Yutaka Taniguchi

Immunocytochemical Delineation of Thyrotrophic Area: Origin of Thyrotropin-Releasing Hormone in the Median Eminence

To identify the specific thyrotropin-releasing hormone (TRH)-containing neurons projecting to the median eminence (ME), a retrograde tracing method with horseradish peroxidase (HRP) was combined with immunocytochemical staining for TRH. Three days after HRP injection restricted to the ME, several TRH-positive neuronal perikarya were found to contain HRP. Such double-stained cells were exclusively distributed in the anterior parts of the periventricular nucleus and the most medial parts of the paraventricular nucleus. Few double-stained cells were observed in other parts of the brain examined. The present observations appear to demonstrate that the specific TRH neurons projecting to the ME are located along the border of the third ventricle, anterior to the ME.

Origin of Septal Thyrotropin-Releasing Hormone in the Rat

Through the combined demonstration of retrograde transport of horseradish peroxidase (HRP) and immunocytochemical staining of thyrotropin-releasing hormone (TRH), the TRH neurons that project to the lateral septum were identified. Following the injection of HRP into the lateral septum, retrogradely labelled neurons were detected in the bed nucleus of stria terminalis (BNST), the ventral pallidum, the anterior commissural nucleus, the lateral preoptic nucleus and the perifornical region. Some neurons in the BNST and the perifornical region were found to contain both TRH and HRP. In contrast, no TRH-containing neurons were labelled with HRP in the paraventricular nucleus, the putative thyrotropic area. These data suggest that TRH neurons projecting to the lateral septum were different from those which send fibers to the median eminence.

Ultrastructural studies on the secretory cycle of the neurosecretory cells and the formation of Herring bodies in the paraventricular nucleus of the rat.

SummaryThe ultrastructure of the neurosecretory cells in the paraventricular nucleus of the normal male rat was studied by electron microscopy during various functional states. Four morphologically distinct types of neurosecretory cells were observed. It appears that they do not represent different classes of cells but different phases of secretory activity of a single cell type. The perikarya of the neurosecretory cells show a definite cycle of formation and transportation of secretory granules. We have designated the phases of this cycle as: (1) phase of synthesis, (2) phase of granule production, (3) phase of granule storage and (4) phase of granule transport. The neurosecretory granules appear to be moved in bulk into the axons, forming a large axonal swelling filled with granules as a result of one cycle in the neurosecretory process. Thus it may be postulated that a secretory cycle in the perikaryon of the neurosecretory cell seems to result in the formation of a Herring body in its axon, and that its content is then conveyed to the posterior pituitary.

Three-dimensional and quantitative observation of the hypertrophy of rat corticotrophs following adrenalectomy

SummaryThe three-dimensional form of corticotrophs in the anterior pitiutary gland of rats was studied by reconstruction from serial semi-thin sections both in control rats and rats one week after adrenalectomy. The corticotrophs have large depressions and cup-shaped cavities on their surface, and these features became more conspicuous after adrenalectomy. The hypertrophy of corticotrophs in adrenalectomized rats was quantified by measuring the area and perimeter of all serially sectioned profiles. The volume of the whole cell increased from 1129±114 μm3 to 2902±201 μm3 (P<0.01) after adrenalectomy, while the surface area of the cells increased from 690±45 μm2 to 1431±116 μm2 (P<0.01). The volume of the nucleus increased from 87±11 μm3 to 172±14 μm3 (P<0.05). Though the complexity of the form of corticotrophs seems to be increased after adrenalectomy, the ratios (adrenalectomized/control) of cell volume and surface area were 2.57 and 2.07, respectively; this indicates that the increase of the cell volume was greater than that of the surface area.