A simple method for obtaining chronic cerebrospinal fluid samples from awake rats

Inhibition of Post-Meningitic Cochlear Injury with Cerebrospinal Fluid Irrigation

OBJECTIVE: Labyrinthitis ossificans, the pathologic ossification of the otic capsule associated with profound deafness and loss of vestibular function occurs frequently as a sequella of bacterial meningitis and subsequent purulent labyrinthitis. Experimentally, in Streptococcus pneumoniae meningitis, it has been shown that a vigorous inflammatory response to teichoic acids in the bacterial cell wall contributes to cochlear damage and subsequent fibrosis and ossification. The hypothesis of this study is that a dilution of concentration of inflammatory mediators through cerebrospinal fluid (CSF) irrigation will lead to a reduction in both inner ear pathology and permanent hearing loss.

STUDY DESIGN AND SETTING: Auditory brainstem response testing was used to determine baseline hearing thresholds in 20 Mongolian gerbils (12 irrigated, 8 sham irrigated animals) at 32 kHz, 16 kHz, 8 kHz, and 4 kHz frequencies. Their thresholds at 14 days and 120 days post-procedure were also obtained. Streptococcus pneumoniae meningitis was induced in both groups of animals by intrathecal (i.t.) injection of bacteria. Both groups received penicillin treatment. Forty-eight hours after inoculation, both groups were implanted with i.t. inflow and outflow catheters. The irrigated group was infused continuously with artificial CSF over 36 hr at a rate of 70 μL/hr and the outflow sampled. The tubing in the sham irrigated group was clamped (without sampling). They were sacrificed at 120 days post-procedure and histomorphometric analysis carried out. The concentration of interleukin 1β (IL-1β) for the CSF samples from the irrigated group were compared to samples collected from an additional control group of 8 non-irrigated meningitic gerbils. IL-1β was chosen to study because it is a potent pro-inflammatory cytokines in bacterial meningitis that is unaffected by the neurosurgical trauma of the experimental protocol.

RESULTS: Twenty animals survived the meningitis (6 irrigation, 6 sham irrigation, 8 non-irrigation meningitic controls). At Days 14 and 120 post-infection, the irrigated animals manifested significantly less hearing loss with a mean loss of 28.82 dB compared to the sham irrigation group mean loss of 40.76 dB ( P < 0.03). The degree of hearing loss in both groups was frequency-dependent with greater loss at higher frequencies (mean loss = 22.4 dB at 32 kHz, 23.0 dB at 16 kHz, 18.6 dB at 8 kHz, and 12.5 dB at 4 kHz). Histomorphometric analysis demonstrated a marked reduction in degeneration of the spiral ligament, spiral ganglion cells, and stria vascularis in experimental animals as compared to controls. Immunohistochemistry showed a significant reduction in IL-β1 concentrations in the irrigated animals compared to the non-irrigated, infected controls ( P < 0.03).

CONCLUSIONS: Irrigation of CSF resulted in a significant reduction in post-meningitic cochlear injury when compared to controls. This model for continuous cerebrospinal fluid irrigation provides a means to evaluate the effects of a dilution of inflammatory mediators on hearing loss and labyrinthitis ossificans after bacterial meningitis.

SIGNIFICANCE: Despite advances in the prevention of meningitis and improved antibiotic treatment, bacterial meningitis continues to have significant associated morbidity. This study provides insight into some of the mechanisms responsible for post-meningitic hearing loss and labyrinthitis ossificans and presents a novel approach to reduce these complications.

EBM rating: C-4

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.

Transcutaneous Cisternal Puncture for Sampling of Cerebrospinal Fluid in Awake Rat

Reported cisternal puncture methods require the anesthetization and fixation of an animal within a stereotaxic frame. To determine the effect of anesthesia and animal fixation on the central nervous system (CNS), amino acid concentrations of cerebrospinal fluid (CSF) sampled by transcutaneous cisternal puncture were compared among awake rats, pentobarbital-anesthetized rats and pentobarbital-anesthetized rats fixed in a stereotaxic frame. Although the concentrations of many amino acids in the CSF of pentobarbital-anesthetized rats were lower than in awake rats, use of the stereotaxic frame resulted in significantly increased amino acid concentrations in the CSF. These data indicate that CSF sampling by transcutaneous cisternal puncture from awake rats is a suitable method for serial measurement of drug effects on the CNS.

Induction of brain glucose uptake by a factor secreted into cerebrospinal fluid

It is well established that the carotid body receptors (CBR), at the bifurcation of the carotid artery, inform the brain of changes in the concentration of CO(2) and O(2) in arterial blood. More recent work suggests that these receptors are also extremely sensitive to blood glucose levels suggesting that they may play an important role as sensors of blood components important for brain energy metabolism. Much less is known about changes in brain glucose metabolism in response to CBR activation. Here we show that 2-8 min after local injection of sodium cyanide (NaCN) into the CBR or after electrical stimulation of the carotid sinus nerve in dogs and rats, brain glucose uptake increased fourfold. Cerebrospinal fluids (CSF) transferred from dogs, 2-8 min after CBR stimulation, into the cisterna magna of non-stimulated dogs or rats induced a similar increase in brain glucose uptake. CSF from stimulated dogs was also active when injected intravenously in anesthetized or awake rats. The activity was destroyed when the stimulated CSF was heated to 100 degrees C or treated with trypsin. We conclude that a peptide important for brain glucose regulation appears in the CSF shortly after CBR stimulation.

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.

Adenosine in the central nervous system: release mechanisms and extracellular concentrations

Adenosine has several functions within the CNS that involve an inhibitory tone of neurotransmission and neuroprotective actions in pathological conditions. The understanding of adenosine production and release in the brain is therefore of fundamental importance and has been extensively studied. Conflicting results are often obtained regarding the cellular source of adenosine, the stimulus that induces release and the mechanism for release, in relation to different experimental approaches used to study adenosine production and release. A neuronal origin of adenosine has been demonstrated through electrophysiological approaches showing that neurones can release significant quantities of adenosine, sufficient to activate adenosine receptors and to modulate synaptic functions. Specific actions of adenosine are mediated by different receptor subtypes (A(1), A(2A), A(2B) and A(3)), which are activated by various ranges of adenosine concentrations. Another important issue is the measurement of adenosine concentrations in the extracellular fluid under different conditions in order to know the degree of receptor stimulation and understand adenosine central actions. For this purpose, several experimental approaches have been used both in vivo and in vitro, which provide an estimation of basal adenosine levels in the range of 50-200 nM. The purpose of this review is to describe pathways of adenosine production and metabolism, and to summarize characteristics of adenosine release in the brain in response to different stimuli. Finally, studies performed to evaluate adenosine concentrations under physiological and hypoxic/ischemic conditions will be described to evaluate the degree of adenosine receptor activation.

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.

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.

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.

In vivo study of the elimination from rat brain of an intracerebrally formed xenobiotic metabolite, 1-naphthyl-beta-D-glucuronide

Among the drug-metabolizing enzymes present in the rat brain, one form of UDP-glucuronyltransferase catalyzes the formation of the polar metabolite 1-naphthyl-beta-D-glucuronide from 1-naphthol. We measured the activity of this isoform in different brain regions and showed its heterogeneous distribution. Conjugation activities were found to be the highest in the olfactory bulbs (25.4 nmol/h/mg protein) and lowest in the cerebellum (4.5 nmol/h/mg protein). As the blood-brain barrier prevents the passage of hydrosoluble molecules, we studied in vivo the characteristics of the efflux of labeled 1-naphthyl-beta-D-glucuronide injected into the lateral ventricle and the cortex tissue, using tritiated water and labeled inulin as reference compounds. The results reported here indicate that intracerebrally formed glucuronide is cleared from brain tissue by both diffusion and a saturable efflux process.

Pharmacological analysis of the enhanced pressor response to central cholinergic stimulation in spontaneously hypertensive rats

Central cholinergic pressor neurons exist at several levels of the neuraxis. Activation of these neurons in spontaneously hypertensive rats (SHR) can lead to an exaggerated hypertensive response when compared with normotensive control animals (WKY). Our earlier studies demonstrated that intravenous injection of the indirect acting agonist physostigmine, but not the direct agonist arecoline, resulted in an exaggerated pressor response in SHR. The purpose of this study was to determine whether discrete injection of cholinergic agonists directly into the CNS would also result in an exaggerated pressor response in SHR. Cholinergic pressor neurons in the posterior hypothalamus may be activated following injection of cholinergic agonists into the lateral cerebral ventricles (l.c.v. injection). Cholinergic pressor neurons in the medulla may be activated following injection of agonists into the cisterna magna (i.c. injection). L.c.v. injection of arecoline in freely-moving animals evoked a pressor response in both SHR and WKY rats that was not significantly different between the two strains. Prior depletion of brain acetylcholine with hemicholinium-3 did not affect the pressor response to l.c.v. arecoline, confirming the postsynaptic site of action of the agonist. Surprisingly, l.c.v. injection of physostigmine also did not result in an exaggerated pressor response in SHR. In contrast, injection of physostigmine into the cisterna magna did produce an enhanced hypertensive response in SHR compared to WKY rats. These results are consistent with the presence of two cholinergic pressor systems; however, only the medullary cholinergic system appears to play a prominent role in spontaneous hypertension. Also the hypothalamic (rostral) cholinergic system does not appear to directly interact with the caudal system.

Participation of different brain regions in the anti-narcotic withdrawal action of clonidine in the dependent rat

The naloxone-precipitated withdrawal response in morphine dependent rats was quantitated by measuring the post-withdrawal increase in mean arterial pressure (MAP), heart rate and several characteristic behavioral changes. Pretreatment with intrathecal injection of clonidine produced a significant reduction in most of the autonomic symptoms of withdrawal, including the increase in MAP, salivation, and chromodacryorrhea, but did not effect the behavioral signs, body shakes, escape attempts or teeth chattering. Central i.c.v. injection of clonidine also reduced the autonomic symptoms of withdrawal. Two differences between the two routes of clonidine administration were with respect to (1) the degree of hind limb kicking where i.t., but not i.c.v. administration was effective at reducing this symptom; and (2) i.c.v., but not i.t. clonidine was effective in significantly reducing the incidence of diarrhea. In contrast, intracisternal (medullary level) injection of clonidine was without effect on the post-withdrawal increase in MAP, and inhibitory effects on the other symptoms included only salivation and diarrhea. Thus the effect of clonidine following intrathecal injection was not due to redistribution of drug to higher centers. Direct intrathecal injection of naloxone also precipitated withdrawal in morphine dependent rats. In this case, intrathecal pretreatment with clonidine did not inhibit the post-withdrawal increase in MAP. These results are consistent with a spinal component for the autonomic and behavioral symptoms of morphine withdrawal in the rat. Clonidine's antiwithdrawal response in mediated at least in part through a spinal action. However, this spinal antiwithdrawal action of clonidine is selective for withdrawal responses which originate from supraspinal centers.

Modification of spino-bulbar autonomic cholinergic systems by activation of alpha-adrenergic receptors

Intrathecal (i.t.) injection of neostigmine was employed to activate spinal cholinergic neurons mediating a hypertensive response in freely-moving rats. Our earlier studies have demonstrated that stimulation of central alpha-adrenergic receptors inhibits the pressor response following inhibition of brain cholinesterase. Clonidine (0.5-5 micrograms) pretreatment by i.t. injection did not alter the magnitude of the pressor response to i.t. injection of neostigmine, but did significantly delay the onset of the response. Since systemic administration of clonidine abolished the pressor response to i.t. neostigmine, clonidine was administered by the intracisternal (i.c.) route to determine whether higher centers mediated the inhibitory response. In this situation, clonidine pretreatment significantly inhibited the pressor response to i.t. injection of neostigmine. I.t. injection of norepinephrine (1-10 micrograms) was more effective, but i.c. pretreatment less effective than clonidine in inhibiting the pressor response to i.t. neostigmine. In order to confirm the ascending nature of the spinal cholinergic system, hemicholinium-3 was injected i.c. to deplete medullary levels of acetylcholine. Carbachol was then injected i.t. (since carbachol is a direct-acting agonist, it is not affected by local depletion of acetylcholine). Depletion of medullary acetylcholine significantly blocked the pressor response to i.t. injection of carbachol. These findings are consistent with the concept of an ascending spinal cholinergic pressor pathway. The pressor response to activation of spinal cholinergic receptors is not sensitive to local injection of clonidine, but, the medullary cholinergic component of the system is inhibited by alpha-receptor stimulation.

The levels of somatostatin in the brain and CSF of rat after carbamazepine administration

Previous studies have suggested that carbamazepine (CBZ), a potent antiepileptic drug, affects the somatostatinergic system in humans and animals; but the results have been contradictory. In the present study we further evaluated the effect of CBZ administration on somatostatin-like immunoreactivity (SLI) in cisternal cerebrospinal fluid (CSF) and in different areas of the rat brain. Somatostatin receptor binding in the cortex of CBZ-treated rats was also studied. Two hours after administration of CBZ at a dose of 30 mg/kg intraperitoneally, which resulted in a serum CBZ concentration of 64 microM, the SLI in CSF was lower than in vehichle-injected controls (P = 0.024, MANOVA). In the hippocampus SLI was elevated to 132% that of vehicle-injected controls (P = 0.016, Mann-Whitney U-test). At a dose of 15 mg/kg a slight decrease in SLI was seen in CSF compared to vehicle-injected controls (P = 0.034, MANOVA) but no change was observed in the hippocampus. After administration of CBZ for 7 days (30 mg/kg intraperitoneally twice a day) we were not able to demonstrate any definitive change in SLI of rat CSF (MANOVA). In these rats the SLI in the hypothalamus was elevated compared to vehicle-injected controls (132%, P = 0.016, Mann-Whitney U-test). In experiments with both acute and chronic administration of CBZ, the somatostatin receptor binding was unchanged. The present study suggests that administration of CBZ only slightly affects the somatostatinergic system in the rat brain.

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.

Avian cerebrospinal fluid: repeated collection and testing for a possible role in food intake regulation

The objective of this study was to determine if a factor(s) involved in the regulation of food intake exists in the cerebrospinal fluid (CSF) of the domestic fowl. A technique was developed that allows blood-free CSF samples to be collected repeatedly from the cisterna magna for up to 6 weeks. Using this technique, CSF was collected from free-feeding and 24-hour fasted broiler cockerels and injected into the lateral cerebral ventricle of 8-week old Leghorn cockerels and 4-week old broiler cockerels. The free-feeding birds received 10 microliter intracerebroventricular injections of CSF either at normal concentration (1 X -CSF) (Experiments 1 and 3) or at four times normal concentration (4 X-CSF) (Experiments 2 and 4). Artificial CSF served as the control. Food and water consumption were monitored following injection. The 1 X- and 4 X-CSF collected from both the free-feeding and 24-hour fasted donors did not affect the food intake of either the Leghorn or the broiler recipients. Water intake, however, was significantly increased in the Leghorns and broilers receiving the 4 X-CSF collected from 24-hour fasted birds. Thus, there does not appear to be a factor(s) present in the CSF collected from the cisterna magna that alters food intake when injected into the lateral ventricle, but a factor may exist in the CSF collected from fasted donors that stimulates water intake.

A technique for repeated sampling of CSF from the anesthetized rat

A method for repeatedly sampling cerebrospinal fluid (CSF) from anesthetized rats is described. The technique reliably and quickly yields blood-free samples of CSF and requires supplies that are commonly available. Samples as large as 250 microliter can be collected in a few minutes. There is no apparent malaise even when CSF is withdrawn once every three days for two weeks. This technique offers an alternative to surgical cannulation for sampling of CSF from the rat.

3,4-Dihydroxyphenylethylamine and 5-hydroxytryptamine metabolism in the rat: acidic metabolites in cisternal cerebrospinal fluid before and after giving probenecid

3,4-Dihydroxyphenylethylamine (DA, dopamine) and 5-hydroxytryptamine (5-HT) turnover values were determined in freely moving male rats by measuring the rates of accumulation of the acidic metabolites of the above transmitters, i.e., 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in cisternal cerebrospinal fluid (CSF) samples after probenecid (200 mg/kg i.p.) administration. Determinations on samples before and after acid hydrolysis showed that the latter procedure was necessary for DA turnover determination. Thus whereas total (DOPAC + HVA) increased linearly with time after probenecid, free (DOPAC + HVA) did not. This was because the percentage of DOPAC + HVA in conjugated form increased with time. Determinations on a group of 28 rats during the dark (red light) period showed that cisternal amine metabolite concentrations before probenecid injection did not parallel turnover values. This was probably because individual differences in metabolite egress strongly affect the pre-probenecid values. The poor correlations between CSF tryptophan and 5-HT turnover suggested that differences of brain tryptophan concentration were not major determinants of differences of brain 5-HT metabolism within this group of normal rats. Considering that the rats were of similar weight and that the turnover values were all determined at approximately the same time of day, the three- to fourfold ranges of the turnover values are remarkable. The positive correlation between the DA and 5-HT turnovers of individual rats suggests the existence of common effects on DA and 5-HT turnover in normal rats.

Pro-opiocortin peptides in rat cerebrospinal fluid

Cerebrospinal fluid (CSF) taken from rats implanted with chronic cisternal cannulae was subjected to gel filtration chromatography on Sephadex G-50. Fractions were monitored using radioimmunoassays for N-terminal pro-opiocortin (N-POC), gamma 3-melanotropin (gamma 3-MSH), C-terminal adrenocorticotropin (C-ACTH), alpha-endorphin, beta-endorphin, gamma-lipotropin (gamma-LPH) and alpha-MSH. Two peaks which corresponded in elution position to rat N-POC (1-74) and gamma 3-MSH were detected. The major C-ACTH-immunoreactive (IR) peak was found to correspond to 14k ACTH. While no alpha-endorphin immunoreactivity was detected in rat CSF, three beta-endorphin-IR peaks were identified in positions expected for beta-LPH, beta-endorphin (1-31) and beta-endorphin (1-27), as well as a major peak of activity with the elution characteristics and cross-reactivity of rat gamma-LPH. HPLC of the alpha-MSH-IR material in rat CSF revealed the presence of a major peak of immunoreactivity whose retention time did not correspond to the known oxidised and reduced forms of alpha-MSH and its desacetylated and diacetylated derivatives. The identity of this peak is unknown.

Pro-enkephalin peptides possessing Met-enkephalin-Arg6-Gly7-Leu8-immunoreactivity in rat CSF, striatum and adrenal gland

Cerebrospinal fluid (CSF) taken from rats implanted with chronic cisternal cannulae and extracts prepared from rat adrenal gland and striatum were subjected to Sephadex G-50 chromatography and HPLC. Fractions were monitored using specific radioimmunoassays (RIA) for the pentapeptide methionine enkephalin (Met-Enk) and methionine enkephalin-Arg6-Gly7-Leu8 (Met-EnkRGL). In rat CSF, striatum and adrenal gland, three Met-EnkRGL-immunoreactive (IR) peaks of Mrs 8000, 5000 and 1000 daltons were detected. The same peaks were also found to possess Met-Enk-immunoreactivity after enzyme digestion of Sephadex G-50 fractions with trypsin and carboxypeptidase B (CPB), suggesting their derivation from proenkephalin. HPLC of the 8K and 5K peaks on a column of Ultrapore RPSC showed them to elute discretely with similar retention times, indicative of hydrophobic peptides of large molecular weight. Their similar hydrophobicities yet significant separation during gel filtration would suggest that the 8K and 5K peptides are structurally closely related yet different with respect to their molecular weights. HPLC of the small molecular weight material from rat striatum and adrenal gland revealed the presence of Met-EnkRGL and Met-EnkRGL sulphoxide in both tissues. In rat striatum Met-Enk and its sulphoxide were also detected. The oxidised pentapeptide was found to be present in rat CSF, together with two unidentified small molecular weight Met-Enk-IR peaks detected without prior enzyme digestion of fractions. The small molecular weight Met-EnkRGL-IR material in rat CSF was found to be comprised of two unknown peptides which were less hydrophobic than Met-EnkRGL and its sulphoxide derivative.

Endorphin-related peptides in rat cerebrospinal fluid

Cerebrospinal fluid (CSF) samples were taken from rats implanted with chronic cisternal cannulae and assayed for methionine-enkephalin, beta-endorphin and corticotropin (ACTH). Immobilization stress had little apparent effect on immunoreactive levels of the peptides in the CSF. Gel chromatographic analysis of the beta-endorphin- and ACTH-immunoreactive profiles in rat CSF revealed several peaks. beta-Endorphin-immunoreactive peaks were present at the expected positions of pro-opiocortin, beta-lipotropin and beta-endorphin. ACTH-immunoreactive peaks eluted at positions corresponding to pro-opiocortin, the 20-23K ACTH biosynthetic intermediate, 14K ACTH, and 4.5K ACTH. These results suggest that rat CSF contains peptides of the pro-opiocortin family similar to those previously described in rat pituitary.