The role of catecholamines and acetylcholine in the regulation of endocrine function

Characterization of Group I Metabotropic Glutamate Receptors in Rat and Human Adrenal Glands

Glutamate and its receptors have been demonstrated to promote both basal and nicotine-evoked catecholamine release in bovine chromaffin cells. Multiple glutamate receptors, including metabotropic glutamate receptors (mGluRs), are found in the adrenal glands of several species, as well as in chromaffin cells. However, there is limited information available regarding the expression of glutamate metabotropic receptor (GRM)1-8 mRNAs and the detailed localization of group I mGluRs (mGluR1 and mGluR5) in the rat and human adrenal cortex and medulla. Therefore, we examined mRNA expression of GRM1-8 subunits using reverse transcription-polymerase chain reaction (RT-PCR) and the distribution of mGluR1 and mGluR5 by immunostaining. The results showed that the GRM1-8 mRNAs were expressed in both the cortex and medulla of rat and human adrenal glands with the exception of GRM1, which was not detectable in the rat adrenal cortex. Immunostaining of mGluR1 revealed that it was localized only in the adrenal medulla of rats but was present in both the adrenal cortex and medulla in humans. In the adrenal medulla, the central part of the adrenal glands, mGluR1 was detected in chromaffin cells but not in nerve fibers and ganglion cells. Immunoactivity of mGluR5 was visible in the capillary wall throughout the adrenal cortex and medulla in rat and human samples. Its immunoactivity was also observed in ganglion cells in the rat adrenal medulla. There was no mGluR5 immunoactivity detected in chromaffin cells and nerve fibers in the rat and human adrenal medulla. Using dissected rat adrenal medulla as a model, we found that treatment with a mGluR1 agonist activated extracellular signal-regulated kinase (ERK) 1/2 and increased the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Moreover, these results showed that mGluR1 signaling was involved in hypoxia-induced upregulation of TH in the rat adrenal medulla. This study shows the expression of GRM1-8 mRNAs in rat and human adrenal glands and indicates that glutamate, through the activation of mGluRs, may play various physiological roles in the adrenal gland. Furthermore, mGluR1 may be involved in catecholamine biosynthesis by regulating TH, and mGluR5 may affect cortical and medullar hormone levels by regulating microvascular function.

Ultrastructural identification of cholinergic neurons in the external cuneate nucleus of the gerbil: acetylcholinesterase histochemistry and choline acetyltransferase immunocytochemistry

Using acetylcholinesterase histochemical and choline acetyltransferase immunocytochemical localization methods, this study has provided conclusive evidence for the existence of cholinergic neurons in the external cuneate nucleus of gerbils. By light microscopy, both acetylcholinesterase and choline acetyltransferase labelling was confined to the rostral portion of the external cuneate nucleus. Ultrastructurally, acetylcholinesterase reaction products were found in the nuclear envelope, cisternae of rough endoplasmic reticulum and Golgi saccules of some somata and large dendrites as well as in the membranes of small dendrites, myelinated axons and axon terminals. These neuronal elements were also stained for choline acetyltransferase; immunoreactivity was associated with nuclear pores, nuclear envelope, perikaryal membrane and all the membranous structures within the cytoplasm. Of the total choline acetyltransferase-labelled neuronal profiles analysed, 79% were myelinated axons, 15% dendrites, 4% somata and 2% axon terminals. The immunostained axon terminals consisted of two types containing either round (Rd type; 62.5%) or pleomorphic (Pd type; 37.5%) vesicles. Both were associated directly with choline acetyltransferase-positive dendrites. In contrast to the paucity of choline acetyltransferase-labelled axon terminals, numerous choline acetyltransferase-positive myelinated axons were present. It may thus be hypothesized that most, if not all, of the external cuneate nucleus cholinergic neurons are projection cells; such cells may give rise to axonal collaterals which synapse onto their own dendrites for possible feedback control. Choline acetyltransferase-positive dendrites were contacted by numerous unlabelled presynaptic boutons, 60% of which contained round or spherical synaptic vesicles (Rd boutons) and 40% flattened vesicles (Fd boutons), suggesting that these neurons are under strong inhibitory control. The preferential concentration of cholinergic components in the rostral external cuneate nucleus may be significant in the light of the highly organized somatotopy in the external cuneate nucleus and its extensive efferent projections to medullary autonomic-related nuclei. Our results suggest that the cholinergic neurons may be involved in somatoautonomic integration.

Primary cultures of corticostriatal cells from newborn rats: a model to study muscarinic receptor subtypes regulation and function

In the present work we characterized both the presynaptic and postsynaptic components of cholinergic transmission in a primary culture of corticostriatal neurons prepared from newborn rat brain. This culture preparation contains a small population of choline acetyltransferase (ChAT) immunoreactive neurons, corresponding to approximately 3% of the total cell number, and synthesizes increasing amounts of acetylcholine (ACh) from the third day in vitro (DIV), which reaches a plateau around the 10 day of culture. Muscarinic cholinergic receptors (mAChR), measured by the binding of the muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB), are detectable from the fifth DIV and increase linearly during the time of culture. At the twelfth DIV, the density of mAChRs (approximately 600 fmol/mg protein) is comparable to the density of mAChR in adult rat cortex. These receptors are coupled to second messenger systems, since muscarinic agonists inhibit adenylate cyclase activity and stimulate phosphoinositide breakdown with efficacies and potencies similar to those found in adult rat cortex. Moreover, by using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique, we were able to demonstrate the presence of the m1, m3, and m4 mAChR subtype mRNAs in this neuronal culture at 12 DIV. Our data suggest that corticostriatal neuronal cultures develop in vitro ACh-synthesizing neurons and functionally active cholinergic receptors. This therefore makes them ideally suited to study the development and properties of brain mAChR subtypes.

Anatomical substrates of cholinergic-autonomic regulation in the rat

Acetylcholine (ACh) plays a major role in central autonomic regulation, including the control of arterial blood pressure (AP). Previously unknown neuroanatomic substrates of cholinergic-autonomic control were mapped in this study. Cholinergic perikarya and bouton-like varicosities were localized by an immunocytochemical method employing a monoclonal antiserum against choline acetyltransferase (ChAT), the enzyme synthesizing ACh. In the forebrain, bouton-like varicosities and/or perikarya were detected in the septum, bed nucleus of the stria terminalis, amygdala (in particular, autonomic projection areas AP1 and AP2 bordering the central subnucleus), hypothalamus (rostrolateral/innominata transitional area, perifornical, dorsal, incertal, caudolateral, posterior [PHN], subparafascicular, supramammillary and mammillary nuclei). Few or no punctate varicosities were labeled in the paraventricular (PVN) or supraoptic (SON) hypothalamic nuclei. In the mid- and hindbrain, immunoreactive cells and processes were present in the nucleus of Edinger-Westphal, periaqueductal gray, parabrachial complex (PBC), a periceruleal zone avoiding the locus ceruleus (LC), pontine micturition field, pontomedullary raphe, paramedian reticular formation and periventricular gray, A5 area, lateral tegmental field, nucleus tractus solitarii (NTS), nucleus commissuralis, nucleus reticularis rostroventrolateralis (RVL), and the ventral medullary surface (VMS). In the PBC, immunoreactive varicosities identified areas previously unexplored for cholinergic autonomic responsivity (superior, internal, dorsal, and central divisions of the lateral subnucleus, nucleus of Koelliker-Fuse and the medial subnucleus). In the NTS, previously undescribed ChAT-immunolabeled cells and processes were concentrated at intermediate and subpostremal levels and distributed viscerotopically in areas receiving primary cardiopulmonary afferents. In the nucleus RVL, cholinergic perikarya were in proximity to the VMS and medial to adrenergic cell bodies of the C1 area. Punctate varicosities of unknown origin and dendrites extending ventrally from the nucleus ambiguus overlapped the C1 area and immediate surround of RVL.

IN CONCLUSION

1) Cholinergic perikarya and putative terminal fields, overlap structures that are rich in cholinoreceptors and express autonomic, neuroendocrine, or behavioral responsivity to central cholinergic stimulation (PHN, NTS, RVL). The role of ACh in most immunolabeled areas, however, has yet to be determined. Overall, these data support the concept that cholinergic agents act at multiple sites in the CNS and with topographic specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Heterogeneity of muscarinic cholinergic receptors in the developing human fetal brain: regional distribution and characterization

The ontogeny of muscarinic cholinergic receptors has been studied in different regions of the human fetal brain. For a comparison, the same study has been carried out on newborn and premature brain. Regarding on the areas examined (frontal cortex, cerebellum, hippocampus, thalamus and basal ganglia) either an increase or a decrease of receptor density during gestation was observed. Thus, the ontogeny of the receptors follows a different pattern in areas which differ in function, cholinergic innervation and embryological origin. However, in all the regions the affinity of the binding site for the ligand [3H]quinuclidinyl benzilate [3H]QNB was very similar to that reported for muscarinic receptors from adult mammalian brain. Data obtained from agonist binding (acetylcholine and carbachol) revealed the presence of a high (H)- and a low-affinity binding site (L) from 10 weeks of gestation. The selective antagonist pirenzepine (PZ) also distinguished two different muscarinic receptor subtypes, which however had higher affinity than that seen in adult brain. In conclusion, during ontogeny, the muscarinic acetylcholine receptor shares some but not all of the pharmacological properties shown in the adult brain.

Muscarinic cholinergic receptors in human foetal brain: characterization and ontogeny of [3H]quinuclidinyl benzilate binding sites in frontal cortex

Twenty-two frontal cortices from normal human foetal brains of gestational ages ranging from 16 to 40 weeks and five postnatal brains ranging from 5 to 50 years were analysed for the ontogeny of muscarinic receptors using [3H]quinuclidinyl benzilate (QNB) as the ligand. QNB binding sites were shown to be stable up to 4 1/2 months of storage at -70 degrees C. QNB binding was characterized in frontal cortices of 28-week-old foetal brains as muscarinic receptors by the following criteria: (1) it was localised mainly in particulate fraction; (2) binding was saturable at a concentration of 1.5 nM; (3) the cholinergic antagonists atropine and scopolamine competed for the binding, with IC50 values of 1 and 0.8 nM, respectively. The agonists oxotremorine, carbachol, and pilocarpine gave IC50 values of 1, 15 and 18 microM, respectively. Nicotinic receptor ligands and noncholinergic drugs could not compete for the binding. Bimolecular association and dissociation rate constants for the reversible binding are 6.23 X 10(8) M-1 X min-1 and 2.0 X 10(-2) X min-1, respectively. The equilibrium dissociation constant is 33 pM. The KD obtained by saturation binding data is 103 pM. Ontogeny of muscarinic receptors showed three distinct phases: In phase I, they appear between 16 and 18 weeks [average concentration 109 fmol/mg protein of total particulate fraction (TPF)] and slowly increase up to 20 weeks (average concentration 147 fmol/mg protein TPF). Phase II is a lag period between 20 and 24 weeks at which time receptor concentration does not change perceptibly (average concentration (67 fmol/mg protein TPF).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute stress on catecholamine content in the hypothalamic nuclei of Japanese quail

Concentration of noradrenaline, adrenaline and dopamine in eight hypothalamic nuclei or areas (nucleus hypothalamicus medialis anterior, n. periventricularis magnocellularis, n. hypothalamicus lateralis anterior, n. hypothalamicus medialis posterior, n. hypothalamicus lateralis posterior, eminentia medialis, n. tuberis, area hypothalamica posterior) have been determined by a sensitive radioenzymatic micromethod in male Japanese quail restrained for 30 min. In control quail the highest concentrations were found in the a. hypothalamica posterior, n. periventricularis magnocellularis and n. hypothalamicus medialis anterior; the lowest was in the n. hypothalamicus medialis posterior. After restraint, noradrenaline concentrations decreased in the n. periventricularis magnocellularis and n. hypothalamicus medialis posterior. However, the concentration of adrenaline increased in the n. tuberis under the same conditions. In stressed animals the dopamine concentration was lower than in controls in the n. periventicularis and higher in the n. tuberis.

Catecholamines and their enzymes in discrete brain areas of rats after space flight on biosatellites Cosmos

The activity of the catecholaminergic system was measured in the hypothalamus of rats which had experienced an 18.5-19.5-day-long stay in the state of weightlessness during space flights on board Soviet biosatellites of the type Cosmos. In the first two experiments, Cosmos 782 and 936, the concentration of norepinephrine and the activities of synthesizing enzymes tyrosine hydroxylase and dopamine-beta-hydroxylase and of the degrading enzyme monoamine oxidase were measured in the total hypothalamus. None of the given parameters was changed after space flight. In the light of the changes of these parameters recorded after exposure to acute stress on Earth, this finding indicates that long-term state of weightlessness does not represent an intensive stressogenic stimulus for the system studied. In the space experiment Cosmos 1129, the concentration of norepinephrine, epinephrine, and dopamine was studied in isolated nuclei of the hypothalamus of rats within 6-10 hr following return from space. Norepinephrine was found to be significantly reduced in the arcuate nucleus, median eminence and periventricular nucleus, epinephrine in the median eminence, periventricular and suprachiasmatic nuclei, whereas dopamine was not significantly changed after space flight. The decreased catecholamine levels found in some hypothalamic nuclei of rats which had undergone space flight indicate that no chronic intensive stressor could have acted during the flight, otherwise the catecholamine concentration would have been increased in the nuclei. The decreased levels must have been induced by the effect of a stressogenic factor acting for a short time only, and that either during the landing maneuver or immediately after landing. Thus long-term exposure of the organism to the state of weightlessness does not represent a stressogenic stimulus for the catecholaminergic system in the hypothalamus, which is one of the regulators of the activation of neuroendocrine reactions under stress.

The inhibiting effect of atropine on growth hormone release during exercise

The effects of atropine upon changes in the circulating levels of growth hormone (GH), cortisol, lactate, glucose, and free fatty acids (FFA) were studied during exercise using both constant and progressively increasing work loads. At low work loads, atropine had no effect upon the changes in either cortisol or lactate levels, but the normal exercise-induced rise in GH was abolished or markedly reduced. At higher work loads, especially when prolonged, the usual rises in cortisol and lactate were enhanced by atropine, but the rise in GH was diminished and delayed. In no circumstances were the changes in FFA or glucose significantly affected by atropine. We regard the effect of atropine upon changes in cortisol and lactate responses as secondary to its cardiovascular effect, but suggest that the inhibition of Gh release may be evidence of a cholinergic mechanism in the control of Gh release during exercise.

Activation of latent Graves' disease in children. Review of possible psychosomatic mechanisms

In some children, psychological events have appeared to be important in the triggering of Graves' disease. This report examines the case histories of three children in whom the appearance of symptomatology of Graves' disease was associated with depression following the death of a loved one. An analysis of neuroendocrine and immunologie pathways suggests that depression, set off by bereavement, causes low levels of norepinephrine in the brain. The latter in turn may mediate an increase in ACTH and cortisol, leading to reductions in immune surveillance and resultant production of thyroid-stimulating immunoglobulins, hence the development of Graves' disease.

Effects of estrogen and progesterone on plasma gonadotropins and on catecholamine levels and turnover in discrete brain regions of ovariectomized rats

Estradiol benzoate (EB) was administered, either alone or followed 48 h later by progesterone to ovariectomized rats. Plasma gonadotropins (FSH and LH) and steady state levels of norepinephrine (NE) and dopamine (DA) in 17 individual brain nuclei were assayed. In addition, catecholamines were measured after administration of the synthesis inhibitor alpha-methyltyrosine (alpha-MT) in order to assess hormonal influences on turnover. Treatment with EB, which lowered plasma FSH and LH, reduced the depletion of NE produced by alpha-MT in the lateral septum, interstitial nucleus of the stria terminalis, and central gray catecholamine area, and reduced the depletion of DA in the nucleus of the tractus diagonalis. EB enhanced NE depletion in the periventricular and anterior hypothalamic nuclei, and raised steady state levels of NE in the medial amygdaloid nucleus. These effects were reversed by subsequent treatment with progesterone, which stimulated FSH and LH release. EB plus progesterone enhanced the alpha-MT-induced depletion of NE over that observed with EB alone in the arcuate nucleus, and similarly enhanced DA depletion in the interstitial nucleus of the stria terminalis. EB plus progesterone prevented the depletion of NE by alpha-MT in the paraventricular and ventromedial nuclei, and also lowered resting NE levels in the paraventricular nucleus. The results suggest that catecholamine neurons in several discrete brain regions participate in the stimulatory and inhibitory feedback effects of ovarian hormones on gonadotropin secretion, and perhaps also on the hormonal induction of sexual receptivity.

Ultrastructural analysis of the action of reserpine on the brain neuroendocrine system of the wax moth, Galleria mellonella L., Lepidoptera

This study concerns the influence of reserpine on the fine structure of peptidergic neurosecretory cells in the pars intercerebralis of Galleria mellonella, and of neurons containing smaller dense-cored vesicles (presumed to be aminergic) localized in the same area of the brain. The drug, administered in doses of 125 microgram and 250 microgram per g of insect body weight, reduces both the amount and the electron opacity of the dense-cored vesicles with a diameter of 60--80 nm in the neuronal perikarya as well as their terminals. Simultaneously, this treatment evokes an abnormal accumulation of secretory granules within the perikarya of peptidergic neurosecretory cells belonging to three types. This accumulation of secretory material is followed by some changes in the fine structure of these cells. One (fourth) type of neurosecretory cells seems to be insensitive to reserpine action. Participation of the aminergic system in the regulation of the secretory activity of some populations of peptidergic neurosecretory neurons of the insect brain is postulated.

Changes in catecholamine content in discrete brain nuclei during the estrous cycle of the rat

Norepinephrine (NE) and dopomine (DA) concentrations were measured in discrete brain nuclei in female rats at different stages of the 4-day estrous cycle. In the medial preoptic and paraventricular nuclei, NE levels were reduced on the days of proestrus and estrus as compared to metestrus-diestrus. NE levels sharply increased between estrus and metestrus in the lateral septal nucleus but did not vary significantly at other times. In the mesencephalic central gray catecholamine area, NE levels were elevated on metestrus as compared to all other days of the cycle. DA concentrations also varied in certain nuclei during the estrous cycle. In the lateral septum, DA levels were highest during diestrus, and in the nucleus of the tractus diagonalis, DA levels were highest on metestrus. The DA concentration of the caudate nucleus decreased between proestrus and estrus and remained low through metestrus. DA in the medial preoptic nucleus showed a similar pattern of change as did NE. In the median eminence DA levels increased significantly from proestrus afternoon to estrus, but did not vary on the other days. It is concluded that cyclic activity of catecholamines in a few discrete areas of the brain may be related to the fluctuations of the gonadotropins and ovarian hormones to influence ovulation and mating behavior.

Drugs affecting dopamine neurons and yawning behavior

Drugs stimulating the dopamine (DA) neurons in different ways (apomorphine, piribedil, amphetamine, nomifensine, L-DOPA) given in low doses (not producing behavioral excitation) induced yawning in rats. Blockade of DA receptors with neuroleptics counteracted DA-agonists induced yawning which may indicate a dopaminergic component of this behavior.

Neurochemical aspects of the ontogenesis of cholinergic neurons in the rat brain

Ontogenic development of central cholinergic neurons in rat brain was examined by measuring the activity of choline acetyltransferase (CAT), concentration of acetylcholine (ACh) after focused microwave irradiation, the activity of the high affinity uptake process for choline and the apparent muscarinic receptor as quantified by specific binding of [3H]3-quinuclidinyl benzilate (QNB). For whole brain, the specific activity of CAT increases from 1 to 8% of adult between 15 days gestation and 7 days postpartum and then increases linearly to 83% by 4 weeks postpartum. The concentration of ACh is 22% of adult at 15 days gestation, rises to 29% by birth and attains adult levels by 4 weeks postpartum. The developmental rise in specific binding of [3H]QNB is intermediate between CAT and ACh with 10% of adult concentration of receptor at birth and a linear increase to 90% by 4 weeks postpartum. The development of the uptake of [3H]choline parallels that of CAT. In all regions of the neonatal rat brain, the relative level (% adult) of ACh is higher than [3H]QNB binding, which is higher than CAT. The neonatal medulla-pons has higher levels of [3H]QNB binding and activity of CAT (% adult) and develops more rapidly than the parietal cortex and corpus striatum; the hypothalamus and midbrain-thalamus exhibit intermediate rates of development.

Monoamine oxidase localization in the ependyma and infundibular recess in the catfish Clarias batrachus and its probable significance

The presence of monoamine oxidase (MAO) in the cerebrospinal fluid (CSF) and MAO positive tracts bridging the CSF and the subependyma strongly suggest the involvement of CSF in the neuroendocrine control of hypophysial function.

Hypothalamic releasing factors: physiological evidence for a regulatory action on central neurons and pathways for their distribution in brain

Recent observations based on single cell recordings obtained in various areas of the brain indicate that TRH, LH-RH and somatostatin have potent effects on the activity of central neurons. There is also electrophysiological evidence for the existence of a system of hypothalamic tuberoinfundibular neurons with widespread extrahypothalamic connections. These connections may indicate possible pathways for the observed widespread distribution of these peptides in the brain. These findings, coupled with behavioral studies and subcellular localization data support the postulate that hypothalamic peptides may have an important role inthe modulation of central neuronal activity.

The uptake of 35S by hypothalamic and neurohypophysial proteins following intraventricular injection of L-cysteine-35S-hydrochloride in rats dehydrated and reserpinized

In rats dehydrated for 48 h and injected intraventricularly with L-cysteine-35S-hydrochloride, the specific activity of TCA-precipitable material, both in the hypothalamus and neurohypophysis, was found to diminish under reserpine treatment.