title: Oxytocin as an appetite suppressant that reduces feeding reward

authors: Herisson, Florence

subjects: Oxytocin

abstract: In the environment in which palatable and highly caloric foods are readily available, eating behavior is oftentimes not dictated by the necessity to replenish lacking energy, but rather by the pleasure of consumption. Centrally acting oxytocin (OT) is known to promote termination of feeding to protect internal milieu by preventing excessive stomach distension, hyperosmolality and ingestion of toxins. Initial evidence suggests that another possible role for OT in mechanisms governing food intake is to reduce consumption of select palatable tastants. This thesis explores the question whether OT is as an appetite suppressant that reduces feeding reward. 
The first set of experiments addresses whether OT affects intake of (a) all carbohydrates, (b) only sweet carbohydrates or (c) sweet non-carbohydrate saccharin in mice. In those studies, generalized injection of a blood brain barrier penetrant OT receptor antagonist, L-368,899, significantly increased the intake of sweet (sucrose, glucose, fructose, polycose) and non-sweet (cornstarch) carbohydrates and promoted a trend approaching significance in saccharin consumption. Consumption of carbohydrate-enriched foods led to an increase in OT mRNA levels in the hypothalamus.
The second set of studies identifies the nucleus accumbens core (AcbC), a key component of the reward system, as a site that mediates anorexigenic effects of OT. Rats injected with OT directly in the AcbC showed a decreased intake of sucrose and saccharin solutions as well as of standard chow. This treatment did not cause taste aversion, hence the outcome was not due to sickness/malaise. The effects of AcbC OT on feeding could be observed only in animals offered a meal in a non-social environment. Once a social setting (devoid of direct antagonistic interactions between individuals) of a meal was introduced, AcbC OT failed to reduce feeding. AcbC levels of OT receptor transcript were affected by exposure to palatable food as well as by food deprivation.
The third and final set of studies shows that aberrant integrity of neuronal circuitry within the neuroendocrine and reward systems due to genetic deletion of connexin 36 (Cx36) gap junctions leads to dysregulation of the OT system’s functioning in the Cx36 KO mouse. This dysregulation is associated with hypersensitivity to aversive properties of foods, reduced interest in feeding for reward (palatable carbohydrates and saccharin) and abnormal ingestion of energy. 
Overall, the findings suggest that OT diminishes feeding for reward, particularly the intake of palatable carbohydrates and saccharin, by acting – at least in part – via the reward system. OT appears to be part of central mechanisms that cross-link homeostasis-driven and palatability-related (i.e., flavor- and macronutrient-specific) termination of consumption.

text: Oxytocin as an appetite suppressant that reduces feeding reward In the environment in which palatable and highly caloric foods are readily available, eating behavior is oftentimes not dictated by the necessity to replenish lacking energy, but rather by the pleasure of consumption. Centrally acting oxytocin (OT) is known to promote termination of feeding to protect internal milieu by preventing excessive stomach distension, hyperosmolality and ingestion of toxins. Initial evidence suggests that another possible role for OT in mechanisms governing food intake is to reduce consumption of select palatable tastants. This thesis explores the question whether OT is as an appetite suppressant that reduces feeding reward. 
The first set of experiments addresses whether OT affects intake of (a) all carbohydrates, (b) only sweet carbohydrates or (c) sweet non-carbohydrate saccharin in mice. In those studies, generalized injection of a blood brain barrier penetrant OT receptor antagonist, L-368,899, significantly increased the intake of sweet (sucrose, glucose, fructose, polycose) and non-sweet (cornstarch) carbohydrates and promoted a trend approaching significance in saccharin consumption. Consumption of carbohydrate-enriched foods led to an increase in OT mRNA levels in the hypothalamus.
The second set of studies identifies the nucleus accumbens core (AcbC), a key component of the reward system, as a site that mediates anorexigenic effects of OT. Rats injected with OT directly in the AcbC showed a decreased intake of sucrose and saccharin solutions as well as of standard chow. This treatment did not cause taste aversion, hence the outcome was not due to sickness/malaise. The effects of AcbC OT on feeding could be observed only in animals offered a meal in a non-social environment. Once a social setting (devoid of direct antagonistic interactions between individuals) of a meal was introduced, AcbC OT failed to reduce feeding. AcbC levels of OT receptor transcript were affected by exposure to palatable food as well as by food deprivation.
The third and final set of studies shows that aberrant integrity of neuronal circuitry within the neuroendocrine and reward systems due to genetic deletion of connexin 36 (Cx36) gap junctions leads to dysregulation of the OT system’s functioning in the Cx36 KO mouse. This dysregulation is associated with hypersensitivity to aversive properties of foods, reduced interest in feeding for reward (palatable carbohydrates and saccharin) and abnormal ingestion of energy. 
Overall, the findings suggest that OT diminishes feeding for reward, particularly the intake of palatable carbohydrates and saccharin, by acting – at least in part – via the reward system. OT appears to be part of central mechanisms that cross-link homeostasis-driven and palatability-related (i.e., flavor- and macronutrient-specific) termination of consumption.

year: 2016

title: A neural-based code for computing image velocity from small sets of middle temporal (MT/V5) neuron inputs

authors: Perrone, John A.

subjects: 2D motion

abstract: It is still not known how the primate visual system is able to measure the velocity of moving stimuli such as edges and dots. Neurons have been found in the Medial Superior Temporal (MST) area of the primate brain that respond at a rate proportional to the speed of the stimulus but it is not clear how this property is derived from the speed-tuned Middle Temporal (MT) neurons that precede area MST along the visual motion pathway. I show that a population code based on the outputs from a number of MT neurons is susceptible to errors if the MT neurons are tuned to a broad range of spatial frequencies and have receptive fields that span a wide range of sizes. I present a solution that uses the activity of just three MT units within a velocity channel to estimate the velocity using a weighted vector average (centroid) technique. I use a range of velocity channels (1, 2, 4, and 88/s) with inhibition between them so that only a single channel passes the velocity estimate onto the next stage of processing (MST). I also include a contrast-dependent redundancy-removal stage which provides tighter spatial resolution for the velocity estimates under conditions of high contrast but which trades off spatial compactness for greater sensitivity at low contrast. The new model produces an output signal proportional to the stimulus input velocity (consistent with MST neurons) and its input stages have properties closely tied to those of neurons in areas V1 and MT.

text: A neural-based code for computing image velocity from small sets of middle temporal (MT/V5) neuron inputs It is still not known how the primate visual system is able to measure the velocity of moving stimuli such as edges and dots. Neurons have been found in the Medial Superior Temporal (MST) area of the primate brain that respond at a rate proportional to the speed of the stimulus but it is not clear how this property is derived from the speed-tuned Middle Temporal (MT) neurons that precede area MST along the visual motion pathway. I show that a population code based on the outputs from a number of MT neurons is susceptible to errors if the MT neurons are tuned to a broad range of spatial frequencies and have receptive fields that span a wide range of sizes. I present a solution that uses the activity of just three MT units within a velocity channel to estimate the velocity using a weighted vector average (centroid) technique. I use a range of velocity channels (1, 2, 4, and 88/s) with inhibition between them so that only a single channel passes the velocity estimate onto the next stage of processing (MST). I also include a contrast-dependent redundancy-removal stage which provides tighter spatial resolution for the velocity estimates under conditions of high contrast but which trades off spatial compactness for greater sensitivity at low contrast. The new model produces an output signal proportional to the stimulus input velocity (consistent with MST neurons) and its input stages have properties closely tied to those of neurons in areas V1 and MT.

year: 2012

title: Racism and bullying as correlates for considering ending psychology training in Aotearoa New Zealand

authors: Tan, Kyle K. H.

abstract: Despite global calls to enhance culturally safe care for Indigenous and minoritised groups, little attention has been given to exploring students’ experiences in psychology training programmes to meet these needs. A series of chi-square tests was performed to examine group differences for participants in the Kia Whakapapa Pounaumu survey (n = 107) in their consideration of ending their training and their decision to seek professional help. Over half (55%) of students reported having considered ending their psychology training. Our findings show that students who have experienced or witnessed forms of injustice such as institutional racism, microaggressions, and bullying, encounter additional barriers in completing their training. If psychology bodies wish to redress the harm caused to Indigenous and minoritised groups in the discipline of psychology, they must ensure the training programmes themselves do not perpetuate harm.

text: Racism and bullying as correlates for considering ending psychology training in Aotearoa New Zealand Despite global calls to enhance culturally safe care for Indigenous and minoritised groups, little attention has been given to exploring students’ experiences in psychology training programmes to meet these needs. A series of chi-square tests was performed to examine group differences for participants in the Kia Whakapapa Pounaumu survey (n = 107) in their consideration of ending their training and their decision to seek professional help. Over half (55%) of students reported having considered ending their psychology training. Our findings show that students who have experienced or witnessed forms of injustice such as institutional racism, microaggressions, and bullying, encounter additional barriers in completing their training. If psychology bodies wish to redress the harm caused to Indigenous and minoritised groups in the discipline of psychology, they must ensure the training programmes themselves do not perpetuate harm.

year: 2025