Distribution of muscarinic acetylcholine receptor mRNA in the brain of the weakly electric fish Apteronotus leptorhynchus

Various neuromodulators have been shown to be involved in shaping the sensory information available to the brain. Acetylcholine (ACh) modulation, through muscarinic receptors, is a particularly widespread mechanism of controlling sensory information transmission. The precise effects of ACh modulation depend on the subtype of muscarinic ACh receptors that are activated. In weakly electric fish, previous work suggested a role of ACh, via muscarinic receptors, in the modulation of information transmission in the electrosensory lateral line lobe (ELL) of the hindbrain. In this study, we determined which muscarinic receptor (mAChR) subtypes are present in the brain of Apteronotus leptorhynchus as well as their spatial distribution. We partially cloned three subtypes of muscarinic receptors (mAChR2, ?3, and ?4) from brain tissue of A. leptorhynchus and used in situ hybridization in transverse sections of the brain to determine their distributions. Sites labeled for the three muscarinic receptor mRNAs were found in various brain regions devoted to the processing of different sensory modalities. The mRNA probes for the three receptor types showed differential distribution but also overlapping presence of two or more receptors in particular nuclei. In addition to the presence of mAChR3 in the ELL region, electrosensory nuclei including the nucleus praeeminentialis, dorsal torus semicircularis and optic tectum showed expression of one or more mAChRs. Thus, the overall pattern of mAChR expression found is in agreement with mAChR expression in other species, with additional presence evident in specialized regions of the electrosensory system, which suggests an important modulating role of ACh in this sensory modality. J. Comp. Neurol. 521:1054–1072, 2013. © 2012 Wiley Periodicals, Inc.     

Regulated expression of N-methyl-D-aspartate receptors and associated proteins in teleost electrosensory system and telencephalon

Several types of N-methyl-D-aspartate (NMDA) receptor-dependent synaptic plasticity are characterized by differences in polarity, induction parameters, and duration, which depend on the interactions of NMDARs with intracellular synaptic and signaling proteins. Here, we examine the NMDAR signaling components in the brain of the weakly electric fish Apteronotus leptorhynchus. Compared with mammalian orthologs, high levels of sequence conservation for known functional sites in both NMDAR subunits (NR1, NR2A-C) and signaling proteins (fyn tyrosine kinase, RasGRF-1 and -2) were found. In situ hybridization analysis demonstrated that, similar to the case in the adult mammal brain, NR2A and NR2B are expressed at moderate levels in most brain regions and at very high levels in the dorsal telencephalon. RasGRF-1 and fyn have a similar distribution and appear to be coexpressed with NR2B in telencephalic regions known to support learning and long-term memory. Both NR2A and NR2B are highly expressed in pyramidal cells of the electrosensory lateral line lobe (ELL) known to exhibit the short-term synaptic plasticity that underlies adaptive feedback cancellation of redundant sensory input. In contrast, nonplastic pyramidal cells expressed only the NR2A subunit. Furthermore, field recordings show that ifenprodil-sensitive NR2B-containing NMDARs predominate for the plastic feedback input to ELL pyramidal cells. However, RasGRF-1 and fyn are expressed only at low levels in a subset of these pyramidal cells. Our data suggest that NMDAR functions are highly conserved between fish and mammals and that synaptic plasticity dynamics in different brain regions are related to the expression patterns of the synaptic signaling proteins interacting with NMDARs.     

Ganglion cell arrangement and axonal trajectories in the anterior lateral line nerve of the weakly electric fish Apteronotus leptorhynchus (Gymnotiformes)

To determine the organizational principles underlying the peripheral electrosensory nervous system of weakly electric gymnotiform teleosts we labelled each of the four anterior lateral line nerve branches with HRP. We determined the position of labelled cell bodies within the ganglion and followed anterogradely filled fibers to their termination sites in one of the four somatotopic maps in the electroreceptive lateral line lobe (ELL). Within the ganglion, cell bodies exhibit a loose somatotopy based on nerve branch position: trunk electroreceptors have their cell bodies located in the caudal ganglion; cell bodies to the head receptors are rostral. Cell bodies to the head exhibit a rough dorsoventral polarity, supraorbital cells tend to be located dorsally, infraorbital cells centrally, and mandibular cells ventrally. Despite this general somatotopy there is substantial overlap (up to 30%) of cell bodies among regions. There appears to be no rostrocaudal topography within nerve branch regions. Iontophoretic WGA-HRP injected into the medial segment of the ELL retrogradely labelled cell bodies that innervate ampullary organs. These cell bodies were dispersed throughout the ganglion, indicating that cell bodies do not cluster by receptor type. Peripherally directed axons from the ganglion appear to undergo an active reorganization in order to form the nerve branches. Within nerve branches, axons to a particular area of skin do not cluster together. Centrally from the ganglion, axons retain the position of their cell body until they reach the ELL border. Once in the ELL, fibers become sorted in the deep fiber layer according to receptor type and the map they terminate in. This reorganization involves rearrangement of fascicles and axons within fascicles. In toto, proceeding from peripheral to central, the electrosensory periphery loses at least a portion of its receptor topography in the distal nerve and ganglion and then acquires both a functional and somatotopic organization after reaching the ELL; conceptually it is torn down and rebuilt again. From an ontogenetic perspective, axonal growth occurs from the ganglion outward; the fact that ganglion cell bodies are not highly organized while the receptors they innervate and their central processes are suggests that active axonal guidance mechanisms are involved.     

Tissue printed cells from teleost electrosensory and cerebellar structures

A modification of the tissue printing technique was used to acutely isolate and culture cells from the electrosensory lateral line lobe (ELL), corpus cerebelli (CCb), and eminentia granularis pars posterior (EGp) of the adult weakly electric fish, Apteronotus leptorhynchus. Cells were isolated without the use of proteolytic enzymes and tissue printed as a monolayer onto glass coverslips through centrifugation in the presence of a medium designed to preserve cell structure. Tissue printed cells were reliably distributed in an organotypic fashion that allowed for the identification of anatomical boundaries between the ELL and cerebellar regions, distinct sensory maps in the ELL, and specific cell laminae. Many cells were isolated with an excellent preservation of soma-dendritic structure, permitting direct identification of all electrosensory cell classes according to morphological or immunocytochemical criteria. Several classes of glial cells were isolated, including small diameter microglia and the complex arborizations of oligodendrocytes. A plexus of fine processes were often isolated in conjunction with cell somata and dendrites, potentially preserving synaptic contacts in vitro. In particular, immunolabel for γ-aminobutyric acid (GABA) revealed a previously unrecognized network of GABAergic axonal processes in the CCb and EGp granule cell body and molecular layers. Tissue printed cells were readily maintained with an organotypic distribution of glial and neuronal elements for up to 27 days in culture. This procedure will allow for the isolation of electrosensory cells from adult central nervous system for electrophysiological analyses of membrane properties or synaptic interactions between identified cells. J. Comp. Neurol. 386:277–292, 1997. © 1997 Wiley-Liss, Inc.     

Interspecific variation in the projection of primary afferents onto the electrosensory lateral line lobe of weakly electric teleosts: different solutions to the same mapping problem

We demonstrate that preterminal axons composing the primary afferent projection onto the four somatotopically organized electrosensory lateral line lobe (ELL) segments in weakly electric gymnotiform teleosts course in fundamentally different directions in the most commonly studied species. Afferents enter the deep fiber layer (dfl) of the ELL and course in variable, but species-specific, directions within a horizontal plane before turning dorsally to terminate within the deep neuropil layer of the ELL (dnl). Among the species considered here, apteronotids exhibit the tightest projection pattern. Afferents enter the rostral ELL from the anterior lateral line nerve ganglion (ALLNG) in a nonsomatotopic fashion. As they course horizontally, these fibers undergo a rostrocaudal somatotopic sorting along the ventrolateral border of the dfl, then turn within a horizontal plane to course medially across the ELL segments. These medially coursing horizontal fibers are sorted: they form sublaminae according to the nerve branch containing their peripheral axon. Horizontal axons then turn dorsally, form fascicles, and terminate within the dnl. Within the dorsal fascicles, axons run directly into the dnl with little deviation, and their terminal fields exhibit no appreciable spread. In sternopygids, dfl horizontal fibers course in directions orthogonal to those in apteronotids. Fibers enter the rostral ELL and course medially across segments before turning caudally within segments. Unlike apteronotids, sternopygid horizontal fibers do not sort tightly by nerve branch. As horizontal axons turn dorsally they also form tight fascicles. But rather than terminating directly and without spreading, as in apteronotids, sternopygid fibers disperse from these fascicles and become sorted horizontally a second time prior to terminating in the dnl.(ABSTRACT TRUNCATED AT 250 WORDS)     

CB1 cannabinoid receptor expression in brain regions associated with zebra finch song control

Cannabinoids have been used for millennia through various preparations of Cannabis sativa. Despite this long history of use, the physiological significance of cannabinoid signaling in the vertebrate CNS is not well understood. High CB1 cannabinoid receptor densities in mammalian telencephalon and the results of behavioral studies suggest that cannabinoids play a role in cognitive function, learning, and memory. Since a network of discrete brain regions in zebra finch telencephalon controls song learning, we hypothesized that cannabinoid signaling may be relevant to songbird vocal development and behavior. Radioligand binding experiments using the cannabinoid agonist [3H]CP-55940 allowed identification of a dense population of high-affinity cannabinoid binding sites in zebra finch neuronal membranes. Northern blotting and RT-PCR experiments demonstrated expression of a predominant zebra finch CB1 mRNA of approximately 5.5 kb. Expression of this CB1 mRNA appears to change over the course of vocal development within the caudal telencephalon. As zebra finch caudal telencephalon contains the higher vocal center (HVC) and the robust nucleus of the archistriatum (RA), regions involved in song learning and production, we further investigated CB1 expression in these areas using in situ hybridization. In situ hybridization revealed that CB1 mRNA is expressed at high levels within both HVC and RA. Overall, these data demonstrate the presence of CB1 signaling systems within songbird telencephalon, notably within regions known to be involved in song learning and production. High-level CB1 expression in song regions suggests a potential role for cannabinoid signaling in zebra finch vocal development.     

Zebrin II distinguishes the ampullary organ receptive map from the tuberous organ receptive maps during development in the teleost electrosensory lateral line lobe

In weakly electric gymnotiform teleosts, monoclonal antibody anti-zebrin II recognizes developing pyramidal cells in the ampullary organ-receptive medial segment of the medullary electrosensory lateral line lobe (ELL) and in the mechanoreceptive nucleus medialis. Developing pyramidal cells in the remaining three tuberous organ-receptive lateral ELL segments are unreactive. These results suggest that certain biochemical features of the ELL ampullary organ-receptive medial segment are more similar to the nucleus medialis than to the tuberous organ-receptive ELL segments, and support the hypothesis that the ampullary system evolved from mechanosensory precursors.     

Development of the electrosensory nervous system of Eigenmannia (gymnotiformes): II. The electrosensory lateral line lobe, midbrain, and cerebellum

The somatotopically and functionally organized electrosensory system of gymnotiform teleosts provides a model for the study of the formation of ordered nerve connections. This paper describes the development of the major electrosensory nuclei within the hind- and midbrain. All three main electrosensory nuclei--the electrosensory lateral line lobe (ELL), dorsal torus semicircularis (torus), and tectum--grow by adding cells at their caudolateral borders. Toral and tectal germinal zones arise from lateral ventricular outpocketings that either completely or partially close by maturity. In the ELL before day 5 postspawning, germinal cells form from an initial periventricular germinal zone, then migrate to the caudolateral border of the hindbrain and begin dividing. The ELL grows from two main germinal zones, one for the medial segment, and one for the three lateral tuberous segments. Within each ELL germinal zone, newly formed cells arise from two areas: granular cells arise from a ventral subzone, pyramidal cells are generated more dorsally. Granular cells remain in situ, whereas pyramidal cells may migrate rostromedially. Cells begin differentiating as soon as they are formed. Spherical and pyramidal cells send ascending axons into the internal plexiform layer by day 14-18 and the ELL gradually begins to assume its mature laminar appearance. The ELL grows caudally, preceding the caudal lobe of the cerebellum, which will eventually lie over and fuse with it. Primary electrosensory afferents enter the ELL by day 6; incoming afferents form four fascicles within the ELL, suggesting the formation of separate ELL segments. Unlabelled projections between labelled fields from a single nerve branch filled with HRP on day 7 suggest that somatotopic order is already present at this early age. In the periphery, receptor addition is unordered, occurring along nerve branch pathways. Meanwhile the ELL adds cells in an orderly fashion at its caudolateral border. This suggests that primary afferents shift position caudally with growth to maintain their somatotopic relationships. Because all three central nuclei are in topographic register and grow by adding cells caudally, during growth ELL efferents to the torus and toral efferents to the tectum may utilize passive mechanisms, such as fiber-fiber interactions, to guide axons.     

A prominent soma-dendritic distribution of Kv3.3 K+ channels in electrosensory and cerebellar neurons.

The expression pattern and subcellular distribution of a teleost homologue of the mammalian Kv3.3 potassium channel, AptKv3.3, was examined in the electrosensory lateral line lobe (ELL) and two cerebellar lobes in the hindbrain of the weakly electric gymnotiform Apteronotus leptorhynchus. AptKv3.3 expression was brain specific, with the highest level of expression in the cerebellum and 56% relative expression in the ELL. In situ hybridization revealed that AptKv3.3 mRNA was present in virtually all cell classes in the ELL as well as in the cerebellar lobes eminentia granularis pars posterior (EGp) and corpus cerebellum (CCb). Immunocytochemistry indicated a distribution of AptKv3.3 channels over the entire soma-dendritic axis of ELL pyramidal, granule, and polymorphic cells and over the soma and at least proximal dendrites (100 microm) of multipolar cells and neurons of the ventral molecular layer. AptKv3.3 immunolabel was present at the soma of cerebellar granule, golgi, eurydendroid, and CCb Purkinje cells, with an equally intense label throughout the dendrites of CCb Purkinje cells and EGp eurydendroid cells. Immunolabel was virtually absent in afferent or efferent axon tracts of the ELL but was detected on climbing fiber axons and on the axons and putative terminal boutons of CCb Purkinje cells. These data reveal a prominent soma-dendritic distribution of AptKv3.3 K+ channels in both principal output and local circuit neurons, a pattern that is distinct from the soma-axonal distribution that characterizes all other Kv3 K+ channels examined to date. The widespread distribution of AptKv3.3 immunolabel in electrosensory cells implies an important role in several aspects of signal processing.     

Functional foveae in an electrosensory system

Several species of Mormyrid weakly electric fish have a mobile chin protuberance that serves as a mobile antenna during prey detection, tracking behaviors, and foraging for food. It has been proposed that it constitutes a fovea of the electrosensory system. The distribution of the three types of receptor organs involved in active imaging of the local surroundings, prey detection, and passive electroreception, and their central projection to the electrosensory lobe (ELL), have been studied in Gnathonemus petersii. Density distributions were compared for different body regions. Primary afferent projections were labeled with biocytin or biotinylated dextrans. This showed that there is considerable central "over-representation" of the mandibular and nasal regions of the sensory surface involved in electrolocation, at the expense of the other body regions investigated. This over-representation is not a mere effect of the very high density of receptor organs in these areas, but is found to be due to central magnification. This magnification differs between the subclasses of electroreceptors, suggesting a functional segregation in the brain. We conclude that the chin protuberance and the nasal region are the regions of greatest sensitivity for the resistive, capacitive, and low-frequency characteristics of the environment, and are probably most important in prey detection, whereas other regions of the skin with a lesser resolution and sensitivity to phase distortion of the EOD, in particular the trunk, are probably designed for imaging larger, inanimate features of the environment. Our data support the hypothesis that the chin appendage and nasal region are functionally distinct electrosensory foveae.     

Correlating gamma-aminobutyric acidergic circuits and sensory function in the electrosensory lateral line lobe of a gymnotiform fish

Electric fish generate an electric field, which they sense with cutaneous electroreceptors. Electroreceptors project topographically onto the medullary electrosensory lateral line lobe (ELL). The ELL of gymnotiform electric fish is divided into four segments specialized to detect different aspects of the electrosensory input; it is also laminated with separate laminae devoted to electroreceptive input, interneurons, projection neurons, and feedback input. We have utilized antisera to glutamic acid decarboxylase (GAD) and γ-aminobutyric acid (GABA) to map the distribution of GABAergic cells and fibers in the ELL of the gymnotiform fish, Apteronotus leptorhynchus. Six types of GABAergic interneurons are found in ELL: Type 2 granular cells (granular layer) project to pyramidal cells; polymorphic cells (pyramidal cell layer) project to the non-GABAergic type 1 granular cells; ovoid cells (deep neuropil layer) project bilaterally upon basilar dendrites of pyramidal cells; multipolar cells (deep neuropil layer) project bilaterally, probably to dendrites and neurons within the deep neuropil layer; and neurons of the ventral molecular layer and stellate cells (molecular layer) project to apical dendrites of pyramidal cells. GABAergic bipolar cells in the nucleus praeminentialis, a rhombencephalic structure devoted to feedback in the electrosepsory system, project in relatively diffuse fashion to pyramidal cells. We hypothesize that the various GABAergic circuits of the ELL can be correlated with specific functions: type 2 granular cells with adaptation, size of receptive field center, and gain; polymorphic cells and type 1 granular cells with regulation of surround inhibition; ovoid cells with common mode rejection; and neurons of the ventral molecular layer with adaptive gain control. The feedback GABAergic input from bipolar cells of n. praeminentialis to pyramidal cells may be part of a searchlight mechanism similar to the one postulated for thalamocortical systems. © 1994, Wiley-Liss, Inc.     

Nestin mRNA expression correlates with the central nervous system progenitor cell state in many,but not all,regions of developing central nervous system

Nestin is a recently discovered intermediate filament (IF) gene. Nestin expression has been extensively used as a marker for central nervous system (CNS) progenitor cells in different contexts, based on observations indicating a correlation between nestin expression and this cell type in vivo. To evaluate this correlation in more detail nestin mRNA expression in developing and adult mouse CNS was analysed by in situ hybridization. We find that nestin is expressed from embryonic day (E) 7.75 and that expression is detected in many proliferating CNS regions; at E10.5 nestin is expressed in cells of both the rostral and caudal neural tube, including the radial glial cells; at E15.5 and postnatal day (P) 0 expression is observed largely in the developing cerebellum and in the ventricular and subventricular areas of the developing telencephalon. Furthermore, the transition from a proliferating to a post-mitotic cell state is accompanied by a rapid decrease in nestin mRNA for motor neurons in the ventral spinal cord and for neurons in the marginal layer of developing telencephalon. In contrast to these data we observe two proliferating areas, the olfactory epithelium and the precursor cells of the hippocampal granule neurons, which do not express nestin at detectable levels. Thus, nestin mRNA expression correlates with many, but not all, regions of proliferating CNS progenitor cells. In addition to its temporal and spatial regulation nestin expression also appears to be regulated at the level of subcellular mRNA localization: in columnar neuroepithelial and radial glial cells nestin mRNA is predominantly localized to the pial endfeet.     

Patterns of expression for the mRNA corresponding to the four isoforms of phospholipase Cβ in mouse brain

Ligand binding to neurotransmitter and hormone receptors which couple to the Gq subclass of GTP-binding protein leads to the activation of phospholipase Cβ (PLCβ) which hydrolyses phosphatidyl-inositol 4,5-bisphosphate, yielding a pair of second messengers, diacylglycerol and inositol 1,4,5-trisphosphate (IP₃). The expression of PLCβ1–4 mRNAs was comparatively examined by in situ hybridization in the mouse brain. In adults, PLCβ1 mRNA was expressed predominantly in the telencephalon, including the cerebral cortex, hippocampus, amygdala, lateral septum and olfactory bulb, with little expression in most thalamic nuclei. PLCβ2 mRNA was distributed in the white matter, suggesting its expression in non-neuronal cells, most likely oligodendrocytes. PLCβ3 mRNA was specifically expressed in cerebellar Purkinje cells. The highest levels of PLCβ4 mRNA were detected in Purkinje cells. High levels of PLCβ4 mRNA were also found in the thalamus and medial septum, whereas weak signals were detected in most telencephalic regions, thus showing an expression pattern almost reciprocal to that of PLCβ1 mRNA. During development, such characteristic regional expression of PLCβ1 and PLCβ4 were observed starting in late foetal stages, while specific expression of PLCβ2 and PLCβ3 appeared in early postnatal stages. We conclude that despite the existence of four PLCβ isoforms, only one or two of them is expressed in individual neurons and glial cells. The distinct expression of PLCβs provides a molecular basis for analysing the nature of the specific signal transduction pathway leading to the production of diacylglycerol and IP₃ in distinct cell types and in different regions of the brain.     

Influence of Chronic Nicotine Administration on Cerebral Type 1 Cannabinoid Receptor Binding: An In Vivo Micro-PET Study in the Rat Using [<Superscript>18</Superscript>F]MK-9470

Several lines of evidence suggest a functional interaction between central nicotinic and endocannabinoid systems. Furthermore, type 1 cannabinoid receptor (CB1R) antagonism is evaluated as antismoking therapy, and nicotine usage can be an important confound in positron emission tomography (PET) imaging studies of the CB1R. We evaluated CB1R binding in the rat brain using the PET radioligand [¹⁸F]MK-9470 after chronic administration of nicotine. Twelve female Wistar rats were scanned at baseline and after chronic administration of either nicotine (1 mg/kg; 2 weeks daily intraperitoneal (IP)) or saline as control. In vivo micro-PET images of CB1R binding were anatomically standardized and analyzed by voxel-based statistical parametric mapping and a predefined volume-of-interest approach. We did not observe changes in [¹⁸F]MK-9470 binding (p _height < 0.001 level; uncorrected) on a group basis in either condition. Only at a less stringent threshold of p _height < 0.005 (uncorrected) was a modest increase observed in tracer binding in the cerebellum for nicotine (peak voxel value + 6.8%, p _cluster = 0.002 corrected). In conclusion, chronic IP administration of nicotine does not produce major cerebral changes in CB1R binding of [¹⁸F]MK-9470 in the rat. These results also suggest that chronic nicotine usage is unlikely to interfere with human PET imaging using this radioligand.     

Identification and characterization of the leech CNS cannabinoid receptor: coupling to nitric oxide release

The present study demonstrates that stereoselective binding sites for anandamide, a naturally occurring cannabinoid substance, can be found in leech (Theromyzon tessulatum and Hirudo medicinalis) central nervous system. The anandamide binding site is monophasic and of high affinity exhibiting a K_d of approximately 32 nM with a B_max of 550 fmol/mg protein in both animals. These sites are highly select as demonstrated by the inability of other types of signaling molecules to displace [³H]anandamide. Furthermore, this binding site is coupled to nitric oxide release. A deduced amino acid sequence (153 residues) analysis from a 480 pb amplified RT-PCR fragment cDNA exhibits a 49.3% and 47.2% sequence identity with human and rat cannabinoid receptors (CB1R), respectively. Thus, the leech cannabinoid receptor may be a G-protein coupled receptor with seven transmembrane domains as in CB1R. Moreover, this sequence exhibits highly conserved regions, particularly in the putative transmembrane domains 1 and 2. The presence of a cannabinoid receptor in these organisms indicates that this signaling system has been conserved during evolution. © 1977 Elsevier Science B.V. All rights reserved.     

Comparative anatomy of the electrosensory lateral line lobe of mormyrids: the mystery of the missing map in the genus Stomatorhinus (family: Mormyridae)

Fish in the family Mormyridae produce weak electric organ discharges that are used in orientation and communication. The peripheral and central anatomy of the electrosensory system has been well studied in the species Gnathonemus petersii, but comparative studies in other species are scarce. Here we report on one genus of mormyrid that displays a remarkable change in the electrosensory lateral line lobe (ELL), the hypertrophied rhombencephalic structure that receives primary electroreceptor input. Although all other mormyrids studied have three distinct zones on each side of the ELL, fish of the genus Stomatorhinus exhibit only two. Therefore, the two-zone ELL is a unique derived characteristic shared by Stomatorhinus. We examined the cutaneous electroreceptors that project to the ELL in Stomatorhinus. All three types of electroreceptors previously described for G. petersii were present, but there was a significant change in one type, the mormyromast. Both mormyromast sensory cell types (A- and B-cells) are present, but the B-cell is not innervated in Stomatorhinus. We conclude that, although all cutaneous sensory cells are present, the missing B-cell afferents account for the loss of the dorsolateral zone of the ELL, and therefore the loss of an entire sensory map. Because mormyromasts are involved in electrolocation behavior, this anatomical difference is probably related to differences in electrolocation abilities. Stomatorhinus could prove to be an excellent system for linking evolutionary changes in behavior with modifications in their neural substrates.     

Müller cells express the cannabinoid CB2 receptor in the vervet monkey retina

The presence of the cannabinoid receptor type 1 (CB1R) has been largely documented in the rodent and primate retinae in recent years. There is, however, some controversy concerning the presence of the CB2 receptor (CB2R) within the central nervous system. Only recently, CB2R has been found in the rodent retina, but its presence in the primate retina has not yet been demonstrated. The aim of this study was twofold: 1) to characterize the distribution patterns of CB2R in the monkey retina and compare this distribution with that previously reported for CB1R and 2) to resolve the controversy on the presence of CB2R in the neural component of the retina. We therefore thoroughly examined the cellular localization of CB2R in the vervet monkey (Chlorocebus sabeus) retina, using confocal microscopy. Our results demonstrate that CB2R, like CB1R, is present throughout the retinal layers, but with striking dissimilarities. Double labeling of CB2R and glutamine synthetase shows that CB2R is restricted to Müller cell processes, extending from the internal limiting membrane, with very low staining, to the external limiting membrane, with heavy labeling. We conclude that CB2R is indeed present in the retina but exclusively in the retinal glia, whereas CB1R is expressed only in the neuroretina. These results extend our knowledge on the expression and distribution of cannabinoid receptors in the monkey retina, although further experiments are still needed to clarify their role in retinal functions. J. Comp. Neurol. J. Comp. Neurol. 521:2399–2415, 2013. © 2013 Wiley Periodicals, Inc.     

Expression of D1 receptor mRNA in projections from the forebrain to the ventral tegmental area

In situ hybridization was combined with Fluoro-Gold retrograde labeling to determine if cells projecting from the forebrain to the ventral tegmental area (VTA) express D₁ receptor mRNA. Cell counts were made in the prefrontal cortex, shell of the nucleus accumbens, and ventral pallidum to estimate the percentage of neurons projecting to the VTA that express D₁ receptor mRNA. Retrogradely labeled cells were observed in the infralimbic and prelimbic regions of the prefrontal cortex, and up to 37% of the retrogradely labeled cells expressed D₁ receptor mRNA. Double-labeled cells constituted up to 89% of retrogradely labeled neurons in the rostral shell and up to 68% in the caudal shell of the nucleus accumbens. The number of retrogradely labeled cells in the ventral pallidum that were double-labeled ranged from 13% in the rostral to less than 10% in the caudal portions. These data provide anatomical support for a role of D₁ receptors in the reciprocal innervation between the forebrain and VTA. Synapse 25:205–214, 1997. © 1997 Wiley-Liss, Inc.