Improving patient outcomes with inguinal hernioplasty-local anaesthesia versus local anaesthesia and conscious sedation: a randomized controlled trial

PURPOSE

Conscious sedation is regularly used in ambulatory surgery to improve patient outcomes, in particular patient satisfaction. We hypothesized that the addition of conscious sedation would provide greater patient satisfaction with inguinal hernioplasty compared to local anesthesia alone.

METHODS

This trial was a single-centre, randomized, placebo-controlled, double-blinded trial where patients undergoing inguinal hernioplasty using local anaesthesia were randomized to receive local anaesthesia alone versus local anaesthesia and conscious sedation. The primary outcome of patient satisfaction was assessed using the Iowa Satisfaction with Anesthesia Scale (ISAS). The study was powered to detect a significant difference in ISAS scores between groups. Comparisons were made using T test and Chi square tests. A p value of less than 0.05 was considered significant.

RESULTS

There were 149 patients randomized: 78 to the local anesthesia (LA) group and 71 to the local anaesthesia and conscious sedation (LACS) group. For the primary outcome measure of patient satisfaction, the mean ISAS score was significantly greater in the LACS group (p = 0.009). The experience of pain and pain severity was greater in the LA group (p = 0.016; p = 0.0162 respectively). No statistically significant difference was found between groups with respect to operative time, time to discharge or postoperative complications.

CONCLUSION

The use of conscious sedation with local anesthesia for inguinal hernioplasty is safe, results in less pain experience and severity and is associated with better patient satisfaction. The use of conscious sedation does not delay patient discharge.

Dengue fever mimicking acute appendicitis: A case report

INTRODUCTION

Dengue fever is an acute viral disease, which usually presents as a mild febrile illness. Patients with severe disease present with dengue haemorrhagic fever or dengue toxic shock syndrome. Rarely, it presents with abdominal symptoms mimicking acute appendicitis. We present a case of a male patient presenting with right iliac fossa pain and suspected acute appendicitis that was later diagnosed with dengue fever following a negative appendicectomy.

PRESENTATION OF CASE

A 13-year old male patient presented with fever, localized right-sided abdominal pain and vomiting. Abdominal ultrasound was not helpful and appendicectomy was performed due to worsening abdominal signs and an elevated temperature. A normal appendix with enlarged mesenteric nodes was found at surgery. Complete blood count showed thrombocytopenia with leucopenia. Dengue fever was now suspected and confirmed by IgM enzyme-linked immunosorbent assay against dengue virus.

DISCUSSION

This unusual presentation of dengue fever mimicking acute appendicitis should be suspected during viral outbreaks and in patients with atypical symptoms and cytopenias on blood evaluation in order to prevent unnecessary surgery.

CONCLUSION

This case highlights the occurrence of abdominal symptoms and complications that may accompany dengue fever. Early recognition of dengue fever mimicking acute appendicitis will avoid non-therapeutic operation and the diagnosis may be aided by blood investigations indicating a leucopenia, which is uncommon in patients with suppurative acute appendicitis.

Minimally invasive surgery training in the Caribbean--a survey of general surgical residents and their trainers

BACKGROUND

There has been debate on the feasibility of incorporating minimally invasive surgery (MIS) into surgical practice in developing countries due to resource and training limitations. Our study establishes the current and desired state of MIS training in surgical residency programmes in the Caribbean.

METHODS

An adapted version of a previously administered questionnaire was issued to surgeons and residents involved in the general surgical residency programme of The University of the West Indies in Barbados, Jamaica and Trinidad and Tobago. Data were analysed using the Statistical Package for the Social Sciences, version 17.0.

RESULTS

The questionnaire was sent to 41 surgeons and 41 residents with a 65% response rate. Most residents had performed less than 25 basic laparoscopic procedures. Up to 82% of residents felt that they would be unable to perform advanced laparoscopic procedures due to lack of training. The principal negative factors influencing MIS training included lack of operating room time, lack of equipment and lack of preceptor expertise. Both surgeons (83.4%) and residents (93.4%) strongly felt that a surgical skills laboratory would be helpful for the acquisition of MIS skills. Both surgeons (85.7%) and residents (100%) felt that there was a role for an MIS surgeon in fulfilling training obligations.

CONCLUSION

The basic and advanced MIS experience of residents in the Caribbean is limited. Surgeon training and resource limitations are major contributing factors. There is a strong desire on the part of surgeons and residents alike for the incorporation of more effective MIS training into the residency programme in the Caribbean.

Open abdominal aortic aneurysm repair in the era of endovascular repair

OBJECTIVES

The development of minimally invasive techniques for abdominal aortic aneurysm (AAA) repair and the establishment of specialized centres have resulted in improved patient outcomes. This study examines open AAA repair at a non-specialized centre where advanced techniques are not practised.

METHODS

We conducted a retrospective analysis on a cohort of 83 patients presenting for AAA repair to a non-specialized hospital, the University Hospital of the West Indies (UHWI). The end points assessed included operative (30-day) mortality, postoperative complications, duration of operation, blood loss, intensive care unit (ICU) stay and overall hospital stay.

RESULTS

The overall operative mortality was 9.4% (23% for ruptured aneurysms and 5% for unruptured aneurysms). Mean operating time, blood loss, ICU stay and hospital stay were 326 +/- 98 minutes, 2420 +/- 1397 mls, 3 +/- 5 days and 9 +/- 5 days, respectively with no significant differences noted between ruptured and unruptured aneurysms. Mean aneurysm diameter was 6.13 +/- 1.59 cm.

CONCLUSION

Mortality rates for open aneurysm repair at the UHWI are consistent with findings in the current literature. Open AAA repair remains a safe treatment option in this environment. Continued improvements need to be made with respect to minimizing blood loss and operation duration, particularly in repairs of unruptured aneurysms.

Laparoscopic colectomy for colonic neoplasms in a developing country

AIM

To report the outcome of patients treated for colonic neoplasms using a laparoscopic assisted technique since its introduction at the University Hospital of the West Indies, Jamaica.

SUBJECTS AND METHODS

All consecutive patients undergoing laparoscopic assisted colectomy were entered into a prospective database and this data analysed. Data collected included patient demographics, pre-operative diagnosis, operative events, post-operative morbidity and outcome.

RESULTS

Over the thirty-six months period July 1, 2005-December 31, 2005 and July 1, 2006-December 31, 2008, thirty patients each underwent laparoscopic assisted colectomy for a colonic neoplasm. Their mean age was 63 years with M: F ratio of 1:2. Seventy-four per cent of the patients had carcinomas which was located on the right and sigmoid colon in 17 and 10 patients respectively. Mean operative time was 98 min for patients with right-sided lesions and blood loss for the entire group was minimal. Two patients were converted to open resections. Median duration of hospitalization was five days. There was no mortality but three patients had complications. After median follow-up of 30 months, there was no local or systemic recurrence.

CONCLUSIONS

Appropriately selected patients with colonic neoplasms can be safely subjected to a laparoscopic assisted resection and expect to enjoy the advantages of this technique even in a developing country setting. The outcome of thirty consecutive laparoscopic assisted colectomies is reported demonstrating that this technique can be safely applied to selected patients with colonic carcinomas in developing countries.

Duodenal fibrosarcoma mimicking Franz tumour complicated by post-resection chylous ascites

This case report presents a young woman who underwent a Whipples resection for a large pan-creato-duodenal tumour. Pathology and immunohistochemical analysis of the tumour suggest duodenal fibrosarcoma. The patient's postoperative management was complicated by chylous ascites. A brief literature review is given to highlight this unusual case.

Hermaphroditism: cytogenetics, gonadal pathology and gender assignment: a case report

True hermaphroditism is a rare intersex disorder in which individuals possess both testicular and ovarian gonadal tissue. A case of true unilateral hermaphroditism presenting with ambiguous external genitalia, right scrotal testis and left pelvic ovotestis is herein outlined Phallic, gonadal and genetic factors were considered before male gender was assigned. Gender assignment procedures have been questioned by intersex activists opposed to early genital surgery. Western societies have a binary perspective on gender and this leads to a stigma being placed on intersex cases. A multidisciplinary approach to this problem involving paediatric specialists in the field, of endocrinology, surgery and psychiatry is necessary, along with educational programmes that promote tolerance in society to variations in gender.

Does exogenous GM1 ganglioside enhance the effects of electrical stimulation in ameliorating degeneration after neonatal deafness?

This study examined the combined effects of administration of exogenous GM1 ganglioside and electrical stimulation on the cochlear nucleus (CN) of cats deafened neonatally by ototoxic drugs. Five normal hearing adult cats served as controls. Another 12 cats were deafened bilaterally by daily injections of neomycin sulfate (60 mg/kg) for 17-21 days after birth until auditory brainstem testing demonstrated profound hearing loss. Six of the deaf animals comprised the GM1 group, which received daily injections of GM1 ganglioside (30 mg/kg) for 28-38 days during the period after profound deafness was confirmed, and prior to receiving a cochlear implant. The non-GM1 group (n=6) received no treatment during this interim period. All the deafened animals underwent unilateral cochlear implantation at 6-9 weeks postnatal and received several months (mean duration, 32 weeks) of chronic electrical stimulation (4 h/day, 5 days/week). Stimulation was delivered by intracochlear bipolar electrodes, using electrical signals that were designed to be temporally challenging to the central auditory system. Results showed that in the neonatally deafened animals, both the GM1 and non-GM1 groups, the volume of the CN was markedly reduced (to 76% of normal), but there was no difference between the animals that received GM1 and those that did not. The cross sectional areas of spherical cell somata in both GM1 and non-GM1 groups also showed a highly significant reduction in size, to < or =75% of normal after neonatal deafening. Moreover, in both the GM1 and non-GM1 groups, the spherical cells in the CN ipsilateral to the implanted cochlea were significantly larger (6%) than cells in the control, unstimulated CN. Again, however, there was no significant difference between the GM1 group and the non-GM1 group in spherical cell size. These results contrast sharply with previous reports that exogenous GM1 prevents CN degeneration after neonatal conductive hearing loss and partially prevents spiral ganglion cell degeneration when administered immediately after ototoxic drug deafening in adult animals. Taken together, findings to date suggest that GM1 may be effective in preventing degeneration only if the GM1 is administered immediately at the time hearing loss occurs.

The effect of electrode configuration and duration of deafness on threshold and selectivity of responses to intracochlear electrical stimulation

This report examines the effects of intracochlear electrode configuration and mode of stimulation (bipolar or monopolar) on neural threshold and spatial selectivity in the inferior colliculus (IC) of the cat. Single and multiunit IC recordings were made in three groups of animals; acutely deafened adults (controls), neonatally deafened animals studied at 6 to 18 months of age and neonatally deafened cats studied at 2.5 to 6.5 years. Response thresholds were plotted versus IC depth to measure the spatial distribution of responses. The response selectivity for each stimulating configuration was defined as the width of the resulting spatial tuning curve (STC) measured at 6 dB above threshold. Spiral ganglion cell (SG) survival was examined histologically in all neonatally deafened animals and correlated with physiological results. Animals studied at less than 1.5 years had SG densities of 23.5%-64.4% of normal (mean=42.7%) while animals studied at greater than 2.5 years had densities of 5.1%-18.3% of normal (mean=9.9%). Electrophysiological results include the following. (1) Monopolar thresholds were 7-8 dB lower than bipolar thresholds in the same animals. (2) Varying the configuration of bipolar contacts (measured as radial, offset radial and longitudinal pairs) did not systematically affect IC threshold in either controls or short-term neonatally deafened animals. In contrast, the long-term neonatally deafened animals showed a difference in threshold with each configuration. (3) The spatial distributions (Q(6 dB)) of responses to bipolar stimulation were approximately 40% more restricted than those for monopolar stimulation. (4) The spatial selectivity of neonatally deafened animals studied at ages up to 1.5 years was equal to that of control animals with normal auditory experience. However, selectivity was degraded in the older animals. (5) Selectivity was decreased in some animals with the longitudinal bipolar configuration and multiple response peaks were seen in several cases using this stimulus configuration.

Plasticity in central representations in the inferior colliculus induced by chronic single- vs. two-channel electrical stimulation by a cochlear implant after neonatal deafness

The goal of this research is to examine the functional consequences of patterned electrical stimulation delivered by a cochlear implant in the deafened developing auditory system. In previous electrophysiological experiments conducted in the inferior colliculus (IC), we have demonstrated that the precise cochleotopic organization of the central nucleus (ICC) develops normally in neonatally deafened unstimulated cats and is unaltered despite the lack of normal auditory input during development. However, these studies also showed that chronic electrical stimulation delivered at a single intracochlear location by one bipolar channel of a cochlear implant induces significant expansion of the central representation of the stimulated cochlear sector and degrades the cochleotopic organization of the IC. This report presents additional data from a new experimental series of neonatally deafened cats that received chronic stimulation on two adjacent bipolar intracochlear channels of a cochlear implant. Results suggest that competing inputs elicited by electrical stimulation delivered by two adjacent channels can maintain the selective representations of each activated cochlear sector within the central auditory system and prevent the expansion seen after single-channel stimulation. Alternating stimulation of two channels and use of highly controlled electrical signals may be particularly effective in maintaining or even sharpening selectivity of central representations of stimulated cochlear sectors. In contrast, simultaneous stimulation using two channels of a model analog cochlear implant processor in one experimental animal failed to maintain channel selectivity and resulted in marked expansion and fusion of the central representations of the stimulated channels. This potentially important preliminary result suggests that under some conditions the central auditory system may be unable to discriminate simultaneous, overlapping inputs from adjacent cochlear implant channels as distinct.

Responses of inferior colliculus neurons to amplitude-modulated intracochlear electrical pulses in deaf cats

Current cochlear prostheses use amplitude-modulated pulse trains to encode acoustic signals. In this study we examined the responses of inferior colliculus (IC) neurons to sinusoidal amplitude-modulated pulses and compared the maximum unmodulated pulse rate (Fmax) to which they responded with the maximum modulation frequency (maxFm) that they followed. Consistent with previous results, responses to unmodulated pulses were all low-pass functions of pulse rate. Mean Fmax to unmodulated pulses was 104 pulses per second (pps) and modal Fmax was 60 pps. Above Fmax IC neurons ceased responding except for an onset burst at the beginning of the stimulus. However, IC neurons responded to much higher pulse rates when these pulses were amplitude modulated; 74% were relatively insensitive to carrier rate and responded to all modulated carriers including those exceeding 600 pps. In contrast, the responses of these neurons (70%) were low-pass functions of modulation frequency, and the remaining (30%) had band-pass functions with a maxFm of 42 and 34 Hz, respectively. Thus temporal resolution of IC neurons for modulated frequencies is significantly lower than that for unmodulated pulses. These two measures of temporal resolution (Fmax and maxFm) were uncorrelated (r(2) = 0.101). Several parameters influenced the amplitude and temporal structure of modulation responses including modulation depth, overall intensity and modulation-to-carrier rate ratio. We observed distortions in unit responses to amplitude-modulated signals when this ratio was 1/4 to 1/6. Since most current cochlear implant speech processors permit ratios that are significantly greater than this, severe distortion and signal degradation may occur frequently in these devices.

Electrical cochlear stimulation in the deaf cat: comparisons between psychophysical and central auditory neuronal thresholds

Cochlear prostheses for electrical stimulation of the auditory nerve ("electrical hearing") can provide auditory capacity for profoundly deaf adults and children, including in many cases a restored ability to perceive speech without visual cues. A fundamental challenge in auditory neuroscience is to understand the neural and perceptual mechanisms that make rehabilitation of hearing possible in these deaf humans. We have developed a feline behavioral model that allows us to study behavioral and physiological variables in the same deaf animals. Cats deafened by injection of ototoxic antibiotics were implanted with either a monopolar round window electrode or a multichannel scala tympani electrode array. To evaluate the effects of perceptually significant electrical stimulation of the auditory nerve on the central auditory system, an animal was trained to avoid a mild electrocutaneous shock when biphasic current pulses (0.2 ms/phase) were delivered to its implanted cochlea. Psychophysical detection thresholds and electrical auditory brain stem response (EABR) thresholds were estimated in each cat. At the conclusion of behavioral testing, acute physiological experiments were conducted, and threshold responses were recorded for single neurons and multineuronal clusters in the central nucleus of the inferior colliculus (ICC) and the primary auditory cortex (A1). Behavioral and neurophysiological thresholds were evaluated with reference to cochlear histopathology in the same deaf cats. The results of the present study include: 1) in the cats implanted with a scala tympani electrode array, the lowest ICC and A1 neural thresholds were virtually identical to the behavioral thresholds for intracochlear bipolar stimulation; 2) behavioral thresholds were lower than ICC and A1 neural thresholds in each of the cats implanted with a monopolar round window electrode; 3) EABR thresholds were higher than behavioral thresholds in all of the cats (mean difference = 6.5 dB); and 4) the cumulative number of action potentials for a sample of ICC neurons increased monotonically as a function of the amplitude and the number of stimulating biphasic pulses. This physiological result suggests that the output from the ICC may be integrated spatially across neurons and temporally integrated across pulses when the auditory nerve array is stimulated with a train of biphasic current pulses. Because behavioral thresholds were lower and reaction times were faster at a pulse rate of 30 pps compared with a pulse rate of 2 pps, spatial-temporal integration in the central auditory system was presumably reflected in psychophysical performance.

Behavioral and neurophysiological thresholds for electrical cochlear stimulation in the deaf cat

Psychophysical detection thresholds for unmodulated electrical pulse trains or for sinusoidally amplitude-modulated (SAM) pulse trains were estimated in deaf juvenile cats using a conditioned avoidance paradigm. Biphasic current pulses (0.2 ms/phase) were delivered by scala tympani electrodes consisting of 4-8 electrode contacts driven as bipolar pairs. Electrical auditory brainstem response (EABR) thresholds were obtained periodically, and at the conclusion of behavioral training, response thresholds were obtained for neurons in the inferior colliculus (IC) and the primary auditory cortex (A1) in acute physiological experiments in the same animals. The results of the study include: (1) detection thresholds for unmodulated pulse trains and for SAM pulse trains were virtually identical; (2) EABR thresholds and behavioral thresholds were significantly correlated, although EABR thresholds consistently overestimated behavioral thresholds; (3) the lowest thresholds in the IC and the A1 were significantly correlated with behavioral thresholds, and (4) mean lowest thresholds in the IC and the A1 were essentially the same as the mean psychophysical detection threshold in the trained deaf cats.

Temporal properties of chronic cochlear electrical stimulation determine temporal resolution of neurons in cat inferior colliculus

As cochlear implants have become increasingly successful in the rehabilitation of adults with profound hearing impairment, the number of pediatric implant subjects has increased. We have developed an animal model of congenital deafness and investigated the effect of electrical stimulus frequency on the temporal resolution of central neurons in the developing auditory system of deaf cats. Maximum following frequencies (Fmax) and response latencies of isolated single neurons to intracochlear electrical pulse trains (charge balanced, constant current biphasic pulses) were recorded in the contralateral inferior colliculus (IC) of two groups of neonatally deafened, barbiturate-anesthetized cats: animals chronically stimulated with low-frequency signals (< or = 80 Hz) and animals receiving chronic high-frequency stimulation (> or = 300 pps). The results were compared with data from unstimulated, acutely deafened and implanted adult cats with previously normal hearing (controls). Characteristic differences were seen between the temporal response properties of neurons in the external nucleus (ICX; approximately 16% of the recordings) and neurons in the central nucleus (ICC; approximately 81% of all recordings) of the IC: 1) in all three experimental groups, neurons in the ICX had significantly lower Fmax and longer response latencies than those in the ICC. 2) Chronic electrical stimulation in neonatally deafened cats altered the temporal resolution of neurons exclusively in the ICC but not in the ICX. The magnitude of this effect was dependent on the frequency of the chronic stimulation. Specifically, low-frequency signals (30 pps, 80 pps) maintained the temporal resolution of ICC neurons, whereas higher-frequency stimuli significantly improved temporal resolution of ICC neurons (i.e., higher Fmax and shorter response latencies) compared with neurons in control cats. Furthermore, Fmax and latencies to electrical stimuli were not correlated with the tonotopic gradient of the ICC, and changes in temporal resolution following chronic electrical stimulation occurred uniformly throughout the entire ICC. In all three experimental groups, increasing Fmax was correlated with shorter response latencies. The results indicate that the temporal features of the chronically applied electrical signals critically influence temporal processing of neurons in the cochleotopically organized ICC. We suggest that such plastic changes in temporal processing of central auditory neurons may contribute to the intersubject variability and gradual improvements in speech recognition performance observed in clinical studies of deaf children using cochlear implants.

Chronic electrical stimulation by a cochlear implant promotes survival of spiral ganglion neurons after neonatal deafness

This investigation examined the consequences of neonatal deafness and chronic intracochlear electrical stimulation delivered by a cochlear implant during maturation. Kittens were bilaterally deafened by an ototoxic drug administered daily for 2 weeks immediately after birth. Unilateral electrical stimulation was initiated at 7-10 weeks of age and continued over periods of 22-47 weeks (4 hours/day; 5 days/week). Bipolar intracochlear electrodes delivered one of several different electrical signals designed to be temporally challenging to the central auditory system. Morphometric evaluation of spiral ganglion (SG) cell somata within Rosenthal's canal demonstrated a mean of approximately 50% of normal cell density maintained in the chronically stimulated ears, compared with approximately 30% on the control deafened side. This 20% difference in density was highly significant and was greater than differences reported in earlier studies using 30 pps stimulation delivered by either intracochlear bipolar or round window monopolar electrodes. However, the duration of stimulation was also longer in the present study, so it is unclear to what extent the nature of the temporally challenging stimulation vs. its duration contributed to the marked increase in survival. Measurements of the SG cell somata revealed a pronounced decrease in cell diameter in neonatally deafened cats studied about 1 year after deafening, and an additional decrease after long-term deafness (2.5-6.5 years). Furthermore, in the cochlear regions with the greatest stimulation-induced differences in SG cell density, direct measurements of cross-sectional soma area of the largest cells revealed that cells were significantly larger in the stimulated ears. Thus, in addition to the marked increase in the number of surviving SG cells, larger soma area contributed modestly to the pronounced increase in neural density following chronic electrical stimulation.

Postnatal development of the organ of Corti in cats: a light microscopic morphometric study

This study quantitatively characterizes the development of the major morphological features of the organ of Corti during the first 2 weeks postnatal, the period when the cat auditory system makes the transition from being essentially non-functional to having nearly adult-like responses. Four groups of kittens (n = 3) were studied at one day postnatal (P1), P5, P10, P15, and compared to adults. Measurements were made of the organ of Corti at 3 cochlear locations: 20%, 60% and 85% of basilar membrane length from the base cochlear locations which in the adult correspond to best frequencies of approximately 20 kHz, 2 kHz and 500 Hz, respectively. In addition, measurements of basilar membrane length and opening of the tunnel of Corti were made in 20 cochlear specimens from kittens aged P0-P6. Results indicate that: (i) at P0 the basilar membrane has attained adult length, and the tunnel of Corti is open over approximately the basal one-half of the cochlea; (ii) the initial opening of the tunnel of Corti occurs at a site about 4 mm from the cochlear base (best frequency of approximately 25 kHz in the adult cochlea); (iii) the thickness of the tympanic cell layer decreases markedly at the basal 20-kHz location; (iv) the areas of the tunnel of Corti and space of Nuel and the angulation of the inner hair cells (IHC) relative to the basilar membrane all show marked postnatal increases at both the middle and apical locations; (v) IHC are nearly adult-like in length and shape at birth, whereas the OHC (at 2-kHz and 500-Hz locations) undergo marked postnatal changes; (vi) disappearance of the marginal pillars and maturation of the supporting cells are not yet complete by P15.

Cochlear pathology induced by aminoglycoside ototoxicity during postnatal maturation in cats

Cochlear pathology resulting from neonatal administration of the aminoglycoside antibiotic, neomycin sulfate, was studied in young kittens at 15-24 days postnatal. Hearing thresholds showed severe to profound hearing loss in all but one animal. Scanning electron microscopy demonstrated that initial hair cell degeneration occurred in the extreme base (hook region) of the cochlea and sequentially progressed to the basal, middle, then the apical coil of the cochlea. The first row of outer hair cells degenerated first, followed by row 2, then row 3; the last cells to degenerate in a given region were the inner hair cells. This pattern of hair cell degeneration is similar to that seen in adults with neomycin ototoxicity. In contrast, the spiral ganglion exhibited a different pattern of degeneration with initial cell loss occurring in the middle of the cochlea, about 40-60% from the base (approximately 2.8-8 kHz). Thus, neuronal degeneration apparently is not secondary to sensory cell loss, but rather comprises an independent process in these neonatal animals. Taken together, the findings suggest that the spiral ganglion cell loss in the middle cochlear turn results from increased aminoglycoside sensitivity associated with an earlier initial onset of function in these neurons as compared to other cochlear regions.

Topography of spiral ganglion projections to cochlear nucleus during postnatal development in cats

A fundamenntal organizational principle of the central auditory system is that virtually all areas are tonotopically organized. However, we know very little about the timing or mechanisms that are responsible for the development of this organization. When cats are born, their auditory nervous systems are extremely immature, and their hearing thresholds are very high. Until postnatal days 7-10 (P7-10), cats have behavioral and physiological thresholds which are near or above the pain threshold for adults and also have poor frequency selectivity. Physiological thresholds for auditory nerve fibers and cochlear nucleus neurons are typically above 100-120 dB SPL (sound pressure level re 20 microPa). Three weeks later (at approximately P31), the sensitivity and frequency discrimination (tuning) of these neurons approximate adult values. This study examines the development of the tonotopic projections from the spiral ganglion to the cochlear nucleus during the period in cat development in which the auditory system undergoes the transition from being essentially nonfunctional to having adult-like function. With the animals heavily anesthetized, the cochleas were surgically exposed in kittens ranging in age from P6 to P45. Focal injections of Neurobiotin (NB) were made into Rosenthal's canal, labeling a small cluster of cells in the spiral ganglion of each cochlea. The projections of these labeled cells were visualized as frequency-specific bands of labeled axons and terminals in all major subdivisions of the cochlear nucleus. The thickness of these bands (i.e., the dimension of the bands orthogonal to the isofrequency representation and across the frequency gradient) were measured and compared to similar projections in adults. As in adult cats, the thickness of the bands varied only slightly with the location of the injection site (frequency representation) over a range of 1-7 mm from the cochlear base (45-13 kHz). Moreover, band thickness did not vary significantly with age. These data indicate that the tonotopic organization of spiral ganglion projections to the cochlear nucleus is as precise in kittens as young as P6 as it is in adults.

Quantitative analysis of spiral ganglion projections to the cat cochlear nucleus

A quantitative examination of the tonotopic organization of primary afferent projections to the cochlear nucleus (CN) in adult cats was conducted by using focal extracellular injections of Neurobiotin (NB) into the spiral ganglion of the basal cochlea. One to three injections separated by intervals of at least 2 mm were positioned along the basal one-third of the cochlea. Each injection produced discrete projection laminae that appeared as parallel horizontal sheets of labeled axons terminals distributed sequentially dorsally to ventrally across each major CN subdivision: the anteroventral, posteroventral, and dorsal cochlear nucleus, (AVCN, PVCN, and DCN, respectively). The length (rostrocaudal dimension), width (mediolateral dimension), thickness (dorsoventral dimension), and relative placement of 18 "frequency-band" laminae were measured in 10 adult cochlear nuclei. The average AVCN projection thickness was approximately twice that of the PVCN and DCN projections. In double injection cases, the center-to-center separation between AVCN laminae was also approximately twice that in the PVCN and equal to that in the DCN. Lamina thickness did not differ significantly as a function of frequency representation. However, in both width and length, mid-frequency laminae were up to two times larger than high-frequency laminae. Thus, the results indicate that DCN projections are the most discrete (i.e., are the thinnest and have the least overlap between adjacent frequency projections), whereas the AVCN projections are the largest but are as discrete as PVCN projections. In addition, high-frequency projections are smaller and more discrete than mild-frequency projections, which are larger and have greater overlap with adjacent frequency projections.

Consequences of chronic extracochlear electrical stimulation in neonatally deafened cats

This investigation examined the consequences of neonatal deafness and chronic electrical stimulation of the cochlea in the developing auditory system. Cats were bilaterally deafened by daily ototoxic drug administration for two weeks after birth. Electrical stimulation was initiated at 6-9 weeks of age and continued for up to 6 months, using monopolar round window electrodes that synchronously excited auditory neurons throughout the cochlea. Morphometric evaluation of the density of spiral ganglion cell somata within Rosenthal's canal demonstrated that chronic stimulation induced an increase of about 6% in neuronal survival. Although this difference was statistically significant, extracochlear stimulation in these cats was less effective in preventing neural degeneration than lower intensity, more restricted intracochlear stimulation that was shown in a previous study to induce an average increase of about 13% in neuronal survival. Electrophysiological recording experiments conducted in the inferior colliculus in these animals indicated that monopolar extracochlear stimulation can induce profound alterations in the spatial (frequency) selectivity of the auditory midbrain. On average, results were similar to those previously reported for bipolar intracochlear stimulation, showing about a two-fold expansion of the central representation of chronically stimulated electrodes. However, results with extracochlear stimulation showed much greater variability among individual animals. The results presented suggest that it is problematic to effect consistent 'whole' nerve stimulation using monopolar round window electrodes. Moreover, this mode of stimulation can induce profound functional alterations in the central nervous system and is substantially less effective in forestalling the degeneration of auditory neurons than intracochlear stimulation. Both these results contraindicate the implantation of such electrodes in young children for the purpose of maintaining the integrity of the auditory system for later application of a multichannel cochlear implant.

Changes in the cat cochlear nucleus following neonatal deafening and chronic intracochlear electrical stimulation

The effects of chronic intracochlear electrical stimulation on the cochlear nucleus (CN) were studied in eight cats that were neonatally deafened by daily intramuscular injections of neomycin. Profound hearing loss was confirmed in each animal by auditory brainstem response (ABR) and frequency following response (500 Hz) testing. Five of the kittens were implanted unilaterally with a scala tympani electrode array at ages 8-16 weeks. These kittens were stimulated daily for four hours at 2 dB above the evoked ABR threshold, over a period of three months, and subsequently euthanized for histological analysis at 26-32 weeks of age. The three remaining deaf kittens were maintained without stimulation over prolonged periods in order to study the long-term consequences of neonatal deafening, and were euthanized at 66-133 weeks of age. This study compares the CN of these deafened experimental animals and the CN of normal adult cats. Three experimental parameters were examined: CN volume, cross-sectional area of spherical cells in the rostral anteroventral cochlear nucleus (AVCN), and spherical cell density in this same region. The CN in animals that received electrical stimulation showed significant bilateral degenerative changes in all three measured parameters. Total nuclear volume was reduced by 35-36%, spherical cell size was reduced by 20-26%, and spherical cell density decreased by 36-42%, as compared to the normal cat CN. Comparisons were also made in the stimulated animals between CN ipsilateral to the stimulated cochlea and the contralateral, unstimulated CN.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial organization of inner hair cell synapses and cochlear spiral ganglion neurons

The morphological organization of the central projections of the cat cochlear spiral ganglion into the cochlear nucleus was previously investigated by creating restricted lesions in the anteroventral cochlear nucleus (AVCN) to ablate selectively either the lateral or the medial aspect of isofrequency projection laminae. Such lesions resulted in highly selective retrograde degeneration of spiral ganglion cells. Ablation of the lateral part of the AVCN caused degeneration of cells within the scala tympani part of the ganglion, whereas medial ablations within the AVCN induced degeneration of the scala vestibuli aspect of the ganglion. The peripheral axons also degenerated and this fiber loss exhibited selective topographies that paralleled the cell loss within the spiral ganglion, although this phenomenon was more prominent in the proximal part of the osseous spiral lamina near the ganglion and less obvious more distally near the habenula perforata. In this investigation, inner hair cells (IHCs) from these selective lesion cases were evaluated by electron microscopy of serial sections through the basal synaptic regions. Results demonstrated differential degeneration of afferent synapses, with greater (but not completely selective) loss of pillar synapses after lateral AVCN lesions and greater loss of modiolar synapses after medial lesions. Because auditory nerve fibers of different spontaneous discharge rates (SRs) have different spatial distributions on the IHC (Liberman, Science 216:1239, 1982), our results suggest that this SR-based organization is maintained in a topographic organization across the vertical (scala tympani-to-scala vestibuli) dimension of the spiral ganglion cell cluster and carried into the ventral cochlear nuclei (VCN). Thus, in addition to the spiral frequency organization represented by the dorsal-to-ventral frequency map in the VCN, there is also an orderly organization of inputs from high- and low-SR fibers across the lateral-to-medial dimension of the VCN such that the lateral isofrequency laminae receive a proportionately greater input from high-SR fibers, whereas medial isofrequency laminae receive preferential input from low- and medium-SR fibers.

Chronic intracochlear electrical stimulation in neonatally deafened cats: effects of intensity and stimulating electrode location

An earlier study conducted in this laboratory suggested that chronic intracochelear electrical stimulation at moderate current levels can at least partially delay or prevent the retrograde degeneration of primary auditory (spiral ganglion) neurons that otherwise is progressive after neonatal deafness induced by ototoxic drug administration. Increased survival of spiral ganglion neurons was observed within the basal cochlear region near the stimulating biopolar electrode pairs, while in more apical regions there was no significant difference between the stimulated and control cochleas. The mechanisms underlying this maintenance of spiral ganglion neurons induced by chronic electrical stimulation are uncertain, especially since increased neuronal survival was observed over broader sectors of the ganglion than would be expected to be directly activated by the bipolar electrodes and moderate stimulation intensity (6 dB above electrically evoked auditory brainstem response threshold) used. In this report, data are presented from a second series of neonatally deafened and chronically stimulated cats. The parameters for chronic electrical stimulation were manipulated in two simple ways. First, the intensity of the electrical stimulus was reduced from the earlier study, while the duration of chronic stimualtion periods was increased; and secondly, two different intracochlear positions of stimulating electrodes were employed in different experimental groups. Results indicate that elecrical stimulation of the cochlea at an extremely low intensity (2 dB above electrically evoked auditory brainstem response threshold) is sufficient to at least partially prevent or delay ganglion cell degeneration in the deafened cochlea. In addition, data suggest a differential distribution of the maintained or conserved ganglion cells, such that when the stimulating electrode pair was positioned near the base of the cochlea increased ganglion survival in a more basal cochlear sector, while stimulation at a more apical site resulted in increased neuronal survival extending to more apical regions.

Topographic organization of the cochlear spiral ganglion demonstrated by restricted lesions of the anteroventral cochlear nucleus

The morphological organization of the central projections of the cat cochlear spiral ganglion into the cochlear nucleus has been investigated by creating restricted lesions in the anteroventral cochlear nucleus (AVCN) in order to ablate selectively either the lateral or the medial aspect of isofrequency projection laminae. Such lesions induced highly selective retrograde degeneration of spiral ganglion cells. Ablation of the lateral part of the AVCN resulted in degeneration of cells within the scala tympani portion of the ganglion, whereas medial lesions within the AVCN induced degeneration of the scala vestibuli portion of the ganglion. Since most, if not all, of the primary afferent axons of the cochlear nerve bifurcate into ascending and descending branches as they enter the brainstem, it is noteworthy that selective damage to the ascending branch in the AVCN was sufficient to induce retrograde degeneration of the spiral ganglion cell somata. The peripheral and central axons also degenerated, and the losses of both the radial nerve fibers in the osseous spiral lamina and the central axons passing into the modiolus displayed selective topographies that paralleled the cell loss within the spiral ganglion. The results of this study support our previous hypothesis, based upon earlier horseradish peroxidase labeling experiments, that there is a topographic organization to the projection of the spiral ganglion within the isofrequency laminae that is orthogonal to the frequency representation within the ventral cochlear nuclei (VCN). That is, in addition to the spiral frequency organization of the ganglion, represented by the dorsal-to-ventral frequency map in the VCN, there is also an orderly and sequential distribution of inputs from the vertical (scala tympani-to-scala vestibuli) dimension of the spiral ganglion across the lateral-to-medial axis of the VCN. The interaction of these two topographic representations, distributed across the three dimensions of the VCN, must partly define the selective and/or integrative neuronal response properties at this first level of central nervous system processing of auditory signals within the cochlear nuclei.

Chronic intracochlear electrical stimulation in the neonatally deafened cat. II. Temporal properties of neurons in the inferior colliculus

The major focus of this study was to define the effects of chronic intracochlear electrical stimulation (ICES) on single unit responses in the inferior colliculus from three experimental groups: 1) normal adults 2) neonatally-deafened/unstimulated adults; and 3) neonatally-deafened/chronically stimulated adults. The major findings include: 1) IC neurons in normal adults showed a diversity of perstimulus responses to ICES which were qualitatively similar to those evoked by acoustic stimuli. They responded with: an onset burst, a sustained discharge, a decrease in their spontaneous activity, or a strong post-stimulus response. The excitatory responses showed either a monotonic or a nonmonotonic increase in activity with increasing stimulus intensity. Response latencies ranged from 5 to over 40 ms. 2) Responses to ICES in normal and deafened/unstimulated animals were virtually indistinguishable from one another. 3) In contrast, responses to ICES in neonatally deafened stimulated animals were different from normal and from deafened, unstimulated animals. Their perstimulus response latencies were significantly shorter, their late response latencies were significantly longer, and the frequency of occurrence of inhibitory and late responses were significantly higher. From these results we conclude that the responses to intracochlear electrical stimulation are directly comparable to those observed following normal acoustic stimulation; that development of cochleotopic organization of the inferior colliculus is not affected by the almost complete lack of normal acoustic input experienced by neonatally deafened animals; and that the basic response properties of IC units are likewise unaffected by neonatal deafening. Moreover, the results suggest that, although the limited regime of electrical stimulation employed in these studies produced no major qualitative distortions in the perstimulus response patterns of IC neurons, it did result in some quantitative changes in those responses.

Chronic intracochlear electrical stimulation induces selective survival of spiral ganglion neurons in neonatally deafened cats

Ten newborn kittens were deafened by systemic administration of neomycin sulfate. Profound hearing losses were documented by ABR and FFR (500 Hz) testing. At 9-17 weeks of age, the young deafened cats were unilaterally implanted with a multichannel scala tympani electrode. Six of the animals were chronically stimulated at 6 dB above electrically evoked ABR thresholds for 1 h/day for periods of 1 month or 3 months. Stimuli were charge-balanced biphasic pulses (200 microseconds/phase, 30 pps.) The remaining 4 cats underwent identical deafening and implantation schedules but were not stimulated. Results indicate that administration of neomycin in neonatal cats induced degeneration of hair cells and spiral ganglion cell loss that was bilaterally symmetrical between the two cochleas of each individual animal, although there was variation between animals in the severity of the ototoxic drug effect. In animals receiving passive (unstimulated) implants, morphometric analysis of spiral ganglion cell density showed no significant difference in ganglion cell survival between the implanted cochleas and the contralateral control ears. In contrast, animals that were chronically stimulated for 3 months showed significantly better neuronal survival in implanted and stimulated cochleas as compared to contralateral deafened control ears. The induced conservation of spiral ganglion neurons was observed consistently within the basal cochlear region near the stimulating electrodes. In more apical regions there was no significant difference between the stimulated and control cochleas. The mechanisms underlying this selective conservation of spiral ganglion neurons induced by chronic intracochlear electrical stimulation are uncertain. Since no comparable chronic stimulation studies have been conducted in adults, it is not known whether similar conservation effects could be induced in mature animals.

Chronic intracochlear electrical stimulation in the neonatally deafened cat. I: Expansion of central representation

Intracochlear electrical stimulation via cochlear prostheses has been employed as a means of providing some hearing to deaf children. Since chronically restricted stimuli are known to have profound effects on central nervous system development, it is important to examine the effects of chronic intracochlear electrical stimulation in a neonatally deafened animal model. In this study neonatally deafened cats were implanted with a scala tympani electrode consisting of two pairs of electrodes. Chronic electrical stimulation was delivered using one electrode pair and consisted of charge-balanced biphasic pulses (200 microseconds/phase, 30 pps) at 2 dB above the electrically evoked auditory brain stem response (EABR) threshold for 4 h/day or at 6 dB 1 h/day, 5 days/week, for up to 3 months. The second electrode pair was unstimulated and served as an internal control. Following chronic stimulation, acute mapping experiments were performed in the central nucleus of the inferior colliculus (ICC) using single unit and multi-unit recording techniques and activating each electrode pair separately. In addition to these chronically stimulated animals, 2 other groups of experimental animals were studied: A normal group consisting of prior normal adult cats that were acutely implanted; and an unstimulated control group consisting of neonatally deafened adult cats that were either acutely implanted or implanted at 8-10 weeks of age but not chronically stimulated. Among the major findings of this study are: Electrical stimulation of the intracochlear bipolar electrode consistently produces activation of a reproducibly limited sector of the ICC. The location of this activated sector was found to be consistent with the known cochleotopic organization of the ICC and the intracochlear location of the stimulating electrodes. No major differences in the spatial representation of activated electrodes were found between prior normal cats and neonatally deafened unstimulated cats. The locations, shapes and widths of these spatial representations were virtually indistinguishable indicating that ICC cochleotopic organizations were equivalent in these two experimental groups. In contrast, the ICC representation of chronically stimulated electrode pairs were found to be significantly different. The average area activated by chronically stimulated electrode pairs at 6 dB above minimum threshold was approximately twice that of unstimulated deafened animals and prior normal animals; and it was larger, but not significantly so, than the average of the unstimulated electrode pair in the same experimental group.(ABSTRACT TRUNCATED AT 400 WORDS)

Connections and frequency representation in the auditory brainstem of the mustache bat, Pteronotus parnellii

The goals of this study were to describe the cochlear frequency map of the mustache bat, Pteronotus parnellii, and to relate the organization of cochlear primary afferents to that of the second-order projections from the cochlear nucleus to the superior olivary complex. Small deposits of horseradish peroxidase (HRP) were placed in the cochlear nucleus at sites that were physiologically characterized with respect to unit-best frequency. From the deposits, labeled fibers were traced in the retrograde direction to the cochlea and in the anterograde direction to the superior olive. Cochleas from both experimental and control animals were examined with light and electron microscopy. The peripheral axons of spiral ganglion neurons were counted in order to quantify the unusual variation in the innervation density along the cochlear spiral of the mustache bat. Regions of increased innervation density were found at the beginning and end of the basal turn of the cochlea. The highest cochlear innervation density consistently occurred in the upper basal turn. In horseradish peroxidase tracing experiments, this region contained labeled fibers only when HRP deposits were made at sites within the cochlear nucleus with unit-best frequencies around 60 kHz. These findings support the suggestion (Kössl and Vater, '85) that the cochlear sites of increased innervation density are related to the neural and behavioral emphasis that this echolocating bat places upon the analysis of the 60 kHz frequency band. The general arrangement of tonotopic maps within the cochlea, cochlear nucleus, and superior olive was consistent with previous observations in this bat and other mammalian species. At all three levels, there was evidence of a disproportionately large representation of frequencies around 60 kHz, similar to the enlarged representation reported within the inferior colliculus and auditory cortex of the mustache bat. In all cases there was a consistent relation between the size of the HRP deposit and the number and distribution of retrogradely labeled neurons in the cochlea. For most cases there was a similar relation between the size of the deposit and the terminal arborization field of anterogradely labeled fibers in the superior olive. However, in cases with deposits associated with the 60 kHz frequency band, the size of the labeled arborization field was more than twice as large as expected from the size of the deposits and from the extent of labeling in the cochlea. These cases suggest that the representation of frequencies around 60 kHz, already overrepresented in both the cochlea and cochlear nucleus, may be further expanded at the level of the superior olivary complex.

Cochlear implant revision: effects of reimplantation on the cochlea

The removal of an indwelling cochlear implant electrode followed by reinsertion of a new device has been a maneuver of uncertain consequences to the cochlea and its surviving neural population. The present study was conducted in an attempt to elucidate the factors that determine whether a reimplantation procedure will be successful. Cochlear implantation followed by explantation and subsequent reimplantation was performed in eight adult cats. Evaluation of cochlear histopathology suggested a significant increase in electrode insertion trauma when there was proliferation of granulation tissue in the round window area and scala tympani. In other cases, atraumatic reinsertion was achieved without apparent injury to the cochlea. The results of a survey of cochlear implant manufacturers and surgeons indicate that electrode replacement can usually be accomplished without adverse effects. Difficulties have been encountered, however, in removing implants with protuberant electrodes and when reimplantation was attempted on a delayed basis following explantation.

Topographic organization of the central projections of the spiral ganglion in cats

The morphological organization of inputs from restricted sectors of the cat cochlear spiral ganglion into the cochlear nucleus was studied by making focal extracellular injections of horseradish peroxidase (HRP) into the spiral ganglion. Injections resulted in Golgi-like labeling of a small cluster of spiral ganglion cells and their peripheral and central axons. Large injections involved most of the cells within Rosenthal's canal in sectors of the spiral ganglion innervating greater than or equal to 1 mm of the basilar membrane and resulted in narrow, complete laminae of labeled axons and preterminal fields within each cochlear nucleus subdivision. The positions of these bands were consistent with the "isofrequency laminae" appropriate for the frequencies represented at the injection sites, with high frequency laminae situated more dorsally, and lower frequencies progressively more ventral. A discrete projection to the small cell cap area was observed that was discontinuous with the main projection laminae in the ventral cochlear nuclei (VCN). In the dorsal cochlear nucleus, projecting fibers and terminals were excluded from the molecular cell layer. No labeled fibers entered the granule cell areas. In contrast to larger injections, very small HRP deposits labeled only part of an isofrequency lamina. Specifically, injections restricted to the scala tympani aspect of the spiral ganglion labeled only the lateral part of VCN isofrequency laminae, whereas injections limited to the scala vestibuli aspect of the ganglion labeled the medial aspect of the isofrequency planes. Thus these data indicate a previously unrecognized topographic representation of the vertical dimension of the spiral ganglion across VCN isofrequency laminae. Some possible functional implications of this projection organization are discussed.

Intrinsic connections within and between cochlear nucleus subdivisions in cat

The cat cochlear nuclear complex (CNC) is divided into three major subdivisions: the anteroventral, the posteroventral, and the dorsal cochlear nuclei (AVCN, PVCN, and DCN, respectively). Each of these subdivisions receives a topographic projection from the cochlea and each consists of a number of different cell types. The interconnections between these subdivisions and the cell types which give rise to them were studied by means of small injections of horseradish peroxidase (HRP) made at physiologically identified locations. DCN injections resulted in few labeled cells in the DCN, suggesting that its internal connections are very limited. In contrast, these same DCN injections resulted in numerous labeled cells in the PVCN and AVCN. Labeled PVCN cells, consisting of multipolar, octopus, and small spindle-shaped cells, were located in spatially restricted laminae stretching the entire rostrocaudal length of the nucleus, while labeled AVCN cells consisting of multipolar, globular, small spindle-shaped and small spherical cells were broadly distributed over the posterior half of the nucleus. Similar injections placed in the PVCN resulted in numerous labeled cells in all three subdivisions. The PVCN and AVCN cells labeled after PVCN injections were widely distributed across the isofrequency representations in both nuclei, while the labeled DCN cells were restricted to locations over the injection sites. Injections placed in the posterior half of the AVCN resulted in only very few labeled cells in the DCN. No cells were labeled following injections in the rostral AVCN.

Cochlear pathology of long term neomycin induced deafness in cats

The long term sequelae of hair cell destruction consequent from administration of the ototoxic aminoglycoside antibiotic, neomycin sulfate, were evaluated in histological and ultrastructural studies of cochlear morphology in cats. Complete hearing loss, as defined by an absence of brainstem evoked responses to click stimulation at 120 dB peak SPL, was induced by intramuscular injections of neomycin at 50 mg/kg body weight/day, and cochlear pathology was studied at 6 months and 1, 3 and 4 years following onset of profound deafness. In these long term ototoxicity cases the organ of Corti was collapsed and resorbed over the basal one-quarter to three-quarters of the cochlear spiral, depending on duration of deafness. Significant progressive reduction in the spiral ganglion cell population and sequential degenerative alterations in the remaining neurons were observed with increasing time elapsed after induced hearing loss. The sequence of pathological alterations in spiral ganglion neurons appeared to be: a) swelling, demyelination and degeneration of the peripheral dendrites; b) demyelination and shrinkage of the cell soma with preservation of the central axon; and c) demyelination of the central axon and degeneration of the cell perikaryon. In apical cochlear regions, severe degeneration of the spiral ganglion preceded the collapse of the tunnel of Corti and regional loss of pillar cells. Residual populations of spiral ganglion neurons were as low as 1-2% of the normal values in the most severely degenerated cochleae in the series. Light microscopic and ultrastructural studies revealed a selective survival advantage for the unmyelinated type II neurons over the myelinated type I neurons with these long survival periods. The prolonged time course and atrophic nature of these pathological alterations suggests that degeneration of spiral ganglion neurons progresses continuously following drug-induced insult to the cochlea. Some possible factors contributing to this long term progressive degeneration will be discussed.

Uptake of horseradish peroxidase from perilymph by cochlear hair cells

The specific mechanisms involved in the uptake of an exogenous protein, horseradish peroxidase (HRP), by cochlear hair cells were studied morphologically in light and electron microscopy. HRP was internalized by coated vesicles which formed from the plasma membrane only in the basal portion of the hair cells. Inner hair cells demonstrated relatively greater uptake than adjacent outer hair cells. The lateral plasma membrane of outer hair cells was unique in that reaction product was never bound to this portion of the membrane. Subsequent to endocytosis, HRP was transported to the Golgi and its associated system of endoplasmic reticulum and lysosomes. The exogenous protein was sequestered in a striking accumulation of secondary lysosomes and multivesicular bodies which were restricted to the infracuticular region of the hair cells and persisted for periods of at least 72 h after introduction of HRP. It is not clear whether the hair cells were slowly degrading the HRP or if the lysosomal enzymes necessary for its breakdown were lacking. The pathway demonstrated by HRP uptake and intracellular transport may represent one route by which macromolecules requisite for basic metabolic or nutritional requirements of the hair cells are supplied from the perilymph.

Survival of chlorophyceae ingested by saprozoic nematodes

The saprozoic nematode, Pristionchus lheritieri ingested cells of four species of unicellular Chlorophyceae (grass-green algae) including Chlamydomonas reinhardi and unidentified species of Ankistrodesmus, Chlamydornonas and Scenedesmus. Additional tests with Ankistrodesmus sp. and Chlamydomonas sp., indicated cells of Ankistrodesmus survived passage through the alimentary canal and were subsequently cultured, while viable cells of Chlarnydomonas were only occasionally recovered.