The Kanoski Lab

EARLY LIFE DIETARY FACTORS AND NEUROCOGNITIVE OUTCOMES

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A typical “Western diet” contains higher than recommended levels of added sugar and saturated fatty acids. Our previous research revealed that habitual consumption of these dietary factors leads to deficits in hippocampal-dependent memory processes via altered neurotrophic signaling. Our ongoing research is expanding this work by showing that the juvenile and adolescent phase of development is a particularly vulnerable period through which sugar consumption disrupts hippocampal-dependent memory function in rats. These memory deficits are long-lasting and not reversible when sugar access is removed during adulthood. Additional results show that early life sugar consumption produces robust changes in the gut microbiome in rats, and our ongoing studies are examining the extent to which these sugar-associated microbiota alterations are functionally related to the long-lasting neurocognitive deficits.

 THE HIPPOCAMPUS AND ENERGY BALANCE CONTROL

Food intake is a complex behavior that can occur or cease to occur for a multitude of reasons. Decisions about where, when, what, and how much to eat are not merely reflexive responses to food-relevant stimuli or to changes in energy status. Rather, feeding behavior is modulated by various contextual factors and by previous experiences. Thus, it follows that in addition to classic hindbrain and hypothalamic feeding centers, brain regions involved in complex cognitive processes must also play a critical role in energy balance control. Our focus in this regard is on the hippocampus, a region historically linked with control of visuospatial and relational memory processes. Our working model is that the hippocampus constitutes an important neural substrate linking the external context, the internal/interoceptive context, and mnemonic and cognitive information to control both appetitive and ingestive behavior. Consistent with this framework, our recent findings reveal that interoceptive energy balance signals are communicated to the hippocampus (particularly the ventral subregion, illustrated in this photomicrograph) via peripherally-derived endocrine signals that function to reduce (leptin, glucagon-like peptide-1) or increase (ghrelin) food intake and learned food reward-driven responding. Collectively our recent results highlight endocrine and neuropeptidergic signaling in hippocampal neurons as a novel substrate of importance in the higher-order regulation of feeding behavior.

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Recent publications on this theme (* indicates corresponding author)

Hsu T.M., Noble E.E., Liu C.M., Cortella A.M., Konanur V.R., Suarez A.N., Reiner D.J., Hahn J.D., Hayes M.R., *Kanoski S.E. (2018). A hippocampus to prefrontal cortex neural pathway inhibits food motivation through glucagon-like peptide-1 signaling. Molecular Psychiatry, 23(7): 1555-1565.

Liu C.M., *Kanoski S.E. (2018). Homeostatic and non-homeostatic controls of feeding behavior: distinct vs. common neural systems. Physiology and Behavior, 193(Pt B): 223- 231.

Hsu T.M., Noble E.E., Reiner D.J., Liu C.M., Suarez A.N., Konanur V.R., Hayes M.R., *Kanoski S.E. (2018). Hippocampal ghrelin receptor signaling promotes socially- mediated learned food preference. Neuropharmacology, 131: 487-496.

*Kanoski S.E., Grill H.J. (2017). Hippocampus contributions to food intake control: mnemonic, neuroanatomical, and endocrine mechanisms. Biological Psychiatry, 81(9): 748-756. (paper recommended by the Faculty of 1000 as being of special significance in its field).

Hsu T.M., Suarez A.N., *Kanoski S.E. (2016). Ghrelin: A link between memory and ingestive behavior. Physiology and Behavior, 162: 10-17.

Hsu T.M., Hahn J.D., Konanur V.R., Noble E.E., Suarez A.N., Thai J., Nakamoto E.M., *Kanoski S.E. (2015). Hippocampus ghrelin signaling mediates appetite through lateral hypothalamic orexin pathways. eLife, 2015;4: e11190.

Hsu T.M., Hahn J.D., Konanur V.K., Lam A., *Kanoski S.E. (2015). Hippocampal GLP- 1 receptors influence food intake, meal size, and effort-based responding for food through volume transmission. Neuropsychopharmacology, 40(2): 327-37.


 THE GUT-BRAIN AXIS REGULATES LEARNING AND MEMORY

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During the preprandial (before a meal), prandial, and postprandial stages of feeding behavior, various endocrine, neuropeptidergic, and neural signals are released to regulate appetite, meal size (satiation), and the inter-meal interval (satiety). Emerging evidence reveals that in addition to regulating feeding behavior, these energy status-related biological systems also play a critical role in learning and memory function, particularly with regards to remembering when, how, and where food was obtained and consumed (e.g., foraging behavior, as depicted in the illustration, ‘Hansel y Gretal’). This makes sense from an evolutionary perspective as feeding is a profoundly important behavior, and remembering critical details of an eating episode will more efficiently guide future foraging behaviors. Our recent findings highlight the vagus nerve as a critical link between gut-originating meal-related signals and hippocampal-dependent memory function. In the absence of gut-to-brain vagal signaling, rats are impaired in visuospatial and episodic memory processes, and these effects appear to be based on reduced neurotrophic and neurogenic signaling in the hippocampus. Our ongoing research is mapping out the precise neuroanatomical pathways connecting the gut and the hippocampus, as well as the molecular signaling pathways through which meal-related signals promote memory function.


 NEUROPEPTIDERGIC CONTROL OF FEEDING BEHAVIOR

Food intake is potently regulated by neuropeptides that are synthesized in the hypothalamus. Our research is focusing on a population of neurons located in the lateral hypothalamus and zona incerta that produce the orexigenic neuropeptide, melanin-concentrating hormone (MCH; depicted in blue in the photomicrograph). Classical signaling mechanisms through which MCH and other neuropeptides influence behavior include neuronal synaptic communication and neuroendocrine signaling. Our recent findings provide evidence for an alternative neural communication mechanism that is relevant for food intake control involving cerebroventricular ‘volume transmission’ of MCH. More specifically, we discovered that MCH increases food intake, in part, via release into the cerbrospinal fluid. Our ongoing work is examining additional MCH signaling pathways that mediate hyperphagia and impulsive responding for palatable food.

Unlike MCH, oxytocin (another hypothalamic neuropeptide) potently reduces food intake. However, the behavioral mechanisms and specific brain regions mediating these effects our poorly understood. Our ongoing work is investigating the interaction between oxytocin’s effects on social behavior and food intake, as well as exploring novel sites of action through which oxytocin reduces food intake.

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Recent publications on this theme (* indicates corresponding author)

Noble E.E., Hahn J.D., Konanur V.R., Hsu T.M., Page S.J., Cortella A.M., Liu C.M., Song M.Y., Suarez A.N., Szujewski C.C., Rider D.R., Clarke J.E., Darvas M., Appleyard S.M.,*Kanoski S.E. (2018). Control of feeding behavior by cerebral ventricular volume transmission of melanin-concentrating hormone. Cell Metabolism, 28(1): 55-68. (article featured on July 2018 Cell Metabolism cover page and highlighted in Nature Reviews Endocrinology; article recommended by the Faculty of 1000 as being of special significance in its field).