weight neurofilament protein in the peripheral motor, sensory and sympathetic neuronal perikarya: system-dependent normal variations and changes in amyotrophic lateral sclerosis and multiple system atrophy.

Using monoclonal antibody (Ta-51) that specifically binds phosphorylated high molecular weight neurofilament (pNFH) proteins, we investigated the occurrence of perikaryal pNFH in the spinal ventral horn motoneurons, intermediolateral column (ILC) neurons, sympathetic ganglion neurons and dorsal root ganglion (DRG) neurons obtained from patients with amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA) and from control cases. In the controls, a system-dependent variation in perikaryal Ta-51 immunoreactivity was observed. Very few ventral horn cells and ILC neurons were stained with Ta-51, while large population of DRG neurons and sympathetic neurons were Ta-51 positive. The incidence of perikaryal immunoreactivity in the ventral horn cells was significantly increased in ALS and MSA. Some ILC neurons in ALS were Ta-51 positive and their incidence was significantly higher than that of the controls. These data suggest that both ILC neurons and ventral horn cells are affected with respect to pNFH metabolism in ALS and MSA. No significant difference was, however, detected in the Ta-51 immunoreactivity of both DRG and sympathetic ganglion neurons in ALS and MSA as compared with the controls.

Ciliary neurotrophic factor supports target-deprived preganglionic sympathetic spinal cord neurons

Spinal cord neurons in the intermediolateral column (IML) that innervate the adrenal medulla require target-derived factor(s) for their maintenance in vivo. Selective destruction of the adult rat adrenal medulla causes an approximate 25 % loss of Nissl-stained IML neurons between spinal cord levels Th 7–10 4 weeks after surgery. We have previously suggested that basic fibroblast growth factor (bFGF) and ciliary neurotrophic factor (CNTF) or closely related molecules are present in adrenal chromaffin cells and granules. Basic FGF supplemented in gelfoams to the medullectomized adrenal gland fully prevented IML neuron losses. These results are now extended by demonstrating that (i) CNTF administered in vivo (7.2 μg/gelfoam) also rescues IML neurons, and (ii) the rescue effect is abolished by splanchnicotomy, i.e. interruption of axonal pathway from the spinal cord to the adrenal gland. These data would be consistent with CNTF being a retrograde trophic messenger to the spinal cord, but do not exclude the possibility that CNTF mimics or induces the formation of an endogenous trophic factor.