Classification, Function, and Location of Cortical Neurons
There are two broad classes of cortical neurons: interneurons, which make local connections; and projection neurons, which extend axons to distant intracortical, subcortical, and subcerebral targets. Projection neurons are glutamatergic neurons characterized by a typical pyramidal morphology that transmit information between different regions of the neocortex and to other regions of the brain. During development, they are generated from progenitors of the neocortical germinal zone located in the dorsolateral wall of the telencephalon. By contrast, GABA (γ-aminobutyric acid)-containing interneurons and Cajal Retzius cells are generated primarily from progenitors in the ventral telencephalon and cortical hem, respectively, and migrate long distances to their final locations within the neocortex. In this manner, multiple progenitor zones contribute to the rich variety of neuronal types found in the neocortex.
Major Subtypes of Projection Neuron within the Neocortex
Fig.1 Major subtypes of projection neurons within the neocortex. (Molyneaux, 2007)
Callosal projection neurons
Projection neurons of small to medium pyramidal size that are primarily located in layers II/III, V, and VI, and extend an axon across the corpus callosum (CC). At least three major types of callosal neurons can be classified. These maintain single projections to the contralateral cortex; dual projections to the contralateral cortex and ipsilateral or contralateral striatum; and dual projections to the contralateral cortex and ipsilateral frontal cortex. These never project axons to targets outside the telencephalon.
Projection neurons primarily located in cortical layer VI, with a smaller population in layer V, that project subcortically to different nuclei of the thalamus (Th).
Subcerebral projection neurons
Subcerebral projection neurons are also referred to as type I layer V projection neurons. These include pyramidal neurons of the largest size, which are located in deep-layer V and extend projections to the brainstem and spinal cord. They can be even further subdivided into several distinct projection neuron subtypes.
Corticotectal neurons are located in the visual area of the cortex and maintain primary projections to the superior colliculus, with secondary collateral projections to the rostral pons (Po).
Corticopontine neurons maintain primary projections to the pons.
Corticospinal motor neurons are located in the sensorimotor area of the cortex and maintain primary projections to the spinal cord, with secondary collaterals to the striatum, red nucleus, caudal pons, and medulla.
Many other subtypes of subcerebral projection neurons exist that send axons to different areas of the brainstem or have different combinations of collaterals but are not depicted here for simplicity.
Cerebral Cortical Neurons and Diseases
Understandably, a holistic appraisal of all steps of cortical development (e.g., proliferation, modes of cell division, cell differentiation, cell migration) is key to unraveling the pathophysiological mechanisms underlying cortical malformations such as microcephaly (small brain), lissencephaly (smooth brain), and heterotopia (abnormally positioned neurons), often associated with intractable epilepsy and intellectual disability. Genetic and environmental factors (e.g., viruses such as Zika) can perturb these critical steps. Elucidating the intrinsic and extrinsic mechanisms controlling progenitor cell proliferation versus (vs) neuronal differentiation will help shed light on cortical expansion, gyrification, and ultimately neocortical evolution.
Services at Creative Biolabs
Creative Biolabs has been focusing on neural differentiation models over years, thus we have accumulated extensive experience from practice. In addition, we have also optimized our platform with advanced facilities and technologies thus we are capable of providing quality-reliable cerebral cortical neurons differentiation model service. If you are interested in custom cerebral cortical neurons differentiation models, or you have any other questions about our services, please don't hesitate to contact us for more information.
Molyneaux, B. J., et al. Neuronal subtype specification in the cerebral cortex. Nat Rev Neurosci. 2007, 8(6): 427-37.