M.A. Ruda

Bio: M.A. Ruda is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Parvalbumin & Calbindin. The author has an hindex of 1, co-authored 1 publications receiving 169 citations.

Postnatal Phenotype and Localization of Spinal Cord V1 Derived Interneurons

Abstract: Developmental studies identified four classes (V0, V1, V2, V3) of embryonic interneurons in the ventral spinal cord. Very little however is known about their adult phenotypes. In order to further characterize interneuron cell types in the adult, the location, neurotransmitter phenotype, calcium-buffering protein expression and axon distributions of V1-derived neurons in the mouse spinal cord was determined. In the mature (P20 and older) spinal cord, most V1-derived neurons are located in lateral LVII and in LIX, few in medial LVII and none in LVIII. Approximately 40% express calbindin and/or parvalbumin, while few express calretinin. Of seven groups of ventral interneurons identified according to calcium-buffering protein expression, two groups (1 and 4) correspond with V1-derived neurons. Group 1 are Renshaw cells and intensely express calbindin and coexpress parvalbumin and calretinin. They represent 9% of the V1 population. Group 4 express only parvalbumin and represent 27% of V1-derived neurons. V1-derived group 4 neurons receive contacts from primary sensory afferents and are therefore proprioceptive interneurons and the most ventral neurons in this group receive convergent calbindin-IR Renshaw cell inputs. This subgroup resembles Ia inhibitory interneurons (IaINs) and represents 13% of V1-derived neurons. Adult V1-interneuron axons target LIX and LVII and some enter the deep dorsal horn. V1-axons do not cross the midline. V1 derived axonal varicosities were mostly (>80%) glycinergic and a third were GABAergic. None were glutamatergic or cholinergic. In summary, V1 interneurons develop into ipsilaterally projecting, inhibitory interneurons that include Renshaw cells, Ia inhibitory interneurons and other unidentified proprioceptive interneurons.

Identifying functional populations among the interneurons in laminae I-III of the spinal dorsal horn.

Abstract: The spinal dorsal horn receives input from primary afferent axons, which terminate in a modality-specific fashion in different laminae. The incoming somatosensory information is processed through complex synaptic circuits involving excitatory and inhibitory interneurons, before being transmitted to the brain via projection neurons for conscious perception. The dorsal horn is important, firstly because changes in this region contribute to chronic pain states, and secondly because it contains potential targets for the development of new treatments for pain. However, at present, we have only a limited understanding of the neuronal circuitry within this region, and this is largely because of the difficulty in defining functional populations among the excitatory and inhibitory interneurons. The recent discovery of specific neurochemically defined interneuron populations, together with the development of molecular genetic techniques for altering neuronal function in vivo, are resulting in a dramatic improvement in our understanding of somatosensory processing at the spinal level.

Morphological and Physiological Features of a Set of Spinal Substantia Gelatinosa Neurons Defined by Green Fluorescent Protein Expression

Abstract: The spinal substantia gelatinosa (SG) is known to be involved in the manipulation of nociceptive and thermal primary afferent input; however, the interrelationships of its neuronal components are poorly understood. As a step toward expanding understanding, we took a relatively unique approach by concentrating on a set of SG neurons selectively labeled by green fluorescent protein (GFP) in a transgenic mouse. These GFP-expressing SG neurons prove to have homogenous morphological and electrophysiological properties, are systematically spaced in the SG, contain GABA, receive C-fiber primary afferent input, and upregulate c-Fos protein in response to noxious stimuli. Together, the properties established for these GFP-labeled neurons are consistent with a modular SG organization in which afferent activity related to nociception or other C-fiber signaling are subject to integration/modulation by repeating, similar circuits of neurons.

Differential vulnerability of oculomotor, facial, and hypoglossal nuclei in G86R superoxide dismutase transgenic mice.

Abstract: In recent years, several mouse models of amyotrophic lateral sclerosis (ALS) have been developed. One, caused by a G86R mutation in the superoxide dismutase-1 (SOD-1) gene associated with familial ALS, has been subjected to extensive quantitative analyses in the spinal cord. However, the human form of ALS includes pathology elsewhere in the nervous system. In the present study, analyses were extended to three motor nuclei in the brainstem. Mutant mice and control littermates were evaluated daily, and mutants, along with their littermate controls, were killed when they were severely affected. Brains were removed after perfusion and processed for Nissl staining, the samples were randomized, and the investigators were blinded to their genetic status. Stereologic methods were used to estimate the number of neurons, mean neuronal volumes, and nuclear volume in three brainstem motor nuclei known to be differentially involved in the human form of the disease, the oculomotor, facial, and hypoglossal nuclei. In the facial nucleus, neuron number consistently declined (48%), an effect that was correlated with disease severity. The nuclear volume of the facial nucleus was smaller in the SOD-1 mutant mice (45.7% difference from control mice) and correlated significantly with neuron number. The oculomotor and hypoglossal nuclei showed less extreme involvement (<10% neuronal loss overall), with a trend toward fewer neurons in the hypoglossal nucleus of animals with severe facial nucleus involvement. In the oculomotor nucleus, neuronal loss was seen only once in five mice, associated with very severe disease. There was no significant change in the volume of individual neurons in any of these three nuclei in any transgenic mouse. These results suggest that different brainstem motor nuclei are differentially affected in this SOD-1 mutant model of ALS. The relatively moderate and late involvement of the hypoglossal nucleus indicates that, although the general patterns of neuronal pathology match closely those seen in ALS patients, some differences exist in this transgenic model compared with the progression of the disease in humans. However, these patterns of cellular vulnerability may provide clues for understanding the differential susceptibility of neural structures in ALS and other neurodegenerative diseases.

Calbindin-D28k: role in determining intrinsically generated firing patterns in rat supraoptic neurones.

Abstract: 1. Physiological activation of rat supraoptic nucleus (SON) neurones leads to phasic firing in vasopressin neurones and fast, continuous firing in oxytocin neurones. Using whole-cell patch clamp methods in brain slices, we investigated the role of endogenous calbindin-D28k (calbindin) in determining these intrinsically generated patterns of firing. 2. Direct introduction of calbindin (0.1-0.2 mM) into twelve of twelve phasically firing neurones suppressed Ca(2+)-dependent depolarizing after-potentials (DAPs) and changed activity from phasic to continuous firing. Bovine calcium binding protein (0.3 mM), an analogue of calbindin, had similar effects on both DAPs and firing patterns in five of five cells tested. 3. Introduction of anti-calbindin antiserum (1:2000-5000) into thirteen of thirteen continuously firing neurones unmasked DAPs and converted continuous into phasic firing. Such effects could not be mimicked either by diffusion of normal rabbit serum or antibodies directed against glial fibrillary acidic protein or against neurophysin. 4. Immunocytochemical staining with antisera directed against calbindin revealed more intense staining in the dorsal, oxytocin-rich and less intense staining in the ventral, vasopressin-rich areas of the SON. 5. Elevated intracellular Ca2+ concentration ([Ca2+]i; 0.1 mM) induced DAPs and phasic firing in all twenty-nine SON cells recorded. During chelation of intracellular Ca2+ with (1.1-11 mM) BAPTA, fifty-eight of fifty-eight neurones recorded displayed regular continuous activity and had no DAPs. 6. These data suggest that firing activities in SON cells are dependent on [Ca2+]i and that calbindin, acting as an endogenous Ca2+ buffer, is involved in regulation of intrinsic firing patterns. It is likely that calcium binding proteins have a similar influence on the firing patterns of many neuronal types throughout the nervous system.