Tiziana Melis

Oxytocin injected into the ventral tegmental area induces penile erection and increases extracellular dopamine in the nucleus accumbens and paraventricular nucleus of the hypothalamus of male rats.

The neuropeptide oxytocin (20–100 ng), induces penile erection when injected unilaterally into the caudal but not rostral mesencephalic ventral tegmental area (VTA) of male Sprague–Dawley rats. Such pro‐erectile effect started 30 min after treatment and was abolished by the prior injection of d(CH2)5Tyr(Me)2‐Orn8‐vasotocin (1 µg), an oxytocin receptor antagonist injected into the same caudal ventral tegmental area or of haloperidol (1 µg), a dopamine receptor antagonist, injected either into the nucleus accumbens shell (NAs) or into the paraventricular nucleus of the hypothalamus (PVN) ipsilateral to the injected ventral tegmental area. Penile erection was seen 15 min after the occurrence of, or concomitantly to, an increase in extracellular dopamine and its metabolite 3,4‐dihydroxyphenylacetic acid (DOPAC) in the dialysate obtained from the nucleus accumbens or the paraventricular nucleus, which was also abolished by d(CH2)5Tyr(Me)2‐Orn8‐vasotocin (1 µg), injected into the ventral tegmental area before oxytocin. In the caudal ventral tegmental area oxytocin‐containing axons/fibres (originating from the paraventricular nucleus) appeared to closely contact cell bodies of mesolimbic dopaminergic neurons retrogradely labelled with Fluorogold injected into the nucleus accumbens shell, suggesting that oxytocin effects are mediated by the activation of mesolimbic dopaminergic neurons, followed in turn by that of incerto‐hypothalamic dopaminergic neurons impinging on oxytocinergic neurons mediating penile erection. As the stimulation of paraventricular dopamine receptors not only induces penile erection, but also increases mesolimbic dopamine neurotransmission by activating oxytocinergic neurons, these results provide further support for the existence of a neural circuit in which dopamine and oxytocin influence both the consummatory and motivational/rewarding aspects of sexual behaviour.

The cannabinoid antagonist SR 141716A (Rimonabant) reduces the increase of extra-cellular dopamine release in the rat nucleus accumbens induced by a novel high palatable food

The assumption of a novel high palatable food (a candied cherry) occurs concomitantly with an increase in the concentration of extra-cellular dopamine and its main metabolite 3,4-dihydroxy-phenylacetic acid (DOPAC) by about 45% in the dialysate obtained by intracerebral microdialysis from the shell of the nucleus accumbens of male rats. Such increase was reversed by SR 141716A (Rimonabant), a selective cannabinoid CB1 receptor antagonist (0.3 mg/kg i.p. and 1 mg/kg i.p.), which also reduces the assumption of the high palatable food, when given 15 min before exposure to the candied cherry. SR 141716A effects on extracellular dopamine and DOPAC were prevented by WIN 55,212-2 (0.3 mg/kg i.p.) or HU 210 (0.1 mg/kg i.p.) given 15 min before SR 141716A. The present results show for the first time that SR 141716A reduces the increase in extra-cellular dopamine induced by a novel high palatable food in the nucleus accumbens. This confirms that cannabinoid CB1 receptors play a key role in food intake and/or appetite and suggests that the mesolimbic dopaminergic system is involved at least in part, in the effects of cannabinoid receptor agonists and antagonists on food intake and/or appetite.

Oxytocin induces penile erection when injected into the ventral tegmental area of male rats: role of nitric oxide and cyclic GMP

Oxytocin (80 ng) injected into the caudal mesencephalic ventral tegmental area (VTA) of male rats induces penile erection. Such an effect occurs together with an increase in nitric oxide (NO) production, as measured by the augmented concentration of NO2− and NO3− found in the dialysate obtained from this brain area by means of intracerebral microdialysis. Both effects are abolished by d(CH2)5Tyr(Me)2‐Orn8‐vasotocin (1 μg), an oxytocin receptor antagonist, by S‐methyl‐l‐thiocitrulline acetate (20 μg), a neuronal NO synthase inhibitor, or by ω‐conotoxin GVIA (50 ng), a N‐type Ca2+ channel blocker, all injected into the VTA 15 min before oxytocin. In contrast, 1H‐[1,2,4]oxadiazole[4,3‐a]quinoxalin‐1‐one (40 μg), a guanylate cyclase inhibitor, given into the VTA 15 min before oxytocin, abolishes penile erection, but not the increase in NO production, while haemoglobin (40 μg), a NO scavenger, injected immediately before oxytocin reduces the increase in NO production, but not penile erection. 8‐Bromo‐cyclic guanosine monophosphate (0.5–10 μg) microinjected into the VTA induces penile erection with an inverted U‐shaped dose–response curve; the maximal effective dose being 3 μg. Immunohistochemistry reveals that in the caudal VTA oxytocin‐containing axons/fibres (originating from the paraventricular nucleus of the hypothalamus) contact cell bodies of mesolimbic dopaminergic (tyrosine hydroxylase‐positive) neurons containing both NO synthase and guanylate cyclase. These results suggest that oxytocin injected into the VTA induces penile erection by activating NO synthase in the cell bodies of mesolimbic dopaminergic neurons. NO in turn activates guanylate cyclase present in these neurons, thereby increasing cyclic GMP concentration.

The cannabinoid CB1 receptor antagonist SR 141716A induces penile erection by increasing extra-cellular glutamic acid in the paraventricular nucleus of male rats

The cannabinoid CB1 receptor antagonist SR 141716A (0.1, 0.5 and 1 microg) induces penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats. The pro-erectile effect of SR 141716A occurs concomitantly with an increase in the concentration of glutamic acid in the paraventricular dialysate obtained by means of intra-cerebral microdialysis. Glutamic acid increase and penile erection did not occur when SR 141716A was given after tetrodotoxin, a voltage-dependent Na(+) channel blocker. Both penile erection and glutamic acid increases were also reduced by the cannabinoid CB1 receptor agonists WIN 55,212-2 or HU 210 given into the paraventricular nucleus before SR 141716A at doses unable to induce penile erection or to modify glutamic acid. In contrast, dizocilpine ((+)MK-801), an antagonist of excitatory amino acid receptors of the N-methyl-d-aspartic acid (NMDA) subtype, given into the paraventricular nucleus reduced penile erection, but was ineffective on the glutamic acid increase induced by the CB1 receptor antagonist. 6-Cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and (+/-)-2-amino-4-phosphono-butanoic acid (AP(4)), antagonists of the excitatory amino acid receptors of the AMPA subtype and of the metabotropic subtype, respectively, were ineffective on both penile erection and glutamic acid increase. SR 141716A responses were also reduced by muscimol, a GABA(A) receptor agonist, but not by baclofen, a GABA(B) receptor agonist, given into the paraventricular nucleus before SR 141716A. The present results show that SR 141716A induces penile erection by activating glutamic acid neurotransmission, which causes in turn the activation of paraventricular oxytocinergic neurons mediating penile erection.

The cannabinoid receptor antagonist SR-141716A induces penile erection in male rats: Involvement of paraventricular glutamic acid and nitric oxide

The cannabinoid CB1 receptor antagonist SR141716A (0.5, 1 and 2 microg) induces penile erection when injected into the paraventricular nucleus of male rats. The pro-erectile effect of SR 141716A occurs concomitantly with an increase in the concentration of NO2- and NO3- in the paraventricular dialysate obtained by means of intracerebral microdialysis. Both penile erection and NO2- increase induced by SR 141716A were reduced by the prior injection into the PVN of the cannabinoid CB1 agonists WIN 55,212-2 (5 microg) or HU 210 (5 microg), given into the paraventricular nucleus at doses unable to induce penile erection or to modify NO2- concentration. SR 141716A responses were also reduced by nitro-L-arginine methylester (20 microg), a non-selective NO synthase inhibitor, S-methyl-L-thiocitrulline (20 microg), a selective neuronal NO synthase inhibitor, the excitatory amino acid NMDA receptor antagonist dizocilpine ((+)MK 801) (1 microg), or the GABAA receptor agonist muscimol (0.2 microg) injected into the PVN 15 min before SR 141716A. In contrast, the inducible NO synthase inhibitor L-N(6)-(1-iminoethyl)lysine (20 microg), the GABAB receptor agonist baclofen (0.2 microg), the mixed dopamine receptor antagonist cis-flupenthixol (10 microg), and the oxytocin receptor antagonist d(CH2)5Tyr(Me)-Orn8 -vasotocin (1 microg), were ineffective. Despite its inability to reduce penile erection and NO2- increase induced by SR 141716A when injected into the PVN, d(CH2)5Tyr(Me)-Orn8 -vasotocin (1 microg) reduced almost completely penile erection without reducing paraventricular NO2- increase when injected into the lateral ventricles 15 min before SR 141716A. The present results show that SR 141716 induces penile erection by a mechanism (possibly activation of excitatory amino acid neurotransmission), which causes the activation of neuronal NO synthase in paraventricular oxytocinergic neurons mediating penile erection.

Pro-VGF-derived peptides induce penile erection in male rats: possible involvement of oxytocin

The effect of five peptides derived from the C‐terminal portion of rat pro‐VGF (VGF577‐617, VGF588‐617, VGF599‐617, VGF556‐576 and VGF588‐597) on penile erection was studied after injection into the hypothalamic paraventricular nucleus of male rats. VGF577‐617, VGF588‐617, VGF599‐617 and, to a lower extent, VGF588‐597 (0.1–2 µg) induced penile erection episodes in a dose‐dependent manner when injected into the paraventricular nucleus, while VGF556‐576 was ineffective. VGF588‐617‐induced penile erection was reduced by nitroω‐l‐arginine methylester (L‐NAME; 20 µg), by morphine (5 µg) and by muscimol (1 µg), but not by dizocilpine [(+)MK‐801; 1 µg], nor by cis‐flupenthixol (10 µg) given into the paraventricular nucleus 10 min before the VGF peptide. d(CH2)5Tyr(Me)‐Orn8‐vasotocin (1 µg) effectively reduced VGF588‐617‐induced penile erection when given into the lateral ventricles but not when injected into the paraventricular nucleus. Immunocytochemistry with antibodies specific for the C‐terminal nonapeptide sequence of pro‐VGF (VGF609‐617) revealed numerous neuronal fibres and terminals within the paraventricular nucleus, including its parvocellular components. Here, many immunostained neuronal terminals impinged on parvocellular oxytocinergic neurons. The present results show for the first time that certain pro‐VGF C‐terminus‐derived peptides promote penile erection when injected into the paraventricular nucleus and suggest that, within this nucleus, these or closely related pro‐VGF‐derived peptides may be released to influence sexual function by activating paraventricular oxytocinergic neurons mediating penile erection.

Effect of acute administration of Pistacia lentiscus L. essential oil on rat cerebral cortex following transient bilateral common carotid artery occlusion

BackgroundIschemia/reperfusion leads to inflammation and oxidative stress which damages membrane highly polyunsaturated fatty acids (HPUFAs) and eventually induces neuronal death. This study evaluates the effect of the administration of Pistacia lentiscus L. essential oil (E.O.), a mixture of terpenes and sesquiterpenes, on modifications of fatty acid profile and endocannabinoid (eCB) congener concentrations induced by transient bilateral common carotid artery occlusion (BCCAO) in the rat frontal cortex and plasma.MethodsAdult Wistar rats underwent BCCAO for 20 min followed by 30 min reperfusion (BCCAO/R). 6 hours before surgery, rats, randomly assigned to four groups, were gavaged either with E.O. (200 mg/0.45 ml of sunflower oil as vehicle) or with the vehicle alone.ResultsBCCAO/R triggered in frontal cortex a decrease of docosahexaenoic acid (DHA), the membrane highly polyunsaturated fatty acid most susceptible to oxidation. Pre-treatment with E.O. prevented this change and led further to decreased levels of the enzyme cyclooxygenase-2 (COX-2), as assessed by Western Blot. In plasma, only after BCCAO/R, E.O. administration increased both the ratio of DHA-to-its precursor, eicosapentaenoic acid (EPA), and levels of palmytoylethanolamide (PEA) and oleoylethanolamide (OEA).ConclusionsAcute treatment with E.O. before BCCAO/R elicits changes both in the frontal cortex, where the BCCAO/R-induced decrease of DHA is apparently prevented and COX-2 expression decreases, and in plasma, where PEA and OEA levels and DHA biosynthesis increase. It is suggested that the increase of PEA and OEA plasma levels may induce DHA biosynthesis via peroxisome proliferator-activated receptor (PPAR) alpha activation, protecting brain tissue from ischemia/reperfusion injury.

Pro-VGF-derived peptides induce penile erection in male rats: Involvement of paraventricular nitric oxide.

The effect of four peptides derived from the C-terminal portion of rat pro-VGF(556-617) (VGF(556-576), VGF(588-617), VGF(599-617), and VGF(588-597)), on penile erection and nitric oxide production in the paraventricular nucleus of the hypothalamus was studied in male rats after injecting into this hypothalamic nucleus. VGF(588-617) (0.5, 1 and 2 microg), VGF(599-617) (0.5, 2 and 5 microg) and, to a lower extent, VGF(588-597) (2 and 5 microg) induced penile erection episodes when injected into the paraventricular nucleus and concomitantly increased paraventricular nitric oxide production, while VGF(556-576) (5 microg) was ineffective. VGF(588-617)-induced nitric oxide production was reduced by N(G)-nitro-l-arginine methylester (l-NAME) (20 microg), a nitric oxide synthase inhibitor, which also reduced penile erection when injected in the paraventricular nucleus 15 min before the VGF peptide. The oxytocin receptor antagonist d(CH(2))(5)Tyr(Me)-Orn(8)-vasotocin (1 microg) also effectively reduced VGF(588-617)-induced penile erection when given into the lateral ventricles, but not when injected into the paraventricular nucleus. In both experimental conditions, d(CH(2))(5)Tyr(Me)-Orn(8)-vasotocin was unable to influence nitric oxide production in the paraventricular nucleus. The present results confirm that C-terminal pro-VGF-derived peptides induce penile erection when injected into the paraventricular nucleus and show that this effect is mediated by an increased nitric oxide production in this hypothalamic nucleus. Apparently, this causes the activation of paraventricular oxytocinergic neurons projecting to extra-hypothalamic brain areas and mediating penile erection, as found with dopamine agonists, oxytocin, excitatory amino acids and hexarelin analogue peptides.

TRPV1, CGRP and SP in scalp arteries of patients suffering from chronic migraine

Objective The transient receptor potential vanilloid type-1 receptor (TRPV1) and the neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) appear to be differently involved in migraine pain. A role of neurovascular scalp structures is also suggested by several data. We performed a quantitative study of TRPV1-like immunoreactive (LI), CGRP-LI and SP-LI innervation of scalp arterial samples from patients affected with chronic migraine (CM). Methods Short segments of scalp arteries were collected from 17 participants undergoing vascular surgery for treatment-resistant CM and from 6 controls who underwent neurosurgery for various indications. The immunoreactivity of the arterial innervation to TRPV1, CGRP, SP and to the pan-neuronal marker protein gene product 9.5 (PGP9.5) was examined. Immunoreactive nerve fibres in vessel cross-sections were quantified by computerised image analysis. Results A significant increase of TRPV1-LI nerve fibres was found in the arterial wall from CM compared with control patients (p<0.05), while no significant difference was found for CGRP and SP. Conclusions This study yields the first evidence for the existence of a TRPV1-LI innervation in human scalp arteries and provides the first quantitative assessment of the TRPV1-LI, CGRP-LI and SP-LI innervation of those vessels. The increase of TRPV1-LI periarterial nociceptive fibres of scalp arteries may represent, at least in some participants, a structural condition favouring CM (and possibly migraine), for example, by causing a higher sensitivity to algogenic agents.

Bortezomib Treatment Produces Nocifensive Behavior and Changes in the Expression of TRPV1, CGRP, and Substance P in the Rat DRG, Spinal Cord, and Sciatic Nerve

To investigate neurochemical changes associated with bortezomib-induced painful peripheral neuropathy (PN), we examined the effects of a single-dose intravenous administration of bortezomib and a well-established “chronic” schedule in a rat model of bortezomib-induced PN. The TRPV1 channel and sensory neuropeptides CGRP and substance P (SP) were studied in L4-L5 dorsal root ganglia (DRGs), spinal cord, and sciatic nerve. Behavioral measures, performed at the end of the chronic bortezomib treatment, confirmed a reduction of mechanical nociceptive threshold, whereas no difference occurred in thermal withdrawal latency. Western blot analysis showed a relative increase of TRPV1 in DRG and spinal cord after both acute and chronic bortezomib administration. Reverse transcriptase-polymerase chain reaction revealed a decrease of TRPV1 and CGRP mRNA relative levels after chronic treatment. Immunohistochemistry showed that in the DRGs, TRPV1-, CGRP-, and SP-immunoreactive neurons were mostly small- and medium-sized and the proportion of TRPV1- and CGRP-labeled neurons increased after treatment. A bortezomib-induced increase in density of TRPV1- and CGRP-immunoreactive innervation in the dorsal horn was also observed. Our findings show that bortezomib-treatment selectively affects subsets of DRG neurons likely involved in the processing of nociceptive stimuli and that neurochemical changes may contribute to development and persistence of pain in bortezomib-induced PN.