Transdermal spinal catheter placement in piglets: Description and validation of the technique

Continual cerebrospinal fluid sampling in the neonatal domestic piglet for biomarker and discovery studies

BACKGROUND

Longitudinal access to cerebrospinal fluid (CSF) is useful for biomarker discovery in neurological disorders or diseases affecting CSF composition. Here, we aim to test a new method for insertion of a permanent intrathecal catheter, facilitating longitudinal collection of CSF.

NEW METHOD

We surgically placed a permanent intrathecal catheter into the cisterna magna of anesthetized neonatal piglets. The thecal sac was accessed at the L5-S1 spinal level and a radiopaque catheter was inserted under fluoroscopic x-ray guidance to position the tip at the cisterna magna. A titanium access port was connected to the catheter and anchored subcutaneously. Immediately after surgery, we confirmed CSF flow through the catheter and port via needle aspiration. Catheter patency over a two-month study period was determined through periodic CSF collection from the port.

RESULTS

Frequent (up to 3 times weekly), longitudinal sampling of CSF was achievable in neonatal piglets up to 60 days after implantation. CSF was readily accessible through the port without major adverse events. Catheterized piglets demonstrated slower, but normal, weight gain compared to control piglets. Post-operative complications were managed with standard access precautions and medications. There were no complications involving the implanted hardware.

COMPARISON WITH EXISTING METHOD(S)

This method fills a critical gap in the existing methods for longitudinal CSF sampling through an implanted intrathecal catheter system in neonatal piglets.

CONCLUSIONS

This novel method is both safe and effective for longitudinal CSF access in the domestic piglet. Catheter patency and access to CSF is maintained over multiple months without major adverse events.

Non-clinical Models to Determine Drug Passage into Human Breast Milk

BACKGROUND

Successful practice of clinical perinatal pharmacology requires a thorough understanding of the pronounced physiological changes during lactation and how these changes affect various drug disposition processes. In addition, pharmacokinetic processes unique to lactation have remained understudied. Hence, determination of drug disposition mechanisms in lactating women and their babies remains a domain with important knowledge gaps. Indeed, lack of data regarding infant risk during breastfeeding far too often results in discontinuation of breastfeeding and subsequent loss of all the associated benefits to the breastfed infant. In the absence of age-specific toxicity data, human lactation data alone are considered insufficient to rapidly generate the required evidence regarding risks associated with medication use during lactation.

METHODS

Systematic review of literature to summarize state-of-the art non-clinical approaches that have been developed to explore the mechanisms underlying drug milk excretion.

RESULTS

Several studies have reported methods to predict (to some extent) milk drug excretion rates based on physicochemical properties of the compounds. In vitro studies with primary mammary epithelial cells appear excellent approaches to determine transepithelial drug transport rates across the mammary epithelium. Several of these in vitro tools have been characterized in terms of transporter expression and activity as compared to the mammary gland tissue. In addition, with the advent of physiology-based pharmacokinetic (PBPK) modelling, these in vitro transport data may prove instrumental in predicting drug milk concentration time profiles prior to the availability of data from clinical lactation studies. In vivo studies in lactating animals have proven their utility in elucidating the mechanisms underlying drug milk excretion.

CONCLUSION

By combining various non-clinical tools (physicochemistry-based, in vitro and PBPK, in vivo animal) for drug milk excretion, valuable and unique information regarding drug milk concentrations during lactation can be obtained. The recently approved IMI project ConcePTION will address several of the challenges outlined in this review.

Neurologic Complications Associated with Transdermal Placement of Intrathecal Catheters in Sheep

A study using an ovine model of transdermal intrathecal catheterization was planned to investigate the neurotoxicity of magnesium sulfate. Nonpregnant Merino cross ewes (n = 8; age, 5 y; weight, 55.0 ± 6.5 kg) were anesthetized for placement of a lumbar intrathecal catheter. The study protocol defined a 5-d recovery period after introduction of the catheter before the administration of test substances (2 mL of 0.9% saline or 50 or 150 mg MgSO4) followed by euthanasia 1 wk later. Although 3 sheep successfully completed the study as planned, one of the remaining 5 sheep was withdrawn when the catheter was accidentally dislodged 2 d after anesthesia; another was withdrawn because of persistent neurologic deficits of the left hindlimb and intense pruritus during the first 24 h after placement of the catheter; and the remaining 3 animals experienced unacceptable complications within the first 4 h of administration of the test substance. These complications included hindlimb weakness, intense irritation or pruritus of the hindlimbs, recumbency, inability to stand, spasm of the hindlimb, and arching of the back. Postmortem examination of 4 sheep with clinical signs revealed similar gross findings: acute, segmental myelomalacia and hemorrhage within the spinal cord parenchyma in the region of the catheter. Histologic changes included segmental areas of acute myelomalacia, consistent with the intraparenchymal placement of the catheter. Postmortem CT imaging of 3 sheep confirmed the location of the catheter within the spinal cord. Procedural refinement for the placement of intrathecal catheters in sheep by avoiding an invasive surgical procedure was unsuccessful. We therefore recommend a complete or partial surgical approach for the insertion of an intrathecal catheter in sheep or fluoroscopy or ultrasonography intraoperatively to confirm correct placement of the catheter.

Diurnal Variation of Melatonin Concentration in the Cerebrospinal Fluid of Unanesthetized Microminipig

BACKGROUND/AIM

The aim of this study was to develop a method for sequentially collecting cerebrospinal fluid (CSF) from an unanesthetized microminipig, which shares many physiological and anatomical similarities with humans, such as diurnality, and investigate the diurnal variation of melatonin concentration in the CSF.

MATERIALS AND METHODS

A catheter was placed percutaneously into the subarachnoid space of an anesthetized animal, and the tip of the catheter was placed into the cisterna magna under X-ray. We then sequentially collected CSF at light-on and -off times from the unanesthetized animal for several weeks. After catheter placement, a period of one week or more was necessary to relieve the contamination of RBCs in the CSF.

RESULTS

A higher melatonin level in the CSF was noted during lights-off time, and the level was higher than that in the serum.

CONCLUSION

This model of sequential collection of CSF will contribute to research in brain functions.

Ultrasound guided spinal catheter insertion in piglet: preliminary results

OBJECTIVE

To describe the ultrasound (US) evaluation of the cervical, thoracic and lumbar spinal tracts in piglets and to evaluate the feasibility of the ultrasound guided spinal catheter placement in newborn and paediatric piglets.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of two piglet cadavers (age, 7 and 14 days) and eight commercial crossbreed piglets divided into four groups according to age: 7 (P7), 14 (P14), 21 (P21) and 28 (P28) days.

METHODS

In the first part of the study an ultrasound examination of the spinal tract was performed in piglet cadavers applying the transverse and the longitudinal approaches in sternal and lateral recumbencies. In the second phase, the piglets were anaesthetized with sevoflurane. A US examination with a 10 MHz linear probe was performed and a spinal catheter was introduced between the spinous processes of L2 and L3 lumbar vertebrae using an in-plane technique and its advancement was monitored with the probe. At the end of procedure, the catheter was removed. The piglets recovered from anaesthesia and were monitored for one week.

RESULTS

In phase I the authors identified the paramedian longitudinal approach as the most feasible for spinal structure evaluation in piglets. In phase II, the paramedian longitudinal views enabled a good visualization of the spinal cord and of the catheter advancement up to the cisterna magna in groups P7 and P14. In groups P21 and P28 it was not possible to visualize the neuroaxial structures and the spinal catheter using the same approach. No clinical alterations were recorded during the procedure or the following days.

CONCLUSIONS AND CLINICAL RELEVANCE

US-guided spinal catheter placement appeared a feasible technique in piglets younger than 14 days but it is not useful in older piglets.

Atlanto-occipital catheterization of young rats for long-term drug delivery into the lumbar subarachnoid space combined with in vivo testing and electrophysiology in situ

BACKGROUND

Catheterization has been widely used in neuroscience and pain research for local drug delivery. Though different modifications were developed, the use of young animals for spinal catheterization remains limited because of a little success rate. A reliable technique is needed to catheterize young animals aimed for in vivo testing combined with spinal cord electrophysiology, often limited by animal age, to facilitate pain research.

NEW METHODS

We describe intrathecal catheterization of young rats (3-week-old) through atlanto-occipical approach for long-lasting drug delivery into the lumbar subarachnoid space. The technique represents a surgical approach of minimized invasiveness that requires PE-10 catheter and few equipment of standard laboratory use.

RESULTS

Behavioral assessments revealed that spinal catheterization does not change peripheral sensitivity of different modalities (thermal and mechanical) and gives no rise to locomotive deficit or anxiety-like behavior in young rats. The long-term administration of genetic material (oligodeoxynucleotides given up to 4days), examined both in vivo and in situ, produced no adverse effects on basal peripheral sensitivity, but changed the AMPA receptor-mediated currents in sensory interneurons of the spinal cord.

COMPARISON WITH EXISTING METHODS

Dissimilar to already described methods, the method is designed for the use of young rats for behavioral testing in vivo and/or spinal cord electrophysiology in situ.

CONCLUSIONS

A practical method for spinal catheterization of young animals designed for studies in vivo and in situ is proposed. The method is rapid and effective and should facilitate investigation of therapeutic effects on both systemic and subcellular levels, as an advantage over the existing methods.

Age-Related 1H NMR Characterization of Cerebrospinal Fluid in Newborn and Young Healthy Piglets

When it comes to neuroscience, pigs represent an important animal model due to their resemblance with humans’ brains for several patterns including anatomy and developmental stages. Cerebrospinal fluid (CSF) is a relatively easy-to-collect specimen that can provide important information about neurological health and function, proving its importance as both a diagnostic and biomedical monitoring tool. Consequently, it would be of high scientific interest and value to obtain more standard physiological information regarding its composition and dynamics for both swine pathology and the refinement of experimental protocols. Recently, proton nuclear magnetic resonance (¹H NMR) spectroscopy has been applied in order to analyze the metabolomic profile of this biological fluid, and results showed the technique to be highly reproducible and reliable. The aim of the present study was to investigate in both qualitative and quantitative manner the composition of Cerebrospinal Fluid harvested form healthy newborn (5 days old-P5) and young (30-P30 and 50-P50 days old) piglets using ¹H NMR Spectroscopy, and to analyze any possible difference in metabolites concentration between age groups, related to age and Blood-Brain-Barrier maturation. On each of the analyzed samples, 30 molecules could be observed above their limit of quantification, accounting for 95–98% of the total area of the spectra. The concentrations of adenine, tyrosine, leucine, valine, 3-hydroxyvalerate, 3-methyl-2-oxovalerate were found to decrease between P05 and P50, while the concentrations of glutamine, creatinine, methanol, trimethylamine and myo-inositol were found to increase. The P05-P30 comparison was also significant for glutamine, creatinine, adenine, tyrosine, leucine, valine, 3-hydroxyisovalerate, 3-methyl-2-oxovalerate, while for the P30-P50 comparison we found significant differences for glutamine, myo-inositol, leucine and trimethylamine. None of these molecules showed at P30 concentrations outside the P05 –P50 range.