DIVISION OF BRAIN BIOLOGYProfessor

YAMAMORI, Tetsuo

Associate Professor

WATAKABE, Akiya

Assistant Professors:

KOMINE, Yuriko
SADAKANE, Osamu
Assistant Professor(Specially appointed):
KOMATSU, Yusuke#NIBB Research Fellow:
OHTSUKA, MasanariTechnical Staff:
OHSAWA, Sonoko
Postdoctoral Fellows:
TAKAJI, Masafumi#OHTSUKA, Masanari*
HATA, Katsusuke#GOTO, Ayako#SASAKI, Tetsuya
Visiting Scientist:
HIRAKAWA, Reiko
Graduate Students:
NAKAGAMI, Yuki*
SHUKLA, RammohanTechnical Assistants:
NAKAMURA,Tohru
TAKEDA, Yuta#NAKAGAMI, Yuki
MORITA, Junko
IMAI, Akiko
KOTANI, Keiko
KON, Yayoi
MIKAWA, Ryuta
IMOTO, EikoHIRAYAMA, Yuka#
TAKAFUJI, Mituse#
KAJITANI, Tomoki#
TAKAHASHI, Yoichi##: SRPBS (Strategic Research Program for Brain Sciences), NIPS

We are studying genes that are expressed in specific areasof the neocortex in order to understand the principles
governing the formation of the primate brain.

I. Genes expressed in specific areas and layersof the neocortex

The neocortex emerged in mammals and evolved mostremarkably in primates. To understand the underlying
mechanisms of the primate brain we study gene expression
patterns within different areas of the neocortex.
We have reported the findings that are schematicallyillustrated in Figure 1.
Using differential display methods, we found three areaspecific expression genes in the primate neocortex. Firstly,occ1 is specifically expressed in the occipital cortex in theprimate brain. Secondly, the other gene that showed marked
difference within the neocortex is gdf7, a member of theBMP/TGF-b family, which is specifically expressed in themotor cortex of the African green monkey (Watakabe et al.,J. Neurochem., 76, 1455-1464, 2001). Thirdly, RBP (retinolbinding protein) is preferentially expressed in the associationand higher areas in the neocortex (Komatsu et al., Cerebral
Cortex, 15, 96-108, 2005).
To further screen area-specific molecules systematically inthe monkey neocortex, we carried out another round ofscreening using the RLCS method (Suzuki et al. 1996;

Figure 1. The expression of visual area specific genes (orange color) andassociation area specific genes (blue) and gdf7 (green) are schematicallyillustrated. Top and bottom views are medial and lateral surfaces,
respectively. (cited from Yamamori & Rockland, Neurosci. Res., 55,11-27, 2006 )Shintani et al. 2004). In this analysis, mRNAs were purified
from 4 distinct cortical areas, converted to cDNA by reverse
transcription and digested with a pair of restriction enzymes
for 2-dimensional analysis. Using the RLCS method weisolated genes that showed marked differences among fourareas (area 46, primary motor area, TE and V1) andcharacterized the expression patterns. Examples of suchgenes we have previously reported are testican-1, -2 (OCC1
related family genes), 5HT1B and 5HT2A (primary visualarea enriched), which are preferentially expressed in theprimary visual cortex, and SPARC (an OCC1 related gene)and PNMA5 whose expressions are similar to RBP (anassociation area enriched gene) as shown in Figure 1.
This year, I reviewed our studies over the last ten years andmore (Yamamori, 2011). The main discussions andconclusions are the functional significance of the two groupsof the genes as shown in Figure 1. The first group of genes
are those highly expressed in the primary sensory areas,
particularly in the primary visual area (V1). In collaboration
with Prof. Hiromichi Sato, Osaka University, we havepreviously shown that 5HT1B works by enhancing signal tonoise (S/N) ratio and 5HT2A works as a gain controller(Figure 2). Recently, it has been reported that, fstl1(follistatin-like 1), the mouse homologue of OCC1, is highly
expressed in mouse dorsal root ganglion (DRG). The
function in DRG has been revealed by the other group,
showing that Fstl1 is directly bound to Na, K. ATPase, which
suppresses sensory evoked presynaptic transmission byenhancing K+ influx and suppressing voltage dependent
Ca++ influx (Li et al., Neuron 69, 974-987, 2011). Thismechanism likely also works in primate V1 where OCC1
(macaque homologue of fstl1) is abundantly expressed. The

Note: Those members appearing in the above list twice under different titles are members whose title changed during 2011. The former title isindicated by an asterisk (*).

39

National Institute for Basic Biology

Neurobiology

major difference between macaque V1 and mouse tissues
that highly express OCC1 and fstl1, respectively, is that
expression of OCC1 in V1 is activity-dependent whereas
fstl1 expression in mouse tissues is not activity-dependent(Takahata et al., J. Chem Neuroanat., 35, 146-157, 2008).
These data of 5HT1B, 5HT2A and OCC1 expressions andfunctions strongly suggest that these genes control or
modulate inputs from the retina in activity-dependent
manners at the expression and functional levels (Figure 2).
Such expression patterns specific to primates have comeabout during the course of primate evolution (Takahata et al.,2011).

Figure 2. Roles of 5HT1B, 5HT2A and OCC1 in primate V1. Right:
Possible roles of OCC1 in primate V1. As shown in rodent DRG, OCC1
is likely bound to Na, K, ATPase (NKA) and suppresses visual stimuli
evoked synaptic transmission. The suppression is further enhanced by
activity-dependent gene expression. Left: Responses to a stimulus with alow contrast are suppressed by the activation of 5HT1B and are enhancedby that of 5HT2A. At a high stimulus contrast, the effects are reversed.
S/N ratio analysis demonstrated that the activation of 5HT1B contributes
to the increase in S/N ratio. We predict that 5HT2A works as a gaincontroller to compensate for the gain or loss caused by 5HT1B receptors
at a certain stimulus contrast. The left picture is drawn by Drs. Hiromichi
Sato and Satoshi Shimegi (Osaka University) and is cited from
Yamamori, T., Progress in Neurobiology 94, 201-222, 2011.

The second group of genes is selectively expressed in theassociation areas of the primate neocortex. Among theassociation area selective-expression genes, RBP, PNMA5,SPARC, and SLT2 are expressed in layers 2, 3, 5 and 6 inassociation areas and most abundantly prefrontal cortex andhigher sensory association areas. SLIT1, on the other hand, isexpressed in layers 2, 4 and 5 and most abundantly in layer 4
in the prefrontal cortex and to a lesser extent in the sensory
association areas (Sasaki et al., Cerab. Cortex. 20, 24962510, 2010). Although the functions of these association
area-selective genes are unknown, SLIT1 works to enhance
dendritic branching in developing cortical neurons in rodents
and thus presumably has a similar function in the primate
neocortex.

II. M ultisensory Information Facilitates
Reaction Speed by Enlarging Activity
Difference between Superior Colliculus
Hemispheres in Rats

Animals can orient responses faster to multisensory

40stimuli than to unisensory stimuli. We have been working on
studies of how animals can respond to multisensory
stimulation in collaboration with Professor Yoshio Sakurai(Kyoto University) using an experimental system that
evaluates audio-visual discrimination tasks in rats (Sakata etal., Exp Brain Res. 159, 409-417, 2004). Using this system,
we identified the brain areas of V2L that are specificallyinvolved in multisensory (visual and auditory) stimuli(Hirokawa et al., Neuroscience, 1402-1417, 2008). Thesestudies were further extended to the superior colliculus (SC).

Figure 3. Two-alternative spatial discrimination tasks based on auditory
and/or visual cues.
A) Timing of task events. Nose poking into the central hole initiated atrial. After a variable foreperiod, a cue stimulus was delivered from theleft or right, randomly chosen from visual, auditory and audiovisualstimuli. Rats responded to the stimulus by withdrawing from the centralhole and selected the direction of the cue stimulus by poking their heads
into the hole ipsilateral to the stimulus. (B) Mean reaction time for eachtype of stimulus across sessions and rats (*p<0.001 in ANOVA and post
hoc Tukey test). Error bars, standard deviation. This figure is cited from
Hirokawa et al., Plos One, 2011.

The superior colliculus (SC), which receives multiple inputs
from different sensory modalities, is thought to be involvedin the initiation of orienting responses. However, themechanism by which multisensory information facilitatesorienting responses had not yet been understood. We
demonstrate that multisensory information modulatescompetition among SC neurons to elicit faster responses. We
conducted multiunit recordings from the SC of rats
performing a two-alternative spatial discrimination taskusing auditory and/or visual stimuli. We found that a large
population of SC neurons showed direction-selective activity
before the onset of movement in response to the stimuli
irrespective of stimulation modality. Trial-by-trial correlation
analysis showed that the premovement activity of many SC
neurons increased with faster reaction speed for thecontraversive movement, whereas the premovement activity

the ipsiversive movement was depressed. Unilateralinactivation of SC using muscimol prolonged reaction timesof contraversive movements, but it shortened those ofipsiversive movements. These findings suggest that thedifference in activity between the SC hemispheres regulates
the reaction speed of orienting responses, and multisensory
information enlarges the activity difference resulting in faster
responses (Hirokawa et al., 2011).
The SC has been considered as a brain region that is
causally essential for integrating visual and auditory
information, as demonstrated by a study of excitotoxic lesionof the SC in cats. On the other hand, our study showed thatunilateral SC inactivation did not affect the facilitation ofreaction speed to multisensory stimuli. It is therefore possiblethat different neural networks are responsive for accurate
sensory detection and rapid response, respectively. In
consistent with a line of this idea, we previously showedusing the same technique as this study that the inactivation of
the secondary visual cortex (V2L) suppresses the facilitationof reaction speed (Hirokawa et al., Neuroscience, 1402-1417,2008).

Figure 4. Direction preference preceding locomotion.
(A) Example of tetrode isolation for single unit. (Top) Average
waveforms of spikes recorded on the four tetrode channels correspond toa cluster in black in the scatter plots below. The scatter plots indicate thepeaks of waveforms from channel 3 plotted against principal component
1 (PC1) from channel 3 recorded from a tetrode. (Right) Corresponding
autocorrelation functions with a window of ±30 ms. The bin size is 0.1
ms. (B) Rasters and spike density functions (SDFs) aligned to the onsetof the target for isolated single unit (black cluster) during spatial
discrimination task. The data were derived from only correct trials in
responses to contralateral stimuli divided into visual, auditory andaudiovisual stimulus conditions. Trials in the raster plot are sorted
according to reaction time. (C) The data of the same neuron as above
were aligned to movement onset and divided into ipsiversive andcontraversive movement trials regardless of the modality of the stimulus.
(D) Direction preference index of above unit was calculated using
receiver operating characteristics (ROC) analysis for each time point(p<0.05, permutation test). (E) Direction preference curves for all cells(225 cells). Each row corresponds to one cell. Cells were sorted by thetime of center of mass of significant positive preferences. Red and bluecolors indicate preference indices with significant positive and negativevalues (p<0.05, permutation test), respectively, and gray points
correspond to insignificant values. (F) Distribution of direction
preference index in premovement period across population (225 cells).
(G) Preference calculated for correct trials plotted against preference
calculated for erroneous trials in premovement period. (H) Directionpreferences calculated for each stimulus modality in each neuron andwere averaged for each stimulus modality condition. The blue periodshows a significant modulation of the preference under the multisensory
condition (AV>unimodal, ANOVA with post hoc tukey test, p<0.05). This
figure is cited from Hirokawa et al., 2011.

Publication List

〔Original papers〕

J., Sadakane, O., Sakata, S., Bosch, M., Sakurai, Y., and• Hirokawa,Yamamori, T. (2011). Multisensory information facilitates reaction••

speed by enlarging activity difference between superior colliculus
hemispheres in rats. PLoS ONE 6, e25283.
Kitsukawa, T., Nagata, M., Yanagihara, D., Tomioka, R., Utsumi, H.,
Kubota, Y., Yagi, T., Graybiel, A.M., and Yamamori, T. (2011). A novel
instrumented multipeg running wheel system, Step-Wheel, formonitoring and controlling complex sequential stepping in mice. J
Neurophysiol. 106, 479-487.
Rossini, L., Moroni. R.F., Tassi, L., Watakabe, A., Yamamori, T.,
Spreafico, R., and Garbelli, R. (2011). Altered layer-specific gene
expression in cortical samples from patients with temporal lobeepilepsy. Epilepsia 52, 1928-1937.

〔Original paper (E-publication ahead of print)〕

T., Shukla, R., Yamamori, T., and Kaas, J.H. Differential• Takahata,
expression patterns of striate cortex-enriched genes among old world,
new world, and prosimian primates. Cereb. Cortex. 2011 Nov. 7.

〔Review article〕

T. (2011). Selective gene expression in regions of primate• Yamamori,neocortex: implications for cortical specialization. Prog. Neurobiol. 94,
201-222.

of another population of neurons decreased with faster
reaction speed for the ipsiversive movement. When visualand auditory stimuli were presented simultaneously, thepremovement activity of a population of neurons for thecontraversive movement was enhanced, whereas thepremovement activity of another population of neurons for41