Auto-inhibition of adenylyl cyclase 9 (AC9) by an isoform-specific motif in the carboxyl-terminal region.

Trans-membrane adenylyl cyclase (tmAC) isoforms show markedly distinct regulatory properties that have not been fully explored. AC9 is highly expressed in vital organs such as the heart and the brain. Here, we report that the isoform-specific carboxyl-terminal domain (C2b) of AC9 inhibits the activation of the enzyme by Gs-coupled receptors (GsCR). In human embryonic kidney cells (HEK293) stably overexpressing AC9, cAMP production by AC9 induced upon the activation of endogenous ß-adrenergic and prostanoid GsCRs was barely discernible. Cells expressing AC9 lacking the C2b domain showed a markedly enhanced cAMP response to GsCR. Subsequent studies of the response of AC9 mutants to the activation of GsCR revealed that residues 1268-1276 in the C2b domain were critical for auto-inhibition. Two main species of AC9 of 130 K and ≥ 170 K apparent molecular weight were observed on immunoblots of rodent and human myocardial membranes with NH2-terminally directed anti-AC9 antibodies. The lower molecular weight AC9 band did not react with antibodies directed against the C2b domain. It was the predominant species of AC9 in rodent heart tissue and some of the human samples. There is a single gene for AC9 in vertebrates, moreover, amino acids 957-1353 of the COOH-terminus are encoded by a single exon with no apparent signs of mRNA splicing or editing making it highly unlikely that COOH-terminally truncated AC9 could arise through the processing or editing of mRNA. Thus, deductive reasoning leads to the suggestion that proteolytic cleavage of the C2b auto-inhibitory domain may govern the activation of AC9 by GsCR.

Cyclophilin D regulates lifespan and protein expression of aging markers in the brain of mice.

Cyclophilin D (cypD) modulates the properties of the permeability transition pore, a phenomenon implicated in the manifestation of many diseases including aging. Here, we examined the effects of partial or complete deletion of cypD on i) lifespan, ii) forebrain protein expression of 18 aging markers as well as regional expression of GFAP, mGluR1, and alpha-synuclein, and iii) behaviour of aged (>24month) male and female mice. Both male and female cypD heterozygous but not KO mice exhibited increased lifespans compared to WT littermates, associated with alterations in the protein expression of some markers, albeit without exhibiting changes in behaviour.

Thalamic neuropeptide mediating the effects of nursing on lactation and maternal motivation.

Nursing has important physiological and psychological consequences on mothers during the postpartum period. Tuberoinfundibular peptide of 39 residues (TIP39) may contribute to its effects on prolactin release and maternal motivation. Since TIP39-containing fibers and the receptor for TIP39, the parathyroid hormone 2 receptor (PTH2 receptor) are abundant in the arcuate nucleus and the medial preoptic area, we antagonized TIP39 action locally to reveal its actions. Mediobasal hypothalamic injection of a virus encoding an antagonist of the PTH2 receptor markedly decreased basal serum prolactin levels and the suckling-induced prolactin release. In contrast, injecting this virus into the preoptic area had no effect on prolactin levels, but did dampen maternal motivation, judged by reduced time in a pup-associated cage during a place preference test. In support of an effect of TIP39 on maternal motivation, we observed that TIP39 containing fibers and terminals had the same distribution within the preoptic area as neurons expressing Fos in response to suckling. Furthermore, TIP39 terminals closely apposed the plasma membrane of 82% of Fos-ir neurons. Retrograde tracer injected into the arcuate nucleus and the medial preoptic area labeled TIP39 neurons in the posterior intralaminar complex of the thalamus (PIL), indicating that these cells but not other groups of TIP39 neurons project to these hypothalamic regions. We also found that TIP39 mRNA levels in the PIL markedly increased around parturition and remained elevated throughout the lactation period, demonstrating the availability of the peptide in postpartum mothers. Furthermore, suckling, but not pup exposure without physical contact, increased Fos expression by PIL TIP39 neurons. These results indicate that suckling activates TIP39 neurons in the PIL that affect prolactin release and maternal motivation via projections to the arcuate nucleus and the preoptic area, respectively.

The CB1 receptor mediates the peripheral effects of ghrelin on AMPK activity but not on growth hormone release.

This study aimed to investigate whether the growth hormone release and metabolic effects of ghrelin on AMPK activity of peripheral tissues are mediated by cannabinoid receptor type 1 (CB1) and the central nervous system. CB1-knockout (KO) and/or wild-type mice were injected peripherally or intracerebroventricularly with ghrelin and CB1 antagonist rimonabant to study tissue AMPK activity and gene expression (transcription factors SREBP1c, transmembrane protein FAS, enzyme PEPCK, and protein HSL). Growth hormone levels were studied both in vivo and in vitro. Peripherally administered ghrelin in liver, heart, and adipose tissue AMPK activity cannot be observed in CB1-KO or CB1 antagonist-treated mice. Intracerebroventricular ghrelin treatment can influence peripheral AMPK activity. This effect is abolished in CB1-KO mice and by intracerebroventricular rimonabant treatment, suggesting that central CB1 receptors also participate in the signaling pathway that mediates the effects of ghrelin on peripheral tissues. Interestingly, in vivo or in vitro growth hormone release is intact in response to ghrelin in CB1-KO animals. Our data suggest that the metabolic effects of ghrelin on AMPK in peripheral tissues are abolished by the lack of functional CB1 receptor via direct peripheral effect and partially through the central nervous system, thus supporting the existence of a possible ghrelin-cannabinoid-CB1-AMPK pathway.

Effect of lesions of A5 or A7 noradrenergic cell group or surgical transection of brainstem catecholamine pathways on plasma catecholamine levels in rats injected subcutaneously by formalin.

The pain-induced activation of the sympatho-adrenal system is modulated by several brain areas, including brainstem catecholamine cell groups. In the present study, we evaluated the effect of bilateral lesions of the A5 or A7 cell groups or bilateral transections of brainstem catecholaminergic pathways on plasma catecholamine levels in Sprague-Dawley rats injected subcutaneously by formalin or saline. Plasma levels of both epinephrine and norepinephrine were slightly elevated after formalin injections within 15-30 min in rats with or without lesions of the A7 catecholamine cell group. However, saline but not formalin elicited a significant increase in plasma epinephrine level in both sham-operated and A5-lesioned groups. It is more likely, that formalin blocks the effect of the handling and the painful injection procedure. In rats with bilateral partial transections of the lower brainstem, formalin was more effective than saline in the elevation of plasma epinephrine and norepinephrine levels at several time-points through the investigation period. Our data indicate the involvement of A5 and A7 norepinephrine neurons and brainstem catecholaminergic pathways in the regulation of the activity of the sympatho-adrenal system during acute painful situations. Their modulatory effect, however, seems to be a very rapid one, short and moderate.

Role of salsolinol in the regulation of pituitary prolactin and peripheral dopamine release.

(R)-Salsolinol (SAL), a dopamine (DA)-related tetrahydroisoquinoline, has been found in extracts of the neuro-intermediate lobes (NIL) of pituitary glands and in the median eminence of the hypothalamus obtained from intact male rats and from ovariectomized and lactating female rats. Moreover, analysis of SAL concentrations in NIL revealed parallel increases with plasma prolactin (PRL) in lactating rats exposed to a brief (10 min) suckling stimulus after 4-h separation. SAL is sufficiently potent in vivo to account for the massive discharge of PRL that occurs after physiological stimuli (i.e. suckling). At the same time, it was without effect on the secretion of other pituitary hormones. It has been also shown that another isoquinoline derivative, 1-methyldihydroisoquinoline (1MeDIQ), which is a structural analogue of SAL, can dose-dependently inhibit the in-vivo PRL-releasing effect of SAL. Moreover, 1MeDIQ can inhibit the elevation of plasma PRL induced by physiological stimuli, for example suckling, or in different stressful situations also. 1MeDIQ also has a psycho-stimulant action, which is fairly similar to the effect of amphetamine, i.e. it induces an increase in plasma catecholamine concentrations. It is clear from these data that this newly discovered endogenous compound could be involved in regulation of pituitary PRL secretion. It has also been observed that SAL is present in peripheral, sympathetically innervated organs, for example the atrium, spleen, liver, ovaries, vas deferens, and salivary gland. Furthermore, SAL treatment of rats results in dose-dependent and time-dependent depletion of the DA content of the organs listed above without having any effect on the concentration of norepinephrine. More importantly, this effect of SAL can be completely prevented by amphetamine and by 1MeDIQ pretreatment. It is clear there is a mutual interaction between SAL, 1MeDIQ, and amphetamine or alcohol, not only on PRL release; their interaction with catecholamine "synthesis/metabolism" of sympathetic nerve terminals is also obvious.

Tuberoinfundibular peptide of 39 residues is activated during lactation and participates in the suckling-induced prolactin release in rat.

Tuberoinfundibular peptide of 39 residues (TIP39) and the PTH-2 receptor (PTH2R) constitute a peptide-receptor neuromodulator system. Based on the abundance of TIP39 fibers and axonal terminals as well as PTH2R-containing neurons and their processes in the hypothalamic para- and periventricular and arcuate nuclei TIP39 has been suggested to play a role in neuroendocrine regulation. We showed previously that TIP39 expression decreased dramatically by adulthood. In the present study, using in situ hybridization histochemistry, real-time RT-PCR, and immunohistochemistry, we found that TIP39 mRNA and peptide expression levels are markedly elevated in the posterior intralaminar complex of the thalamus (PIL) of lactating dams, one of the three locations of TIP39-containing cell bodies in the brain. In addition, in mother rats, these TIP39 neurons showed Fos expression in response to pup exposure. Transection of TIP39 fibers originating in the PIL resulted in an ipsilateral disappearance of TIP39 immunoreactivity throughout the mediobasal hypothalamus of mother rats, suggesting that TIP39 fibers there arise from the PIL. To elucidate the function of TIP39 activation in dams, mothers separated from their pups for 4 h on postpartum d 9 received injection of a PTH2R antagonist into the lateral ventricle 5 min before returning the pups. Blood samples were taken seven times during the experimental period through jugular cannulae. The PTH2R antagonist administered in two different concentrations markedly inhibited suckling-induced elevation of plasma prolactin levels in a dose-dependent manner. These results suggest that TIP39 neurons in the PIL may regulate suckling-induced prolactin release in rat dams.

Nesfatin-1/NUCB2 may participate in the activation of the hypothalamic-pituitary-adrenal axis in rats.

Nesfatin-1 is an anorexigenic peptide originating from nucleobinding-2 (NUCB2) protein. Nesfatin-1/NUCB2-immunoreactive neurons are present in the hypothalamic paraventricular nucleus, the center of the stress-axis, and in the medullary A1 and A2 catecholamine cell groups. The A1 and A2 cell groups mediate viscerosensory stress information toward the hypothalamic paraventricular nucleus. They contain noradrenaline, but subsets of these neurons also express prolactin-releasing peptide acting synergistically with noradrenaline in the activation of the hypothalamic paraventricular nucleus during stress. We investigated the possible role of nesfatin-1/NUCB2 in the stress response. Intracerebro-ventricular administration of nesfatin-1 elevated both plasma adrenocorticotropin and corticosterone levels, while in vitro stimulation of the hypophysis was ineffective. Single, long-duration restraint stress activated (Fos positivity) many of the nesfatin-1/NUCB2-immunoreactive neurons in the parvocellular part of the hypothalamic paraventricular nucleus, evoked nesfatin-1/NUCB2 mRNA expression in the parvocellular part of the paraventricular nucleus and in the A1, but not in the A2 cell group. Nesfatin-1/NUCB2 was shown to co-localize in a high percentage of prolactin-releasing peptide producing neurons, in both medullary catecholamine cell groups further supporting its involvement in the stress response. Finally, bilateral adrenalectomy evoked an increasing nesfatin-1/NUCB2 mRNA expression, indicating that it is under the negative feedback of adrenal steroids. These data provide the first evidence for possible participation of nesfatin-1/NUCB2 in the stress-axis regulation, both at the level of the brainstem and in the hypothalamus.

Dephosphorylation/inactivation of tyrosine hydroxylase at the median eminence of the hypothalamus is required for suckling-induced prolactin and adrenocorticotrop hormone responses.

We have recently found that dopamine (DA) released from terminals of the hypothalamic neuroendocrine dopamine (NEDA) neurons plays a role not only in prolactin (PRL), but also in adrenocorticotrop hormone (ACTH) secretion, without having any influence on alpha-melanocyte-stimulating hormone (alpha-MSH) release in lactating dams. The aim of our present studies was to further investigate this DAerg regulation of ACTH using consecutively applied physiological stimulation (suckling) and pharmacological inhibition of the rate-limiting enzyme of DA synthesis (tyrosine hydroxylase, TH) by alpha-methyl-p-tyrosine (alpha-MpT) that acutely affect secretion of these pituitary hormones during lactation. Following 4h separation period, two experimental groups were formed. In the first group, lactating rats were assembled with their litters for 60 min prior to alpha-MpT. In the second group, the alpha-MpT was injected first and 60 min later suckling stimulus was applied. Plasma samples were taken in every 15 min during the 90 min experimental period. Concentrations of plasma PRL, ACTH and alpha-MSH were measured by specific RIAs. Both stimuli applied in the first sequence, significantly elevated plasma PRL and ACTH levels in separated lactating dams, without having any effect on alpha-MSH secretion. Suckling applied in the first sequence was able to block the alpha-MpT-induced elevation of ACTH secretion, while PRL response was also significantly attenuated. alpha-MpT pretreatment prevented both PRL and ACTH responses to suckling stimulus. Investigating the dephosphorylation/inactivation of TH in the arcuate nucleus-ME (TIDA) regions, no pTH-immunoreactive perikarya or terminals can be found in continuously suckled dams. In contrast, after 4h separation of the mothers from their litters, pTH-immunoreactivity can be clearly visualized in the external zone of ME. In alpha-MpT pretreated mothers following 4h separation no pTH positive terminals are visible. No changes in the TH immunostaining can be observed in any of these experimental groups. In conclusion, dephosphorylation/inactivation of TH (the rate-limiting enzyme of the DA biosynthesis) in NEDA neurons is required for suckling-induced PRL and ACTH responses.

Glutamate receptor antagonist infused into the hypothalamic suprachiasmatic nuclei interferes with the diurnal fluctuations in plasma prolactin and corticosterone levels and injected into the mesencephalic dorsal raphe nucleus attenuates the suckling stimulus-induced release of prolactin of the rat.

The aim of the present investigations was to examine the involvement of the rich glutamatergic innervation of the hypothalamic suprachiasmatic nucleus, a key structure in the control of circadian rhythms, in the regulation of the diurnal fluctuations in plasma prolactin and corticosterone, and to test the involvement of the glutamatergic innervation of the mesencephalic dorsal raphe nucleus in the prolactin response induced by the suckling stimulus. By means of a mini-pump a non-NMDA receptor antagonist (6-cyano-7- nitroquinoxaline-2,3-dione disodium, CNQX) was microinfused between the two suprachiasmatic nuclei for 3 days and on the third day blood samples were taken at different time points of the day. CNQX inhibited the afternoon rise in plasma prolactin and corticosterone. In lactating rats CNQX, similarly to the NMDA antagonist MK-801, microinjected into the dorsal raphe nucleus significantly attenuated the prolactin response to the suckling stimulus. The findings indicate that the glutamatergic innervation of the suprachiasmatic nuclei is involved in the diurnal fluctuations in plasma prolactin and corticosterone levels, and the glutamatergic innervation of the dorsal raphe nucleus has a prominent role in the mediation of the suckling stimulus to the hypothalamus.

Demonstration of autoantibody binding to muscarinic acetylcholine receptors in the salivary gland in primary Sjögren's syndrome.

A significant pathogenetic role of antimuscarinic acetylcholine receptor-3 (anti-m3AChR) autoantibodies in primary Sjögren's syndrome (pSS) has been suggested. However, the binding of these antibodies to the receptors in the target tissues has not yet been demonstrated. In this study, the binding characteristics of pSS sera and anti-m3AChR-monospecific sera affinity-purified from pSS patients to labial salivary gland samples from healthy subjects were studied with light- and electron microscopy. Furthermore, the ultrastructural localisation of in vivo deposited antibodies in pSS salivary glands was also investigated. Light microscopic immunohistochemistry revealed the binding of the anti-m3AChR-specific sera to the membrane of acinar cells. Similar reaction end-products were observed in the pSS salivary gland epithelial cell membranes. With electron microscopy, the autoantibody binding was observed to be localised to the junctions of epithelial cell membranes with nerve endings, both in normal and pSS glands. The results indicate that anti-m3AChR antibodies bind to the receptors in the salivary glands.

The response of plasma catecholamines in rats simultaneously exposed to immobilization and painful stimuli.

Immobilization represents a strong stressor inducing a profound increase in plasma epinephrine and norepinephrine levels. We have previously demonstrated that a subcutaneous injection of formalin (0.2 mL of 4% solution/100 g bw) attenuated the immobilization-induced elevation of plasma epinephrine levels in rats. In the present study, we investigated whether other painful and stressful stimuli, such as capsaicin, hydrochloric acid, mechanical pressure, heat, and cold, might also attenuate the increase of plasma epinephrine in rats exposed to acute immobilization stress. With the exception of formalin, all of the painful stimuli applied failed to attenuate the increase of plasma epinephrine levels in immobilized animals. Our data suggest that the attenuation of an immobilization-induced increase in plasma epinephrine levels is specific for subcutaneous formalin administration.

Stress-induced alterations in catecholamine enzymes gene expression in the hypothalamic dorsomedial nucleus are modulated by caudal brain and not hypothalamic paraventricular nucleus neurons.

The hypothalamic dorsomedial nucleus (DMN) represents an important coordinate center for regulation of autonomic and neuroendocrine systems, especially during stress response. The present study was focused on the gene expression of catecholamine-synthesizing enzymes and the protein levels of tyrosine hydroxylase in DMN, both in control and stressed rats. Moreover, pathways modulating the gene expression of tyrosine hydroxylase in DMN during immobilization (IMO) stress were also investigated. Gene expressions of all catecholamine-synthesizing enzymes were detected in DMN samples. While the levels of tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA were increased in IMO rats, aromatic L-amino acid decarboxylase and dopamine-beta-hydroxylase mRNA remained unchanged. Tyrosine hydroxylase protein levels were significantly elevated in the DMN only after repeated IMO stress. Postero-lateral deafferentations of the DMN, or transections of the ascending catecholaminergic pathways originating in the lower brainstem abolished the IMO-induced increase of tyrosine hydroxylase gene expression in the DMN. Nevertheless, postero-lateral deafferentations of the hypothalamic paraventricular nucleus (PVN), which separate the DMN from the PVN, had no effect on IMO-induced elevation of tyrosine hydroxylase mRNA in the DMN. The present data indicate that certain DMN neurons synthesize mRNA of catecholamine enzymes. The stress-induced increase of tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA in DMN neurons indicates the involvement of these catecholaminergic neurons in stress response. The gene expression of tyrosine hydroxylase in DMN is modulated by lower brainstem and/or spinal cord, but not by PVN afferents.

Prolactin response to formalin is related to the acute nociceptive response and it is attenuated by combined application of different stressors.

Subcutaneous injection of diluted formalin (0.2 ml of 4% solution/100 g BW) can influence the increase of plasma epinephrine levels in rats exposed to exteroceptive (handling, immobilization), as well as to interoceptive stressors (insulin-induced hypoglycemia), without having any effect on norepinephrine release. In the present studies, the effect of the above-mentioned stressors has been investigated on formalin-induced prolactin (PRL) and corticosterone secretion. Administrations of formalin via chronically implanted subcutaneous cannula into the hind limb without handling induce an immediate increase in both plasma PRL and corticosterone levels. While PRL concentration reaches its peak value within 5 min then returns to the basal level by the end of the 30th min, corticosterone level also starts to rise immediately after formalin administration reaching its highest concentration within 15-30 min, but it remains at this high level during the next 60 min, then it declines and returns to the pre-injection level. Application of formalin to animals exposed to different heterotypic stressors (like handling or insulin-induced hypoglycemia) produces an attenuated PRL response, while plasma corticosterone levels induced by the same nociceptive component remained unchanged. Combinations of formalin injection with immobilization also show an attenuated PRL response. The present data indicate that plasma PRL response to formalin is related to its acute nociceptive phase, and application of different stressors prior to formalin injection significantly attenuate plasma PRL levels, while it does not influence corticosterone responses.

Salsolinol and the peripheral sympathetic activity: the effects of hypophysectomy, adrenalectomy and adrenal medullectomy.

The endogenous isoquinoline salsolinol (SALS) is a recently identified prolactin (PRL) releasing factor, a selective and potent stimulator of PRL secretion both in vivo and in vitro. SALS decreased the peripheral tissue dopamine (DA) level dose dependently, consequently increased the NE/DA ratio, indicating reduced release of newly formed norepinephrine (NE) from sympathetic terminals. The aim of our study was to investigate the effect of adrenal medullectomy (MEDX), adrenalectomy (ADX) and hypophysectomy (HYPOX) on the action of SALS on the PRL secretion, and on the catecholamine concentration of the selected sympathetically innervated peripheral tissues (atrium, spleen, etc). The experiments were done in male rats of 200-300 g body weight kept in air conditioned room with regular lighting. We used high-pressure liquid chromatography with electrochemical detection (HPLC-EC) for measurement of NE and DA concentrations, and radioimmunoassay for prolactin measurement. In MEDX as well as in ADX rats, SALS (25 mg/kg i.p.) was able to reduce DA level and increase the NE/DA ratio. The changes of prolactin secretion (increase by SALS) were not affected either by ADX or MEDX. Therefore the presence of the adrenal gland is not required for the changes of prolactin secretion, nor for the reduction of peripheral sympathetic activity induced by SALS. Investigating the possible effect of pituitary hormones on the peripheral sympathetic system, the action of SALS has been tested in HYPOX rats. We have found that the effect of SALS on peripheral sympathetic terminals is not affected by HYPOX, consequently the role of pituitary hormones in the effect of SALS on the peripheral catecholamine metabolism may be excluded.

Effect of local (intracerebral and intracerebroventricular) administration of tyrosine hydroxylase inhibitor on the neuroendocrine dopaminergic neurons and prolactin release.

BACKGROUND AND PURPOSE: Hypothalamic dopamine (DA), the physiological regulator of pituitary prolactin (PRL) secretion, is synthesized in the neuroendocrine dopaminergic neurons that projects to the median eminence and the neurointermediate lobe of the pituitary gland. The rate-limiting step of DA biosynthesis is catalyzed by the phosphorylated, therefore activated, tyrosine hydroxylase (TH) that produces L-3,4-dihydroxy-phenylalanine from tyrosine. The aims of our present study were to investigate 1. the effect of local inhibition of the DA biosynthesis in the hypothalamic arcuate nucleus on PRL release, and to get 2. some information whether the phosphorylated TH is the target of enzyme inhibition or not. METHODS: A TH inhibitor, alpha-methyl-p-tyrosine was injected either intracerebro-ventricularly or into the arcuate nucleus of freely moving rats and plasma PRL concentration was measured. Immunohistochemistry, using antibodies raised against to native as well as phosphorylated TH were used to compare their distributions in the arcuate nucleus-median eminence region. RESULTS: Intracerebro-ventricular administration of alpha-methyl-p-tyrosine has no effect, unlike the intra-arcuatus injection of enzyme inhibitor resulted in a slight but significant elevation in plasma PRL. Parallel with this, the level of DA and DOPAC were reduced in the neurointermediate lobe while no change in norepinephrine concentration can be detected indicating a reduced biosynthesis of dopamine following TH inhibition. On the other hand, systematic application of the alpha-methyl-p-tyrosine that inhibits TH activity located in DA terminals of the median eminence and the neurointermediate lobe, resulted in the most significant elevation of PRL. CONCLUSION: Our results suggest that alpha-methyl-p-tyrosine administered close to the neuroendocrine dopaminergic neurons was able to inhibit only a small proportion of the TH. Moreover, it also indicate that the majority of the activated TH can be found in the axon terminals of dopaminergic neurons, therefore, the DA released into the pituitary portal circulation is synthesized at this site.

Non-NMDA glutamate receptor antagonist injected into the hypothalamic paraventricular nucleus inhibits the prolactin response to formalin stress of male rats.

The aim of the present investigations was to test the involvement of the glutamatergic innervation of the hypothalamic paraventricular nucleus in the prolactin response to stress. A non-NMDA (6-cyano-7-nitroquinoxaline-2,3-dione disodium, CNQX) or an NMDA glutamate receptor antagonist (dizocilpine hydrogen malate, MK-801) was injected bilaterally into the paraventricular nucleus of freely moving male rats and 15 min later the animals were exposed to formalin stress. Blood samples for prolactin and corticosterone were taken at different time points before and after administration of formalin. CNQX, when injected into the paraventricular nucleus, inhibited the formalin-induced rise in plasma prolactin and not significantly the increase in corticosterone. A similar effect was not observed if MK-801 was administered into the paraventricular nuclei or CNQX was injected outside the cell group. The findings indicate that the glutamatergic innervation of the paraventricular nucleus is involved in the mediation of the formalin-induced prolactin release.

Effect of lesion of a5 and a7 brainstem noradrenergic areas or transection of brainstem pathways on sympathoadrenal activity in rats during immobilization stress.

Both A5 and A7 brainstem noradrenergic cell groups innervate dorsal horns of the spinal cord. Moreover, A5 cell group directly innervates sympathetic preganglionic neurons. Thus, A5 and A7 noradrenergic neurons could modulate the sympathoadrenal system (SAS) activity. We investigated the role of A5 and A7 noradrenergic cell groups in regulation of the SAS activity under control and stressful conditions. We evaluated the effect of electrolytical lesions of A5 or A7 cell groups and also the effect of bilateral brainstem cuts interrupting brainstem pathways on tyrosine hydroxylase gene expression in A5 and A7 areas and on the SAS activity measured by plasma epinephrine and norepinephrine levels. We have found that immobilization stress increases activity of the A5 and A7 brainstem areas and also levels of the gene expression of tyrosine hydroxylase, the rate-limiting catecholamine biosynthetic enzyme. Immobilization of sham-operated and brainstem pathways transected or A5 or A7 lesioned animals induced a similar, highly significant increase in plasma epinephrine and norepinephrine levels in both sham-operated and A5 or A7 destroyed or transected groups. Our data suggest that both A5 and A7 noradrenergic cell groups are activated during immobilization stress. However, transection of brainstem pathways innervating A5 and A7 neurons or lesion of A5 or A7 cell groups is not sufficient enough for changes in immobilization stress-induced activation of the SAS. We suggest that neither A5 and A7 noradrenergic neurons nor the transected brainstem pathways represent structures crucial for an activation of the SAS during immobilization stress. We hypothesize that during regulation of the stress response, various areas and pathways are involved and the elimination just one of them might be compensated by the remained intact areas and pathways.

Non-NMDA glutamate receptor antagonist injected into the hypothalamic paraventricular nucleus blocks the suckling stimulus-induced release of prolactin.

The aim of the present investigations was to test the involvement of the glutamatergic innervation of the hypothalamic paraventricular nucleus in the prolactin response to the suckling stimulus. A non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-dione disodium (CNQX), or an NMDA receptor antagonist, dizocipine hydrogen malate (MK-801), was injected bilaterally into the hypothalamic paraventricular nucleus of lactating freely moving rats before the end of a 4-h separation of the dams from their pups. The litters were then returned. Blood samples for prolactin were taken at different time points. The effect of the non-NMDA receptor antagonist was also tested in animals receiving the drug bilaterally into the dorsomedial nucleus area or the arcuate nucleus. Bilateral injection of CNQX into the paraventricular nucleus blocked the elevation in plasma prolactin concentration induced by the suckling stimulus. In contrast, bilateral administration of the NMDA receptor antagonist MK-801 into the paraventricular nucleus or bilateral injection of CNQX into the dorsomedial nucleus area or the arcuate nucleus did not interfere with the prolactin response to the suckling stimulus. The findings indicate that the glutamatergic innervation of the paraventricular nucleus is involved in the mediation of the neural signal of the suckling stimulus inducing prolactin release.

Control of prolactin secretion by excitatory amino acids.

This article provides an overview of the increasing number of observations indicating that excitatory amino acids are involved in the control of prolactin secretion. The information available suggests that these amino acids exert a stimulatory action on hypophysial prolactin. Administration of a glutamate receptor agonist induces significant increase in prolactin release in rats, monkeys, and rams. In contrast, noncompetitive antagonists of N-methyl-D-aspartate receptors decrease plasma levels and attenuate the preovulatory surge of prolactin. It appears that the endogenous glutamatergic system participates not only in the regulation of basal secretion of prolactin, but also in the control of physiological prolactin responses induced by the suckling stimulus or by stress. Recent findings suggest that the glutamatergic innervation of the hypothalamic paraventricular nucleus is involved in the mediation of the neural signal of the suckling stimulus-induced prolactin release as well as in the mediation of the stress-induced release of prolactin.