Changes in extracellular and rat brain tissue concentrations of D-beta-hydroxybutyrate after 1,3-butanediol treatment.

1,3-Butanediol (BD) treatment was previously shown to produce a dose-related increase of the plasma levels of D-beta-hydroxybutyrate (BHB) and to protect brain tissue against hypoxia and ischemia. The purpose of this study was to test whether BD-induced hyperketonemia was associated with changes in brain extracellular and tissue concentrations of BHB. Changes in extracellular levels of BHB were continuously monitored in anesthetized rats before and after intraperitoneal injection of BD (25 mmol/kg), using intracerebral microdialysis coupled to online analysis of BHB in the dialysate. Cortical tissue concentrations of BHB were determined in control and BD-treated rats (25 and 50 mmol/kg, i.p.) after freezing of the brain in situ. Butanediol produced a rapid increase in dialysate levels of BHB, with a linear relationship between dialysate and plasma BHB concentrations (r = 0.81, p < 0.001). In contrast, and although brain tissue levels of BHB were markedly increased after BD treatment, they were not related to the plasma concentration of BHB. Our results suggest that BHB produced from BD did not accumulate in brain and that BD protects against hypoxia or ischemia by increasing brain BHB availability.

Combined intracerebral microdialysis and electrophysiological recording: methodology and applications.

A microdialysis probe is described that can simultaneously monitor indices of electrical activity, ionic homeostasis and changes in the composition of the extracellular fluid at the same brain site in anaesthetised laboratory animals. The probe is no larger than its conventional counterpart and avoids tissue injury problems due to implantation of separate recording electrodes. Examples are given of its application to the study of changes following probe implantation, cerebral ischaemia and local high K(+)-induced depolarisation.

Changes in extracellular glutamate concentration produced in the rat striatum by repeated ischemia.

BACKGROUND AND PURPOSE: Evidence suggesting that ischemia-induced neuronal damage may be linked to an extracellular overflow of glutamate has accumulated, and previous studies have shown that repetitive ischemic insults may have a cumulative effect. The purpose of this study was to investigate changes in the extracellular glutamate concentration produced by repeated brief ischemic episodes of varied severity. METHODS: Four consecutive 3- or 5-minute periods of bilateral hemispheric ischemia were produced in rats, each ischemic period followed by 27 minutes of reperfusion. Extracellular glutamate in the striatum was monitored using microdialysis, and the electroencephalogram and extracellular direct current potential were recorded in the same tissue site to assess the severity of ischemia. RESULTS: The results suggest that the kinetics of the increase in the extracellular glutamate concentration produced by a brief ischemic episode are similar, irrespective of whether it is a single insult or part of a repeated sequence. In all cases, the extracellular glutamate concentration increased throughout ischemia and returned to its preischemic level early during reperfusion. The pattern of changes in the ischemia-induced glutamate overflow during repetitive insults varied with the severity of ischemia, in common with the pattern of changes in the direct current potential, supporting the concept that ionic changes associated with anoxic depolarization are a major determinant of ischemia-induced glutamate overflow. CONCLUSIONS: There may be no cumulative effect of brief repeated episodes of ischemia on the extracellular glutamate concentration, even though repeated 5-minute ischemic episodes apparently caused progressive deterioration of ionic homeostasis in some cases.

Evidence for postsynaptic mediation of the hypothermic effect of 5-HT1A receptor activation.

1. The 5-HT1A ligand BMY 7378 (8-[2[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]8-azaspirol [4,5]-decane-7,9-dione dihydrochloride, 0.032-2 mg kg-1, s.c.) caused hyperphagia, a response to the activation of presynaptic 5-HT1A receptors. 2. BMY 7378 (8 mg kg-1, s.c.) and the 5-HT1A agonist (8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), 0.10 and 0.25 mg kg-1 s.c.) also caused hypothermia. This was inhibited by (-)-pindolol (1-mg kg-1, i.p.) and not prevented by pretreatments with p-chlorophenylalanine which grossly depleted 5-hydroxytryptamine (5-HT) from terminal regions. The hypothermic effects are explicable by activation of postsynaptic 5-HT1A receptors. Infusion of BMY 7378 (8-64 micrograms) into the dorsal raphe was without convincing hypothermic effect. 3. BMY 7378 (8 mg kg-1, s.c.) inhibited another effect of activation of postsynaptic 5-HT1A receptors, i.e., the induction of components of the 5-HT syndrome by 8-OH-DPAT (0.5, 1.0 mg kg-1, s.c.) which suggests that BMY 7378 has antagonistic as well as agonistic effects at these sites. 4. Partial agonist properties of BMY 7378 at postsynaptic sites were also indicated by doses for hypothermia being much greater than those for hyperphagia i.e., ED50 (hypothermia) greater than 2 mg kg-1, ED50 (hyperphagia) = 0.010 mg kg-1. This contrasts with the similar ED50 values for both the hypothermic (ED50 = 0.08-0.10 mg kg-1) and hyperphagic (ED50 = 0.06-0.10 mg kg-1) effects of 8-OH-DPAT.5. The evidence obtained for mediation of the hypothermic response to 5-HTIA agonists by postsynaptic sites is relevant to the interpretation of the effects on it of antidepressant treatments and depressive illness.

Efflux of glutamate produced by short ischemia of varied severity in rat striatum.

BACKGROUND AND PURPOSE: Evidence has accumulated suggesting that ischemia-induced neuronal damage may be linked to an extracellular overflow of glutamate. The purpose of this study was to provide new information about the time course of the increase in extracellular glutamate concentration associated with moderate and severe ischemia, and its relationship with electrical changes including anoxic depolarization. METHODS: Changes in the extracellular concentration of glutamate were continuously monitored in the rat striatum by microdialysis. Ischemia was induced by four-vessel occlusion for 3 or 5 minutes, and in some cases its severity was increased with a neck tourniquet. The severity of ischemia was assessed by electroencephalogram and direct current potential recording to detect anoxic depolarization. RESULTS: In all experiments, the extracellular glutamate concentration began to increase shortly after the onset of ischemia and steadily rose throughout the ischemic period. Increases up to 35.0 mumol/l (2-3 mumol/l baseline; p less than 0.005) were observed when ischemia provoked the rapid occurrence of a large and sustained anoxic depolarization. Relatively smaller but still significant increases (6.9 mumol/l; p less than 0.005) were observed in penumbral conditions (electroencephalogram loss without anoxic depolarization). Glutamate began to be cleared immediately after reperfusion and 90% of released glutamate was cleared within 5 minutes, even when the preceding ischemia had been severe. CONCLUSIONS: We propose that the extracellular glutamate concentration may not reach critical levels during short episodes of penumbral ischemia, but this might happen with a longer ischemic period.

The effects of tianeptine and other antidepressants on a rat model of depression.

A model of depression based on measurements made after restraining rats for two hours has been developed. The model is associated with elevation in corticosterone, reflects the higher incidence of depression in women, and shows increased post-synaptic 5-HT function with adaptation. The effects of tianeptine and other antidepressants on the model were studied. Chronic pre-treatment with desipramine, sertraline (amine uptake inhibitors), and chlordiazepoxide normalised open field activity after restraint. Single high doses, post-restraint, of 8-OH-DPAT, gepirone (5-HT agonists), and tianeptine normalised open field activity, whereas desipramine, chlordiazepoxide, and diazepam did not. It is of considerable interest that tianeptine decreased the availability of 5-HT to receptors.

Detection of interleukin-1 and interleukin-6 in adult rat brain, following mechanical injury, by in vivo microdialysis: evidence of a role for microglia in cytokine production.

In vivo levels of interleukin-1 (IL-1) and IL-6, present in the interstitial spaces of brain, have been repeatedly monitored up to 7 days after insertion of a microdialysis probe, designed to induce mechanical trauma to the brain. IL-1 is barely detectable immediately after implantation but over a 24-48 h period a 15-fold increase is seen. In contrast IL-6 levels at day 0 are high, increasing slightly (10%) by day 1 but decreasing to 40% by day 2. The temporal pattern of IL-6 recovery in the cerebrospinal fluid was similar to that in the dialysate but the levels were significantly lower and may reflect diffusion from the site of the probe lesion. Cellular sources of these cytokines include macrophages and neutrophils, which have infiltrated the lesion and microglia resident in the brain, which can be identified at the lesion site within 24 h of probe implantation. The astrocytic response to injury, evidenced by increased glial fibrillary acidic protein staining occurs much later, by day 7, and is unlikely to be responsible for IL-1 and IL-6 production found at 24-48 h. Since upon isolation and stimulation of microglia in vitro with lipopolysaccharide IL-1 and IL-6 can be measured in the supernatant, it would appear that they have the capacity to produce cytokines in vivo. Localised synthesis of cytokines at sites of brain injury by microglia would further stimulate microglia in an autocrine manner and also propagate the astrocytic reaction.

Measurements of tacrine and monoamines in brain by in vivo microdialysis argue against release of monoamines by tacrine at therapeutic doses.

1. The concentration of tacrine (tetrahydroaminoacridine or THA) in plasma, regions of brain and cerebral extracellular fluid has been studied in the rat at various times following injection of a dose of 5 mg kg-1, i.p. 2. The peak plasma THA concentration was 2.46 nmol ml-1, and occurred 30 min post injection and clearance was first order (t1/2 = 90 min). The concentration in the brain peaked between 30-60 min, and was around 30 times plasma concentration (striatum peak concentration = 65 +/- 3 nmol g-1). Extracellular cerebral concentration measured by in vivo microdialysis was similar to plasma concentration with the peak occurring 100 min post-injection. 3. No evidence was obtained by in vivo dialysis for THA inducing dopamine release from striatum or 5-hydroxytryptamine (5-HT) release from the frontal cortex. Enhanced release of dopamine did occur after (+)-amphetamine (5 mg kg-1, i.p.) injection, while KCl (100 mM) in the probe released both dopamine and 5-HT. 4. Since the minimum plasma THA concentration achieved in this study was at least twice that found in the plasma of patients given THA for the treatment of dementia, these results suggest that monoamine release in the brain does not occur during therapy.

Changes in rat brain extracellular glutamate concentration during seizures induced by systemic picrotoxin or focal bicuculline injection: an in vivo dialysis study with on-line enzymatic detection.

An on-line enzymatic assay of dialysis fluid has been used to monitor the extracellular glutamate concentration in the rat hippocampus. Perfusion with artificial cerebrospinal fluid containing a glutamate uptake inhibitor (either dihydrokainate or 4,4'-diisothiocyanatostilbene-2,2' disulfonic acid) produced a marked stable increase in glutamate concentration; 10 min perfusion with 100 mM K+ produced a transient increase. Sustained epileptiform EEG discharges were induced in the hippocampus by focal injection of bicuculline into the piriform cortex or by systemic injection of picrotoxin. Extracellular glutamate did not change significantly during seizure activity, either in the absence or in the presence of glutamate uptake inhibitors. It is concluded that seizure activity is not necessarily accompanied by an overall increase in extracellular glutamate concentration.

Effect of tryptophan on extracellular concentrations of tryptophan and 5-hydroxyindoleacetic acid in the striatum and cerebellum.

The effects of L-tryptophan (50 mg/kg i.p.) on extracellular concentrations of tryptophan and the 5-hydroxytryptamine (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat striatum and cerebellum, regions with rich and poor 5-HT innervation, respectively. Determinations were on perfusates from dialysis probes in the brains of conscious, freely moving rats. The pharmacokinetic profiles of dialysate tryptophan after tryptophan load (peak concentration, time to peak concentration, area under curve, and half-life) in the two regions did not differ significantly. The dialysate 5-HIAA concentration in the striatum rose two- to threefold after the administration of tryptophan. Therefore, as 5-HIAA was undetectable in the cerebellum either before or after the administration of tryptophan, the increase of 5-HIAA in the striatum is unlikely to depend appreciably on its production within the cerebral vasculature or outside the brain or on its entering the striatum through a blood-brain barrier damaged by placement of the dialysis probe. Overall, the findings strengthen previous evidence that extracellular 5-HIAA concentrations determined by cerebral dialysis are a valid measure of the metabolism of 5-HT of brain neuronal origin.

Effect of p-chlorophenylalanine on release of 5-hydroxytryptamine from the rat frontal cortex in vivo.

1. Rats were given p-chlorophenylalanine (PCPA, 150 mg kg-1, i.p.) to inhibit partially 5-hydroxytryptamine (5-HT) synthesis so that its concentration in the frontal cortex fell by about half. The effects of this treatment on frontal cortex dialysate 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined before and after stimulation by increasing K+ concentration in the perfusion fluid by 100 mM for 20 min. Rates of 5-HT synthesis as indicated by the effects of 3-hydroxybenzylhydrazine (NSD 1015, 150 mg kg-1, i.p.) on frontal cortex tissue and dialysate 5-hydroxytryptophan (5-HTP) and dialysate 5-HIAA were also measured in rats that had not been stimulated with K+. 2. Dialysate 5-HT and 5-HIAA concentrations of both vehicle- and PCPA-treated rats fell into major (group 1) and minor (group 2) populations statistically distinguishable from each other by the high 5-HT and low 5-HIAA values of the latter group. 3. In group 1 animals, PCPA decreased both the dialysate 5-HT concentration and its rise following stimulation by K+ in proportion with the decrease of 5-HT in frontal cortex tissue. 5-HIAA fell more markedly than 5-HT and in similar proportion in both tissue and dialysate. The fall of dialysate 5-HIAA on stimulation by K+ was also attenuated to the same degree. The elevated 5-HT/5-HIAA ratios after PCPA treatment imply increased conservation of the depleted 5-HT stores. 4. PCPA decreased the above 5-HIAA values and the effects of NSD 1015 on tissue 5-HTP or dialysate 5-HIAA concentrations in similar proportion. However, PCPA had little effect on corresponding dialysate 5-HTP values. 5. The results are discussed with respect to relationships between synthesis, storage and release of 5-HT. They indicate that (under the conditions of the present study) the availability of 5-HT to receptors is directly proportional to total vesicular stores under both basal conditions and during neuronal firing.

The effect of the novel antidepressant tianeptine on the concentration of 5-hydroxytryptamine in rat hippocampal dialysates in vivo.

Tianeptine is a novel tricyclic antidepressant which, in marked contrast to other antidepressants, increases the uptake of 5-HT in brain tissue and blood platelet preparations ex vivo. In the present study it was shown, by microdialysis, that tianeptine (10 mg/kg i.p.), whether given as a single dose or as daily doses for 14 days, attenuated the K(+)-evoked rise of extracellular 5-HT in the hippocampus in vivo. Tianeptine (10 mg/kg i.p.), given acutely, did not reduce basal levels of 5-HT in hippocampal dialysates in the presence of the 5-HT reuptake inhibitor, citalopram. These results suggest mutually opposing effects of tianeptine and citalopram on neuronal uptake of 5-HT. Their significance in relation to the role of 5-HT in the action of antidepressants is discussed.

Effects of tianeptine on stress-induced behavioural deficits and 5-HT dependent behaviour.

The novel tricyclic antidepressant drug tianeptine had an antidepressant-like effect on a rat model of depression based on the deficit in open field activity observed on the day after 2 h restraint. Thus, when tianeptine (10 mg/kg IP) was given 2 h after the end of the restraint to either untreated rats or to animals previously given 10 mg/kg of the drug per day for 13 days, then the deficit was opposed. Tianeptine, given acutely but not chronically, moderately enhanced the 5-HT1C receptor-dependent hypolocomotor effect of m-chlorophenylpiperazine (mCPP) but did not alter other 5-HT1 receptor subtype-dependent behaviour. Acute but not chronic tianeptine also decreased 5-HT2 receptor-dependent body shakes induced by 5-hydroxytryptophan. Shakes induced by the 5-HT2 agonist 1-(2,5-dimethoxy-4-iodophenyl)-2 aminopropane (DOI) were unaffected. The results are discussed in relation to the possible mechanism of antidepressant action of tianeptine.

Effect of transient cerebral ischaemia and cardiac arrest on brain extracellular dopamine and serotonin as determined by in vivo dialysis in the rat.

The effects of 20-min transient, global, forebrain ischaemia and cardiac arrest on extracellular concentrations of dopamine (DA), serotonin (5-HT), and their respective metabolites, homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in vivo by dialysis of rat striatum and hippocampus. During the ischaemic period, striatal DA content increased (250-fold basal concentrations) with parallel but much less marked increases of both striatal and hippocampal 5-HT content (eight- to 10-fold). Baseline values were restored during reperfusion. Subsequent increases of DA and 5-HT levels on cardiac arrest were comparable after both sham operation and ischaemia. Significant decreases of HVA and 5-HIAA levels were observed following ischaemia or cardiac arrest. The differential effects of ischaemia on DA and 5-HT suggest selective alterations in disposition or metabolism of the two transmitters and that dopaminergic neurones may be more vulnerable to ischaemic insults.

Extracellular striatal dopamine and its metabolites during transient cerebral ischaemia.

Severe cerebral ischaemia has been repeatedly shown to provoke a massive increase in striatal extracellular dopamine (DA). These experiments were undertaken to determine the duration of the DA increase produced by transient ischaemia, and the fate of the released DA during recirculation. Experiments were performed in anaesthetised rats subjected to 20 min of cerebral ischaemia, followed by 80 min of reperfusion, before cardiac arrest. Measurements of catechols were made in the striatum using in vivo differential pulse voltammetry (DPV), each 4 min, throughout the experiment and for 60 min after cardiac arrest. DPV data were substantiated with intracerebral dialysis; 20-min dialysate samples were analysed for DA and homovanillic acid (HVA) using HPLC. In 6 of 11 rats, ischaemia induced a massive DA release in the striatum, resulting in a marked increase in extracellular levels (350-1,200%), which persisted throughout ischaemia. DPV and intracerebral dialysis demonstrated that DA was totally cleared from the extracellular space within minutes of reperfusion, whereas both its acidic metabolites (3,4-dihydroxyphenylacetic acid and HVA) increased slightly. These results indicate that DA released during 20-min ischaemia is rapidly cleared during reperfusion, mainly via reuptake. In the five other rats, only a relatively small and transient increase in the DPV catechol peak was detectable, cleared before the end of ischaemia, probably reflecting less severe ischaemia; small or no changes were detectable in the corresponding dialysate. The latter data suggest that different change(s) in the nigrostriatal dopaminergic system may occur, according to the severity of ischaemia.

Brain edema after an experimental missile wound.

We have developed an experimental model to study cerebral pathophysiology associated with a missile wound to the brain. After wounding, vasogenic edema occurs about the missile wound track in the injured cerebral hemisphere. This edema is relatively mild, does not appear life-threatening, peaks at 48 hr after wounding, and spontaneously resolved in 1 week.

Brain edema following an experimental missile wound to the brain.

Brain edema occurs after brain injury and may be life threatening. The occurrence and type of brain edema, its magnitude, and time course have never been ascertained following a missile wound to the brain. We therefore measured the development of brain edema in a series of cats in which a right cerebral hemisphere wound was made with a 2.0 mm, 31.7 mg steel sphere with a velocity of 240-300 m/s (0.9-1.4 J). The entire brain was surveyed for postwounding brain edema by determining the wet weight minus dry weight. Brain edema was seen to develop only in the white matter about the missile wound track in the injured cerebral hemisphere. There, brain water rose from 66 to 73%; white matter sodium also increased significantly from approximately 150 mEq/kg dry weight to 254 mEq/kg dry weight. Potassium levels remained essentially unchanged. This vasogenic edema was relatively mild, peaked at 24-48 h after wounding, and resolved spontaneously within a week without specific treatment. We infer that brain edema following an uncomplicated cerebral missile wound in the human brain is also mild, self-limited, and may resolve spontaneously without special treatment.

Experimental missile wound to the brain.

Among civilians in the United States, 33,000 gunshot wound deaths occur each year; probably half of these involve the head. In combat, head wounds account for approximately half of the immediate mortality when death can be attributed to a single wound. No significant reduction in the neurosurgical mortality associated with these wounds has occurred between World War II and the Vietnam conflict, and very little research into missile wounds of the brain has been undertaken. An experimental model has been developed in the anesthetized cat whereby a ballistic injury to the brain may be painlessly reproduced in order that the pathophysiological effects of brain wounding may be studied and better treatments may be designed to lower the mortality and morbidity rates associated with gunshot wounds. Prominent among physiological effects observed in this model was respiratory arrest even though the missile did not injure the brain stem directly. The incidence of prolonged respiratory arrest increased with increasing missile energy, but arrest was often reversible provided respiratory support was given. It is possible that humans who receive a brain wound die from missile-induced apnea instead of brain damage per se. The mortality rate in humans with brain wounding might be reduced by prompt respiratory support. Brain wounding was associated with persistently increased intracranial pressure and reduced cerebral perfusion pressure not entirely attributable to intracranial bleeding. The magnitude of these derangements appeared to be missile energy-dependent and approached dangerous levels in higher-energy wounds. All wounded cats exhibited postwounding increases in blood glucose concentrations consistent with a generalized stress reaction. A transient rise in hematocrit also occurred immediately after wounding. Both of these phenomena could prove deleterious to optimal brain function after injury.

[Extracellular concentration of dopamine and dopamine metabolites in the rat striatum during cerebral ischemia and reperfusion].

Many data suggest that the presence of dopamine (DA) is a prerequisite for the development of neuronal damage in the striatum; neural injury could be initiated by a massive release from dopaminergic nerve terminals during ischemia. The current study was undertaken in order to define the mechanism through which ischemia alters dopaminergic neurotransmission, and to examine the subsequent events early during recirculation. Experiments were performed on 14 male anesthetized Sprague Dawley rats. The ischemic insult consisted of 20 min global cerebral ischemia (4-vessel occlusion) followed by 80 min reperfusion. Cardiac arrest concluded this phase of the experiment, but measurements were continued for 60 min more. Measurements of catechols were made in the striatum using in vivo differential pulse voltammetry (DPV), each 4 min, throughout the experiment and for 60 min post-mortem. DPV data were substantiated with intracerebral dialysis; 20 min dialysate samples were analysed for dopamine (DA) and homovanillic acid (HVA; DA metabolite) using high performance liquid chromatography (HPLC). Repeated in vivo DPV measurements of striatal catechols during ischemia/reperfusion were collected in 11 of 14 experiments. In 6 out of 11 rats, ischemia induced a massive catechols release in the striatum, resulting in a marked increase in extracellular level (350 to 1200% of control), which persisted throughout ischemia. In these rats, a marked rise in extracellular DA was detected in the dialysate sample collected in the contralateral striatum during ischemia, together with a fall in HVA, probably due to ischemic inhibition of the enzymatic oxidation of DA. Catechol was cleared from the extracellular space within minutes of reperfusion, indicating functional catechol uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Hippocampal 5-HT synthesis and release in vivo is decreased by infusion of 8-OHDPAT into the nucleus raphe dorsalis.

Infusion of the serotonin-1A (5-HT1A) agonist, 8-hydroxy-2-di(n-propylamino)tetralin (8-OHDPAT) (0.5, 1.0 and 2.0 micrograms) into the dorsal raphe, decreased extracellular 5-HT as measured by dialysis in the ventral hippocampus and also decreased 5-HT synthesis in both the hippocampus and the rest of the brain as measured by 5-hydroxytryptophan (5-HTP) accumulation following decarboxylase inhibition by NSD 1015.