title: Finding synaptic couplings from a biophysical model of motor evoked potentials after theta-burst transcranial magnetic stimulation

authors: Wilson, Marcus T.

subjects: Cortical plasticity

abstract: OBJECTIVE: We aimed to use measured input-output (IO) data to identify the best fitting model for motor evoked potentials. METHODS: We analyzed existing IO data before and after intermittent and continuous theta-burst stimulation (iTBS & cTBS) from a small group of subjects (18 for each). We fitted individual synaptic couplings and sensitivity parameters using variations of a biophysical model. A best performing model was selected and analyzed. RESULTS: cTBS gives a broad reduction in MEPs for amplitudes larger than resting motor threshold (RMT). Close to threshold, iTBS gives strong potentiation. The model captures individual IO curves. There is no change to the population average synaptic weights post TBS but the change in excitatory-to-excitatory synaptic coupling is strongly correlated with the experimental post-TBS response relative to baseline. CONCLUSIONS: The model describes population-averaged and individual IO curves, and their post-TBS change. Variation among individuals is accounted for with variation in synaptic couplings, and variation in sensitivity of neural response to stimulation. SIGNIFICANCE: The best fitting model could be applied more broadly and validation studies could elucidate underlying biophysical meaning of parameters.

text: Finding synaptic couplings from a biophysical model of motor evoked potentials after theta-burst transcranial magnetic stimulation OBJECTIVE: We aimed to use measured input-output (IO) data to identify the best fitting model for motor evoked potentials. METHODS: We analyzed existing IO data before and after intermittent and continuous theta-burst stimulation (iTBS & cTBS) from a small group of subjects (18 for each). We fitted individual synaptic couplings and sensitivity parameters using variations of a biophysical model. A best performing model was selected and analyzed. RESULTS: cTBS gives a broad reduction in MEPs for amplitudes larger than resting motor threshold (RMT). Close to threshold, iTBS gives strong potentiation. The model captures individual IO curves. There is no change to the population average synaptic weights post TBS but the change in excitatory-to-excitatory synaptic coupling is strongly correlated with the experimental post-TBS response relative to baseline. CONCLUSIONS: The model describes population-averaged and individual IO curves, and their post-TBS change. Variation among individuals is accounted for with variation in synaptic couplings, and variation in sensitivity of neural response to stimulation. SIGNIFICANCE: The best fitting model could be applied more broadly and validation studies could elucidate underlying biophysical meaning of parameters.

year: 2023-02-15

title: Gracilaria transtasmanica: a potential novel target species for the bioremediation of nutrient enriched estuaries

authors: Ross, Bethany Grace

subjects: Macroalgae

abstract: Estuaries are increasingly becoming eutrophic due to anthropogenically induced nutrient enrichment. Presently, 24% of global anthropogenically derived nutrients released into coastal catchments are delivered directly into coastal waters such as estuaries. Thirty five percent of New Zealand’s estuaries are susceptible to eutrophication and some are already severely degraded. In-situ macroalgal bioremediation – the cultivation of live macroalgae directly in nutrient-enriched waters for the primary purpose of nutrient assimilation – could help prevent and reduce estuarine eutrophication.

The indigenous red macroalga Gracilaria transtasmanica has been identified as a potential target species for bioremediation in New Zealand estuaries. Samples of G. transtasmanica were collected from estuaries in the Bay of Plenty region of New Zealand, and were isolated, formally identified and scaled up into stock cultures. Controlled experiments were then used to assess the bioremediation potential of this species in winter and summer conditions under ambient and extreme nutrient and sediment levels. Biomass productivity, photosynthetic health, and N removal were assessed to quantify performance. Biomass productivity and total N removed were 45 and 50% higher respectively in summer compared to winter. Biomass productivity ranged from 0.4 – 4.3 g DW m² in summer and 0.6 – 1.8 g DW m² in winter, and total N removed ranged from 6.0 – 30.7 mg N in summer and 6.1 – 9.1 mg N in winter. In contrast, standardised N removal rates were higher in winter (37.8 mg g DW biomass growth⁻¹ ± 0.6 S.E.) compared to summer (22.3 mg g DW biomass growth⁻¹ ± 1.2 S.E.), suggesting that the biomass was storing N and therefore that N uptake was independent of productivity under sub-optimal growing conditions. Productivity was significantly affected by sediment treatment, however this effect differed seasonally, with higher productivity in the high

sediment treatments in summer, and lower productivity in the high sediment treatments in winter. These results demonstrate that G. transtasmanica can assimilate nutrients under a range of environmental conditions that are representative of both local background and high levels of suspended sediment and nutrient concentrations, and therefore is a viable target species for the bioremediation of nutrient enriched estuaries.In addition to nutrient uptake and productivity, target species for in-situ estuarine bioremediation need to maintain productivity under a range of challenging abiotic conditions. In chapter three of this thesis, a series of independent experiments assessed the tolerance of G. transtasmanica to ambient and extreme levels of salinity, exposure, and light limitation that are likely to be experienced in an estuary. Photosynthetic functioning and growth were used to quantify the tolerance range of G. transtasmanica in each experiment. Specific Growth Rate (SGR) was significantly affected by salinity, exposure, and light limitation. Gracilaria transtasmanica was able to grow in salinities ranging from 5 to 35 ppt, but growth rates decreased with decreasing salinity. Exposure periods of up to 9 hours were tolerated, but growth rates were decreased as exposure period increased. Gracilaria transtasmanica was able to maintain growth with a loss of up to 75% of ambient light and was also able to tolerate short periods of no light. Measurements of optimal quantum yields showed photosynthetic function was unaffected by salinity, exposure, or light limitation. 

These results demonstrate the high tolerance and adaptability of G. transtasmanica to a broad range of challenging abiotic estuarine conditions. In combination, these findings demonstrate that Gracilaria transtasmanica is well suited to estuarine conditions. However, selection of habitats with optimal conditions for growth will maximise productivity. Moreover, as nutrient uptake appears to be independent of growth under challenging conditions, low productivity may not result in reduced bioremediation capability. These characteristics make G. transtasmanica an ideal species for in-situ bioremediation in New Zealand estuaries. Additionally, G. transtasmanica biomass is suitable for use in a range of bioproducts. Therefore, there is potential for a bioremediation based circular economy approach with the use of harvested G. transtasmanica biomass following bioremediation. In-situ trials are required to verifying the findings reported here and enable optimisation of both bioremediation efficiency and biomass productivity.

text: Gracilaria transtasmanica: a potential novel target species for the bioremediation of nutrient enriched estuaries Estuaries are increasingly becoming eutrophic due to anthropogenically induced nutrient enrichment. Presently, 24% of global anthropogenically derived nutrients released into coastal catchments are delivered directly into coastal waters such as estuaries. Thirty five percent of New Zealand’s estuaries are susceptible to eutrophication and some are already severely degraded. In-situ macroalgal bioremediation – the cultivation of live macroalgae directly in nutrient-enriched waters for the primary purpose of nutrient assimilation – could help prevent and reduce estuarine eutrophication.

The indigenous red macroalga Gracilaria transtasmanica has been identified as a potential target species for bioremediation in New Zealand estuaries. Samples of G. transtasmanica were collected from estuaries in the Bay of Plenty region of New Zealand, and were isolated, formally identified and scaled up into stock cultures. Controlled experiments were then used to assess the bioremediation potential of this species in winter and summer conditions under ambient and extreme nutrient and sediment levels. Biomass productivity, photosynthetic health, and N removal were assessed to quantify performance. Biomass productivity and total N removed were 45 and 50% higher respectively in summer compared to winter. Biomass productivity ranged from 0.4 – 4.3 g DW m² in summer and 0.6 – 1.8 g DW m² in winter, and total N removed ranged from 6.0 – 30.7 mg N in summer and 6.1 – 9.1 mg N in winter. In contrast, standardised N removal rates were higher in winter (37.8 mg g DW biomass growth⁻¹ ± 0.6 S.E.) compared to summer (22.3 mg g DW biomass growth⁻¹ ± 1.2 S.E.), suggesting that the biomass was storing N and therefore that N uptake was independent of productivity under sub-optimal growing conditions. Productivity was significantly affected by sediment treatment, however this effect differed seasonally, with higher productivity in the high

sediment treatments in summer, and lower productivity in the high sediment treatments in winter. These results demonstrate that G. transtasmanica can assimilate nutrients under a range of environmental conditions that are representative of both local background and high levels of suspended sediment and nutrient concentrations, and therefore is a viable target species for the bioremediation of nutrient enriched estuaries.In addition to nutrient uptake and productivity, target species for in-situ estuarine bioremediation need to maintain productivity under a range of challenging abiotic conditions. In chapter three of this thesis, a series of independent experiments assessed the tolerance of G. transtasmanica to ambient and extreme levels of salinity, exposure, and light limitation that are likely to be experienced in an estuary. Photosynthetic functioning and growth were used to quantify the tolerance range of G. transtasmanica in each experiment. Specific Growth Rate (SGR) was significantly affected by salinity, exposure, and light limitation. Gracilaria transtasmanica was able to grow in salinities ranging from 5 to 35 ppt, but growth rates decreased with decreasing salinity. Exposure periods of up to 9 hours were tolerated, but growth rates were decreased as exposure period increased. Gracilaria transtasmanica was able to maintain growth with a loss of up to 75% of ambient light and was also able to tolerate short periods of no light. Measurements of optimal quantum yields showed photosynthetic function was unaffected by salinity, exposure, or light limitation. 

These results demonstrate the high tolerance and adaptability of G. transtasmanica to a broad range of challenging abiotic estuarine conditions. In combination, these findings demonstrate that Gracilaria transtasmanica is well suited to estuarine conditions. However, selection of habitats with optimal conditions for growth will maximise productivity. Moreover, as nutrient uptake appears to be independent of growth under challenging conditions, low productivity may not result in reduced bioremediation capability. These characteristics make G. transtasmanica an ideal species for in-situ bioremediation in New Zealand estuaries. Additionally, G. transtasmanica biomass is suitable for use in a range of bioproducts. Therefore, there is potential for a bioremediation based circular economy approach with the use of harvested G. transtasmanica biomass following bioremediation. In-situ trials are required to verifying the findings reported here and enable optimisation of both bioremediation efficiency and biomass productivity.

year: 2022

title: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change

authors: Newnham, Rewi M.

subjects: New Zealand

abstract: Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

text: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

year: 2018