Biomedical subjects

R A Code

Publications and source records attributed to R A Code.

At least 19 recordsLinked to original sources

PubMed2000

Calretinin expression in the chick cochlear nucleus after deafferentation.

The expression of the calcium-binding protein calretinin (CR) in the chick cochlear nucleus, nucleus magnocellularis (NM), was examined after unilateral cochlea removal in hatchlings and 3-week-old birds. Following survival times of 3, 6 or 12 h or 1, 3 or 7 days, CR mRNA was localized by in situ hybridization using a radiolabeled chick CR probe. Levels of CR protein were assessed by CR-immunoreactivity (CR-I) using a calcium-independent CR antiserum and immunohistochemistry. At survival times of 1 day or less, cochlea removal did not change relative levels of CR mRNA or CR-I in NM between the deafferented and the unoperated sides of the brain. Decreases in CR expression on the cochlea removal side were observed, however, at times that coincide with deafferentation-induced cell loss (3 and 7 days). Additionally, bilateral cochlea removal had no apparent effect on CR-I in NM neurons when compared to those in normal animals. Thus, CR mRNA and protein appear to be constitutively expressed in NM neurons and are not affected by sensory deprivation.

Afferent Pathways↗

PubMed1998

Development of dynorphin-like immunoreactive auditory nerve terminals in the chick.

The novel discovery that auditory nerve terminals in the chick cochlear nucleus magnocellularis (NM) are immunoreactive for the opioid peptide dynorphin (DYN) was recently reported [3]. The present study examines the development of DYN-immunoreactivity (DYN-I) in auditory nerve terminals in NM from embryos through young post-hatch chicks. No DYN-I was observed in NM at embryonic day 13 (E13). DYN-I first appeared at E16 as short flat structures partially surrounding NM cell bodies. Around post-hatch day 1 (P1), these structures had a more rounded, chalice-type of morphology reminiscent of the specialized auditory nerve terminals found in birds, the end-bulbs of Held. At P6, most NM neurons were circumscribed by a prominent DYN-I calyceal-type of ending. By P13, fewer NM cells were ringed by this DYN-I and by the third post-hatch week, there was very little DYN-I in NM. There were no obvious differences in the density of DYN-I terminals across either the rostrocaudal length or the mediolateral width of NM at any age examined. These results suggest that during a restricted time of development, end-bulbs of Held in the chick NM contain DYN.

Animals↗

PubMed1998

Effects of columella removal on inner ear morphology in the chick.

We are currently removing the single middle ear bone (columella) in the domestic chick to introduce chemical agents directly into the inner ear. Since we are interested in the effect of these agents on neural structures within the avian basilar papilla (BP), we are concerned about any subtle changes that might result from the surgical procedure of columella removal alone. The purpose of this study was to use light and transmission electron microscopy to analyze morphological changes in the inner ear after columella removal. Fifteen-day-old chicks underwent a unilateral, bilateral or a sham removal of the columella. After columella removal, the oval window was either plugged with Gelfoam or Kimwipe (standard accepted procedure to prevent possible perilymph leak) or left uncovered. After a 5-day survival period, morphological changes were observed in the tegmentum vasculosum (TV) of all ears receiving a columella removal as compared to unoperated ears. Further, ears with Gelfoam plugging the oval window also had damage to the hair cells and support cells of the basilar papilla. In contrast, there were no observable differences in either auditory afferent or efferent nerve terminals on hair cells in the BP from any ears that had the columella removed compared to those from unoperated ears. These results suggest that columella removal alone may produce morphological changes to the TV within 5 days of surgery but not to structures within the BP. On the other hand, columella removal with a Gelfoam plug results in damage not only to the TV but also to cells within the basilar papilla during this same survival time. Despite damage to other structures within the inner ear, cochlear efferent and afferent terminals on surviving hair cells were unaffected by columella removal with or without plugging.

Animals↗

PubMed1997

Calretinin expression in the chick brainstem auditory nuclei develops and is maintained independently of cochlear nerve input.

The expression of the calcium-binding protein calretinin (CR) in the chick brainstem auditory nuclei angularis (NA), laminaris (NL), and magnocelularis (NM) was studied during normal development and after deafening by surgical removal of the otocyst (embryonic precursor of the inner ear) or columella (middle ear ossicle). CR mRNA was localized by in situ hybridization by using a radiolabeled oligonucleotide chick CR probe. CR immunoreactivity (CR-IR) was localized on adjacent tissue sections. CR mRNA signal in the auditory nuclei was expressed at comparable levels at embryonic day (E)9 and E11 and increased thereafter to reach the highest levels in posthatch chicks. CR-IR neurons were apparent in NM and NA at E11 and in NL by E13, and CR-IR increased in all three auditory nuclei thereafter. Neither unilateral nor bilateral otocyst removal caused detectable changes in the intensity of CR mRNA expression or CR-IR in the auditory nuclei at any of the several ages examined. Similarly, columella removal at posthatching day 2 or 3 failed to significantly affect CR mRNA or CR-IR levels at 3 hours, 1 day, or 3-4 days survival times. We conclude that cochlear nerve input is not necessary for expression of either calretinin mRNA or protein and that the profound decrease in sound-evoked activity caused by columella removal does not affect the maintenance of CR expression after hatching.

Acoustic Stimulation↗

PubMed1996

Chick auditory terminals contain dynorphin-like immunoreactivity.

Dynorphin-like immunoreactivity (DYN-I) was studied in the auditory brain stem of chick hatchlings using an antiserum to dynorphin-B. DYN-I was found in a few small cells in the nucleus laminaris (NL) and in the superior olive (SO). Dendrites in NL also appeared immunostained. DYN-I, however, was especially prominent in the cochlear nucleus magnocellularis (NM). A few DYN-I somata could be found within NM particularly in medial regions of this nucleus. Most DYN-I, however, was localized to calyceal-type structures, reminiscent of primary auditory nerve terminals, surrounding nerve cell bodies in NM. To determine whether DYN-I is contained within auditory end-bulbs of Held, the basilar papilla (avian cochlea) was removed unilaterally. After 5 days survival, there were very few DYN-I terminals in NM on the operated side of the brain compared with the unoperated side. This novel finding suggests that primary auditory nerve terminals in NM may contain the opioid peptide, dynorphin.

Animals↗

PubMed1996

Chick cochlear efferent neurons are not immunoreactive for calcitonin gene-related peptide.

The fluorescent retrograde tracer, rhodamine dextran amine, was unilaterally injected into the cochlear duct of anesthetized chicks. Retrogradely labeled cells were found bilaterally in the brainstem ventromedial to the superior olivary nucleus and to the ventral facial nucleus, and in the caudal pontine reticular formation between the dorsal facial nucleus and the abducens nerve root. Tissue sections containing retrogradely labeled cells were incubated in an antiserum to calcitonin gene-related peptide (CGRP) and a fluorescently labeled secondary antiserum. No double-labeled neurons were found, suggesting that chick cochlear efferent neurons do not contain CGRP or that levels of CGRP in these cells may be too low to be detected immunohistochemically.

Animals↗

PubMed1995

Efferent neurons to the macular lagena in the embryonic chick.

The lipophilic dye, DiI, was placed into the macula lagena of paraformaldehyde-fixed embryonic chicks. Retrogradely labeled cells were found bilaterally in the pontine reticular formation (RF) between the dorsal facial nucleus and the abducens nerve root. This location is similar to that of the dorsomedial group of efferent cells that project to the basilar papilla. No lagenar efferent neurons, however, were found near the superior olivary nucleus where the ventrolateral group of cochlear efferents is located. Whether efferent neurons in the pontine RF send collaterals to both the basilar papilla and to the macula lagena has yet to be determined.

Acoustic Maculae↗

PubMed1995

Enkephalin-like immunoreactivity in the chick brainstem: possible relation to the cochlear efferent system.

Mammalian lateral olivocochlear (LOC) neurons that are immunoreactive for choline acetyltransferase (ChAT) are also immunoreactive for enkephalin (Enk). To determine whether cochlear efferent neurons in birds might also contain Enk-like immunoreactivity (Enk-LI), we studied the auditory brainstem of the domestic chicken using antisera to ChAT, leucine-enkephalin (L-Enk) and methionine-enkephalin (M-Enk). Enk-LI terminals are found around, but not within, the superior olivary nucleus (SO) and the nucleus of the lateral lemniscus, pars intermedia (LLi). A moderate concentration of Enk-LI terminals is found ventromedial to the ventral facial nucleus (VIIv) where the ventrolateral group of ChAT-I cochlear efferent neurons is located. After colchicine injections into the lateral ventricle, a population of intensely stained Enk-LI perikarya was found in the nucleus of the lateral lemniscus, pars ventralis (LLv) with scattered cells in the LLi and the nucleus subceruleus ventralis (SCv). The distribution of Enk-LI and ChAT-I somata, however, never overlapped, even in adjacent sections. Thus, in the chick, Enk-LI perikarya are not distributed in areas where cochlear efferent neurons are found. Instead, a dense concentration of Enk-I terminals can be found in areas containing ChAT-I cochlear efferent neurons. The source of these enkephalinergic terminals may be a population of Enk-LI cells in the LLv.

Animals↗

PubMed1994

Choline acetyltransferase-immunoreactive cochlear efferent neurons in the chick auditory brainstem.

Cholinergic neurons in the chick auditory brainstem were studied with the aid of an antiserum to choline acetyltransferase (ChAT), the biosynthetic enzyme for acetylcholine. ChAT-immunoreactive (ChAT-I) neurons were found in a ventrolateral and a dorsomedial cell group. The ventrolateral group is a rostrocaudally directed column of cells that surround the superior olive (SO), are ventromedial to the ventral facial nucleus (VIIv), and are lateral to the nucleus pontis lateralis (PL) as far rostrally as the nucleus subceruleus ventralis. Cells in the dorsomedial group were found in the pontine reticular formation medial to the dorsal facial nucleus and lateral to the abducens nerve root. Occasionally, small ChAT-I cells were found in the crossed dorsal cochlear tract and in the medial vestibular nucleus near the dorsal border of the caudal nucleus magnocellularis (NM). No ChAT-I neurons or fibers were observed in NM, nucleus angularis, nucleus laminaris, in the nuclei of the lateral lemniscus, or in the nucleus mesencephalicus lateralis pars dorsalis. To determine which cholinergic neurons project to the cochlea, a double-labeling technique was used combining ChAT-I and the retrograde transport of biotinylated dextran amine (BDA) from the inner ear. Double-labeled cells were found bilaterally in both the ventrolateral and dorsomedial cell groups, with the exception of large ChAT-I cells dorsal to the SO, which do not appear to project to the cochlea. Cholinergic cells that project to the cochlea were classified into three morphological groups: multipolar, elongate, and round-to-oval. Both the ventrolateral and the dorsomedial cell groups appear to have a mixture of these different cell types. The average somal area of cholinergic cochlear efferents was 246 microns 2. Only about 70% of the cochlear efferent neurons, however, are cholinergic.

Animals↗

PubMed1994

Pharmacology of a mixed 5-hydroxytryptamine1A/dopamine agonist.

U-67413B (4-hydroxydipropylaminodihydrophenalene) bound with high affinity to both 5-hydroxytryptamine (HT)1A and D2-dopamine (DA) receptor sites. U-67413B depressed 5-HT and DA cell firing rates and depressed synthesis of both neurotransmitters. The drug depressed mouse body temperatures by an amount similar to that for buspirone, gepirone and ipsapirone, but less than that for 8-hydroxy-N,N-dipropyl-2-aminotetralin. In rats, it produced the 5-HT1A behavioral syndrome. In contrast to 5-HT1A agonists having DA antagonist effects, U-67413B mildly depressed rather than stimulated firing rates of noradrenaline (NA) neurons in the locus ceruleus by a non-alpha-2 receptor mechanism. In behavioral tests designed to measure anxiolytic activities, U-67413B was a slightly more effective anxiolytic than standard 5-HT1A anxiolytics (buspirone, gepirone and ipsapirone). The data are consistent with the hypothesis that effects of 5-HT1A agonists on NA neuron activity are mediated through effects on dopaminergic mechanisms, and that effects on NA neurons could modulate anxiolytic activities of 5-HT1A agonists.

Animals↗

PubMed1993

Antagonism of hypothermia produced by benzodiazepine-related compounds by U-78875 in mice.

The benzodiazepine receptor agonists, flurazepam, zolpidem, ZK 93423, and the benzodiazepine inverse agonist, FG 7142, all produced hypothermia when injected i.p. in mice. These compounds are structurally different and do not have the same affinity for the GABAA/benzodiazepine receptor subtypes. Pretreatment with flumazenil (30 mg/kg) completely blocked the hypothermia produced by flurazepam (30 mg/kg), zolpidem (3 mg/kg), and FG 7142 (60 mg/kg), only partially reversed ZK 93423 (3 mg/kg), and was ineffective against 10 mg/kg zolpidem. In comparison, 3 mg/kg of U-78875 completely antagonized all these benzodiazepine agonists. When injected before 30 mg/kg pentobarbital, U-78875 (3 mg/kg) slightly enhanced and prolonged the hypothermic effect of pentobarbital, while flumazenil had very little effect. The results show that U-78875 is a potent antagonist against benzodiazepine receptor agonists, while having demonstrable intrinsic activity.

Animals↗

PubMed1993

Development of metabolic activity patterns in the somatosensory cortex of cats.

1. The development of cortical responses to somatic stimulation was studied in kittens 2-5 wk of age using the 2-deoxyglucose (2DG) technique. During the 2DG experiment each kitten received an innocuous intermittent vertical displacement stimulus to the forepaw. 2. The pattern of metabolic activity was substantially different in young animals compared with adults. In the individual autoradiographs of the 2-wk-old kittens stimulus-evoked 2DG uptake in primary somatosensory cortex was localized to a small spot in the upper portion of the cortex, whereas in the adult the label extended vertically through the cortical layers and appeared more column-like. Individual patches of label were substantially smaller and less dense in young animals. Over a period of several weeks the evoked activity evolved to the more extensive adult pattern. The 2DG uptake displayed a mature distribution by approximately 4-5 wk of age. During this period, the cortical architecture also evolved from an immature to a mature arrangement. 3. The evoked activity was reconstructed into two-dimensional maps; the distribution of label > or = 1.5 SD above background was considered to be stimulus related. In the adult, the pattern appeared as a strip or strips of increased metabolic activity that extended in the rostrocaudal direction for approximately 1 mm. In contrast, the activity pattern in animals 2-4 wk old was less discretely organized into "strips" and was more diffusely spread over several mms of somatosensory cortex. The two-dimensional pattern gradually coalesced into a more localized strip by approximately 4-5 wk of age. Although the pattern of label was more widespread in the young animals, the absolute distance of the spread of activity did not vary substantially, regardless of the age of the animal. 4. Other measurements regarding the distribution of activity at different ages indicate that the amount of cortex activated increases in absolute terms, although the percent of cortex activated by the stimulus decreases. The overall intensity of the 2DG uptake as measured on the two-dimensional maps increases with age, as does the variability of the 2DG uptake; a wider range of intensity values is seen in the adult. Plots created from the individual two-dimensional reconstructions allowed a measure of "patch strength" at different ages. These histograms relate the most intense region of uptake in a given map to the spatial distribution of activity spreading in the medial and lateral directions.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1992

Expansion of stimulus-evoked metabolic activity in monkey somatosensory cortex after peripheral denervation.

The 2-deoxy-glucose (2DG) technique was used to study changes in stimulus-evoked metabolic activity in the somatosensory cortex of the squirrel monkey Saimiri sciureus after unilateral digit amputation. Two to 52 weeks after digit 2 on the left hand was removed, a somatic stimulus was applied to digit 3 bilaterally. In area 3b corresponding to the deafferented side of the brain, the area of stimulus-evoked metabolic activity was greater than that on the opposite, control side of the brain within the same animal. The extent of the topographic projection map of 2DG label in area 3b on the deafferented side of the brain was 1.92 to 4.75 times greater than that on the control side. There was no difference, however, in the topographical area of stimulus-evoked metabolic activity between the left and right somatosensory cortices in a normal, unoperated animal. These data suggest that the changes in functional organization observed using electrophysiological recordings in somatosensory cortex after peripheral denervation may have a metabolic substrate.

Animals↗

PubMed1991

Basal forebrain lesions alter stimulus-evoked metabolic activity in rat somatosensory cortex.

Acetylcholine (ACh) has been suggested to play a crucial role in normal cortical functioning. To assess the impact of cortical ACh depletion on metabolic activity in the barrel field of rat somatosensory cortex, unilateral lesions of the basal forebrain were made. One to 9 weeks later, a 2-deoxyglucose experiment was conducted. Stimulus-evoked metabolic activity in the barrel field ipsilateral to the lesion was significantly reduced compared with the contralateral side. These results suggest that ACh plays a significant role in processing stimulus-evoked sensory information.

Acetylcholine↗

PubMed1991

Yawning produced by dopamine agonists in rhesus monkeys.

Yawning was recorded from five rhesus monkeys restrained in a chair after i.m. injection of dopaminergic compounds: apomorphine (0.03 mg/kg), quinpirole (0.01 mg/kg), and (-)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine (1 mg/kg). SKF 38393 or physostigmine produced no yawning. Yawning from apomorphine was blocked by chlorpromazine or SCH 23390 (0.03 mg/kg). Sulpiride (10 mg/kg) was ineffective. The difference between rats and monkeys in their yawning response to dopaminergic compounds is discussed.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1991

GABAA receptors in auditory brainstem nuclei of the chick during development and after cochlea removal.

The presence of GABAA receptors (GABARs) in auditory brainstem nuclei of the chick was determined by immunocytochemical (ICC) and receptor autoradiographic techniques. A monoclonal antibody to the GABAR/benzodiazepine/chloride channel complex and radiolabeled ligand binding using [3H]-muscimol, a GABA agonist, revealed labeling in nucleus magnocellularis (NM), nucleus laminaris (NL), nucleus angularis (NA), and the superior olive (SO) in both posthatch and embryonic chicks. GABAR-immunoreactivity (GABAR-I), as well as [3H]-muscimol binding, appear homogeneous throughout these nuclei at all ages studied. During development, GABAR-I is first observed in these nuclei around embryonic day 13 (E13). GABAR-I, which appears heavier in embryos than in posthatch chicks, becomes less intense with age in all 4 nuclei. Levels of receptor binding are also greater in embryos compared to posthatch chicks. [3H]-Muscimol binding is consistently greatest in SO followed by that in NL. NM and NA exhibit the least amount of binding at all ages studied. [3H]-Muscimol binding decreases in auditory brainstem nuclei as a function of age. Two days after unilateral cochlea removal, there is an apparent increase in GABAR-I in the ipsilateral NM compared to controls. This, however, may be the result of a decrease in the cross-sectional area of NM neurons as a result of de-afferentation (Born and Rubel, 1985). In contrast, there is a 28% decrease in [3H]-muscimol binding in the ipsilateral NM compared to controls probably reflecting the 30% reduction in the number of NM neurons due to cochlea removal (Born and Rubel, 1985). Fourteen days after cochlea removal, there is still a small, but not significant, decrease in [3H]-muscimol binding in the ipsilateral NM. In the contralateral NM, GABAR-I is less intense compared to that in the ipsilateral NM and controls. Additionally, there is a slight but insignificant decrease in [3H]-muscimol binding compared to that in controls 2 days after cochlea removal. After 14 days survival, however, the average binding is similar to that in controls. Thus, cochlea removal appears to transiently decrease the number of GABARs in the ipsilateral NM and may have a similar, but not as dramatic, effect in the contralateral NM. These GABARs are most likely to be postsynaptic, that is, located on NM neurons.

Animals↗

PubMed1990

Effects of cochlea removal on GABAergic terminals in nucleus magnocellularis of the chicken.

The effects of unilateral cochlea removal on GABA-immunoreactive (GABA-I) terminals in nucleus magnocellularis (NM) of the chick were assessed by immunocytochemical (ICC) techniques. Posthatch chicks (5-8 days old) survived from 1-37 days following unilateral cochlea removal. In the ipsilateral NM, the density of GABA-I terminals appeared to increase relative to normal controls 10-37 days after cochlea removal. However, most of that increase could be attributed to a decrease in cell size, cell number, and volume of the nucleus as a result of deafferentation. In the contralateral NM, the density of GABA-I terminals decreased relative to the ipsilateral NM and to normal animals 1-21 days after cochlea removal. The number of GABA-I terminals per NM neuron also decreased in the contralateral NM while that in the ipsilateral NM was comparable to normal controls. To ascertain whether these changes represented changes in the number of terminals or in the amount of GABA contained within the terminals, we also examined these terminals using an antibody to glutamic acid decarboxylase (GAD), the biosynthetic enzyme for GABA. Following unilateral cochlea removal, there was no difference in the density of GAD-I terminals in NM between the two sides of the brain for any of the survival times. Similarly, bilateral cochlea removal had no discernible effect on the density of GABA-I terminals in NM. These data suggest that unilateral deafferentation may temporarily downregulate the biosynthesis of GABA in the contralateral NM.

Animals↗

PubMed1989

GABAergic neurons in brainstem auditory nuclei of the chick: distribution, morphology, and connectivity.

The second- and third-order auditory nuclei in the brainstem of the chicken, nucleus magnocellularis (NM) and nucleus laminaris (NL), receive afferents that are immunoreactive to gamma-aminobutyric acid (GABA). In order to investigate the source(s) of these GABAergic afferents, we examined the distribution, morphology, and connectivity of GABAergic neurons in and adjacent to NM and NL in chicks from 7 days of incubation to 12 days posthatch. Immunocytochemical techniques revealed the presence of approximately 150 GABA-labeled neurons within the neuropil surrounding NM and NL on each side of the brainstem. Most of these neurons are located between NM and NL and along the lateral border of NM. GABAergic neurons are multipolar; their thick dendritic processes branch extensively and give rise to several thin, secondary processes. Frequently, the GABA-labeled processes arborize within NM or NL. The morphology of these non-NM/NL neurons was investigated further with Golgi impregnation and specific neuronal markers (antisera to microtubule-associated protein). Our observations suggest that a considerable portion of GABAergic input to NM and NL originates from local GABAergic neurons. In order to determine other possible sources of GABAergic input to NM and NL, we injected tracers unilaterally into NM/NL. A small number (20-30) of neurons were retrogradely labeled in the trapezoid body, almost exclusively ipsilaterally. No labeled cells were found in other regions of the brainstem, except for the contralateral NM. Unilateral injections of horseradish-peroxidase-labeled wheat germ agglutinin into the paraflocculus revealed only minor terminal labeling in the lateral region of NL bilaterally. The number and distribution of GABAergic terminals in NM and NL appeared normal after transection of the crossed dorsal cochlear tract.

Animals↗