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mise à jour du
4 septembre 2019
Behav Brain Res
2019
 Oxytocin induces penile erection and yawning
when injected into
the bed nucleus of the stria terminalis:
A microdialysis and immunohistochemical study
 
Bratzu J, Bharatiya R, Manca E, Cocco C, Argiolas A,
Melis MR, Sanna F.
Department of Biomedical Sciences, Section of Neuroscience and Clinical Pharmacology, University of Cagliari, Cagliari, Italy.

Chat-logomini

 
Tous les travaux de MR Melis & A Argiolas 
Tous les travaux de M Eguibar & G Holmgren
 
Abstract
Oxytocin (5, 20 and 100_ng) injected unilaterally into the bed nucleus of the stria terminalis (BNST) of male rats stereotaxically implanted with a microinjection cannula coupled to a microdialysis probe, induces penile erection and yawning that occur concomitantly with a dose-dependent increase in the extracellular concentration of glutamic acid, dopamine and its main metabolite 3,4-dihydroxyphenilacetic acid (DOPAC), and nitrites (NO2-) in the dialysate obtained from the BNST by intracerebral microdialysis.
 
The responses induced by oxytocin (100_ng) were all abolished by the oxytocin receptor antagonist d(CH2)5Tyr(Me)2-Orn8-vasotocin (1__g), and reduced by CNQX (1__g), a competitive antagonist of the AMPA receptors, both given into the BNST 25_min before oxytocin.
 
In contrast, (+) MK-801 (1__g), a non-competitive antagonist of NMDA receptors, and SCH 23390 (1__g), a selective dopamine D1 receptor antagonist, reduced penile erection and yawning, but not glutamic acid and dopamine increases in the BNST dialysate induced by oxytocin.
 
Immunohistochemistry revealed oxytocin-labelled neuronal structures in close proximity to tyrosine hydroxylase-labelled neurons or nitric oxide synthase-labelled cell bodies surrounded by intense vesicular glutamate transporter1-stained synapses in BNST sections where oxytocin injections induce the above responses. Together, these findings show that oxytocin injected into the BNST induces penile erection and yawning by activating not only the glutamatergic (and nitrergic) but also the dopaminergic neurotransmission, leading in turn to the activation of neural pathways mediating penile erection and yawning.
 
Résumé
L'ocytocine (5, 20 et 100 ng) injectée unilatéralement dans le noyau de la stria terminalis (BNST) de rats mâles implantés stéréotaxiquement avec une canule de microinjection couplée à une sonde de microdialyse induit une érection du pénis et des bâillements concomitants, parallèlement à l'augmentation de la concentration extracellulaire en acide glutamique, en dopamine et en son métabolite principal, l'acide 3,4-dihydroxyphénilacétique (DOPAC) et en nitrites (NO2-) dans le dialysat obtenu à partir du BNST par microdialyse intracérébrale et cela proportionnellement de façon doses dépendantes.
 
Les réponses induites par l'ocytocine (100ng) ont toutes été supprimées par l'antagoniste du récepteur de l'ocytocine d (CH2) 5Tyr (Me) 2-Orn8-vasotocine (1µg) et réduites par CNQX (1µg), un antagoniste compétitif de l'AMPA récepteurs, tous deux administrés dans le BNST 25 minutes avant l'ocytocine.
 
En revanche, le (+) MK-801 (1 _g), antagoniste non compétitif des récepteurs NMDA, et le SCH 23390 (1 _g), antagoniste sélectif des récepteurs D1 de la dopamine, réduisent l'érection du pénis et les bâillements, mais non l'augmentation de l'acide glutamique et de la dopamine dans le dialysat de BNST induite par l'ocytocine.
 
L'immunohistochimie a révélé des structures neuronales marquées à l'ocytocine proches des neurones marqués à la tyrosine hydroxylase ou à des corps cellulaires marqués à l'oxyde nitrique synthase entourés par des intenses vésicules du transporteur glutamate1 vésiculaire dans les sections de BNST où les injections d'oxytocine induisent les réponses ci-dessus.
Ensemble, ces résultats montrent que l'ocytocine injectée dans la BNST induit l'érection du pénis et les bâillements en activant non seulement la neurotransmission glutamatergique (et nitrergique) mais également dopaminergique, entraînant à son tour l'activation des voies neurales induisant l'érection du pénis et les bâillements.
 
bed nucleus
 
1. Introduction
The bed nucleus of the stria terminalis (BNST) is a limbic forebrain structure that includes many distinct nuclei broadly organized into an anterior-posterior sequence and that is also divided horizontally in a dorsal and ventral part by the anterior commissure [1&endash;4]. Extensive anatomical studies of its connectivity suggest that BNST is a relay center within neurocircuits coordinating the activity of autonomic, neuroendocrine, and somatic motor systems into fully organized physiological functions and behaviors through the action of numerous neurotransmitters and neuropeptides present in this structure, which include GABA, glutamic acid, noradrenaline, dopamine, serotonin, nitric oxide (NO), corticotropin-releasing factor (CRF) and oxytocin [5&endash;8].
 
Among functions and behaviors in which the BNST plays a role, are also erectile function and sexual behavior. Accordingly, different studies have shown that i) an increase in the expression of c-fos (a putative marker of neuronal activity) occurs in the BNST during sexual behavior [9&endash;11], ii) electrical stimulation of the BNST induces penile erection in unanaesthetized and, to a lesser extent, anesthetized rats [12], and iii) radiofrequency or chemical excitotoxic lesions produce a marked decrease in noncontact erections [13, 14], which are observed in sexually potent male rats exposed to an inaccessible receptive female [15&endash;17].
However, the above BNST lesions were found able to exert only minor effects on reflexive erections (induced by local stimulation of the penis) and in some aspects of copulatory behavior [13, 14, 18].
Recently oxytocin, which plays a main role in socio-sexual behaviors (see [19] and references therein), including erectile function and sexual behavior (see [20&endash;23]), was found able to induce penile erection and yawning when injected into the BNST of male rats, apparently by increasing glutamatergic neurotransmission, with dopamine and NO being involved in both behavioral responses at BNST sites yet to be identified [24]. Oxytocin induces penile erection and yawning also when injected in the paraventricular nucleus of the hypothalamus (PVN)(from which oxytocinergic neurons projecting to the BNST originate), the hippocampus [25&endash;29], the ventral tegmental area (VTA) [30, 31] and the posterior nucleus of the amygdala of male rats [27].
These oxytocin responses are mediated by the stimulation of oxytocin receptors, since both were abolished by the prior injection of d (CH2)5Tyr(Me)2-Orn8-vasotocin, a potent oxytocin receptor antagonist [32], into the above brain areas, as found in the BNST [24]. Interestingly, the above brain areas are all connected with the BNST. Accordingly, i) the BNST receives a dense glutamatergic innervation from the ventral hippocampus and the amygdala (see [33&endash;37]), ii) these glutamatergic synapses in the BNST are rich in dopaminergic receptors (mainly of the D2 type), which are activated by dopamine released from a neuronal projection originating in the VTA (see [35] and references therein) and iii), the BNST contains the cell bodies of glutamatergic neurons projecting back to the VTA, the hypothalamus and its nuclei (i.e., PVN), the medial preoptic area (MPOA), the ventral subiculum of the hippocampus and the amygdala (see [33&endash;38]), all areas well known to play a role in penile erection and yawning (see [24, 27&endash;31, 39&endash;42]).
This raises the possibility that the BNST participates in the complex central neural circuit, which includes all the above brain areas, earlier hypothesized to control both the motivational anticipatory and consummatory aspects of erectile function and sexual behavior and also yawning, at least in part (see [22&endash;24, 40]).
 
In order to provide further evidence supporting the above hypothesis, we studied first the effect of increasing doses of oxytocin injected into the BNST not only on penile erection and yawning but also on the extracellular concentrations of glutamic acid, dopamine and its main metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) and on the concentration of nitrites (NO2_) (an index of NO production) (see [31, 43, 44]), in the dialysate obtained from the BNST by means of intracerebral microdialysis. As oxytocin was found able to increase both extracellular dopamine and glutamic acid concentrations in the BNST dialysate, we studied then whether the changes in the extracellular concentration of the above neurotransmitters induced by oxytocin in the BNST dialysate were antagonized by d(CH2)5-Tyr(Me)2-Orn8-vasotocin, which blocks oxytocin receptors, by (+)MK-801 and CNQX, which block NMDA and AMPA receptors, respectively, and by SCH 23390, which blocks dopamine D1-receptors, all given into the BNST at a dose that antagonizes oxytocin-induced penile erection and yawning.
Finally, the relationship between oxytocin axons/fibers, dopamine, glutamic acid and NO was studied in parallel within the BNST sections where oxytocin injections induce penile erection and yawning, by using oxytocin, tyrosine hydroxylase (TH), NO synthase and vesicular glutamate transporter (V-GLUT1) immunohistochemistry (IHC).
 
In conclusion, the results of this study show that oxytocin injected into the BNST induces penile erection and yawning by acting on oxytocin receptors whose stimulation leads to the release of glutamic acid and dopamine in the BNST. While it is confirmed that glutamic acid released by oxytocin activates glutamatergic neurons containing neuronal NO synthase possibly projecting to brain areas involved in the control of these behavioral responses (see [23]), it is still unclear whether dopamine released by oxytocin activates the same neurons activated by glutamic acid or other neurons that control penile erection and yawning, mainly through the activation of dopamine D1 receptors.
Although further experiments are necessary to verify this possibility, these results provide further evidence for a role of the BNST in the complex circuitry controlling yawning and both the consummatory (penile erection and sexual performance) and the anticipatory phases of sexual behavior (sexual arousal and sexual motivation) through dopaminergic, glutamatergic and oxytocinergic pathways that reciprocally interconnect many of the brain areas recalled above (see [23])