Biomedical subjects

Georgia A Bishop

Publications and source records attributed to Georgia A Bishop.

7 recordsLinked to original sources

PubMed2006

Evidence for the presence of the type 2 corticotropin releasing factor receptor in the rodent cerebellum.

Corticotropin releasing factor (CRF), localized in afferent inputs to the cerebellum, binds to two receptors defined as the Type 1 (CRF-R1) and the Type 2 (CRF-R2alpha). CRF-R1 has been localized to the cerebellum, as has a truncated isoform of CRF-R2alpha. Evidence for the presence of the full length isoform of CRF-R2alpha in the cerebellum is conflicting. We used RT-PCR, immunohistochemical, and physiologic techniques to resolve this conflict. RT-PCR data show low levels of CRF-R2alpha in the vermis and hemisphere of the cerebellum. These observations were confirmed by the Gene Expression Nervous System Atlas (GENSAT) database. A CRF-R2alpha antibody was used to determine the cellular distribution of the receptor in the cerebellum. The vast majority of the receptors are localized to Bergmann glial cells located throughout the cerebellum, as well as astrocytes in the granule cell layer. Neuronal labeling is present in sub-populations of Purkinje cells, Golgi cells, basket cells, and cerebellar nuclear neurons. Physiologic data show that urocortin II, which binds selectively to CRF-R2alpha, increases the firing rate of both Purkinje cells and nuclear neurons; this response can be blocked by the CRF-R2alpha-specific antagonist, antisauvagine-30. The present results confirm that CRF-R2alpha is present in the cerebellum and functions in circuits that modulate the firing rate of Purkinje cells and cerebellar nuclear neurons. A comparative analysis showed that the patterns of distribution of CRF-R1, CRF-R2alpha and CRF-R2alpha-tr are distinct. These data indicate that the CRF family of peptides modulates cerebellar output by binding to multiple CRF receptors.

Animals↗

PubMed2006

Ionic channels and conductance-based models for hypothalamic neuronal thermosensitivity.

Thermoregulatory responses are partially controlled by the preoptic area and anterior hypothalamus (PO/AH), which contains a mixed population of temperature-sensitive and insensitive neurons. Immunohistochemical procedures identified the extent of various ionic channels in rat PO/AH neurons. These included pacemaker current channels [i.e., hyperpolarization-activated cyclic nucleotide-gated channels (HCN)], background potassium leak channels (TASK-1 and TRAAK), and transient receptor potential channel (TRP) TRPV4. PO/AH neurons showed dense TASK-1 and HCN-2 immunoreactivity and moderate TRAAK and HCN-4 immunoreactivity. In contrast, the neuronal cell bodies did not label for TRPV4, but instead, punctate labeling was observed in traversing axons or their terminal endings. On the basis of these results and previous electrophysiological studies, Hodgkin-Huxley-like models were constructed. These models suggest that most PO/AH neurons have the same types of ionic channels, but different levels of channel expression can explain the inherent properties of the various types of temperature-sensitive and insensitive neurons.

Action Potentials↗

PubMed2003

Increased expression of the glial glutamate transporter EAAT2 modulates excitotoxicity and delays the onset but not the outcome of ALS in mice.

The glial glutamate transporter EAAT2 is primarily responsible for clearance of glutamate from the synaptic cleft and loss of EAAT2 has been previously reported in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. The loss of functional EAAT2 could lead to the accumulation of extracellular glutamate, resulting in cell death known as excitotoxicity. However, it is still unknown whether it is a primary cause in the cascade leading to neuron degeneration or a secondary event to cell death. The goals of this study were to generate transgenic mice overexpressing EAAT2 and then to cross these mice with the ALS-associated mutant SOD1(G93A) mice to investigate whether supplementation of the loss of EAAT2 would delay or rescue the disease progression. We show that the amount of EAAT2 protein and the associated Na+-dependent glutamate uptake was increased about 2-fold in our EAAT2 transgenic mice. The transgenic EAAT2 protein was properly localized to the cell surface on the plasma membrane. Increased EAAT2 expression protects neurons from L-glutamate induced cytotoxicity and cell death in vitro. Furthermore, our EAAT2/G93A double transgenic mice showed a statistically significant (14 days) delay in grip strength decline but not in the onset of paralysis, body weight decline or life span when compared with G93A littermates. Moreover, a delay in the loss of motor neurons and their axonal morphologies as well as other events including caspase-3 activation and SOD1 aggregation were also observed. These results suggest that the loss of EAAT2 may contribute to, but does not cause, motor neuron degeneration in ALS.

Amyotrophic Lateral Sclerosis↗

PubMed2003

Localization of the type 1 corticotropin releasing factor receptor (CRF-R1) in the embryonic mouse cerebellum.

Corticotropin releasing factor (CRF) is present in the adult, as well as in the embryonic and postnatal rodent cerebellum. Further, the distribution of the type 1 CRF receptor has been described in adult and postnatal animals. The focus of the present study is to determine the distribution and cellular relationships of the type 1 CRF receptor (CRF-R1) during embryonic development of the cerebellum. Between embryonic day (E)11 and E12, CRF-R1 immunoreactive puncta are uniformly distributed in the ventricular zone, the site of origin of Purkinje cells, nuclear neurons, and GABAergic interneurons, as well as the germinal trigone, the birthplace of the precursors of granule cells. Between E13 and 18, the distribution of immunolabeled puncta decreases in both the ventricular zone and the germinal trigone and increases in the intermediate zone, as well as in the dorsal aspect of the cerebellar plate. Between E14 and 18, antibodies that label specific populations of cerebellar neurons were combined with the antibody for the receptor to determine the cellular elements that expressed CRF-R1. At E14, CRF-R1 immunoreactivity is co-localized in neurons immunolabeled with PAX-2, an antibody that is specific for GABAergic interneurons. These neurons continue to express CRF-R1 as they migrate dorsally toward the cerebellar surface. Between E16 and 18, Purkinje cells, immunolabeled with calbindin, near the dorsal surface of the cerebellum express CRF-R1 in their cell bodies and apical processes. CRF has been shown to have a depolarizing effect on adult and postnatal Purkinje cells. Further, CRF has been shown to contribute to excitability of hippocampal neurons during embryonic development by binding to CRF-R1; depolarization induced excitability appears to be critical for cell survival. The location of the type one CRF receptor and the presence of its primary ligand, CRF, in the germinal zones of the cerebellum and in migrating neurons suggest that this receptor/ligand interaction could be important in the regulation of neuronal survival through cellular mechanisms that lead to depolarization of embryonic cerebellar neurons.

Animals↗

PubMed2002

Development of a corticotropin-releasing factor-mediated effect on the firing rate of Purkinje cells in the postnatal mouse cerebellum.

Corticotropin-releasing factor (CRF), present in climbing and mossy fiber afferents to the adult mouse cerebellum, acts as a neuromodulator to enhance the spontaneous and amino-acid-induced firing rate of Purkinje cells. CRF also is present during development of the mouse cerebellum, at ages that precede synaptogenesis, which suggests that it may have a different function during development compared to its modulatory role in the adult. The intent of this study was to determine when CRF begins to affect the firing rate of Purkinje cells as well as the time course over which this effect matures. The earliest effect of CRF was elicited at postnatal day (P) 9 at which time a weak enhancement in the amplitude of the firing rate was recorded. However, the amplitude, time to peak, sustainability, and duration of the response were significantly different from that recorded in the older animals or adults. The excitatory effect of CRF became stronger and the duration of the response increased progressively from P9 until it was adult-like by P20. Purkinje cells in the posterior lobe vermis developed a mature response before those in the anterior lobe or hemispheres. Data from previous studies have shown that CRF and its type 1 receptor are present in the cerebellum before birth and that both undergo major reorganization around P10. Taken together, these immunohistochemical observations and the present physiologic data indicate that CRF does not modulate the activity of Purkinje cells until the peptide begins to assume an adult-like distribution in cerebellar afferents.

Action Potentials↗

PubMed2002

The distribution and cellular localization of CRF-R1 in the vermis of the postnatal mouse cerebellum.

The distribution of corticotropin-releasing factor (CRF), the development of CRF-binding sites, and the age at which application of CRF elicits a physiological response have been described previously in the postnatal mouse cerebellum. The intent of the present study was to determine the cellular and subcellular distribution of the CRF type 1 receptor (CRF-R1) in the vermis of the postnatal mouse cerebellum and to correlate these data with those presented in previous studies. On P0, CRF-R1 is present in the apical processes of migrating Purkinje cells. Between P0 and P8, CRF-R1 immunostaining is confined to a supranuclear position in Purkinje cell bodies. Between P9 and P14, the receptor immunolabeling circumscribes Purkinje cell nuclei and extends into their primary dendrites. An adult-like distribution is achieved between P16 and P21. Between P0 and P14, the CRF-R1 antibody also labels processes of migrating GABAergic interneurons that are directed toward the pial surface. By P12, labeling begins to circumscribe the nucleus of GABAergic cells in the internal granule cell layer. Finally, astrocytic processes in the white matter, as well as radial glial processes, show focal labeling with the CRF-R1 antibody beginning at P3 and throughout postnatal development. A previous study demonstrated that CRF does not elicit a physiological response in Purkinje cells until P9. This observation, together with the data presented in this study, suggests that the binding of CRF to the type 1 receptor may be involved in regulating the development of cerebellar neurons and glia immediately after birth, before CRF assumes its function as a neuromodulator later in postnatal development and in the adult.

Animals↗

PubMed2002

Stimulus-dependent activation of c-Fos in neurons and glia in the rat cerebellum.

The intent of the present study was to use chemical or electrical stimulation of cerebellar afferents to determine how different stimulation paradigms affect the pattern of activation of different populations of neurons in the cerebellar cortex. Specifically, we analyzed immediate changes in neuronal activity, identified neurons affected by different stimulation paradigms, and determined the time course over which neuronal activity is altered. In the present study, we used either systemic (harmaline) or electrical stimulation of the inferior cerebellar peduncle (10 and 40 Hz) to alter the firing rate of climbing and mossy fiber afferents to the rat cerebellum and an antibody made against the proto-oncogene, c-fos, as a marker to identify activated neurons and glia. In control animals, only a few scattered granule cells express nuclear Fos-like immunoreactivity. Although no other cells show Fos-like immunoreactivity in their nuclei, Purkinje cells express Fos-like immunoreactivity within their somatic and dendritic cytoplasm in control animals. Within 15 min of chemical or electrical stimulation, numerous granule and glial cells express Fos-like immunoreactivity in their nuclei. Cells in the molecular layer express Fos-like immunoreactivity following harmaline stimulation in a time and lobule specific manner; they do not appear to be activated in the electrical stimulation paradigm. Following harmaline injections, there is an initial loss of Fos-like immunoreactivity in the cytoplasm of Purkinje cells; 90 min later, nuclear staining is observed in a few scattered Purkinje cells. Following electrical stimulation, the cytoplasmic staining in Purkinje cells is enhanced; it is never present in the nucleus. Data derived from this study reveal cell-specific temporal and spatial patterns of c-Fos activation that is unique to each paradigm. Further, it reveals the presence of an activity dependent protein in the cytoplasm of Purkinje cell somata and dendrites.

Animals↗