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Central Modulation of Pain
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Terminations of descending pathways interact with several different neural elements in the dorsal horn. These include projection neurons that transmit information from the spinal cord to the brain, local interneurons within the spinal cord and primary afferent terminals. Inhibition may occur presynaptically by modulation of transmitter release or postsynaptically by either excitation of local inhibitory interneurons or direct inhibition of second-order projection neurons. The bulk of evidence suggests that descending inhibition is exerted via postsynaptic mechanisms.
Discussions (D)
Published in Terence R. Anthoney, Neuroanatomy and the Neurologic Exam, 2017
Ambiguity regarding the term “projection fibers” is fueled by the more general term “projection neuron” and use of the related verb “project” and noun “projection.” The term “projection neuron” is a relatively infrequent synonym for a Golgi type I neuron (e.g., K&S, p. 17; N&F, p. 50). AS pointed out by Nauta and Feirtag, since these neurons have long axons, “they ‘project’ to other regions, namely other nuclei or other fields of cortex” (1986, p. 50). Since projection neurons, widespread throughout the nervous system, “project” their axons, it seems only reasonable to consider these “projections” to be “projection fibers.” Hence, the use of the term by a few authors to describe fibers arising in the cerebellum, spinal cord, and brain stem, as well as in the cerebral cortex and thalamus.
The Central Nervous System Organization of Behavior
Published in Rolland S. Parker, Concussive Brain Trauma, 2016
Projection neurons or pathways connect different levels of the neuraxis (e.g., corticospinal [from cortex to spine]). They include reciprocal connections between the cerebral cortex and the thalamus, brainstem, and spinal cord. Fibers converge toward the brainstem. These fibers form the internal capsule, which includes ascending and descending tracts between the cortex and the spinal cord, as well as to the motor nuclei of the brainstem and to the thalamus (Figure 3.6).
Studying neural circuits of decision-making in Drosophila larva
Published in Journal of Neurogenetics, 2020
In order to understand the underlying mechanisms of decision-making it is not enough to look at the local circuits. There are two main views of how is the decision-making process organized in the nervous system. According to centralized models of decision-making decisions are made in specialized decision-making centers based on highly-processed sensory information that arrives there and then is relayed to the motor planning areas for execution (Miller, Galanter, & Pribram, 1960). The non-centralized models say the decision-making process is distributed in the nervous system from the sensory to the motor side and it will be by competitive interactions between the different sensorimotor pathways that the decision will emerge (Cisek, 2007). It is therefore essential to be able to study the processes underlying decisions at the level of the entire nervous system. A compact brain such as the one of Drosophila larva can help us understand the organization of a decision-making process. In addition to mapping local circuits, in the larval brain, it is possible to trace the long-range projection neurons that connect the sites of competitions with distant regions of the nervous system. Determining the brain-wide connectivity of a ‘decision’ network using both structural and functional studies would help us determine whether decision-making is distributed or centralized and to which extent.
Cortical projection neurons as a therapeutic target in multiple sclerosis
Published in Expert Opinion on Therapeutic Targets, 2020
Tatjana Beutel, Julia Dzimiera, Hannah Kapell, Maren Engelhardt, Achim Gass, Lucas Schirmer
In contrast to cortical interneurons, which with exceptions [15,16] usually form local short-range connections with neighboring cells, excitatory projection neurons generally establish long-range corticocortical, commissural, and corticofugal fiber tracts within the cortex and other caudal CNS regions (Figure 1) [17]. Traditionally, cortical neurons have been studied using morphological and/or functional parameters and with a focus on specific cortical regions such as the prefrontal or the somatosensory cortex [18]. With recent technical developments, methods such as single-nucleus RNA-sequencing enabled the characterization of specific neuronal subtypes by assessing their signature marker genes [19]. Neocortical neurons like glutamatergic excitatory pyramidal neurons and GABAergic inhibitory interneurons can thus be identified through their cell type-specific gene expression with signature transcripts such as SLC17A7 for excitatory neurons and GAD2 for inhibitory neurons [12]. CUX2 (a marker of supragranular layers), RORB (a layer IV marker), TLE4 (a marker of infragranular layers), and PVALB, SST, VIP, SV2C (interneuron subtype markers) are further examples differentiating subsets of neurons by their gene expression profile. Besides CUX2, supragranular layer markers such as CUX1 and LHX2 are additional layer II/III/IV marker genes for excitatory projection neurons [12,17,20]. Axons arising from layer II/III projection neurons mainly form commissural connections to both local and distant cortical regions and project particularly through the corpus callosum [17,21]. Also, it has been demonstrated that CUX2-expressing neurons are necessary for subventricular zone formation as well as for the regulation of dendrite branching, spine development, and synapse formation specifically in callosal projection neurons [20,22].
Antennae sense heat stress to inhibit mating and promote escaping in Drosophila females
Published in Journal of Neurogenetics, 2018
Yusuke Miwa, Masayuki Koganezawa, Daisuke Yamamoto
Gr28b.d-expressing neurons innervate the VP2 glomerulus in the antennal lobe, where the thermal information conveyed by these sensory neurons is relayed to warm projection neurons. The warm projection neurons are classified into several types each innervating distinct brain regions (Liu, et al., 2015; Tanaka, Endo, & Ito, 2012). One type of these projection neurons has axon terminals in the posterior lateral protocerebrum (p.l.p. Liu, et al., 2015; Tanaka et al., 2012). The l.p. region of the brain represents a higher integration center that is particularly related to sexually dimorphic behaviors, including mating behavior (see Yamamoto & Koganezawa, 2013 for review). For instance, dsx-positive pC1 cluster neurons, which have been implicated in the regulation of virgin female mating behavior, densely innervate the l.p. (Zhou et al., 2014). Although pC1 arbors generally occupy regions more medial to the regions where warm projection neurons terminate, the possibility remains that the warm projection neurons directly synapse onto pC1 arbors to confer temperature sensitivity onto the latter for the control of female copulation success. The male homolog of the pC1 cluster contains ∼20 fruitless-expressing male-specific neurons known as the P1 neurons that function as the decision-making center for male courtship (Kimura, Hachiya, Koganezawa, Tazawa, & Yamamoto, 2008; Kohatsu, Koganezawa, & Yamamoto, 2011). An intriguing possibility is that male-specific P1 neurons may also receive thermal input via a homologous sensory pathway initiated by the Gr28b.d-expressing sensory neurons, affecting the male decision to court or escape at high ambient temperatures. Given that no sex difference has been reported in the structure and function of hot cells per se or in Gr28b.d gene expression, the sexual dimorphism in the tolerance to high temperature for mating might arise from a sexually dimorphic physiology of pC1 neurons. This possibility awaits rigorous experimental tests.