Phosphodiesterase 1b (PDE1B) Regulates Spatial and Contextual Memory in Hippocampus

Augmentation of cyclic nucleotide signaling through inhibition of phosphodiesterase (PDE) activity has long been understood to enhance memory. Efforts in this domain have focused predominantly on PDE4, a cAMP-specific phosphodiesterase implicated in consolidation. But less is known about the function of other PDEs expressed in neuroanatomical regions critical to memory. The PDE1 isoforms are the only PDEs to regulate neuronal cAMP and cGMP levels in a Ca2+/Calmodulin (CaM) dependent manner. Here, we show that knock-down of PDE1B in hippocampus of adult mice enhances contextual and spatial memory without effect on non-cognitive behaviors. Pharmacological augmentation of memory in rats was observed with a selective inhibitor of PDE1 dosed before and immediately after training, but not with drug dosed either 1 h after training or before recall. Our data clearly demonstrate a role for the PDE1B isoforms as negative regulators of memory, and they implicate PDE1 in an early phase of consolidation, but not retrieval. Inhibition of PDE1B is a promising therapeutic mechanism for treating memory impairment

Segregation of Odor Identity and Intensity during Odor Discrimination in Drosophila Mushroom Body

Molecular and cellular studies have begun to unravel a neurobiological basis of olfactory processing, which appears conserved among vertebrate and invertebrate species. Studies have shown clearly that experience-dependent coding of odor identity occurs in “associative” olfactory centers (the piriform cortex in mammals and the mushroom body [MB] in insects). What remains unclear, however, is whether associative centers also mediate innate (spontaneous) odor discrimination and how ongoing experience modifies odor discrimination. Here we show in naïve flies that Gαq-mediated signaling in MB modulates spontaneous discrimination of odor identity but not odor intensity (concentration). In contrast, experience-dependent modification (conditioning) of both odor identity and intensity occurs in MB exclusively via Gαs-mediated signaling. Our data suggest that spontaneous responses to odor identity and odor intensity discrimination are segregated at the MB level, and neural activity from MB further modulates olfactory processing by experience-independent Gαq-dependent encoding of odor identity and by experience-induced Gαs-dependent encoding of odor intensity and identity

Specific requirement of NMDA receptors for long-term memory consolidation in Drosophila ellipsoid body

In humans and many other animals, memory consolidation occurs through multiple temporal phases and usually involves more than one neuroanatomical brain system. Genetic dissection of Pavlovian olfactory learning in Drosophila melanogaster has revealed multiple memory phases, but the predominant view holds that all memory phases occur in mushroom body neurons. Here, we demonstrate an acute requirement for NMDA receptors (NMDARs) outside of the mushroom body during long-term memory (LTM) consolidation. Targeted dsRNA-mediated silencing of Nmdar1 and Nmdar2 (also known as dNR1 or dNR2, respectively) in cholinergic R4m-subtype large-field neurons of the ellipsoid body specifically disrupted LTM consolidation, but not retrieval. Similar silencing of functional NMDARs in the mushroom body disrupted an earlier memory phase, leaving LTM intact. Our results clearly establish an anatomical site outside of the mushroom body involved with LTM consolidation, thus revealing both a distributed brain system subserving olfactory memory formation and the existence of a system-level memory consolidation in Drosophila

Developmental expression of an amn(�) transgene rescues the mutant memory defect of amnesiac adults

The Drosophila memory gene amnesiac (amn) has been proposed to encode a neuropeptide protein, which includes regions homologous to vertebrate pituitary adenylyl cyclaseactivating peptide (PACAP; Feany and Quinn, 1995). Definitive experiments to link this gene to memory formation, however, have not yet been accomplished (Kandel and Abel, 1995). The experiments described here demonstrate that the putative amn transcript is involved in adult memory formation. With the use of a UAS–amn � transgene, we show complete rescue of memory defects in amn 28A, a mutant allele caused by the insertion of a GAL4 enhancer trap transposon (Moore et al., 1998). Study of the amn 28A reporter reveals widespread expression in the adult brain but also enriched expression in the embryonic and larval nervous systems. To begin addressing the temporal requirement of amn in memory, we asked whether the memory defect

A30P flies showed non-odor-specific discrimination deficits.

<p>Fifteen-days old flies were tested for the ability to discriminate the presence of different odors made in 15% MCH versus 15% MCH alone. Chemical structures of each odor are shown and arranged from aromatics on the left, to esters on the right, based on structure similarity to MCH, the background odor. Behavior-equivalent concentrations used were 1.5% of BA^e, 20% MS^e, 1% of 1-Pro^e, 20% of EA^e, 10% of ButA^e and 5% of EH^e made in 15% of MCH^e. BA: benzaldehyde, MS: methyl salicylate, 1-Pro: 1-propanol, EA: ethyl acetate, ButA: butyl acetate, EH: ethyl hexanoate. For CT vs. A30P comparisons from left to right, t_BA(6) = 5.915,<i>**P</i> = 0.001, t_MS(7) = 2.,<i>*P</i> = , t_1-Pro(6) = 8.986, <i>***P</i> = 0.0001, t_EA(8) = 3.651,<i>**P</i> = 0.0065, t_ButA(12) = 4.750,<i>***P</i> = 0.0005, and t_EH(11) = 8.404,<i>***P</i><0.0001; Student <i>t</i>-test.</p

A30P flies show climbing deficit.

<p>(A) A30P expression in A30P flies. A30P protein from heads of five days old flies was probed using human-specific αSyn antibody. Pan-actin expression was used as an internal control. (B) Climbing assay. Climbing performance was measured based on negative geotaxis using countercurrent apparatus. By moving the upper five climbing tubes back and forward between each trial per test, flies would distribute between tubes 0 through 5. Each trial is 10 seconds. Details are in materials and methods. (C) Left: Fly distribution based on climbing performance. More CT flies reached the No.5 tube, while more A30P flies stayed in the No.1 tube. The percentage distribution (%) for a tube is [(# of flies in the tube)/(# of flies per test)]×100. The assays were performed with flies of fifteen days old. Fifty to eighty flies were used per trial. Ct <i>vs.</i> A30P: t₀ (8) = 3.588, <i>**P</i>₀ = 0.007; t₄(8) = 3.770, <i>**P</i>₄ = 0.0054; t₅(8) = 3.846, <i>**P</i>₅ = 0.0049. Right: The compounded climbing performance index (PI) from the left. PI = 100%×[Σ⁵_i = (# of flies)_i×i/(# of flies per test)×5]. t(8) = 4.768, <i>**P</i> = 0.0014; CT is +/+: A30P/+; A30P is Elav/+: A30P/+, hereafter unless noted otherwise. Student <i>t</i>-test.</p

Fly odor acuity (OA) and odor discrimination (OD) assays.

<p>Fly odor acuity (OA) and odor discrimination (OD) were tested using T-maze apparatus. Flies loaded into T-maze were dropped to a choice point between [BA] and air in the odor acuity assay or between [BA]^e and [MCH]^e+[BA]^e in the odor discrimination assay. To avoid an inherent directional reference in assays, an odor of a pair was delivered from one end of T-maze during the first trial (PI₁) and from the opposite end during the second trial (PI₂). A test comprised two trials. The performance index (PI) of a test is the average of PI₁ and PI₂. When the equilibrium concentrations of BA ([BA]^e) and MCH ([MCH]^e) were delivered from the opposite ends of T-maze, flies would show no preference for either [BA]^e or [MCH]^e by equally distributing between the two end-tubes. Flies with health odor discrimination would detect the presence of [BA]^e, a foreground odor, in the background of [MCH]^e and run to [MCH]^e tube, avoiding the [MCH]^e+[BA]^e tube. The formula for PI calculation was expressed as a percentage of the absolute number of flies that were differentially distributed between two end-tubes, divided by the total number of flies in a trial. PI₁ or ₂ = 100%×|(# of L)- (# of R)|/(# of total flies in a test).</p

A30P expression in dopaminergic neurons causes odor acuity and discrimination deficits in aged A30P flies.

<p>Fifteen-days old A30P flies expressing A30P under Elav-gal4 (Elav), TH-gal4 (TH), Cha-gal4 (Cha) or Or83b-gal4 (Or83b) drivers were tested for odor acuity (A) and the performance of odor discrimination (B). Young wild-type flies of 1–2 days old were used as internal assay control. Only A30P expressed in dopamine neurons, A30P_TH, showed olfactory acuity and discrimination deficits as seen in A30PElav. The corresponding controls for each comparison were CT_Elav (Elav/+; +/+; +/+), CT_TH (+/+; +/+; TH/+), CT_Cha (+/+; +/+; Cha/+), and CT_Or83b (Or83b/+; +/+; +/+). OA: t_Elav(14) = 6.388, <i>***P</i><0.0001, t_TH(14) = 3.773, <i>**P</i> = 0.0021; OD: t_Elav(14) = 3.338, <i>**P</i> = 0.0049, t_TH(14) = 3.257, <i>**P</i> = 0.0057; Student <i>t</i>-test.</p