Prolactin modulates luteal regression from the coeliac ganglion via the superior ovarian nerve in the late-pregnant rat.

There is considerable evidence of the neuroendocrine control involved in luteal regression in the rat. In addition, circulating prolactin (PRL), which increases during the night before parturition, may gain access to the coeliac ganglion (CG), indirectly impacting the physiology of the ovary because of the known connection between the CG and the ovary via the superior ovarian nerve (SON). In this work we investigated in the CG-SON-ovary system and whether PRL added to the CG has an impact, indirectly via the SON, on luteal regression on Day 21 of pregnancy. The system was incubated without (control) or with PRL added to the CG. We measured the ovarian release of progesterone (P), oestradiol and prostaglandin F2 alpha (PGF2α) by radioimmunoassay, and nitrites (NO) by the Griess method. Luteal mRNA expression of 3ß-hydroxysteroid dehydrogenase (3ß-HSD), 20α-HSD, aromatase, inducible nitric oxide synthase (iNOS) and apoptosis regulatory factors was analysed by reverse transcription-polymerase chain reaction. P release, the expression of Bcl-2 and the Bcl-2:Bax ratio was lower than control preparations, while the expression of 20α-HSD and the release of NO and PGF2α were higher in the experimental group. In conclusion, PRL acts at the CG and, by a neural pathway, modulates luteal function at the end of pregnancy.

Neuromodulation of the luteal regression: presence of progesterone receptors in coeliac ganglion.

NEW FINDINGS: What is the central question of this study? The processes involved in luteal involution have not yet been clarified and, in general, have been studied only from a hormonal point of view. We investigated whether progesterone, from the coeliac ganglion through the superior ovarian nerve, is able to modify the luteal regression of late pregnancy in the rat. What is the main finding and its importance? We showed that the luteal regression might be reversed by the neural effect of progesterone and demonstrated the presence of its receptors in the coeliac ganglion. This suggests that the peripheral neural pathway, through neuron-hormone interaction, represents an additional mechanism to control luteal function in addition to the classical endocrine regulation. The corpus luteum (CL) is a transitory endocrine gland that produces progesterone (P). At the end of its useful life, it suffers a process of functional and structural regression until its complete disappearance from the ovary. To investigate whether P is able to regulate the process of luteal regression through the peripheral neural pathway, we used the coeliac ganglion (CG)-superior ovarian nerve-ovary system from rats on day 21 of pregnancy. We stimulated the CG with P and analysed the functional regression through ovarian P release measured by radioimmunoassay, expression by RT-PCR and activity of luteal 3ß- and 20α-hydroxysteroid dehydrogenase (anabolic and catabolic P enzymes, respectively). The luteal structural regression was evaluated through a study of apoptosis measured by TUNEL assay and the expression of apoptotic factors, such as Bcl-2, Bax, Fas and Fas ligand (FasL) by RT-PCR. To explore whether the effects mediated by P on the CL may be associated with P receptors, their presence in the CG was investigated by immunohistochemistry. In the group stimulated with P in the CG, the ovarian P release and the 3ß-hydroxysteroid dehydrogenase activity increased, whereas the expression and activity of 20α-hydroxysteroid dehydrogenase decreased. In addition, a decrease in the number of apoptotic nuclei and a decrease of the expression of FasL were observed. We demonstrated the presence of P receptors in the CG. Overall, our results suggest that the regression of the CL of late pregnancy may be reprogrammed through the peripheral neural pathway, and this effect might be mediated by P bound to its receptor in the CG.

An increase in glucose concentration in the lateral ventricles of the brain induces changes in autonomic nervous system activity.

OBJECTIVE: Changes in glucose levels mobilize a neuroendocrine response that prevents or corrects glycemia. The hypothalamus is the main area of the brain that regulates glycemic homeostasis. Metabolic diseases, such as obesity and diabetes, are related to imbalance of this control. The modulation of autonomic nervous system (ANS) activity is mediated by neuronal hypothalamic pathways. In the present work, we investigate whether glucose concentration in the hypothalamic area changes ANS activity. METHODS: Glucose was administered intracerebroventricularly to 90-day-old rats, and samples of blood were collected during brain glucose infusion to measure the blood glucose and insulin levels. The electric activity of the superior vagus nerve and superior sympathetic ganglion was directly registered. RESULTS: Glucose 5·6 mM infused in the hypothalamus induced a 67·6% decrease in blood insulin concentration compared to saline infusion (P<0·01); however, no glycemia changes occurred. During glucose 5·6 mM intracerebroventricular infusion, the firing rate of the vagus nerve was decreased 39% and sympathetic nerve activity was increased 177% compared to saline infusion (P<0·01). DISCUSSION: Glucose injection into the brain in the hypothalamic area modulates glucose homeostasis, which might be mediated by the sensitivity of the hypothalamic area to local changes in glucose concentration. We suggest that gluconeurons in the hypothalamus contribute to the control of glycemia through ANS activity.

Estradiol promotes luteal regression through a direct effect on the ovary and an indirect effect from the celiac ganglion via the superior ovarian nerve.

There is evidence suggesting that estradiol (E(2)) regulates the physiology of the ovary and the sympathetic neurons associated with the reproductive function. The objective of this study was to investigate the effect of E(2) on the function of late pregnant rat ovaries, acting either directly on the ovarian tissue or indirectly via the superior ovarian nerve (SON) from the celiac ganglion (CG). We used in vitro ovary (OV) or ex vivo CG-SON-OV incubation systems from day 21 pregnant rats. Various concentrations of E(2 )were added to the incubation media of either the OV alone or the ganglion compartment of the CG-SON-OV system. In both experimental schemes, we measured the concentration of progesterone in the OV incubation media by radioimmunoassay at different times. Luteal messenger RNA (mRNA) expression of 3ß-hydroxysteroid dehydrogenase (3ß-HSD) and 20α-hydroxysteroid dehydrogenase (20α-HSD) enzymes, respectively, involved in progesterone synthesis and catabolism, and of antiapoptotic B-cell lymphoma 2 (Bcl-2) and proapoptotic Bcl-2-associated X protein (Bax), were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) at the end of the incubation period. Estradiol added directly to the OV incubation or to the CG of the CG-SON-OV system caused a decline in the concentration of progesterone accumulated in the incubation media. In addition, E(2), when added to the OV incubation, decreased the expression of 3ß-HSD and the ratio of Bcl-2/Bax. We conclude that through a direct effect on the OV, E(2) favors luteal regression at the end of pregnancy in rats, in association with neural modulation from the CG via the SON.

Effect of transcutaneous electrical nerve stimulation on muscle metaboreflex in healthy young and older subjects.

Transcutaneous electrical nerve stimulation (TENS) increases local blood flow. It is not known whether increase in blood flow may be caused by inhibition of sympathetic activity, mediated by muscle metaboreflex activity. The purpose of this study was to evaluate the effect of TENS on metaboreflex activation and heart rate variability (HRV) in young and older individuals. Eleven healthy young (age 25 ± 1.3 years) and 11 healthy older (age 63 ± 4.2 years) were randomized to TENS (30 min, 80 Hz, 150 µs) or placebo (same protocol without electrical output) applied on the ganglion region. Frequency domain indices of HRV and hemodynamic variables were evaluated during the pressor response to static handgrip exercise at 30% of maximal voluntary contraction, followed by recovery with (PECO+) or without (PECO-) circulatory occlusion, in a randomized order. At the peak exercise, the increase in mean blood pressure was attenuated by TENS (P < 0.05), which was sustained during PECO+ and PECO-. TENS promoted a higher calf blood flow and lower calf vascular resistance during exercise and recovery. Likewise, TENS induced a reduction in the estimated muscle metaboreflex control both in young (placebo: 28 ± 4 units vs. TENS: 6 ± 3, P < 0.01) and in older individuals (placebo: 13 ± 3 units vs. TENS: 5 ± 3, P < 0.01). HRV analysis showed similar improvement in sympatho-vagal balance with TENS in young and older individuals. We conclude that application of TENS attenuates blood pressure and vasoconstrictor responses during exercise and metaboreflex activation, associated with improved sympatho-vagal balance in healthy young and older individuals.

Atrial stretch increases the gastric tonus of anesthetized rats.

AIMS: We assessed the effects of right atrial stretch on gastric tone and neuro-humoral pathways involved in this phenomenon. MAIN METHODS: Anesthetized male rats were submitted for monitoring of the mean arterial pressure (MAP) and central venous pressure (CVP). A balloon catheter positioned into the stomach monitored by plethysmography the gastric volume (GV). All rats were monitored for 55-min. After the first 20-min of monitoring (basal period), rats were either submitted to a 5-min interval of atrial stretch (AS) or maintained as controls. An intra-atrial balloon catheter was distended with 30, 50, or 70 microL of saline. GV and hemodynamic data were also monitored for a further 30-min. Another set of rats, either previously submitted to subdiaphragmatic vagotomy or splanchnicectomy plus celiac ganglionectomy or maintained as controls (sham), were also submitted to AS. Each subset consisted of six rats. The plasma level of the atrial natriuretic peptide (ANP) was measured in another group of rats. Data were compared by ANOVA followed by Bonferroni's test. KEY FINDINGS: In control rats, the GV, MAP, and CVP remained at stable levels throughout the studies. In addition to increase the CVP, AS also decreased (P<0.05) the GV by 14%, 11.5%, and 16.5% in the 30, 50, and 70 microL groups, respectively. Vagotomy prevented the GV decrease. In contrast, the AS decreased (P<0.05) the GV by 21.3% in splanchnicectomized rats. SIGNIFICANCE: AS decreased the GV of rats in a volume-dependent manner, a phenomenon prevented by vagotomy but enhanced by celiac ganglionectomy.

Differential contribution of extracellular and intracellular calcium sources to basal transmission and long-term potentiation in the sympathetic ganglion of the rat.

Calcium involved in basal ganglionic transmission and long-term potentiation (LTP) can arise either by influx from the extracellular medium or release from intracellular stores. No attempts have yet been made to concurrently explore the contributions of extracellular and intracellular Ca2+ to basal ganglionic transmission or LTP. Here, we investigate this subject using the superior cervical ganglion of the rat. To explore the extracellular Ca2+ contribution, we evaluated basal transmission and LTP at different extracellular Ca2+ concentrations. To assess intracellular Ca2+ release, we explored the contribution of the calcium-induced calcium release process by overactivation or blockade of ryanodine-sensitive Ca2+ receptor channel with caffeine, and also by blocking either IP3R with Xestospongin C or the sarco(endo)plasmic reticulum Ca2+-ATPase pump with thapsigargin. Extracellular Ca2+ affected ganglionic basal transmission and LTP to different extents. While 25% of the physiological Ca2+ concentration supported 80% of basal transmission, 50% of normal Ca2+ was required to achieve 80% of LTP. Notably, disruption of intracellular Ca2+ release by all the drugs tested apparently did not affect basal ganglionic transmission but impaired LTP. We conclude that basal transmission requires only a small level of Ca2+ entry, while LTP expression not only requires more Ca2+ entry but is also dependent on Ca2+ release from intracellular stores.

Nitric oxide in prepubertal rat ovary contribution of the ganglionic nitric oxide synthase system via superior ovarian nerve.

Both peripheral innervation and nitric oxide (NO) participate in ovarian steroidogenesis. Considering the existence of the nitric oxide/ nitric oxide synthase system in the peripheral neural system and in the ovary, the aim of this work was to analyze if the liberation of NO in the ovarian compartment of prepubertal rats is of ovarian and/or ganglionic origin. The analysis is carried out from a physiological point of view using the experimental coeliac ganglion--Superior Ovarian Nerve--ovary model with and without ganglionic cholinergic stimulus Acetylcholine (Ach) 10(-6) M. Non selective and selective inhibitors of the synthase nitric oxide enzyme were added to the ovarian and ganglionic compartment, and the liberation of nitrites (soluble metabolite of the nitric oxide) in the ovarian incubation liquid was measured. We found that the non-selective inhibitor L-nitro-arginina methyl ester (L-NAME) in the ovarian compartment decreased the liberation of nitrites, and that Aminoguanidine (AG) in two concentrations in a non-dose dependent form provoked the same effect. The addition of Ach in ganglion magnified the effect of the inhibitors of the NOS enzyme. The most relevant results after the addition of inhibitors in ganglion were obtained with AG 400 and 800 microM. The inhibition was made evident with and without the joint action of Ach in ganglion. These data suggest that the greatest production of NO in the ovarian compartment comes from the ovary, mainly the iNOS isoform, though the coeliac ganglion also contributes through the superior ovarian nerve but with less quantity.

Ischaemia-induced sympathoexcitation in spinalyzed rats.

Systemic ischaemia increases sympathetic activity via both reflex and direct effects on the nervous system, which include the hypothalamus and brainstem structures that provide excitatory drive to sympathetic pre-ganglionic motoneurones. Using an arterially perfused working heart-brainstem preparation (WHBP), we evaluated the sympathoexcitatory response recorded from the thoracic sympathetic chain (tSC) in response to systemic ischaemia (produced by arresting perfusion for 30 s) before and after transecting consecutively at both the ponto-medullary and medullary-spinal cord junctions. Ischaemia produced a striking increase in tSC activity that persisted after transecting at both the ponto-medullary and medullary-spinal cord levels (intact: 70+/-3%; ponto-medullary: 77+/-7%; medullary-spinal cord: 61+/-6%; n=9). In sino-aortic denervated (SAD) rats (n=4), sympathoexcitatory responses were smaller in both intact and ponto-medullary, but not in medullary-spinal cord transected versus intact rats. Following administration of a ganglionic blocker [hexamethonium (hex), 25 mg/kg] after medullary-spinal cord transection the ischaemia-induced sympathoexcitatory response was reduced (12+/-6% increase relative to control, n=4). In medullary-spinal cord transected preparations, intrathecal injection of N2-saturated saline increased tSC discharge (22+/-3%, n=4), which was attenuated by hex (5+/-1%). We propose that neural mechanisms within the cervical-thoracic segments can make a substantial contribution to the sympathoexcitatory response during systemic ischaemia.

The celiac ganglion modulates LH-induced inhibition of androstenedione release in late pregnant rat ovaries.

BACKGROUND: Although the control of ovarian production of steroid hormones is mainly of endocrine nature, there is increasing evidence that the nervous system also influences ovarian steroidogenic output. The purpose of this work was to study whether the celiac ganglion modulates, via the superior ovarian nerve, the anti-steroidogenic effect of LH in the rat ovary. Using mid- and late-pregnant rats, we set up to study: 1) the influence of the noradrenergic stimulation of the celiac ganglion on the ovarian production of the luteotropic hormone androstenedione; 2) the modulatory effect of noradrenaline at the celiac ganglion on the anti-steroidogenic effect of LH in the ovary; and 3) the involvement of catecholaminergic neurotransmitters released in the ovary upon the combination of noradrenergic stimulation of the celiac ganglion and LH treatment of the ovary. METHODS: The ex vivo celiac ganglion-superior ovarian nerve-ovary integrated system was used. This model allows studying in vitro how direct neural connections from the celiac ganglion regulate ovarian steroidogenic output. The system was incubated in buffer solution with the ganglion and the ovary located in different compartments and linked by the superior ovarian nerve. Three experiments were designed with the addition of: 1) noradrenaline in the ganglion compartment; 2) LH in the ovarian compartment; and 3) noradrenaline and LH in the ganglion and ovarian compartments, respectively. Rats of 15, 19, 20 and 21 days of pregnancy were used, and, as an end point, the concentration of the luteotropic hormone androstenedione was measured in the ovarian compartment by RIA at various times of incubation. For some of the experimental paradigms the concentration of various catecholamines (dihydroxyphenylalanine, dopamine, noradrenaline and adrenaline) was also measured in the ovarian compartment by HPLC. RESULTS: The most relevant result concerning the action of noradrenaline in the celiac ganglion was found on day 21 of pregnancy resulting in the inhibition of androstenedione release from the ovarian compartment. In addition on day 15 of pregnancy, LH placed in the ovarian compartment led to an inhibition of the release of androstenedione, and this inhibitory effect was further reinforced by the joint action of noradrenaline in the celiac ganglion and LH in the ovary. The levels of catecholamines in the ovarian compartment showed differences among the experiments; of significance, the joint treatment of noradrenaline in the celiac ganglion and LH in the ovary resulted in a remarkable increase in the ovarian levels of noradrenaline and adrenaline when compared to the effect achieved by either one of the compounds added alone. CONCLUSION: Our results demonstrate that the noradrenergic stimulation of the celiac ganglion reinforces the LH-induced inhibition of androstenedione production by the ovary of late pregnant rats, and that this effect is associated with marked changes in the release of catecholamines in the ovary.

Pregnancy in rats is modulated by ganglionic cholinergic action.

The control of ovarian steroidogenesis during pregnancy is mainly of endocrine origin. At present, there is little information about the influence of neural factors on the gestation physiology. The purpose of this work was to study the action of cholinergic agents in celiac ganglion upon the liberation of progesterone and ovarian androstenedione in the second half of pregnancy in rats. We used the ex vivo celiac ganglion-superior ovarian nerve-ovary integrated system (celiac ganglion-SON-ovary) that was incubated in buffer solution for 180 min, with the celiac ganglion and the ovary located in different compartments and linked by the SON. The results obtained indicate that the control values of ovarian androstenedione vary according to the pregnancy day analyzed. The addition of acetylcholine in ganglion decreased the liberation of both steroids on Day 15 whereas at the end of pregnancy it decreased the liberation of androstenedione without modifying progesterone. Due to the effect observed with atropine and hexametonium, acetylcholine action might occur through unspecific ganglionic pathways (Days 15 and 21) or through muscarinic ganglionic receptors (Days 19 and 20). Thus, we conclude that the cholinergic sympathetic system from the celiac ganglion might be a fine modulator of the pregnancy physiology.

Neural activity between ovaries and the prevertebral celiac-superior mesenteric ganglia varies during the estrous cycle of the rat.

The ovaries' innervation arrives via the superior ovarian nerve, which originates from the celiac ganglion. Using True Blue as an antidromic marker, the present study analyzed the changes in the anatomical relation between each ovary and the prevertebral celiac-superior mesenteric ganglia during the estrous cycle. The number of labeled neurons increased from the day of diestrus 1 to the day of proestrus. The largest number of labeled cells was observed when tracer was injected into the left ovary on proestrus. The number of labeled cells was significantly higher when the tracer was injected into the left ovary on proestrus than when it was done in the right one. When tracer was injected into the left ovary, the average labeled area of cells increased significantly from diestrus 1 to proestrus, and declined at estrus. In contrast, when True Blue was injected into the right ovary, the average labeled area was similar in diestrus 1 and diestrus 2, and the values increased in proestrus and estrus. The results indicate an apparent asymmetry in the activity of neural connections between ovaries and the prevertebral celiac-superior mesenteric ganglia, and that the number of active neurons of these connections varies during the estrous cycle.

Pressor effects of electrical stimulation of medial prefrontal cortex in unanesthetized rats.

The medial prefrontal cortex (MPFC) is involved in central nervous system (CNS)-mediated cardiovascular modulation. We compared the cardiovascular effects of electrical stimulation (EE) of the MPFC in unanesthetized rats to those observed after stimulation of the same area in urethane-anesthetized rats. Electrical stimulation (35, 106, 177, 247, 318, and 389 microA rms/10 sec, 60-Hz sine wave) of the MPFC of urethane-anesthetized rats caused depressor responses of stimulus-related intensity. The cardiovascular response to electrical stimulation of the MPFC in unanesthetized rats was characterized by stimulus-related pressor responses. No significant heart rate changes were observed during the EE period in any case. The pressor response to electrical stimulation (106 microA rms/10 sec, 60-Hz sine wave) of the MPFC was not affected by intravenous pretreatment with the vasopressin antagonist dTyr(CH(2))(5)(Me)AVP (50 microg/kg, intravenously), by hypophysectomy, or by intravenous pretreatment with the angiotensin II antagonist losartan (1 mg/kg, intravenously). The pressor response was blocked by intravenous pretreatment with the ganglionic blocker mecamylamine (2 mg/kg, intravenously) but was not affected by adrenal demedullation, thus suggesting involvement of the neural component of the sympathetic nervous system without a major involvement of its hormonal component. Our results confirmed the occurrence of depressor responses after electrical stimulation of the MPFC in urethane-anesthetized rats and evidenced that only pressor responses are observed after its stimulation in unanesthetized rats. The fact that the pressor response to the stimulation of the MPFC was blocked by a ganglioplegic suggests that the MPFC has functional excitatory actions over the sympathetic nervous system.

Neural mechanisms involved in the delay of gastric emptying and gastrointestinal transit of liquid after thoracic spinal cord transection in awake rats.

Spinal cord transection (SCT) delays gastric emptying (GE), and intestinal and gastrointestinal (GI) transit of liquid in awake rats. This study evaluates the neural mechanisms involved in this phenomenon. Male Wistar rats (N = 147) were fasted for 16 h and had the left jugular vein cannulated followed by laminectomy or laminectomy + complete SCT between T4 and T5 vertebrae. The next day, a test meal (1.5 ml of a phenol red solution, 0.5 mg/ml in 5% glucose) was administered by gavage feeding and 10 min later cervical dislocation was performed. Dye recovery in the stomach, and proximal, mid and distal small intestine was determined by spectrophotometry. SCT inhibited GE and GI transit since it increased gastric recovery by 71.3% and decreased mid small intestine recovery by 100% (P < 0.05). Subdiaphragmatic vagotomy, celiac ganglionectomy + section of the splanchnic nerves, i.v. hexamethonium (20 mg/kg) or yohimbine (3 mg/kg) prevented the development of the SCT effect on GE and GI transit. Pretreatment with i.v. naloxone (2 mg/kg), L-NAME (3 mg/kg) or propranolol (2 mg/kg) was ineffective. Bilateral adrenalectomy or guanethidine (10 mg/kg) increased the magnitude of the GE inhibition, while i.v. prazosin (1 mg/kg) or atropine (0.5 mg/kg) decreased the magnitude but did not abolish the GE inhibition. In summary, the inhibition of GI motility observed 1 day after thoracic SCT in awake rats seems to involve vagal and possibly splanchnic pathways.

Sympathetic mediation of salivation induced by intracerebroventricular pilocarpine in rats.

Central cholinergic activation by pilocarpine induces salivation dependent on the integrity of forebrain areas. The present work investigates the autonomic mediation of this salivation. Pilocarpine (500 nmol/rat) was injected into the lateral ventricle (LV) of tribromoethanol-anesthetized adult male rats. Preweighed cotton balls were inserted into the oral cavity and weighed again 7 min later. Alpha-adrenoceptor antagonists (3-50 micromol/kg) prazosin (alpha1), yohimbine (alpha2) or propranolol (beta) injected intraperitoneally (i.p.) produced, 80%, 20% and 0% inhibition respectively of the LV pilocarpine-induced salivation. Intracerebroventricular injections (160 nmol) of the antagonists did not alter the effects of pilocarpine injected into the LV. Bilateral section of chorda tympani nerve or bilateral sympathetic cervical ganglionectomy produced 0% and 40% inhibition of pilocarpine-induced salivation, respectively. Ganglionectomy did not alter salivation induced by i.p. injection of pilocarpine (4 micromol/kg). The results indicate that there is a large sympathetic contribution to the salivation induced by central cholinergic activation.

Different calcium channels mediate transmitter release evoked by transient or sustained depolarization at mammalian sympathetic ganglia.

We have compared the effect of calcium channel blockers on the potassium-evoked release of tritium-labeled acetylcholine and on preganglionic spike-evoked synaptic transmission in the rat superior cervical ganglion. Transmitter release at the nerve terminals is mediated by the influx of calcium through voltage-gated calcium channels. While four types of voltage-gated calcium channels (T, L, N and P) have been identified in neurons, it is not clear which may actually be involved in excitation-secretion coupling. Release of tritiated acetylcholine evoked by sustained depolarization in high (40 mM) extracellular potassium decreased markedly in the absence of calcium or the presence of cadmium. High potassium-evoked release was substantially inhibited by the P-type channel blockers, purified from funnel-web spider toxin, and omega-agatoxin-IVA, and by the N-type channel blocker omega-conotoxin-GVIA, but was unaffected by the L-type channel blocker nitrendipine. In contrast, postganglionic compound action potentials synaptically triggered by preganglionic stimulation were strongly blocked by funnel-web spider toxin and slightly blocked by a high concentration of omega-agatoxin-IVA, but were unaffected by either omega-conotoxin-GVIA, nitrendipine or a low concentration of omega-agatoxin-IVA. Thus, at the superior cervical ganglion, funnel-web spider toxin-sensitive calcium channels play a dominant role in transmitter release evoked by transient, spike-mediated depolarization, but other types of voltage-gated calcium channels in addition to the funnel-web spider toxin-sensitive channel mediate the transmitter release that is evoked by sustained high potassium depolarization.

Influence of the autonomic nervous system on calcium homeostasis in the rat.

The local surgical manipulation of sympathetic and parasympathetic nerves innervating the thyroid-parathyroid territory was employed to search for the existence of a peripheral neuroendocrine link controlling parathyroid hormone (PTH) and calcitonin (CT) release. From 8 to 24 h after superior cervical ganglionectomy (SCGx), at the time of wallerian degeneration of thyroid-parathyroid sympathetic nerve terminals, an alpha-adrenergic inhibition, together with a minor beta-adrenergic stimulation, of hypercalcemia-induced CT release, and an alpha-adrenoceptor inhibition of hypocalcemia-induced PTH release were found. In chronically SCGx rats PTH response to EDTA was slower, and after CaCl2 injection, serum calcium attained higher levels in face of normal CT levels. SCGx blocked the PTH increase found in sham-operated rats stressed by a subcutaneous injection of turpentine oil, but did not affect the greater response to EDTA. The higher hypocalcemia seen after turpentine oil was no longer observed in SCGx rats. The effects of turpentine oil stress on calcium and CT responses to a bolus injection of CaCl2 persisted in rats subjected to SCGx 14 days earlier. Interruption of thyroid-parathyroid parasympathetic input conveyed by the thyroid nerves (TN) and the inferior laryngeal nerves (ILN) caused a fall in total serum calcium, an increase of PTH levels and a decrease of CT levels, when measured 10 days after surgery. Greater responses of serum CT and PTH were detected in TN-sectioned, and in TN- or ILN-sectioned rats, respectively. Physiological concentrations of CT decreased, and those of PTH increased, in vitro cholinergic activity in rat SCG, measured as specific choline uptake, and acetylcholine synthesis and release. The results indicate that cervical autonomic nerves constitute a pathway through which the brain modulates calcium homeostasis.

Modulated intra-train spike responses in the cat superior cervical ganglion in vivo.

The known two-stage facilitation/depression pattern of postganglionic responses was found at high (24 Hz) frequency stimulation of the preganglionic nerves. We found that the depression stage was exaggerated under partial hexamethonium blockade but it was not affected by partial transection of the preganglionic trunk. At low frequency (8 Hz) normal recruitment turned into the familiar two-stage pattern under moderated hexamethonium doses. The depression course under the competitive nicotinic antagonist dihydro-beta-erythroidine was markedly slower than under hexamethonium. These observations are accountable to the known use-dependence effect of hexamethonium.

Neurochemical evidence for a neuronal GABAergic system in the rat sympathetic superior cervical ganglion.

Some characteristics of gamma aminobutyric acid (GABA) uptake and release in rat superior cervical ganglion (SCG) were investigated. Kinetic analysis of GABA uptake indicated the existence of both high affinity (Km = 18.6 microM) and low affinity (Km = 485 microM) uptake systems. 3H-GABA influx was decreased by inhibitors of glial (beta-alanine), neuronal (2,4-diaminobutyric acid, DABA), or glial and neuronal GABA uptake (nipecotic acid). 3H-GABA efflux was elicited by K+ depolarization in a dose-dependent manner, an effect unaltered by severing the preganglionic nerve fibers. Superfusion of SCG explants with DABA or beta-alanine resulted in increased 3H-GABA efflux from tissue, an effect amplified by the absence of calcium in the superfusion medium. 3H-GABA loading in the presence of DABA, but not in the presence of beta-alanine, resulted in abolition of K(+)-elicited 3H release. At 20 mM, but not at 50 mM K+, the release of 3H-GABA was inhibited by replacing Ca2+ by Mg2+ and by adding EGTA, or by incubating SCG in the presence of the Ca(2+)-channel blocker verapamil. Veratrine evoked GABA release in Ca(2+)-independent manner. None of several putative SCG autacoids or agonists (nicotine, muscarine, norepinephrine, dopamine, serotonin, baclofen, muscimol) significantly modified GABA release.

Anterograde nerve degeneration after superior cervical ganglionectomy coexists with a decrease in arginine vasopressin release in rats.

After bilateral superior cervical ganglionectomy (SCGx) in adult male rats, norepinephrine content of the pituitary neurointermediate lobe (NIL) decreased at 12-24 h after surgery to attain concentrations 40-60% of controls between 24 and 60 h after surgery. To assess arginine vasopressin (AVP) secretion during this time, plasma and NIL-AVP levels were measured by radioimmunoassay. In sham SCGx controls, plasma AVP increased about 2-fold within 6 h after surgery and decreased thereafter, to attain presurgical values by 60 h after surgery. In SCGx rats, a significant increase in plasma AVP concentration was observed at the 6th h after surgery, as compared to presurgical concentrations, with a decrease to values significantly lower than those of presurgical controls at 16-18 h after SCGx. As compared to sham-operated rats, significantly higher plasma AVP levels 6 h after surgery and significantly lower plasma AVP levels 16-24 h after surgery were found. NIL-AVP concentration in SCGx and sham-operated ras were significantly lower than presurgical levels at 6 h after surgery. SCGx rats had significantly higher amounts of AVP in NIL at 16-24 h after surgery. The changes in plasma and NIL-AVP levels found 6 or 16 h after SCGx or sham SCGx were unaffected by a prior pinealectomy. Two injections of the alpha 1-adrenoceptor blocker prazosin 45 and 90 min before sacrifice, alone or together with the beta-blocker propranolol, prevented the increase in plasma AVP found in SCGx rats 6 h after surgery, and the decrease in plasma AVP and the increase of NIL-AVP found 16 h after SCGx.(ABSTRACT TRUNCATED AT 250 WORDS)