On spirality in the intestinal wall

Methods of stripping did not demonstrate a significant spiral course of fibers within longitudinal muscle coats of the jejuno-ileum of the dog, cat, hog or man. Similar lack of spirality also characterized the large intestine of the dog. The presence of taeniae in the hog and man, and the extremely thin layer of muscle between them, permitted only the demonstration of directly longitudinal muscle in taeniae. Bands of muscle stripped from circular coats of the small intestine of the dog and hog came off overwhelmingly in complete rings. Stripping of the human intestine did not yield complete rings; breakage at anastomoses with the adjoining muscle sheet may indicate oblique bands that link up a fiber system, essentially circular, into a functionally spiral system. Bands stripped from circular coats of the large intestine of the dog came off overwhelmingly as circles. The taeniae of the hog and man prevent obtaining complete strips. Stripping of the submucosal stratum of the small intestine of the dog and man, and of the large intestine of the dog, revealed a latticed tube. Its fibers intersect in double spirals, coursing at angles of approximately 45° to the longitudinal axis of the intestine.     

Activity of oxytocinergic neurons in the paraventricular nucleus mirrors the periodicity of the endogenous stimulatory rhythm regulating prolactin secretion.

PRL secretion is regulated by an endogenous stimulatory rhythm of PRL-releasing factors within the hypothalamus. The endogenous rhythm has a bimodal periodicity with a nocturnal component which peaks at approximately 0300 h and a diurnal component that peaks at approximately 1700 h. Several PRL-releasing factors are known to be involved in this rhythm. Among these are oxytocin (OT), vasoactive intestinal peptide, and serotonin. We have proposed that OT is the neurohormone that stimulates PRL release from the lactotroph. In this study, we examined the activity of OTergic neurons in the paraventricular nucleus using the expression of the protooncogene c-fos (Fos) as a marker of neuronal activity. Ovariectomized rats were killed at either 0300, 1200, or 1700 h and brains quickly fixed by perfusion with 2.5% acrolein in 4% paraformaldehyde. Brains were blocked and processed for OT/Fos immunohistochemistry. Rats killed at 0300 and 1700 h had significantly greater proportion of Fos expressing OTergic neurons than control rats (1200 h). Percent of Fos-positive OTergic neurons were 2- and 1.5-fold greater at 0300 and 1700 h than 1200 h, respectively. The majority of these neurons were located in the medial parvocellular paraventricular nucleus and periventricular area. In another experiment, groups of OVX rats were killed every 2 h over a 24-h period and OT extracted from their anterior and posterior pituitaries. OT was present in the anterior pituitary in a bimodal rhythm. OT concentrations were greatest at approximately 0400 h and slowly declined to baseline by 1000 h. Another peak of OT was present in the anterior pituitary at approximately 2000 h and quickly declined to baseline by 2400 h. This rhythm of OT was not reflected in either the posterior pituitary or trunk blood. These data suggest that activity of a specific population of OTergic neurons of the paraventricular nucleus is rhythmic. The periodicity of these neurons mirrors that of the endogenous stimulatory rhythm. Furthermore, the anatomical location of these neurons suggests that they may project to the median eminence. Indeed, this heightened activity is reflected in a bimodal rhythm of OT in the anterior pituitary. Taken together, the data presented here provide compelling support for the role of OT as the neurohormone in the mechanism of the endogenous stimulatory rhythm.