Neuronal degeneration and lipopigment formation in rat sympathetic ganglion after treatment with high-dose guanethidine

Sympathetic renal denervation: hypertension beyond SYMPLICITY

Despite a wide range of drug treatment for hypertension, resistant hypertension rates remain high. The Symplicity™ Renal Denervation System (Medtronic, Santa Rosa, CA), which creates renal nerve denervation, has shown initial success in lowering blood pressure among patients with resistant hypertension. Given the enormous market for this treatment approach, an estimated two dozen other companies are pursuing technologies with alternative approaches. Despite this fact, very little has been published on preclinical and clinical experience with these new devices. The current review summarizes the most prominent technologies in the pipeline and provides insight into the mechanism of action, preclinical, and clinical experience with these new devices.

The lysosomal system in neuronal cell death: a review

The lysosomal system has often been considered a prominent morphologic marker of distressed or dying neurons. Lysosomes or their constituent hydrolases have been viewed in different neuropathologic states as either initiators and direct agents of cell death, agents of cellular repair and recompensation, effectors of end-stage cellular dissolution, or autolytic scavengers of cellular debris. Limited data and limitations of methodology often do not allow these potential roles to be discriminated. In all forms of neurodegeneration, it may be presumed that lysosomes ultimately rupture and release various hydrolases that promote cell autolysis during the final stages of cellular disintegration. Beyond this perhaps universal contribution to cell death, the degree to which the lysosomal system may be involved in neurodegenerative states varies considerably. In many conditions, morphologic evidence for activation of the lysosomal system is minimal or undetectable. In other cases, lysosomal activation is evident only when other morphologic signs of cell injury are also present. This level of participation may be viewed as either an attempt by the neuron to compensate for or repair the injury or a late-stage event leading to cell dissolution. The early involvement of the lysosomal system in neurodegeneration occurs most commonly in the form of intraneuronal accumulations of abnormal storage profiles or residual bodies (tertiary lysosomes). Very often the lysosomal involvement can be traced to a primary defect or dysfunction of lysosomal components or to accelerated or abnormal membrane breakdown that leads to the buildup of modified digestion-resistant substrates within lysosomes. Because they are often striking, changes in the lysosomal system are a sensitive morphologic indicator of certain types of metabolic distress; however, whether they reflect a salutary response of a compromised neuron or a mechanism to promote cell death and removal of debris from the brain remains to be established for most conditions. Factors that may influence the lysosomal response during lethal neuronal injury include species differences, stage of neuronal development, duration of injury and pace of cell death. The lysosomal system may be more closely coupled to certain forms of neuronal cell death in lower vertebrate or invertebrate systems than in mammalian systems.

Effects of neonatal sympathectomy with 6-hydroxydopamine or guanethidine on survival of neurons in the intermediolateral cell column of rat spinal cord

The effects of removing target cells on survival of, and inputs to, sympathetic preganglionic neurons were studied in rats that were sympathectomized with 6-hydroxydopamine (6-OHDA) or guanethidine sulfate. Separate groups of neonatal and 1-week male rats were given injections of 6-OHDA for 10 days and of guanethidine for 3 weeks (5 days/week), respectively. Histofluorescence results suggest that catecholaminergic neurons in most ganglia are destroyed with treatment except for adrenal medulla, which is unaffected [14], and the pelvic ganglion where only partial destruction occurs. Cells in the intermediolateral cell column from representative spinal cord segments of treated and control adult rats were counted. In 6-OHDA-treated rats, cells decreased in number in all segments compared to controls. In guanethidine-treated rats, cells were also decreased in number; in some segments the decrease was significantly greater than with 6-OHDA. Sympathectomy had no effect on neurons in the intermediate gray of L5 or in the ventral horn of T3. The results of this study demonstrate that peripheral sympathectomy causes loss of sympathetic preganglionic neurons and that guanethidine is slightly more effective than 6-OHDA.

Suramin-induced changes in sympathetic neurons: correlation between catecholamine fluorescence, tyrosine hydroxylase immunoreactivity and accumulation of pigment bodies

The effect of suramin, a strong inhibitor of lysosomal enzymes, was studied in rat superior cervical (SCG) and dorsal root ganglia (DRG). Ten days after administration both types of ganglion showed increased intraneuronal pigment fluorescence; in DRG there were also accumulated pigments in Schwann cells. Ultrastructurally the pigment bodies were membranous or lamellar inclusion bodies. In SCG suramin-induced inclusion bodies were associated with decreased catecholamine fluorescence and tyrosine hydroxylase immunoreactivity, suggesting that altered activity of lysosomal enzymes and the formation of lysosomal inclusion bodies may be coupled with decreased synthesis of neurotransmitters in rat sympathetic neurons.

Age pigments in different populations of peripheral neurons in vivo and in vitro

The distribution and ultrastructure of lipopigments in the rat sympathetic, vagus and spinal ganglion neurons were studied in vivo and in vitro using fluorescence and electron microscopy. Newborn, 3-6 mo and 24-30 mo-old male Wistar rats were used. In vivo, the age pigments in the sympathetic neurons showed a tendency to form unipolar or bipolar caps, whereas in the vagus and spinal ganglion neurons pigment granules were packed in the peripheral area of the perikarya during aging. Ultrastructurally, lipid-like vacuoles and a rather homogeneous matrix were the components shared by pigment bodies of all types of peripheral neurons. However, pigment granules in sympathetic neurons frequently had a third, osmiophilic component, which likely represents neuromelanin. In vitro, the cytoplasmic area occupied by autofluorescent pigments was increased in most of the neurons. Some neurons, however, showed the same amount of lipopigments as in vivo. In electron microscopy, age pigment granules typical of each type of neuron were found, and their number and intracellular distribution seemed to be comparable with those in vivo. In most of the neurons cultured from all ages and of all types of ganglion, there appeared to be accumulations of another, very homogeneous and large type of pigment body. In some cases, they were structurally connected with classical pigment bodies or they had a finger print-like substructure. Large homogeneous pigment bodies were also seen in surrounding satellite cells. All these changes were most frequently seen in cultures of spinal ganglia from old animals. It is concluded that although classical age pigments maintain their characteristics in cultured peripheral neurons, there is, in addition, a rapid accumulation of ceroid-like pigments, which may be caused by the inability of the cultured neurons to cope with increased peroxidative damage.