Biomedical subjects

L D Barnett

Publications and source records attributed to L D Barnett.

14 recordsLinked to original sources

PubMed1994

The onset of response habituation during the growth of the lateral giant neuron of crayfish.

1. The postembryonic development of the crayfish LG tailflip command neuron's response to mechanosensory input was studied with standard electrophysiological techniques in animals between 1 and 12 cm long. 2. LG neurons are present in each abdominal hemisegment where they receive direct and indirect excitatory input from mechanosensory afferents. In both small and large crayfish, electrical stimulation of an abdominal ganglionic nerve containing those afferents evoked a compound excitatory postsynaptic potential (EPSP) with an early, reliable alpha component and a later, depression-prone beta wave. It is known that the alpha and beta components are produced by inputs from primary mechanosensory afferents and interneurons, respectively. 3. In crayfish < 2 cm long, LG was excited by the alpha component. When superthreshold, the alpha component triggered a single spike; additional excitation provided by the later beta wave presumably was preempted by refractoriness following the alpha spike and by recurrent inhibition of LG excited by the spike. LG was excited reliably by the alpha component in response to repeated superthreshold stimulation. 4. In crayfish between 2 and 3 cm, LG was excited more readily by the beta wave than by the alpha component. LG's beta spike response habituated to repeated stimulation at 1 Hz, and the beta EPSP depressed whereas the alpha component was largely unchanged. The appearance of the cellular substrates of habituation correlates with the reported onset of behavioral habituation of the tailflip response. Higher stimulus levels brought the alpha EPSP to threshold. Repetitive stimulation at these levels reliably evoked LG spikes from the alpha EPSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1994

Changes in synaptic integration during the growth of the lateral giant neuron of crayfish.

1. The effect of growth on the electrotonic structure and synaptic integrative properties of the lateral giant (LG) interneuron was assessed from anatomic and electrophysiological measurements of LGs in small (1-2.4 cm) and large (9-11.2 cm) crayfish and from calculated responses of mathematical models of these neurons. Postsynaptic responses of small and large LGs were compared with model responses to determine whether the differences in the neurons' responses result from growth-related changes in their physical characteristics. 2. LG neurons in the terminal abdominal ganglia of small and large crayfish are similar in shape but differ in size according to an approximately isometric pattern of growth. The soma diameter of the large LG is 2.2 times larger than the small LG, the major ipsilateral dendrite is 2.8 times longer and 3.6 times greater in diameter, and the axon is 7.6 times longer and 4.5 times greater in diameter. The projected area of the major ipsilateral dendrite of LG in the horizontal plane of the terminal abdominal ganglion is 27 times larger in the large than in the small crayfish. 3. LG's input resistance was nearly 80% smaller in the large (167 K omega) than in the small (742 K omega) crayfish when measured at or near the initial axon segment. The cell's membrane time constant displayed an opposite relationship, with the value in the large crayfish (20.9 ms) nearly two-and-a-half times larger than the value in the small crayfish (8.6 ms). 4. Simultaneous recordings were made from the distal portion of the ipsilateral dendrite and the initial axon segment of small and large LGs to determine how excitatory postsynaptic potentials (EPSPs) are attenuated or filtered by the electrotonic properties of the different sized cells. In the small LG, the fast alpha and the slower beta components of compound EPSPs evoked by sensory nerve stimulation were similarly attenuated. In the large LG, the alpha component of the compound EPSP was much more attenuated and smoothed than the slower beta component. 5. Multicompartment models of small and large LGs were constructed and used to test whether differences in the two neurons' physical properties could account for the differences in their passive response properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1993

Identification, characterisation and genomic cloning of a O-linked N-acetylglucosamine-containing cytoplasmic Leishmania glycoprotein.

Antibodies against Leishmania major wheat germ agglutinin-binding glycoproteins were used to select from a genomic lambda gt11 expression library a clone coding for a L. major glycoprotein. The partial DNA sequence indicated the presence of a mosaic of repetitive sequences. Southern blot hybridisation on genomic DNA using the cloned gene as a probe at high stringency suggested a single gene, which was localised to chromosome band 18. Northern blot analysis of L. major mRNA detected a major transcript of 7.5 kb and a minor 4.0-kb transcript. Antibodies affinity-purified on the fusion protein identified a complex of two water-soluble cytoplasmic polypeptides of approximately 96 kDa and 92 kDa in L. major promastigotes and amastigotes. They also recognised polypeptides in other Leishmania species, in Crithidia lucilliae and very weakly in Leptomonas. The apparent molecular weight of these polypeptides, while conserved within each species, varied between species. A peptide map of the two polypeptides from L. major generated an identical pattern suggesting a close relatedness at the protein level. This protein complex was not hydrolysed by N-glycanase and was not affected by tunicamycin, but treatment with anhydrous hydrogen fluoride suggested that it is O-glycosylated. The glycan moiety appears to be N-acetylglucosamine, and N-acetylglucosamine beta-1,4-galactosyltransferase was capable of adding [3H]galactose to it. This was susceptible to beta elimination and beta-galactosidase treatment. Taken together, the data indicates that gp96/92 belongs to the newly described class of cytoplasmic and nuclear glycoproteins containing O-linked N-acetylglucosamine.

Acetylglucosamine↗

PubMed1991

Cloning and partial nucleotide sequence of human glutamic acid decarboxylase cDNA from brain and pancreatic islets.

We report partial nucleotide sequences of the human enzyme glutamic acid decarboxylase (GAD) from brain and pancreatic islets which encode the middle 180 amino acids of GAD. The brain and islet GAD sequences display a high degree of sequence homology with the equivalent region of other mammalian brain GAD cDNAs. Alignment of the brain and islet GAD sequences showed that there were 45 nucleotide differences which, at the translational level, would result in seven amino acid substitutions. These results which suggest that different isomeric forms of human GAD exist in brain and pancreas may be relevant to the pathogenesis of stiff man syndrome (SMS) and insulin-dependent diabetes mellitus (IDDM), respectively, two distinct but associated clinical disorders in which GAD is the target of autoantibodies.

Amino Acid Sequence↗

PubMed1976