Glucose utilization in sympathetic ganglia of male Fischer-344 rats at different ages

Histochemical detection of age- and injury-related changes in signal transduction in the superior cervical ganglion

The superior cervical ganglion (SCG) is thought to be a good model for correlation studies of morphology, function and metabolism of neurons. The SCG has a relatively simple organization, it can be easily manipulated in situ, and it maintains synaptic transmission and a high metabolic rate during in vitro incubations. The histology and structure of SCG neurons have been characterized in detail, and physiologic stimuli, injury and aging have all been found to induce changes in the SCG morphology. During the last decade, research in the field of signal transduction has greatly expanded. Several signal transduction pathways have been identified that participate in the regulation of neurotransmitter synthesis, gene expression, neuronal excitability and growth factor responses of sympathetic neurons. We have been interested in using the SCG to study some of the second and third messengers involved in converting external stimuli received by sympathetic neurons into cellular short- and long-term events. Using immunohistochemistry, we have investigated protein kinase C-subtypes and the immediate early gene product Fos in the SCG, and characterized some of the changes induced by injury and aging in these messenger molecules. We will review the results and discuss the advantages and disadvantages of using histological methods in the study of signal transduction in sympathetic neurons.

Reactions of rat sympathetic neurons to ethanol exposure are age-dependent

Age-differences in the sensitivity of peripheral sympathetic neurons to chronic ethanol exposure and ethanol withdrawal were studied in male Wistar rats aged 4 months, 12 months, or 24 to 25 months. The superior cervical ganglia (SCG) of the young (4 months) and the 2-year-old rats responded to a 12-day or 4-week ethanol exposure with significantly increased catecholamine turnover, while the ganglia of the middle-aged rats (12 months) showed only a minor increase in the intensity of catecholamine fluorescence and tyrosine hydroxylase immunoreactivity. Extensive neuronal vacuolation was found in the 4 months ethanol-exposed SCG, probably as a reaction of a subpopulation of neurons to increased stimulation. Ethanol-induced neuronal loss was most prominent in the SCG of the oldest age group. Contrary to the marked changes in SCG functional and morphometric parameters, the pelvic sympathetic neurons in the hypogastric ganglion showed no significant changes after ethanol exposure. The pattern of ethanol-induced morphological alterations found in the present study did not provide unambiquous support for either the "accelerated aging" or the "increased vulnerability" concept regarding ethanol-aging interactions in the nervous system.

Morphometric and neurochemical changes in rat superior cervical ganglion during growth and adulthood

We have previously found in rat superior cervical ganglion that there is a fall in neuron numbers and in cellular neuropeptide Y (NPY) immunoreactivity over the first year of life. In this study, we have used computerized image analysis to quantitate changes in neuron size, numbers and immunoreactivity for neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and NPY in this ganglion between 1 and 85 weeks of age. Neuronal cytoplasmic area increased between 1 and 11 weeks and then remained stable until after 67 weeks, when there was a further increase in size of both NPY-positive and NPY-negative cells. Numbers of NPY-positive cells, but not those of NPY-negative cells, fell between 11 and 30 weeks. Both populations were stable after this time. Neuronal levels of NSE and TH remained constant, but levels of NPY fell between 58 and 67 weeks. These results indicate that changes in adult neuronal size, numbers and neurochemistry are independent phenomena. The increase in cell size and the fall in NPY after 58 weeks correspond to the time of withdrawal of some preganglionic inputs and may be responses to this event. By contrast, the decrease in NPY-positive cell numbers occurs some months before this time.

Lifelong ethanol consumption enhances the age-related changes in rat sympathetic neurons

The effects of aging and chronic ethanol administration on the histochemical and morphometric features of rat superior cervical ganglion were studied in a rat strain selected for voluntary alcohol consumption. Ethanol was administered to the experimental group ad libitum (10% v/v in drinking water) from 3 months to 28 months of age, the average ethanol intake being 6.4-5.4 g/kg per day. The sympathetic neurons of the ethanol consuming rats showed several signs of enhanced degeneration, e.g. decreased neuronal packing density, increased amount of age-pigment and decreased intensity of catecholamine histofluorescence and tyrosine hydroxylase immunoreactivity. The results may indicate a selective vulnerability of peripheral sympathetic neurons rather than a universal accelerated aging due to chronic ethanol exposure.

Age-related increase in c-fos expression in the sympathetic neurons of the rat superior cervical ganglion

C-fos expression was studied immunocytochemically in sympathetic neurons of the rat superior cervical ganglion (SCG). Fos-like immunoreactivity was confined to the principal neurons of the ganglion and was exclusively localized within their nuclei. In 2-month-old rats, the immunoreactivity was detected in 1.2% of the principal neurons with a density of 4.95 Fos-positive cells/mm2 of ganglion area. This proportion increased with age and reached a value which was 6.5-fold higher in the 26-month-old rats than that in the young adult. A density of 24.5 Fos-positive cells/mm2 of ganglion area was seen in the 26-month-old animals. The age-enhanced c-fos expression suggests that Fos may be involved in regulation of the genetic events associated with the adaptive changes in neuronal activity of the sympathetic ganglion during aging.

Age-related morphometric and histochemical features of rat sympathetic neurons

The correlation between catecholamine histofluorescence, tyrosine hydroxylase (TH) immunoreactivity and accumulation of age pigment was studied in the superior cervical ganglia (SCGL) of young (3 months) and old (28 months) rats. In the young animals there was a positive correlation between TH-immunoreactivity and catecholamine stores in most of the neurons. A pigment accumulation covering the profile area was found in approximately 10 per cent of the neurons in the young rats. In these neurons strong TH-immunoreactivity was associated with weak catecholamine histofluorescence. In the ganglia of the old animals there were considerable differences between individual cells in TH-activities, catecholamine stores and amounts of age pigment. In addition, there was a marked uncoupling between TH-activity and catecholamine fluorescence in a number of neurons, i.e. there were neurons with strong TH-immunoreactivity but weak catecholamine histo- fluorescence and vice versa. The functional implications of this uncoupling are discussed in the article.

Morphometric studies on the microvasculature of pre- and paravertebral sympathetic ganglia in the adult and aged rat by light and electron microscopy

Morphometric measurements have been made by light and electron microscopy on sections of perfused sympathetic ganglia from rats of 6-24 months of age with special reference to the microvascular bed. Capillaries, postcapillary venules and small venules comprised the majority of the vessels studied but small arterioles were, in addition, included in the light microscopical part of the study. Light microscopical measurements using image analysis showed that there was a decrease in the density of the microvascular bed (number of vascular profiles/area) and in the total vascular luminal area with age in both ganglia. The ratio of neurons to microvessels remained constant in the superior cervical ganglion (SCG) but decreased with age in the coeliac-superior mesenteric ganglion (CSMG). However, the distribution of microvessels in relation to individual neurons remained unchanged throughout life in both ganglia. Ultrastructural studies revealed fenestrations in 12% of SCG microvessel profiles and in 38% of CSMG microvessels at 6 months, but the percentage of fenestrated profiles in the CSMG had declined by 24 months. There were no significant differences in the number of fenestrations per fenestrated profile. The basal lamina surrounding the microvessels increased significantly (almost doubling) in thickness with age. The range and distribution of microvessel wall thicknesses, expressed as harmonic mean wall thickness, were comparable in both ganglia at both ages and increased linearly according to the amount of pericyte covering present. No consistently significant relationships could be discerned between the microvessel wall thickness and luminal diameter or between the wall thickness and the area available to a given volume of blood for exchange of metabolites (luminal perimeter/luminal area). We conclude that the ganglionic capillary bed is similar in both ganglia and, in old age, accommodates structural changes that occur in the ganglion by maintaining its structure and relationship to individual neurons.

Morphometric studies on pre- and paravertebral sympathetic neurons in the rat: changes with age

Morphometric measurements have been made on rat sympathetic neurons at ages between 6 and 24 months. In neurons of the coeliac-superior mesenteric ganglion there is a marked decrease in the neuronal packing density between 12 and 18 months which is accompanied by increases in the size of the neurons and their nuclei. In the superior cervical ganglion, no changes in packing density are seen until 18 months after which a decrease occurs, accompanied by slight increases in the neuronal parameters. These post-maturation changes occurring throughout adult life reveal a continued dynamism of sympathetic neurons into old age as well as revealing further differences between populations of sympathetic neurons.

Indices of neurotransmitter synthesis and release in aging sympathetic nervous system

Activities of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and choline acetyltransferase (ChAT) were assayed in sympathetic ganglia and adrenal glands of young and aged Fischer-344 rats. The recovery of reserpine-depleted catecholamine stores and catecholamine loss following inhibition of synthesis and intraneuronal degradation also were assessed in sympathetic ganglia of young and aged rats. No age differences were observed in DBH activity of any tissues examined or in the activities of any enzymes in the coeliac-mesenteric ganglion complex. However, TH and ChAT activities were significantly higher in the superior cervical ganglia and adrenal glands of aged rats. In the hypogastric ganglion, only TH activity was higher in the old rats. Recoveries of reserpine-depleted catecholamine stores in the superior cervical and hypogastric ganglia of aged rats were slower than in young rats. Catecholamine loss following inhibition of synthesis and intraneuronal degradation was faster in the superior cervical ganglia but not in the hypogastric ganglia of old rats as compared with young rats. These findings suggest that neurotransmitter synthesis and release are enhanced with age in the superior cervical ganglion. The lack of age-related changes in the hypogastric ganglion might reflect the different cellular composition as well as the physiological role of this ganglion.

The effect of aging on extra-adrenal catecholamine storing cells of the rat

Cell number and catecholamine histofluorescence were determined in three extra-adrenal chromaffin tissues: the abdominal paraganglia, the carotid body and SIF (small intensely fluorescent)-cells, of male Fischer-344 rats at different ages. Catecholamines were demonstrated using the formaldehyde-induced fluorescence method. The number of paraganglia cells in the retroperitoneal area increased 13.6 fold between 3 and 33 months of age, and the volume of abdominal paraganglia approached 65% of the volume of one adrenal medulla. The emission color of some paraganglia cells shifted from greenish-yellow to yellowish-brown with aging, but differences were not observed in cell number of fluorophore color in the carotid body, a chemoreceptor type of paraganglion. The number of SIF cells (an intraganglionic variant of extra-adrenal chromaffin tissue) in the hypogastric ganglion increased significantly between 3 and 33 months. The pronounced increase of the volume of the paraganglia in aged rats may contribute to elevated concentrations of circulating catecholamines in these animals.