Recurrent laryngeal nerve transposition in guinea pigs.

Improved control of prosthetic voice aids for laryngectomees might be possible to obtain with residual laryngeal motor nerve signals. We were able to recover motor signals from the recurrent laryngeal nerve (RLN) by transposing it into the ipsilateral denervated sternohyoid muscle (SH) in 8 guinea pigs. Reinnervation was monitored by electromyographic recordings from surface and intramuscular needle electrodes in awake animals. Within 4 to 14 weeks after surgery, all animals demonstrated laryngeal-like motor activity in the reinnervated SH, including activity during respiration, sniffing, swallowing, and/or vocalizing. After 3 to 6 months, the animals were reanesthetized, and nerve stimulation and section experiments confirmed the RLN as the source of reinnervation in all cases. In several animals, activity of the RLN-innervated SH was demonstrated to be correlated with that of contralateral laryngeal muscles. Histochemical analysis of the SH indicated a unilateral transformation from mostly fatigable to mostly fatigue-resistant fiber types ipsilateral to the RLN transposition, a phenotype more typical of laryngeal muscles. Thus, RLN transposition at the time of laryngectomy may be a method for salvaging laryngeal control signals that could be used to control prosthetic voice devices.

Effects of lesions of the central nucleus of the anterior archistriatum on contact call and warble song production in the budgerigar (Melopsittacus undulatus).

We studied the effects of both unilateral and bilateral lesions of the central nucleus of the anterior archistriatum (AAc) on the production of contact calls and warble song in adult male and female budgerigars. Birds were sorted into three experimental groups based on the percentage of AAc destroyed and whether lesions were unilateral or bilateral. The experimental groups were Unilateral Lesion (N = 8), Partial Bilateral Lesion (N = 5), and Bilateral Lesion birds (N = 12). Each group contained both sexes. Unilateral lesions had no demonstrable effects on contact call or warble song production. Bilateral lesions resulted in immediate and permanent disruption of all learned temporal and spectral characteristics of contact calls, although call initiation was not dependent on the AAc. Partial bilateral lesion effects varied with lesion size and location. At least 20-30% sparing of the AAc, including sparing portions of both the dorsal (AAcd) and ventral (AAcv) subdivisions on the same side of the brain, is necessary for production of prelesion contact call patterns. Warble song was absent in birds with complete bilateral destruction. Two birds with large yet incomplete lesions of the AAc sang after surgery, although the warble song of these birds was extremely impoverished and contained only a few of the typical warble song elements. Lesion results indicate that the AAc mediates the production of learned vocal features in male and female budgerigars, with each hemisphere capable of supporting a normal vocal repertoire.

Telencephalic nuclei control late but not early nestling calls in the budgerigar.

Bilateral lesions targeting the central nucleus of the anterior archistriatum (AAc) were placed in nestling budgerigars (Melopsittacus undulatus) aged 5, 9, 13, 22, 26, and 33 days post-hatch in order to evaluate the role of the telencephalon in producing nestling vocalizations in this species. In budgerigars, AAc is the final common pathway from telencephalic vocal control nuclei to brainstem respiratory and syringeal motorneuron pools. The results show that lesions destroying AAc bilaterally in addition to surrounding archistriatum and neostriatum do not alter the production of early simple patterned foodbegging calls but do prevent both the normal transition at 3-4 weeks post-hatch to more complex begging calls as well as the emergence of individually-distinctive contact calls around the time of fledging. These vocal results are strikingly similar to those obtained in previous studies in which early deafening of nestlings (Heaton and Brauth, 1999) and early lesioning of auditory areas in the anterior telencephalon (Hall WS, Brauth SE, Heaton JT. Comparison of the effects of lesions in nucleus basalis and field 'L' on vocal control learning and performance in the budgerigar (M. undulatus), Brain Behav. Evol., 1994;44:133-148) did not affect call production until 3-4 weeks post-hatch. These data combined support the idea that neither auditory feedback nor telencephalic sensorimotor circuits are necessary for the production of nestling calls before 3 weeks post-hatch.

Effects of deafening on the development of nestling and juvenile vocalizations in budgerigars (Melopsittacus undulatus).

The effects of complete and partial cochlear extirpation at ages 9-11 days posthatch were assessed in 5 nestling budgerigars (Melopsittacus undulatus) to determine if auditory feedback is necessary for the production of nestling vocalizations. Although early deafening had no effect on the production of food-begging calls produced during the first 2 weeks posthatch, deafening did disrupt the expected transition from these early calls to the longer and more complex frequency-modulated, patterned food-begging calls normally appearing 3-4 weeks posthatch. All birds sustaining either complete or partial cochlear extirpation failed to develop stereotyped contact calls around the time of fledging at 5 weeks. These results are consistent with previous research showing that deafened nestlings do not develop normal contact calls (R. J. Dooling, B. F. Gephart, P. H. Price, C. McHale, & S. E. Brauth, 1987) and also indicate that a form of sensorimotor learning is involved in the production of mature, patterned food-begging calls in budgerigars.

Analysis of the forces and position required for direct laryngoscopic exposure of the anterior vocal folds.

The sniffing position is traditionally considered optimal for direct laryngoscopic examination of the vocal folds. This study examined head and neck positions associated with ideal exposure of the anterior glottal commissure with a variety of laryngoscopes. A prospective investigation was done in 20 patients by comparing the force required to expose the anterior vocal folds by utilizing 3 head and neck positions with 3 different-sized tubular laryngoscopes. The completeness of anterior glottal exposure was rated and the force required to achieve this exposure was measured with a strain gauge. Three positions relating the atlanto-occipital and cervicothoracic vertebrae were analyzed: 1) extension-extension. 2) sniffing: extension-flexion, and 3) flexion-flexion. Head and neck position and laryngoscope size were both statistically significant factors for achieving complete anterior vocal fold exposure. Regardless of the laryngoscope, the number of patients in whom complete exposure could be achieved increased gradually when the position was changed from extension-extension to extension-flexion to flexion-flexion. Complete exposure was inversely related to larger laryngoscope size. According to the data herein, the flexion-flexion position provides the best glottal exposure for endotracheal intubation in those patients who are anatomically predisposed to difficulty in direct examination of the glottis. Because this places the laryngoscope lumen in a vertical position, this position is inappropriate for microlaryngoscopy. The study reinforced the concept that the sniffing position is the optimal position for microlaryngoscopy because it enables the use of the largest-lumened laryngoscope. This facilitates ideal exposure of the anterior vocal folds, which is necessary for phonomicrosurgery.

Cytoarchitecture of vocal control nuclei in nestling budgerigars: relationships to call development.

Changes in the cytoarchitecture of vocal control nuclei were investigated in nestling budgerigars (Melopsittacus undulatus) from hatching to fledging (five to six weeks) in relation to changes in vocalizations produced by nestlings during this period. The nuclei investigated were the hypoglossal nucleus, dorsomedial nucleus of the intercollicular midbrain, central nucleus of the archistriatum, central nucleus of the lateral neostriatum, oval nucleus of the hyperstriatum ventrale, medial division of the oval nucleus of the anterior neostriatum, and magnocellular nucleus of the lobus parolfactorius. These nuclei have been shown to form functional circuits in adults related to vocal learning. Consistent with previously reported results, we found that call development could be described in terms of five different phases based on changes in the duration and segmentation of single and multiple segment food begging calls and the appearance of the first socially learned contact calls around the time of fledging. We also found that call segment duration exhibited an inverted U-shaped developmental function during the nestling period, as has been found for total call duration. Cytoarchitectonic studies revealed striking changes in the cellular architecture of vocal control nuclei during the first four weeks posthatching. At hatching the hypoglossal nucleus exhibits adult-like cytoarchitecture, and the central nucleus of the archistriatum and the central nucleus of the lateral neostriatum are distinguishable from surrounding fields. By one week posthatch, the central nucleus of the archistriatum exhibits an adult-like appearance, while other telencephalic vocal control nuclei do not exhibit adult-like cytoarchitecture until three to four weeks posthatching. By two weeks posthatching, the dorsomedial nucleus of the intercollicular midbrain also exhibits adult-like cytoarchitecture. We observed substantial decreases in the thickness of ventricular proliferation zones during this period, with decreases in ventricular zones occurring at about the same point that nuclei at corresponding levels come to exhibit adult-like cytoarchitectonic features. Of interest is the fact that cytoarchitectural development occurs asynchronously in different brain regions, with the appearance of adult-like characteristics in the hindbrain and midbrain occurring before the appearance of adult-like cytoarchitectonic characteristics in telencephalic nuclei. These results are consistent with recent lesion studies indicating that neither auditory feedback nor telencephalic vocal control nuclei are necessary for the production of food begging and other nestling calls until three to four weeks posthatching.

Effects of deafening on the calls and warble song of adult budgerigars (Melopsittacus undulatus).

Budgerigars are small Australian parrots that learn new vocalizations throughout adulthood. Earlier work has shown that an external acoustic model and auditory feedback are necessary for the development of normal contact calls in this species. Here, the role of auditory feedback in the maintenance of species-typical contact calls and warble song in adult budgerigars is documented. Deafened adult birds (five male, one female) vocalized less frequently and showed both suprasegmental and segmental changes in their contact calls and warble song. Contact calls of all adult-deafened budgerigars showed abnormalities in acoustic structure within days to a few weeks following surgery. Within 6 months of surgery, nearly all contact calls produced by deafened birds were strikingly abnormal, showing highly variable patterns of frequency modulation and duration. The warble song of deafened male budgerigars also differed significantly from that of normal budgerigars on several acoustic measures. These results show that auditory feedback is necessary for the maintenance of a normal, species-typical vocal repertoire in budgerigars.

Functional anatomy of forebrain vocal control pathways in the budgerigar (Melopsittacus undulatus).

Budgerigars throughout life are capable of learning to produce many different sounds including those of human speech. Like humans, budgerigars use multiple craniomotor systems and coordinate both orosensory and auditory feedback in specialized forebrain nuclei. Although budgerigar auditory-vocal learning has a different evolutionary origin from that of human speech, both the human and budgerigar systems can control F0 and can alter the distribution of energy in spectral bands by adjusting the filter properties of the vocal tract. This allows budgerigars to produce an extremely diverse array of calls including many broadband and highly complex sounds.

Vocal control pathways through the anterior forebrain of a parrot (Melopsittacus undulatus).

A feature of the telencephalic vocal control system in the budgerigar (Melopsittacus undulatus) that has been hypothesized to represent a profound difference in organization from the oscine vocal system is its reported lack of an inherent circuit through the anterior forebrain. The present study reports anatomical connections that indicate the existence of an anterior forebrain circuit comparable in important ways to the "recursive" pathway of oscine songbirds. Results from anterograde and retrograde tracing experiments with biocytin and fluorescently labeled dextran amines indicate that the central nucleus of the anterior archistriatum (AAc) is the source of ascending projections upon the oval nuclei of the anterior neostriatum and ventral hyperstriatum (NAo and HVo, respectively). Efferent projections from the latter nuclei terminate in the lateral neostriatum afferent to AAc, thereby forming a short recurrent pathway through the pallium. Previously reported projections from HVo and NAo upon the magnocellular nucleus of the lobus parolfactorius (LPOm), and after LPOm onto the magnocellular nucleus of the dorsal thalamus (DMm; G.F. Striedter [1994] J. Comp. Neurol. 343:35-56), are confirmed. A specific projection from DMm onto NAom is also demonstrated; therefore, a recurrent pathway through the basal forebrain also exists in the budgerigar vocal system that is similar to the anterior forebrain circuit of oscine songbirds. Parallels between these circuits and mammalian basal ganglia-thalamo-cortical circuits are discussed. It is hypothesized that vocal control nuclei of the avian anterior neostriatum may perform a function similar to the primate supplemental motor area.

Mechanisms of vocal production in budgerigars (Melopsittacus undulatus).

Songbirds vocalizing in helium show a change in the spectral quality of their vocalizations. This effect is due to an increase in the speed of sound in helium that in turn alters the resonance properties of the vocal tract. Here, this approach is extended to a psittacine, the budgerigar (Melopsittacus undulatus), whose syringeal anatomy and innervation differ from that of a songbird. Contact calls from birds vocalizing in heliox (70/30 helium/oxygen environment) showed an overall increase in the amount of energy at frequencies above the fundamental, slight changes in the frequency of the fundamental and harmonics, and some change in the level of harmonics. Calls produced by a syringeally denervated bird showed more dramatic changes. Recordings from live birds were compared with sounds produced by various simple "artificial" tracheal and syringeal models. Results suggest that budgerigars produce contact calls using the syringeal membranes as a unitary sound source which produces acoustic energy in a narrow frequency band whose fundamental frequency is matched to the resonant frequency of the trachea. The syrinx is not normally coupled to the tracheal resonator, and resonances probably play only a minor role in shaping the spectrum of contact calls.

Distribution of choline acetyltransferase and acetylcholinesterase in vocal control nuclei of the budgerigar (Melopsittacus undulatus).

The present study used histochemical methods to map the distributions of choline acetyl transferase (ChAT) and acetylcholinesterase (AChE) in the vocal control nuclei of a psittacine, the budgerigar (Melopsittacus undulatus). The distributions of ChAT and AChE in budgerigars appeared similar to that in oscine songbirds despite evidence that these systems have evolved independently. The magnicellular nucleus of the lobus parolfactorius in budgerigars, like the area X in songbirds, contained many ChAT labeled somata, fibers, and varicosities and stained densely for AChE. In contrast, the robust nucleus of the archistriatum (RA) and the supralaminar area of the frontal neostriatum in budgerigars, like the RA and the magnicellular nucleus of the neostriatum (MAN) in songbirds, respectively, contained few or no ChAT labeled somata, fibers, and varicosities and stained lightly for AChE. The central nucleus of the lateral neostriatum in budgerigars, like the higher vocal center (HVC) in songbirds, contained no ChAT labeled somata, moderate densities of ChAT labeled fibers and varicosities, and moderate levels of AChE staining. Two nuclei, the oval nucleus of the hyperstriatum ventrale (HVo) and the oval nucleus of the anterior neostriatum (NAo), contained no ChAT labeled somata, dense ChAT labeled fibers and varicosities, and moderate to high levels of AChE staining. The HVo and the NAo have no counterparts in songbirds but may be important vocal control nuclei in the budgerigar. Cholinergic enzymes are also described in other regions which may be involved in budgerigar vocal behavior, including the basal forebrain, the torus semicircularis, and the hypoglossal nuclei (nXII).

Effect of syringeal denervation in the budgerigar (Melopsittacus undulatus): the role of the syrinx in call production.

In the budgerigar, the left and right tracheosyringeal nerves (ts) were sectioned both above and below the common anastomosis in order to assess the roles of the hypoglossal nuclei and syringeal muscle halves in the control of call production. Signal processing software was used to quantify changes in contact call fundamental frequency and duration, and similarity analysis for pre- and postsurgical contact calls was performed by means of spectrogram cross-correlation. After resecting a portion of either the right or left ts nerve above the anastomosis (thereby eliminating the input from the ipsilateral half of the brainstem), contact call fundamental frequency decreased 40-50% on Day 1 postsurgery, while call structure and duration remained largely unaffected. Fundamental frequency returned to normal within 4-7 days after surgery. In contrast, nerve sectioning below the anastomosis on either side of the syrinx (thereby eliminating input to the ipsilateral half of the syringeal muscles) resulted in moderately noisy harsh-sounding calls with little change in temporal characteristics. Thus, budgerigars differ from many oscines studied to date in that they do not demonstrate laterality in vocal control at the level of the syrinx. Vocalizations produced by birds after bilateral syringeal denervation were abnormal, consisting entirely of broadband harmonic sounds with very low fundamental frequencies (i.e., less than 900 Hz) and poor frequency modulation. In contrast, individual call durations, as well as the rhythm and patterning of vocalizations resembling warble song, were remarkably similar to presurgical recordings after both unilateral and bilateral ts nerve resection.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of lesions in nucleus basalis and field 'L' on vocal learning and performance in the budgerigar (Melopsittacus undulatus).

Lesions were placed in either nucleus basalis (Bas) or the primary thalamorecipient portion of Field 'L' (i.e. centered in Field L2a) in budgerigars at 3-5 weeks posthatching and as adults. The calls of birds sustaining Bas lesions before fledging, or as adults, were markedly abnormal in that they showed little frequency modulation and individual distinctiveness. Call durations, however, were similar for lesioned and unlesioned birds. In contrast, the calls of Field 'L' lesioned birds were similar to those of siblings and cagemates. This implies that the roles of the isthmofrontal (i.e., direct projections from the ventrolateral nucleus of the lateral lemniscus to Bas) and thalamotelencephalic (i.e., direct projections from nucleus ovoidalis thalami to Field L2a) auditory pathways in providing auditory feedback during vocal learning and performance are different and that the isthmofrontal pathway plays an essential role in these processes throughout the life of the animal.

Functional anatomy of forebrain auditory pathways in the budgerigar (Melopsittacus undulatus).

Interconnections of forebrain auditory and vocal control nuclei were mapped in the budgerigar using pathway tracing techniques. The anatomical results indicate four circuits by which auditory information may influence the vocal motor system: (1) direct auditory thalamic projections from nucleus dorsomedialis posterior (DMP) to both the neostriatal higher vocal center (HVC) and robust archistriatal nucleus (RA); (2) direct projections from a neostriatal projection field of DMP (i.e., MAN, the magnocellular nucleus of the neostriatum) to HVC and RA; (3) projections from DMP and other 'accessory' auditory thalamic nuclei to the ventral paleostriatum (VP), which in turn projects to MAN and RA; (4) projections to HVC from the lateral hyperstriatum ventrale (HV), which receives input from nucleus basalis (Bas) as well as from the oval nucleus of the HV (HVo), which receives direct input from RA. Lesion methods were used to evaluate the roles of auditory pathways in call learning and production. The results show that pathways associated with Bas are essential for call production in both adult and unfledged budgerigars, while VP efferents influence vocalization only in young, unfledged budgerigars. Lesions centered in either the primary auditory neostriatum (Field L2a) or the neostriatal area in receipt of Field L input (the ventrolateral neostriatum intermedium or NIVL) did not affect vocalization in juvenile or adult budgerigars.

Effects of yohimbine as a reversing agent for ketamine-xylazine anesthesia in budgerigars.

Fourteen adult budgerigars (Melopsittacus undulatus) were anesthetized with a combination of ketamine hydrochloride (40 mg/kg) and xylazine hydrochloride (10 mg/kg) intramuscularly. Forty-five minutes after ketamine-xylazine injection, one of four yohimbine hydrochloride doses (0.0, 0.11, 0.275, or 0.44 mg/kg, IM) was administered in a 0.7% saline vehicle. Latencies were recorded in minutes from yohimbine injection until subjects' behavior indicated three different points of recovery: 1) lifting the head, 2) standing unaided without ataxia, and 3) perching. Means for all three recovery point latencies were significantly reduced by 0.275 mg/kg of yohimbine compared with saline vehicle alone. Mean latencies among treatment groups for each of the three recovery points were not significantly different, other than control versus treated groups. Based on these results, we recommend a yohimbine dose of 0.275 mg/kg as an effective reversing agent for ketamine-xylazine anesthesia in budgerigars.