Adrenocorticotrophic Hormone Secretion in Rats after Partial or Total Deafferentation of the Medial Basal Hypothalamus

Halász, Béla; Slusher, Margaret A.; Gorski, Roger A.

doi:10.1159/000121528

Cited by 108 publications

(23 citation statements)

References 2 publications

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“…The finding that this response is essentially intact is consistent with reports that ether is capable of eliciting a rise in plasma corticosterone levels in rats with acutely-prepared median emi nence-pituitary islands or hypothalamic-pi tuitary islands [Dunn and Critchlow, 1969b], and in rats with chroni cally-isolated MBH [Halász et al, 1967;Voloschin et al, 1968;Palka et al, 1969;Feldman et al, 1970]. Previous investigations dem onstrated that hippocampal lesions are compatible with ether-and im mobilization-induced stress responses [Knigge, 1961;Knigge and Hays, 1963], Because dexamethasone produced comparable suppression of non stress corticosterone levels in experimentáis and controls, these data imply that the hippocampo-fornix system is not an essential mediator of this feedback effect.…”

Section: Discussionsupporting

confidence: 88%

Effect of Fornix Transection or Hippocampectomy on Rhythmic Pituitary-Adrenal Function in the Rat

Wilson

Critchlow

1973

Neuroendocrinology

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To determine whether the hippocampo-fornix system is essential for the circadian rhythm in non-stress pituitary-adrenal function, adult female rats were subjected to fornix transection or hippocampectomy. Non-stress plasma corticosterone levels, measured fluorometrically in blood samples obtained at different times during the 24 h light-dark cycle, were used to assess rhythmic pituitary-adrenal function. At 1–2 and 4–5 weeks after surgery, morning and afternoon non-stress plasma corticosterone levels were comparable in all groups, and all groups showed significant diurnal variations in steroid levels. To follow non-stress diurnal corticosterone fluctuations in individual rats, 3 small (0.5 ml) samples of blood were collected at 10 h intervals (07.00, 17.00, 03.00) 11–12 weeks after surgery. Both fornix transection and hippocampectomy were compatible with normal steroid patterns in individual rats. Similar results were obtained in adult males following hippocampectomy. These findings suggest that ablation of the hippocampo-fornix system does not impose a deficit in the circadian rhythm in non-stress pituitary-adrenal function. Alterations in steroid levels following administration of ether stress or dexamethasone appeared intact in female rats, implying that the hippocampo-fornix system is not essential for these responses.

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Section: Discussionsupporting

confidence: 88%

Effect of Fornix Transection or Hippocampectomy on Rhythmic Pituitary-Adrenal Function in the Rat

Wilson

Critchlow

1973

Neuroendocrinology

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“…This is clearly shown by the fact that, 3 weeks after fornix-sectioning, plasma corticosterone levels follow the pattern seen in the sham-operated controls, i.e., they are low in the morning and elevated in the afternoon. If, in addition, one takes into account that, in the animals with complete deafferentation of the HTA or with a frontal cut behind the optic chiasm the diurnal variation in pituitary ACTH secretion is still blocked 4 weeks after surgery [HalAsz et al, 1967a, b], then it may be concluded that the critical neural input essential for the diurnal fluctuation in the release of CRF, and reaching the HTA from anterior direction, is not mediated by the fornix as was postulated by Moberg et al This, of course, does not mean that the fornix can be excluded as a possible route through which the hippocampus might modify, either directly or indirectly, the cyclic activity of the CRF-producing HTA. The only assumption that can be made is that this influence is probably not fundamental in nature or, at least, can very easily be replaced by other nervous structures.…”

Section: Discussionmentioning

confidence: 99%

“…Complete deafferentation of the medial basal hypothalamus, the hypophysiotrophic area (HTA), blocks the diurnal ACTH cycle [HalAsz et a!., 1967a, b; Palka et al, 1969]. This observation indicates that the above-mentioned hypothalamic area, which presumably produces the releasing factors including corticotrophic hormone releasing factor (CRF) [for references, see H alAsz, 1968], is not capable per se of maintaining the rhythm, but that neural impulses from other parts of the brain are required for this purpose.…”

Section: Abstract Acth Rhythm Biological Rhythms Fornix Acth Corticomentioning

confidence: 99%

Evidence for a Diurnal Fluctuation in Plasma Corticosterone Levels After Fornix Transection in the Rat

Lengvári¹,

Halász

1973

Neuroendocrinology

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The effect of fornix transection on the diurnal fluctua-tion in plasma corticosterone levels was investigated in adult male rhythm rats. Using the stereotaxic approach, the fornix was cut by means of a small piece of a razor blade. Plasma corticosterone levels at 8 a.m. and 6 p.m. were measured 1 week or 3 weeks after surgery. There was no diurnal variation in the plasma corticosterone concentration 1 week after fornix transection. At 3 weeks post-operatively, however, significant diurnal variations were present. The data suggest that, contrary to the assumption of other authors, the fornix is not the key structure in the mediation of extrahypothalamic influences to the medial basal hypothalamus that are essential for the diurnal rhythm in plasma corticosterone levels.

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“…The work with hypothalamic islands has shown that the isolated hypothalamus in vivo is functional (Halasz, Slusher & Gorski, 1967). In the rat the hypophysiotrophic area of the hypothalamus is small, being some 5 mm long, 3 mm wide and 2 mm thick.…”

mentioning

confidence: 99%

Stimulation electrically and by acetylcholine of the rat hypothalamus in vitro

Bradbury¹,

Burden²,

Hillhouse³

et al. 1974

The Journal of Physiology

101

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SUMMARY1. The hypophysiotrophic area of the rat hypothalamus was studied in vitro. The preparation remained viable for at least 3 hr and showed oxygen consumption varying between 68-9-120 ,umole/g. hr. The tissue potassium ion content (per unit wet weight) fell to about 50 % ofthe in vivo concentration during this time compared with 15 % in the presence of ouabain (104 M). Histological examination of tissue incubated for 3 hr showed variable perineuronal oedema but the nuclei were of normal appearance and none showed the pyknotic changes that would be associated with cell degeneration.2. Corticotrophin releasing hormone (CRH) in the medium pooled from five to twenty hypothalami was assayed in five to twelve rats which were median-eminence lesioned 48 hr earlier. In vitro corticosterone production of quartered adrenals was used as the end point of the assay. Regression lines of the dose-response curves for ACTH, crude CRH and different volumes of medium from electrically stimulated hypothalami were parallel.CRH output was maximal at 75 Hz and 100,uA when the square-wave pulses lasted for 1 msec. No CRH activity was found on stimulation of cerebral cortex or thalamic tissue pieces of equivalent size.3. Hypothalami taken from rats, adrenalectomized 7-14 days previously, released several-fold more CRH into the medium during electrical stimulation than the initial content of the tissue, showing that the tissue was capable of synthesizing CRH in vitro. The hypothalami taken from intact rats released considerably less CRH into the medium than tissue taken from 12 to 14 day adrenalectomized rats. The hyper-secretion of CRH observed in hypothalami taken from adrenalectomized rats was abolished by pre-treatment with 5 mg/100 g s.C. of corticosterone 24 hr before removal of the tissue. It is therefore proposed that the delayed negative feed-back action of corticosterone at the hypothalamic level is by the suppression of CRH synthesis and that the effect of secretion is secondary to the effect on synthesis.4. The presence of Ca2+ in the medium was essential for the release of CRH.5. CRH secretion increases linearly with doses of acetylcholine from 5.5 X 10-1k-5-5 X 10--14 M. Cerebral cortex incubated with acetylcholine showed no CRH activity. The effect of acetylcholine was reduced by atropine (3.5 x 10-13 M). Median eminence-pituitary stalk fragments (which contain mainly terminal axons of neurones) incubated with acetylcholine showed no CRH stimulation in the doses that activate the release of CRH using the hypophysiotrophic hypothalamus. Acetylcholine may act as a neurotransmitter at the dendritic level in the CRH neurone.

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Adrenocorticotrophic Hormone Secretion in Rats after Partial or Total Deafferentation of the Medial Basal Hypothalamus

Cited by 108 publications

References 2 publications

Effect of Fornix Transection or Hippocampectomy on Rhythmic Pituitary-Adrenal Function in the Rat

Effect of Fornix Transection or Hippocampectomy on Rhythmic Pituitary-Adrenal Function in the Rat

Evidence for a Diurnal Fluctuation in Plasma Corticosterone Levels After Fornix Transection in the Rat

Stimulation electrically and by acetylcholine of the rat hypothalamus in vitro

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