Corticotrophin release induced by surgical trauma after transection of various afferent nervous pathways to the hypothalamus

Corticotrophin (ACTH) release induced by surgical trauma under pentobarbitone anaesthesia was studied in rats. The plasma corticosterone level was used as an index of 'rapid' ACTH release.

One hour after surgical trauma the plasma corticosterone level had risen in rats with various cuts around the medial basal hypothalamus except in the group with lateral cuts. After stress no significant difference was found between the plasma levels of the controls and those of the rats with anterior, 'low' superior, 'low' anterosuperior, and 'short' posterior cuts. In contrast, in rats with 'high' superior, 'high' anterosuperior, 'long' posterior and lateral cuts the plasma corticosterone level was lower than in the appropriate sham-operated controls.

It is suggested that the nerve fibres initiating ACTH release after surgical trauma ascend the spinal cord to the medulla and mid-brain whence the pathways pass forward in the region of the dorsal longitudinal fasciculus and/or the median forebrain bundle to the lateral hypothalamic area, and from there to the medial basal hypothalamus.

Fecal streptococci on barley and malt kernels and instant malted milk powder

Among 500 barley kernels, tested singly, 1.8% (9 kernels) were positive for fecal streptococci. Among 800 malt kernels, tested singly by the same procedure, 68% (540 kernels) were positive for fecal streptococci. In unsulfured and sulfured malts, 67 and 68% of the kernels, respectively, were positive for these bacteria. Fecal streptococci were also isolated by an enrichment procedure from two brands of instant malted milk powder sold in supermarkets. Seventy randomly picked isolates from malts were identified to be fecal streptococci, belonging probably to more than one species.

Afferent pathways of stressful stimuli: corticotrophin release after hypothalamic deafferentation

SUMMARY

Corticotrophin (ACTH) release induced by stressful stimuli has been studied in rats with completely deafferentated medial basal hypothalamus (MBH) pituitary islands or median eminence (ME)-stalk pituitary islands. The plasma corticosterone level was used as index of ACTH release.

In rats with MBH pituitary islands, capsaicin failed to raise the plasma corticosterone level, but the intraperitoneal administration of E. coli endotoxin, histamine, insulin or a large subcutaneous dose of formaldehyde caused ACTH release which could not be distinguished from that in the controls. Histamine and insulin induced ACTH release even in rats with a ME-stalk pituitary island.

It is suggested that E. coli endotoxin, histamine, insulin hypoglycaemia and large doses of formaldehyde may be classified as 'humoral' stimuli of ACTH release, since a neural afferent input to the MBH is not essential for their action. On the other hand, the integrity of some neural pathways to the MBH is essential for the ACTH-releasing effect of capsaicin.

Afferent pathways of stressful stimuli: corticotropin release after partial deafferentation of the medial basal hypothalamus

Corticotrophin (ACTH) release induced by various stressful stimuli has been studied in rats with antero-lateral deafferentation of the medial basal hypothalamus (MBH). The plasma corticosterone level was determined as an index of ACTH release.

In rats with antero-lateral deafferentation of the MBH, ACTH release was prevented after exposure to noise and vibration, sham adrenalectomy and s.c. injection of 1% formalin. ACTH release induced by the injection of histamine (1 mg./100 g., i.p.) and capsaicin (0·25 mg./100 g., s.c.) was significantly less than in the controls. Escherichia coli lipopolysaccharide (25 μg./100 g., i.p.) induced an ACTH release that could not be distinguished from that in the controls.

We suggest that (a) noise and vibration, sham adrenalectomy and injection of 1% formalin trigger ACTH release through neural pathways arriving at the MBH from anterior, lateral and dorsal directions, (b) histamine or capsaicin releases ACTH partly through antero-lateral neural afferents to the MBH. In contrast, the ACTH-releasing stimulus of bacterial endotoxin injection reaches the hypothalamo—hypophysial unit by humoral pathways and/or posterior nerve fibres.

The hypophyseal-adrenocortical response to various different stressing procedures in ACTH-treated rats

Twenty-four hours after the last of 14 daily injections of ACTH, the administration of ether, histamine, 1% formalin, or lysine-8-vasopressin produced no rise in the plasma corticosterone level in rats but raised it significantly in saline-treated control animals. As assayed by the plasma corticosterone concentration, ACTH release was found to be inhibited when hypophyseal–adrenocortical responsiveness was not impaired and the peripheral corticosterone level was normal or less than normal. Endotoxin induced nearly the same statistically significant elevation in the ACTH-treated and saline-treated animals. It would appear that it is the high corticosterone level produced by the last ACTH injection that suppresses the corticotrophin-releasing factor (CRF) 24 h later (feedback action) when this level returns to normal or less than normal; and that certain stressors liberate CRF whereas others do not. An explanation for the latter assumption may be found either in the difference in intensity between the stimuli or, more probably, in that the high corticosterone level inhibits the ACTH release mechanism for certain individual stressors, but not for others.

The effect of long-term corticotrophin treatment on the corticosteroid-binding capacity of transcortin

In rats consecutive daily doses of corticotrophin significantly reduced the corticosterone-binding capacity of transcortin as measured by the gel filtration method, even after previous removal of the adrenals or ovaries. Treatment with formalin for 14 days produced similar, though slightly lesser, changes.

Sites at which formalin and capsaicin act to stimulate corticotropin secretion

The sites at which injected Formalin and capsaicin act to stimulate ACTH secretion, as concluded from changes in the plasma corticosterone level, were studied in male Wistar rats. Formalin injected into an area deafferentated by denervation or spinal cord transection failed to raise the plasma corticosterone level, showing that it acted locally and that the nervous impulses it produced travelled to the hypothalamus through ascending pathways in the spinal cord. Capsaicin proved to be a potent stressor agent, and it produced a rise in the corticosterone level even when injected into a denervated area. This shows that chemonociceptor excitation at the site of injection is only one of several factors responsible for the stimulation of ACTH secretion by capsaicin. Pretreatment with capsaicin "desensitizing" the chemonociceptors in the skin and the mucous membranes merely inhibited, but did not suppress, the rise in the corticosterone level produced by a subsequent injection of capsaicin; it had no effect on the "nociceptive response" and the rise in the corticosterone level elicited by Formalin.

An extra-adrenal effect of corticotrophin

Administered intravenously, a commercial preparation of naturally occurring corticotrophin as well as synthetic corticotrophin were found to raise ovarian blood flow both in the normal and in the adrenalectomized dog and cat, without affecting systemic blood pressure. Peaks and periods of time for which flow remained increased were dose-dependent.

Effect of a single glycocorticoid injection on the first day of life in rats

A single large dose of glycocorticoid injected in the rat on the first day of life produces a fatal cachectic condition which is very similar to the wasting syndrome which follows post-neonatal thymectomy. After smaller doses the survival time is longer and the mortality rate is less. Body weights, weights of thymus, spleen and adrenals are lower in treated rats than in non-treated control littermates. So is the number of small lymphocytes in the peripheral blood and in the lymphoid organs.

PITUITARY AND ADRENAL RESPONSIVENESS IN RATS AFTER PROLONGED TREATMENT WITH ACTH

Prolonged exposure to ACTH considerably increased adrenal responsiveness in the rat both in vivo and in vitro. The last of 5 and 14 daily injections each produced a significantly higher blood corticosterone level than did a single injection. In the presence of ACTH added in vitro, adrenal corticosterone production in animals subjected to prolonged treatment with ACTH significantly exceeded the production per unit of weight and unit of time measured in saline-treated animals. Reduced adrenal responsiveness in the stage of resistance, elicited by formalin as a non-specific stress, cannot be invoked as an explanation for the absence of an increase in corticosterone secretion. The conclusion is that after prolonged exposure to non-specific stress there is no longer any ACTH hypersecretion.Twenty-four hours after the last injection of prolonged ACTH treatment there was inhibition of endogenous ACTH release by the pituitary gland, formalin produced no rise in the corticosterone level of the peripheral blood, and operative trauma caused substantially less ascorbic acid depletion than it did in saline-treated controls, although the plasma corticosterone level was normal or below normal.