Ontogenesis of the Corpora Pedunculata: Integral Relay Structures of Chemosensory Content Addressable Memory Networks of Hexapods: A Synthesis of Development and Function

Hehn, Christian A (1995) Ontogenesis of the Corpora Pedunculata: Integral Relay Structures of Chemosensory Content Addressable Memory Networks of Hexapods: A Synthesis of Development and Function. MSc(R) thesis, University of Glasgow.

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Biological memory is the temporal storage of information as a function of evolution. Several mechanisms have evolved by which memory can be stored. There are two components involved in the storage of memory in metazoan organisms. Innate memory is strictly teleonomically determined, and hence, depends on the phylogenic predisposition of an organisms' ontogenesis. 'Learned' memory is, in contrast, strictly ontogenically determined and, hence, influenced by the organisms environment. Whilst strictly ontogenic determined memory is stored in the spatial arrangement of nerve cells, phylogenic memory is stored in the sequential arrangement of the four components of the DNA. Accordingly, ontogenic memory is lost in subsequent generations, whereas phylogenic memory is passed on and recalled during the course of evolution. Insects are among the best understood organisms. The fruit fly Drosophila melanogaster, for instance, has been widely used as a model to unravel the genetic components of development. Most of the genes that are involved in this process are known. Other insect species have been physiologically and behaviourally well researched. By assembling the information derived from the latest research on Drosophila melanogaster and other insect species, I have made the attempt to characterise the different components of molecular memory formation (hereafter referred to as mnemogenesis) in insects. Chemosensory memory pathways of Drosophila are composed of at least two different entities: the morphogenic fields such as the peripheral and the central nervous system. I have concluded that during the ontogenesis of the Drosophila chemosensory memory pathways, genes are active that function as modules during this process. Most of the genes which mediate this process are not strictly employed during the morphogenesis of the chemosensory memory pathways. However, they are redeployed to a large extent during development of other germ layers and morphogenic fields, as well. Only certain key genes, which expression is initiated by the several coinciding morphogenic signals, determine the specificity of the different components of the chemosensory memory pathways. Hence, the specificity of the chemosensory memory pathways of Drosophila is determined by the temporally and spatially distinct expression of genes, in addition to the modification of their products. Whilst stage and cell specific gene expression is primarily regulated on the level of chromosome structure and transcriptional activity, the specific function of genes that are expressed in the different regions during different stages of ontogenesis is generated by messenger ribonucleic acid and protein processing. The morphogenic cascades are probably frozen down once the chemosensory memory pathways have reached the state of maturity. The mature insect has maintained the ability to employ some components of the developmental cascade to modulate its memory in response to environmental stimuli. Imaginal chemosensory memory pathways comprise at least four levels. Chemosensory receptor (level I) cells receive environmental information. Projection neurones (level II) reduce the background noise and transfer the information to diverging memory structures, in addition to the control centres (levels III/i and III/ii). Whereas memory structures modulate chemosensory information, the control centres feed this modulated information into output fibres that link the chemosensory memory networks with the premotor fibres (level IV). The function of the memory structures, which in insects are called the corpora pedunculata, is to compare input information to the information stored intrinsically in these organs. The information that is stored intrinsic to these structures is able to modulate the behaviour of an signal, which exits the chemosensory pathways via the premotor neurones. It has been postulated that the modulation of this information depends on the synaptic configuration within the corpora pedunculata. Hence, the synaptic arrangement is thought to underlie the modulation of the information transfer within the chemosensory memory networks. Long term memory is associated with the alteration of this synaptic configuration, which in turn requires the activity of several genetic circuits. Intriguingly, these genetic circuits are probably identical to those employed during axonogenesis, in addition to other morphogenic events.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Neurosciences, Genetics
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-75372
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 20:23
Last Modified: 19 Nov 2019 20:23
URI: https://theses.gla.ac.uk/id/eprint/75372

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