title: Dense gap-junction connections support dynamic Turing structures in the cortex

authors: Steyn-Ross, D. Alistair

abstract: The recent report by Fukuda et al [1] provides convincing evidence for dense gap-junction connectivity between inhibitory neurons in the cat visual cortex, each neuron making 60 +/- 12 gap-junction dendritic connections with neurons in both the same and adjoining orientation columns. These resistive connections provide a source of diffusive current to the receiving neuron, supplementing the chemical-synaptic currents generated by incoming action-potential spike activity. Fukuda et al describe how the gap junctions form a dense and homogeneous electrical coupling of interneurons, and propose that this diffusion-coupled network provides the substrate for synchronization of neuronal populations.

To date, large-scale population-based mathematical models of the cortex have ignored diffusive communication between neurons. Here we augment a well-established mean-field cortical model [2] by incorporating gap-junction-mediated diffusion currents, and we investigate the implications of strong diffusive coupling. The significant result is the model prediction that the 2D cortex can spontaneously generate centimetre-scale Turing structures (spatial patterns), in which regions of high-firing activity are intermixed with regions of low-firing activity (see Fig. 1). Since coupling strength decreases with increases in firing rate, these patterns are expected to exchange contrast on a slow time-scale, with low-firing patches increasing their activity at the expense of high-firing patches. These theoretical predictions are consistent with the slowly fluctuating large-scale brain-activity images detected from the BOLD (blood oxygen-level-dependent) signal [3].

text: Dense gap-junction connections support dynamic Turing structures in the cortex The recent report by Fukuda et al [1] provides convincing evidence for dense gap-junction connectivity between inhibitory neurons in the cat visual cortex, each neuron making 60 +/- 12 gap-junction dendritic connections with neurons in both the same and adjoining orientation columns. These resistive connections provide a source of diffusive current to the receiving neuron, supplementing the chemical-synaptic currents generated by incoming action-potential spike activity. Fukuda et al describe how the gap junctions form a dense and homogeneous electrical coupling of interneurons, and propose that this diffusion-coupled network provides the substrate for synchronization of neuronal populations.

To date, large-scale population-based mathematical models of the cortex have ignored diffusive communication between neurons. Here we augment a well-established mean-field cortical model [2] by incorporating gap-junction-mediated diffusion currents, and we investigate the implications of strong diffusive coupling. The significant result is the model prediction that the 2D cortex can spontaneously generate centimetre-scale Turing structures (spatial patterns), in which regions of high-firing activity are intermixed with regions of low-firing activity (see Fig. 1). Since coupling strength decreases with increases in firing rate, these patterns are expected to exchange contrast on a slow time-scale, with low-firing patches increasing their activity at the expense of high-firing patches. These theoretical predictions are consistent with the slowly fluctuating large-scale brain-activity images detected from the BOLD (blood oxygen-level-dependent) signal [3].

year: 2007-07

title: Development and field assessment of a quantitative PCR for the detection and enumeration of the noxious bloom-former Anabaena planktonica

authors: Rueckert, Andreas

subjects: biology

abstract: Anabaena planktonica is a harmful, bloom-forming freshwater cyanobacterium, which has arrived recently in New Zealand. In the short time since its incursion (<10 yr), A. planktonica has spread rapidly throughout lakes in the North Island. To date, the identification and enumeration of A. planktonica has been undertaken using light microscopy. There is an urgent demand for a highly sensitive and specific quantitative detection method that can be combined with a high sample processing capability in order to increase sampling frequency. In this study, we sequenced 36 cyanobacterial 16S rRNA genes (partial), complete intergenic transcribed spacers (ITS), and 23S rRNA genes (partial) of fresh-water cyanobacteria found in New Zealand. The sequences were used to develop an A. Planktonica specific TaqMan QPCR assay targeting the long ITS1-L and the 5´ terminus of the 23S rRNA gene. The QPCR method was linear (R2 = 0.999) over seven orders of magnitude with a lower end sensitivity of approximately five A. planktonica cells in the presence of exogenous DNA. The quantitative PCR (QPCR) method was used to assess the spatial distribution and seasonal population dynamics of A. planktonica from the Lower Karori Reservoir (Wellington, New Zealand) over a five-month period. The QPCR results were compared directly to microscopic cell counts and found to correlate significantly (95% confidence level) under both bloom and non-bloom conditions. The current QPCR assay will be an invaluable tool for routine monitoring programs and in research investigating environmental factors that regulate the population dynamics and the blooming of A. planktonica.

text: Development and field assessment of a quantitative PCR for the detection and enumeration of the noxious bloom-former Anabaena planktonica Anabaena planktonica is a harmful, bloom-forming freshwater cyanobacterium, which has arrived recently in New Zealand. In the short time since its incursion (<10 yr), A. planktonica has spread rapidly throughout lakes in the North Island. To date, the identification and enumeration of A. planktonica has been undertaken using light microscopy. There is an urgent demand for a highly sensitive and specific quantitative detection method that can be combined with a high sample processing capability in order to increase sampling frequency. In this study, we sequenced 36 cyanobacterial 16S rRNA genes (partial), complete intergenic transcribed spacers (ITS), and 23S rRNA genes (partial) of fresh-water cyanobacteria found in New Zealand. The sequences were used to develop an A. Planktonica specific TaqMan QPCR assay targeting the long ITS1-L and the 5´ terminus of the 23S rRNA gene. The QPCR method was linear (R2 = 0.999) over seven orders of magnitude with a lower end sensitivity of approximately five A. planktonica cells in the presence of exogenous DNA. The quantitative PCR (QPCR) method was used to assess the spatial distribution and seasonal population dynamics of A. planktonica from the Lower Karori Reservoir (Wellington, New Zealand) over a five-month period. The QPCR results were compared directly to microscopic cell counts and found to correlate significantly (95% confidence level) under both bloom and non-bloom conditions. The current QPCR assay will be an invaluable tool for routine monitoring programs and in research investigating environmental factors that regulate the population dynamics and the blooming of A. planktonica.

year: 2007

title: Te Ira Atua: The spiritual spark of the child

authors: Rameka, Lesley Kay

abstract: “E ai ki tā te Māori he atua tonu kei roto i te mokopuna ina whānau mai ana ia ki tēnei ao” (Ministry of Education, 1996, p. 35). This quote is from the New Zealand Ministry of Education’s early childhood curriculum policy statement, Te Whāriki: He Whāriki Matauranga mo ngā Mokopuna o Aotearoa/Early Childhood Curriculum (Ministry of Education, 1996). It speaks of the godliness or spiritual essence each child inherits from their ancestors when they are born (Early Childhood Development, 1999; Reedy, 2003). From a traditional Māori perspective, not only is the child endowed with spiritual potential or a divine spirit, but the world the child is born into is also endowed with spiritual influences.

text: Te Ira Atua: The spiritual spark of the child “E ai ki tā te Māori he atua tonu kei roto i te mokopuna ina whānau mai ana ia ki tēnei ao” (Ministry of Education, 1996, p. 35). This quote is from the New Zealand Ministry of Education’s early childhood curriculum policy statement, Te Whāriki: He Whāriki Matauranga mo ngā Mokopuna o Aotearoa/Early Childhood Curriculum (Ministry of Education, 1996). It speaks of the godliness or spiritual essence each child inherits from their ancestors when they are born (Early Childhood Development, 1999; Reedy, 2003). From a traditional Māori perspective, not only is the child endowed with spiritual potential or a divine spirit, but the world the child is born into is also endowed with spiritual influences.

year: 2015