Golda Anne Kevetter

Serotonergic projections to the caudal brain stem: a double label study using horseradish peroxidase and serotonin immunocytochemistry

Cells of origin of serotonergic and non-serotonergic projections to the caudal brain stem in the primate were examined using a double label technique. Following HRP injections into medullary raphe nuclei and the adjacent reticular formation double labeled cells were found in the dorsal raphe nucleus, the central superior nucleus and the ventrolateral tegmentum. Retrogradely labeled cells that did not stain for serotonin-like immunoreactivity were found primarily in the periaqueductal gray (PAG) and the mesencephalic and pontine reticular formation. The results are discussed in relation to the descending pathway(s) mediating the effects of PAG stimulation.

Chronic phencyclidine induces behavioral sensitization and apoptotic cell death in the olfactory and piriform cortex.

In this study, we tested the hypothesis that chronic administration of phencyclidine (PCP), an N‐methyl‐D‐aspartate (NMDA) receptor antagonist, would cause a long‐lasting behavioral sensitization associated with neuronal toxicity. Female Sprague‐Dawley rats were administered PCP (20 mg/kg, i.p.) once a day for 5 days, withdrawn for 72 hr, placed in locomotor activity chambers, and challenged with 3.2 mg/kg PCP. Following assessment of locomotor activity, the rats were killed and their brains processed for analysis of apoptosis by either electron microscopy or terminal dUTP nick‐end labeling (TUNEL). In study I, PCP challenge produced a much more robust and long‐lasting increase in locomotor activity in rats chronically treated with PCP than in those chronically treated with saline. In study II, clozapine pretreatment blunted the degree of sensitization caused by PCP. In study I, a marked increase in TUNEL‐positive neurons was found in layer II of the olfactory tubercle and piriform cortex of rats chronically treated with PCP. Many of these neurons had crescent‐shaped nuclei consistent with apoptotic condensation and margination of nuclear chromatin under the nuclear membrane. Acute PCP had no effect. Electron microscopy revealed that PCP caused nuclear condensation and neuronal degeneration consistent with apoptosis. Cell counts in layer II of the piriform cortex revealed that chronic PCP treatment resulted in the loss of almost 25% of the cells in this region. However, an increase in glial fibrillary acidic protein (GFAP)‐positive cells in the molecular layer suggests that this neurotoxicity also may involve necrosis. In study II, the PCP‐induced neuronal degeneration was essentially completely abolished by clozapine pretreatment. This pattern of degeneration was found to coincide with the distribution of the mRNA of the NR1 subunit of the NMDA receptor. The relevance of these data to a PCP model of chronic NMDA receptor hypofunction is discussed. J. Neurosci. Res. 52:709–722, 1998.

Projections from the Sacculus to the Cochlear Nuclei in the Mongolian Gerbil

The projections of the saccule, an otolith end organ, to the cochlear nuclei were studied using both transganglionic transport and intracellular injection techniques. Labeled fibers and terminals were observed in the anterior and posterior portions of the ventral cochlear nucleus and the dorsal cochlear nucleus. Most terminals were present in the granule cell domain, especially in the subpeduncular corner between the anteroventral cochlear nucleus and the floccular peduncle of the cerebellum. It has been hypothesized that the cochlea in mammals may have developed phylogenetically from the saccule. The projections from the saccule to the cochlear nuclei were investigated in a mammalian species, the Mongolian gerbil, in an attempt to obtain initial information supporting or refuting this hypothesis. The presence of an otolith end organ projection to the cochlear nuclei in rodents should encourage comparative studies in additional aspects of the evolution of the auditory system.

Spinothalamic cells in the rat lumbar cord with collaterals to the medullary reticular formation.

Abstract Cells with dual projections to both the thalamus and the medullary reticular formation were identified in the rat lumbar cord after separate injections of different retrogradely transported markers into each area. Most double-labeled cells were located in the intermediate zone or in lamina V of the contralateral spinal cord.

Molecular probes of the vestibular nerve: I. Peripheral termination patterns of calretinin, calbindin and peripherin containing fibers

Vestibular afferents have different physiological properties that can be at least partially correlated with the morphology that the peripheral ending makes with type I and type II hair cells. If the location of the ending in the sensory epithelium is included, the correlations are further improved. It is also known that vestibular afferents can be immunohistochemically stained for a variety of different substances. We have concentrated on three of these markers, calretinin, calbindin and peripherin, because the sources of afferents to the vestibular nuclear complex that contain these substances are restricted, in two cases to the primary afferents. We demonstrate that calretinin is found only in the calyx-only afferents that are located at the apex of the cristae ampullaris and along the striola of the maculae. The area containing stained calyces is equal to or slightly smaller than the central zone of the cristae as defined by the Goldberg group [J. Neurophysiol. 60 (1988) 167]. Calbindin is also found in calyces at the apex of the cristae and along the striola of the otoliths. Examination of adjacent sections of all endorgans indicates that calbindin staining overlaps with calretinin, but is always several hair cells wider on each side. Peripherin also stains fibers in the neuroepithelium. The greatest density of staining is in the peripheral zone of the cristae, i.e. at the base and toward the planum semilunatum. We suggest that these substances are useful markers for specific sets of vestibular afferents.

Molecular probes of the vestibular nerve

Abstract An unambiguous delineation of the exact numbers and/or proportions of calyx-only, dimorph, and bouton-only vestibular afferents is needed to continue studies concerning vestibular integration in the nervous system. Here, we take advantage of immunocytochemical properties of three groups of vestibular afferents. We utilize calretinin to delineate the calyx-only population, and peripherin to stain the bouton-only afferents. An additional subgroup of afferents that stain with calbindin, but not calretinin is also introduced. The size of the cells that stain with these markers was determined. Cells that are calbindin-positive overlap the sizes of Nissl-stained somata. Cells that stain with peripherin or calretinin are non-overlapping with calretinin cells being the largest and peripherin-positive cells the smallest. Twenty percent of the ganglion cells were peripherin positive, another 20% stained with calretinin antibodies, 30% stained with calbindin, and all cells in Scarpa’s ganglion stained with parvalbumin. Most of the calretinin-positive cells also stained with calbindin. One-third of the calbindin-positive population stained only with calbindin. These studies indicate that the calyx- and bouton-only populations of vestibular afferents in gerbil comprise at least 40% of the nerve. In addition, at least 10% of the nerve also stains with calbindin and neither calretinin nor peripherin. Based on indirect evidence, we hypothesize that these are a subpopulation of dimorph afferents. This study has provided an anatomical instrument (in addition to intracellular physiological methods) to study separate populations of vestibular afferents.

Collateralization in the spinothalamic tract: New methodology to support or deny phylogenetic theories

Components of the spinothalamic system that ascend in the anterolateral funiculus are reviewed. The presence of collateralization in this system in mammals is discussed with regard to theories of the phylogenetic development of pathways. The major theory investigated suggested that collateralization is an intermediate stage between a multisynaptic pathway and a direct non-collateralized lemniscus. The evidence and theories are reviewed. Methods for confirming or rejecting this theory are discussed. The literature reporting ascending spinal projections for non-mammalian vertebrates is reviewed. Certain reptiles have projections analogous to both the mammalian neospinothalamic and paleospinothalamic tracts. The presence of spinothalamic projections in elasmobranchs and amphibians is still controversial. Confirmation of earlier reports of projections in salamander and dogfish shark based on degeneration techniques have not been done. In addition, results from too few species of these classes have been reported. However, it is possible that paleospinothalamic connections are present in some species (e.g. salamander, nurse shark) and not in others (e.g. frog, dogfish shark) of the same class. Spinothalamic projections have not been reported for teleosts. A plea for new research in this area is made.

PATTERN OF SELECTED CALCIUM-BINDING PROTEINS IN THE VESTIBULAR NUCLEAR COMPLEX OF TWO RODENT SPECIES

The distribution of immunoreactivity to calbindin, calretinin, and parvalbumin in the vestibular nuclear complex and the adjacent nucleus prepositus hypoglossi was studied in rats and gerbils. The distribution of stained fibers was the same for both rodent species. All three calcium‐binding proteins were present in vestibular afferents. However, none of the three proteins were present in all afferent fibers. Many fibers were labeled in the vestibular nerve and in fascicles of the descending vestibular nucleus, as well as ascending fibers in the superior vestibular nucleus and fibers directed to the medial vestibular nucleus. Labeled terminals were present in the medial vestibular nucleus, especially along the ventricular border, in the neuropil of the superior vestibular nucleus, and scattered in the descending and ventral portions of the lateral vestibular nucleus. Calbindin‐ and parvalbumin‐positive terminals, but not calretinin‐positive terminals, were present in the neuropil of the dorsal lateral vestibular nucleus, especially surrounding the large neuronal somas. Some of these terminals are presumably from cerebellar Purkinje cells, which were also labeled by both antibodies. The pattern of parvalbumin immunoreactivity was slightly different from that of calbindin, indicating that parvalbumin might be contained in additional fibers.

Use of Calcium-Binding Proteins to Map Inputs in Vestibular Nuclei of the Gerbil

We wished to determine whether calbindin and/or calretinin are appropriate markers for vestibular afferents, a population of neurons in the vestibular nuclear complex, or cerebellar Purkinje inputs. To accomplish this goal, immunocytochemical staining was observed in gerbils after lesions of the vestibular nerve central to the ganglion, the cerebellum, or both. Eleven to fourteen days after recovery, the brain was processed for immunocytochemical identification of calretinin and calbindin. After lesion of the vestibular nerve, no calretinin staining was seen in any of the vestibular nuclei except for a population of intrinsic neurons, which showed no obvious change in number or staining pattern. Calbindin staining was reduced in all nuclei except the dorsal part of the lateral vestibular nuclei. The density of staining of each marker, measured in the magnocellular medial vestibular nucleus, was significantly reduced. After the cerebellar lesion, no differences in calretinin staining were noted. However, calbindin staining was greatly reduced in all nuclei. The density of staining, measured in the caudal medial vestibular nucleus, was significantly lower. After a combined lesion of the cerebellum and vestibular nerve, the distribution and density of calretinin staining resembled that after vestibular nerve section alone, whereas calbindin staining was no longer seen. This study demonstrates that calretinin and calbindin are effective markers for the identification of vestibular afferents. J. Comp. Neurol. 386:317–327, 1997.

Central projections of the utricular nerve in the gerbil.

The central projections of primary afferent fibers in the utricular nerve, which convey linear head acceleration signals to neurons in the brainstem and cerebellum, are not completely defined. The purpose of this investigation was twofold: 1) to define the central projections of the gerbil utricular afferents by injecting horseradish peroxidase (HRP) and biotinylated dextran amine (BDA) into the utricular macula; and 2) to investigate the projections of individual utricular afferents by injecting HRP intracellularly into functionally identified utricular neurons. We found that utricular afferents in the gerbil projected to all divisions of the vestibular nuclear complex, except the dorsal lateral vestibular nucleus. In addition, terminals were observed in the interstitial nucleus of the eighth nerve, nucleus Y, external cuneate nucleus, and lobules I, IV, V, IX, and X of the cerebellar vermis. No projections appeared in the flocculus or paraflocculus. Fibers traversed the medial and intermediate cerebellar nuclei, but terminals appeared only occasionally. Individual utricular afferents collateralize extensively, projecting to much of the brainstem area innervated by the whole of the utricular nerve. This study did not produce complete filling of individual afferent collateral projections into the cerebellar cortex. J. Comp. Neurol. 452:11–23, 2002.