The distribution of phosphodiesterase 2A in the rat brain

Abstract

The phosphodiesterases (PDEs) are a superfamily of enzymes that regulate spatio-temporal signaling by the intracellular second messengers cAMP and cGMP. PDE2A is expressed at high levels in the mammalian brain. To advance our understanding of the role of this enzyme in regulation of neuronal signaling, we here describe the distribution of PDE2A in the rat brain. PDE2A mRNA was prominently expressed in glutamatergic pyramidal cells in cortex, and in pyramidal and dentate granule cells in the hippocampus. Protein concentrated in the axons and nerve terminals of these neurons; staining was markedly weaker in the cell bodies and proximal dendrites. In addition, in both hippocampus and cortex, small populations of non-pyramidal cells, presumed to be interneurons, were strongly immunoreactive. PDE2A mRNA was expressed in medium spiny neurons in neostriatum. Little immunoreactivity was observed in cell bodies, whereas dense immunoreactivity was found in the axon tracts of these neurons and their terminal regions in globus pallidus and substantia nigra pars reticulata. Immunostaining was dense in the medial habenula, but weak in other diencephalic regions. In midbrain and hindbrain, immunostaining was restricted to discrete regions of the neuropil or clusters of cell bodies. These results suggest that PDE2A may modulate cortical, hippocampal and striatal networks at several levels. Preferential distribution of PDE2A into axons and terminals of the principal neurons suggests roles in regulation of axonal excitability or transmitter release. The enzyme is also in forebrain interneurons, and in mid- and hindbrain neurons that may modulate forebrain networks and circuits.

Fig. 1

Distribution of PDE2A mRNA in coronal sections of rat brain, determined by in situ hybridization. Hybridization signal is black. Numbers at bottom of panels are distance from bregma, according to the atlas of Paxinos and Watson (1997). Message is high in cortical regions, striatum, and the habenula. Abbreviations used in the figures: A, cerebral aqueduct; ac, anterior commissure; Acb, n. accumbens; ACo, anterior cortical amygdaloid n; Amg, amygdaloid complex; AOn, anterior olfactory n.; BLA, basolateral amygdaloid n; CB, cerebellum; CC, central canal; cc, corpus callosum; Cg, cingulate cortex; Ce, central amygdaloid n; CP, caudate-putamen; CPu, caudate n. and putamen; dc, dorsal columns; dcs, dorsal corticospinal tract; DG, dentate gyrus; DR, dorsal raphe; FCx, frontal cortex; GC, granule cell layer; GP, globus pallidus; GPe; external part of globus pallidus; hb, habenula; Ht, hypothalamus; IC, inferior colliculus; IGr, internal granule cell layer of olfactory bulb; In, interpeduncular nucleus; LL, lateral lemniscus; LS, lateral septal n.; M, molecular layer; MR, median raphe; MVe, medial vestibular nucleus; OCx, occipital cortex; Opt, optic tract; PC, Purkinje cell layer; PCx, parietal cortex; Pir, piriform cortex; Pl, plexiform layer of olfactory bulb; Py, pyramidal cell layer; RF, rhinal fissure; SG, substantia gelatinosa; SL, stratum lucidum; SN, substantia nigra; SNc, substantia nigra, pars compacta; SNr, substantia nigra, pars reticulata; SO, stratum oriens; SR, stratum radiatum; Th, thalamus; 3v, 3rd ventricle; VH, ventral horn. Scale bar in G = 2.5 mm.

Fig. 2

Distribution of PDE2A immunoreactivity in coronal sections of rat brain, as determined by immunohistochemistry. Immunoreaction is brown; blue is counterstain. Numbers at bottom of panels are distance from bregma. Primary antibody was replaced by control IgG in F. Immunostaining is especially prominent in olfactory tubercule, globus pallidus, habenula, and substantia nigra (see text). Scale bar (panel H): 1 mm for panel A, 2 mm for all other panels. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Distribution of PDE2A immunostaining in somatosensory cortex (approximately 1 mm caudal to bregma). (A) Staining is strongest in superficial layers (cortical layers are denoted by Roman numerals). Black arrow points to a strongly stained non-pyramidal cell body in layer VI. (B) Higher magnification micrograph from II/III. Immunostaining is generally weaker in pyramidal cell bodies than in the surrounding neuropil. White arrow points to the pyramidal cell where granular staining appears to line cell body and the apical dendrite. (C) Black arrow points to a strongly immunopositive non-pyramidal cell located in upper layer IV of somatosensory cortex. Scale bars: Panel A = 500 μm; panel C (for B, C) = 10 μm.

Fig. 4

PDE2A immunoreactivity in hippocampus. (A) Low magnification view; staining is conspicuous in stratum oriens of CA1, the terminal field of mossy fibers in CA3, and the hilus of dentate gyrus. White and black arrows indicate the areas depicted in B and C (which were from different material). (B) Higher magnification view of CA1. Very weak staining in cell bodies and primary dendrites of hippocampal pyramidal neurons contrasts with stronger diffuse staining in the neuropil of stratum radiatum. (C) Detail from dentate gyrus. Note strong immunostaining in hilus, sublaminar pattern of staining in the molecular layer, and the low density of immunoreactivity in the cell bodies of granule cells. Scale bar in C = 500 μm (for panel A); 250 μm (for B, C). Panel A is revised from a figure previously published (Stephenson et al., 2009), and is used with permission.

Fig. 5

Double immunofluorescent labeling for PDE2A (green) and MAP2 (red) in CA3 field of hippocampus (section is 3.5 mm caudal to bregma). (A) PDE2A channel; staining concentrates in stratum lucidum, likely associated with terminals of mossy fibers. (B) MAP2 channel stains dendritic shafts. (C) Merged image; note minimal overlap between PDE2A and MAP2 fluorescence. Scale bar = 50 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

PDE2A immunoreactivity in the region of the amygdala (section is ∼2.5 mm caudal to bregma). A band of immunopositive neurons (indicated by arrows) runs between piriform cortex and amygdala, extending medially between anterior cortical and central/basolateral amygdaloid nuclei.

Fig. 7

PDE2A immunoreactivity in basal ganglia. (A) Staining in caudate-putamen is less dense than in globus pallidus (section 2 mm caudal to bregma). (B) Dense staining in substantia nigra (pars reticulata) contrasts with weak staining in substantia nigra pars compacta (section is 5.8 mm caudal to bregma). Very dense staining is also present in the interpeduncular nucleus. Scale bar = 1 mm.

Fig. 8

PDE2A immunoreactivity in midbrain. (A) Immunostaining is visible in superficial layers of inferior colliculus, the central gray, raphe nuclei, and pyramidal tract, though markedly weaker than in occipital cortex (visible at top); section is ∼8.5 mm caudal to bregma. (B) Higher magnification of boxed zone in A illustrates immunostaining in dorsal and median raphe. (C) A more caudal section (section ∼9.2 mm caudal to bregma); note labeling in the region of lateral dorsal tegmentum (black arrow). (D) Higher magnification of boxed zone in C shows immunopositive cell bodies. Black arrows point to immunostained endothelial cells lining an arteriole that runs through the section. Scale bar = 1 mm (A, C); 200 μm (B); 100 μm (D).

Fig. 9

PDE2A immunoreactivity in hindbrain and cerebellum. (A) Low magnification view; staining is weak in cerebellar cortex, stronger in vestibular nuclei and pyramidal tract (section is 10.3 mm caudal to bregma). (B) Higher magnification view shows the molecular/granule cell border of cerebellar cortex, illustrating weakly stained Purkinje cells (black arrows) and immunoreactive fibers and puncta in the molecular layer. Scattered strongly immunopositive neurons are visible in molecular and granule cell layers (readily identified by the densely packed blue cells). Scale bar = 1 mm (A); 100 μm (B). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 10

PDE2A immunoreactivity in rostral spinal cord (section is from C2). Immunostaining is strongest in the neuropil of the superficial dorsal horn; some immunopositive neurons are scattered about the spinal gray, extending into ventral horn. Note light staining of fibers in corticospinal tract. Scale bar = 500 μm.