Efferent Neuroendocrine Pathways of Sympathetic Superior Cervical Ganglia

Abstract

The acute effect of superior cervical ganglionectomy (SCGx) on the pituitary-thyroid axis was examined in rats subjected to surgery 3–24 h earlier. SCGx caused an abrupt decline in thyroid norepinephrine content (an index of degeneration of sympathetic nerve terminals) to 5–10% of controls between 8 and 16 h. Rats subjected to SCGx 14 h earlier exhibited a significant depression of thyroid ¹³¹I uptake, total and free serum T₄ levels and serum TSH levels. The injection of 250 mU of bovine TSH, while resulting in similar increases of radioimmunoassayable serum TSH in both SCGx and sham-operated rats, brought about a significant increase of total and free serum T₄ only in sham-operated controls; TSH treatment augmented serum T₃ levels in both groups. In order to assess the involvement of the pineal gland in the changes of activity of the pituitary-thyroid axis after SCGx, rats were pinealectomized (Px) or sham-Px and 3 days later they were subjected to SCGx or sham-SCGx; all animals were killed at the time of expected degeneration of nerve terminals (i.e. 14 h after SCGx). The depressive effects of SCGx on ¹³¹I uptake and free serum T₄ levels were observed regardless of whether the pineal was present; in contrast, Px impaired significantly or blocked the effect of SCGx on TSH and total serum T₄ levels. Pineal removal resulted in a significant increase of serum T₃ levels of SCGx rats. Blood flow estimated from the uptake of a tracer dose of ⁸⁶Rb diminished significantly in the thyroid and pineal glands of SCGx rats while remaining unchanged in the adenohypophysis or medial basal hypothalamus. These results indicate that at the time of nerve terminal degeneration in the SCG territory a functional depression of the pituitary-thyroid axis takes place, as revealed by the occurrence of low serum TSH and Tt levels and impaired thyroid ¹³¹I uptake. The effect of acute SCGx is best explained by both central and peripheral mechanisms rather than by an exclusive central depressive effect on TSH secretion because: (a) exogenous TSH injection did not increase serum T₃ levels in SCGx rats; (b) depressed thyroid ¹³¹I uptake and serum-free T₄ levels, and normal serum TSH concentration were found in SCGx previously subjected to Px.

Increase in Adrenocorticotropin Release during Wallerian Degeneration of Peripheral Sympathetic Neurons after Superior Cervical Ganglionectomy of Rats

“…Summarizing, the present results underline a role of periph eral sympathetic projections to the hypothalamic adenohypo physial axis in ACTH release mechanisms. PRL and ACTH are the only two adenohypophysial hormones so far examined that showed increased release during wallerian degeneration of sym pathetic nerves in the SCG territory, acute SCGx decreasing TSH, GH, LH, and FSH release in a number of paradigms [2,4,[6][7][8]. Although further experiments are needed to establish in a more detailed way the participation of SCG neurons in stress reaction, it is tempting to postulate that parallel central and pe ripheral noradrenergic channels convey information to the neu roendocrine system to allow the full response of the stress hor mones ACTH and PRL.…”

“…Rats subjected to pinealectomy (Px) or sham-Px 1 week earlier and killed 22 h earlier exhibited similar responses in plasma ACTH and MBH CRH to SCGx regardless of pineal intactness. These results demonstrate a stimulatory, pineal-independent, effect on ACTH release of wallerian degeneration of nerve fibers in the superior cervical ganglia field of projection.The existence of a functionally relevant peripheral sympa thetic projection to the hypothalamic-pituitary axis, derived from the superior cervical ganglia (SCG), has been proposed on the basis of anatomic and physiologic studies [1,2]. Antero grade labeling of vascular and parenchymatous nerve terminals in the median eminence and the adeno-and neurohypophysis was revealed by horseradish peroxidase injection in rat SCG [3], Bilateral superior cervical ganglionectomy (SCGx) brought about a 40-60% decrease of rat median eminence norepineph rine (NE) content, made apparent 10-12 h after surgery and completed in about 24-36 h [4], That decrease is an index of NE release from sympathetic nerve terminals undergoing walle rian degeneration in the denervated territory [5], and the postsynaptic activation caused by such a temporary, supraliminal 1 Supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and the University of Buenos Aires.…”

“…Growth hormone (GH) release is decreased, while ether-induced PRL increase is amplified, at the time of walle rian degeneration after SCGx in rats [8]. At least for TSH the acute inhibitory effect of nerve degeneration is exerted at a hy pothalamic rather than at a pituitary site [2],…”

Mechanism for the Inhibitory Action of 2-Deoxy-Glucose on Thyroid Hormone Secretion in the Mouse

“…Furthermore, during anterograde degeneration of sympathetic varicosities after ganglionectomy, in the rat, the T» secretory response to TSH is inhibited [8], and sympathetic nerves seem to be of importance for thyroid growth [30]. Hence, the sympathtic nervous system seems to be capable of exerting a multitude of effects in the thyroid.…”

Estrous Cycle Delay and Inhibition of Gonadotropin and Prolactin Release during Sympathetic Nerve Degeneration after Superior Cervical Ganglionectomy of Rats

“…These results demonstrate that the coincidence of anterograde degeneration of sympathetic termi nals in the superior cervical ganglion field of projection with the spontaneous or induced gonadotropin and PRL release in female rats (1) disrupts temporarily estrous cyclicity and (2) decreases estradiol-progesterone-induced LH, FSH, and PRL release through a pineal gland independent mechanism. Noradrenergic transmitter release from degenerating sympathetic nerves acts via cxiadrenoceptors to decrease gonadotropin and PRL secretion.Recent experimental work supports the existence of a func tionally relevant peripheral sympathetic projection to the hypo thalamic-pituitary axis derived from the superior cervical ganglia (SCG) [9]. Such a projection has been documented histochemically by anterograde labeling of vascular and paren chymatous nerve terminals in median eminence and anterior and posterior pituitary after horseradish peroxidase injection into SCG neurons of rats [ 13].…”