ABSTRACT
We studied functional and structural differences between the two neurotoxins, wasp toxin pompilidotoxin (PMTX) and sea anemone toxin (ATXII). Although PMTX and ATXII inhibited inactivation of sodium currents both toxins had distinct actions on the lobster axon and on the rat hippocampal cells. To determine structural basis of the difference we compared arrangement of polar and non-polar amino acids of the two toxins and found that similar sequence of PMTX exist in a discrete position of three-dimensional structure of ATXII. The sequence may be responsible for the binding site in the neuronal Na(+) channel molecule because PMTX is insensitive to cardiac Na(+) channel. Differential actions of ATXII from PMTX may come from other regions than the overlapped sequence. PMTX has diverse actions in the central neurons and is useful to classify Na(+) channel subtypes.
Subject(s)
Hippocampus/drug effects , Neuromuscular Junction/drug effects , Neurons/drug effects , Neurotoxins/pharmacology , Sodium Channels/drug effects , Action Potentials/drug effects , Action Potentials/physiology , Amino Acid Sequence/physiology , Animals , Cell Membrane/drug effects , Cell Membrane/metabolism , Cells, Cultured , Cnidarian Venoms/pharmacology , Hippocampus/metabolism , Insect Proteins , Myocytes, Cardiac/drug effects , Myocytes, Cardiac/metabolism , Nephropidae , Neuromuscular Junction/metabolism , Neurons/metabolism , Neurotoxins/chemistry , Patch-Clamp Techniques , Protein Structure, Tertiary/physiology , Rats , Sodium/metabolism , Sodium Channels/classification , Sodium Channels/metabolism , Structure-Activity Relationship , Wasp VenomsABSTRACT
By using a heterotopic brain graft model, we have made histological and electrophysiological studies of the infant rat brain after prolonged ischemia. An infant rat head which had undergone ischemia for more than 90 min, was grafted onto an adult rat by anastomosing the thoracic vessels to the femoral vessels of the host rat. Histological and histochemical studies carried out 10 days after the operation showed that the development of the hippocampus and cerebellum in the grafted brain appeared to be normal. Interneuron growth in the hippocampus and migration of the granule cells in the cerebellum had occurred to a similar extent as in control rats. Extracellular recordings in the hippocampus showed normal characteristics of the postsynaptic potentials including long-term potentiation. This heterotopic graft model would be useful for studying brain function after long periods of ischemia.
Subject(s)
Brain Ischemia/physiopathology , Brain , Nerve Tissue/transplantation , Transplantation, Heterotopic , Animals , Animals, Newborn , Brain/growth & development , Brain/pathology , Brain/physiopathology , Brain Ischemia/pathology , Cell Division , Cell Movement , Cerebellum/pathology , Cerebellum/physiopathology , Chronic Disease , Disease Models, Animal , Interneurons/pathology , Interneurons/physiology , Long-Term Potentiation , Male , Rats , Rats, Inbred Lew , Reference Values , Synaptic TransmissionABSTRACT
GIRK2 (G protein-gated inwardly rectifying K(+) channel 2) located on the Down syndrome region 21q22.2 in humans has been reported to have several alternative transcripts and transcripts longer than 4 kb that do not have the poly-A tail. We sequenced GIRK2 transcripts with a long 3'-untranslated region (3'-UTR) containing multiple adenylate uridylate-rich elements (AREs) with the poly-A tail. In a 16-kb transcript, 28 AUUUA pentanucleotides, 9 AUUUUA hexanucleotides, 5 AUUUUUA heptanucleotides, and 3 UUAUUUA[U/A][U/A] nonanucleotides were found. Northern blot and in situ hybridization revealed abundant expression of the 16-kb transcripts in the rat brain despite no detectable signals in other tissues examined. The AREs have been reported to mediate the turnover of mRNAs encoding proteins regulating cellular proliferation/differentiation and body response to inflammatory and environmental stimuli. This is the first study indicating that ion channel transcripts have multiple AREs.
Subject(s)
Brain/metabolism , Potassium Channels, Inwardly Rectifying , Potassium Channels/genetics , Repetitive Sequences, Nucleic Acid/genetics , 3' Untranslated Regions/analysis , Animals , Cloning, Molecular , DNA, Complementary/analysis , G Protein-Coupled Inwardly-Rectifying Potassium Channels , In Situ Hybridization , Male , Molecular Sequence Data , Molecular Weight , Poly A/genetics , Potassium Channels/metabolism , RNA, Messenger/chemistry , RNA, Messenger/metabolism , Rats , Rats, Sprague-Dawley , Tissue DistributionABSTRACT
GFAP (glial fibrillary acidic protein) is an intermediate filament protein found exclusively in the astrocytes of the central nervous system. We studied the role of GFAP in the neuronal degeneration in the hippocampus after transient ischemia using knockout mice. Wild-type C57 Black/6 (GFAP(+/+)) mice and mutant (GFAP(-/-)) mice were subjected to occlusion of both carotid arteries for 5-15 min. Hippocampal slices were prepared 3 days after reperfusion and the field excitatory postsynaptic potentials (fEPSP) in the CA1 were recorded. High frequency stimulation induced robust long-term potentiation (LTP) in GFAP(-/-), as in GFAP(+/+) mice. After ischemia, however, the LTP in GFAP(-/-) was significantly depressed. Similarly, paired pulse facilitation (PPF) displayed little difference between GFAP(+/+) and GFAP(-/-), but after ischemia, the PPF in GFAP(-/-) showed a depression. Histological study revealed that loss of CA1 and CA3 pyramidal neurons after ischemia was marked in GFAP(-/-). MAP2 (dendritic) immunostaining in the post-ischemic hippocampus showed little difference but NF200 (axonal) immunoreactivity was reduced in GFAP(-/-). S100beta (glial) immunoreactivity was similar in the post-ischemic hippocampus of the GFAP(+/+) and GFAP(-/-), indicating that reactive astrocytosis did not require GFAP. Our results suggest that GFAP has an important role in astrocyte-neural interactions and that ischemic insult impairs LTP and accelerates neuronal death.
