Stereological and allometric studies on neurons and axo-dendritic synapses in the superior cervical ganglia of rats, capybaras and horses.

The research investigates the structural variations of the superior cervical ganglion (SCG) in different mammalian species (rats, capybaras, and horses) in relation to various factors including body size, age, and gender. The results indicate that while there is a predictable relationship between the number of neurons and the volume of SCG, it’s not the case for synapses.

Study Methodology

• The research employed design-based stereological tools, a quantitative method of studying form, at the light-microscopic level to measure the volume of ganglia and estimate the numbers and sizes of neurons in the SCGs of rats, capybaras, and horses.
• Transmission electron microscopy was used to obtain design-based estimates of the surface coverage of dendrites by postsynaptic apposition zones as well as model-based estimates of the numbers and sizes of synaptophysin-labelled axo-dendritic synaptic disks.
• Finally, to determine relationships, linear regression analysis of log-transformed data was performed.

Findings

• The superior cervical ganglion (SCG) in mammals shows variations according to factors such as developmental age, body size, gender, lateral asymmetry, neuron size and nuclear content, and dendritic tree complexity and synaptic coverage.
• For smaller and medium-sized mammals, neuron count and size increase from birth to adulthood. Body size was previously thought to directly correlate with neuron count, but recent studies on larger animals suggest that body weight cannot accurately predict neuron count.
• This study found a predictable allometric relationship for neuron number in relation to SCG volume. However, it also showed that the synapse count couldn’t be accurately predicted using the same method.
• Larger mammals, like horses, show more complex arborizations in SCG neurons as well as higher numbers of axo-dendritic synapses compared to smaller mammals.