Determination of brain 5-hydroxytryptamine turnover in freely moving rats using repeated sampling of cerebrovascular fluid

Refinement of a model of repeated cerebrospinal fluid collection in conscious rats

The cannulation of the cisterna magna in rats for in vivo sampling of cerebrospinal fluid serves as a valuable model for studying the delivery of new drugs into the central nervous system or disease models. It offers the advantages of repeated sampling without anesthesia-induced bias and using animals as their own controls. An established model was retrospectively reviewed for the outcomes and it was hypothesized that by refining the method, i.e. by (1) implementing pathophysiological-based anesthesia and analgesia, (2) using state-of-the-art peri-operative monitoring and supportive care, (3) increasing stability of the cement-cannula assembly, and (4) selecting a more adaptable animal strain, the outcome in using the model - quantified by peri-operative mortality, survival time and stability of the implant - could be improved and could enhance animal welfare. After refinement of the technique, peri-operative mortality decreased significantly (7 animals out of 73 compared with 4 out of 322; P = 0.001), survival time increased significantly (36 ± 14 days compared with 28 ± 18 days; P < 0.001), as well as the stability of the cement-cannula assembly (47 ± 8 days of adhesion compared with 33 ± 15 days and 34 ± 13 days using two other cement types; P < 0.001). Overall, the 3R concept of Russell and Burch was successfully addressed and animal welfare was improved by (1) the reduction in the total number of animals needed as a result of lower mortality or fewer euthanizations due to technical failure, and frequent use of individual rats over a time frame; and (2) improving the scientific quality of the model.

Evaluation of brain-targeting for the nasal delivery of estradiol by the microdialysis method

The uptake of estradiol into the cerebrospinal fluid (CSF) after intranasal and intravenous administration in rats was investigated to study whether direct nose-CSF transport of estradiol exits or not. Animals received 0.48 mg kg(-1) estradiol randomly methylated beta-cyclodextrin (RAMEB) inclusion complex intranasally and intravenously. Following nasal delivery, estradiol reached a C(max) value (mean+/-S.D.) in plasma (26.70+/-11.37 ng ml(-1)) and CSF (54.76+/-32.84 ng ml(-1)) after 20 min in each case, while after intravenous infusion, estradiol reached a C(max) value in plasma (170.08+/-64.67 ng ml(-1)) and CSF (26.48+/-11.34 ng ml(-1)) at 5 min and 60 min, respectively. The AUC(CSF)/AUC(plasma) ratio (1.60+/-0.67) after intranasal delivery differed significantly from the ratio (0.61+/-0.16) observed after intravenous infusion (P<0.05). All these results indicate that estradiol is transported into CSF via olfactory neurons, and, hence, there is a direct transport route from the nasal cavity into the CSF for estradiol.

Method for the determination of the levels of β-amyloid peptide in the CSF sampled from freely moving rats

INTRODUCTION

In the present study, a model was developed to determine the effect of secretase inhibition on beta-amyloid peptide (Abeta) levels in the cerebrospinal fluid (CSF) of freely moving adult rats.

METHODS

Rats were chronically implanted with a cannula into the cisterna magna and CSF samples were collected at different time points from the same animal without anaesthesia. The levels of CSF Abeta were measured by a sandwich ELISA assay.

RESULTS

Administration of DAPT, a functional gamma-secretase inhibitor, resulted in a substantial reduction of Abeta40 and Abeta42, confirming the in vivo functionality of the CSF as a biomarker source for endogenous APP processing modulation by secretase inhibitors.

DISCUSSION

Thus, the present work provides clear evidence for the usefulness of CSF sampling from the freely moving rat model for testing the effectiveness of small molecule inhibitors of Abeta production.

Somatodendritic autoreceptor regulation of serotonergic neurons: dependence on L-tryptophan and tryptophan hydroxylase-activating kinases

The somatodendritic 5-HT(1A) autoreceptor has been considered a major determinant of the output of the serotonin (5-HT) neuronal system. However, recent studies in brain slices from the dorsal raphe nucleus have questioned the relevance of 5-HT autoinhibition under physiological conditions. In the present study, we found that the difficulty in demonstrating 5-HT tonic autoinhibition in slice results from in vitro conditions that are unfavorable for sustaining 5-HT synthesis. Robust, tonic 5-HT(1A) autoinhibition can be restored by reinstating in vivo 5-HT synthesizing conditions with the initial 5-HT precursor l-tryptophan and the tryptophan hydroxylase co-factor tetrahydrobiopterin (BH(4)). The presence of tonic autoinhibition under these conditions was revealed by the disinhibitory effect of a low concentration of the 5-HT(1A) antagonist WAY 100635. Neurons showing an autoinhibitory response to L-tryptophan were confirmed immunohistochemically to be serotonergic. Once conditions for tonic autoinhibition had been established in raphe slice, we were able to show that 5-HT autoinhibition is critically regulated by the tryptophan hydroxylase-activating kinases calcium/calmodulin protein kinase II (CaMKII) and protein kinase A (PKA). In addition, at physiological concentrations of L-tryptophan, there was an augmentation of 5-HT(1A) receptor-mediated autoinhibition when the firing of 5-HT cells activated with increasing concentrations of the alpha(1) adrenoceptor agonist phenylephrine. Increased calcium influx at higher firing rates, by activating tryptophan hydroxylase via CaMKII and PKA, can work together with tryptophan to enhance negative feedback control of the output of the serotonergic system.

Pharmacokinetic Characterization of Dehydroevodiamine in the Rat Brain

The objective of this study was to examine the kinetics of the distribution of dehydroevodiamine (DHED) in the rat brain. After an intravenous infusion of 15 min (dose of 1-10 mg/kg), the temporal profiles of the plasma levels of DHED declined in a multiexponential manner. Moment analysis indicated that the clearance and steady-state volume of distribution for DHED were not statistically different with the dose, indicating that the pharmacokinetics for DHED is linear in the range examined. Nonlinear regression analysis of DHED concentrations in the plasma and the brain revealed that the linear kinetics into and out from the brain reasonably described the data and that the clearances for influx into and efflux from the brain were comparable. Transport clearances for DHED across MBEC4 monolayers, an in vitro model of the blood-brain barrier, were also comparable for influx and efflux, and were independent of the medium concentration. The concentration of DHED in cerebrospinal fluid was negligible compared with that found in plasma, indicating that the drug is not primarily distributed to the brain via the blood-cerebrospinal fluid barrier. These observations indicate that DHED is transported from the systemic circulation to the brain via the blood-brain barrier by linear kinetics.

Serial cerebrospinal fluid sampling in a rat model to study drug uptake from the nasal cavity

Drug transport from the nasal cavity to the brain has gained much interest in the last decade. In the present study, a model was developed to determine the uptake of drugs into the cerebrospinal fluid (CSF) after nasal delivery in rats. CSF samples were taken using a cisternal puncture method. In this method, a needle is advanced through the skin and muscles overlying the atlanto-occipital membrane into the cisterna magna, while the rat is fixed in a stereotaxic frame. This method appears to be superior over cannulation of the atlanto-occipital membrane for CSF sampling. The major advantages of the puncture method is the ability of serial and simultaneous CSF and blood sampling for over 2 h in the same rat. To obtain maximal drug absorption from the nasal cavity and uptake into CSF, different positions of the rat's head (upright-90 degrees, supine-90 degrees, supine-45 degrees and supine-70 degrees angles) were tested in nasal delivery studies using hydrocortisone (HC) as a model drug. Putting the rat in the supine-90 degrees angle position increased the absorption of HC into plasma and CSF 2-fold compared to the upright-90 degrees angle position. The supine-70 degrees angle position did not change the HC plasma and CSF levels compared to the supine-90 degrees angle position. However, the supine-70 degrees angle position showed the fastest CSF sampling rate, enabling more accurate CSF sampling and therefore preferred for further studies. In conclusion, the cisternal puncture method using the supine-70 degrees and 90 degrees angle position is a suitable method to study drug transport from the nasal cavity into the CSF, with the ability of multiple CSF sampling.

Technique for collecting cerebrospinal fluid in the cisterna magna of non-anesthetized rats

We developed a technique for collecting cerebrospinal fluid (CSF) from the cisterna magna in non-anesthetized adult and young pup rats. In the adults, CSF was collected through a previously implanted guide cannula without previous disruption of the cisterna magna. In the pups, CSF was directly aspirated through a syringe from the cisterna in awake animals without previous surgery. In the adults, the volume of CSF collected varied from 50 to 120 microl, and in pups 7 to 10 days old, it was approximately 25 microl. The technique can easily be done by anyone who is familiar with stereotaxic surgery, and the material needed is cheap and easy to obtain commercially. A simple procedure to calculate the parameters for the implantation of guide cannula in rats other than Wistar ones is also presented.

Anti-human immunodeficiency virus type 1 activity, intracellular metabolism, and pharmacokinetic evaluation of 2'-deoxy-3'-oxa-4'-thiocytidine

The racemic nucleoside analogue 2'-deoxy-3'-oxa-4'-thiocytidine (dOTC) is in clinical development for the treatment of human immunodeficiency virus (HIV) type 1 (HIV-1) infection. dOTC is structurally related to lamivudine (3TC), but the oxygen and sulfur in the furanosyl ring are transposed. Intracellular metabolism studies showed that dOTC is phosphorylated within cells via the deoxycytidine kinase pathway and that approximately 2 to 5% of dOTC is converted into the racemic triphosphate derivatives, which had measurable half-lives (2 to 3 hours) within cells. Both 5'-triphosphate (TP) derivatives of dOTC were more potent than 3TC-TP at inhibiting HIV-1 reverse transcriptase (RT) in vitro. The K(i) values for dOTC-TP obtained against human DNA polymerases alpha, beta, and gamma were 5,000-, 78-, and 571-fold greater, respectively, than those for HIV RT (28 nM), indicating a good selectivity for the viral enzyme. In culture experiments, dOTC is a potent inhibitor of primary isolates of HIV-1, which were obtained from antiretroviral drug-naive patients as well as from nucleoside therapy-experienced (3TC- and/or zidovudine [AZT]-treated) patients. The mean 50% inhibitory concentration of dOTC for drug-naive isolates was 1.76 microM, rising to only 2.53 and 2.5 microM for viruses resistant to 3TC and viruses resistant to 3TC and AZT, respectively. This minimal change in activity is in contrast to the more dramatic changes observed when 3TC or AZT was evaluated against these same viral isolates. In tissue culture studies, the 50% toxicity levels for dOTC, which were determined by using [(3)H]thymidine uptake as a measure of logarithmic-phase cell proliferation, was greater than 100 microM for all cell lines tested. In addition, after 14 days of continuous culture, at concentrations up to 10 microM, no measurable toxic effect on HepG2 cells or mitochondrial DNA replication within these cells was observed. When administered orally to rats, dOTC was well absorbed, with a bioavailability of approximately 77%, with a high proportion (approximately 16.5% of the levels in serum) found in the cerebrospinal fluid.

Alteration of dopamine metabolites in CSF and behavioral impairments induced by neonatal hippocampal lesions

Alterations of monoamine metabolites in CSF and behavioral abnormalities were studied in rats with neonatal hippocampal lesions and controls. Lesions of the ventral hippocampus were produced bilaterally by ibotenic acid on postnatal day 7. Lesion-induced neurochemical alterations and behavioral impairments were examined concurrently when rats were 12 weeks old. CSF from the cisterna magna was sampled repeatedly from freely moving rats. The levels of free 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in CSF were determined. An exposure to a novel environment induced hyperexploratory behavior and elevated the level of free DOPAC in CSF in lesioned rats. Although a swim stress increased the levels of free DOPAC and 5-HIAA in CSF in both control and lesioned groups, rats with hippocampal lesions had a further elevation of free DOPAC in CSF and greater spontaneous activity relative to controls shortly after stress. Amphetamine (1.5 mg/kg, i.p.) induced hyperlocomotion in lesioned rats compared to controls. For the control group, the levels of the three monoamine metabolites in CSF were not significantly influenced by amphetamine. However, for the lesioned group, the level of DOPAC significantly decreased compared to preinjection of amphetamine. The results indicate that neonatal hippocampal lesion-induced impairments can be manifested by behavioral and neurochemical abnormalities. Alterations of monoamine metabolites in CSF may be determined quantitatively and used as indices for monitoring lesion-impaired monoaminergic function in the central nervous system.

No effect of age on the dose requirement of thiopental in the rat

With increasing human age (20-80 years), the electroencephalogram (EEG) dose requirement for the intravenous anesthetic thiopental decreases approximately 10% per decade of life. The goal of this study was to compare the dose required to attain isoelectric EEG in young (4-5 month) vs. aged (24-25-month) Fischer 344 rats. One second isoelectricity was found to be an endpoint where minimal cardiorespiratory depression occurred. The effects of age, infusion rate, and repeated administration were examined in nine young and nine old rodents. Thiopental dose requirement increased with increasing infusion rates. Repeated administration at two-day intervals did not demonstrate tolerance to thiopental. No difference in thiopental dose requirement was detected in the young vs. elderly rats. In a separate group of five young and five old rats, thiopental plasma, brain, heart, and CSF concentrations were measured when five seconds of EEG isoelectricity was achieved: no consistent differences were noted. The rat may not be an appropriate model to investigate acute age-related anesthetic effects in humans, because cardiovascular changes with age are dissimilar between species.

Comparison among different approaches for sampling cerebrospinal fluid in rats

Two approaches for time-resolved sampling of cerebrospinal fluid (CSF) in rats were compared regarding performance, reproducibility, and extent of the inevitable trauma caused by the implantation of a sampling tube. Several parameters were checked to evaluate the injury: blood cell contamination of CSF; concentrations in CSF of the cytosolic proteins neuron-specific enolase (NSE) and S-100 (chiefly present in astrocytes); blood-brain barrier leakage of a dye-protein complex; viability of nervous tissue cells as assessed by dye exclusion; light and electron microscopy. In one sampling method, a tube was forced epidurally into the cisterna magna via a hole in the calvarium, consistently damaging the meninges and the nervous tissue. When using the alternative sampling method, the tube was instead affixed to the posterior atlanto-occipital membrane and connected with the cisterna magna via a hole in the membrane. Such a procedure caused negligible damage. Both techniques induced an inflammatory response. We advocate the use of the second approach, i.e., to sample CSF via a hole in the atlanto-occipital membrane, as the method of choice due to its high reproducibility. It is fairly rapid, and associated with a negligible injury.

A new approach for multiple sampling of cisternal cerebrospinal fluid in rodents with minimal trauma and inflammation

A new approach was developed to minimize inevitable damage to nervous and meningeal tissue due to implantation of a sampling tube allowing multiple withdrawal of cerebrospinal fluid (CSF) from the cisterna magna in adult rats. A tube was secured on the atlanto-occipital membrane. Thereafter, a hole was cut through the membrane, allowing flow of CSF from the cisterna magna to the tube. CSF could be sampled repeatedly for at least 1 week. There was no blood-brain barrier damage. The pressure in the cisterna magna remained normal as did the estimated rate of CSF formation. Very few blood cells contaminated the CSF. There was very little evidence of inflammation. The nervous tissue was undamaged as shown by exclusion of a dye-protein complex. The CSF concentrations of the cytosolic neuronal protein neuron-specific enolase (NSE), and of the astrocyte protein S-100 were very low. The pattern of amino acids remained within normal limits. Scanning electron microscopy revealed that clot and reactive changes were restricted to the vicinity of the connecting hole. We conclude that our approach to positioning a tube on the atlanto-occipital membrane and then connecting it to the cisterna magna reproducibly and reliably enables 'atraumatic' multiple sampling of CSF.

The significance of neuron specific enolase levels in cerebrospinal fluid and serum after experimental traumatic brain damage

In the posttraumatic period, measurement of neural tissue enzymes in serum and cerebrospinal fluid gives quantitative information about the severity of the head injury. In our study, we evaluated the relationship between the serum and cerebrospinal fluid levels of neuron specific enolase and the severity of trauma. Head traumas at different severity were applied experimentally (Mild 0.038 N, Moderate 0.057 N, Severe 0.3 N). Serum and cerebrospinal fluid levels of neuron specific enolase were measured in trauma and control groups of rats. Only in the severe trauma group, the neuron specific enolase levels of cerebrospinal fluid were significantly increased. There was no statistically significant difference between the groups when serum neuron specific enolase levels were evaluated. Our data leads us to conclude that trauma, causing significant neural damage, results in an increase in cerebrospinal fluid neuron specific enolase levels, however the serum neuron specific enolase levels do not seem to run parallel with that increase.

Effect of probenecid on 5-hydroxyindoleacetic acid in cisternal cerebrospinal fluid of rats with portacaval anastomosis

Portal-systemic encephalopathy (PSE) is characterized by a neuropsychiatric disorder progressing through personality changes, to stupor and coma. Previous studies have revealed alterations of serotonin and of its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in brain tissue and CSF in experimental (rat) and human PSE. Increased brain 5-HIAA concentrations could result from its decreased removal rather than to increased serotonin metabolism. In order to evaluate this possibility, CSF 5-HIAA concentrations were measured using an indwelling cisterna magna catheter technique at various times following end-to-side portacaval anastomosis in rats (the most widely used animal model of PSE) treated with probenecid, a competitive inhibitor that blocks the active transport of acid metabolites out of the brain and CSF. Following portacaval anastomosis and probenecid treatment, CSF concentrations of 5-HIAA were increased to a greater extent than in sham-operated controls. When data were expressed as per-cent baseline values, the relative increase of CSF 5-HIAA in portacaval shunted rats following probenecid treatment was not significantly different from sham-operated controls. These findings confirm that increased 5-HIAA in the CNS in experimental PSE results from increased 5HT metabolism or turnover and that the probenecidsensitive acid metabolite carrier is intact in PSE.

Effects of citalopram, a synthetic serotonin uptake inhibitor, on indoleamine and catecholamine concentrations in the cerebrospinal fluid of freely moving rats

We studied changes in the concentrations of 5-hydroxytryptamine (5-HT), other indoleamines, and catecholamines in the cerebrospinal fluid (CSF) of freely-moving rats that had been administered citalopram, +/-1-[3- (Dimethylamino)propyl)-1-(4-fluorophenyl)-1, 3-dihydro-5-isobenzo-furancarbonitrile hydrobromide), a selective inhibitor of 5-HT uptake. In a microdialysis experiment, the intracerebral extracellular free 5-HT increased significantly, peaking 60 to 90 min after citalopram (30 mg/kg p.o.) was administered. The 5-HT concentrations in CSF from the cisterna magna increased significantly, reaching a maximum 6 hours after a single dose of citalopram (30 mg/kg p.o.) was given. Six hours after this dose, the CSF 5-HT concentration in the cisterna magna was significantly increased, and the 5-hydroxyindoleacetic acid (5-HIAA) concentration was significantly decreased. There were non-significant changes in the other indoleamines (tryptophan, 5-hydroxytryptophan, and kynurenine) and in the catecholamines (dopamine, homovanillic acid, normetanephrine, and 3-methoxy-4-hydroxyphenethyleneglycol). The 5-HT/tryptophan ratio was correlated significantly with the kynurenine/tryptophan ratio before treatment with citalopram (r = 0.81, p = 0.051), indicative that there is coordination of the serotonin and kynurenine pathways in normal rats. In the animals posttreatment there was no such correlation, suggesting that the changes in 5-HT are independent of the kynurenine system at least within the 6 hours postreatment. These CSF results appear to reflect selective inhibition of 5-HT uptake in brain tissues by citalopram that is not associated with changes in catecholamines.

Changes in amino acid levels in rat plasma, cisternal cerebrospinal fluid, and brain tissue induced by intravenously infused arginine-vasopressin

Circulating arginine-vasopressin (AVP) is known to reduce the blood-to-brain transfer of large neutral amino acids (AA). As a first step to examine whether the reduced uptake by brain endothelial cells is reflected in changes in large neutral amino acid levels of the extracellular fluid environment of cells within the nervous tissue, we measured the concentrations of amino acids in plasma, cerebrospinal fluid (CSF), and hippocampal tissue of rats before and after infusion of AVP (34 and 68 ng/min/kg, respectively) over the time period of 60 min. AA levels changed in all compartments investigated during both saline and AVP infusions. Whereas in the saline-infused controls changes in CSF AA levels paralleled those in plasma, this correlation was abolished by raising AVP concentrations. The effect of AVP was found to be i) dependent on the AA, ii) different with respect to direction and iii) magnitude of changes in AA levels, and iv) in some cases dose dependent. In summary, AVP infusion increased plasma levels of 10 AA, but decreased all 15 AA measured by some 30% in CSF. In contrast to CSF, levels of AA were slightly enhanced in the hippocampal tissue. The results are not solely explicable by a reduced blood-to-brain transfer of AA. We conclude that further mechanisms by which AVP affects the availability of AA to the brain may exist. The physiological significance of the findings might be related to brain osmoregulation, especially in situations of stress.

Simple high-performance liquid chromatographic analysis of free primary amino acid concentrations in rat plasma and cisternal cerebrospinal fluid

The quantitation of 16 acidic, basic, small and large neutral amino acids was performed using 10-microliters sample aliquots of cisternal cerebrospinal fluid (CSF) and blood plasma of rats. The analytical technique is based upon a two-buffer HPLC system with fluorimetric detection of pre-column derivatized primary amino acids with o-phthaldialdehyde (OPA). A modification of a well established method, the power of the present technique comes from an improved resolution and sensitivity by installing a column heater adjusted to 43 degrees C and strictly reducing any contamination by background amino acids. The analysis is simplified by separating the amino acid derivatives with a linear buffer gradient and less time consuming by the use of a short analytical column with a higher flow-rate. Analytical precision, linearity of response and reproducibility were highly acceptable at both CSF and plasma concentrations of amino acids without changing any of the separation or detection parameters.

Effect of prolactin on the sleep-wake cycle in the rat

The purpose of this study was to examine the effects of prolactin on the sleep-wake cycle. Ovine prolactin was injected subcutaneous at a dose of 10 micrograms/animal or intra-cerebro-ventricularly at doses of 100, 10 and 1 ng/animal. The subcutaneous injections were given during either the diurnal or nocturnal period. Results indicate that oPRL decreases paradoxical sleep duration when injected during the dark period and increases it when injected during the light period. The i.c.v. injections were given only during the dark period and the effects were similar to those obtained with the s.c. injections. There was no effect on slow-wave sleep duration irrespective of injection time or injection site.

Monitoring of neurotransmitter amino acids by means of an indwelling cisterna magna catheter: a comparison of two rodent models of fulminant liver failure

Alterations of brain and cerebrospinal fluid amino acids have consistently been described in human and experimental fulminant liver failure. To evaluate the significance of such changes in the pathogenesis of hepatic encephalopathy in fulminant liver failure, brain and cerebrospinal fluid amino acids (glutamate, aspartate, GABA, glycine, taurine) were measured at various stages during the development of neurological dysfunction in rats after hepatic devascularization or thioacetamide treatment to induce acute liver failure. To facilitate repetitive removal of cerebrospinal fluid, a technique employing long-term implantation of cisterna magna catheters in conscious, freely moving rats was developed. Brain but not cerebrospinal fluid concentrations of the excitatory amino acids glutamate and aspartate were reduced in both animal models of fulminant liver failure in parallel with deterioration of neurological status. Brain and cerebrospinal fluid GABA levels were not significantly altered. Cerebrospinal fluid glycine levels were increased two to three times in parallel with increasing brain glycine content in the devascularized rat but were unchanged in thioacetamide-induced liver failure, suggesting distinct pathophysiological mechanisms in these two experimental situations. On the other hand, onset of coma in both animal models of fulminant liver failure was accompanied by significantly increased cerebrospinal fluid taurine levels. We suggest that such changes result from taurine release from astrocytes in brain into the extracellular fluid; this is consistent with taurine's role in the regulation of intracellular osmolarity in brain. Sequential measurements of amino acids in the cerebrospinal fluid of small rodents with indwelling cisterna magna catheters adds a useful new approach for exploring the neurobiology of hepatic encephalopathy in fulminant liver failure.

Simultaneous effects of p-chloroamphetamine, d-fenfluramine, and reserpine on free and stored 5-hydroxytryptamine in brain and blood

The effects of acute treatment with p-chloramphetamine, d-fenfluramine, and reserpine on intracellular (brain tissue and whole blood) and extracellular (CSF and platelet-free plasma) compartments of 5-hydroxytryptamine (5-HT) in the brain and blood of the same rats have been examined. These treatments affected 5-HT in brain tissue and whole blood similarly (r = 0.823). Reserpine significantly reduced both intracellular pools at 2 and 24 h. p-Chloroamphetamine and d-fenfluramine were more effective on brain tissue 5-HT. The concentration of 5-HT in CSF was significantly increased by all treatments. p-Chloroamphetamine induced a dramatic 70-fold increase of CSF 5-HT, paralleling a 42% decrease in brain tissue. d-Fenfluramine significantly increased CSF 5-HT to 212% of controls and reduced whole brain 5-HT (-23%). The effects of p-chloroamphetamine and d-fenfluramine on 5-HIAA in brain, CSF, and plasma were nonsignificant. Individual values of 5-hydroxyindoleacetic acid (5-HIAA) in CSF and brain were highly correlated (r = 0.855), indicating that CSF 5-HIAA reflects well the concentration of 5-HIAA in brain tissue. Yet the intra- and extracellular concentrations of 5-HIAA were unrelated to the 5-HT changes. This indicates that CSF 5-HIAA does not reflect the active (extracellular) compartment of 5-HT in brain.

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics (cerebrospinal fluid): hematological and biochemical characterization and kinetic evaluation using carbamazepine

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics [cerebrospinal fluid (CSF)] is described. The blood (jugular vein) and CSF (cisterna magna) catheters employed are simple, reliable, and inexpensive. The blood catheter was made of soft and flexible Silastic tubing and sealed with heparin. The CSF catheter consisted of intersliding polythene tubing and interlocking Silastic tubing, which allowed maneuverability within the cisternal magna space and thus prolonging patency for chronic studies. Both catheters were well tolerated by the animals, and the postoperative success rate was 80%-100%; after 8 days 80%-85% of catheters were still patent. Using a sampling protocol considered suitable for kinetic studies, we determined numerous biochemical and hematological parameters and compared them with those values obtained postsurgically and in control rats. The parameter changes associated with the sampling protocol did not affect the kinetics of the commonly prescribed antiepileptic drug carbamazepine and its primary pharmacologically active metabolite carbamazepine-10, 11-epoxide. Therefore, the model can be used to study the interrelationship between drug kinetics at central and peripheral sampling sites and mechanism(s) of drug action.

CSF neuron-specific enolase as a quantitative marker of neuronal damage in a rat stroke model

A technique for chronic cisternal cerebrospinal fluid (CSF) sampling in conscious rats was used to obtain multiple 50 microliters samples before and up to 7 days after middle cerebral artery occlusion. Neuron-specific enolase (NSE) concentrations were measured by radioimmunoassay using a readily available kit. The volume of infarction was measured by integrating the area of damage on 9 evenly spaced histological sections of the forebrain. This correlated well (r = 0.97, P less than 0.001) with the concentration of CSF neuron-specific enolase integrated over the first 5 days post occlusion, in animals with pure cortical and mixed cortical and striatal lesions. The correlation was maintained in animals given the NMDA antagonist MK-801. There was also a good correlation between the CSF NSE concentration 3 days post-MCAO and the volume of infarction (r = 0.92, P less than 0.01). It is therefore possible that CSF neuron-specific enolase may be useful as a quantitative marker of ischaemic damage in humans and provide a useful adjunct in the assessment of neuroprotective drugs in stroke.

Intracranial pressure changes following middle cerebral artery occlusion in rats

Prolonged recording of intracranial pressure (ICP) was performed on rats subjected to middle cerebral artery (MCA) occlusion. ICP was repeatedly recorded before and after occlusion of the vessel via a narrow catheter placed in the cisterna magna. MCA occlusion was followed by an increase in ICP, and a pressure peak occurred after 12-24 h in all animals. Subsequently, essentially two patterns of ICP changes were observed. These seemed to be related to the severity of neurological deficits and extension of the infarct area. In the most severely affected animals, raised ICP was noted throughout the 1st week after MCA occlusion; in rats with reversible neurological deficits, ICP returned to normal values after the first peak at 12-24 h. The present investigation shows that prolonged ICP recording is feasible in MCA-occluded rats. The MCA occlusion model in rats is well characterized. Thus, ICP registration can be used in conjunction with other methods for evaluating treatment against increased ICP.

Changes in physiological parameters of rat cerebrospinal fluid during chronic sampling: evaluation of two sampling methods

Although rat cerebrospinal fluid (CSF) is increasingly being used in pharmacological and biochemical research, methodological studies on basic physiological data are lacking. We have determined the albumin content and number of erythrocytes and leukocytes in CSF obtained by two different methods of sampling from cisterna magna-repeated sampling from an implanted cannula and by repeated punctures. In the initial samples the albumin content was 0.08 +/- 0.03 micrograms/microliters. Chronic cannulation of the cisterna magna resulted in a meningeal reaction with increased cell and albumin content: a reaction that could be reduced but not prevented by using a sterile cannula. The number of leukocytes but not erythrocytes was highly correlated to the albumin content. Repeated sampling in the absence of a permanent cannula did not significantly increase albumin content but carried a higher risk for erythrocyte contamination.

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.

Plasma and CSF levels of dizocilpine (MK-801) required for neuroprotection in the quinolinate-injected rat striatum

This study has identified the range of plasma and cerebrospinal fluid (CSF) concentrations of the uncompetitive N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801) required for neuroprotection in the quinolinate-lesioned rat striatum. Dizocilpine was given i.v. as a bolus injection followed by a continuous infusion for 4 h, drug administration starting 30 min after a unilateral, intrastriatal injection of 200 nmol quinolinate. Neurodegeneration was assessed 7 days later in striatal homogenates by measuring the activities of the enzymes choline acetyltransferase and glutamate decarboxylase. Stable plasma levels of dizocilpine were achieved over the 4 h of infusion and the drug appeared rapidly in the CSF to reach steady state levels which were approximately 50% of the corresponding plasma values. When the degree of drug bound to plasma and CSF protein (as determined in in vitro experiments with [3H]dizocilpine) was taken into account, the steady state plasma and CSF concentrations were equivalent, indicating free exchange of dizocilpine between these compartments. A small, but significant, neuroprotective effect with respect to both enzyme markers was obtained with free steady state plasma and CSF concentrations of 24 and 21 nM. A high degree of neuroprotection occurred with steady state plasma and CSF concentrations of 47 and 40 nM, respectively, which was not improved by raising the dizocilpine concentration in these compartments further, indicating a maximal effect. The CSF concentrations required for neuroprotection in this model are close to the known affinity of dizocilpine for the N-methyl-D-aspartate receptor as determined in in vitro experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Tryptophan availability modulates serotonin release from rat hypothalamic slices

Application of a novel in vitro experimental system has allowed us to describe the relationship between tryptophan availability and serotonin release from rat hypothalamic slices. Superfusing hypothalamic slices with a physiologic medium containing l-tryptophan (1, 2, 5, or 10 microM) caused dose-dependent elevations in tissue tryptophan levels; the magnitude of the elevations produced by supplementing the medium with less than 5 microM tryptophan was within the physiologic range for rat brain tryptophan levels. Slice serotonin levels rose biphasically as the tryptophan concentration in the medium was increased. Superfusing the slices with medium supplemented with a low tryptophan concentration (1 or 2 microM) caused proportionally greater incremental changes in serotonin levels than the increases caused by further elevating the tryptophan concentration (5 or 10 microM). The spontaneous release of serotonin from the slices exhibited a dose-dependent relationship with the tryptophan concentration of the superfusion medium. Electrically evoked serotonin release, which was calcium-dependent and tetrodotoxin-sensitive, also increased in proportion to the medium tryptophan concentration. These data suggest that the rate at which serotonin is released from hypothalamic nerve terminals is coupled to brain tryptophan levels. Accelerations in hypothalamic serotonin synthesis, caused by elevating brain tryptophan levels, result in proportionate increases in the rates of serotonin release during rest and with membrane depolarization.

Tryptophan, 5-HTP, 5-HT and 5-HIAA in the cerebrospinal fluid and sexual behavior in male rats

No changes were found in the concentration of tryptophan (Trp), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT) or 5-hydroxyindole acetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of male rats either before sexual activity, immediately after ejaculation of after the postejaculatory refractory period (PEI). Injection of the Trp hydroxylase inhibitor p-chlorophenylalanine (PCPA, 25 or 100 mg/kg i.p. for 3 days) in combination with an injection of the monoamine oxidase inhibitor pargyline (100 mg/kg i.p.) increased the concentration of Trp while decreasing the concentration of 5-HTP, 5-HT and 5-HIAA in the CSF. Furthermore 100 (but not 25) mg/kg PCPA in combination with pargyline caused a significant reduction in the latency to ejaculation. Injection of probenecid (200 mg/kg i.p.), an inhibitor of the transport of 5-HIAA from the CSF, increased the concentration of 5-HIAA in the CSF and slightly prolonged the latency to ejaculation. Sexual activity caused no further increase in CSF 5-HIAA levels in the probenecid-treated rats. Since drug-induced changes in sexual behavior are associated with marked alterations in 5-HT metabolism in the CSF, whereas the changes in the behavior which occur normally are not, these results question the physiological significance of the proposed inhibitory role of 5-HT in male rat sexual behavior.

Neuron-specific enolase is a marker of cerebral ischemia and infarct size in rat cerebrospinal fluid

Neuron-specific enolase concentrations were measured in samples of rat cerebrospinal fluid obtained repeatedly before and after occlusion of the middle cerebral artery. A method for reliable, repeated sampling of cisternal cerebrospinal fluid was developed for this purpose. Occlusion of the middle cerebral artery induced cerebral infarcts of slightly variable size with good correlation to raised neuron-specific enolase concentrations. Sham operation caused only superficial cortical damage at the site of surgery and was followed by an early, slight, and transient increase in neuron-specific enolase concentration. With our technique, the development of cerebral infarcts can be studied in individual rats under experimentally controlled conditions over an extended period of time. Analysis of neuron-specific enolase can be used in trials of drugs for mitigating the effect of ischemia. Information concerning the release of neuron-specific enolase from ischemic cerebral tissue to the cerebrospinal fluid is important because neuron-specific enolase in the cerebrospinal fluid can be determined in patients suffering from cerebrovascular insult.

Intraventricular microdialysis: a new method for determining monoamine metabolite concentrations in the cerebrospinal fluid of freely moving rats

A new method is described to estimate the cerebrospinal fluid (CSF) concentrations of monoamine metabolites (dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA] in the lateral ventricle of freely moving rats by use of in vivo microdialysis. Both the baseline concentrations of these metabolites and the rate of dopamine (DA) turnover (estimated by the accumulation of total DA metabolites after 200 mg/kg probenecid) were within the range reported when other methods were used to sample CSF. A series of preliminary studies were conducted to demonstrate that this method can be used to repeatedly sample CSF, and to show that the method is sensitive to local changes in dopaminergic activity induced by lesions, drugs or grafts. (1) Unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra produced a significant decrease in the CSF concentrations of DOPAC and HVA ipsilateral to the lesion, relative to the contralateral side or to concentrations in animals without lesions. (2) When left and right lateral ventricles were sampled simultaneously in animals with a unilateral 6-OHDA lesion, haloperidol induced an increase in DOPAC and HVA concentrations in CSF on both sides of the brain. Interestingly, the haloperidol-induced increase in CSF concentrations of DA metabolites was greater adjacent to the intact striatum of rats with unilateral 6-OHDA lesions than in animals with no lesion. (3) Finally, in animals with adrenal medulla tissue grafted into the lateral ventricle there was an increase in the CSF concentration of DOPAC compared to pregraft values or to those of animals with control grafts.

Application of serial sampling of cerebrospinal fluid in pharmacodynamic studies with a drug active in the CNS: heptabarbital concentrations at onset and offset of loss of righting reflex in rats

As cerebrospinal fluid (CSF) possesses unique characteristics in order to explore concentration-pharmacological response relationships of drugs active in the CNS, the practicability of serial sampling of CSF was tested in a study with heptabarbital. Concentrations in CSF and plasma were measured simultaneously in individual rats during and after an intravenous infusion for 30 min. At the end of the infusion, the distribution equilibrium was attained with a CSF/plasma concentration ratio of 0.38, roughly equal to the fraction unbound to protein. When concentrations in blood and CSF were determined at the onset and offset of loss of righting reflex concentrations in blood were significantly greater at onset (146 +/- 19 mg/l) than at offset (108 +/- 16 mg/l, n = 6), whereas concentrations in CSF were identical (39 +/- 5 and 38 +/- 5 mg/l, respectively). This confirmed the earlier observation that the CSF is pharmacokinetically indistinguishable from the site of action. When the duration of the loss of righting reflex was varied, concentrations of heptabarbital in CSF at onset and offset were similar, independent of the duration of the loss of righting reflex (1-5 hr). These findings demonstrate the absence of the development of acute tolerance and confirmed that no (inter)active metabolites interfered with the pharmacological response. In a total number of 26 rats the concentrations in CSF at onset and offset of loss of the righting reflex were compared. The interindividual variation was 13-15% and the intra-individual variation was only 4-6%. The results demonstrate the usefulness of serial sampling of CSF in pharmacodynamic studies with centrally acting drugs.

The effect of valproic acid on the 5-hydroxyindoleacetic, homovanillic and lactic acid levels of cerebrospinal fluid

In this study the cisternal cerebrospinal fluid (CSF) contents of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) were sequentially measured in free-moving rats which were administered 50-500 mg X kg-1 valproic acid. Animals receiving 100-500 mg X kg-1 valproic acid showed significant increases in CSF 5-HIAA and HVA content, with maximal accumulation rates of 1.80-2.10 and 0.25-0.30 nmol X ml-1 X h-1, respectively, being reached at the 250-mg X kg-1 dose. The combination of valproic acid 500 mg X kg-1 and probenecid 300 mg X kg-1 failed to increase the accumulation rates of 5-HIAA and HVA over those seen with valproic acid 500 mg X kg-1 or probenecid 300 mg X kg-1 alone. This pattern of change indicates that valproic acid and probenecid share a common site of action in blocking the clearance of 5-HIAA and HVA from CSF. The tranquillizer diazepam produced progressive increases in CSF 5-HIAA and HVA content which suggested a similar action to that of valproic acid and probenecid. The anticonvulsants phenytoin and phenobarbital produced selective increases in 5-HIAA, whereas the tranquillizer chlorpromazine produced proportionally larger increases in HVA, changes which seem to indicate a more selective effect of these drugs on the serotonergic or dopaminergic systems, respectively. Valproic acid was associated with increases in CSF lactate which occurred in the absence of similar increases of blood or tissue lactate. This indicated that valproic acid, like probenecid, can inhibit the monocarboxylic acid transport system which removes lactate from the CSF.

Probenecid-induced accumulation of 5-hydroxyindoleacetic acid and homovanillic acid in rat brain

The accumulation of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in rat brain has been examined after probenecid infusion over 8 h. At plasma probenecid concentrations of 200-400 micrograms mL-1 a steady state level in the accumulation of 5-HIAA and HVA was achieved, the increase above the endogenous levels being 135% and 65%, respectively. When the plasma concentration of probenecid rose above 400 micrograms mL-1 there was further accumulation of both 5-HIAA and HVA probably induced by increased neuronal activity or toxicity due to probenecid. The explanation for the plateau of 5-HIAA and HVA obtained over the plasma probenecid concentration interval of 200-400 micrograms mL-1 could be that the levels were reached when there was complete inhibition of active transport, and when the rate of formation of the metabolites equalled the rate of elimination by alternative routes i.e. bulk flow and diffusion. Therefore when probenecid is used to inhibit the active transport of acid monoamine metabolites across the blood-brain barrier, its plasma concentration should be within the range of 200-400 micrograms mL-1.

Monoamine metabolite levels in rat CSF: kinetic studies

The kinetics of monoamine metabolites, 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), in cisternal CSF were determined after monoamine oxidase (MAO) inhibition (pargyline, 100 mg/kg) and tyrosine hydroxylase inhibition (alpha-methyl-p-tyrosine, alpha-MPT, 250 mg/kg) in awake rats. In addition, the possibility of a peripheral contribution to CSF MHPG levels was investigated by infusing large amounts of the metabolite into vena jugularis. Pargyline induced an exponential decrease of CSF MHPG, 5-HIAA and HVA, with respective half-lives of 51, 86 and 46 min. alpha-MPT caused a slower decline of MHPG and HVA, while 5-HIAA was unaffected. Results from the MHPG-infusion experiments indicate minor peripheral contribution to CSF MHPG levels in acute pharmacological studies. The present paper gives further support for the validity of our new animal model in detecting acute changes in central monoaminergic activity.

Oxytocin in the central nervous system and sexual behaviour in male rats

Concentrations of oxytocin (OT) and vasopressin (AVP) were measured in cerebrospinal fluid (CSF) obtained from the cisterna magna of freely moving rats. Basal levels of OT and AVP were approximately 9 fmol/ml in both male and female. In the male rats this increased to approximately 18 fmol/ml 5 min after ejaculation, and 27 fmol/ml 20 min after ejaculation. No increase from basal levels occurred when males were placed with unreceptive females, or alone in the test environment. AVP levels were unchanged in any condition. Preliminary investigations indicate that discrete electrolytic lesions to the lateral and posterior parvocellular hypothalamic paraventricular nucleus (PVN) abolished this ejaculation-associated increase in CSF OT, prolonged mount and intromission latencies and reduced the absolute postejaculatory interval (PEI). We conclude that intracerebrally projecting OT systems may be activated during coitus and may contribute to the mechanisms underlying postejaculatory refractoriness.

Enhancement of brain dopamine metabolism by tyrosine during immobilisation: an in vivo study using repeated cerebrospinal fluid sampling in conscious rats

Central dopamine (DA) and 5-hydroxytryptamine (5-HT) metabolism was monitored in conscious, freely moving rats by determination of levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) in CSF samples withdrawn repeatedly from the cisterna magna and treated with acid to hydrolyse DOPAC and HVA conjugates. The effect of tyrosine on DA metabolism was investigated. Time courses of metabolite concentrations in individual rats in a quiet room showed that tyrosine (20, 50, or 200 mg/kg i.p.) was without significant effect; brain changes were essentially in agreement. However, the increases of CSF DOPAC and HVA levels that occurred on immobilisation for 2 h were further enhanced by tyrosine (200 mg/kg). The associated increases of 5-HIAA level were unaffected. The corresponding increases of DA metabolite concentrations in the brains of immobilised rats given tyrosine were less marked than the CSF changes and only reached significance for "rest of brain" DOPAC. The CSF studies revealed large interindividual variation in the magnitude and duration of the effects of immobilisation on transmitter amine metabolism. These results may help toward the elucidation of possible relationships between the neurochemical and behavioural effects of stress.

An in vivo kinetic model with L-[35S]methionine for the determination of local cerebral rates for methionine incorporation into protein in the rat

A method has been developed for the simultaneous in vivo measurement of local rates for methionine incorporation into cerebral protein in the rat. It is based on the use of L-[35S]methionine as a tracer for reflecting the bidirectional exchange of methionine between plasma and brain and its incorporation into cerebral protein, using a dynamic three-compartment model. An operational equation based on this model has been derived in terms of determinable variables. The method has been applied to the normal freely moving rat and to the rat under chloral hydrate anesthesia. In the freely moving rat, the values of methionine incorporation into cerebral protein in the gray matter vary widely from structure to structure (50-300 nmol/100 g/min), with the highest values in structures related to neurosecretory functions, e.g., supraoptic and paraventricular nuclei. The values for white matter are more uniform (24-28 nmol/100 g/min) at levels approximately six- to seven-fold lower than for gray matter. Chloral hydrate anesthesia depresses the rate of methionine incorporation in all the structures examined. Anesthesia did not reduce the heterogeneity normally present within gray matter.

Effect of probenecid on cerebral and cisternal cerebrospinal fluid lactate content

In this study, the cisternal CSF contents of lactate and glucose were sequentially measured in free-moving rats that had been administered probenecid, 200 mg/kg-1, drug diluent, or no injections. In animals receiving either no injections or injections of drug diluent, CSF lactate and glucose were constant over a 6-h period (93-106% of control), whereas rats receiving probenecid showed increased lactate at 1 and 2 h (170 and 125% control, respectively) and increased glucose at 1, 2, and 3 h (169, 141 and 129% control, respectively). Cerebral cortex content of energy metabolites and lactate and blood lactate levels were statistically unaltered at 0.5-6 h exposure to probenecid, whereas cerebral and blood glucose contents were increased after 1 and 2 h exposure to probenecid. Rats exposed to 5% O2 and probenecid for 0.5 h showed a statistically higher CSF lactate at 0.5 and 1.5 h reoxygenation (169 and 168% control, respectively). A similar effect was also seen in rats exposed to 5% O2 and the 5-hydroxyindoleacetic acid (5-HIAA) transport inhibitor Na divalproate. The results suggested that the increase in CSF glucose was secondary to a probenecid-induced elevation of blood glucose, whereas the increase in CSF lactate seemed to be secondary to a reduced rate of efflux of lactate from the CSF. It is suggested that it may be possible to increase the CSF lactate content by mechanisms that are independent of direct effects on the processes of cerebral energy metabolism.

5-HT and 5-HIAA in cerebrospinal fluid in depression

CSF 5-HT and 5-HIAA were measured in endogenously depressed patients (ICD-9) (n = 23) and controls (n = 11). Distribution of sex, age and body height was similar in the two groups. Non-parametric statistics were used. In depressed patients CSF 5-HT concentrations were found to be higher (P less than or equal to 0.01) than in controls. A further classification of the depressed patients by the Newcastle Scale showed that the highest values were found in the endogenous group compared to the non-endogenous group (P less than or equal to 0.02). CSF 5-HIAA was found to be equal in the two groups, even when pairs matched for height were compared. No relation between clinical recovery due to drug treatment and changes in CSF 5-HT was seen. Our data support a possible involvement of 5-HT in the biology of depression, but the anatomical and functional levels of a serotonin derangement are still unknown.

CSF tryptophan and transmitter amine turnover may predict social behaviour in the normal rat

Central 5-hydroxytryptamine (5-HT) and dopamine (DA) turnovers and tryptophan concentrations were estimated in individual male rats using repeated CSF withdrawal. On subsequent pairing, the major biters of each pair (neck + body bites) were predicted by their higher concentrations of the 5-HT precursor tryptophan but not by 5-HT turnover. However, bites/pair correlated highly significantly with the lower 5-HT and DA turnover values in each pair. The investigation illustrates a new and flexible approach to the neurochemistry of social behaviour.

Monitoring 5HT metabolism in the brain of the freely moving rat

The techniques of repeated CSF withdrawal and intracerebral dialysis are described. They were used to monitor 5HT metabolism in the brains of freely moving rats. Evidence indicates that results obtained proportionately reflect changes of 5HT metabolism in whole brain (CSF method) and in the striatum (intracerebral dialysis). The potential value of the methods is illustrated by two behavioral studies. The first suggested that 5HT turnover values (determined two weeks prior to behavioral testing by the CSF method) were predictive for neck + body biting in a social interaction test. The second study showed a consistent pattern of change of hypothalamic dialysate 5HIAA concentration associated with feeding in rats on a restricted food intake schedule.

Effects of yohimbine and idazoxan on monoamine metabolites in rat cerebrospinal fluid

Effects of two alpha 2-adrenoceptor antagonists, idazoxan and yohimbine, on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were investigated. Both drugs caused a dose-dependent, up to 250% increase in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) in CSF indicating enhanced release, metabolism and turnover of noradrenaline in the central nervous system (CNS). In addition, a similar increase in homovanillic acid (HVA) in CSF was observed, while the level of 5-hydroxyindoleacetic acid was unchanged. The present results demonstrate the usefulness of monitoring drug-induced alterations in noradrenergic activity in the CNS by measurement of free MHPG in repeatedly collected cisternal CSF samples from awake rats. The possibility that the observed increase in the concentration of HVA after the highly specific alpha 2-antagonist idazoxan reflects increased noradrenergic rather than dopaminergic neuronal activity is discussed.

A method for repeated CSF sampling in the freely moving rat

With the use of a holder mounted on the skull of rats, a cannula can be implanted so that one end rests on the atlanto-occipital membrane overlying the cisterna magna. Needles introduced through the cannula allow repeated access to the cisterna magna in the freely moving animal. This system is stable for periods of up to 4 weeks and is suited for repeated sampling of the cerebrospinal fluid.