1
|
Leroy F, Brann DH, Meira T, Siegelbaum SA. Input-Timing-Dependent Plasticity in the Hippocampal CA2 Region and Its Potential Role in Social Memory. Neuron 2017; 95:1089-1102.e5. [PMID: 28823730 DOI: 10.1016/j.neuron.2017.07.036] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Revised: 05/26/2017] [Accepted: 07/28/2017] [Indexed: 02/01/2023]
Abstract
Input-timing-dependent plasticity (ITDP) is a circuit-based synaptic learning rule by which paired activation of entorhinal cortical (EC) and Schaffer collateral (SC) inputs to hippocampal CA1 pyramidal neurons (PNs) produces a long-term enhancement of SC excitation. We now find that paired stimulation of EC and SC inputs also induces ITDP of SC excitation of CA2 PNs. However, whereas CA1 ITDP results from long-term depression of feedforward inhibition (iLTD) as a result of activation of CB1 endocannabinoid receptors on cholecystokinin-expressing interneurons, CA2 ITDP results from iLTD through activation of δ-opioid receptors on parvalbumin-expressing interneurons. Furthermore, whereas CA1 ITDP has been previously linked to enhanced specificity of contextual memory, we find that CA2 ITDP is associated with enhanced social memory. Thus, ITDP may provide a general synaptic learning rule for distinct forms of hippocampal-dependent memory mediated by distinct hippocampal regions.
Collapse
Affiliation(s)
- Felix Leroy
- Department of Neuroscience, Kavli Institute of Brain Science, Columbia University Medical Center, 1051 Riverside Drive, New York, NY, USA.
| | - David H Brann
- Department of Neuroscience, Kavli Institute of Brain Science, Columbia University Medical Center, 1051 Riverside Drive, New York, NY, USA
| | - Torcato Meira
- Department of Neuroscience, Kavli Institute of Brain Science, Columbia University Medical Center, 1051 Riverside Drive, New York, NY, USA; Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Braga, Portugal; ICVS/3B's, PT Government Associate Laboratory, Braga/Guimarães, Portugal
| | - Steven A Siegelbaum
- Department of Neuroscience, Kavli Institute of Brain Science, Columbia University Medical Center, 1051 Riverside Drive, New York, NY, USA.
| |
Collapse
|
2
|
Mazid S, Hall BS, Odell SC, Stafford K, Dyer AD, Van Kempen TA, Selegean J, McEwen BS, Waters EM, Milner TA. Sex differences in subcellular distribution of delta opioid receptors in the rat hippocampus in response to acute and chronic stress. Neurobiol Stress 2016; 5:37-53. [PMID: 27981195 PMCID: PMC5145913 DOI: 10.1016/j.ynstr.2016.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2016] [Revised: 10/18/2016] [Accepted: 11/07/2016] [Indexed: 02/06/2023] Open
Abstract
Drug addiction requires associative learning processes that critically involve hippocampal circuits, including the opioid system. We recently found that acute and chronic stress, important regulators of addictive processes, affect hippocampal opioid levels and mu opioid receptor trafficking in a sexually dimorphic manner. Here, we examined whether acute and chronic stress similarly alters the levels and trafficking of hippocampal delta opioid receptors (DORs). Immediately after acute immobilization stress (AIS) or one-day after chronic immobilization stress (CIS), the brains of adult female and male rats were perfusion-fixed with aldehydes. The CA3b region and the dentate hilus of the dorsal hippocampus were quantitatively analyzed by light microscopy using DOR immunoperoxidase or dual label electron microscopy for DOR using silver intensified immunogold particles (SIG) and GABA using immunoperoxidase. At baseline, females compared to males had more DORs near the plasmalemma of pyramidal cell dendrites and about 3 times more DOR-labeled CA3 dendritic spines contacted by mossy fibers. In AIS females, near-plasmalemmal DOR-SIGs decreased in GABAergic hilar dendrites. However, in AIS males, near-plasmalemmal DOR-SIGs increased in CA3 pyramidal cell and hilar GABAergic dendrites and the percentage of CA3 dendritic spines contacted by mossy fibers increased to about half that seen in unstressed females. Conversely, after CIS, near-plasmalemmal DOR-SIGs increased in hilar GABA-labeled dendrites of females whereas in males plasmalemmal DOR-SIGs decreased in CA3 pyramidal cell dendrites and near-plasmalemmal DOR-SIGs decreased hilar GABA-labeled dendrites. As CIS in females, but not males, redistributed DOR-SIGs near the plasmalemmal of hilar GABAergic dendrites, a subsequent experiment examined the acute affect of oxycodone on the redistribution of DOR-SIGs in a separate cohort of CIS females. Plasmalemmal DOR-SIGs were significantly elevated on hilar interneuron dendrites one-hour after oxycodone (3 mg/kg, I.P.) administration compared to saline administration in CIS females. These data indicate that DORs redistribute within CA3 pyramidal cells and dentate hilar GABAergic interneurons in a sexually dimorphic manner that would promote activation and drug related learning in males after AIS and in females after CIS. Females have more near-plasmalemmal DORs in pyramidal CA3 dendrites than males. Acute stress in males relocates DORs in CA3 & GABA dendrites to promote activation. Chronic stress in females relocates DORs in GABA dendrites in females to promote activation. Chronic stress in males relocates DORs in GABA dendrites opposite of females. DOR-stress relocation may contribute to sexually dimorphic effects on drug related learning.
Collapse
Affiliation(s)
- Sanoara Mazid
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States
| | - Baila S Hall
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States; Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, 1300 York Ave, New York, NY 10021, United States
| | - Shannon C Odell
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States; Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, 1300 York Ave, New York, NY 10021, United States
| | - Khalifa Stafford
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States
| | - Andreina D Dyer
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States
| | - Tracey A Van Kempen
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States; Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, 1300 York Ave, New York, NY 10021, United States
| | - Jane Selegean
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States
| | - Bruce S McEwen
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, United States
| | - Elizabeth M Waters
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, United States
| | - Teresa A Milner
- Feil Family Brain and Mind Research Institute, Weill Cornell Medicine, 407 East 61st Street, New York, NY 10065, United States; Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, 1300 York Ave, New York, NY 10021, United States; Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, United States
| |
Collapse
|
3
|
Bajic D, Van Bockstaele EJ, Proudfit HK. Ultrastructural analysis of rat ventrolateral periaqueductal gray projections to the A5 cell group. Neuroscience 2012; 224:145-59. [PMID: 22917613 DOI: 10.1016/j.neuroscience.2012.08.021] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2012] [Revised: 07/05/2012] [Accepted: 08/09/2012] [Indexed: 11/15/2022]
Abstract
Stimulation of neurons in the ventrolateral periaqueductal gray (PAG) produces antinociception as well as cardiovascular depressor responses that are mediated in part by pontine noradrenergic neurons. A previous report using light microscopy has described a pathway from neurons in the ventrolateral PAG to noradrenergic neurons in the A5 cell group that may mediate these effects. The present study used anterograde tracing and electron microscopic analysis to provide more definitive evidence that neurons in the ventrolateral PAG form synapses with noradrenergic and non-catecholaminergic A5 neurons in Sasco Sprague-Dawley rats. Deposits of anterograde tracer, biotinylated dextran amine, into the rat ventrolateral PAG labeled a significant number of axons in the region of the rostral subdivision of the A5 cell group, and a relatively lower number in the caudal A5 cell group. Electron microscopic analysis of anterogradely-labeled terminals in both rostral (n=127) and caudal (n=70) regions of the A5 cell group indicated that approximately 10% of these form synapses with noradrenergic dendrites. In rostral sections, about 31% of these were symmetric synapses, 19% were asymmetric synapses, and 50% were membrane appositions without clear synaptic specializations. In caudal sections, about 22% were symmetric synapses, and the remaining 78% were appositions. In both rostral and caudal subdivisions of the A5, nearly 40% of the anterogradely-labeled terminals formed synapses with non-catecholaminergic dendrites, and about 45% formed axoaxonic synapses. These results provide direct evidence for a monosynaptic pathway from neurons in the ventrolateral PAG to noradrenergic and non-catecholaminergic neurons in the A5 cell group. Further studies should evaluate if this established monosynaptic pathway may contribute to the cardiovascular depressor effects or the analgesia produced by the activation of neurons in the ventrolateral PAG.
Collapse
Affiliation(s)
- D Bajic
- Department of Pharmacology, University of Illinois at Chicago, 835 S. Wolcott Avenue, Chicago, IL 60612, USA.
| | | | | |
Collapse
|
4
|
Williams TJ, Mitterling KL, Thompson LI, Torres-Reveron A, Waters EM, McEwen BS, Gore AC, Milner TA. Age- and hormone-regulation of opioid peptides and synaptic proteins in the rat dorsal hippocampal formation. Brain Res 2010; 1379:71-85. [PMID: 20828542 DOI: 10.1016/j.brainres.2010.08.103] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Revised: 08/13/2010] [Accepted: 08/31/2010] [Indexed: 02/05/2023]
Abstract
Circulating estrogen levels and hippocampal-dependent cognitive functions decline with aging. Moreover, the responses of hippocampal synaptic structure to estrogens differ between aged and young rats. We recently reported that estrogens increase levels of post-synaptic proteins, including PSD-95, and opioid peptides leu-enkephalin and dynorphin in the hippocampus of young animals. However, the influence of ovarian hormones on synaptic protein and opioid peptide levels in the aging hippocampus is understudied. Here, young (3- to 5-month-old), middle-aged (9- to 12-month-old), and aged (about 22-month-old) female rats were ovariectomized and then, 4 weeks later, subcutaneously implanted with a silastic capsule containing vehicle or 17β-estradiol. After 48 h, rats were subcutaneously injected with progesterone or vehicle and sacrificed 1 day later. Coronal sections through the dorsal hippocampus were processed for quantitative peroxidase immunohistochemistry of leu-enkephalin, dynorphin, synaptophysin, and PSD-95. With age, females showed opposing changes in leu-enkephalin and dynorphin levels in the mossy fiber pathway, particularly within the hilus, and regionally specific changes in synaptic protein levels. 17β-estradiol, with or without progesterone, altered leu-enkephalin levels in the dentate gyrus and synaptophysin levels in the CA1 of young but not middle-aged or aged females. Additionally, 17β-estradiol decreased synaptophysin levels in the CA3 of middle-aged females. Our results support and extend previous findings indicating 17β-estradiol modulation of hippocampal opioid peptides and synaptic proteins while demonstrating regional and age-specific effects. Moreover, they lend credence to the "window of opportunity" hypothesis during which hormone replacement can modulate hippocampal structure and circuitry to improve cognitive outcomes.
Collapse
Affiliation(s)
- Tanya J Williams
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Cornell Medical College, New York, NY 10065, USA.
| | | | | | | | | | | | | | | |
Collapse
|
5
|
Torres-Reveron A, Williams TJ, Chapleau JD, Waters EM, McEwen BS, Drake CT, Milner TA. Ovarian steroids alter mu opioid receptor trafficking in hippocampal parvalbumin GABAergic interneurons. Exp Neurol 2009; 219:319-27. [PMID: 19505458 DOI: 10.1016/j.expneurol.2009.06.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2009] [Accepted: 06/01/2009] [Indexed: 10/20/2022]
Abstract
The endogenous hippocampal opioid systems are implicated in learning associated with drug use. Recently, we showed that ovarian hormones regulate enkephalin levels in the mossy fiber pathway. This pathway overlaps with parvalbumin (PARV)-basket interneurons that contain the enkephalin-activated mu opioid receptors (MORs) and are important for controlling the "temporal timing" of granule cells. Here, we evaluated the influence of ovarian steroids on the trafficking of MORs in PARV interneurons. Two groups of female rats were analyzed: cycling rats in proestrus (relatively high estrogens) or diestrus; and ovariectomized rats euthanized 6, 24 or 72 h after estradiol benzoate (10 microg, s.c.) administration. Dorsal hippocampal sections were dually immunolabeled for MOR and PARV and examined by light and electron microscopy. As in males, in females MOR-immunoreactivity (-ir) was in numerous PARV-labeled perikarya, dendrites and terminals in the dentate hilar region. Variation in ovarian steroid levels altered the subcellular distribution of MORs in PARV-labeled dendrites but not terminals. In normal cycling rats, MOR-gold particles on the plasma membrane of small PARV-labeled dendrites (area <1 microm2) had higher density in proestrus rats than in diestrus rats. Likewise, in ovariectomized rats MORs showed higher density on the plasma membrane of small PARV-labeled dendrites 72 h after estradiol exposure. The number of PARV-labeled cells was not affected by estrous cycle phase or estrogen levels. These results demonstrate that estrogen levels positively regulate the availability of MORs on GABAergic interneurons in the dentate gyrus, suggesting cooperative interaction between opioids and estrogens in modulating principal cell excitability.
Collapse
Affiliation(s)
- Annelyn Torres-Reveron
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Cornell Medical College, 407 East 61st Street, New York, NY 10065, USA.
| | | | | | | | | | | | | |
Collapse
|
6
|
Ovarian steroids modulate leu-enkephalin levels and target leu-enkephalinergic profiles in the female hippocampal mossy fiber pathway. Brain Res 2008; 1232:70-84. [PMID: 18691558 DOI: 10.1016/j.brainres.2008.07.058] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2008] [Revised: 07/11/2008] [Accepted: 07/15/2008] [Indexed: 02/05/2023]
Abstract
In the hippocampal formation (HF), the enkephalin opioids and estrogen are each known to modulate learning and cognitive performance relevant to drug abuse. Within the HF, leu-enkephalin (LENK) is most prominent in the mossy fiber (MF) pathway formed by the axons of dentate gyrus (DG) granule cells. To examine the influence of ovarian steroids on MF pathway LENK levels, we used quantitative light microscopic immunocytochemistry to evaluate LENK levels in normal cycling rats and in estrogen-treated ovariectomized rats. Rats in estrus had increased levels of LENK-immunoreactivity (ir) in the DG hilus compared to rats in diestrus or proestrus. Rats in estrus and proestrus had higher levels of LENK-ir in CA3a-c compared to rats in diestrus. Ovariectomized (OVX) rats 24 h (but not 6 or 72 h) after estradiol benzoate (EB; 10 microg) administration had increased LENK-ir in the DG hilus and CA3c. Electron microscopy showed a larger proportion of LENK-labeled small terminals and axons in the DG hilus compared to CA3 which may have contributed to region-specific changes in LENK-ir densities. Next we evaluated the subcellular relationships of estrogen receptor (ER) alpha, ERbeta and progestin receptor (PR) with LENK-labeled MF pathway profiles using dual-labeling electron microscopy. ERbeta-ir colocalized in some LENK-labeled MF terminals and smaller terminals while PR-ir was mostly in CA3 axons, some of which also showed colocalization with LENK. ERalpha-ir was in dendritic spines, but no colocalization with LENK-labeled profiles was observed. The present studies indicate that estrogen can modulate LENK in subregions of the MF pathway in a dose-and time-dependent manner. These effects might be triggered by direct activation of ERbeta or PR in LENK-containing terminals.
Collapse
|
7
|
Blaabjerg M, Zimmer J. The dentate mossy fibers: structural organization, development and plasticity. PROGRESS IN BRAIN RESEARCH 2007; 163:85-107. [PMID: 17765713 DOI: 10.1016/s0079-6123(07)63005-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Hippocampal mossy fibers are the axons of the dentate granule cells and project to hippocampal CA3 pyramidal cells and mossy cells of the dentate hilus (CA4) as well as a number of interneurons in the two areas. Besides their role in hippocampal function, studies of which are still evolving and taking interesting turns, the mossy fibers display a number of unique features with regard to axonal projections, terminal structures and synaptic contacts, development and variations among species and strains, as well as to normal occurring and lesion-induced plasticity and neural transplantation. These features are the topic of this review, which will use the mossy fiber system of the rat as basis and reference in its aim to provide an up-to-date, yet historically based guide to students in the field.
Collapse
Affiliation(s)
- Morten Blaabjerg
- Anatomy and Neurobiology, Institute of Medical Biology, University of Southern Denmark, Winslowparken 21, DK-5000 Odense C, Denmark
| | | |
Collapse
|
8
|
Abstract
Opiate drugs alter cognitive performance and influence hippocampal excitability, including long-term potentiation (LTP) and seizure activity. The dentate gyrus (DG) contains two major opioid peptides, enkephalins and dynorphins, which have opposing effects on excitability. Enkephalins preferentially bind to delta- and mu-opioid receptors (DORs and MORs) while dynorphins preferentially bind to kappa-opioid receptors (KORs). Opioid receptors can also be activated by exogenous opiate drugs such as the MOR agonist morphine. Enkephalins are contained in the mossy fiber pathway, in the lateral perforant path (PP) and in scattered GABAergic interneurons. MORs and DORs are predominantly in distinct subpopulations of GABAergic interneurons known to inhibit granule cells, and are present at low levels within granule cells. MOR and DOR agonists increase excitability and facilitate LTP in the molecular layer. Anatomical and physiological evidence is consistent with somatodendritic and axon terminal targeting of both MORs and DORs. Dynorphins are in the granule cells, most abundantly in mossy fibers but also in dendrites. KORs have been localized to granule cell mossy fibers, supramammillary afferents to granule cells, and PP terminals. KOR agonists, including endogenous dynorphins, diminish the induction of LTP. Recent evidence indicates that opiates and opioids also modulate other processes in the hippocampal formation, including adult neurogenesis, the actions of gonadal hormones, and development of neonatal transmitter systems.
Collapse
Affiliation(s)
- Carrie T Drake
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill-Cornell Medical College, 411 East 69th Street, New York, NY 10021, USA
| | | | | |
Collapse
|
9
|
Hebb ALO, Drolet G, Mendella PD, Roach SP, Gauthier MS, Zacharko RM. Intracerebroventricular d-Pen2, d-Pen5-enkephalin administration soon after stressor imposition influences behavioral responsivity to a subsequent stressor encounter in CD-1 mice. Pharmacol Biochem Behav 2005; 82:453-69. [PMID: 16290012 DOI: 10.1016/j.pbb.2005.10.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2005] [Revised: 09/21/2005] [Accepted: 10/04/2005] [Indexed: 11/25/2022]
Abstract
Endogenous opioid peptide systems diminish stress-induced autonomic nervous system, neuroendocrine (hypothalamic-pituitary-adrenal axis) and behavioral responses, attenuating a collection of physiological symptoms basic to emotional and affective states. Neurogenic stressors may incite specific central changes in opioid peptide availability as well as changes in mu and delta-opioid receptor function. The present investigation evaluated the proactive influence of an intracerebroventricular injection of the opioid receptor agonist D-Pen2, D-Pen5-enkephalin (DPDPE) (0 microg, 0.005 microg, 1.0 microg or 2.5 microg) on locomotor behavior of mice following uncontrollable footshock (Shock) or novel shock chamber exposure (No Shock). It was expected that DPDPE administration following Shock on Day 1 would restore locomotor activity up to 1 week and prevent shock-associated behavior of mice encountering a brief session of footshock 18 days later. Exposure to Shock reduced horizontal locomotor and vertical locomotor (rearing) activity of mice while 2.5 microg DPDPE restored behavior. Eighteen days following Shock and DPDPE challenge, mice were exposed to either an abbreviated session of footshock (Mild Stress) or the shock chamber (Cues). Mice in the No Shock and Shock groups administered 2.5 microg DPDPE on Day 1 did not exhibit any locomotor deficits in response to Mild Stress on Day 18. Mice in the Shock group administered 0.005 microg DPDPE on Day 1, did not exhibit exaggerated rearing deficits following ensuing Mild Stressor encounter relative to mice reexposed to Cues on Day 18. Taken together, these data show that (a) footshock differentially affects rearing and locomotor activity, (b) DPDPE administration increases locomotor activity for up to 1 week following footshock and DPDPE administration, (c) reexposure to Mild Stress affects rearing and locomotor performance differently depending on previous stressor history and DPDPE dose, (d) DPDPE affords long-lasting protection to previously non-stressed mice against the deleterious effects of subsequent mild stress on locomotor activity, while a low dose of DPDE is sufficient to prevent shock-induced sensitization of rearing deficits, 18 days following original stressor and drug presentation. Finally, our investigation demonstrates that DPDPE administration alters the behavioral impact of future stressful encounters and emphasizes the importance of investigating opioid mechanisms in chronic stress disorders.
Collapse
Affiliation(s)
- Andrea L O Hebb
- Laboratory of Molecular Neurobiology, Dalhousie University, Halifax, NS, Canada.
| | | | | | | | | | | |
Collapse
|
10
|
Zhao H, Xu H, Xu X. Effects of naloxone on the long-term potentiation of EPSPs from the pathway of Schaffer collateral to CA1 region of hippocampus in aged rats with declined memory. Brain Res 2004; 996:111-6. [PMID: 14670637 DOI: 10.1016/j.brainres.2003.10.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Morris water maze (MWM) was employed to distinguish the aged rats with declined memory to investigate the effect of naloxone on the synaptic plasticity of hippocampus in declined memory aged rats. After administration with naloxone for 7 days, LTP of excitatory post-synaptic potentials (EPSPs) from Schaffer collateral to CA1 region was recorded. The results showed that the maintenance of LTP of EPSPs from Schaffer collateral to CA1 subfield in isolate hippocampal brain slice was prolonged by naloxone with improved Morris water maze performance and reduced threshold of EPSPs. It is suggested that naloxone can improve learning and memory through enhancement of the synaptic plasticity of hippocampus in aged rats with declined memory.
Collapse
Affiliation(s)
- Hu Zhao
- Department of Forensic Medicine, Medical College, Shantou University, 22 Rd. Xinlin, Shantou, 515031, Guangdong, PR China.
| | | | | |
Collapse
|
11
|
Drake CT, Milner TA. Mu opioid receptors are in discrete hippocampal interneuron subpopulations. Hippocampus 2002; 12:119-36. [PMID: 12000113 DOI: 10.1002/hipo.1107] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the rat hippocampal formation, application of mu opioid receptor (MOR) agonists disinhibits principal cells, promoting excitation-dependent processes such as epileptogenesis and long-term potentiation. However, the precise location of MORs in particular inhibitory circuits, has not been determined, and the roles of MORs in endogenous functioning are unclear. To address these issues, the distribution of MOR-like immunoreactivity (-li) was examined in several populations of inhibitory hippocampal neurons in the CA1 region using light and electron microscopy. We found that MOR-li was present in many parvalbumin-containing basket cells, but absent from cholecystokinin-labeled basket cells. MOR-li was also commonly in interneurons containing somatostatin-li or neuropeptide Y-li that resembled the "oriens-lacunosum-moleculare" (O-LM) interneurons innervating pyramidal cell distal dendrites. Finally, MOR-li was in some vasoactive intestinal peptide- or calretinin-containing profiles resembling interneurons that primarily innervate other interneurons. These findings indicate that MOR-containing neurons form a neurochemically and functionally heterogeneous subset of hippocampal GABAergic neurons. MORs are most frequently on interneurons that are specialized to inhibit pyramidal cells, and are on a limited number of interneurons that target other interneurons. Moreover, the distribution of MORs to different neuronal types in several laminae, some relatively far from endogenous opioids, suggests normal functional roles that are different from the actions seen with exogenous agonists such as morphine.
Collapse
Affiliation(s)
- Carrie T Drake
- Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA.
| | | |
Collapse
|
12
|
Kozicz T. Met-enkephalin immunoreactive neurons recruited by acute stress are innervated by axon terminals immunopositive for tyrosine hydroxylase and dopamine-alpha-hydroxylase in the anterolateral division of bed nuclei of the stria terminalis in the rat. Eur J Neurosci 2002; 16:823-35. [PMID: 12372018 DOI: 10.1046/j.1460-9568.2002.02129.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The bed nuclei of the stria terminalis (BST) are highly heterogeneous forebrain structures, which play a central role in the regulation/modulation of stress responses. Studies using the inducible immediate early gene c-fos as a marker of activated neurons have demonstrated significant stress-induced neuronal activation in this limbic region. The BST also exhibit a dense network of dopamine and noradrenaline immunoreactive (ir) axon terminals. These catecholaminergic projections from various brainstem sources to the BST play an important role in a neurochemically mediated coordination of stress responses. In the anterolateral division of bed nuclei of the stria terminalis, the distribution of several Met-enkephalin immunopositive perikarya overlaps with that of catecholaminergic axon terminals. Both monoaminergic and enkephalinergic structures have been postulated to play a role in the regulation/modulation of the central regulatory pathways of endocrine, behavioural and physiological responses during stress. Therefore the aims of this study were: (i). to study the possible involvement of dopaminergic fibre terminals in stress-induced activation of BST perikarya; (ii). to investigate whether Met-enkephalin-immunoreactive neurons are recruited by acute volumen/osmotic challenge; and (iii). to demonstrate synaptic interactions between Met-enkephalin-ir neurons and fibre terminals immunopositive for dopamine or noradrenaline in the anterolateral division of the BST. From the results of this study we can conclude that depletion of dopamine in fibre terminals completely abolished stress-induced activation of perikarya in the anterolateral division of BST. Furthermore, the innervation of stress-induced Met-enkephalin-ir perikarya by dopaminergic fibre terminals in the oval nucleus of BST was demonstrated, whereas noradrenergic axons contacted enkephalinergic structures in the fusiform and subcomissural nuclei of BST. These interactions can be central in the modulatory control of the major stress regulatory pathway, the limbic hypothalamo-pituitary-adrenal axis.
Collapse
Affiliation(s)
- Tamás Kozicz
- University of Pécs, Medical Faculty, Department of Human Anatomy, Pécs, Szigeti ut 12., H-7624, Hungary.
| |
Collapse
|
13
|
Drake CT, Chang PC, Harris JA, Milner TA. Neurons with mu opioid receptors interact indirectly with enkephalin-containing neurons in the rat dentate gyrus. Exp Neurol 2002; 176:254-61. [PMID: 12093103 DOI: 10.1006/exnr.2002.7948] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the dentate gyrus, mu opioid receptors (MORs) and their enkephalin agonists have overlapping distributions and influence excitability and plasticity. Released endogenous enkephalins can activate at least some of these MORs; however, whether these interactions involve synaptically associated profiles or more distant associations and whether some subcellular compartments (e.g., terminals or dendrites) are more likely to be targeted than others are not known. To elucidate the relationships between potential sites of enkephalin release and MORs, MOR1 and leucine-enkephalin (LE) immunoreactivities were localized in the hilus by electron microscopy, using immunoperoxidase and immunogold markers. Of the 573 MOR-immunoreactive (ir) profiles analyzed, most were axons and terminals (51 and 30%, respectively), and fewer were dendrites (12%), glia (3%), or unclassifiable (4%). Most MOR-ir profiles resembled interneuron processes, while most LE-ir terminals resembled mossy fibers. One third of MOR-ir profiles were within 3 microm and approximately half were within 4 microm of the nearest LE-ir profile. In contrast, few (3%) MOR-ir profiles contacted LE-ir profiles; only 16% of these contacts included observable synapses, and very few profiles (0.5%) colocalized MOR and LE immunoreactivity. MOR-ir axons, terminals, and dendrites were not distributed differently relative to LE-ir profiles. These results suggest that activation of hilar MORs by LE usually involves short-range volume transmission and that dendritic MORs are as likely as axonal and terminal MORs to be activated by released LE. However, the greater abundance of MOR-ir axons and terminals compared to dendrites indicates that presynaptic profiles are a more prominent target for enkephalins and exogenous MOR agonists such as morphine.
Collapse
Affiliation(s)
- C T Drake
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, 411 East 69th Street, New York, New York 10021, USA
| | | | | | | |
Collapse
|
14
|
Rácz B, Halasy K. Kappa opioid receptor is expressed by somatostatin- and neuropeptide Y-containing interneurons in the rat hippocampus. Brain Res 2002; 931:50-5. [PMID: 11897088 DOI: 10.1016/s0006-8993(02)02259-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In our previous studies (J. Chem. Neuroanat. 2000;19:233-241), kappa opioid receptors were immunocytochemically identified in inhibitory interneurons of the dentate hilus and CA1 area of the rat hippocampus. From among the known interneuron subtypes, somatostatin- (SOM) and neuropeptide Y- (NPY) immunoreactive (IR) hippocampal interneurons show morphology and distribution similar to the kappa opioid receptor (KOR) immunopositive cells. In the present study, with the help of double immunocytochemical labelling, we provide direct evidence that the majority of the interneurons immunoreactive for SOM and/or NPY also express the kappa opioid receptor. The receptor was localized on the perikaryal and proximal dendritic region of the SOM- and NPY-immunopositive neurons in the dentate hilus and the CA1 region. From among the SOM-immunoreactive cells, 77% in the dentate hilus and 51% in the CA1 stratum oriens was double labelled. In the case of NPY-immunoreactive neurons this proportion was 56 and 65%, respectively. The co-expression of KOR and SOM/NPY suggests that hippocampal interneurons can selectively be activated by the different opioids under different physiological circumstances.
Collapse
Affiliation(s)
- Bence Rácz
- Department of Anatomy and Histology, Faculty of Veterinary Science, Szent István University, István u. 2, H-1078, Budapest, Hungary.
| | | |
Collapse
|
15
|
Bajic D, Van Bockstaele EJ, Proudfit HK. Ultrastructural analysis of ventrolateral periaqueductal gray projections to the A7 catecholamine cell group. Neuroscience 2001; 104:181-97. [PMID: 11311541 DOI: 10.1016/s0306-4522(01)00052-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Stimulation of neurons in the ventrolateral periaqueductal gray produces antinociception that is mediated in part by pontine noradrenergic neurons. Previous light microscopic analysis provided suggestive evidence for a direct projection from neurons in the ventrolateral periaqueductal gray to noradrenergic neurons in the A7 cell group that innervate the spinal cord dorsal horn. Therefore, the present ultrastructural study used anterograde tracing combined with tyrosine hydroxylase immunoreactivity to provide definitive evidence that neurons in the ventrolateral periaqueductal gray form synapses with the somata and dendrites of noradrenergic neurons of the A7 cell group. Injections of the anterograde tracers biotinylated dextran amine or Phaseolus vulgaris leucoagglutinin into the ventrolateral periaqueductal gray of Sasco Sprague-Dawley rats yielded a dense innervation in the region of the lateral pons containing the A7 cell group. Electron microscopic analysis of anterogradely labeled terminals (n=401) in the region of the A7 cell group indicated that approximately 10% of these formed plasmalemmal appositions to tyrosine hydroxylase-immunoreactive dendrites with no intervening astrocytic processes. About 23% of these were asymmetric synapses, 10% were symmetric synapses, and 67% did not exhibit clearly differentiated synaptic specializations. The majority of anterogradely labeled terminals (60%) formed plasmalemmal appositions with dendrites and somata that lacked detectable tyrosine hydroxylase immunoreactivity. About 35% of these were symmetric synapses, 9% were asymmetric synapses and 56% did not form synaptic specializations. Approximately 30% of all anterogradely labeled terminals displayed features characteristic of axo-axonic synapses.The present results provide direct ultrastructural evidence to support the hypothesis that the analgesia produced by stimulation of neurons in the ventrolateral periaqueductal gray is mediated, in part, by activation of spinally projecting noradrenergic neurons in the A7 catecholamine cell group.
Collapse
Affiliation(s)
- D Bajic
- Department of Pharmacology, University of Illinois at Chicago, 835 S. Wolcott Avenue, Chicago, IL 60612, USA
| | | | | |
Collapse
|
16
|
Abstract
Brain functions are based on the dynamic interaction of excitatory and inhibitory inputs. Spillover of glutamate from excitatory synapses may diffuse to and modulate nearby inhibitory synapses. By recording unitary inhibitory postsynaptic currents (uIPSCs) from cell pairs in CA1 of the hippocampus, we demonstrated that low concentrations of Kainate receptor (KAR) agonists increased the success rate (P(s)) of uIPSCs, whereas high concentrations of KAR agonists depressed GABAergic synapses. Ambient glutamate released by basal activities or stimulation of the stratum radiatum increases the efficacy of GABAergic synapses by activating presynaptic KARs, which facilitate Ca(2+)-dependent GABA release. The results suggest that glutamate released from excitatory synapses may also function as an intermediary between excitatory and inhibitory synapses to protect overexcitation of local circuits.
Collapse
Affiliation(s)
- L Jiang
- Department of Cell Biology and Anatomy, New York Medical College, Basic Science Building, Room 220, Valhalla, NY 10595, USA
| | | | | | | |
Collapse
|
17
|
Abstract
Seizure induction tends to be followed by the development of a predisposition to future seizure activity and the concurrent sprouting of the mossy fiber pathway into the inner molecular layer of the dentate gyrus, where recurrent excitatory synapses are formed. To determine whether synaptic remodeling of mossy fiber terminals within the hilus also occurs, rats were administered pentylenetetrazol and, 2 days later, control and experimental tissue was processed for the ultrastructural immunohistochemical identification of mossy fiber terminals. Examination of the structure of these terminals within random hilar fields indicated that selective changes had occurred, which were only observed in the ventral hilus, and which were specific to terminals forming synapses with mossy cell spines (vs. interneurons). This terminal population displayed significant parallel increases in both the total active zone area and the surface area of an average terminal (measured from random two-dimensional samples of terminal structure). Increases in total active zone area must reflect increases in the number and/or size of individual active zones. These findings suggest that changes in terminal size can subserve adjustments in the overall strength of a set of synaptic connections. In the context of the ventral hilus, a selective increase in the apparent strength of mossy fiber connections with mossy cells could support increases in excitability following seizure induction. Mossy cells form connections with granule cell proximal dendrites, providing another pathway for recurrent excitation.
Collapse
Affiliation(s)
- J P Pierce
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA.
| | | |
Collapse
|
18
|
Milner TA, Drake CT. Ultrastructural evidence for presynaptic mu opioid receptor modulation of synaptic plasticity in NMDA-receptor-containing dendrites in the dentate gyrus. Brain Res Bull 2001; 54:131-40. [PMID: 11275401 DOI: 10.1016/s0361-9230(00)00415-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Physiological studies have demonstrated that long-term potentiation (LTP) induction in N-methyl-D-aspartate (NMDA) receptor containing dentate granule cells following lateral perforant path stimulation is opioid dependent, involving mu-opioid receptors (MORs) on gamma-aminobutyric acid (GABA)-ergic neurons. To determine the cellular relationships of MORs to postsynaptic NMDA receptor-containing dendrites, immunoreactivity (-I) against MOR and the NMDA receptor subunit 1 (NMDAR1) was examined in the outer molecular layer of the dentate gyrus using electron microscopy. MOR-I was predominantly in axons and axon terminals. NMDAR1-I was almost exclusively in spiny dendrites, but was also in a few terminals. Using immunogold particles to localize precisely NMDAR1, one-third of the NMDAR1-I was detected on the dendritic plasmalemma; in dendritic spines plasmalemmal immunogold particles were near synaptic densities. Many MOR-labeled axons and terminals contacted NMDAR1-labeled dendrites. MOR-labeled terminals formed symmetric (inhibitory-type) synapses on NMDAR1-labeled dendritic shafts or nonsynaptically contacted NMDAR1-labeled shafts and spines. MOR-labeled axons often abutted NMDAR1-containing dendritic spines which received asymmetric (excitatory-type) synapses from unlabeled terminals. Occasionally, MOR-labeled terminals and dendrites were apposed to NMDAR1-containing terminals. These results provide anatomical evidence that endogenous enkephalins or exogenous opioid agonists could inhibit GABAergic terminals that modulate granule cell dendrites, thus boosting depolarizing events in granule cells and facilitating the activation of NMDA receptors located on their dendrites.
Collapse
MESH Headings
- Animals
- Dendrites/chemistry
- Dendrites/ultrastructure
- Dentate Gyrus/chemistry
- Dentate Gyrus/ultrastructure
- Interneurons/chemistry
- Interneurons/ultrastructure
- Male
- Microscopy, Electron
- Neuronal Plasticity
- Presynaptic Terminals/chemistry
- Presynaptic Terminals/ultrastructure
- Rats
- Rats, Sprague-Dawley
- Receptors, N-Methyl-D-Aspartate/chemistry
- Receptors, N-Methyl-D-Aspartate/ultrastructure
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/physiology
- Receptors, Opioid, mu/ultrastructure
Collapse
Affiliation(s)
- T A Milner
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY 10021, USA.
| | | |
Collapse
|
19
|
Commons KG, Pfaff DW. Ultrastructural evidence for enkephalin mediated disinhibition in the ventromedial nucleus of the hypothalamus. J Chem Neuroanat 2001; 21:53-62. [PMID: 11173220 DOI: 10.1016/s0891-0618(00)00093-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The ventromedial nucleus of the hypothalamus (VMN) regulates the estrogen-dependent appearance of female mating behavior, lordosis. Accumulating evidence suggests that estrogen might exert its control over lordosis by acting, in part, on neurons that contain enkephalin in the VMN. The expression of the enkephalin precursor gene is robustly stimulated by estrogen and is correlated with the later appearance of lordosis. GABA has also been implicated as an important neurotransmitter for the appearance of lordosis. Because enkephalin is thought to act in several brain areas to modulate the activity of GABAergic neurons, we studied the ultrastructural morphology and relationship between neurons containing these neurochemicals using dual-labeling immunocytochemistry in ovariectornized rats, half of which received estrogen replacement. Immunolabeling for enkephalin was almost always detected within axon terminals (695 axonal profiles sampled), while GABA immunoreactivity was more often localized to cell bodies and dendrites (191 profiles), than to axons (63 profiles). Axon terminals containing enkephalin immunolabeling provided a major innervation to soma or dendrites containing GABA. That is, over one third (94/245) of the axon terminals in contact with GABA-immunoreactive dendrites contained enkephalin. Furthermore, these GABA-immunoreactive dendrites accounted for a fifth of the somatodendritic processes associated with enkephalin-containing axon terminals. These findings support the hypothesis that enkephalin may act in the VMN by inhibiting GABAergic neurons, which could result in the disinhibition of neural circuits relevant for lordosis.
Collapse
Affiliation(s)
- K G Commons
- Laboratory of Neurobiology and Behavior, The Rockefeller University, 1230 York Avenue, Box 275, New York, NY 10012, USA.
| | | |
Collapse
|
20
|
Bajic D, Proudfit HK, Van Bockstaele EJ. Periaqueductal gray neurons monosynaptically innervate extranuclear noradrenergic dendrites in the rat pericoerulear region. J Comp Neurol 2000; 427:649-62. [PMID: 11056470 DOI: 10.1002/1096-9861(20001127)427:4<649::aid-cne11>3.0.co;2-m] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Previous reports using light microscopy have provided anatomical evidence that neurons in the ventrolateral periaqueductal gray (PAG) innervate the medial pericoerulear dendrites of noradrenergic neurons in the nucleus locus coeruleus (LC). The present study used anterograde tracing and electron microscopic analysis to provide more definitive evidence that neurons in the ventrolateral PAG form synapses with the somata or dendrites of noradrenergic LC neurons. Deposits of either biotinylated dextran amine or Phaseolus vulgaris leucoagglutinin into the rat ventrolateral PAG labeled a moderate to high number of axons in the region of the medial pericoerulear region and Barrington's nucleus, but a relatively low number were labeled in the nuclear core of the LC. Ultrastructural analysis of anterogradely labeled terminals at the levels of the rostral (n = 233) and caudal (n = 272) subdivisions of the LC indicated that approximately 20% of these form synapses with tyrosine hydroxylase-immunoreactive dendrites; most of these were located in the medial pericoerulear region. In rostral sections, about 12% of these were symmetric synapses, 9% were asymmetric synapses, and 79% were membrane appositions without clear synaptic specializations. In caudal sections, about 30% were symmetric synapses, 11% were asymmetric synapses, and 59% were appositions. In both rostral and caudal sections, 60% of the anterogradely labeled terminals formed synapses with noncatecholamine dendrites, and 20% formed axoaxonic synapses. These results provide direct evidence for monosynaptic projections from neurons in the ventrolateral PAG to the extranuclear dendrites of noradrenergic LC neurons. This monosynaptic pathway may mediate in part the analgesia, reduced responsiveness to external stimuli, and decreased excitability of somatic motoneurons produced by stimulation of neurons in the ventrolateral PAG.
Collapse
Affiliation(s)
- D Bajic
- Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois 60612, USA
| | | | | |
Collapse
|
21
|
Abstract
The hippocampal mossy fiber pathway between the granule cells of the dentate gyrus and the pyramidal cells of area CA3 has been the target of numerous scientific studies. Initially, attention was focused on the mossy fiber to CA3 pyramidal cell synapse because it was suggested to be a model synapse for studying the basic properties of synaptic transmission in the CNS. However, the accumulated body of research suggests that the mossy fiber synapse is rather unique in that it has many distinct features not usually observed in cortical synapses. In this review, we have attempted to summarize the many unique features of this hippocampal pathway. We also have attempted to reconcile some discrepancies that exist in the literature concerning the pharmacology, physiology and plasticity of this pathway. In addition we also point out some of the experimental challenges that make electrophysiological study of this pathway so difficult.Finally, we suggest that understanding the functional role of the hippocampal mossy fiber pathway may lie in an appreciation of its variety of unique properties that make it a strong yet broadly modulated synaptic input to postsynaptic targets in the hilus of the dentate gyrus and area CA3 of the hippocampal formation.
Collapse
Affiliation(s)
- D A Henze
- Department of Neuroscience and Center for Neural Basis of Cognition, University of Pittsburgh, PA 15260, USA
| | | | | |
Collapse
|
22
|
Drake CT, Milner TA. Mu opioid receptors are in somatodendritic and axonal compartments of GABAergic neurons in rat hippocampal formation. Brain Res 1999; 849:203-15. [PMID: 10592303 DOI: 10.1016/s0006-8993(99)01910-1] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Activation of mu opioid receptors (MORs) has a net excitatory effect in the hippocampal formation through inhibition of gamma-amino butyric acid (GABA)-containing interneurons. To determine the precise subcellular targets of MOR agonists, immunoreactivity against MOR1 and GABA was examined in single sections of the hippocampal formation prepared for dual-labeling electron microscopy. In both the CA1 region of hippocampus and the dentate gyrus, MOR-like immunoreactivity (-li) was present in neuronal somata, dendrites, axons, and axon terminals, as well as a very few glial processes. Axon terminals with MOR-li formed symmetric synapses with principal cell dendrites and somata. Many MOR-labeled profiles of all types also contained GABA-li, and the vast majority possessed the ultrastructural characteristics of interneurons. Additionally, in the dentate gyrus a very small proportion of granule cell dendrites contained MOR-li. MOR-li, identified using immunogold-silver particles, was often affiliated with the extrasynaptic regions of neuronal plasma membranes, consistent with responsiveness to diffusing endogenous neuropeptide ligands. Semiquantitative analysis of the distribution of MOR-li revealed significantly more "presynaptic" (axons and terminals) than "postsynaptic" (somata and dendrites) labeled profiles in most laminae. We conclude that in addition to previously described somatodendritic MOR-li, a substantial amount of MOR-li in hippocampal formation is presynaptic. Furthermore, MORs are almost exclusively in GABAergic interneurons.
Collapse
Affiliation(s)
- C T Drake
- Department of Neurology, Division of Neurobiology, Weill Medical College of Cornell University, 411 East 69th Street, New York, NY, USA.
| | | |
Collapse
|
23
|
Jin W, Chavkin C. Mu opioids enhance mossy fiber synaptic transmission indirectly by reducing GABAB receptor activation. Brain Res 1999; 821:286-93. [PMID: 10064815 DOI: 10.1016/s0006-8993(99)01089-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The cellular mechanisms underlying mu opioid facilitation of mossy fiber (MF) long-term potentiation (LTP) and synaptic transmission were investigated in the rat hippocampal slice. Naloxone (10 microM) significantly inhibited the induction of mossy fiber LTP, an effect attributed by Derrick and Martinez [B.E. Derrick, J.L.J. Martinez, Opioid receptor activation is one factor underlying the frequency dependence of mossy fiber LTP induction, J. Neurosci. 14 (1994) 4359-4367] to antagonism of endogenous opioid peptide action. We found that the inhibitory effects of naloxone were not blocked by bicuculline, suggesting that endogenous opioids did not enhance mossy fiber LTP by depressing GABAA inhibition. [d-Ala2, NMePhe4, Glyol5] enkephalin, DAMGO (300 nM), a mu opioid agonist, mimicked the action of endogenous opioids, enhancing both mossy fiber LTP induction and paired-pulse facilitation. DAMGO potentiation of the paired-pulse facilitation of mossy fiber response was also insensitive to bicuculline but was blocked by the mu selective antagonist CTOP. Further analysis of the cellular mechanism showed that the depletion of internal Ca2+ stores by thapsigargin (1 microM), or inhibition of protein kinases by application of staurosporine (1 microM) did not block the DAMGO facilitation of mossy fiber-CA3 synaptic transmission. However, application of phaclofen (100 microM GABAB receptor antagonist or SCH 50911, a more potent GABAB antagonist significantly inhibited the DAMGO effect (49+/-15%; 51+/-19% inhibition, P<0.05). The data indicate that the DAMGO effect on the mossy fiber pathway is partially mediated by a reduction in GABA activation of GABAB receptors. These findings further suggest that endogenous opioid peptides activate mu opioid receptors to facilitate mossy fiber LTP and synaptic transmission in rat hippocampus partially by GABAB receptor-mediated disinhibitory mechanism.
Collapse
Affiliation(s)
- W Jin
- Department of Pharmacology, University of Washington, Box 357280, Seattle, WA 98195-7280, USA
| | | |
Collapse
|
24
|
Commons KG, Kow LM, Milner TA, Pfaff DW. In the ventromedial nucleus of the rat hypothalamus, GABA-immunolabeled neurons are abundant and are innervated by both enkephalin- and GABA-immunolabeled axon terminals. Brain Res 1999; 816:58-67. [PMID: 9878688 DOI: 10.1016/s0006-8993(98)01084-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Immunohistochemical-labeling for the neurochemicals gamma-aminobutyric acid (GABA) and enkephalin are abundant in the ventromedial nucleus of the hypothalamus (VMN). In VMN, both GABA and enkephalin may function to regulate feeding behavior, as well as other hormone-controlled behaviors. Importantly, in several brain areas, enkephalin is often thought to modulate GABAergic neurotransmission. Therefore, we used dual-labeling immunohistochemistry with electron microscopic analysis to study the circuitry of neurons containing GABA- and/or enkephalin-labeling within the VMN. Somato-dendritic profiles containing GABA-labeling were three fold more abundant than GABA-labeled axon terminals (117 soma or dendrites vs. 34 axons). In addition, axon terminals containing GABA-labeling sometimes synapsed onto GABA-labeled somata or dendrites (25% or 9/34). In contrast, under these conditions labeling for enkephalin was primarily restricted to axon terminals, which were very abundant throughout VMN. Enkephalin-containing terminals accounted for a large fraction (25% 23/92) of the axons in contact with GABA-labeled dendrites, although they also contacted unlabeled dendrites. These observations suggest that a population of VMN neurons are GABAergic. These may be either local circuit 'interneurons' or projection neurons. In addition, GABA-labeled VMN neurons may be regulated by either enkephalin or GABA. These morphologic observations provide the basis for disinhibitory mechanisms to function within the VMN.
Collapse
Affiliation(s)
- K G Commons
- Laboratory of Neurobiology and Behavior, The Rockefeller University Box 275, 1230 York Avenue, New York, NY 10021, USA
| | | | | | | |
Collapse
|
25
|
Opioid inhibition of hippocampal interneurons via modulation of potassium and hyperpolarization-activated cation (Ih) currents. J Neurosci 1998. [PMID: 9736632 DOI: 10.1523/jneurosci.18-18-07084.1998] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The actions of mu- and delta-opioid agonists (DAMGO and DPDPE, respectively) on GABAergic interneurons in stratum oriens of area CA1 of the hippocampus were examined by using whole-cell voltage-clamp recordings in brain slices. Both agonists consistently generated outward currents of similar magnitude (15-20 pA) in the majority of cells. However, under control conditions, current-voltage (I/V) relationships revealed that only a small number of these cells (3 of 77) demonstrated clear increases in membrane conductance, associated with the activation of the potassium current known as Girk. These interneurons also exhibited a slowly activating, inwardly rectifying current known as Ih on hyperpolarizing step commands. Ih was blocked by the extracellular application of cesium (3-9 mM) or ZD 7288 (10-100 microM) but was insensitive to barium (1-2 mM). In an effort to determine whether the holding current changes were attributable to the modulation of Girk and/or Ih, we used known blockers of these ion channels (barium or cesium and ZD 7288, respectively). Extracellular application of cesium (3-9 mM) or ZD 7288 (25-100 microM) blocked Ih and significantly reduced the opioid-induced outward currents by 58%. Under these conditions the opioid agonists activated a potassium current with characteristics similar to Girk. Similarly, during barium (1-2 mM) application the opioid-induced outward currents were reduced by 46%, and a clear reduction in Ih and the whole-cell conductance was revealed. These data suggest that the opioids can modulate both Ih and Girk in the same population of stratum oriens interneurons and that the modulation of these ion channels can contribute to the inhibition of interneuron activity in the hippocampus.
Collapse
|
26
|
Commons KG, Milner TA. Localization of delta opioid receptor immunoreactivity in interneurons and pyramidal cells in the rat hippocampus. J Comp Neurol 1997. [DOI: 10.1002/(sici)1096-9861(19970512)381:3<373::aid-cne8>3.0.co;2-#] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Kathryn G. Commons
- Division of Neurobiology, Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021
| | - Teresa A. Milner
- Division of Neurobiology, Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021
| |
Collapse
|
27
|
Endogenous activation of mu and delta-1 opioid receptors is required for long-term potentiation induction in the lateral perforant path: dependence on GABAergic inhibition. J Neurosci 1997. [PMID: 8987837 DOI: 10.1523/jneurosci.16-24-08123.1996] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Opioid peptides costored with glutamate have emerged as powerful regulators of long-term potentiation (LTP) induction in several hippocampal pathways. The objectives of the present study were twofold: (1) to identify which opioid receptor types (mu, delta, or kappa) regulate LTP induction at lateral perforant path-granule cell synapses and (2) to test the hypothesis that endogenous opioids regulate LTP induction via modulation of GABAergic inhibition. LTP of lateral perforant path-evoked field EPSPs was induced selectively by high-frequency stimulation applied to the outer third of the molecular layer of the dentate gyrus of rat hippocampal slices. No changes in medial perforant path responses occurred. LTP was blocked when high-frequency stimulation was applied in the presence of the mu receptor antagonist CTAP, the selective delta-1 receptor antagonist BNTX, or the delta-1 and delta-2 receptor antagonist naltrindole. By contrast, the kappa-1 opioid receptor antagonist NBNI had no effect on LTP induction. The role of GABAergic inhibition was investigated by comparing the effect of naloxone on LTP induction in slices maintained in standard buffer and picrotoxin-containing buffer. Naloxone blocked LTP in standard buffer, whereas normal LTP was induced in picrotoxin-treated, disinhibited slices. Finally, NMDA receptor blockade completely inhibited LTP in both standard and disinhibited slices. The results show that mu and delta-1 opioid receptors regulate LTP induction and that this mechanism critically depends on GABAergic inhibition. A key issue then becomes how endogenous opioids fine-tune the activity of intact inhibitory networks in the dentate gyrus, effectively gating synaptic plasticity in specific dendritic strata.
Collapse
|
28
|
Commons KG, Milner TA. Cellular and subcellular localization of delta opioid receptor immunoreactivity in the rat dentate gyrus. Brain Res 1996; 738:181-95. [PMID: 8955512 DOI: 10.1016/s0006-8993(96)00774-3] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
To study a potential locus of action of opioids in the rat dentate gyrus, we examined the localization of the delta opioid receptor (DOR) by immunocytochemistry. Two antisera raised to unique, non-overlapping peptide sequences located within the extracellular N-terminal sequence of DOR were tested. By light microscopy, numerous neurons in the central hilar region were intensely labeled for DOR, while the granule cell layer contained light DOR immunoreactivity. To further characterize hilar neuron cell types which contained DOR, sections through the dentate gyrus were double labeled using immunofluorescence with antisera to DOR and either gamma-aminobutyric acid (GABA), neuropeptide Y (NPY), or somatostatin-28 antisera. Most DOR-labeled perikarya also contained GABA and NPY, while a subpopulation contained somatostatin. Electron microscopic examination of sections labeled for DOR revealed that the immunoreactivity was common in profiles which exhibited the morphological characteristics of granule cells, as well as those of non-granule cells. DOR immunoreactivity was located at postsynaptic sites within neuronal perikarya (2%), dendrites (27%), and dendritic spines (22%); as well as in presynaptic axon terminals (25%) and glia (23%) (n = 279). In dendrites and dendritic spines, DOR immunoreactivity was most often associated with the plasmalemmal surface near asymmetric synapses. In axon terminals, DOR immunoreactivity primarily surrounded small, clear vesicles, and was less consistently found on the plasmalemmal surface. The distribution of DOR-labeled profiles overlapped with, but was not restricted to regions known to contain enkephalin. These data suggest that opiates acting at the DOR can modulate both hilar neurons and granule cells both pre- and postsynaptically.
Collapse
Affiliation(s)
- K G Commons
- Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA
| | | |
Collapse
|