Peter B. F. Bergqvist

Neocortical dialysate monoamines of rats after acute, subacute, and chronic liver shunt

Abstract: Intracerebral microdialysis was applied to monitor the neocortical extracellular levels of the aromatic amino acids phenylalanine, tyrosine, and tryptophan, the neurotransmitters dopamine (DA), noradrenaline (NA), and serotonin (5‐HT), and the metabolites 3,4‐dihydroxyphenylacetic acid (DOPAC) and 5‐hydroxyindole‐3‐acetic acid (5‐HIAA) in rats with various forms of experimental hepatic encephalopathy (HE). The extracellular aromatic amino acid levels were clearly increased in acute, subacute, and chronic HE. No changes compared with controls in the neocortical DA release could be detected in the three experimental HE rat models investigated. The NA release showed a significant increase only in the subacute HE group. These data suggest that HE may not be associated with any major reduction of neocortical DA or NA release as previously suggested. In acute and subacute HE, decreased extracellular DOPAC but elevated 5‐HIAA concentrations were seen. In chronic HE, elevations of both DOPAC and 5‐HIAA were observed. Neocortical 5‐HT release did not change in subacute and chronic HE, whereas it decreased in acute HE compared with control values. Significant increase in extracellular concentrations of 5‐HIAA and of the 5‐HIAA/5‐HT ratio in the present study are in agreement with previously reported increases in 5‐HT turnover in experimental HE. However, a substantially increased 5‐HT turnover in experimental HE does not appear to be related to an increase in neuronal neocortical 5‐HT release.

Reactivity of serotonin in whole blood: relationship with drug response in obsessive-compulsive disorder

BACKGROUND Obsessive-compulsive disorder responds almost only to potent serotonin reuptake inhibitors. Previous studies have suggested a relation between serotonergic function and clinical outcome in serotonin reuptake inhibitor treatment of obsessive-compulsive disorder. METHODS In a randomized, double-blind trial, comparing clomipramine, paroxetine, and a placebo in obsessive-compulsive disorder, serotonin levels in whole blood (WB-5-HT) were measured at baseline, after 1 week, and after 4 weeks of treatment and related to clinical outcome in 36 patients. RESULTS In patients treated with serotonin reuptake inhibitors there was a pronounced decrease of WB-5-HT, variable after 1 week and uniformly maximal after 4 weeks. The decrease of WB-5-HT after 1 week of serotonin reuptake inhibitor treatment correlated negatively with clinical outcome after 12 weeks (r = -.61, p =.0006); hence, patients with slower WB-5-HT reactivity eventually responded better to treatment. Baseline WB-5-HT, but not WB-5-HT reactivity, was related to season. Depression, autistic traits, and previous serotonin reuptake inhibitor treatment predicted nonresponse. CONCLUSIONS A fast decrease of WB-5-HT was associated with poor clinical outcome. This may be related to faster serotonin efflux from platelets, which has previously been linked to autism. Further studies are necessary to identify the underlying mechanism and discern whether serotonin reuptake inhibitor-induced WB-5-HT decrease is clinically useful.

Altered open-field behavior in experimental chronic hepatic encephalopathy after single venlafaxine and citalopram challenges.

Rationale: Latent or manifest chronic hepatic encephalopathy (HE) symptomatology often includes affective symptoms. It is therefore warranted to investigate the functional outcome of novel antidepressants when chronic HE prevails. Objective: Portacaval shunt (PCS) in rats is a widely used experimental model for chronic HE, a neuropsychiatric syndrome accompanying liver dysfunction. HE is believed to arise from a primary alteration in neurotransmission in the CNS. PCS has been reported to increase the metabolism of serotonin in the brain, and thus the central serotonin nerve of PCS rats may contain more serotonin than normal. However, the functional relevance of this serotonergic alteration in terms of affecting behavioral performance of PCS rats has been only rarely studied. Methods: Locomotor and rearing activities were recorded in PCS and sham-operated control rats. A single subcutaneous challenge with saline versus either the mixed serotonin/noradrenaline reuptake inhibitor venlafaxine (10 mg × kg–1) or the selective serotonin reuptake inhibitor citalopram (5 mg × kg−1) were performed. Results: The PCS-saline injected rats showed reduced locomotor and rearing activity compared with sham-saline treated rats. While no significant differences could be observed following the venlafaxine challenge to controls, the PCS-venlafaxine challenged rats displayed reduced behavioral activity as compared to PCS-saline treated rats. The PCS-citalopram rats, however, displayed increased activity compared with the PCS-saline rats while, again, no effect of the citalopram challenge to controls was found. Conclusions: The present study show altered but opposite behavior in PCS rats, when challenged with either venlafaxine or citalopram, compared to PCS control rats. These findings therefore support the contention that caution should be advocated when CNS monoamine active drugs are used in liver-impaired subjects until better delineation of the combined pharmacodynamic and pharmacokinetic outcome for each such drug in this condition has been made.

Brain extracellular quinolinic acid in chronic experimental hepatic encephalopathy as assessed by in vivo microdialysis: Acute effects of L-tryptophan

Increased brain quinolinic acid (QUIN) levels have been suggested to play a role in hepatic encephalopathy (HE). Previous brain tissue studies have been unable to confirm this hypothesis. Because QUIN is a potent NMDA-receptor agonist, it also is relevant to determine brain extracellular QUIN levels in HE. For this purpose, we assessed frontal neocortical extracellular QUIN levels by in vivo microdialysis in rats subjected to a portacaval shunt (PCS). We also evaluated the acute effects of altered L-tryptophan (L-TRP) availability on brain extracellular QUIN levels. The basal extracellular L-TRP levels were significantly (p <. 001) higher in the PCS rats than in the sham-operated controls. However, the QUIN level (p <. 05) and the QUIN to L-TRP ratio (p <. 01) were significantly lower in the PCS rats. Elevated L-TRP availability increased the QUIN levels to a similar degree in both sham and PCS rats. This study, in conjunction with our previous results, does thereby not support a major involvement of QUIN in the pathogenesis of HE.

Ammonium acetate challenge in experimental chronic hepatic encephalopathy induces a transient increase of brain 5-HT release in vivo

Ammonia has been shown to cause release of neurotransmitters such as serotonin (5-hydroxytryptamine; 5-HT) from synaptosomal preparations in vitro. In the present study, frontal neocortical extracellular levels of 5-HT and its major metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were determined in vivo by the use of microdialysis in portacaval shunted (PCS) rats, an experimental model of chronic hepatic encephalopathy (HE), prior to and after an acute coma-inducing administration of ammonium acetate (NH4Ac; 5.2 mmol/kg, i.p.). PCS rats displayed elevated (P < 0.01) 5-HIAA but unaltered 5-HT extracellular levels compared with controls, supporting the contention of an increased neocortical 5-HT metabolism but unaltered neuronal 5-HT output in chronic HE. However, a transient elevation of extracellular 5-HT levels was observed when PCS-NH4Ac rats were in coma. Increased brain ammonia may thus augment neuronal 5-HT release in chronic HE, which in turn could be a causative for precipitation of more severe stages of HE.

Potassium-Evoked Neuronal Release of Serotonin in Experimental Chronic Portal-Systemic Encephalopathy

Portal-systemic encephalopathy (PSE) is associated with an increased brain tissue turnover of serotonin (5-HT). Despite increased 5-HT metabolism, brain 5-HT release in rats with a portacaval shunt (PCS) seems to be unaltered. Although this may indicate that the overall 5-HT output is unaltered in PSE, it is also possible that the 5-HT release pattern might be altered in some way. In the present study, the potassium-evoked frontal neocortical release of 5-HT was studied in experimental chronic PSE. KCl (60 mM) produced marked increases in the 5-HT output compared with basal values both in PCS and sham rats. Simultaneously, the KCl challenge resulted in significant elevations in the 5-HT release of PCS compared with sham. In Ca2+-free medium, the difference between PCS and sham rats in the KCl-evoked release of 5-HT was abolished. In the presence of TTX (1 mM), both groups displayed increased extracellular 5-HT levels. Again, a difference with higher amplitude of the 5-HT release in PCS compared with sham was evident. It is concluded that in experimental chronic PSE an augmented neocortical 5-HT release compared with the normalin vivo situation is available. The possible mechanism(s) responsible for the difference in neocortical 5-HT output between PCS and sham-operated rats in response to the KCl-challenge is discussed.

Effect of citalopram on brain serotonin release in experimental hepatic encephalopathy: implications for thymoleptic drug safety in liver insufficiency.

In the present study, effects of citalopram (CIT) on brain 5-hydroxytryptamine (5-HT) release in experimental chronic hepatic encephalopathy (HE) were investigated. Neocortical administration of CIT (1.0 μM) increased the brain 5-HT output to a similar extent in portacaval shunted (PCS) rats and sham-operated controls, indicating that a previous described mismatch between increased 5-HT turnover and unchanged release in PCS rats is not explained by an accelerated brain 5-HT reuptake. Subsequent systemic administration of CIT (5 mg/kg subcutaneously) resulted in a more pronounced attenuation of the brain 5-HT release in PCS rats than in sham-operated controls, possibly indicating a higher susceptibility to indirect mid-brain 5-HT1A autoreceptor activation in experimental portal-systemic encephalopathy (PSE). A KCl (60 mM) challenge in the presence of locally administered CIT (1 μM) induced a more marked neocortical 5-HT response in PCS rats than in sham-operated controls, confirming previous results of a higher than normal amount of 5-HT available for depolarization-induced release in PCS rats. Although the pharmacodynamic parameters in this study was investigated for CIT, the likelihood of a parallel pharmacokinetic alteration existing for this drug in the PCS condition also was indicated. It is thus suggested that otherwise generally safe central nervous system 5-HT-active drugs may represent a potential hazard in patients with liver failure with or without PSE.

Neuropsychiatry Implications of Brain Tryptophan Perturbations Appearing in Hepatic Encephalopathy

The metabolic encephalopathies exhibit CNS-symptoms that rapidly may alter in location of brain region of engagement, indicating a continuous fluctuation of the level of which brain functions are disturbed. This is particularly obvious in chronic conditions, such as chronic or latent hepatic encephalopathy (HE), where the fluctuating level of consciousness may be a dangerous sudden developing symptom in a person otherwise appearing to have normal brain functions. If these individuals are occupied with e.g. driving vehicle in traffic or working in heavy industrial practice, such chronic portal-systemic encephalopathy (PSE) (Sherlock et al., 1954) may be a particular hazard to both themselves and others. Unfortunately, the pathogenesis of PSE is still unknown. Hence, the delineation of the pathogenesis for HE/PSE, and therapeutic modalities developing therefrom, is highly warrented. Numerous pathogenetic mechanisms and etiological factors for PSE have been suggested (Conn and Liebertahl, 1979).

Brain Quinolinic Acid in Chronic Experimental Hepatic Encephalopathy: Effects of an Exogenous Ammonium Acetate Challenge

Abstract: Elevated brain concentrations of the neurotoxin and NMDA receptor agonist quinolinic acid (QUIN) have been demonstrated in portacaval‐shunted (PCS) rats, a chronic hepatic encephalopathy (HE) model. Increased brain QUIN levels have also been shown in acute hyperammonemic rats. In the present study, the plasma and brain (neocortical) QUIN levels in chronic PCS rats were investigated. The study also included a single exogenous ammonium acetate (NH4Ac; 5.2 mmol/kg, i.p.) challenge to precipitate a reversible hepatic coma. Compared with sham‐operated controls, chronic PCS rats exhibited decreased rather than increased plasma and brain QUIN levels. The plasma‐to‐brain QUIN ratio was not found to be altered. The NH4Ac administration induced coma in all of the PCS rats 20–25 min after the challenge, and this coma was resolved within 60–75 min. No relevant temporal relationship between changes in brain QUIN levels and the neurological status in the PCS rats was observed. Therefore, our results do not support the contention that increased brain QUIN levels per se are involved in the pathogenesis of HE.

Acute effects of L-tryptophan on brain extracellular 5-HT and 5-HIAA levels in chronic experimental portal-systemic encephalopathy

Portal-systemic encephalopathy (PSE) is associated with increased brain turnover of serotonin (5-hydroxytryptamine; 5-HT). Despite this metabolic increase, neuronal release of 5-HT is unaltered in neocortex of portacaval shunted (PCS) rats. In the present study, frontal neocortical extracellular 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) levels were determined in PCS rats and sham-operated controls prior to, as well as, after acute challenge with L-tryptophan (L-TRP; a bolus dose of 280 mg/kg i.p. followed by 5 consecutive hourly doses of 50 mg/kg). Neither basal 5-HT nor 5-HIAA extracellular levels were significantly altered in PCS rats compared to controls. L-TRP administration resulted in unaltered extracellular 5-HT but elevated 5-HIAA levels in PCS and sham rats. These findings do not suggest that changes in brain neuronal 5-HT release play any major functional role in the pathogenesis of chronic PSE. The present data also emphasize the importance of distinguishing between brain 5-HT metabolism and brain 5-HT release.