Claudia Bregonzio

A glutamate-dopamine interaction in the persistent enhanced response to amphetamine in nucleus accumbens core but not shell following a single restraint stress.

The administration of psychostimulant drugs or stress can elicit a sensitized response to the stimulating and reinforcing properties of the drug. We previously demonstrated that a single restraint stress session enhanced d-amphetamine (d-AMPH)-induced locomotion the day after the stress session, which lasted up to 8 days. The present experiments were designed to identify the contribution of major dopamine (DA) brain areas in the short- and long-lasting enhancement of d-AMPH-induced locomotion following a single stress, and to test the involvement of N-methyl-D-aspartate (NMDA) receptors in that phenomena. To achieve our goal, 24 h and 8 days after a 2-h restraint stress session either with or without a NMDA receptor blockade, we measured locomotor activity and DA overflow in nucleus accumbens (NAcc) core and shell and caudate putamen (CPu) following a d-AMPH injection (0.5 mg/kg i.p.). The stimulant effect of d-AMPH on DA overflow was enhanced in all nuclei at 24 h after a single stress, while at 8 days the enhanced responsiveness was maintained only in the NAcc core. When the rats were administered with MK-801 (0.1 mg/kg i.p.) 30 min before restraint stress, the d-AMPH-induced enhancement on locomotor activity and DA neurotransmission was prevented in all studied brain areas at both times. These findings show that a glutamate–dopamine link is underlying the short- and long- term d-AMPH-induced enhancement on DA and locomotor activity following stress. The persistent glutamate-dependent DA enhancement in NAcc core highlights the relevance of this region in the long-term proactive effects of stress on vulnerability to drug abuse.

The AT1 angiotensin II receptor blockade attenuates the development of amphetamine-induced behavioral sensitization in a two-injection protocol

It has been shown that a single exposure to amphetamine is sufficient to induce long‐term behavioral, neurochemical, and neuroendocrine sensitization in rats. Dopaminergic neurotransmission in the nucleus accumbens and the caudate‐putamen plays a critical role in the addictive properties of drugs of abuse. Angiotensin (Ang) II receptors are found on the soma and terminals of mesolimbic dopaminergic neurons and it has been shown that Ang II acting through its AT1 receptors facilitates dopamine release. The hypothesis was tested that Ang II AT1 receptors are involved in the neuroadaptative changes induced by a single exposure to amphetamine and that such changes are related to the development of behavioral and neurochemical sensitization. For this purpose, the study examined the expression of amphetamine‐enhanced (0.5 mg kg−1 i.p.) locomotor activity in animals pretreated with candesartan, an AT1 blocker, (3 mg kg−1 p.o × 5 days), 3 weeks after an amphetamine injection (5 mg kg−1 i.p.). Dopaminergic hyperreactivity was tested by measuring the 3H‐DA release in vitro from caudate‐putamen and nucleus accumbens slices, induced by K+ stimulus. It was confirmed the behavioral sensitization in the two‐injection protocol and candesartan pretreatment attenuate this response. It was also found that AT1 blockade pretreatment did not affect the locomotor response to dopamine agonists. In respect to the neurochemical sensitization tested using ex vivo 3H‐DA release experiments it was found that AT1 receptor pretreatment blunted the enhanced response induced by K+ stimulus. The results support the idea that the development of neuroadaptive changes induced by amphetamine involves brain AT1 Ang II receptor activation. Synapse, 2011.

Dopaminergic Mechanisms Involved in Prolactin Release after Mifepristone and Naloxone Treatment during Late Pregnancy in the Rat

Background/Aims: During late pregnancy, the antiprogesterone mifepristone facilitates prolactin release. This effect is enhanced by administration of the opioid antagonist naloxone, suggesting an inhibitory-neuromodulatory role of the opioid system. Since hypothalamic dopamine (DA) is the main regulator of prolactin release, in this study we explored the role of DA on prolactin release induced by mifepristone and naloxone treatment. Methods/Results: Rats on day 19 of pregnancy were used. Naloxone treatment did not modify the 3,4-dihydroxyphenylacetic acid/DA (DOPAC/DA) ratio or serum prolactin concentration in control rats. After mifepristone treatment, DA activity diminished significantly without modifying serum prolactin levels. Naloxone administration to antiprogesterone-treated rats did not change the DOPAC/DA ratio but increased serum prolactin. Tyrosine hydroxylase (TH) expression in medial basal hypothalamus (MBH) protein extracts was lowered by pretreatment with mifepristone, with no additional effect of naloxone. While mifepristone decreased the intensity of TH immunoreactivity in the arcuate and periventricular nuclei and in fibers of the median eminence, naloxone treatment had no further effect. Conclusions: (1) A reduction of tuberoinfundibular dopaminergic (TIDA) neuron activity is suggested by the fall of the DOPAC/DA ratio and the low expression of MBH TH; (2) this reduction facilitates prolactin secretion by naloxone, indicating that progesterone stimulates DA neurons to maintain low serum prolactin; (3) naloxone action seems to depend on a previous decrease of DA tone induced by mifepristone, without involve a direct effect on neuronal DA activity, and (4) endogenous opioids may inhibit prolactin secretion through a non-dopaminergic neuronal system that regulates prolactin secretion in which as yet undetermined prolactin-releasing factors may participate.

Involvement of the brain renin-angiotensin system (RAS) in the neuroadaptive responses induced by amphetamine in a two-injection protocol.

A single or repeated exposure to psychostimulants induces long-lasting neuroadaptative changes. Different neurotransmitter systems are involved in these responses including the neuropeptide angiotensin II. Our study tested the hypothesis that the neuroadaptative changes induced by amphetamine produce alterations in brain RAS components that are involved in the expression of the locomotor sensitization to the psychostimulant drug. Wistar male rats, pretreated with amphetamine were used 7 or 21 days later to study AT1 receptors by immunohistochemistry and western blot and also angiotensinogen mRNA and protein in caudate putamen and nucleus accumbens. A second group of animals was used to explore the possible role of Ang II AT1 receptors in the expression of behavioral sensitization. In these animals treated in the same way, bearing intra-cerebral cannula, the locomotor activity was tested 21 days later, after an amphetamine challenge injection and the animals received an AT1 blocker, losartan, or saline 5min before the amphetamine challenge. An increase of AT1 receptor density induced by amphetamine was found in both studied areas and a decrease in angiotensinogen mRNA and protein only in CPu at 21 days after treatment; meanwhile, no changes were established in NAcc. Finally, the increased locomotor activity induced by amphetamine challenge was blunted by losartan administration in CPu. No differences were detected in the behavioral sensitization when the AT1 blocker was injected in NAcc. Our results support the hypothesis of a key role of brain RAS in the neuroadaptative changes induced by amphetamine.

Angiotensin II AT₁ receptors are involved in neuronal activation induced by amphetamine in a two-injection protocol.

It was already found that Ang II AT1 receptors are involved in the neuroadaptative changes induced by a single exposure to amphetamine, and such changes are related to the development of behavioral and neurochemical sensitization. The induction of the immediately early gene c-fos has been used to define brain activated areas by amphetamine. Our aim was to evaluate the participation of AT1 receptors in the neuronal activation induced by amphetamine sensitization. The study examined the c-fos expression in mesocorticolimbic areas induced by amphetamine challenge (0.5 mg/kg i.p) in animals pretreated with candesartan, a selective AT1 receptor blocker (3 mg/kg p.o × 5 days), and amphetamine (5 mg/kg i.p) 3 weeks before the challenge. Increased c-fos immunoreactivity was found in response to the amphetamine challenge in the dorsomedial caudate-putamen and nucleus accumbens, and both responses were blunted by the AT1 receptor blocker pretreatment. In the infralimbic prefrontal cortex, increased c-fos immunoreactivity was found in response to amphetamine and saline challenge, and both were prevented by the AT1 receptor blocker. No differences were found neither in ventral tegmental area nor prelimbic cortex between groups. Our results indicate an important role for brain Ang II in the behavioral and neuronal sensitization induced by amphetamine.

Opioid modulation of prolactin secretion induced by stress during late pregnancy. Role of ovarian steroids

BACKGROUND The opioid system modulates prolactin release during late pregnancy. Its role and the participation of ovarian hormones in this modulation are explored in ether stress-induced prolactin release. METHODS/RESULTS Estrous, 3-day and 19-day pregnant rats were used. We administered the antagonist mifepristone (Mp) and tamoxifen to evaluate progesterone and estradiol action in naloxone (NAL, opioid antagonist) or saline treated rats. Ether stress had no effect on serum prolactin levels in controls but increased prolactin release in NAL-treated rats. Prolactin response to stress in NAL-treated rats was blocked by l-DOPA administration. Mp treatment on day 18 of pregnancy increased prolactin levels after stress without alterations by NAL. Tamoxifen on days 14 and 15 of pregnancy completely blocked Mp and NAL effects on prolactin release at late pregnancy. In contrast, stress significantly increased prolactin levels in estrous rats and pretreatment with NAL prevented this. On day 3 of pregnancy, at 6.00 p.m., stress and NAL treatment inhibited prolactin levels in saline-treated rat. No effect of stress or NAL administration was detected on day 3 of pregnancy at 9.00 a.m. icv administration of specific opioids antagonist, B-Funaltrexamine but not Nor-Binaltorphimine or Naltrindole, caused a significant increase in stress-induced prolactin release. CONCLUSIONS Opioid system suppression of prolactin stress response during late pregnancy was observed only after progesterone withdrawal, involving a different opioid mechanism from its well-established stimulatory role. This mechanism acts through a mu opioid receptor and requires estrogen participation. The opioid system and progesterone may modulate stress-induced prolactin release, probably involving a putative prolactin-releasing factor.

A previous history of repeated amphetamine exposure modifies brain angiotensin II AT1 receptor functionality

UNLABELLED Previous results from our laboratory showed that angiotensin II AT1 receptors (AT1-R) are involved in the neuroadaptative changes induced by amphetamine. The aim of the present work was to study functional and neurochemical responses to angiotensin II (ANG II) mediated by AT1-R activation in animals previously exposed to amphetamine. For this purpose male Wistar rats (250-320 g) were treated with amphetamine (2.5mg/kg/day intraperitoneal) or saline for 5 days and implanted with intracerebroventricular (i.c.v.) cannulae. Seven days after the last amphetamine administration the animals received ANG II (400 pmol) i.c.v. One group was tested in a free choice paradigm for sodium (2% NaCl) and water intake and sacrificed for Fos immunoreactivity (Fos-IR) determinations. In a second group of rats, urine and plasma samples were collected for electrolytes and plasma renin activity determination and then they were sacrificed for Fos-IR determination in Oxytocinergic neurons (Fos-OT-IR). RESULTS Repeated amphetamine exposure (a) prevented the increase in sodium intake and Fos-IR cells in caudate-putamen and accumbens nucleus induced by ANG II i.c.v. (b) potentiated urinary sodium excretion and Fos-OT-IR in hypothalamus and (c) increased the inhibitory response in plasma renin activity, in response to ANG II i.c.v. Our results indicate a possible functional desensitisation of AT1-R in response to ANG II, induced by repeated amphetamine exposure. This functional AT1-R desensitisation allows to unmask the effects of ANG II i.c.v. mediated by oxytocin. We conclude that the long lasting changes in brain AT1-R functionality should be considered among the psychostimulant-induced neuroadaptations.

Neurovascular unit alteration in somatosensory cortex and enhancement of thermal nociception induced by amphetamine involves central AT1 receptor activation

The use of psychostimulants, such as amphetamine (Amph), is associated with inflammatory processes, involving glia and vasculature alterations. Brain Angiotensin II (Ang II), through AT1‐receptors (AT1‐R), modulates neurotransmission and plays a crucial role in inflammatory responses in brain vasculature and glia. Our aim for the present work was to evaluate the role of AT1‐R in long‐term alterations induced by repeated exposure to Amph. Astrocyte reactivity, neuronal survival and brain microvascular network were analysed at the somatosensory cortex. Thermal nociception was evaluated as a physiological outcome of this brain area. Male Wistar rats (250–320 g) were administered with AT1‐R antagonist Candesartan/vehicle (3 mg/kg p.o., days 1–5) and Amph/saline (2.5 mg/kg i.p., days 6–10). The four experimental groups were: Veh‐Sal, CV‐Sal, Veh‐Amph, CV‐Amph. On day 17, the animals were sacrificed and their brains were processed for Nissl staining and immunohistochemistry against glial fibrillary acidic protein (GFAP) and von Willebrand factor. In another group of animals, thermal nociception was evaluated using hot plate test, in the four experimental groups, on day 17. Data were analysed with two‐way anova followed by Bonferroni test. Our results indicate that Amph exposure induces an increase in: neuronal apoptosis, astrocyte reactivity and microvascular network, evaluated as an augmented occupied area by vessels, branching points and their tortuosity. Moreover, Amph exposure decreased the thermal nociception threshold. Pretreatment with the AT1‐R blocker prevented the described alterations induced by this psychostimulant. The decreased thermal nociception and the structural changes in somatosensory cortex could be considered as extended neuroadaptative responses to Amph, involving AT1‐R activation.

Neurovascular Cognitive Alterations: Implication of Brain Renin–Angiotensin System

The neurovascular unit which comprises the microenvironment within small blood vessels in the brain parenchyma is responsible for the maintenance of normal neuronal function by a continuous supply of nutrients. Inflammatory processes and loss of brain–blood-barrier (BBB) integrity can lead to vascular dysfunction and pathological interactions between microvasculature, neurons, and astrocytes. These events have been closely related to the development of brain disorders such as cognitive decline, supported by numerous studies using hypertension animal models. There is a large body of evidence showing the implication of circulating and local renin angiotensin system in cerebral microvasculature function. Angiotensin II, trough AT1 receptor activation, has been related to elevated reactive oxygen species production, endothelial dysfunction, elevated permeability, inflammatory events, and vascular structure alterations. The angiotensin receptor blockers, used in antihypertensive treatments, are an important pharmacologic tool with neuroprotective effects because they can modify vascular damage and improve cognitive alterations. The development of vascular diseases can be influenced and promoted by external factors such as stress and drug abuse. Stress is related to induction of structural changes in arteries and cytokine production leading to endothelial damage and inflammation. It is known that psychostimulants have cardiovascular stimulant effects that can promote cerebral vasculitis and intracranial hemorrhage by direct and indirect mechanisms on the vasculature. The brain renin–angiotensin system is becoming an interesting new therapeutic target for vascular and related cognitive disorders.

Mechanisms Involved in Memory Processes: Alterations Induced by Psychostimulants—Targeting the Central AT 1 Receptors

Learned experiences are indispensable for adaptation and survival of every living organism. The generation of a memory trace is an active physiological process which implies association and organization of the new impressions with already stored ones. Therefore, memory is explained as activity-dependent synaptic plasticity, involving electrophysiological, biochemical and morphological changes in functional synapse.