Spinal relay neurons for central control of autonomic pathways in a photoperiodic rodent

Location and distribution of spinal sympathetic preganglionic neurons projecting to the superior cervical ganglion were investigated in a rodent model organism for photoperiodic regulation, the Djungarian hamster (Phodopus sungorus). Upon unilateral injection of Fluoro-Gold into the superior cervical ganglia, retrograde neuronal tracing demonstrated labeled neurons ipsilateral to the injection site. They were seen in spinal segments C8 to Th5 of which the segments Th1 to Th3 contained about 98% of the labeled cells. Neurons were found in the spinal cord predominantly in the intermediolateral nucleus pars principalis and pars funicularis. At the same time, the central autonomic area and the intercalated region contained only very few labeled cells. In the intermediolateral nucleus, cells often were arranged in clusters, of which several were seen in each spinal segment. Selected sections were exposed to antibodies directed against arginine-vasopressin, neuronal nitric oxide synthase, neuropeptide Y, neurotensin, oxytocin or substance P. It was found that about two-thirds of sympathetic preganglionic neurons produced the gaseous neuroactive substance nitric oxide and that few contained small amounts of neuropeptide Y. Fibers of putative supraspinal origin immunopositive for either arginine-vasopressin, neuronal nitric oxide synthase, neuropeptide Y, neurotensin, oxytocin or, in particular, substance P were found in the vicinity of labeled sympathetic preganglionic neurons. These results demonstrate the location of relay neurons for autonomic control of cranial and cardial structures and provide further knowledge on neurochemical properties of sympathetic preganglionic neurons and related structures.

Activated Microglia in the Rat Spinal Cord Following Peripheral Axon Injury Promote Glial and Neuronal Plasticity Which is Necessary for Long-Term Neuronal Survival

Following the transection of peripheral sympathetic preganglionic axons comprising the cervical sympathetic trunk (CST), we observe robust glial and neuronal plasticity at 1 week post-injury in the rat spinal cord intermediolateral cell column (IML), which houses the injured parent neuronal cell bodies. This plasticity contributes to neuroprotection, as no neuronal loss in the IML is present at 16 weeks post-injury. Here, we administered the antibiotic minocycline or vehicle (VEH) daily for 1 week after CST transection to investigate the role of activated microglia in IML glial and neuronal plasticity and subsequent neuronal survival. At 1 week post-injury, minocycline treatment did not alter microglia number in the IML, but led to a dampened microglia activation state. In addition, the increases in oligodendrocyte (OL) lineage cells and activated astrocytes following injury in VEH rats were attenuated in the minocycline-treated rats. Further, the normal downregulation of choline acetyltransferase (ChAT) in the injured neurons was blunted. At 16 weeks post-injury, fewer ChAT+ neurons were present in the minocycline-treated rats, suggesting that activated microglia together with the glial and neuronal plasticity at 1 week post-injury contribute to the long-term survival of the injured neurons. These results provide evidence for beneficial crosstalk between activated microglia and neurons as well as other glial cells in the cord following peripheral axon injury, which ultimately leads to neuroprotection. The influences of microglia activation in promoting neuronal survival should be considered when developing therapies to administer minocycline for the treatment of neurological pathologies.

Morphological maladaptations in sympathetic preganglionic neurons following an experimental high-thoracic spinal cord injury

Spinal cord injury (SCI) disrupts the supraspinal vasomotor pathways to sympathetic preganglionic neurons (SPNs) leading to impaired blood pressure (BP) control that often results in episodes of autonomic dysreflexia and orthostatic hypotension. The physiological cardiovascular consequences of SCI are largely attributed to the plastic changes in spinal SPNs induced by their partial deafferentation. While multiple studies have investigated the morphological changes in SPNs following SCI with contrasting reports. Here we investigated the morphological changes in SPNs rostral and caudal to a high thoracic (T3) SCI at 1-, 4- and 8-weeks post injury. SPNs were identified using Nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH- diaphorase) staining and were quantified for soma size and various dendritic measurements. We show that rostral to the lesion, soma size was increased at 1 week along with increased dendritic arbor. The total dendritic length was also increased at chronic stage (8 weeks post SCI). Caudal to the lesion, the soma size or dendritic lengths did not change with SCI. However, dendritic branching was enhanced within a week post SCI and remained elevated throughout the chronic stages. These findings demonstrate that SPNs undergo significant structural changes form sub-acute to chronic stages post-SCI that likely determines their functional consequences. These changes are discussed in context of physiological cardiovascular outcomes post-SCI.

Evidence of axon connectivity across a spinal cord transection in rats treated with epidural stimulation and motor training combined with olfactory ensheathing cell transplantation

Olfactory ensheathing cells (OECs) are unique glia that support axon outgrowth in the olfactory system, and when used as cellular therapy after spinal cord injury, improve recovery and axon regeneration. Here we assessed the effects of combining OEC transplantation with another promising therapy, epidural electrical stimulation during a rehabilitative motor task. Sprague-Dawley rats received a mid-thoracic transection and transplantation of OECs or fibroblasts (FBs) followed by lumbar stimulation while climbing an inclined grid. We injected pseudorabies virus (PRV) into hindlimb muscles 7 months post-injury to assess connectivity across the transection. Analyses showed that the number of serotonergic (5-HT) axons that crossed the rostral scar border and the area of neurofilament-positive axons in the injury site were both greater in OEC- than FB-treated rats. We detected PRV-labeled cells rostral to the transection and remarkable evidence of 5-HT and PRV axons crossing the injury site in 1 OEC- and 1 FB-treated rat. The axons that crossed suggested either axon regeneration (OEC) or small areas of probable tissue sparing (FB). Most PRV-labeled thoracic neurons were detected in laminae VII or X, and ~25% expressed Chx10, a marker for V2a interneurons. These findings suggest potential regeneration or sparing of circuits that connect thoracic interneurons to lumbar somatic motor neurons. Despite evidence of axonal connectivity, no behavioral changes were detected in this small-scale study. Together these data suggest that when supplemented with epidural stimulation and climbing, OEC transplantation can increase axonal growth across the injury site and may promote recovery of propriospinal circuitry.

Development of nNOS-positive preganglionic sympathetic neurons in the rat thoracic spinal cord

To gain a better understanding of the neuroplasticity of sympathetic neurons during postnatal ontogenesis, the distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity was studied in sympathetic preganglionic neurons (SPN) in the spinal cord (Th2 segment) of female Wistar rats at different ages (newborn, 10-, 20-, 30-day-old; 2-, 6-month-old; 3-year-old). In all age groups, the majority of nNOS-immunoreactive (IR) neurons was observed in the nucleus intermediolateralis thoracolumbalis pars principalis. In the first month, the proportion of nNOS-IR neurons decreased significantly from 92 ± 3.4% in newborn to 55 ± 4.6% in 1-month-old, while the number of choline acetyltransferase (ChAT)-IR neurons increased from 74 ± 4.2% to 99 ± 0.3% respectively. Decreasing nNOS expression in the first 10 days of life was also confirmed by western blot analysis. Some nNOS-IR SPN also colocalized calbindin (CB) and cocaine and amphetamine-regulated transcript (CART). The percentage of NOS(+)/CB(-) SPN increased from 23 ± 3.6% in 10-day-old to 36 ± 4.2% in 2-month-old rats. Meanwhile, the proportion of NOS(+)/CART(-) neurons decreased from 82 ± 4.7% in newborn to 53 ± 6.1% in 1-month-old rats. The information provided here will also serve as a basis for future studies investigating the mechanisms of autonomic neuron development.

Olfactory ensheathing cells but not fibroblasts reduce the duration of autonomic dysreflexia in spinal cord injured rats

Autonomic dysreflexia is a common complication after high level spinal cord injury and can be life-threatening. We have previously shown that the acute transplantation of olfactory ensheathing cells into the lesion site of rats transected at the fourth thoracic spinal cord level reduced autonomic dysreflexia up to 8weeks after spinal cord injury. This beneficial effect was correlated with changes in the morphology of sympathetic preganglionic neurons despite the olfactory cells surviving no longer than 3weeks. Thus the transitory presence of olfactory ensheathing cells at the injury site initiated long-term functional as well as morphological changes in the sympathetic preganglionic neurons. The primary aim of the present study was to evaluate whether olfactory ensheathing cells survive after transplantation within the parenchyma close to sympathetic preganglionic neurons and whether, in this position, they still reduce the duration of autonomic dysreflexia and modulate sympathetic preganglionic neuron morphology. The second aim was to quantify the density of synapses on the somata of sympathetic preganglionic neurons with the hypothesis that the reduction of autonomic dysreflexia requires synaptic changes. As a third aim, we evaluated the cell type-specificity of olfactory ensheathing cells by comparing their effects with a control group transplanted with fibroblasts. Animals transplanted with OECs had a faster recovery from hypertension induced by colorectal distension at 6 and 7weeks but not at 8weeks after T4 spinal cord transection. Olfactory ensheathing cells survived for at least 8weeks and were observed adjacent to sympathetic preganglionic neurons whose overall number of primary dendrites was reduced and the synaptic density on the somata increased, both caudal to the lesion site. Our results showed a long term cell type-specific effects of olfactory ensheathing cells on sympathetic preganglionic neurons morphology and on the synaptic density on their somata, and a transient cell type-specific reduction of autonomic dysreflexia.

Confocal imaging of autonomic preganglionic neurons in the spinal cord of the caecilian Typhlonectes natans (Amphibia: Gymnophiona)

Little is known about the spinal sympathetic organization in the caecilian amphibians. We examined for the first time the location of sympathetic preganglionic neurons (SPNs) in the spinal cord using a panel of specific markers expressed in SPNs. The SPNs of anuran amphibians form two cell columns segregated mainly in the lateral and medial marginal areas of the central gray matter. In the caecilian Typhlonectes natans immunoreactivity for galanin and ChAT is found in most laterally arranged neurons lying in spinal segments 2-7. They are encircled by TH- and nNOS-immunoreactive nerve fibers. These neurons might project specifically to a population of adrenergic sympathetic postganglionic neurons in paravertebral ganglia and/or non-adrenergic sympathetic postganglionic neurons in the celiac ganglia. However the segmental restriction and target specificity of the neurons of the species studied are not known. As mucous and granular glands in the dermis may represent one of the peripheral targets of the adrenergic ganglion cells and reflect the prominent preganglionic cell columns, an immunohistochemical study was done also on these glands. Retrograde-tracing studies are, however, needed to study the segmental localization of the preganglionic neurons and their projections to the postganglionic neurons in sympathetic ganglia.