Analysis of Normal and Denerved Laryngeal Vocalization in Guinea Pigs (Cavia porcellus)
Introduction
The larynx is fundamental to vocalize, is anatomically related to structures such as the esophagus, trachea, hyoids, thyroid and parathyroid glands, lymph nodes, and large blood vessels.1, 2
Phoniatric pathology has revealed problems associated with laryngeal nerves, such as unilateral or bilateral paralysis of the vocal chords, frequently caused by iatrogenic lesions produced by recurring laryngeal nerves found in neck surgery.3, 4, 5 In addition, another cause involving one or two larynx nerves is the bilateral paralysis of the vocal chords because of iatrogenia or neck tumors,6, 7 resulting in respiratory problems, such as inspiratory dyspnea.8
Lesion to the nerves is also common in tracheotomy, and thyroid and parathyroid surgeries.2, 4, 9, 10
It is well known that the human larynx has important functions such as preventing solids or liquids from passing to the respiratory tract, regulation of air pressure in breathing, and generating sounds (the last being what is analyzed in this work).11 The diversity and complexity of this function have to be coordinated by a complex nervous system driven primarily by the vagus nerve and a series of motor and sensory fibers. The motor fibers send specific information to the intrinsic laryngeal muscles so that they can carry out their function. The sensory fibers transport the information to the central nervous system and the autonomic fibers control the vasomotor reaction and secretion from the laryngeal glands.11
Shindo et al12 analyzed a different process while removing the laryngeal nerve, to become familiar with the functional recuperation of various organs where the nerve had been removed. The anatomy of the superior laryngeal nerve (SLN) from the guinea pig is very similar to the one from the human, the SLN emerges from the ganglion nodosa that later divides and branches off internally and externally, and the inferior laryngeal nerve (ILN) or recurrent that is joined to the larynx and is called the internal larynx nerve deriving from the fore and after branch.1
The guinea pig (Cavia porcellus) is neurologically mature at birth, it is born with its eyes open and with fur; it has functional sight and audition from birth.13, 14 It is supposed that the emission vocalizations can be attributed to stress caused by the absence of sight, smell, and sounds of the mother. The production vocalizations in the newborn cause the mother to go into protection behavior. Some ontogeny studies have been made on voice behavior in guinea pigs.15, 16
The guinea pig is an ideal model for audiological and phonological research17 because of the anatomical and physiological characteristics of the ear and the audible vocalizations in the human audible range.17, 18, 19, 20, 21
The emission audible vocalization in the guinea pig is fundamental from birth to early age for auditive memory development, compared with other rodents that are born immature.18, 22, 23 The guinea pig normally makes very characteristic vocalizations when separated from the mother, which are called “isolation calls”; these cries may be induced by separating newborns in new environments from their dams.24, 25, 26, 27 As mentioned before, these rodents emit acoustic sounds within the range of human audition. Berryman (1976) has described 11 different types of audible vocalizations in these species.15
Paralysis of the left vocal chord is frequent in clinical practice because the recurrent laryngeal nerve is long and surrounds the ascending aorta, for which it is more vulnerable because of medical intervention and the highly sensitive anatomical position.17, 28 The aim of this study was to analyze longitudinally the guinea pig vocalizations with denerved laryngeal surgery at the birth.
Section snippets
Laboratory animals used
Forty newborn male guinea pigs (Cavia porcellus) were used; animals were later divided into two groups: (1) 20 males were used as a control group (CG) and (2) 20 males were used for the experimental group (EG). The rodents were selected from 20 guinea pig litters; the colonies were formed by the mother and the litters. The average number of pups per litter was four, of which two animals were chosen for the study, one for the EG and the other for the CG. Two males with higher weight and similar
Results
The F test was run (P ≤ 0.05) to look for significant differences between groups over the 20-day period; no significant differences were found. However, vocalization analyses show that denerved guinea pigs had a trend to increase the frequency of their vocalizations, compared with the CG. This vocal behavior decreased over the week, and was back again on Monday of the next week. It is worth mentioning that this behavior was shown in both groups with different intensities (Table 1). At the end of
Discussion
Cutting the left larynx nerve caused the ipsilateral vocal function to modify and distort with changes visible in the spectrograms over the 20 days during recording and after denerving the larynx, showing these tendencies during the first days in comparison with the CG.
The present analysis of vocalizations produced by the denerved guinea pigs and the CG during the 20 days postsurgery reports that the denerved tend to vocalize more than the (normal) guinea pigs in the CG, under the three
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