Sympathetic Innervation 53 



taneously. Stimulation of the chorda accelerates the flow. Stimu- 

 lation of the sympathetic, likewise, increases the rate of flow ; and 

 there is no compensatory decrease after the stimulation, as seen in 

 the sheep's parotid. 



5. In some glands, such as the submaxillary gland of the cat, the 

 flow of saliva seen during sympathetic stimulation is usually so 

 rapid and persists for such a long time that it can only be due to 

 a real secretory effect. That the gland cells are affected by the 

 stimulation is further evidenced by the fact that their membrane 

 potential changes, as seen with intracellular recording (Lundberg, 

 1955); in exceptional submaxillary glands, which do not secrete on 

 sympathetic stimulation, no electrical responses are found. 



Although the secretory effect of sympathetic stimulation on most 

 submaxillary glands of cats is unmistakable, the existence of secre- 

 tory sympathetic fibres has been denied. In the histological investi- 

 gation by Kuntz and Richins (1946), quoted above, it was inferred 

 that the innervation of the glandular elements is mainly, perhaps 

 exclusively, parasympathetic. In a later paper (Richins and Kuntz, 

 1953) the same authors express the view that the secretion from the 

 cat's submaxillary and parotid glands which follows sympathetic 

 stimulation, is caused by the transmitter released from the endings 

 of vasomotor fibres, diffusing from the vascular bed to the gland 

 cells. This theory was based on the observation that the secretory 

 effect of sympathetic, but not of parasympathetic stimulation, was 

 abolished by occlusion of the external carotid artery. 



Such a theory might perhaps explain the variability in the secre- 

 tory responses to sympathetic stimulation. As shown by Lundberg 

 (1955) the electrical responses of the single gland cell appear with 

 a longer latency after sympathetic than after chorda stimulation; 

 further, whereas single shocks to the chorda cause the response, 

 repetitive stimulation of the sympathetic is required. These facts 

 might be in agreement with the theory of Richins and Kuntz. It is 

 certainly easier to accept effects as due to diffusion of the relatively 

 stable sympathetic transmitter than to acetylcholine. 



In order to prove that secretory fibres for the salivary glands are 

 really present in the sympathetic trunk it would be desirable to be 

 able to excite the various types of fibres separately. The different 

 effects of the stimulation can be separated. After a suitable dose of 

 chlorpromazine, for instance, the secretory effect of sympathetic 

 stimulation is abolished but the vasoconstriction retained; after 



