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Perilymph sampling from the cochlear apex: a reliable method to obtain higher purity perilymph samples from scala tympani.
J Neurosci Methods. 2006 May 15; 153(1):121-9.JN

Abstract

Measurements of drug levels in the fluids of the inner ear are required to establish kinetic parameters and to determine the influence of specific local delivery protocols. For most substances, this requires cochlear fluids samples to be obtained for analysis. When auditory function is of primary interest, the drug level in the perilymph of scala tympani (ST) is most relevant, since drug in this scala has ready access to the auditory sensory cells. In many prior studies, ST perilymph samples have been obtained from the basal turn, either by aspiration through the round window membrane (RWM) or through an opening in the bony wall. A number of studies have demonstrated that such samples are likely to be contaminated with cerebrospinal fluid (CSF). CSF enters the basal turn of ST through the cochlear aqueduct when the bony capsule is perforated or when fluid is aspirated. The degree of sample contamination has, however, not been widely appreciated. Recent studies have shown that perilymph samples taken through the round window membrane are highly contaminated with CSF, with samples greater than 2microL in volume containing more CSF than perilymph. In spite of this knowledge, many groups continue to sample from the base of the cochlea, as it is a well-established method. We have developed an alternative, technically simple method to increase the proportion of ST perilymph in a fluid sample. The sample is taken from the apex of the cochlea, a site that is distant from the cochlear aqueduct. A previous problem with sampling through a perforation in the bone was that the native perilymph rapidly leaked out driven by CSF pressure and was lost to the middle ear space. We therefore developed a procedure to collect all the fluid that emerged from the perforated apex after perforation. We evaluated the method using a marker ion trimethylphenylammonium (TMPA). TMPA was applied to the perilymph of guinea pigs either by RW irrigation or by microinjection into the apical turn. The TMPA concentration of the fluid sample was compared with that measured in perilymph prior to taking the sample using a TMPA-selective microelectrode sealed into ST. Data were interpreted with a finite element model of the cochlear fluids that was used to simulate each aspect of the experiment. The correction of sample concentration back to the perilymph concentration prior to sampling can be performed based on the known ST volume (4.7microL in the guinea pig) and the sample volume. A more precise correction requires some knowledge of the profile of drug distribution along the cochlear prior to sampling. This method of sampling from the apex is technically simple and provides a larger sample volume with a greater proportion of perilymph compared to sampling through the RW.

Authors+Show Affiliations

Department of Otolaryngology, Box 8115, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA. salta@msnotes.wustl.eduNo affiliation info availableNo affiliation info available

Pub Type(s)

Evaluation Study
Journal Article
Research Support, N.I.H., Extramural

Language

eng

PubMed ID

16310856

Citation

Salt, Alec N., et al. "Perilymph Sampling From the Cochlear Apex: a Reliable Method to Obtain Higher Purity Perilymph Samples From Scala Tympani." Journal of Neuroscience Methods, vol. 153, no. 1, 2006, pp. 121-9.
Salt AN, Hale SA, Plonkte SK. Perilymph sampling from the cochlear apex: a reliable method to obtain higher purity perilymph samples from scala tympani. J Neurosci Methods. 2006;153(1):121-9.
Salt, A. N., Hale, S. A., & Plonkte, S. K. (2006). Perilymph sampling from the cochlear apex: a reliable method to obtain higher purity perilymph samples from scala tympani. Journal of Neuroscience Methods, 153(1), 121-9.
Salt AN, Hale SA, Plonkte SK. Perilymph Sampling From the Cochlear Apex: a Reliable Method to Obtain Higher Purity Perilymph Samples From Scala Tympani. J Neurosci Methods. 2006 May 15;153(1):121-9. PubMed PMID: 16310856.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Perilymph sampling from the cochlear apex: a reliable method to obtain higher purity perilymph samples from scala tympani. AU - Salt,Alec N, AU - Hale,Shane A, AU - Plonkte,Stefan K R, Y1 - 2005/11/28/ PY - 2005/08/24/received PY - 2005/10/03/revised PY - 2005/10/13/accepted PY - 2005/11/29/pubmed PY - 2006/7/28/medline PY - 2005/11/29/entrez SP - 121 EP - 9 JF - Journal of neuroscience methods JO - J Neurosci Methods VL - 153 IS - 1 N2 - Measurements of drug levels in the fluids of the inner ear are required to establish kinetic parameters and to determine the influence of specific local delivery protocols. For most substances, this requires cochlear fluids samples to be obtained for analysis. When auditory function is of primary interest, the drug level in the perilymph of scala tympani (ST) is most relevant, since drug in this scala has ready access to the auditory sensory cells. In many prior studies, ST perilymph samples have been obtained from the basal turn, either by aspiration through the round window membrane (RWM) or through an opening in the bony wall. A number of studies have demonstrated that such samples are likely to be contaminated with cerebrospinal fluid (CSF). CSF enters the basal turn of ST through the cochlear aqueduct when the bony capsule is perforated or when fluid is aspirated. The degree of sample contamination has, however, not been widely appreciated. Recent studies have shown that perilymph samples taken through the round window membrane are highly contaminated with CSF, with samples greater than 2microL in volume containing more CSF than perilymph. In spite of this knowledge, many groups continue to sample from the base of the cochlea, as it is a well-established method. We have developed an alternative, technically simple method to increase the proportion of ST perilymph in a fluid sample. The sample is taken from the apex of the cochlea, a site that is distant from the cochlear aqueduct. A previous problem with sampling through a perforation in the bone was that the native perilymph rapidly leaked out driven by CSF pressure and was lost to the middle ear space. We therefore developed a procedure to collect all the fluid that emerged from the perforated apex after perforation. We evaluated the method using a marker ion trimethylphenylammonium (TMPA). TMPA was applied to the perilymph of guinea pigs either by RW irrigation or by microinjection into the apical turn. The TMPA concentration of the fluid sample was compared with that measured in perilymph prior to taking the sample using a TMPA-selective microelectrode sealed into ST. Data were interpreted with a finite element model of the cochlear fluids that was used to simulate each aspect of the experiment. The correction of sample concentration back to the perilymph concentration prior to sampling can be performed based on the known ST volume (4.7microL in the guinea pig) and the sample volume. A more precise correction requires some knowledge of the profile of drug distribution along the cochlear prior to sampling. This method of sampling from the apex is technically simple and provides a larger sample volume with a greater proportion of perilymph compared to sampling through the RW. SN - 0165-0270 UR - https://www.unboundmedicine.com/medline/citation/16310856/Perilymph_sampling_from_the_cochlear_apex:_a_reliable_method_to_obtain_higher_purity_perilymph_samples_from_scala_tympani_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0165-0270(05)00369-9 DB - PRIME DP - Unbound Medicine ER -