Ultrasound-assisted collection of cerebrospinal fluid from the lumbosacral space in equids

OBJECTIVE

To describe ultrasonographic landmarks for use in collection of CSF from the lumbosacral region in equids.

DESIGN

Prospective study.

ANIMALS

37 equids (27 with neurologic disease and 10 with nonneurologic disease).

PROCEDURES

Standing equids (n = 17) were sedated with detomidine hydrochloride (0.006 to 0.01 mg/kg [0.003 to 0.005 mg/lb], IV) followed by butorphanol tartrate (0.01 mg/kg, IV) and restrained with a nose twitch for collection of CSF. The CSF was collected from 20 laterally recumbent equids (10 sedated and 10 immediately after euthanasia). Anatomic landmarks were identified ultrasonographically. Height at the dorsal point of the shoulders, body weight, depth of the spinal needle, number of attempts to collect CSF, and cytologic evaluation of CSF were recorded.

RESULTS

Lumbosacral puncture cranial to the cranial border of the most superficial location of both tuber sacrale along the midline was consistently successful for CSF collection (35/37 equids). Two horses had anatomic abnormalities that precluded CSF collection. Mean number of attempts to collect CSF per animal was 1.1. Height and body weight were strongly correlated with needle depth for CSF collection. Pelvic and sacral displacement was observed in several laterally recumbent animals, which resulted in discrepancies of the midline between the cranial and caudal aspects of the vertebral column. In most equids, the spinal needle was aligned on the midline of the caudal aspect of the vertebral column.

CONCLUSIONS AND CLINICAL RELEVANCE

Ultrasonography was a useful aid for collection of CSF from the lumbosacral space and decreased the risk of repeated trauma and contamination in equids.

Evaluation of nephelometry for albumin measurement in serum and cerebrospinal fluid: experiences with an indwelling subarachnoidal catheter system for repetitive cerebrospinal fluid collection in horses

The measurement of albumin concentrations in cerebrospinal fluid (CSF) and serum for albumin quotient (AQ) calculations in normal horses was performed by 2 methods: 1) total protein measurement, followed by electrophoresis of the samples to obtain an albumin percentage; and 2) albumin immunoprecipitation quantitated by nephelometry. The results of both methods correlated well, and nephelometry was chosen to determine the albumin concentrations in CSF samples obtained from an indwelling subarachnoidal catheter for daily sampling. Because the use of an indwelling catheter to collect repetitive CSF samples is a novel technique, routine cytological CSF analysis was performed along with daily clinical evaluation to ascertain the well-being of the horses. The catheters were placed in 2 horses for periods of 14 and 17 days. One horse exhibited pleocytosis on cytological evaluation of CSF on 2 occasions for a 1-2-day duration; however, the AQ showed a significant increase on only 1 occasion. The other horse had a normal cell count in CSF but showed 2 sudden changes in the AQ value; however, these values remained within the 95% confidence interval for AQ in horses. Albumin quotient values of the second horse were consistently below the lower range of the confidence interval. Results from this study indicate that nephelometry can be used for albumin determination in serum and CSF samples from horses. Furthermore, an indwelling subarachnoidal catheter system can provide serial CSF samples in horses, thus obviating the need for repetitive centesis for serial CSF sampling.

Cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture

OBJECTIVE

To determine cutaneous analgesia, hemodynamic and respiratory effects, and beta-endorphin concentration in spinal fluid and plasma of horses after acupuncture and electroacupuncture (EA).

ANIMALS

8 healthy 10- to 20-year-old mares that weighed between 470 and 600 kg.

PROCEDURE

Each horse received 2 hours of acupuncture and 2 hours of PAES at acupoints Bladder 18, 23, 25, and 28 on both sides of the vertebral column as well as sham needle placement (control treatment). Each treatment was administered in a random order. At least 7 days elapsed between treatments. Nociceptive cutaneous pain threshold was measured by use of skin twitch reflex latency (STRL) and avoidance to radiant heat (< or = 50 degrees C) in the lumbar area. Skin temperature, cardiovascular and respiratory variables, and beta-endorphin concentration in spinal fluid (CSF-EN) and plasma (plasma-EN) were measured.

RESULTS

Acupuncture and PAES significantly increased STRL and skin temperature. The CSF-EN was significantly increased from baseline values 30 to 120 minutes after onset of PAES, but it did not change after acupuncture and control treatments. Heart and respiratory rates, rectal temperature, arterial blood pressure, Hct, total solids and bicarbonate concentrations, base excess, plasma-EN, and results of blood gas analyses were not significantly different from baseline values after acupuncture, PAES, and control treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of PAES was more effective than acupuncture for activating the spinal cord to release beta-endorphins into the CSF of horses. Acupuncture and PAES provided cutaneous analgesia in horses without adverse cardiovascular and respiratory effects.

Characterization of lipoproteins in cerebrospinal fluid of mares during pregnancy and lactation

OBJECTIVE

To measure apolipoproteins in cerebrospinal fluid (CSF) from healthy mares and to determine whether CSF concentrations of apolipoproteins change during pregnancy and lactation.

ANIMALS

5 healthy pregnant mares.

PROCEDURE

2 sets of CSF samples were obtained; initial samples were obtained 10 to 30 days before parturition (mean, 18 days; median, 17 days), and second samples were obtained 19 to 26 days after parturition (mean, 23 days; median, 23 days). Cerebrospinal fluid was collected from the lumbosacral subarachnoid space of standing horses by use of routine collection techniques. Cerebrospinal fluid cholesterol concentrations were measured by use of a sensitive enzymatic assay. Ultracentrifugal fractions of CSF lipoproteins were characterized by determining the distribution of apolipoproteins, using polyacrylamide gel electrophoresis.

RESULTS

Analyses of isolated ultracentrifugal fractions by polyacrylamide gel electrophoresis revealed 2 apolipoproteins, with the expected molecular weights for apolipoprotein E and apolipoprotein A-I. No significant differences were observed between pre- and postpartum values in mares. The concentration of cholesterol in CSF fluid of mares was comparable to values reported in other mammals.

CONCLUSIONS AND CLINICAL RELEVANCE

Apolipoprotein E in CSF of horses is a major apolipoprotein associated with high-density lipoproteins, which is similar to findings in other mammals. Additional characterization of the role of apolipoproteins in mammalian CSF may provide critical insight into various degenerative neurologic disease processes.

Cerebrospinal fluid and serum concentrations of ponazuril in horses

Ponazuril was administered orally to 10 adult horses at 5 mg/kg body weight, once a day for 28 days. Blood was collected once a week from each horse from Days 0 through 35, daily from Days 35 through 42, and on Day 49. Cerebrospinal fluid (CSF) was also collected once a week from Day 0 through Day 49. Concentrations of ponazuril in the serum and CSF were determined, and pharmacokinetic calculations were performed. Ponazuril was readily absorbed following oral administration; and after 7 days of dosing, the serum concentration was 4.33 +/- 1.10 mg/L, and the mean CSF concentration was 0.162 +/- 0.05 mg/L. Cerebrospinal fluid concentration did not vary during the 28 days of dosing and concentrations declined rapidly after cessation of administration on Day 28. The terminal elimination half-life ofponazuril in serum (using Day 28 to 42 results) was 4.3 +/- 0.6 days. Repeated CSF collections from the atlanto-occipital space did not induce changes in the immunoglobulin G index or albumin quotient. It was concluded that oral administration of ponazuril to healthy horses at 5 mg/kg provided concentrations of ponazuril in the CSF that are presumed to be adequate for the treatment of equine protozoal myeloencephalitis (EPM). These results indicate that this dosage rate should be investigated for efficacy against EPM.

Differences in total protein concentration, nucleated cell count, and red blood cell count among sequential samples of cerebrospinal fluid from horses

OBJECTIVE

To examine total protein concentration and cell counts of sequentially collected samples of CSF to determine whether blood contamination decreases in subsequent samples and whether formulas used to correct nucleated cell count and total protein concentration are accurate.

DESIGN

Case series.

ANIMALS

22 horses.

PROCEDURE

For each horse, 3 or 4 sequential 2-ml samples of CSF were collected from the subarachnoid space in the lumbosacral region into separate syringes, and blood was obtained from the jugular vein. Total protein concentration, nucleated cell count, and RBC counts were determined in all samples.

RESULTS

Among 3 sequential samples, total protein concentration and RBC count were significantly lower in samples 2 and 3, compared with sample 1. Nucleated cell count was significantly lower in sample 3, compared with sample 1. Among 4 sequential samples, total protein concentration and RBC count were significantly lower in samples 2, 3, and 4, compared with sample 1. Nucleated cell count was significantly lower in samples 3 and 4, compared with sample 1. For 3 correction formulas, significant differences in corrected values for nucleated cell count and total protein concentration were detected between sample 1 and sample 3 or 4.

CONCLUSIONS AND CLINICAL RELEVANCE

Because iatrogenic blood contamination decreases in sequential CSF samples, a minimum of 3 samples should be collected before submitting the final sample for analysis. Formulas to correct nucleated cell count and total protein concentration are inaccurate and should not be used to correct for blood contamination in CSF samples.

Study of intragastric administration of doxycycline: pharmacokinetics including body fluid, endometrial and minimum inhibitory concentrations

The objectives of this study were to determine the pharmacokinetics and tissue concentrations of doxycycline after repeated intragastric administration, and to determine the minimum inhibitory concentrations (MIC) for equine pathogenic bacteria. In experiment 1, 2 mares received a single intragastric dose of doxycycline hyclate (3 mg/kg bwt). Mean peak serum concentration was 0.22 microg/ml 1 h postadministration. In experiment 2, 5 doses of doxycycline hyclate (10 mg/kg bwt), dissolved in water, were administered to each of 6 mares via nasogastric tube at 12 h intervals. The mean +/- s.e. peak serum doxycycline concentration was 0.32+/-0.16 microg/ml 1 h after the first dose and 0.42+/-0.05 microg/ml 2 h after the fifth dose. The mean trough serum concentrations were > 0.16 microg/ml. Highest mean synovial concentration was 0.46+/-0.13 microg/ml and highest mean peritoneal concentration was 0.43+/-0.07 microg/ml, both 2 h after the fifth dose. Highest urine concentration was mean +/- s.e. 145+/-25.4 microg/ml 2 h after the last dose. Highest endometrial concentration was mean +/- s.e. 1.30+/-0.36 microg/ml 3 h after the fifth dose. Doxycycline was not detected in any of the CSF samples. Mean +/- s.e. Vd(area) was 25.3+/-5.0 l/kg and mean t1/2 was 8.7+/-1.6 h. In experiment 3, minimum inhibitory concentrations of doxycycline were determined for 168 equine bacterial culture specimens. The MIC90 was < or = 1.0 microg/ml for Streptococcus zooepidemicus and 0.25 microg/ml for Staphylococcus aureus. Based on drug concentrations achieved in the serum, synovial and peritoneal fluids and endometrial tissues and MIC values determined in the present study, doxycycline at a dose of 10 mg/kg bwt per os every 12 h may be appropriate for the treatment of infections caused by susceptible (MIC < 0.25 microg/ml) gram-positive organisms in horses.

Cerebrospinal fluid and blood concentrations of toltrazuril 5% suspension in the horse after oral dosing

Toltrazuril 5% suspension (Baycox, Bayer Canada, Ontario, Canada) was administered to six adult horses followed by blood collection and assay to determine the concentration of toltrazuril and its principal metabolites, toltrazuril sulfone and toltrazuril sulfoxide. From this data, the maximum concentration (C(max)), elimination half-life (T 1/2), and mean residence times of the plasma were determined from standard pharmacokinetic formulas. After a single oral dose of 10 mg/kg body weight a rapid absorption was found, with a mean peak serum concentration of 11.17 mg/L at 18 hours. Elimination was prolonged, with a mean T 1/2 for elimination of 61.4 hours. In addition, toltrazuril was administered to nine horses, and blood serum and cerebrospinal fluid (CSF) concentrations of toltrazuril and its principal metabolites were determined. Horses were randomly assigned to one of three treatment groups and received either 2.5 mg/kg body weight (Group A), 5.0 mg/kg body weight (Group B), or 7.5 mg/kg body weight (Group C) orally, once daily, for 10 days. Jugular venous blood was collected routinely on treatment days 2, 6, and 10, and CSF was collected on treatment day 10. Assay of toltrazuril and its metabolites revealed a dose-dependent effect within both the blood and CSF compartments. Mean concentrations within the CSF after 10 days of treatment were 0.146 mg/L in Group A, 0.190 mg/L in Group B, and 0.386 mg/L in Group C. Toltrazuril sulfone was the primary metabolite after 10 days of treatment, with concentrations that ranged from 39% to 116% of the parent drug in individual animals. Toltrazuril sulfone was also the predominant metabolite in the serum at treatment day 10; however, it did not always exceed the concentration of toltrazuril sulfoxide in the serum on treatment day 2. In the serum, drug concentrations at treatment day 2 were variable in the low-dose group (Group A), ranging from 4.0 to 11.61 mg/L; less variable in the high-dose group (Group C), ranging from 9.9 to 10.46 mg/L; and intermediate in Group B. This study confirms that toltrazuril is absorbed in the horse after oral administration and reaches effective in vitro concentrations within the CSF of the horse after once-daily dosing of 5 or 7.5 mg/kg. Although these data suggest that toltrazuril may have clinical value in the treatment of equine protozoal myeloencephalitis, clinical efficacy remains to be confirmed using appropriate methods. Effective in vitro concentrations are known; however, therapeutic concentrations in vivo have not been established. Further research in this area is needed to determine various drug values in the CSF (e.g., half-life, C(max), time to reach steady state).

Diclazuril in the horse: its identification and detection and preliminary pharmacokinetics

Diclazuril (4-chlorophenyl [2,6-dichloro-4-(4,5-dihydro-3H-3,5-dioxo-1,2,4-triazin-2-yl)pheny l] acetonitrile), is a benzeneacetonitrile antiprotozoal agent (Janssen Research Compound R 64433) marketed as Clinacox . Diclazuril may have clinical application in the treatment of Equine Protozoal Myeloencephalitis (EPM). To evaluate its bioavailability and preliminary pharmacokinetics in the horse we developed a sensitive quantitative high-pressure liquid chromatography (HPLC) method for diclazuril in equine biological fluids. MS/MS analysis of diclazuril in our HPLC solvent yielded mass spectral data consistent with the presence of diclazuril. After a single oral dose of diclazuril at 2.5 g/450 kg (as 500 g Clinacox), plasma samples from four horses showed good plasma concentrations of diclazuril which peaked at 1.077 +/- 0.174 microg/mL (mean +/- SEM) with an apparent plasma half-life of about 43 h. When this dose of Clinacox was administered daily for 21 days to two horses, mean steady state plasma concentrations of 7-9 microg/mL were attained. Steady-state levels in the CSF ranged between 100 and 250 ng/mL. There was no detectable parent diclazuril in the urine samples of dosed horses by HPLC or by routine postrace thin layer chromatography (TLC). These results show that diclazuril is absorbed after oral administration and attains steady-state concentrations in plasma and CSF. The steady state concentrations attained in CSF are more than sufficient to interfere with Sarcocystis neurona, whose proliferation is reportedly 95% inhibited by concentrations of diclazuril as low as 1 ng/mL. These results are therefore entirely consistent with and support the reported clinical efficacy of diclazuril in the treatment of clinical cases of EPM.

The effects of equivalent doses of tromethamine or sodium bicarbonate in healthy horses

OBJECTIVE

To describe the effects of tromethamine, a putative treatment for metabolic acidosis, and to compare its biochemical effects with those of sodium bicarbonate.

DESIGN

Randomized intervention study with repeated measures.

ANIMALS

16 healthy horses, 3 to 17 years old, weighing 391 to 684 kg.

METHODS

Ten horses received 3 mEq/kg tromethamine and six received 3 mEq/kg sodium bicarbonate. Samples of venous blood and cerebrospinal fluid (CSF) were collected at intervals before and after drug administration. Heart rate and breathing rate were also recorded at intervals.

RESULTS

Median standard base excess increased significantly (P < .05) from baseline immediately after both bicarbonate and tromethamine. These increases were not significantly different between treatments. Standard base excess returned toward baseline but remained significantly increased 3 hours after infusion of either treatment. After tromethamine, there was a significant decrease in plasma sodium concentration that lasted for at least 90 minutes. After sodium bicarbonate, no change in plasma sodium concentration was detected. Both sodium bicarbonate and tromethamine increased carbon dioxide tension in venous blood and CSF. Despite venous alkalemia, the pH of CSF decreased after both treatments.

CONCLUSIONS

Tromethamine and sodium bicarbonate have similar alkalinizing ability. Tromethamine causes hyponatremia, whereas both tromethamine and sodium bicarbonate increase carbon dioxide tension in venous blood and CSF.

CLINICAL RELEVANCE

If hyponatremia, hypercarbia, and acidosis of the CSF occur after tromethamine is given to horses with existing metabolic acidosis, some of the potential advantages of tromethamine may prove theoretical rather than practical.

High resolution protein electrophoresis of equine cerebrospinal fluid

OBJECTIVE

To determine normal CSF electrophoresis patterns in horses, and to determine whether the electrophoretic scans from horses with cervical compression differ from those of neurologically normal horses.

ANIMALS

32 horses assigned to 1 of 2 groups: neurologically normal (n = 18) or cervical compression (n = 14).

PROCEDURE

CSF was collected from 18 neurologically normal horses referred to the Marion duPont Scott Equine Medical Center, and protein electrophoresis was performed to describe the normal equine CSF electrophoretogram. Results of CSF electrophoresis from 14 horses with cervical compression were then compared with results for the neurologically normal horses.

RESULTS

Horses with cervical compression had decreased beta-globulin fraction, and 1 or 2 prominent post-beta 2 peak(s). When the presence of post-beta peaks was used as a diagnostic criterion for cervical compression, the test had sensitivity of 71.4% and specificity of 81.8%. The positive and negative predictive values were 83.3 and 69.2%, respectively.

CONCLUSION AND CLINICAL IMPLICATIONS

Electrophoresis of CSF may be a useful diagnostic aid in evaluation of horses with neurologic disease.

Endocrine changes in cerebrospinal fluid, pituitary effluent, and peripheral plasma of anesthetized ponies

OBJECTIVE

To investigate the effects of inhalation and total IV anesthesia on pituitary-adrenal activity in ponies.

ANIMALS

9 healthy ponies: 5 geldings and 4 mares.

PROCEDURE

Catheters were placed in the cavernous sinus below the pituitary gland and in the subarachnoid space via the lumbosacral space. After 72 hours, administration of acepromazine was followed by induction of anesthesia with thiopentone and maintenance with halothane (halothane protocol), or for the IV protocol, anesthesia induction with detomidine and ketamine was followed by maintenance with IV infusion of a detomidine-ketamine-guaifenesin combination. Arterial blood pressure and gas tensions were measured throughout anesthesia. Peptide and catecholamine concentrations were measured in pituitary effluent, peripheral plasma, and CSF. Peripheral plasma cortisol, glucose, and lactate concentrations also were measured.

RESULTS

Intravenous anesthesia caused less cardiorespiratory depression than did halothane. ACTH, metenkephalin, arginine vasopressin, and norepinephrine pituitary effluent and peripheral plasma concentrations were higher during halothane anesthesia, with little change during intravenous anesthesia. Pituitary effluent plasma beta-endorphin and peripheral plasma cortisol concentrations increased during halothane anesthesia only. Dynorphin concentrations did not change in either group. Hyperglycemia developed during intravenous anesthesia only. Minimal changes occurred in CSF hormonal concentrations during anesthesia.

CONCLUSION

The pituitary gland has a major role in maintaining circulating peptides during anesthesia. Compared with halothane, IV anesthesia appeared to suppress pituitary secretion.

Albumin quotient, IgG concentration, and IgG index determinations in cerebrospinal fluid of neonatal foals

Total protein (TP), albumin, and IgG concentrations were measured in CSF from the atlanto-occipital (AO) and lumbosacral (LS) sites and in serum of 15 clinically normal neonatal foals < or = 10 days old (mean, 7.0 days). The albumin quotient (AQ; CSF albumin/serum albumin x 100) and IgG index ([CSF IgG/serum IgG] x [serum albumin/CSF albumin]), indicators of blood-brain barrier permeability and intrathecal IgG production, respectively, were then calculated. Mean +/- SD values obtained from the foals of this study were: serum albumin, 2,900 +/- 240 mg/dl; serum IgG, 1,325 +/- 686 mg/dl; AO CSF total protein (TP), 82.8 +/- 19.2 mg/dl; LS CSF TP, 83.6 +/- 16.1 mg/dl; AO CSF albumin, 52.0 +/- 8.6 mg/dl; LS CSF albumin, 53.8 +/- 15.7 mg/dl; AO CSF IgG, 10.2 +/- 5.5 mg/dl; LS CSF IgG, 9.9 +/- 5.7 mg/dl; AO AQ, 1.86 +/- 0.29; LS AQ, 1.85 +/- 0.51, AO IgG index, 0.52 +/- 0.28; and LS IgG index, 0.48 +/- 0.27. Significant difference between values for the AO and LS sites was not found. A CSF albumin concentration > 85.2 mg/dl or AQ > 2.4, as determined by mean +/- 2 SD, may indicate increased blood-brain barrier permeability. An IgG index value > 1.0 may indicate intrathecal IgG production. Values obtained for foals of this study should serve as baseline for comparison in the evaluation of blood-brain barrier permeability and intrathecal IgG production in neonatal foals with neurologic disease.

Cerebrospinal fluid variables in clinically normal foals from birth to 42 days of age

To determine the effects of age on each analyte, CSF variables were evaluated in healthy foals from birth through 42 days of age. Cerebrospinal fluid was collected from 14 clinically normal, naturally delivered cross-bred foals and was analyzed for glucose, sodium, potassium, magnesium, and total protein concentrations, total and differential WBC counts, RBC count, and lactate dehydrogenase, aspartate transaminase, and creatine kinase activities. Samples were collected in 3 foals < 48 hours old, and at 11 to 14 days of age in 4 foals, 21 to 22 days of age in 3 foals, and 31 to 42 days of age in 4 foals. Each foal was tested only once, to avoid any effects of CSF sample collection on subsequent analysis. Regression analysis confirmed age-related effects on CSF glucose, protein, and magnesium concentrations, but did not indicate an effect of age on CSF sodium and potassium concentrations or cell counts. Results indicate that CSF glucose concentration decreases with age; foals < 2 days old had the highest CSF glucose values, 98.8 +/- 12.0 mg/dl (mean +/- 1 SD). In foals 10 to 14 days old, CSF glucose concentration was 67.3 +/- 12.0 mg/dl, was 65.3 +/- 4.5 mg/dl in foals 21 to 22 days old, was 70.0 +/- 5.4 mg/dl in foals 31 to 42 days old, and was 51.1 +/- 2.5 mg/dl in adults.(ABSTRACT TRUNCATED AT 250 WORDS)

A new technique for accessing the cerebral ventricles of the horse

A technique is described for catheterisation of the ventricular recess within the olfactory bulb of the horse. Twelve adult horses were used. The olfactory recess is in the frontal region, 42 +/- 3 mm below the skin, on the line joining the supraorbital foramina, and approximately 18 +/- 2 mm from the midline. The approach is relatively easy under normal experimental conditions.

Effect of hypercapnia or xylazine on lateral ventricle and lumbosacral cerebrospinal fluid pressures in pentobarbital-anesthetized horses

Facial artery pressure, central venous pressure, heart rate, and lateral ventricle cerebrospinal fluid (CSF) pressure (LV-CSFP) were measured in 10 pentobarbital-anesthetized horses at arterial partial pressure of carbon dioxide (PaCO2) values of 40, 60, and 80 mm Hg, produced by varying the inspired carbon dioxide concentration. Variables were recorded at 5-minute intervals for 15 minutes at each level of PaCO2. Arterial blood gas analysis was performed at the end of the 15-minute time period for each level of PaCO2. Lateral ventricle CSF pressure was significantly increased (p < .05) at a PaCO2 of 80 mm Hg. Cardiovascular variables were not significantly changed by changing PaCO2. The PaCO2 was returned to 40 mm Hg; 1.1 mg xylazine/kg body weight was injected intravenously in eight horses, and data were collected for 60 minutes. No significant changes were observed. No changes were observed in two control horses not receiving xylazine. Subsequently, placement of a lumbosacral subarachnoid catheter allowed simultaneous measurement of LV-CSFP and lumbosacral CSF pressure (LS-CSFP) at PaCO2 values of 40, 60, and 80 mm Hg. The Pearson Correlation Coefficient between LV-CSFP and LS-CSFP was 0.94 (p < .0001) It was concluded that changes in CSF pressure could be detected at the lateral ventricle and the lumbosacral space; increasing PaCO2 to 80 mm Hg resulted in significant increases in LV-CSFP; xylazine does not increase LV-CSFP in pentobarbital-anesthetized, normocapnic horses; and under the conditions of this experiment, LV-CSFP and LS-CSFP were closely correlated.

Concentrations of trimethoprim and sulfamethoxazole in cerebrospinal fluid and serum in mares with and without a dimethyl sulfoxide pretreatment

Each of seven mares was given an intravenous (IV) injection of 40% dimethyl sulfoxide (DMSO) at a dosage of 1 g/kg, over 35 min, immediately followed by a single IV injection of a trimethoprim (TMP) and sulfamethoxazole (SMZ) combination (SMZ 83%, TMP 17%) at a combined dosage of 44 mg/kg (7.48 mg/kg TMP; 36.52 mg/kg SMZ). Each horse served as its own control and was alternately treated with an identical dose of TMP-SMZ treatment alone at least seven days following or preceding the DMSO and TMP-SMZ treatment. Serum and cerebrospinal fluid (CSF) concentrations of TMP and SMZ were measured over a six hour period. Dimethyl sulfoxide treatment caused no significant difference in the mean serum concentration of SMZ or in the mean CSF concentrations of TMP or SMZ. The mean serum concentration of TMP was significantly (p less than 0.05) increased at the two, four and six hour sampling time in the mares receiving pretreatment with DMSO. The clearance of TMP was also significantly (p less than 0.05) decreased from 675 mL/h/kg to 327 mL/h/kg by DMSO administration. Concentrations of TMP and SMZ in the CSF in both treatment groups exceeded the minimum inhibitory concentrations for many common bacterial pathogens of equine origin. In addition, CSF concentration of TMP exceeded the serum concentrations required for 50% inhibition of dihydrofolate reductases of protozoan origin. Serum TMP and SMZ concentration were similar to those reported to be effective against Toxoplasma gondii in in vitro studies on the killing or inhibition of the organism.

Dopamine in the cerebrospinal fluid of prepubertal and adult horses

Catecholamine concentrations (pg/ml) in the cerebrospinal fluid (CSF) of prepubertal (n = 9) and adult (n = 18) horses were determined by radioenzymatic assay. Norepinephrine was low or non detectable in all CSF samples. In contrast, measurable CSF dopamine concentrations were effected by age, reproductive status and exogenous steroid treatments. The concentration of dopamine in the CSF of prepubertal females (733 +/- 92) was greater (p less than 0.05) than the concentration in the CSF of prepubertal males (117 +/- 67). Prepubertal male horses which were treated with testosterone for 5 days (50 mg/day) had elevated (p less than 0.05) dopamine concentrations (2,533 +/- 1,160) in the CSF compared to control males. In adult mares, dopamine was lower (p less than 0.05) in the ovulatory season (25 +/- 10) than during the anovulatory season (200 +/- 101). Daily intramuscular estradiol-17 beta (5 mg/day) injections had no effect (p less than 0.05) on dopamine concentrations in the CSF of seasonally anovulatory mares (250 +/- 35). Further, concentrations of dopamine in the CSF of long-term ovariectomized mares (80 +/- 21) were not influenced (p less than .05) by season. These results suggest that age, sex and gonadal steroids may effect dopamine, but not norepinephrine, concentrations in the brain ventricular system of the equine species. Further, seasonal effects on CSF dopamine concentrations are dependent upon the presence of the ovaries.

Different gradients for neurotransmitter metabolites and protein in horse cerebrospinal fluid

The serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA) and the dopamine metabolite, homovanillic acid (HVA) in the cerebrospinal fluid (CSF) of seven clinically normal horses were evaluated with reverse phase high pressure liquid chromatography and electrochemical detection. Comparisons of the neurotransmitter metabolite concentrations were made on CSF collected simultaneously from the atlanto-occipital and lumbosacral regions. There were significantly higher amounts of 5-HIAA and HVA in atlanto-occipital CSF than in lumbosacral CSF. Mean 5-HIAA concentrations in atlanto-occipital and lumbosacral CSF were 206.1 +/- 37.0 nmol/L and 68.5 +/- 12.6 nmol/L, respectively. The mean HVA concentration in atlanto-occipital CSF was 254.4 +/- 50.4 nmol/L. No HVA was detected in lumbosacral CSF. In contrast, significantly greater protein concentrations were present in lumbosacral CSF than in atlanto-occipital CSF. Lumbosacral and atlanto-occipital CSF contained 32.1 +/- 3.7 mg protein/dl and 25.0 +/- 1.3 mg protein/dl, respectively. Thus, between the atlanto-occipital and lumbosacral space of the horses, a rostrocaudal gradient existed for neurotransmitter metabolites and a caudorostral gradient existed for protein.

Analysis of equine cisterna magna cerebrospinal fluid for the presence of some monoamine neurotransmitters and transmitter metabolites

Small volumes (0.05 ml) of cisterna magna cerebrospinal fluid (CSF) from 23 neurologically normal horses were analysed for the monoamine neurotransmitters dopamine, norepinephrine, epinephrine, serotonin and their metabolites using high pressure liquid chromatography and electrochemical detection. Two metabolites, homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were present in all CSF samples. The deaminated and methylated metabolite of dopamine, HVA, was present at a mean concentration of 42.33 +/- 3.14 ng/ml of CSF. The deaminated metabolite of serotonin, 5-HIAA, was present at a mean concentration of 45.52 +/- 3.65 ng/ml of CSF. A positive correlation was found between the CSF concentrations of HVA and 5-HIAA (r = 0.72, p = 0.0003). The mean ratio of HVA to 5-HIAA concentrations was 1.07 +/- 0.05. The ratios of HVA to 5-HIAA concentrations were found to be more indicative of the serotonergic metabolite 5-HIAA (r = -0.62, p = 0.0016) than the dopaminergic metabolite HVA (r = 0.11, p = 0.60). There was a stronger relationship between the concentrations of 5-HIAA and the ratios of HVA to 5-HIAA in male CSF (r = -0.85, p = 0.0006) than in female CSF (r = -0.54, p = 0.01). Concentrations of CSF neurotransmitter metabolites were evaluated in horses grouped by age (0-4, 5-9 and 10-13 years). The youngest group of horses had a significantly (p = 0.003) greater CSF concentration of HVA than of 5-HIAA. The 10-13-year-old horses had a significantly (p = 0.02) lower mean CSF HVA concentration than the 0-4-year-old horses. No age-related differences in CSF 5-HIAA concentrations were detected.

Spinal fluid concentrations of mepivacaine in horses and procaine in cows after thoracolumbar subarachnoid analgesia

The CSF concentrations of mepivacaine in 10 Standardbred horses and of procaine in 10 Holstein cows given the drugs by thoracolumbar subarachnoid injection were determined. Mepivacaine hydrochloride was injected into the horses (502 +/- 60.5 kg) at an average dosage of 30 mg (1.5 ml of 20 mg/ml solution). Analgesia was produced 7.5 +/- 4.3 minutes after injection, extended between spinal cord segments T13 and L3 on both sides of the spinal column, and lasted 47 +/- 18.7 minutes at the T18 dermatome. Procaine hydrochloride was injected into cows (614 +/- 51.5 kg) at a dosage ranging between 75 mg and 100 mg (1.5 ml and 2 ml of 50 mg/ml solution). Analgesia was produced 8.2 +/- 2.0 minutes after injection, extended between spinal cord segments T11 and L4 on both sides of the spinal column, and lasted 47 +/- 17.5 minutes at the T13 dermatome. The critical CSF concentrations of local anesthetics required to eliminate response to pinprick stimulation were 204.4 +/- 90.3 micrograms of mepivacaine/ml in horses and 197.0 +/- 86.1 micrograms of procaine/ml in cows. Average CSF concentrations at 120 minutes after injections were made were 16.8 +/- 15.5 micrograms of mepivacaine/ml and 30.6 +/- 17.1 micrograms of procaine/ml. In in vitro experiments to determine the rates of hydrolysis of mepivacaine and procaine in CSF, significant changes (P greater than 0.05) were not seen in the CSF concentrations of mepivacaine in horses and procaine in cattle after a 120-minute incubation (37 C). The analgesic threshold concentrations of mepivacaine in CSF of horses and procaine in CSF of cows were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytology of equine cerebrospinal fluid

The cytology of cerebrospinal fluid samples from horses is described. The samples were obtained from 24 normal horses, 35 horses with axonal degeneration and/or spinal cord compression, 29 horses with encephalomyelitis, 14 horses with other lesions of the nervous system, and eight horses with signs of neurologic dysfunction of undetermined origin. (Three of the latter were suspected botulinum intoxications.) Fluid was aspirated from the atlanto-occipital space following general anesthesia or immediately after a lethal dose of barbiturate. In two horses, fluid also was aspirated from the lumbosacral space. Small mononuclear cells were predominant in normal horses, and in most horses with axonal degeneration and encephalomyelitis. Several horses with encephalomyelitis also had neutrophils, eosinophils, and some mitotic figures. Although the cytologic findings were abnormal in many of the horses with disease of the central nervous system, in most horses the cytologic findings were normal.

Biochemical constituents of cerebrospinal fluid in premature and full term foals

Total protein content and a variety of enzyme activities and electrolyte values were determined in 73 cerebrospinal fluid (CSF) samples from 66 horses and ponies. The foals (48) were divided into 3 categories-spontaneously delivered normal foals (Group A), full term induced normal foals (Group B) and premature induced non-surviving foals (Group C). CSF samples from a group of 18 normal adults (Group D) were included for comparison. Paired serum and CSF samples were collected on 32 occasions and subjected to similar analyses. CSF sodium and chloride were always higher than serum sodium and chloride; the reverse occurred with potassium. The CSF protein and enzyme levels were always lower than corresponding serum values. The foals had higher total protein and creatine kinase in CSF than the adults, except for Group C (non-survivors) which had significantly lower creatine kinase than either of the other 2 foal groups. Creatine kinase values tended to fall towards adult levels over 40 h post partum. It was also noted that foals with both high total protein and creatine kinase in CSF, compared with adult values, had a better chance of survival than those with high total protein but low creatine kinase.

Enzootic and epizootic Venezuelan equine encephalomyelitis virus in horses infected by peripheral and intrathecal routes

Forty-five horses were infected peripherally or intrathecally with enzootic or epizootic strains of Venezuelan equine encephalomyelitis (VEE) virus. Low titers of virus appeared in cerebrospinal fluid (CSF) after peripheral inoculation of enzootic or epizootic VEE virus strains. Intrathecal infection with either epizootic or enzootic VEE virus produced higher titers of virus in CSF than did peripheral infection. In contrast to peripheral infections with enzootic strains, intrathecal infections with these strains caused death. The animals that died had widespread histopathologic changes and large amounts of virus in brain tissue. The attenuated VEE virus vaccine strain, TC-83, also multiplied in the brain of horses inoculated intrathecally but caused no clinical disease and little histopathologic damage.

Equine cerebrospinal fluid: reference values of normal horses

Cerebrospinal fluid (CSF) samples were collected from the atlanto-occipital (AO) and lumbosacral (LS) subarachnoid spaces of 24 horses and 21 ponies that had no clinical evidence of neurologic disease. Depth of needle insertion, pressures, refractive index, rapid reagent strip test (protein, glucose, blood, pH) results, cell counts, content of protein, glucose, sodium, potassium, chloride, calcium, phosphorus, urea nitrogen, and cholesterol, and activities of creatine phosphokinase, aspartate transaminase, lactic dehydrogenase, and alkaline phosphatase were determined. The resulting clinical reference values obtained were discussed in light of the published normal values for CSF from horses, other animals, and man. White cell counts in CSF were found to be from 0 to 6/microliters. Values for protein content were distributed between wider limits than previously reported values. The LS-AO difference is proposed as a criterion for clinical evaluation of CSF protein content. Ponies were found to have more protein in their CSF than did the horses, and CSF from the LS site contained more glucose than that from the AO site. The CSF electrolyte composition was similar to that of previous reports. Enzyme activities in equine CSF are reported for the 1st time.

Effects of blood contamination on cerebrospinal fluid analysis

Data were obtained from 190 cerebrospinal fluid samples collected from both clinically normal and diseased dogs, cats, cows, and horses. Red blood cells, indicating blood contamination, were identified in 115 samples. White blood cells were a rare finding in normal animals. Blood contamination appeared to have little effect on white blood cell numbers even though, in several samples, thousands of red blood cells were identified. An accepted formula to correct for blood contamination was found to be an unreliable method to determine "uncontaminated" values for white blood cells, total protein, or creatine phosphokinase.

Analysis of serum proteins and cerebrospinal fluid in clinically normal horses, using agarose electrophoresis

Using agarose as a supporting matrix, electrophoresis was conducted on 50 serum samples and 20 cerebrospinal fluid samples from clinically normal horses (n = 50) of various ages and breeds. The technique was shown to be reliable. A positive correlation between age and gamma-globulin concentration was found in young horses. Features of the electrophoretograms of serum and cerebrospinal fluid samples are discussed, and a nomenclature based on Rf values is proposed.

Collection of cerebrospinal fluid from the horse

Methods for atlanto-occipital and lumbosacral collection of cerebrospinal fluid from the horse are described in detail, and the techniques and complications discussed.