Follow-up of glycemic index before and after Ramadan fasting in type 2 diabetes patients under antidiabetic medications.

INTRODUCTION: Fasting has no adverse effects on healthy Muslims during Ramadan. However, it can induce serious complications for patients with type 2 diabetes (T2D). We aimed to follow the variation of some biochemical and clinical parameters in T2D patients before and after Ramadan; and to determine the incidence of fasting on hypoglycaemia and lactic acidosis associated with antidiabetic agents such as metformin. MATERIALS AND METHODS: This work is a prospective study conducted during Ramadan on 150 patients, recruited 2 to 3 weeks prior to the start. These patients were sensitized about the Ramadan lifestyle and diet as well as the medications to take. RESULTS: This study results indicated a significant decrease of glycated haemoglobin (from 8.06% to 7.42%) and a similar trend in the fasting plasma glucose (from 1.81 to 1.36g/L) before and after Ramadan respectively. The serum lipid profile showed significant variations during the study period, and antidiabetic medications was associated with low serum lactate. The plasma creatinine and uric acid were reduced but remained insignificant. DISCUSSION AND CONCLUSION: Based on data from our study, we concluded that a safe fasting with a lower risk hypoglycaemia, can be achieved in a well-controlled patients, under antidiabetic drugs. However, the diabetes medication was associated with a small increase in serum lactate levels that seemed to be dose-independent and not affected by treatment duration.

A potential role for the secretogranin II-derived peptide EM66 in the hypothalamic regulation of feeding behaviour.

EM66 is a conserved 66-amino acid peptide derived from secretogranin II (SgII), a member of the granin protein family. EM66 is widely distributed in secretory granules of endocrine and neuroendocrine cells, as well as in hypothalamic neurones. Although EM66 is abundant in the hypothalamus, its physiological function remains to be determined. The present study aimed to investigate a possible involvement of EM66 in the hypothalamic regulation of feeding behaviour. We show that i.c.v. administration of EM66 induces a drastic dose-dependent inhibition of food intake in mice deprived of food for 18 hours, which is associated with an increase of hypothalamic pro-opiomelanocortin (POMC) and melanocortin-3 receptor mRNA levels and c-Fos immunoreactivity in the POMC neurones of the arcuate nucleus. By contrast, i.c.v. injection of EM66 does not alter the hypothalamic expression of neuropeptide Y (NPY), or that of its Y1 and Y5 receptors. A 3-month high-fat diet (HFD) leads to an important decrease of POMC and SgII mRNA levels in the hypothalamus, whereas NPY gene expression is not affected. Finally, we show that a 48 hours of fasting in HFD mice decreases the expression of POMC and SgII mRNA, which is not observed in mice fed a standard chow. Taken together, the present findings support the view that EM66 is a novel anorexigenic neuropeptide regulating hypothalamic feeding behaviour, at least in part, by activating the POMC neurones of the arcuate nucleus.

Assessment of hemodialysis impact by Polysulfone membrane on brain plasticity using BOLD-fMRI.

PURPOSE: Hemodialysis (HD) is considered the most common alternative for overcoming renal failure. Studies have shown the involvement of HD membrane in the genesis of oxidative stress (OS) which has a direct impact on the brain tissue and is expected to be involved in brain plasticity and also reorganization of brain function control. The goal of this paper was to demonstrate the sensitivity of the blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) to characterize the OS before and after the HD session. PATIENTS, MATERIALS AND METHODS: Twelve male patient-volunteers following chronic HD for more than 6months were recruited among 86 HD-patients. All patients underwent identical assessment immediately before and after the full HD-session. This consisted of full biological assessment, including malondialdehyde (MDA) and total antioxidant activity (TAOA); and brain BOLD-fMRI using the motor paradigm in block-design. RESULTS: Functional BOLD-fMRI maps of motor area M1 were obtained from the HD patient before and after the hemodialysis session, important decrease in the intensity of brain activation of the motor area after HD, and important increase of the size of the volume of brain activation were observed, these changes are reflecting brain plasticity that is well correlated to OS levels. Individual patients MDA and TAOA before and after the hemodialysis sessions demonstrated a clear and systematic increase of the OS after HD (P-value=0.03). Correlation of BOLD-fMRI maximal signal intensity and volume of activated cortical brain area behaviors to MDA and total TAOA were close to 1. CONCLUSION: OS is systematically increased in HD-patients after the HD-process. Indeed, the BOLD-fMRI shows a remarkable sensitivity to brain plasticity studied cortical areas. Our results confirm the superiority of the BOLD-fMRI quantities compared to the biological method used for assessing the OS while not being specific, and reflect the increase in OS generated by the HD. BOLD-fMRI is expected to be a suitable tool for evaluating the plasticity process evolution in hemodialysis brain patients.

Distribution and seasonal variation in hypothalamic RF-amide peptides in a semi-desert rodent, the jerboa.

The jerboa is a semi-desert rodent, in which reproductive activity depends on the seasons, being sexually active in the spring-summer. The present study aimed to determine whether the expression of two RF-amide peptides recently described to regulate gonadotrophin-releasing hormone neurone activity, kisspeptin (Kp) and RF-amide-related peptide (RFRP)-3, displays seasonal variation in jerboa. Kp and/or RFRP-3 immunoreactivity was investigated in the hypothalamus of jerboas captured in the field of the Middle Atlas mountain (Morocco), either in the spring or autumn. As in other rodents, the Kp-immunoreactive (-IR) neurones were found in the anteroventro-periventricular and arcuate nuclei. RFRP-3 neurones were noted within the dorso/ventromedial hypothalamus. A marked sexual dimorphism in the expression of Kp (but not RFRP-3) was observed. The number of Kp-IR neurones was nine-fold higher, and the density of Kp-IR fibres and terminal-like elements in the median eminence was two-fold higher in females than in males. Furthermore, a significant seasonal variation in peptide expression was obtained with an increase in both Kp- and RFRP-3-IR cell bodies in sexually active male jerboas captured in the spring compared to sexually inactive autumn animals. In the arcuate nucleus, the level of Kp-IR cells and fibres was significant higher during the sexually active period in the spring than during the autumnal sexual quiescence. Similarly, the number of RFRP-3-IR neurones in the ventro/dorsomedial hypothalamus was approximately three-fold higher in sexually active jerboa captured in the spring compared to sexually inactive autumn animals. Altogether, the present study reports the distribution of Kp and RFRP-3 neurones in the hypothalamus of a desert species and reveals a seasonal difference in their expression that correlates with sexual activity. These findings suggest that these two RF-amide peptides may act in concert to synchronise the gonadotrophic activity of jerboas with the seasons.

Overwinter body temperature patterns in captive jerboas (Jaculus orientalis): influence of sex and group.

The jerboa (Jaculus orientalis) has been described in the past as a hibernator, but no reliable data exist on the daily and seasonal rhythmicity of body temperature (T (b)). In this study, T (b) patterns were determined in different groups of jerboas (isolated males and females, castrated males and grouped animals) maintained in captivity during autumn and winter, and submitted to natural variations of light and ambient temperature (T (a)). T (b) and T (a) variations were recorded with surgically implanted iButton temperature loggers at 30-min intervals for two consecutive years. About half (6/13) of isolated female jerboas hibernated with a T (b) < 33°C, with hibernation bouts interspersed with short periods of normothermy from November to February. Hibernation bout durations were longer (4-5 days) than those of normothermia phases (1-4 days). During hibernation, the minimum T (b) was low (T (b)min ~10.7°C). In contrast, one of the 12 isolated males showed short hibernation bouts of ca. 2 days late in the hibernation season, February-March. The males had T (b)min values of 15.1°C. In contrast to predictions, no castrated males hibernated. When jerboas were grouped, females and males exhibited concomitant torpor bouts. In males, the longest bouts were observed during the late hibernation season. These data suggest complex regulation of hibernation in jerboas.

Immunocytochemical detection of cholecystokinin and corticotrophin-releasing hormone neuropeptides in the hypothalamic paraventricular nucleus of the jerboa (Jaculus orientalis): modulation by immobilisation stress.

The hypothalamic response to an environmental stress implicates the corticotrophin-releasing hormone (CRH) neuroendocrine system of the hypothalamic parvicellular paraventricular nucleus (PVN) in addition to other neuropeptides coexpressed within CRH neurones and controlling the hypothalamo-pituitary-adrenal (HPA) axis activity as well. Such neuropeptides are vasopressin, neurotensin and cholecystokinin (CCK). It has previously been demonstrated that the majority of the CRH neuronal population coexpresses CCK after a peripheral stress in rats. In the present study, we explored such neuroendocrine plasticity in the jerboa in captivity as another animal model. In particular, we studied CCK and CRH expression within the hypothalamic PVN by immunocytochemistry in control versus acute immobilisation stress-submitted jerboas. The results show that CCK- and CRH-immunoreactive neuronal systems are located in the hypothalamic parvicellular PVN. The number of CCK-immunoreactive neurones within the PVN was significantly increased (138% increase) in stressed animals compared to controls. Similarly, the number of CRH-containing neurones was higher in stressed jerboas (128%) compared to controls. These results suggest that the neurogenic stress caused by immobilisation stimulates CCK as well as CRH expression in jerboas, which correlates well with previous data obtained in rats using other stressors. The data obtained also suggest that, in addition to CRH, CCK is another neuropeptide involved in the response to stress in jerboa, acting by controlling HPA axis activity. Because CCK is involved in the phenotypical plasticity of CRH-containing neurones in response to an environmental stress, we also explored their coexpression by double immunocytochemistry within the PVN and the median eminence (i.e. the site of CRH and CCK corelease in the rat) following jerboa immobilisation. The results show that CCK is not coexpressed within CRH neurones in either control or stressed jerboa, suggesting differences between jerboas and rats in the neuroendocrine regulatory mechanisms of the stress response involving CRH and CCK. The adaptative physiological mechanisms to environmental conditions might vary from one mammal species to another.

Vasopressin-containing neurons of the hypothalamic parvocellular paraventricular nucleus of the jerboa: plasticity related to immobilization stress.

The corticotropin-releasing hormone (CRH) neurons of the hypothalamic parvocellular paraventricular nucleus (PVN) have a high potential for phenotypical plasticity, allowing them to rapidly modify their neuroendocrine output, depending upon the type of stressors. Indeed, these neurons coexpress other neuropeptides, such as cholecystokinin (CCK), vasopressin (VP), and neurotensin, subserving an eventual complementary function to CRH in the regulation of the pituitary. Unlike in rats, our previous data showed that in jerboas, CCK is not coexpressed within CRH neurons in control as well as stressed animals. The present study explored an eventual VP participation in the phenotypic plasticity of CRH neurons in the jerboa. We analyzed the VP expression within the PVN by immunocytochemistry in male jerboas submitted to acute stress. Our results showed that, contrary to CRH and CCK, no significant change concerned the number of VP-immunoreactive neurons following a 30-min immobilization. The VP/CRH coexpression within PVN and median eminence was investigated by double immunocytochemistry. In control as well as stressed animals, the CRH-immunopositive neurons coexpressed VP within cell bodies and terminals. No significant difference in the number of VP/CRH double-labeled cells was found between both groups. However, such coexpression was quantitatively more important into the posterior PVN as compared with the anterior PVN. This suggests an eventual autocrine/paracrine or endocrine role for jerboa parvocellular VP which is not correlated with acute immobilization stress. VP-immunoreactive neurons also coexpressed CCK within PVN and median eminence of control and stressed jerboas. Such coexpression was more important into the anterior PVN as compared with the posterior PVN. These results showed the occurrence of at least two VP neuronal populations within the jerboa PVN. In addition, the VP expression did not depend upon acute immobilization stress. These data highlight differences in the neuroendocrine regulatory mechanisms of the stress response involving CRH/CCK or VP. They also underline that adaptative physiological mechanisms to stress might vary from one mammal species to another.

Biochemical characterisation and immunohistochemical localisation of the secretogranin II-derived peptide EM66 in the hypothalamus of the jerboa (Jaculus orientalis): modulation by food deprivation.

The neuroendocrine protein secretogranin II is the precursor of several neuropeptides, including secretoneurin and a novel 66-amino acid peptide, EM66, the sequence of which has been highly conserved across the vertebrae phylum. The presence of EM66 has been detected in the adult and fetal human adrenal gland, as well as the rat pituitary and adrenal glands. The present study aimed to explore a possible neuroendocrine role of EM66 by analysing its occurrence and distribution within the jerboa hypothalamus, and its potential implication in the control of feeding behaviour. High-performance liquid chromatography analysis of jerboa hypothalamic extracts combined with a radioimmunoassay of EM66 revealed a single peak of immunoreactive material exhibiting the same retention time as recombinant EM66. Immunocytochemical labelling showed that EM66-producing neurones are widely distributed in several hypothalamic regions, including the preoptic area, the suprachiasmatic, supraoptic, parvocellular paraventricular and arcuate nuclei, and the lateral hypothalamus. Food deprivation for 5 days induced a significant increase in the number of EM66-containing neurones within the arcuate nucleus (105% increase) and the parvocellular aspect of the paraventricular nucleus (115% increase), suggesting that EM66 could be involved in the control of feeding behaviour and/or the response to stress associated with fasting. Altogether, these data reveal the physiological plasticity of the EM66 system in the hypothalamus and implicate this novel peptide in the regulation of neuroendocrine functions.

Neuropeptide Y gene expression in the jerboa arcuate nucleus: modulation by food deprivation and relationship with hibernation.

Using in situ hybridization, the mRNA levels encoding neuropeptide Y (NPY) was investigated in the arcuate nucleus (ARC) of jerboas under three different states of energy balance. (1) normally feeding animals, (2) hibernating animals and finally (3) animals food deprived for 5 days. The hibernating and food deprived jerboas exhibited a significant increase (130%; P < 0.05 and 210%; P < 0.01, respectively) of mRNA expression as compared with controls. This elevated NPY mRNA expression supports the hypothesis that NPY may be implicated in abnormal feeding behaviour associated with eating deprivation. The stimulation of NPY gene expression in hibernating jerboas may be related to food deprivation and / or cold exposure since NPY is known to be an hypothermiant factor. It is thus envisaged that NPY within neurons of the ARC plays an integrative role in the control of energy metabolism.

Neuropeptide Y gene expression in the jerboa arcuate nucleus: modulation by food deprivation and relationship with hibernation.

Using in situ hybridization, the mRNA levels encoding neuropeptide Y (NPY) was investigated in the arcuate nucleus (ARC) of jerboas under three different states of energy balance. (1) normally feeding animals, (2) hibernating animals and finally (3) animals food deprived for 5 days. The hibernating and food deprived jerboas exhibited a significant increase (130%; P<0.05 and 210%; P<0.01, respectively) of mRNA expression as compared with controls. This elevated NPY mRNA expression supports the hypothesis that NPY may be implicated in abnormal feeding behaviour associated with eating deprivation. The stimulation of NPY gene expression in hibernating jerboas may be related to food deprivation and / or cold exposure since NPY is known to be a hypothermiant factor. It is thus envisaged that NPY within neurons of the ARC plays an integrative role in the control of energy metabolism.

Tachykinin-induced stimulation of neuropeptide Y gene expression in the rat arcuate nucleus.

Previous neurocytochemical data indicate the presence of synaptic contacts between tachykinergic terminals and neuropeptide Y (NPY) neurons in the arcuate nucleus of the rat suggesting that tachykinins may regulate NPY neuronal activity. To examine the functional signification of such regulation, the effect of intracerebroventricular administration of neurokinin A on NPY mRNA levels was studied using in situ hybridization. Repeated treatment with NKA (40 microg/day for 3 days) induced a 44% increase in NPPY mRNA expression compared with saline-injected control animals. These results demonstrate a positive effect of tachykinins on NPY gene expression and suggest either a direct or indirect control of arcuate NPY neurons by endogenous tachykinins.

The gonadotropin-releasing hormone neurosecretory system of the jerboa (Jaculus orientalis) and its seasonal variations.

The distribution of cells expressing gonadotropin-releasing hormone (GnRH) immunoreactivity was examined in the brain of adult jerboa during two distinct periods of the reproductive cycle. During spring-summer, when the jerboa is sexually active, a high density of cell bodies and fibres immunoreactive (IR) for GnRH was observed at the level of separation of the frontal lobes, in the medial septal nucleus (MS) and in the diagonal band of Broca (DBB), in the preoptic area (POA), in the organum vasculosum laminae terminalis (OVLT), in the retrochiasmatic area and hypothalamus. In autumn, when the jerboa is sexually inactive, GnRH-immunoreactivity was less intense than during spring-summer. In the POA, we noted a 55% decrease in the number of GnRH containing cells with no change in cell numbers in the MS-DBB. Furthermore, a lower density of GnRH immunopositive axon fibres is observed in all the previously mentioned structures and the immunoreaction intensity was very weak particularly within the median eminence and OVLT. Independently of the season, the GnRH immunoreactivity within neurones and fibres was similar in jerboas living in captivity and in jerboas living in their natural biotope. The effects of photoperiod on the density of POA-GnRH and arcuate nucleus beta-endorphin-containing cells were studied in jerboas maintained in long day [(LD) 16-h light, 8-h dark] and short day [(SD) 8-h light, 16-h dark] for 8 weeks. In the POA, the GnRH-IR cell number was not significantly altered by the photoperiod. Similarly, in the mediobasal hypothalamus, the number of beta-endorphin-IR neurones was not affected by such a parameter. Consequently, the GnRH seasonal variations cannot be correlated to changes in the photoperiod alone.

Developmental regulation of amyloid precursor protein at the neuromuscular junction in mouse skeletal muscle.

Amyloid precursor protein (APP), associated with Alzheimer's disease plaques, is known to be present in synapses of the brain and in the adult neuromuscular junction (NMJ). In the present study we examined protein and gene expression of APP during the development of mouse skeletal muscle. Using immunocytochemical approaches, we found that APP is first detected in myotube cytoplasm at embryonic day 16 and becomes progressively concentrated at the NMJ beginning at birth until adulthood. The colocalization between APP and acetylcholine receptors at the NMJ is only partial at birth, but becomes complete upon reaching adulthood. We observed that all APP isoforms, including the Kunitz-containing (protease inhibitor or KPI) forms, are up-regulated from birth to postnatal day 5 and then decreased to reach the low levels observed in the adult. This suggests the involvement of APP during the events which lead to a mature mono-innervated synapse. A 92-kDa band, characteristic of a cleaved APP695 isoform and not due to a new muscle-specific alternative spliced form, was observed from postnatal day 15 following completion of polyneuronal synapse elimination. Taken together, these data suggest that skeletal muscle APP may well play a role in the differentiation of skeletal muscle and in the formation and maturation of NMJs.

Differential effects of potassium channel blockers on the activity of the locomotor network in neonatal rat.

The role played by various K+ channels during locomotor activity was studied using an in vitro neonatal rat spinal cord preparation. Locomotor-like activity was elicited by bath-applying serotonin (5-HT) and N-methyl-d-l-aspartate (NMA). Four different K+ channel blockers were tested by adding them to the superfusing saline. Each of the K+ channel blockers elicited a characteristic motor pattern with specific temporal parameters. Cs+ and tetraethyl ammonium both decreased the motor period, but had opposite effects on the burst amplitude. Apamin increased both the motor period and the burst amplitude. A dose-response relationship was established for the K+ channel blockers. The blockers elicited an unstable rhythmic activity, contrary to what occurred under control conditions. We also found that due to the specific changes that they elicit, the various blockers produce selective changes in the burst ratio. These results suggest that the various K+ channels contribute differently to the generation of locomotor activity.

Neuronal activity in the mediobasal hypothalamus of hibernating jerboas (Jaculus orientalis).

The expression of the c-fos protein in the mediobasal hypothalamus (MBH) of the jerboa was examined both during hibernation and on arousal from hibernation. Expression was examined by c-fos immunohistochemistry using a polyclonal antibody raised against c-fos protein. In jerboas hibernating for 2 days, a significant number of c-fos immunopositive neurons were found in the median eminence and ventrolateral arcuate nucleus. Such an immunoreaction was not observed in non hibernating control animals. In animals hibernating for 10 days, c-fos immunoreactivity was localized in the lateral arcuate nucleus and ventromedial hypothalamus (VMH), the median eminence displayed no immunoreaction. After arousal from hibernation, the fos immunoexpression within the MBH was exclusively limited to the VMH nucleus. Thus, the present study shows different patterns of c-fos protein expression during hibernation, notably in the neuroendocrine systems of MBH. Consequently, the mediobasal hypothalamus seems to be implicated in a physiological regulation during hibernation. Moreover, the present data suggest that the c-fos gene is either implicated in mediating or is a consequence of physiological activation of specific neuron systems of the desert jerboa.

Tachykinin-induced changes in beta-endorphin gene expression in the rat arcuate nucleus.

Previous neuroanatomical data have indicated the presence of synaptic connections between tachykinergic terminals and proopiomelanocortin (POMC) neurons in the arcuate nucleus. Consequently, tachykinins may regulate the activity of POMC neurons. To evaluate the functional signification of this regulation, the effect of intracerebroventricular injections of neurokinin A (NKA) on POMC mRNA levels was studied by using in situ hybridization. Repeated injection of NKA (40 micrograms/animal per day during 3 days) induced a 48% increase in POMC mRNA expression as compared to NaCl injected control animals. In conclusion the results of this study show an excitatory effect of tachykinin on POMC neurons and suggest a direct and/or indirect excitatory control of POMC neuronal activity by endogenous tachykinins.

Visualization of an efferent projection route of the hypothalamic rat arcuate nucleus through the stria terminalis after labeling with carbocyanine dye (DiI) or proopiomelanocortin-immunohistochemistry.

The hypothalamic arcuate nucleus is known to be reciprocally connected to various limbic regions, such as the bed nucleus of the stria terminalis (BST). The route of this reciprocal connection, in particular with the BST, remains unknown. In order to visualize this pathway, we used the fluorescent tracer carbocyanine dye (DiI), that was inserted in the arcuate nucleus in fixed and dissected brains. This allowed us to label an arcuate-BST pathway DiI-labeled coursing through the stria terminalis. Immunohistochemistry for the arcuate-derived peptide adrenocortico-tropin (ACTH) revealed the presence of ACTH-immunoreactive axons in the stria terminalis. Together, these results provide arguments in favour of the existence of an arcuatofugal projection to the BST via the stria terminalis.

Tachykinergic synaptic inputs to neurons of the medial preoptic region which project to the rat arcuate nucleus.

Anatomical relationships between tachykinin-containing terminals and neurons of the medial preoptic area that innervate the arcuate nucleus were studied using silver staining of the retrograde tracer wheat germ agglutinin-apoperoxidase-gold (WGA-ApoHRP-gold) complex injected in the arcuate nucleus and pre-embedding immunocytochemistry for neurokinin A (NKA). At the histological level, retrogradely labeled cells not stained for NKA were seen to be surrounded by numerous NKA-immunopositive punctate profiles, in particular in the dorsal part of the medial preoptic area. At the ultrastructural level, retrogradely labeled cell bodies and dendritic profiles displayed highly electron-dense silver particle accumulations over the cytoplasm. The were seen in synaptic contact with one or several NKA-immunoreactive axon terminals containing small clear vesicles and dense-cored vesicles. Such synapses were either symmetrical or asymmetrical. The occurrence of synaptic contacts between tachykinin terminals and cells innervating the arcuate nucleus in the medial preoptic region provides a morphological support for a tachykinergic regulation of preoptic afferences to the arcuate nucleus. These results suggest that tachykinins are implicated in the indirect control of neuronal activity in the arcuate nucleus notably via the preoptic area. Consequently, tachykinins are potentially able to regulate indirectly numerous neuroendocrine events involving the tuberoinfundibular system.

Ultrastructural evidence for synaptic inputs of enkephalinergic nerve terminals to target neurons in the rat arcuate nucleus.

The morphological support of interactions between enkephalins and three systems--beta-endorphin (beta-END), tyrosine hydroxylase (TH), or neuropeptide Y (NPY)--well represented in the arcuate nucleus, was examined by using an electron microscopic double immunostaining combining two sensitive chromogens, diaminobenzidine (DAB) and tetramethylbenzidine (TMB). The first step consisted of visualizing Metenkephalinergic terminals with DAB reaction product, and the second one involved detecting the antigens TH, beta-END, and NPY in their respective neurons with TMB reaction product. Ultrastructural analysis revealed enkephalinergic terminals presynaptic to TH-immunopositive cells and dendrites, principally in the dorsal portion of the arcuate nucleus. Enkephalinergic nerve terminals also contacted synaptically ventrolaterally located beta-END-immunoreactive cells. In the ventromedial arcuate nucleus, few synaptic contacts were observed between enkephalinergic boutons and NPY neurons, which were principally in close apposition with glial processes. Enkephalin-immunoreactive synapses were more frequently seen on TH-immunopositive neurons. This TH neuronal group is known to correspond to the dopaminergic tuberoinfundibular neurons implicated in the control of reproductive functions. The pattern of distribution of the different synapses within the arcuate nucleus (TH dorsal, beta-END ventrolaterally; NPY ventromedially) suggests that enkephalins may play a role in the neuroendocrine regulation of gonadotropin and prolactin secretion. The results provide evidence that enkephalins, in the arcuate nucleus, exert a postsynaptic action on the beta-END cells in addition to the presynaptic regulation previously demonstrated in the mediobasal hypothalamus, related to beta-END release. Moreover, the arcuate nucleus is a site of intercellular relationships between enkephalins and dopamine and between enkephalins and other peptides such as NPY.

Synaptic inputs of tachykinin-containing nerve terminals to target tyrosine-hydroxylase-, beta-endorphin- and neuropeptide Y-producing neurons of the arcuate nucleus. Double pre-embedding immunocytochemical study in the rat.

Anatomical connections between tachykinin-containing terminals and three neuronal populations of the arcuate nucleus, chemically defined respectively by beta-endorphin (beta-END), tyrosine-hydroxylase or neuropeptide Y (NPY) and well represented in the arcuate nucleus, were studied using electron microscope double pre-embedding immunocytochemistry involving a combination of two sensitive chromogens: diaminobenzidine and tetramethylbenzidine. Following tachykinin immunodetection by diaminobenzidine, and tyrosine-hydroxylase, beta-END or NPY immunolabelling by tetramethylbenzidine, tachykinin-immunoreactive terminals were seen presynaptic to tyrosine-hydroxylase immunopositive cells and dendrites principally in the dorsomedial portion of the arcuate nucleus. Tachykinin-immunoreactive processes were also seen in synaptic contact with ventrolaterally located beta-END immunopositive perikarya. Tachykinin-immunopositive terminals also contacted NPY-immunoreactive cells and dendritic processes ventromedially. These results demonstrate the existence of a direct tachykinergic input onto three neuronal populations expected to play a role in the control of reproductive events. Consequently, they suggest, at least, an indirect action for tachykinins in the regulation of reproduction. Especially, tachykinins may indirectly control the luteinizing hormone-releasing hormone neurons via dopamine, beta-END and NPY cells and thereby influence luteinizing hormone secretion.