Glutamate receptor binding in juvenile and adult Rana pipiens CNS

Abstract

Autoradiographic methods were used to map NMDA- and quisqualate-sensitive glutamate binding sites in the brain of mature and juvenile Rana pipiens frogs. NMDA- and quisqualate-sensitive sites were consistently co-localized in the CNS. The highest glutamate binding occurred in the telencephalon, hypothalamus, and cerebellum. Glutamate binding sites were also specifically localized in visual pathways, including the superficial neuropil of the optic tectum, consistent with glutamate being the retinal ganglion cell neurotransmitter. The distribution of glutamate binding sites in the brain of juvenile postmetamorphic frogs was similar to that in adults. In general, Quis binding increased about twofold in adults compared to juveniles, whereas NMDA binding did not show a comparable developmental increase. To test whether glutamate binding sites are located on retinal axon terminals or on tectal cell dendrites in the optic tectum, juvenile postmetamorphic frogs were enucleated unilaterally, and receptor binding was performed following 1, 3, 7, and 14 days survival. The denervated tectal neuropil showed a delayed decrease in NMDA- and quisqualate-sensitive binding, consistent with the receptors being located on postsynaptic tectal cell dendrites.

Immunohistochemical localization and biological activity of the steroidogenic enzyme cytochrome P450 17α‐hydroxylase/C17, 20‐lyase (P450C17) in the frog brain and pituitary

“…1997; Louiset et al . 2000) and NMDA receptors (Cline et al . 1994), suggests that neurosteroids synthesized within the frog brain and pituitary may regulate GABAergic and glutamatergic neurotransmission through allosteric modulation of the GABA A and NMDA receptors.…”

“…In mammals, DHEA acts both as a negative modulator of the c-aminobutyric acid type A (GABA A ) receptor (Majewska 1992;Patchev et al 1996;Le Foll et al 1997a,b), and an activator of NMDA Debonnel et al 1996;Lhullier et al 2004) and sigma receptors Romieu et al 2003). The presence of P450 C17 -immunoreactive cells in the telencephalon, diencephalon, mesencephalon, cerebellum and pituitary of the frog, which actively express GABA A (Aller et al 1997;Louiset et al 2000) and NMDA receptors (Cline et al 1994), suggests that neurosteroids synthesized within the Fig. 11 Effect of graded concentrations of ketoconazole, a P450 C17 inhibitor, on the conversion of [ 3 H]pregnenolone into tritiated 17OH-D 5 P, 17OH-P, DHEA, and D 4 by frog diencephalon slices.…”

NMDA Receptor-Mediated Refinement of a Transient Retinotectal Projection during Development Requires Nitric Oxide

“…The first aim of this study was to examine the role of NMDA receptors in elimination of the ipsilateral retinotectal projection during chick development. Retinal ganglion cells are glutamatergic (Kalloniatis et al, 1994;Dye and Karten, 1996) and make synaptic connections with cells that express NMDA receptors (Esguerra et al, 1992;Cline et al, 1994;Fohr et al, 1995;Guido et al, 1997). To determine whether retinotectal communication mediated by NMDA receptors is important in elimination of the ipsilateral projection, we treated embryos with an NMDA receptor antagonist, MK-801, during the period of refinement.…”

“…Previous studies showed that activation of NMDA receptors resulted in the synthesis of NO in cultured cerebellar granule cells (Garthwaite et al, 1988;Bredt and Snyder, 1989). Because both NMDA receptors and NOS are expressed in the developing tectum (Esguerra et al, 1992;Cline et al, 1994;Williams et al, 1994;Fohr et al, 1995;Guido et al, 1997), it is likely that activation of NMDA receptors in the tectum leads to synthesis of NO. The present study implies a link between NMDA receptor activation and NO synthesis by showing a reduction in NOS activity in tectal cells after treatment of embryos with MK-801 in vivo.…”

Anin vitrostudy of retinotectal transmission in the chick: Role of glutamate and GABA in evoked field potentials

“…First, biochemical studies have shown that glutamate uptake in the optic tecta of chicks (Bondy & Purdy, 1977) and pigeons ) is specifically and markedly reduced by enucleation, and that glutamate and aspartate are released into the tectum in response to optic nerve stimulation in the pigeon (Canzek et al, 1981). Second, there is now a considerable body of published electrophysiological work indicating that glutamate is the principal transmitter in the retinotectal pathways of other species, notably the goldfish (Langdon & Freeman, 1986), the frog (Nistri et al, 1990;Hickmott & Constantine-Paton, 1993;Cline et al, 1994), the rat (Sakurai et al, 1990;Roberts et al, 1991;Sakurai & Okada, 1992), the guinea pig (Miyamoto et al, 1990), and the cat (Binns & Salt 1994). In the chick, transmission appears to be mediated largely by non-NMDA receptors (Figs.…”