An unbiased estimation of the total number of synapses in the superior cervical ganglion of adult rats established by the disector method. Lack of change after long-lasting sodium bromide administration

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Abstract
Summary Previous physiological and morphological studies suggested that sodium bromide promotes synaptogenesis of implanted cholinergic nerves in the superior cervical ganglion of adult rats. To check whether sodium bromide also modifies synaptic numbers in the intact ganglion, quantitative electron microscopy was used to determine the total number of synaptic junctions in the superior cervical ganglion of adult rats. Untreated controls were compared with animals which drank water containing 280 mg ml−1 sodium bromide for 7 days. The disector method, an unbiased estimator of volume density of certain particles, has been adapted to this particular case. To accomplish the task, an on-line counting procedure was developed, which permitted the efficient adaptation of the disector method for the superior cervical ganglion, in which the synapses are known to be distributed sparsely. Three pairs of (control and treated) ganglia have been completely processed by three independent examiners. The estimated number of synapses in the ganglia ranged from 4 to 8 million while the volumes of the ganglia varied from 0.65 to 0.90 mm3. Evaluation of the results showed that variations in the total number of synapses were in each case proportional to differences in ganglionic volumes. This suggests that: (1) sodium bromide does not lead to changes in density of intrinsic synapses; and (2) the morphogenetic action of sodium bromide on principal ganglion cells previously described is essentially postsynaptic and requires additional presynaptic elements to increase the number of synapses.