C0228398_NEU

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?:definition	refers to the densely cellular core-structure surrounding the dorsal and lateral aspects of the cerebral aqueduct of the midbrain. Extending approximately from the posterior commissure rostrally to the locus ceruleus caudally, it is bounded dorsally by the commissure of the inferior colliculus and commissure of the superior colliculi; it is bounded laterally by the tectospinal tract and the mesencephalic tract of the trigeminal nerve ( Carrive-2012 ). Identified classically by Nissl stain, it is found in the human ( Carpenter-1983 ), macaque ( Martin-2000 ), rat ( Paxinos-2009b ) and the mouse ( Franklin-2008 ). The periaqueductal gray is distinguished from the cellular structures ventral to the aqueduct by its homogeneity. Indistinct internal boundaries have been identified on the basis of the shapes and sizes of cells, but they have resulted in several different segmentations within and across species. The simplest segmentation reported to show a similar pattern across species is based on multiple criteria including, in particular, segmentation on the basis of differential staining for NADPH-diaphorase (nitric oxide synthase) ( Carrive-2012 ). Areas stained with greater or lesser intensity for that enzyme are grouped alternately into four longitudinal columns. In cross-section each column is narrowest at the aqueductal surface and widens toward the outer surface. The surface abutting the aqueduct is lined by ependyma ( Paxinos-2012). The four columns are the dorsomedial periaqueductal gray, dorsolateral periaqueductal gray, lateral periaqueductal gray, and ventrolateral periaqueductal gray. Other substructures include the intercalated periaqueductal gray, supraoculomotor cap, pleioglia periaqueductal gray, and the nucleus of Darkshevich; some authors consider the supraoculomotor nucleus a component ( Paxinos-2001; Paxinos-2009a; Paxinos-2009b; Paxinos-2012 ). Authors differ as to whether these other structures are to be regarded as parts of the longitudinal columns or as independent structures ( Carrive-2012; Paxinos-2012 ). Functionally the periaqueductal gray belongs to the behavior control column of the motor system ( Swanson-2004 ). See also: motor periaqueductal gray. refers to the part of the functionally-defined central gray that largely surrounds the cerebral aqueduct in the midbrain tegmentum ( Swanson-2004 ). Based primarily on studies in the rat, it includes four nuclei in addition to the classical periaqueductal gray: the precommissural nucleus, medial accessory oculomotor nucleus, interstitial nucleus of Cajal, and nucleus of Darkshevich. In the motor definition, the periaqueductal gray is subdivided somewhat differently than in the classical version. It is composed of a narrow medial division of the periaqueductal gray, which surrounds the cerebral aqueduct throughout its course; the dorsomedial periaqueductal gray, which caps the aqueduct as it emerges from beneath the posterior commissure and extends caudally to the junction of the aqueduct with the fourth ventricle; the dorsolateral periaqueductal gray that lies lateral to it throughhalf of its course; the commissural nucleus, the rostromedial division of the periaqueductal gray, and the rostrolateral division of the periaqueductal gray, which occupy the area ventral to the dorsomedial and dorsolateral divisions and lateral to the medial division in the rostral quarter of the periaqueductal gray, and the ventrolateral division of the periaqueductal gray, which occupies that area in the caudal three quarters of the structure. Functionally the motor periaqueductal gray is a component of the behavior control column of the subcortical motor system ( Swanson-2004 ).
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?:definition

refers to the densely cellular core-structure surrounding the dorsal and lateral aspects of the cerebral aqueduct of the midbrain. Extending approximately from the posterior commissure rostrally to the locus ceruleus caudally, it is bounded dorsally by the commissure of the inferior colliculus and commissure of the superior colliculi; it is bounded laterally by the tectospinal tract and the mesencephalic tract of the trigeminal nerve ( Carrive-2012 ). Identified classically by Nissl stain, it is found in the human ( Carpenter-1983 ), macaque ( Martin-2000 ), rat ( Paxinos-2009b ) and the mouse ( Franklin-2008 ). The periaqueductal gray is distinguished from the cellular structures ventral to the aqueduct by its homogeneity. Indistinct internal boundaries have been identified on the basis of the shapes and sizes of cells, but they have resulted in several different segmentations within and across species. The simplest segmentation reported to show a similar pattern across species is based on multiple criteria including, in particular, segmentation on the basis of differential staining for NADPH-diaphorase (nitric oxide synthase) ( Carrive-2012 ). Areas stained with greater or lesser intensity for that enzyme are grouped alternately into four longitudinal columns. In cross-section each column is narrowest at the aqueductal surface and widens toward the outer surface. The surface abutting the aqueduct is lined by ependyma ( Paxinos-2012). The four columns are the dorsomedial periaqueductal gray, dorsolateral periaqueductal gray, lateral periaqueductal gray, and ventrolateral periaqueductal gray. Other substructures include the intercalated periaqueductal gray, supraoculomotor cap, pleioglia periaqueductal gray, and the nucleus of Darkshevich; some authors consider the supraoculomotor nucleus a component ( Paxinos-2001; Paxinos-2009a; Paxinos-2009b; Paxinos-2012 ). Authors differ as to whether these other structures are to be regarded as parts of the longitudinal columns or as independent structures ( Carrive-2012; Paxinos-2012 ). Functionally the periaqueductal gray belongs to the behavior control column of the motor system ( Swanson-2004 ). See also: motor periaqueductal gray.
refers to the part of the functionally-defined central gray that largely surrounds the cerebral aqueduct in the midbrain tegmentum ( Swanson-2004 ). Based primarily on studies in the rat, it includes four nuclei in addition to the classical periaqueductal gray: the precommissural nucleus, medial accessory oculomotor nucleus, interstitial nucleus of Cajal, and nucleus of Darkshevich. In the motor definition, the periaqueductal gray is subdivided somewhat differently than in the classical version. It is composed of a narrow medial division of the periaqueductal gray, which surrounds the cerebral aqueduct throughout its course; the dorsomedial periaqueductal gray, which caps the aqueduct as it emerges from beneath the posterior commissure and extends caudally to the junction of the aqueduct with the fourth ventricle; the dorsolateral periaqueductal gray that lies lateral to it throughhalf of its course; the commissural nucleus, the rostromedial division of the periaqueductal gray, and the rostrolateral division of the periaqueductal gray, which occupy the area ventral to the dorsomedial and dorsolateral divisions and lateral to the medial division in the rostral quarter of the periaqueductal gray, and the ventrolateral division of the periaqueductal gray, which occupies that area in the caudal three quarters of the structure. Functionally the motor periaqueductal gray is a component of the behavior control column of the subcortical motor system ( Swanson-2004 ).

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