Biomedical subjects

V M Pickel

Publications and source records attributed to V M Pickel.

At least 19 recordsLinked to original sources

PubMed2006

Predominant surface distribution of neurokinin-3 receptors in non-dopaminergic dendrites in the rat substantia nigra and ventral tegmental area.

Neurokinin-3 (NK(3)) receptors are prevalent within the substantia nigra (SN) and ventral tegmental area (VTA), where their activation can affect motor and motivational behaviors as well as cardiovascular function and stress responses. These actions are mediated, in part, by dopaminergic neurons in each region. To determine the relevant sites for activation of these receptors, we examined the electron microscopic localization of NK(3) receptors and tyrosine hydroxylase (TH), the catecholamine synthesizing enzyme in dopaminergic neurons in the SN and VTA of rat brain. In each region, immunogold-silver labeling for NK(3) receptors was detected in many somatodendritic profiles, some of which contained TH-immunoreactivity. NK(3)-immunogold particles were largely associated with endomembranes resembling smooth endoplasmic reticulum, and only occasionally located on the plasma membrane in TH-labeled dendrites. In comparison with these dendrites, non-TH immunoreactive dendrites contained significantly more total (VTA) and more plasmalemmal (VTA and SN) NK(3)-immunogold particles. In each region, NK(3) gold particles also were seen in axonal as well as glial profiles, some of which contacted TH-immunoreactive dendrites. The NK(3)-labeled axon terminals formed either symmetric or asymmetric, excitatory-type synapses, the latter of which were significantly more prevalent in the VTA, compared with SN. These results provide the first ultrastructural evidence indicating that NK(3) receptors are available in cytoplasmic reserve in dopaminergic neurons, but more immediately accessible at the plasmalemmal surface of non-dopaminergic dendrites in both the SN and VTA. The activation of these receptors, together with the NK(3) receptors in either the presynaptic axon terminals or glia may contribute to the diverse physiological effects of tachykinins in each region, and most prominently involving excitatory inputs to the VTA.

Animals↗

PubMed2006

Subcellular localization of nicotinamide adenine dinucleotide phosphate oxidase subunits in neurons and astroglia of the rat medial nucleus tractus solitarius: relationship with tyrosine hydroxylase immunoreactive neurons.

Superoxide produced by the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase mediates crucial intracellular signaling cascades in the medial nucleus of the solitary tract (mNTS), a brain region populated by catecholaminergic neurons, as well as astroglia that play an important role in autonomic function. The mechanisms mediating NADPH oxidase (phagocyte oxidase) activity in the neural regulation of cardiovascular processes are incompletely understood, however the subcellular localization of superoxide produced by the enzyme is likely to be an important regulatory factor. We used immunogold electron microscopy to determine the phenotypic and subcellular localization of the NADPH oxidase subunits p47(phox), gp91(phox,) and p22(phox) in the mNTS in rats. The mNTS contains a large population of neurons that synthesize catecholamines. Significantly, catecholaminergic signaling can be modulated by redox reactions. Therefore, the relationship of NADPH oxidase subunit labeled neurons or glia with respect to catecholaminergic neurons was also determined by dual labeling for the superoxide producing enzyme and tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. In the mNTS, NADPH oxidase subunits were present primarily in somatodendritic processes and astrocytes, some of which also contained TH, or were contacted by TH-labeled axons, respectively. Immunogold quantification of NADPH oxidase subunit localization showed that p47(phox) and gp91(phox) were present on the surface membrane, as well as vesicular organelles characteristic of calcium storing smooth endoplasmic reticula in dendritic and astroglial processes. These results indicate that NADPH oxidase assembly and consequent superoxide formation are likely to occur near the plasmalemma, as well as on vesicular organelles associated with intracellular calcium storage within mNTS neurons and glia. Thus, NADPH oxidase-derived superoxide may participate in intracellular signaling pathways linked to calcium regulation in diverse mNTS cell types. Moreover, NADPH oxidase-derived superoxide in neurons and glia may directly or indirectly modulate catecholaminergic neuron activity in the mNTS.

Animals↗

PubMed2006

Dopamine D1 receptors co-distribute with N-methyl-D-aspartic acid type-1 subunits and modulate synaptically-evoked N-methyl-D-aspartic acid currents in rat basolateral amygdala.

Activation of dopamine D1 or glutamate, N-methyl-d-aspartic acid (NMDA) receptors in the basolateral amygdala (BLA) can potently influence affective behaviors and associative learning. Physical protein-protein interactions also can occur between C-terminal peptides of D1 receptors and the NMDA-receptor subunit-1 (NR1), suggesting intracellular associations of direct relevance to dopaminergic modulation of NMDA currents. We examined this possibility by combining electron microscopic immunolabeling of the D1 and NR1 C-terminal peptides with in vitro patch-clamp recording in the rat BLA. In the in vivo preparations, D1 and NR1 were localized to the surface or endomembranes of many of the same somata and dendrites as well as a few axon terminals, including those forming asymmetric, excitatory-type synapses. In vitro analysis of physiologically characterized projection neurons revealed an excitatory response to bath application of either dopamine or the preferential D1 receptor agonist, dihydrexidine. In these neurons, dopamine also selectively reduced stimulation-evoked isolated NMDA receptor-mediated currents, but not isolated non-NMDA receptor-mediated currents or the response to exogenous NMDA application. The selective reduction of the NMDA receptor-mediated currents suggests that this effect occurs at a postsynaptic locus. Moreover, both D1 and NR1 were localized to postsynaptic surfaces of biocytin-filled and physiologically characterized projection neurons. Our results provide ultrastructural evidence for D1/NR1 endomembrane associations that may dynamically contribute to the attenuation of NMDA receptor-mediated currents following prior activation of D1 receptors in BLA projection neurons. The potential for postsynaptic cross-talk between D1 and NMDA receptors in BLA projection neurons as well as a similar interaction in presynaptic terminals could have important implications for the formation and extinction of affective memories.

Amygdala↗

PubMed2005

Subcellular distribution and plasticity of neurokinin-1 receptors in the rat substantia nigra and ventral tegmental area.

Neurokinin-1 receptors show activity-dependent changes in their surface distributions that are critical in spinal pain mechanisms, and also may play an important role in the motor and affective behaviors influenced by dopaminergic projections from the substantia nigra and ventral tegmental area. To determine the relevant sites for neurokinin-1 receptor activation in these midbrain regions, we examined the electron microscopic immunolabeling of neurokinin-1 receptors and the dopamine-synthesizing enzyme, tyrosine hydroxylase in normal rats. We also examined whether neurokinin-1 receptor distributions in one or both regions are affected by (1) startle-evoking intense auditory stimulation or (2) acute administration of apomorphine, a dopamine D1/D2 agonist that enhances startle while paradoxically reducing the prepulse inhibition produced by low intensity conditioning stimuli in rat models of schizophrenia. In each region, neurokinin-1 immunogold was located on the plasma membrane and endomembranes of somatodendritic profiles with or without tyrosine hydroxylase. As compared with controls, animals receiving intense auditory stimulation either alone or together with smaller low intensity prepulses showed a significant increase in neurokinin-1-plasmalemmal labeling in non-dopaminergic dendrites of both regions, and a reduction in this labeling in dopaminergic dendrites of the ventral tegmental area. Both effects were diminished following apomorphine administration. In absence of the intense auditory stimulation, however, apomorphine increased neurokinin-1-immunogold particles on the plasma membrane of the non-dopaminergic dendrites exclusively in the substantia nigra. Our results are the first to show that neurokinin-1 receptors have plasmalemmal distributions in dopaminergic and non-dopaminergic neurons that can be differentially modified by startle-evoking auditory stimulation. They suggest that while apomorphine can independently affect neurokinin-1 receptor trafficking in substantia nigra motor circuits, its effects on neurokinin-1 receptor distributions in the ventral tegmental area are exclusively dependent on sensory activation.

Acoustic Stimulation↗

PubMed2005

Angiotensin II AT-1A receptor immunolabeling in rat medial nucleus tractus solitarius neurons: subcellular targeting and relationships with catecholamines.

The angiotensin II AT-1A receptor (AT-1A) is the major mediator of the hypertensive actions of angiotensin II (ANG II) in the medial nucleus of the solitary tract (mNTS). The localization of the AT-1A receptor at surface or intracellular sites is an important determinant of its signaling properties, including intercellular or intracrine communication. However, the spatial localization of this protein, particularly within small distal or intermediate size dendrites of mNTS neurons, is unknown. Within the mNTS, ANG II and catecholamines interact in the regulation of autonomic function; however, it is unknown if AT-1A receptors are present at functional sites in catecholamine containing dendrites, or are contacted by catecholamine containing axon terminals. We compared surface and intracellular distributions of the AT-1A receptor in dendritic processes from the mNTS using immunogold electron microscopy in conjunction with immunoperoxidase labeling for tyrosine hydroxylase (TH) and morphometric analysis. Collapsed across all AT-1A-labeled dendritic profiles, immunogold labeling was more frequent in intracellular sites as compared with the plasma membrane. Small (<0.6 microm) dendritic profiles contained a higher ratio of particles associated with the surface membrane when compared with larger profiles. Approximately 27% of all AT-1A receptor-labeled dendritic profiles also contained labeling for TH. Approximately 12% of dendritic profiles single labeled for the AT-1A receptor were contacted by TH containing axons or axon terminals. The present results provide the first quantitative demonstration of select plasmalemmal and intracellular localizations of AT-1A receptors in dendritic processes of mNTS neurons, including those containing TH, or contacted by catecholaminergic axon terminals. These results suggest that AT-1A receptors are positioned for modulation of catecholamine signaling in the mNTS.

Animals↗

PubMed2004

Compartment-specific localization of cannabinoid 1 (CB1) and mu-opioid receptors in rat nucleus accumbens.

Interactions between cannabinoid and opioid systems have been implicated in reward and drug seeking behaviors involving neuronal circuitry in the nucleus accumbens (Acb) shell and core. To determine the relevant sites, we examined the electron microscopic localization of cannabinoid type-1 (CB1) receptors and mu-opioid receptors in each Acb compartment in rat brain. CB1 receptor immunogold labeling was seen on the plasma membrane and within the cytoplasm of neuronal and glial profiles throughout the Acb. These neuronal profiles included somata and dendrites as well as axon terminals, many of which formed excitatory-type, asymmetric synapses with notable perforations that are often associated with synaptic plasticity. The number of CB1-labeled terminals within the neuropil of the Acb shell was significantly greater than in the core. Mu-opioid receptors were also detected in axonal and dendritic profiles. These dendrites were most prevalent in the Acb shell, where mu-receptors also were located in 21% of the dendritic profiles and 3% of the axon terminals containing CB1 receptors. More of the CB1-labeled terminals contacted dendrites expressing mu-opioid receptors in the shell (19%) compared with the core (13%). Conversely, of the synaptic mu-labeled terminals, 20% in the shell and 10% in the core contacted dendrites containing CB1 receptors. These findings provide ultrastructural evidence that cannabinoid-opioid interactions are mediated by activation of CB1 and mu-opioid receptors within the same or synaptically linked neurons in the Acb shell and core. They also suggest a particularly important role for presynaptic CB1 receptors in the reward circuit of the Acb shell.

Animals↗

PubMed2003

Postnatal development of mu-opioid receptors in the rat caudate-putamen nucleus parallels asymmetric synapse formation.

The mu-opioid receptor (MOR) in the caudate-putamen nucleus (CPN) appears early during prenatal development, and shows a patch-like distribution throughout the postnatal period and adulthood. In the adult rat CPN, neurons in patch compartments receive glutamatergic excitatory input mainly from the cortex through synapses onto spines, many of which express MORs. Thus, MOR expression in spines may be related to corticostriatal synaptogenesis. We used electron microscopic immunocytochemistry to determine potential age-dependent changes in the distribution pattern of MOR during postnatal synaptogenesis in the rat CPN. Immunogold-silver labeling revealed that the dendritic plasmalemmal density of MOR at postnatal day (P) 0 was significantly lower than, but after P10 was similar to, that of adult. In contrast, such age-dependent changes were not observed in axon terminals. Stereological analysis of immunoperoxidase labeling for MOR showed a good correlation in the developmental numerical densities of synapses with MOR-labeled spines and those of total asymmetric axospinous synapses, linear correlation coefficient r=0.99. Synapses with MOR-labeled dendrites, however, had a low correlation with axodendritic synapses (r=0.61), and synapses with MOR-labeled terminals showed no correlation with axospinous and axodendritic synapses (r=0.19). These results provide ultrastructural evidence that the targeting of MOR on the plasma membrane of dendrites and spines parallels the peak period of synaptogenesis during the third postnatal week in the rat CPN. Thus, the postnatal spatiotemporal expression pattern of MOR appears to match the functional maturation of corticostriatal glutamate transmission.

Aging↗

PubMed2003

Angiotensin II subtype 1A (AT1A) receptors in the rat sensory vagal complex: subcellular localization and association with endogenous angiotensin.

Angiotensin II (Ang II) type 1 (AT1) receptors are prevalent in the sensory vagal complex including the nucleus tractus solitarii (NTS) and area postrema, each of which has been implicated in the central cardiovascular effects produced by Ang II. In rodents, these actions prominently involve the AT1A receptor. Thus, we examined the electron microscopic dual immunolabeling of antisera recognizing the AT1A receptor and Ang II to determine interactive sites in the sensory vagal complex of rat brain. In both the area postrema and adjacent dorsomedial NTS, many somatodendritic profiles were dually labeled for the AT1A receptor and Ang II. In these profiles, AT1A receptor-immunoreactivity was often seen in the cytoplasm beneath labeled portions of the plasma membrane and in endosome-like granules as well as Golgi lamellae and outer nuclear membranes. In addition, AT1A receptor labeling was detected on the plasma membrane and in association with cytoplasmic membranes in many small axons and axon terminals. These terminals were morphologically heterogeneous containing multiple types of vesicles and forming either inhibitory- or excitatory-type synapses. In the area postrema, AT1A receptor labeling also was detected in many non-neuronal cells including glia, capillary endothelial cells and perivascular fibroblasts that were less prevalent in the NTS. We conclude that in the rat sensory vagal complex, AT1A receptors are strategically positioned for involvement in modulation of the postsynaptic excitability and intracrine hormone-like effects of Ang II. In addition, these receptors have distributions consistent with diverse roles in regulation of transmitter release, regional blood flow and/or vascular permeability.

Angiotensin II↗

PubMed2002

Ultrastructural localization of enkephalin and mu-opioid receptors in the rat ventral tegmental area.

Enkephalins are endogenous ligands for opioid receptors whose activation potently modulates the output of mesocorticolimbic dopaminergic neurons within the ventral tegmental area. Many of the reinforcing effects of enkephalins in the mesocorticolimbic system are mediated by mu-opioid receptors. To determine the sites for Leu(5)-enkephalin activation of mu-opioid receptors in the ventral tegmental area, we examined the dual electron microscopic immunocytochemical localization of their respective antigens in this region of rat brain. Enkephalin immunoperoxidase reaction product and mu-opioid receptor immunogold-silver labeling showed similar cellular and subcellular distribution in both the paranigral and parabrachial subdivisions of the ventral tegmental area. Enkephalin immunoreactivity was mainly localized in small unmyelinated axons (50.4%) and in axon terminals (40.4%). The majority of these terminals formed symmetric, inhibitory-type synapses, many of which were on dendrites expressing plasmalemmal mu-opioid receptors. Appositional contacts were also often seen between axons or terminals that were differentially labeled for the two antigens. In addition, some of the enkephalin-labeled terminals and a few somatodendritic profiles showed a plasmalemmal or vesicular localization of mu-opioid receptors. Our results indicate that dendritic targets of inhibitory terminals, as well as nearby axon terminals, are potential sites for enkephalin activation of mu-opioid receptors throughout the ventral tegmental area. Moreover, co-localization of enkephalin and mu-opioid receptors in selective neuronal profiles may indicate an autoregulatory role for these receptors or their internalization along with the bound ligand in this brain region.

Animals↗

PubMed2002

Identification of a novel membrane-associated protein expressed in neurons of the squid and rodent nervous systems.

In a previous communication, we reported the isolation of a novel cDNA clone (pA6) from a library constructed from squid axonal mRNAs. The partial cDNA clone contained a unique open reading frame that encoded 84 amino acids and was complementary to a moderately abundant mRNA approximately 550-600 nucleotides in length [Chun et al., J. Neurosci. Res. 49 (1997) 144-153]. In this report, we identify the pA6 gene product, and characterize its expression in the squid and rodent brain. Results of immunoblot analyses conducted in squid, using a polyclonal antibody raised against a synthetic peptide corresponding to the C-terminus of the putative protein, established the presence of two pA6 immunoreactive proteins of approximately 14 kDa and 26 kDa in size. In contrast, mouse brain contained only a single 26-kDa immunoreactive species. In both the squid and mouse brain, the expression of pA6 appears highly selective, being detected in certain neurons but not in non-neuronal cells, as judged by both in situ hybridization and immunocytochemistry. Findings derived from light microscopic, double-label immunohistofluorescence studies indicate that pA6 protein co-localizes with prohibitin, a mitochondrial marker protein. Consistent with these results, electron microscopy localized pA6 immunoreactivity to several membrane compartments to include the outer membrane of mitochondria, as well as to the smooth endoplasmic reticulum and tubulovesicles in dendrites, axons, and axon terminals of neurons in the rat brain. Taken together, these findings indicate that pA6 is a novel, membrane-associated protein, which is expressed in the distal structural/functional domains of neurons in both the invertebrate and vertebrate nervous systems.

Animals↗

PubMed2001

Major coexpression of kappa-opioid receptors and the dopamine transporter in nucleus accumbens axonal profiles.

The behavioral effects of psychostimulants, which are produced at least in part through inhibition of the dopamine transporter (DAT), are modulated by kappa-opioid receptors (KOR) in the nucleus accumbens (Acb). Using electron microscopic immunocytochemistry, we reveal that in the Acb KOR labeling is mainly, and DAT immunoreactivity is exclusively, presynaptic. From 400 KOR-labeled presynaptic structures, including axon terminals, intervaricosities, and small axons, 51% expressed DAT and 29% contacted another population of terminals exclusively labeled for DAT. Within axonal profiles that contained both antigens, DAT and KOR were prominently localized to plasma membrane segments that showed overlapping distributions of the respective immunogold-silver and immunoperoxidase markers. KOR labeling was also localized to membranes of small synaptic vesicles in terminals with or without DAT immunoreactivity. In addition, from 24 KOR-immunoreactive dendritic spines 42% received convergent input from DAT-containing varicosities and unlabeled terminals forming asymmetric, excitatory-type synapses. Our results provide the first ultrastructural evidence that in the Acb, KOR is localized to strategic sites for involvement in the direct presynaptic release and/or reuptake of dopamine. These data also suggest a role for KOR in the presynaptic modulation of other neurotransmitters and in the postsynaptic excitatory responses of single spiny neurons in the Acb. Dual actions on dopamine terminals and their targets in the Acb may account for KOR-mediated attenuation of drug reinforcement and sensitization.

Animals↗

PubMed2001

Plasmalemmal mu-opioid receptor distribution mainly in nondopaminergic neurons in the rat ventral tegmental area.

Opiate-evoked reward and motivated behaviors reflect, in part, the enhanced release of dopamine produced by activation of the mu-opioid receptor (muOR) in the ventral tegmental area (VTA). We examined the functional sites for muOR activation and potential interactions with dopaminergic neurons within the rat VTA by using electron microscopy for the immunocytochemical localization of antipeptide antisera raised against muOR and tyrosine hydroxylase (TH), the synthesizing enzyme for catecholamines. The cellular and subcellular distribution of muOR was remarkably similar in the two major VTA subdivisions, the paranigral (VTApn) and parabrachial (VTApb) nuclei. In each region, somatodendritic profiles comprised over 50% of the labeled structures. MuOR immunolabeling was often seen at extrasynaptic/perisynaptic sites on dendritic plasma membranes, and 10% of these dendrites contained TH. MuOR-immunoreactivity was also localized to plasma membranes of axon terminals and small unmyelinated axons, none of which contained TH. The muOR-immunoreactive axon terminals formed either symmetric or asymmetric synapses that are typically associated with inhibitory and excitatory amino acid transmitters. Their targets included unlabeled (30%), muOR-labeled (25%), and TH-labeled (45%) dendrites. Our results suggest that muOR agonists in the VTA affect dopaminergic transmission mainly indirectly through changes in the postsynaptic responsivity and/or presynaptic release from neurons containing other neurotransmitters. They also indicate, however, that muOR agonists directly affect a small population of dopaminergic neurons expressing muOR on their dendrites in VTA and/or terminals in target regions.

Animals↗

PubMed2001

Mu-opioid receptors in the ventral tegmental area are targeted to presynaptically and directly modulate mesocortical projection neurons.

Mesocorticolimbic projections originating from dopaminergic and GABAergic neurons in the ventral tegmental area (VTA) play a critical role in opiate addiction. Activation of mu-opioid receptors (MOR), which are located mainly within inhibitory neurons in the VTA, results in enhanced dopaminergic transmission in target regions, including the medial prefrontal cortex (mPFC). We combined retrograde tract-tracing and electron microscopic immunocytochemistry to determine if neurons in the VTA that project to the mPFC contain MOR or receive input from MOR-containing terminals. Rats received unilateral injections of the retrograde tracer Fluoro-Gold (FG) into the mPFC. Tissue sections throughout the VTA were then processed for electron microscopic examination of FG and MOR. Immunoperoxidase labeling for FG was present in VTA cell bodies that contained immunogold-silver particles for MOR that often were contacted by profiles exclusively immunoreactive for MOR, including somata and axon terminals. The majority of dually labeled profiles were dendrites that received convergent input from unlabeled axon terminals forming either symmetric or asymmetric type synapses. Within retrogradely labeled cell bodies and proximal dendrites, MOR immunoreactivity was mainly sequestered within the cytoplasm. In contrast, distal retrogradely labeled dendrites contained MOR gold particles located along the plasma membranes. These data suggest that opiates active at MOR in the VTA modulate cortical activity through 1) presynaptic actions on MOR in terminals contacting mesocortical cell bodies, and 2) direct activation of MOR in distal dendrites of projection neurons.

Animals↗

PubMed2001

High-affinity neurotensin receptors in the rat nucleus accumbens: subcellular targeting and relation to endogenous ligand.

Neurotensin is present in selective mesolimbic dopaminergic projections to the nucleus accumbens (NAc) shell but also is synthesized locally in this region and in the motor-associated NAc core. We examined the electron microscopic immunolabeling of the high-affinity neurotensin receptor (NTR) and neurotensin in these subdivisions of rat NAc to determine the sites for receptor activation and potential regional differences in distribution. Throughout the NAc, NTR immunoreactivity was localized discretely within both neurons and glia. NTR-labeled neuronal profiles were mainly axons and axon terminals with diverse synaptic structures, which resembled dopaminergic and glutamatergic afferents, as well as collaterals of inhibitory projection neurons. These terminals had a significantly higher numerical density in the NAc core than in the shell but were prevalent in both regions, suggesting involvement in both motor and limbic functions. In each region, neurotensin was detected in a few NTR-immunoreactive axon terminals and in terminals that formed symmetric, inhibitory type synapses with NTR-labeled somata and dendrites. The NTR labeling, however, was not seen within these synapses and, instead, was localized to segments of dendritic and glial plasma membranes often near excitatory type synapses. Neuronal NTR immunoreactivity also was associated with cytoplasmic tubulovesicles and nuclear membranes. Our results suggests that, in the NAc shell and core, NTR is targeted mainly to presynaptic sites, playing a role in the regulated secretion and/or retrograde signaling in diverse, neurotransmitter-specific neurons. The findings also support a volume mode of neurotensin actions, specifically affecting excitatory transmission through activation of not only axonal but also dendritic and glial NTR.

Animals↗

PubMed2001

Vesicular acetylcholine transporter in the rat nucleus accumbens shell: subcellular distribution and association with mu-opioid receptors.

Cholinergic interneurons in the nucleus accumbens shell (AcbSh) are implicated in the reinforcing behaviors that develop in response to opiates active at mu-opioid receptors (MOR). We examined the electron microscopic immunocytochemical localization of the vesicular acetylcholine transporter (VAChT) and MOR to determine the functional sites for storage and release of acetylcholine (ACh), and potential interactions involving MOR in this region of rat brain. VAChT was primarily localized to membranes of small synaptic vesicles in axon terminals. Less than 10% of the VAChT-labeled terminals were MOR-immunoreactive. In contrast, 35% of the cholinergic terminals formed symmetric or punctate synapses with dendrites showing an extrasynaptic plasmalemmal distribution of MOR. Membranes of tubulovesicles in other selective dendrites were also VAChT-labeled, and almost half of these dendrites displayed plasmalemmal MOR immunoreactivity. The VAChT-labeled dendritic tubulovesicles often apposed unlabeled axon terminals that formed symmetric synapses. Our results indicate that in the AcbSh MOR agonists can modulate the release of ACh from vesicular storage sites in axon terminals as well as in dendrites where the released ACh may serve an autoregulatory function involving inhibitory afferents. These results also suggest, however, that many of the dendrites of spiny projection neurons in the AcbSh are dually influenced by ACh and opiates active at MOR, thus providing a cellular substrate for ACh in the reinforcement of opiates.

Acetylcholine↗

PubMed2001

Targeting of serotonin 1A receptors to dopaminergic neurons within the parabrachial subdivision of the ventral tegmental area in rat brain.

Serotonin (5-hydroxytryptamine [5-HT]) modulates dopamine-related cognitive functions and motor activity through activation of selective receptor subtypes including 5-HT1A. Potential targets for these 5-HT1A-mediated actions of 5-HT include mesocortical and mesolimbic dopaminergic neurons having partially segregated distribution in the parabrachial and paranigral subdivisions of the ventral tegmental area (VTA), respectively. We therefore examined the ultrastructural immunocytochemical localization of the 5-HT1A receptor in the parabrachial (VTApb) and paranigral (VTApn) subdivisions of rat VTA, to determine 1) the functional sites for receptor activation, and 2) the cellular associations between this receptor and dopaminergic neurons identified by their tyrosine hydroxylase (TH) content. In each region, 5-HT1A immunoreactivity was mainly observed in somatodendritic profiles, but it was also present in small unmyelinated axons and in a few axon terminals and glia, suggesting a role for 5-HT1A receptors in presynaptic and glial functions, as well as postsynaptic neuronal activation, in VTA. In somatodendritic profiles, 5-HT1A gold particles were mainly localized to tubulovesicles presumed to be smooth endoplasmic reticulum. In addition, however, in distal dendrites receiving multiple inputs the receptor was targeted to selective postsynaptic junctions, or more randomly distributed on nonsynaptic portions of the plasma membrane. Of the 5-HT1A-labeled dendrites, 64% in VTApb and 44% in VTApn contained TH. These findings suggest a reserve of cytoplasmic 5-HT1A receptors that are mobilized to functional postsynaptic sites on the plasma membrane by afferent input to distal dendrites in the VTA. They also indicate that 5-HT1A activation may affect a larger population of dopaminergic neurons in VTApb compared with VTApn, thus having a potentially greater impact on cognitive functions modulated by mesocortical dopaminergic neurons.

Animals↗

PubMed2001

Preferential cytoplasmic localization of delta-opioid receptors in rat striatal patches: comparison with plasmalemmal mu-opioid receptors.

The activation of delta-opioid receptors (DORs) in the caudate-putamen nucleus (CPN) produces regionally distinct changes in motor functions, many of which are also influenced by opioids active at micro-opioid receptors (MORs). These actions most likely occur in MOR-enriched patch compartments in the CPN. To determine the functional sites for DOR activation and potential interactions involving MOR in these regions, immunoperoxidase and immunogold-silver labeling methods were applied reversibly for the ultrastructural localization of DOR and MOR in single rat brain sections containing patches of the CPN. DOR immunoreactivity was commonly seen within the cytoplasm of spiny and aspiny neurons, many of which also expressed MOR. In dendrites and spines, DOR labeling was preferentially localized to membranes of the smooth endoplasmic reticulum and spine apparatus, whereas MOR showed a prominent plasmalemmal distribution. DOR- and/or MOR-labeled spines received asymmetric, excitatory synapses, some of which showed notable perforations, suggesting the involvement of these receptors in activity-dependent synaptic plasticity. DORs were more frequently detected than were MORs within axon terminals that formed either asymmetric synapses with spine heads or symmetric synapses with spine necks. Our results suggest that in striatal patches, DORs, often in cooperation with MORs, play a direct modulatory role in controlling the postsynaptic excitability of spines, whereas presynaptic neurotransmitter release onto spines is mainly influenced by DOR activation. In comparison with MOR, the prevalent association of DOR with cytoplasmic organelles that are involved in intracellular trafficking of cell surface proteins suggests major differences in availability of these receptors to extracellular opioids.

Animals↗

PubMed2001

Subcellular localization of alpha-2A-adrenergic receptors in the rat medial nucleus tractus solitarius: regional targeting and relationship with catecholamine neurons.

alpha-2A-adrenergic receptor (alpha2A-AR) agonists modulate diverse autonomic functions. These actions are believed to involve functionally specialized, second-order neurons in catecholamine-containing portions of the medial nucleus tractus solitarius (mNTS) at both intermediate (NTSi) and caudal (NTSc) levels. However, the cellular mechanisms subserving alpha2A-AR-mediated actions within the mNTS have yet to be established. Immunocytochemistry was employed to examine the subcellular distribution of alpha2A-AR in both the intermediate and caudal mNTS and its association with cells containing the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Quantitative regional comparison using immunogold showed that this receptor was distributed differentially to dendrites (NTSi, 46%; NTSc, 31%) and glia (NTSi, 29%; NTSc, 48%) at different levels of the NTS. Somata, axons, and terminals less frequently contained alpha2A-AR. The subcellular distribution of alpha2A-AR relative to catecholaminergic neurons also was similar within both subregions. Approximately 50% of alpha2A-AR-labeled somata also contained TH. In somatic profiles, alpha2A-AR labeling was often found in the cytosol and in association with endoplasmic reticulum and Golgi complexes, sites of receptor synthesis and trafficking. Approximately 20% of alpha2A-AR-immunoreactive dendrites also contained TH, where the receptor was often found on extrasynaptic portions of the plasma membrane near unlabeled terminals, some of which made symmetric contacts. However, TH-labeled terminals and dendrites usually were detected in the neuropil at a short distance (<10 microm) from alpha2A-AR-labeled neurons. alpha2A-AR-labeled glia frequently apposed unlabeled dendrites and terminals and were often located near TH-immunoreactive dendrites. These results indicate that, within the mNTS, alpha2A-AR is involved in a variety of autonomic processes, including postsynaptic modulation of mostly noncatecholaminergic dendrites, as well as influencing glia functions.

Animals↗