Endocrine cells in the gastrointestinal tract of the stomachless teleostean fish, Notemigonus crysoleucas, were studied using electron microscopy. Located between the absorptive cells of the intestinal epithelium, the enteroendocrine cells were very few in number. While some of the cells had their secretory granules located basally and a long narrow part extending toward the lumen, many appeared rounder and the plane of the section did not indicate that they extended to the lumen. Based upon size and shape of secretory granules, there appear to be several different types of cells: those with the smallest granules distributed throughout the intestine, those with intermediate sized granules more commonly found in the middle and distal segments and a few with large granules seen most often in the distal intestine.
The gross morphology of 10 teleostean alimentary canals was compared. Each short, tubular esophagus was connected either to a stomach or, in the agastric species, to a proximal intestinal swelling. 3 stomach types were differentiated according to their shapes, which appeared to be correlated somewhat with diet. Intestines showed variations in amount of coiling and in numbers of pyloric ceca. Ratios of gut lengths to body lengths (RGL, relative gut length) were calculated and the results of previous studies were confirmed in that the RGL of a planktivore was small, while that of an organic detritus feeder was large, and that of a carnivore fell in between.
After finding that ergocristine and somatostatin can cause extensive changes in mammotroph ultrastructure within 2 min of administration, we chose dopamine, the putative physiological prolactin-inhibiting factor, to correlate ultrastructural changes to inhibition of prolactin release. In order to choose a dose of dopamine for this study we tested the effects of 2 doses of dopamine (10 and 1,000 µg/kg) on inhibition of prolactin release. The higher dose of dopamine (1,000 µg/kg) completely inhibited prolactin release immediately (in less than 2 min) and maintained complete blockage for a period of 14 min. For the ultrastructural study we injected dopamine (1,000 µg/kg) in the right atrium of conscious free-moving rats through indwelling cannulae, and killed the rats by decapitation 2 min after dopamine administration. The following changes in mammotrophs were observed after the dopamine treatment:(1) increased numbers of secretory granules, (2) peripheral relocation of rough endoplasmic reticulum, and (3) increased numbers of 'intracellular bodies' (putative prolactin granule disposal system) associated with secretory granules. Because these rapid ultrastructural changes have been observed after treatment with three different compounds (dopamine, somatostatin and ergocristine), we do not believe that they are the unique effect of any one compound but the common denominator of the three compounds, i.e., inhibition of prolactin secretion being closely linked to the ultrastructural changes. We thus propose that the extensive ultrastructural changes that occurred in such a short period of time following dopamine administration are the mechanism of inhibition of prolactin release.
Hypophysectomized male rats with adenohypophyses grafted under the kidney capsule (HG rat) for 3 weeks with or without estradiol implantation, were used to examine prolactin (PRL) secretion independent of hypothalamic influence. Changes in the circulating PRL concentration were monitored by taking blood samples every 2 min via an indwelling atrial cannula. The circulating PRL concentration did not remain at a constant level but fluctuated with time. When estradiol (100 µg/kg) was administered to HG rats through the indwelling cannula the size of the PRL pulses was magnified. The ability of the grafted adenohypophyses to generate pulsatile changes in the plasma PRL indicates that the adenohypophysis possesses an inherent interlactotroph communication system to permit synchronized PRL secretion without the direct involvement of hypothalamic PRL-releasing factors or inhibiting factors.
Abstract Using magnetic resonance imaging (MRI), the internal neural and craniofacial malformations of a cyclopic fetus are described. External facial features were characterized by a tubular proboscis situated above a single eye slit. The brain was recognized as ‘pancake’ type alobar holoprosencephaly (a condition where the undifferentiated telencephalon partially surrounds a monoventricle). Displacement of some bones that normally contribute to the orbit could be clearly discerned. Absence of neural structures (e.g. falx cerebri, corpus callosum) and missing components of the ethmoid bone indicated a midline deficit. This correlates with proposed theories of cyclopic embryopathy, which suggest that the prechordal plate and the neural crest cells are affected during the third week of gestation in cyclopia.
