Electrophysiological analysis on the neuromodulatory effects of dopamine in the goldfish olfactory bulb

Abstracts / Neuroscience Research 71S (2011) e46–e107

O3-H-2-4 Maximization of learning speed in motor cortex due to neuron redundancy

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Many kinds of redundancies play various functional and computational roles in motor control and motor learning. Kinematic and muscle redundancies contribute to stabilizing posture and impedance control, respectively. Another redundancy is neuron redundancy; there are overwhelmingly more neurons than muscles, and many combinations of neural activities can generate identical muscle activities. A question remains as to what are the functional and computational roles of this neuron redundancy. Analysis on a redundant neural network model makes it possible to investigate the functional and computational roles with varying the number of model neurons. Our analysis revealed that learning speed reaches its maximum value if and only if the model includes sufficient neuron redundancy. This analytical result does not depend on whether the distribution of preferred direction is uniform or skewed bimodal, both of which are reported in neurophysiological studies. Neuron redundancy also yields the equivalence between a learning rule of synaptic weights and a model for sensorimotor learning, which can explain the results of behavioral experiments. We subsequently run numerical simulations of more biologically plausible neural network models. As a result, neuron redundancy maximizes learning speed even if the models include recurrent connections or a two-layer structure. Thus, the present study suggests that one of the functional and computational roles of neuron redundancy is to maximize learning speed.

movements. To investigate neural mechanisms for such robust behavioral responses, it is necessary to quantitatively analyze the time-course changes in the correlation between the stimulus and behavioral response. For this, we quantitatively analyzed stimulus as well as behavior of the nematode C. elegans’ avoidance response to repulsive odor 2-nonanone. In a previous study, we have shown that C. elegans exhibited a constant average velocity of avoidance from 2-nonanone for 10 min (Kimura et al., J. Neurosci., 2010), suggesting a neural mechanism for such constant avoidance. In addition to the quantitative analysis of avoidance response to 2-nonanone, we recently developed a technique to measure the concentration of 2-nonanone at specific spatial and temporal points of gas phase in the assay plate. Based on this measured gradient of 2-nonanone, we determined the 2-nonanone concentration that each worm experienced during the avoidance assay (Cworm ) and observed the followings: (1) after 2 min of 12 min assay, worms started to migrate farther away from the odor source, and Cworm was maintained at around the order of ␮M, despite increase in the concentration gradient. (2) Cworm decreased effectively during runs, while it increased and decreased largely during pirouettes. (3) When compared between the early and late phases of the assay, the maximum dCworm /dt in each run decreased several fold along with the avoidance behavior, even though the orientation directions did not change considerably; that is, even when the gradient of 2-nonanone became shallower, the accuracy of worm orientation appeared maintained. These results suggest that worms may increase sensitivity to dC/dt during exposure to a certain concentration of 2-nonanone. Further analysis may help us uncover the mechanism of maintaining proper behavioral responses.

doi:10.1016/j.neures.2011.07.336

doi:10.1016/j.neures.2011.07.338

O3-I-1-1 In vivo imaging of Ras activity in olfactory neurons suggests its transient activation is important for olfactory behaviour

O3-I-1-3 Temporal summation properties of the olfactory projection neurons in the moth antennal lobe revealed by optogenetic stimulation

Takayuki Uozumi 1 , Takaaki Hirotsu 2 , Kazushi Yoshida 3 , Takayuki Teramoto 2 , Ryuji Yamada 2 , Akiya Suzuki 2 , Yuichi Ino 3 , Takeshi Ishihara 2

Masashi Tabuchi 1,2 , Takeshi Sakurai 2 , Hidefumi Mitsuno 2 , Shigehiro Namiki 2 , Ryo Minegishi 1,2 , Shuichi S. Haupt 2 , Takahiro Shiotsuki 3 , Keiro Uchino 3 , Hideki Sezutsu 3 , Toshiki Tamura 3 , Kei Nakatani 4 , Ryohei Kanzaki 1,2

Ken Takiyama 1 , Masato Okada 1,2 1

Grad. Sch. of Frontier Sci., The University of Tokyo, Kashiwa, Japan 2 RIKEN

1

Grad. Sch. of Sys Life Sci., Kyushu Univ., Fukuoka, Japan 2 Dept. of Biol., Grad. Sch. of Sci., Kyushu Univ., Fukuoka, Japan 3 Dept. of Biophy and Biochem, Grad. Sch. of Sci., Tokyo Univ., Tokyo, Japan

1

Dept. of AIS., Grad. Sch. of Eng., The University of Tokyo, Tokyo, Japan RCAST, The University of Tokyo, Tokyo, Japan 3 NIAS, Tsukuba, Japan 4 Grad. Sch. of Life & Env., The University of Tsukuba, Tsukuba, Japan

2

The Ras-MAPK pathway plays important roles for olfactory perception in C. elegans. Our previous immunohistochemical studies have revealed that this pathway is activated within 10 s by odorant stimuli in olfactory neurons. To elucidate the spatio-temporal regulation of activation of the Ras-MAPK pathway in living animals, we introduced Raichu-Ras, the Förster resonance energy transfer (FRET)-based sensors for Ras activity, into the olfactory neurons of C. elegans. We found that Ras is transiently activated within a few seconds in the olfactory neurons after the odorant stimulus. Activation of Ras occurred depending on increase in the concentration of odorants compared to the previous concentration of them. We also observed that this activation of Ras is dependent on olfactory signaling pathway and RGEF-1 (RasGRP). The activity of Ras was decreased to the basal level within 5–6 s despite the continued presence of the odorant. This rapid inactivation could not be observed in the mutants of MAPK, suggesting that a negative feedback loop regulates the inactivation of Ras. To elucidate the function of the activation of Ras in the olfactory neurons, we analyzed the behavior to the odorants in let-60(lf) and let-60(gf) mutants and found that they showed defects in the weathervane mechanism, which is olfactory behavioral strategy in C. elegans. Furthermore, in let-60(gf) mutants, Ca2+ response after the odorant stimuli could not be observed in the interneurons that receive synaptic inputs from the olfactory neurons. On the other hand, in let-60(lf) mutants, the olfactory stimulus induced an unstable Ca2+ response in the interneurons. These results suggest that rapid activation and inactivation of Ras is important to regulate the activities of the interneurons for the proper olfactory behaviors. Our studies will reveal novel kinetics and biological implication of rapid activation and inactivation of Ras in the olfactory neurons.

Male moths possess exquisite olfactory system that can detect and recognize conspecific pheromones dispersed and greatly diluted in air plumes. In the silkmoth, Bombyx mori, only 180 molecules of sex pheromone of that species could release sexual behavior in male moths. Although olfactory system in moth pheromone reception is a well-characterized model, it is unclear how subtle odor signal in olfactory receptor neurons (ORNs) can be relayed through the brain to give rise to allow high behavioral responsiveness. Here, we show that temporal summation of ORN inputs in second order projection neurons (PNs) contribute to extremely high sensitivity of behavioral response. To control ORN inputs with high temporal resolution, channelrhodopsin-2 was genetically introduced in pheromone responsive ORNs. Paired-pulse photostimulation revealed that there is a defined time window in which temporal summation of ORN inputs occurs in PN in response to weak ORN inputs. Such temporal summation was not observed in response to strong ORN inputs. Pharmacological dissection revealed that summation properties of PN were sensitive to GABA receptor antagonists only in response to strong ORN inputs, showing an important role of GABAergic inhibitory networks in gain control of olfactory circuit. Notably, probability of behavioral response was also increased with a similar interstimulus interval of paired-pulse photostimulation that caused temporal integration in PN, showing integration time in PN response was directly reflected at the timescale of behavioral output. Taken together, our results indicate that the temporal summation properties of PN provide an important gain control function on a behaviorally relevant timescale. Research fund: KAKENHI(18370028).

doi:10.1016/j.neures.2011.07.337

doi:10.1016/j.neures.2011.07.339

O3-I-1-2 C. elegans maintain their response to the repulsive odor 2-nonanone during avoidance behavior

O3-I-1-4 Electrophysiological analysis on the neuromodulatory effects of dopamine in the goldfish olfactory bulb

Akiko Yamazoe 1 , Yuishi Iwasaki 2 , Kotaro Kimura 1 1

Dept. of Biol. Sci., Grad. Sch. of Sci., Osaka Univ., Osaka, Japan 2 Dept. of Int. Sys. Eng., Ibaraki Univ., Ibaraki, Japan Animals can maintain their behavioral response to environmental stimuli even under unstable environmental conditions and during various animal

Takafumi Kawai , Hideki Abe, Yoshitaka Oka Dept. of Biol. Sci., Grad. Sch. of Sci., The Univ. of Tokyo, Tokyo, Japan Teleosts are one of the important models for the studies of olfactory information processing in the olfactory bulb, and there is an accumulating knowledge on its underlying mechanisms. However, the functional role of dopamine

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Abstracts / Neuroscience Research 71S (2011) e46–e107

(DA), which is known to be a potent neuromodulator endogenous to the mammalian olfactory bulb, has not been analyzed in the teleost olfactory bulb. Here, we investigated the function of DA in the olfactory bulb of the goldfish, which offers several advantages for the electrophysiological experiments. First, in the goldfish olfactory bulb, we found by immunohistochemistry that the cell bodies of the dopaminergic neurons are distributed abundantly in the mitral cell layer, and they extended fine processes towards the olfactory nerve terminals. Next, we performed in vitro field potential recordings and showed that synaptic transmissions from mitral cells to granule cells in the goldfish olfactory bulb were suppressed by DA application. DA also increased the paired-pulse ratio, suggesting that the suppression of synaptic transmission is caused by a decrease in the presynaptic glutamate release from the mitral cells. Furthermore, DA significantly suppressed the odorant-induced oscillatory activity of the olfactory bulb. Although it is reported that DA suppresses the synaptic inputs from the olfactory nerve terminals to the olfactory bulbar neurons in mammals, such phenomenon was not observed in the goldfish olfactory bulb in the present patch-clamp experiments. These findings indicate that the suppression of synaptic transmission in the reciprocal synapses in the goldfish olfactory bulb has an important role in the negative regulation of olfactory responsiveness. Research fund: JSPS (22-8084), MEXT (20770054), JSPS (20247005), MEXT (20021012), PROBRAIN. doi:10.1016/j.neures.2011.07.340

O3-I-2-1 TRPV1 lineage neurons and their functional role in thermal nociception Santosh Mishra , Mark Hoon National Institute of Dental and Craniofacial Research, National Institutes of Health TRPV1-ion channel is known to mediate thermal sensation in mammals and is believed to be a major sensor of noxious heat. However, animals where the TRPV1 gene is knocked out display almost normal responses to high temperature. Our study demonstrates the thermal and nociceptive functions of TRPV1-cells by utilizing mice in which TRPV1-expressing neurons are genetically labeled or ablated. We designed a novel transgenic mouse in which Cre-recombinase was expressed in all TRPV1-cells including during their development. Our data reveals that TRPV1 is an embryonic marker for the majority of nociceptive neurons including all cells expressing the receptors for hot and cold stimuli (TRPV1 and TRPM8) and the Mrg-expressing cells. Animals lacking these classes of neurons are entirely insensitive to hot and cold sensation however in contrast touch and noxious mechanical responses remain normal. We further investigated the thermal regulation of core body temperatures. Interestingly, we found that the mutant mice lacking TRPV1-cells were not able to control body temperature appropriately. In addition, testing of pruritus and chemically induced nociception showed mutant animals had lost both reactions to itch inducing and noxious compounds. Altogether, our finding expands knowledge about the role of TRPV1-neurons in thermosensation, thermoregulation, nociception and pruriception and together with other recent studies hint at a labeled line model for somatosensory coding. Research fund: Division of intramural research, NIDCR/NIH. doi:10.1016/j.neures.2011.07.341

pathic pain-like behavior and microglial activation, late treatment did not. Early treatment with minocycline also blocked LPA-evoked new LPA production and the increased activation of LPA synthesis-related enzyme. Similar results were also observed in the nerve injury model. These findings suggest that the early phase of microglial activation is involved in new LPA production, and this underlies the initial mechanisms of nerve injury-induced neuropathic pain. On the other hand, we tried the quantitative mass spectrometrical method to define the species of produced LPA. Research fund: MEXT KAKENHI (17109015 to Hiroshi Ueda). doi:10.1016/j.neures.2011.07.342

O3-I-2-3 Modulatory role of C-tactile fibres in overt and covert muscle pain Saad S. Nagi 1 , Vaughan G. Macefield 1,2 , David A. Mahns 1 1 2

School of Medicine, University of Western Sydney, Sydney, Australia Neuroscience Research Australia, Sydney, Australia

We recently showed that low-threshold cutaneous mechanoreceptors contribute to the crossover between neutral-touch (vibration) and painful-touch (allodynia) during hypertonic saline (HS) evoked muscle pain. However, it remains unclear whether allodynia results from activation of a single class of cutaneous fibres or the convergence of inputs from multiple classes. Moreover, it is unknown whether the expression of allodynia in a super-perceptual pain-state can be extrapolated to a sub-perceptual pain-state. No existing study has examined contribution of C-tactile (CT) fibres to allodynia. Methods: Psychophysical observations were made in 50 healthy subjects. In experimental Series I (super-perceptual), muscle pain was induced by infusing HS into tibialis anterior muscle (TA). In experimental Series II (subperceptual), delayed onset muscle soreness (DOMS) was induced in TA by eccentric exercise (weight bearing during muscle lengthening). DOMS was confirmed by systematically mapping the emergence of tender points. In both series, sinusoidal vibration (200 Hz–200 ␮m) was applied before, during and after HS-infusion/DOMS to the skin overlying TA. Pain ratings were recorded using a Visual Analog Scale. The contribution of different fibre classes to allodynia was determined by myelinated-compression of sciatic nerve and anaesthesia of unmyelinated cutaneous afferents (Xylocaine 0.25%). Results: During HS-pain and DOMS, vibration evoked a significant and reproducible allodynia that persisted following compression of myelinated afferents. Contrarily, allodynia was abolished by anaesthesia of unmyelinated cutaneous afferents. Prior to induction and upon cessation of HS-pain and DOMS, all subjects described vibration as non-painful. Conclusions: This is the first study to demonstrate the role of CT fibres in pain processing. These observations suggest that sensory-perceptual realignment – a common manifestation of clinical pain-states – can be elicited by sub-perceptual events. Research fund: National Health and Medical Research Council of Australia. doi:10.1016/j.neures.2011.07.343

O3-I-2-4 Inter-regional remodeling between the primary somatosensory cortex and anterior cingulate cortex accelerates chronic pain behavior Kei Eto , Hiroaki Wake, Hitoshi Ishibashi, Miho Watanabe, Junichi Nabekura Div. of Homeostatic Dev., NIPS, Okazaki, Japan

O3-I-2-2 Lysophosphatidic acid 3 (LPA3 ) receptormediated LPA production via microglial activation underlies the initial mechanisms of nerve injury-induced neuropathic pain Lin Ma , Jun Nagai, Kayo Taira, Hiroshi Ueda Div. of Mol. Pharmacol. & Neurosci., Nagasaki Univ. Grad. Sch. of Biomed. Sci., Nagasaki, Japan Lysophosphatidic acid (LPA) is a bioactive lipid mediator. We previously reported that LPA1 receptor signaling initiates nerve injury-induced neuropathic pain and its underlying mechanisms (Nature Medicine, 2004). In the present study, we found that LPA was newly produced in the early phase after LPA injection or nerve injury. This LPA production was abolished in LPA3 receptor knockout mice. Also, we examined the possible involvement of spinal cord microglia in such LPA production. Intrathecal LPA injection rapidly increased the gene expression of CD11b and protein expression of phosphor-p38, accompanied by a morphological change of microglia from a ramified to amoeboid shape. Although early treatment with minocycline, a microglial activation inhibitor, significantly inhibited LPA-induced neuro-

The experience of pain is a result of both sensory and emotional aspects involving the primary somatosensory cortex (S1) and the anterior cingulate cortex (ACC), respectively. Although both types of cortical areas have been expected to interact with each other, little is known about whether and how S1 interact with ACC and what is the role of the interaction in chronic pain. Here, we first provided that the inter-regional remodeling between cortical areas involved in sensory and emotional processing and contribution of this remodeling to chronic pain behavior. Using two-photon Ca2+ imaging, we found that the excitability of layer 2/3 (L2/3) excitatory neurons in the S1, which project to other pain-related cortical areas, increased in chronic pain conditions. In addition, excitatory postsynaptic responses in the L2/3 pyramidal neurons evoked by layer 4 stimulation increased. The ACC also displayed enhanced excitability to peripheral stimulation. Both pain behavior and ACC excitability to peripheral stimulation successfully correlated with S1 neuronal activity. In addition, inhibition of ACC activity alleviated the mechanical allodynia. To our knowledge, this is the first evidence that plastic change within the sensory related brain area interregionally modulates neuronal activity in the emotional center, which in turn accelerates pain behavior. The present results will provide development of