Recently the medullary salivary nuclei have been explored systemically using electrical stimulation in animals and it is well known that salivary nuclei situated in the medulla acts as a primary salivary center on salivary secretion.
Many clinical observations and experiments in which drugs and electrical stimulation had been applied to the different parts of the central nervous system suggested that suprabular structure, especially diencephalon, may exert excitatory and inhibitory actions on the primary salivary center in the brain stem.
However, very little is known as to the region of the central nervous system engaged in the control
of secretion of saliva.
It seemed, therefore, worth-while to investigate the central nervous system which functions as a: higher center for the salivary nuclei in the medulla.
In this study, the author observed the flow of parotid saliva in response to osmotic stimulation and pilocarpine injection into the hypothalamus and certain area which have connection with the hypothalamus by nerve fibers.
Male rabbits, weighing 1.8 kg., were subjected for this study.
The animal were not anesthetized before or during the experiments.
Parotid saliva was collected through the polyethylene tube which was inserted into the parotid duct. It was established by preliminary study that concentration of pilocarpine at 0.02% in amount of 0.1cc has no effect on salivary secretion when it was administered intramuscularly.
0.02% pilocarpine, 0.05 cc and osmotic stimulations-3% Nacl solution and distilled water in amount of 0.05 cc-were applied using stereotaxic apparatus bilaterally into the caudate nucleus; putamen, hippocampus; amygdala; Preoptic area: anterior, mid-median, mid-lateral, and posterior hypothalamus;. mammillary body; midbrain; and salivary nucleus.
Following resulted wVe obtained.
1) Caudate nucleus: Neither distilled water nor 0.02% pilocarpine caused change in parotid secretion when both were injected into this area whereas 3% NaCl solution did increase parotid secretion in all crsm
2) Hippocampus: Injections of 3% NaCl solution and of 0.02% pilocarpine into this area. produced an increase of parotid secretion but no change was resulted from injections of distilled_ water.
3) Amygdala: When distilled water was injected into this an a no change in the parotid secretion. occurred. However, the area was injected either 3% NaCl solution or 0.027% pilocarpine the parotid_ secretion was increased slightly.
4) Putamen: The parotid secretion was enhanced when this area was injected with either 3% NaCl solution or 0.02% pilocarpine but distilled water did not.
5) Preoptic area: In this area, only 0.02% pilocarpine produced increase in the parotid secretion despite distilled water and 3% NaCl failed to cause any change in the parotid secretion.
6) Alterior hypothalamus: All the three agents, distilled water, 3% NaCl, and 0.02% pilocarpine failed to influence the parotid secretion when they were administered into this area.
7) Mid-median hypothalamus: In this area, the parotid secretion was increased by injection of 0.02% pilocarpine. Neither distilled water nor 3% NaCl solution caused any change in the parotid secretion when either of them was injected in the area.
8) Mid-lateral hypothalamus: There was a prompt and marked increase in the parotid secretion when the area was injected with 0.02% pilocarpine although distilled water and 3% NaCl solution injected in the area failed to affect the parotid secretion.
9) Posterior hypothalamus: None of three agents, distilled water, 3 % NaCl solution or 0.02 pilocarpine affected that parotid secretion when the area was injected with them.
10) Mammillary body: In this area, injection of all except distilled water caused an increase in the parotid secretion.
11) Midbrain: All of three agents, failed to produce significant changes in the parotid secretion when they were injected into this area.
12) Salivary nucleus: There was prompt and the biggest increase in the parotid secretion in all cases when this area was injected with 0.02% pilocarpine. Marked increase in the parotid secretion was noted when the area was injected by 3% NaCl solution and also slight increase was observed
when the area was injected by the distilled water.
13) Following a transection of the rabbit´s brain through the corpus quadrigemina, no changes of the parotid secretion was observed by the injections of either 3% NaCl solution or 0.02% pilocarpine into the various areas of the central nervous system where an increase in the parotid secretion occurred by the injection of both agents.
It can be concluded from the foregoings that the hypothalamus as well as areas such as the caudate nucleus, putamen, hippocampus, amygdala and preoptic area which are connected by nerve fibers with the hypothalamus act as higher regulatory centers for the salivary nucleus. The mechanism of injected pilocarpine solution into the various part of the central nervous system appears that pilocarpine acts directly on the higher regulatory center of the parotid secretion rather than peripheral actions.
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