Hiroshi Kawahara

The locus coeruleus noradrenergic system in the rat brain studied by dual-probe microdialysis

A dual-probe microdialysis technique was applied to the locus coeruleus (LC) and prefrontal cortex (PFC) of the brain of conscious rats. One probe was implanted close to the LC and was used to apply receptor-specific compounds by retrograde microdialysis. The effects of the LC infusions were recorded by a sampling noradrenaline by a second probe that was implanted in the ipsilateral prefrontal cortex. Infusion of sodium channel blocker tetrodotoxin (1 microM; 90 min) into the LC decreased extracellular noradrenaline in the PFC to approximately 20% of control values. Infusion of alpha2-adrenoceptor agonist clonidine (100 microM, infused during 15 or 45 min) near to the LC, decreased extracellular noradrenaline in the PFC to 35 and 20% of controls, respectively. These results indicate that > 80% of the extracellular levels of noradrenaline in the PFC is derived from LC innervation, and confirms the importance of alpha2-autoreceptors on noradrenergic neurons in the LC. Infusion of the cholinergic receptor agonist, carbachol (100 microM, 45 min) near to the LC increased extracellular noradrenaline in the PFC to approximately 150% of controls. Infusions of the excitatory amino-acid agonists NMDA and kainate into the LC caused marked increases in extracellular noradrenaline in the PFC to 240 and 200% of controls, respectively. The experiments with clonidine, carbachol, NMDA and kainate were repeated in anesthetized rats. Clonidine and carbachol were similarly effective as in conscious animals but the effects of NMDA and kainate on extracellular noradrenaline in the PFC were clearly suppressed: 145 and 130% of controls, respectively. These results suggest that increased arousal or behavioural activation might have contributed to the increases in extracellular noradrenaline that was seen after infusion of the glutamate agonists. These results also provide evidence for localization of cholinergic-, NMDA-, non-NMDA-receptor on noradrenergic neurons in the LC. Finally it is concluded that dual-probe microdialysis is a useful method to further investigate the pharmacology of LC-noradrenergic neurons. Carbachol and clonidine are suitable tools for a rapid and reversible stimulation or inhibition, respectively, of noradrenergic LC neurons.

Comparison of effects of hypotension and handling stress on the release of noradrenaline and dopamine in the locus coeruleus and medial prefrontal cortex of the rat

Abstract The effects of two different types of stress (hypotension and handling) on the release of dopamine, noradrenaline and DOPAC in the locus coeruleus (LC) and medial prefrontal cortex (mPFC) was studied by means of the dual-probe microdialysis technique. One probe was implanted in the vicinity of the LC and a second probe was implanted in the mPFC. Both probes were used to record simultaneously noradrenaline, dopamine and DOPAC. Samples from the LC were collected in the presence of nomifensine, which was added to the perfusion fluid in a concentration of 50xa0µM. Hypotension (20xa0min) induced by intravenous administration of nitroprusside stimulated the release of noradrenaline in the LC and mPFC to about 190% and 150% of control values, respectively. Hypotension also strongly stimulated the release of dopamine in the mPFC (to 320% of control) and DOPAC in the LC (to 270% of control). The effect of hypotension on extracellular dopamine, noradrenaline and DOPAC was decreased by halothane anaesthesia, and was blocked by chloral hydrate anaesthesia. Handling stress (10xa0min) stimulated the release of noradrenaline in the LC and mPFC to 180% and 160% of control values, respectively. Handling stimulated the release of dopamine in the mPFC to about 160% of control. The effect of hypotension or handling stress was further evaluated in animals in which the LC was lesioned by an infusion of 6-OH-dopamine. Lesioning of the noradrenergic LC neurons did not the prevent the hypotension-related stimulation of dopamine release, but shortened the time course of the effect dramatically. Lesioning of the noradrenergic neurons had no effect on the stimulatory effect of handling on the release of dopamine in the mPFC.This study shows that mesocortical dopamine neurons, in contrast to noradrenaline neurons, respond much stronger to hemodynamic stress than to an emotional stress. During certain conditions like hypotension stress, but not during handling stress, the LC activity is able to modulate the release of dopamine from mesocortical neurons.

The noradrenaline-dopamine interaction in the rat medial prefrontal cortex studied by multi-probe microdialysis

Multi-probe microdialysis was used to investigate the interaction between the release of noradrenaline and dopamine in the medial prefrontal cortex. Retrograde microdialysis was used to stimulate or inhibit the activity of the locus coeruleus for a restricted period of time, and the response of extracellular noradrenaline and dopamine in the ipsilateral and contralateral medial prefrontal cortex was recorded with microdialysis probes. Infusion of clonidine into the locus coeruleus (100 microM for 45 min) suppressed noradrenaline release and slightly inhibited dopamine release in the ipsilateral medial prefrontal cortex. Application of carbachol to the locus coeruleus (100 microM for 45 min) stimulated both the noradrenaline and dopamine release in the ipsilateral medial prefrontal cortex. No changes were seen in the contralateral medial prefrontal cortex. In the ipsilateral nucleus accumbens, extracellular noradrenaline levels increased, but dopamine levels remained unchanged. Application to the locus coeruleus (during 10 min) of the glutamate receptor agonists N-methyl-D-aspartate (NMDA) (300 microM) or kainate (100 microM) strongly increased extracellular noradrenaline and dopamine levels in the ipsilateral medial prefrontal cortex. However, in the contralateral probe the release of dopamine (but not of noradrenaline) was also stimulated. Application of carbachol to the locus coeruleus was used as a model to further investigate the presumed noradrenaline-dopamine interaction. In a series of dual-probe experiments, alpha(1)-, alpha(2)-, and beta-adrenoceptor antagonists (prazosin, idazoxan, propranolol) or a reuptake-inhibitor (nomifensine) was administered during carbachol stimulation of the locus coeruleus. Prazosin and propranolol were administered systemically in a dose of 3 mg/kg, whereas idazoxan (10 microM) and nomifensine (100 microM) were infused into the medial prefrontal cortex. However, none of these pretreatments modified the effects of the control carbachol-infusions. The results did not identify a receptor-interaction or a common reuptake site that explained the presumed interaction between dopamine and noradrenaline in the medial prefrontal cortex. Therefore, the noradrenaline-dopamine interaction hypothesis could not be confirmed or refuted.

Long-term administration of citalopram reduces basal and stress-induced extracellular noradrenaline levels in rat brain

RationalePanic disorders are commonly treated with selective serotonin reuptake inhibitors (SSRIs). However, the effect of SSRIs on noradrenaline systems in the brain has not been fully elucidated at the present time.ObjectivesThe effects of long-term administration of citalopram, an SSRI, on basal as well as stress-induced extracellular noradrenaline levels in the basolateral nucleus of the amygdala (BLA) and the locus coeruleus (LC) were determined. In addition, the responsiveness of noradrenaline transporters and α2-adrenoceptors were determined after long-term administration of citalopram.Materials and methodsBrain microdialysis was used to assess the extracellular levels of noradrenaline in conscious rats. Desipramine and clonidine were used to functionally evaluate the noradrenaline transporter and α2-adrenoreceptor, respectively.ResultsIn rats treated daily for 14xa0days with citalopram (10xa0mg kg−1 day−1 s.c.), dialysate noradrenaline levels showed remarkable decreases in both the BLA and the LC to about 25 and 45% of controls, respectively. The stress-induced increase of noradrenaline was almost completely abolished in the BLA, but was relatively stable in the LC. The effect of local application of desipramine tended to be suppressed only in the LC. The effect of local application of clonidine was enhanced only in the BLA.ConclusionThe present results indicate that chronic administration of citalopram strongly decreases the extracellular levels of noradrenaline in the brain. The anti-panic effect of citalopram might be due to sensitization of the α2-adrenoceptors leading to suppression of the stress response through noradrenergic activity. This mechanism is specific for the BLA.

Food reward-sensitive interaction of ghrelin and opioid receptor pathways in mesolimbic dopamine system

Ghrelin is a stomach-derived orexigenic peptide. The goal of the study was to investigate the roles of mu and kappa opioid receptors in systemic ghrelin-mediated regulation of the mesolimbic dopamine system. To evaluate the interaction of systemic ghrelin with values of food reward, rats were exposed to food removal, regular food or palatable food after systemic ghrelin administration. Extracellular dopamine levels were quantified in the nucleus accumbens (NAc) and receptor-specific compounds were infused into the ventral tegmental area (VTA) using dual-probe microdialysis. Consumption of regular or palatable food without systemic ghrelin administration induced an increase in dopamine levels in the NAc via activation of mu opioid receptors in the VTA. Systemic ghrelin administration (3xa0nmol, i.v.) followed by no food induced a decrease in dopamine levels via activation of kappa opioid receptors in the VTA. Systemic ghrelin administration followed by consumption of regular food induced an increase in dopamine levels via preferential activation of mu opioid receptors, whereas systemic ghrelin administration followed by consumption of palatable food suppressed the increase in dopamine levels via preferential activation of kappa opioid receptors. Thus, natural food reward and systemic ghrelin activate mu and kappa opioid receptor pathways in the VTA, respectively, resulting in opposite influences on dopamine release in the NAc. Furthermore, systemic ghrelin induces switching of the dominant opioid receptor pathway for highly rewarding food from mu to kappa, resulting in suppression of the mesolimbic dopamine system. These novel findings might provide insights into the neural pathways involved in eating disorders.

Upregulation of the dorsal raphe nucleus-prefrontal cortex serotonin system by chronic treatment with escitalopram in hyposerotonergic Wistar-Kyoto rats

Wistar-Kyoto (WKY) rats are sensitive to chronic stressors and exhibit depression-like behavior. Dorsal raphe nucleus (DRN) serotonin (5-HT) neurons projecting to the prefrontal cortex (PFC) comprise the important neurocircuitry underlying the pathophysiology of depression. To evaluate the DRN-PFC 5-HT system in WKY rats, we examined the effects of escitalopram (ESCIT) on the extracellular 5-HT level in comparison with Wistar rats using dual-probe microdialysis. The basal levels of 5-HT in the DRN, but not in the PFC, in WKY rats was reduced as low as 30% of Wistar rats. Responses of 5-HT in the DRN and PFC to ESCIT administered systemically and locally were attenuated in WKY rats. Feedback inhibition of DRN 5-HT release induced by ESCIT into the PFC was also attenuated in WKY rats. Chronic ESCIT induced upregulation of the DRN-PFC 5-HT system in WKY rats, with increases in basal 5-HT in the DRN, responsiveness to ESCIT in the DRN and PFC, and feedback inhibition, whereas downregulation of these effects was induced in Wistar rats. Thus, the WKY rat is an animal model of depression with low activity of the DRN-PFC 5HT system. The finding that chronic ESCIT upregulates the 5-HT system in hyposerotonergic WKY rats may contribute to improved understanding of mechanisms of action of antidepressants, especially in depression with 5-HT deficiency.

The spontaneously hypertensive rat/Izm (SHR/Izm) shows attention deficit/hyperactivity disorder-like behaviors but without impulsive behavior: Therapeutic implications of low-dose methylphenidate

The spontaneously hypertensive rat (SHR) has been used as a genetic animal model of attention deficit/hyperactivity disorder (ADHD). SHR/Izm is derived from stroke-resistant SHR as SHR/NIH and SHR/NCrl but from 22nd to 23rd generation descendants of the SHR/NIH ancestor and therefore may show different behavioral phenotypes compared to other SHR sub-strains. In this study, ADHD-like behaviors in SHR/Izm were evaluated compared to Wistar rats. SHR/Izm showed high locomotor activity in the habituation phase in a novel environment, although locomotor activity in the initial exploratory phase was low. In a behavioral test for attention, spontaneous alternation behavior in the Y-maze test was impaired in SHR/Izm. However, impulsive behavior in the elevated-plus maze test, which is designed to detect anxiety-related behavior but also reflects impulsivity for novelty seeking, was comparable to Wistar rats. Hyperactivity and inattention, detected as ADHD-like behaviors in SHR/Izm, were ameliorated with methylphenidate at a low dose (0.05mg/kg, i.p.). Therefore, SHR/Izm represents a unique animal model of ADHD without anxiety-related impulsive behavior.

Hypotension‐induced dopamine release in prefrontal cortex is mediated by local glutamatergic projections at the level of nerve terminals

In a previous study it was shown that nitroprusside‐induced hypotension strongly enhances the release of dopamine (DA) in the prefrontal cortex (PFC). In the present study we have further investigated the mechanism involved in this effect. Glutamate receptor antagonists were infused into the ventral tegmental area (VTA) or PFC, while DA release was measured in the ipsilateral PFC and hypotension was applied by intravenous infusion of nitroprusside. Infusion into the VTA of neither a NMDA receptor antagonist (CPP), nor a non‐NMDA antagonist (DNQX) affected the hypotension‐induced increase of DA in the PFC. Intracortical infusion of CPP also failed to affect significantly, whereas local infusion of DNQX inhibited the hypotension‐enhanced release of DA dose‐dependently. The stimulation of DA release was relatively small in the VTA as well as in the nucleus accumbens when compared with the response in the PFC. It is concluded that DA released from mesocortical neurons can be modulated by two different mechanisms: first, by glutamate afferents to the VTA that modify the nerve‐impulse flow of DA neurons; and, second, by glutamate afferents to the PFC that act at the level of the DA nerve terminals. The behaviour context (arousal or stress versus hypotension) determines which type of interaction predominates.

Effects of intraoperative administration of carbohydrates during long-duration oral and maxillofacial surgery on the metabolism of carbohydrates, proteins, and lipids

PurposeInsulin resistance in patients undergoing invasive surgery impairs glucose and lipid metabolism and increases muscle protein catabolism, which may result in delayed recovery and prolonged hospital stay. We examined whether intraoperative administration of carbohydrates during long-duration oral and maxillofacial surgery under general anesthesia affects carbohydrate, proteins, and lipid metabolism and the length of hospital stay.MethodsWe studied 16 patients with normal liver, kidney, and endocrine functions, and ASA physical status I or II, but without diabetes. Patients were randomly assigned to receive 0.1xa0g/kg/h of (nu2009=u20098) or lactated Ringer’s solution (nu2009=u20098). Blood was collected before (T0) and 4xa0h after (T1) the start of surgery. We analyzed the plasma levels of glucose, ketone bodies, 3-methylhistidine (3-MH), and the length of hospital stay.ResultsAt T0, no statistically significant differences were observed in the levels of glucose, ketone bodies, and 3-MH between the groups. At T1, no statistically significant difference in glucose levels was found between the groups. However, ketone bodies were significantly lower, and the changes in 3-MH levels were significantly less pronounced in the glucose-treated group compared with controls. No significant differences were observed between the groups in terms of length of hospital stay.ConclusionsThe administration of low doses of glucose during surgery was safe, did not cause hyperglycemia or hypoglycemia, and inhibited lipid metabolism and protein catabolism. Additional experiments with larger cohorts will be necessary to investigate whether intraoperative management with glucose facilitates postoperative recovery of patients with oral cancer.

Long-term citalopram treatment alters the stress responses of the cortical dopamine and noradrenaline systems: the role of cortical 5-HT1A receptors

Background: Cortical dopamine and noradrenaline are involved in the stress response. Citalopram, a selective serotonin reuptake inhibitor, has direct and indirect effects on the serotonergic system. Furthermore, long-term treatment with citalopram affects the dopamine and noradrenaline systems, which could contribute to the therapeutic action of antidepressants. Methods: The effects of long-term treatment with citalopram on the responses of the dopamine and noradrenaline systems in the rat prefrontal cortex to acute handling stress were evaluated using in vivo microdialysis. Results: Acute handling stress increased dopamine and noradrenaline levels in the prefrontal cortex. The dopamine and noradrenaline responses were suppressed by local infusion of a 5-HT1A receptor agonist, 7-(Dipropylamino)-5,6,7,8-tetrahydronaphthalen-1-ol;hydrobromide, into the prefrontal cortex. The dopamine response was abolished by long-term treatment with citalopram, and the abolished dopamine response was reversed by local infusion of a 5-HT1A receptor antagonist, (Z)-but-2-enedioic acid;N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexanecarboxamide into the prefrontal cortex. On the other hand, long-term treatment with citalopram reduced the basal noradrenaline levels (approximately 40% of the controls), but not the basal dopamine levels. The noradrenaline response was maintained despite the low basal noradrenaline levels. Signaling from the 5-HT1A receptors and α2-adrenoceptors was not involved in the decrease in the basal noradrenaline levels but partially affected the noradrenaline response. Conclusions: Chronic citalopram treatment differentially suppresses the dopamine and noradrenaline systems in the prefrontal cortex, and the dopamine stress response was preferentially controlled by upregulating 5-HT1A receptor signaling. Our findings provide insight into how antidepressants modulate the dopamine and noradrenaline systems to overcome acute stress.