The micturition reflex relies on complex neural signaling to enable the coordination of the lower urinary tract. In neonates, this reflex is organized in the lumbosacral spinal cord and responds automatically to distension of the bladder or, in animals, to stimulation of the perigenital region by the mother. During development, competitive reorganization by supraspinal inputs places the reflex under conscious control and gives rise to the mature micturition reflex. Traumatic injury to the spinal cord that interrupts supraspinal inputs to the lumbosacral spinal cord can result in reversion to an automatic, spinal micturition reflex accompanied by lower urinary tract dysfunction such as neurogenic detrusor overactivity and detrusor–sphincter dyssynergia. This is accompanied by a number of changes in the anatomy and function of the lower urinary tract; various signaling pathways, including neurotrophins and neuropeptides; and reorganization of spinal circuitry. Evidence suggests that, following spinal cord injury, the bladder hypertrophies and urothelial and external urethral sphincter function are altered, giving rise to phasic spontaneous behavior and reduced bladder outlet bursting during voiding, respectively. Sensitization of Aδ-fiber afferents and “awakening” of C-fibers in the lumbosacral micturition pathway contribute to the emergence of a spinal micturition reflex and subsequent lower urinary tract dysfunction, with substantial evidence indicating a primary role for altered neurotrophin and neuropeptide signaling.
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Article
Plasticity in the Micturition Circuit During Development and Following Spinal Cord Injury
Harrison W. Hsiang and Margaret A. Vizzard
Article
The Medieval Cell Doctrine
Douglas J. Lanska
The medieval cell doctrine was a series of speculative psychological models derived from ancient Greco-Roman ideas in which cognitive faculties were assigned to “cells,” typically but not exclusively corresponding to the cerebral ventricles. During Late Antiquity and continuing during the Early Middle Ages, Christian philosophers reinterpreted Aristotle’s De Anima, along with later modifications by Herophilos and Galen, in a manner consistent with Christian doctrine. The resulting medieval cell doctrine was formulated by the fathers of the early Christian Church in the 4th and 5th centuries. Illustrations of the medieval cell doctrine were included in manuscripts since at least the 11th century. Printed images of the doctrine appeared in medical, philosophical, and religious works beginning with “graphic incunabula” at the end of the 15th century. Some of these early psychological models assigned various cognitive faculties to different nonoverlapping “cells” within the brain, while others specifically promoted or implied a linear sequence of events. By the 16th century, printed images of the doctrine were usually linear three-cell versions, with few exceptions having four or five cells. These psychological models were based on philosophical speculations rather than clinicopathologic evidence or experimentation. Despite increasingly realistic representations of the cerebral ventricles from the end of the 15th century until the middle of the 16th century, and direct challenges by Massa and Vesalius in the early 16th century and Willis in the 17th century, the doctrine saw its most elaborate formulations in the late 16th and early 17th centuries with illustrations by the Paracelsian physicians Bacci and Fludd. In addition, Descartes reinvigorated the ventricular localization of cerebral faculties in the 17th century beginning with his La Dioptrique (1637) and later with the Latin and French editions of his posthumously published Treatise of Man (1662-1667). Overthrow of the doctrine had to await the development of alternative models of brain function in the 17th and 18th centuries.
Article
Investigating Learning and Memory in Humans
Evangelia G. Chrysikou, Elizabeth Espinal, and Alexandra E. Kelly
Memory refers to the set of cognitive systems and the neural structures that support them that allow humans to learn from experience, leverage this knowledge to understand and guide behavior in the present, and use past memories to think about and plan for the future. Neuroscience research on learning and memory has leveraged advances in behavioral methods, structural and functional brain imaging, noninvasive brain stimulation, and lesion studies to evaluate synergies and dissociations among small- and large-scale neural networks in support of memory performance. Overall, this work has converged to a conceptualization of new memories as representations of distributed patterns of neural activity across cortical and subcortical brain systems that provide neural grounding of sensorimotor and perceptual experiences, actions, thoughts, and emotions, and which can be reinstated as a result of internal or external cues.
Most of this literature has supported dissociations among working and long-term memory, as well as between procedural, episodic, and semantic memories. On the other hand, progress in human neuroscience methodologies has revealed the interdependence of these memory systems in the context of complex cognitive tasks and suggests a dynamic and highly interactive neural architecture underlying human learning and memory. Future neuroscience research is anticipated to focus on understanding the neural mechanisms supporting this interactivity at the cellular and systems levels, as well as investigating the time course of their engagement.
Article
Plasticity of Information Processing in the Auditory System
Andrew J. King
Information processing in the auditory system shows considerable adaptive plasticity across different timescales. This ranges from very rapid changes in neuronal response properties—on the order of hundreds of milliseconds when the statistics of sounds vary or seconds to minutes when their behavioral relevance is altered—to more gradual changes that are shaped by experience and learning. Many aspects of auditory processing and perception are sculpted by sensory experience during sensitive or critical periods of development. This developmental plasticity underpins the acquisition of language and musical skills, matches neural representations in the brain to the statistics of the acoustic environment, and enables the neural circuits underlying the ability to localize sound to be calibrated by the acoustic consequences of growth-related changes in the anatomy of the body. Although the length of these critical periods depends on the aspect of auditory processing under consideration, varies across species and brain level, and may be extended by experience and other factors, it is generally accepted that the potential for plasticity declines with age. Nevertheless, a substantial degree of plasticity is exhibited in adulthood. This is important for the acquisition of new perceptual skills; facilitates improvements in the detection or discrimination of fine differences in sound properties; and enables the brain to compensate for changes in inputs, including those resulting from hearing loss. In contrast to the plasticity that shapes the developing brain, perceptual learning normally requires the sound attribute in question to be behaviorally relevant and is driven by practice or training on specific tasks. Progress has recently been made in identifying the brain circuits involved and the role of neuromodulators in controlling plasticity, and an understanding of plasticity in the central auditory system is playing an increasingly important role in the treatment of hearing disorders.
Article
Nicotinic Acetylcholine Receptors and Affective Responses
Kalynn Schulz, Marcia Chavez, and Arthur Castaneda
Nicotinic acetylcholine receptors (nAChRs) are present throughout the central nervous system and involved in a variety of physiological and behavioral functions. Nicotinic acetylcholine receptors are receptive to the presence of nicotine and acetylcholine and can be modulated through a variety of agonist and antagonist actions. These receptors are complex in their structure and function, and they are composed of multiple α and β subunits. Many affective disorders have etiological links with developmental exposure to the nAChR agonist nicotine. Given that abnormalities in nAChRs are associated with affective disorders such as depression and anxiety, pharmacological interventions targeting nAChRs may have significant therapeutic benefits.
Article
Regulating Systems in Neuroimmunology
William H. Walker II and A. Courtney DeVries
Neuroimmunology is the study of the interaction between the immune system and nervous system during development, homeostasis, and disease states. Descriptions of neuroinflammatory diseases dates back centuries. However, in depth scientific investigation in the field began in the late 19th century and continues into the 21st century. Contrary to prior dogma in the field of neuroimmunology, there is immense reciprocal crosstalk between the brain and the immune system throughout development, homeostasis, and disease states. Proper neuroimmune functioning is necessary for optimal health, as the neuroimmune system regulates vital processes including neuronal signaling, synapse pruning, and clearance of debris and pathogens within the central nervous system. Perturbations in optimal neuroimmune functioning can have detrimental consequences for the host and underlie a myriad of physical, cognitive, and behavioral abnormalities. As such, the field of neuroimmunology is still relatively young and dynamic and represents an area of active research and discovery.
Article
Regulators and Integration of Peripheral Signals
Michelle T. Foster
In mammals, reproductive function is closely regulated by energy availability. It is influenced by both extremes of nutrition, too few calories (undernutrition) and an excessive amount of calories (obesity). Atypical decreases or increases in weight can have adverse effects on the reproductive axis. This includes suppression of reproductive function, decreases in ovarian cyclicity, reduction in fertility, anovulation, and dysregulation of spermatogenesis. The balance between energy regulation and reproduction is supervised by a complex system comprised of the brain and peripheral tissues. The brain senses and integrates various systemic and central signals that are indicative of changes in body physiology and energy status. This occurs via numerous factors, including metabolic hormones and nutrients. Adipokines, endocrine factors primarily secreted by white adipose tissue, and adipose tissue related cytokines (adipocytokines) contribute to the regulation of maturity, fertility, and reproduction. Indeed, some adipokines play a fundamental role in reproductive disorders. The brain, predominantly the hypothalamus, is responsible for linking adipose-derived signals to pathways controlling reproductive processes. Gonadotropin-releasing hormone (GnRH) cells in the hypothalamus are fundamental in relaying adipose-derived signals to the pituitary–gonadal axis, which consequently controls reproductive processes. Leptin, adiponectin, apelin, chermin, resistin, and visfatin are adipokines that regulate reproductive events via the brain.
Article
Enhancing the Regeneration of Neurons in the Central Nervous System
Romain Cartoni, Frank Bradke, and Zhigang He
Injured axons fail to regenerate in the adult mammalian central nervous system, representing a major barrier for effective neural repair. Both extrinsic inhibitory environments and neuron-intrinsic mechanisms contribute to such regeneration failure. In the past decade, there has been an explosion in our understanding of neuronal injury responses and regeneration regulations. As a result, several strategies have been developed to promote axon regeneration with the potential of restoring functions after injury. This article will highlight these new developments, with an emphasis on cellular and molecular mechanisms from a neuron-centric perspective, and discuss the challenges to be addressed toward developing effective functional restoration strategies.
Article
Annelid Vision
Cynthia M. Harley and Mark K. Asplen
Annelid worms are simultaneously an interesting and difficult model system for understanding the evolution of animal vision. On the one hand, a wide variety of photoreceptor cells and eye morphologies are exhibited within a single phylum; on the other, annelid phylogenetics has been substantially re-envisioned within the last decade, suggesting the possibility of considerable convergent evolution. This article reviews the comparative anatomy of annelid visual systems within the context of the specific behaviors exhibited by these animals. Each of the major classes of annelid visual systems is examined, including both simple photoreceptor cells (including leech body eyes) and photoreceptive cells with pigment (trochophore larval eyes, ocellar tubes, complex eyes); meanwhile, behaviors examined include differential mobility and feeding strategies, similarities (or differences) in larval versus adult visual behaviors within a species, visual signaling, and depth sensing. Based on our review, several major trends in the comparative morphology and ethology of annelid vision are highlighted: (1) eye complexity tends to increase with mobility and higher-order predatory behavior; (2) although they have simple sensors these can relay complex information through large numbers or multimodality; (3) polychaete larval and adult eye morphology can differ strongly in many mobile species, but not in many sedentary species; and (4) annelids exhibiting visual signaling possess even more complex visual systems than expected, suggesting the possibility that complex eyes can be simultaneously well adapted to multiple visual tasks.
Article
Cephalochordate Nervous System
Simona Candiani and Mario Pestarino
The central and peripheral nervous systems of amphioxus adults and larvae are characterized by morphofunctional features relevant to understanding the origins and evolutionary history of the vertebrate CNS. Classical neuroanatomical studies are mainly on adult amphioxus, but there has been a recent focus, both by TEM and molecular methods, on the larval CNS. The latter is small and remarkably simple, and new data on the localization of glutamatergic, GABAergic/glycinergic, cholinergic, dopaminergic, and serotonergic neurons within the larval CNS are now available. In consequence, it has been possible begin the process of identifying specific neuronal circuits, including those involved in controlling larval locomotion. This is especially useful for the insights it provides into the organization of comparable circuits in the midbrain and hindbrain of vertebrates. A much better understanding of basic chordate CNS organization will eventually be possible when further experimental data will emerge.
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