Asymmetric post-natal development of superior cervical ganglion of paca (Agouti paca)

Stereological and allometric studies on neurons and axo-dendritic synapses in superior cervical ganglia

The superior cervical ganglion (SCG) plays an important role in neuropathies including Horner's syndrome, stroke, and epilepsy. While mammalian SCGs seem to share certain organizational features, they display natural differences related to the animal size and side and the complexity and synaptic coverage of their dendritic arborizations. However, apart from the rat SCG, there is little information concerning the number of SCG neurons and synapses, and the nature of relationships between body weight and the numbers and sizes of neurons and synapses remain uncertain. In the recognition of this gap in the literature, in this chapter, we reviewed the current knowledge on the SCG structure and its remodeling during postnatal development across a plethora of large mammalian species, focusing on exotic rodents and domestic animals. Instrumentally, we present stereology as a state-of-the-art 3D technology to assess the SCG 3D structure unbiasedly and suggest future research directions on this topic.

SCG postnatal remodelling--hypertrophy and neuron number stability--in Spix's yellow-toothed cavies (Galea spixii)

Whilst a fall in neuron numbers seems a common pattern during postnatal development, several authors have nonetheless reported an increase in neuron number, which may be associated with any one of a number of possible processes encapsulating either neurogenesis or late maturation and incomplete differentiation. Recent publications have thus added further fuel to the notion that a postnatal neurogenesis may indeed exist in sympathetic ganglia. In the light of these uncertainties surrounding the effects exerted by postnatal development on the number of superior cervical ganglion (SCG) neurons, we have used state-of-the-art design-based stereology to investigate the quantitative structure of SCG at four distinct timepoints after birth, viz., 1-3 days, 1 month, 12 months and 36 months. The main effects exerted by ageing on the SCG structure were: (i) a 77% increase in ganglion volume; (ii) stability in the total number of the whole population of SCG nerve cells (no change--either increase or decrease) during post-natal development; (iii) a higher proportion of uninucleate neurons to binucleate neurons only in newborn animals; (iv) a 130% increase in the volume of uninucleate cell bodies; and (v) the presence of BrdU positive neurons in animals at all ages. At the time of writing our results support the idea that neurogenesis takes place in the SCG of preás, albeit it warrants confirmation by further markers. We also hypothesise that a portfolio of other mechanisms: cell repair, maturation, differentiation and death may be equally intertwined and implicated in the numerical stability of SCG neurons during postnatal development.

Hypertrophy and neuron loss: structural changes in sheep SCG induced by unilateral sympathectomy

Recently, superior cervical ganglionectomy has been performed to investigate a variety of scientific topics from regulation of intraocular pressure to suppression of lingual tumour growth. Despite these recent advances in our understanding of the functional mechanisms underlying superior cervical ganglion (SCG) growth and development after surgical ablation, there still exists a need for information concerning the quantitative nature of the relationships between the removed SCG and its remaining contralateral ganglion and between the remaining SCG and its modified innervation territory. To this end, using design-based stereological methods, we have investigated the structural changes induced by unilateral ganglionectomy in sheep at three distinct timepoints (2, 7 and 12 weeks) after surgery. The effects of time, and lateral (left-right) differences, were examined by two-way analyses of variance and paired t-tests. Following removal of the left SCG, the main findings were: (i) the remaining right SCG was bigger at shorter survival times, i.e. 74% at 2 weeks, 55% at 7 weeks and no increase by 12 weeks, (ii) by 7 weeks after surgery, the right SCG contained fewer neurons (no decrease at 2 weeks, 6% fewer by 7 weeks and 17% fewer by 12 weeks) and (iii) by 7 weeks, right SCG neurons were also larger and the magnitude of this increase grew substantially with time (no rise at 2 weeks, 77% by 7 weeks and 215% by 12 weeks). Interaction effects between time and ganglionectomy-induced changes were significant for SCG volume and mean perikaryal volume. These findings show that unilateral superior cervical ganglionectomy has profound effects on the contralateral ganglion. For future investigations, it would be interesting to examine the interaction between SCGs and their innervation targets after ganglionectomy. Is the ganglionectomy-induced imbalance between the sizes of innervation territories the milieu in which morphoquantitative changes, particularly changes in perikaryal volume and neuron number, occur? Mechanistically, how would those changes arise? Are there any grounds for believing in a ganglionectomy-triggered SCG cross-innervation and neuroplasticity?

The semi-automatic nucleator

The nucleator is a well-established manual stereological method of estimating mean cell volume from observations on random cell transects through reference points of the cells. In this paper, we present an automated version of the nucleator that uses automatic segmentation of the boundaries of the cell transects. An expert supervises the process. If the segmentation is judged to be satisfactory, an estimate of the cell volume is calculated automatically on the basis of the whole cell transect. In the remaining cases, the expert intervenes and uses the classical nucleator. The resulting estimator is called the semi-automatic nucleator. In this paper, we study the statistical properties of the semi-automatic nucleator. Formulae for the bias and mean square error are derived. The semi-automatic nucleator may have a small bias but will still in most cases be more efficient than the classical nucleator. Procedures for estimating bias and mean square error from a pilot study are provided. The application of the semi-automatic nucleator is illustrated in a study of somatostatin positive inhibitory interneurons which were genetically labelled with green fluorescent protein (GFP). The cells were sampled with an optical disector. The centre of mass in a central cell transect was used as reference point. It is found in this study that the number of cells needed for obtaining, for instance, a 5% precision of the estimate of mean cell volume is 150 and 189 for the semi-automatic and the classical nucleator, respectively. Taking into account that the time spent analysing one cell is shorter for the semi-automatic nucleator than for the classical nucleator, the semi-automatic nucleator is superior to the classical nucleator.

The developing and restructuring superior cervical ganglion of guinea pigs (Cavia porcellus var. albina)

Post-natal development comprises both maturation (from newborn to adult) and ageing (from adult to senility) and, during this phase, several adaptive mechanisms occur in sympathetic ganglia, albeit they are not fully understood. Therefore, the present study aimed at detecting whether post-natal development would exert any effect on the size and number of a guinea pig's superior cervical ganglion (SCG) neurons. Twenty right SCGs from male subjects were used at four ages, i.e. newborn (7 days), young (30 days), adult (7 months) and old animals (50 months). Using design-based stereological methods the volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated using the vertical nucleator. The main findings of this study were a combination of post-natal-dependent increases and decreases in some variables: (i) 27% increase in ganglion volume, (ii) 24% and 43% decreases in the total number of mono and binucleate neurons, respectively, and (iii) 27.5% and 40% decreases in the mean perikaryal volume of mono and binucleate neurons, respectively. Despite the fall in neuron numbers found here, post-natal development is not only associated with neuron loss, but also embraces other structural adaptive mechanisms, which are discussed in this paper.