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Inhibitory inputs of CCKpositive neurons to PVexpressing neurons
in mouse neocortex
1 1 1 1 2
1 1,3 1
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2
3 CREST
Neocortical GABAergic interneurons are roughly classified into three subgroups
by chemical markers, parvalbumin PV, somatostatin SS and others such
as vasoactive intestinal polypeptide VIP and cholecystokinin CCK. PV
expressing neurons, fastspiking neurons, are a major component of GABAergic
interneurons in neocortex. We generated transgenic mice expressing dendritic
membranetargeted GFP selectively in PVexpressing neurons, and succeeded in
visualizing somata and dendrites in a Golgi stainlike fashion.
We previously investigated inhibitory inputs to PVexpressing neurons from PV,
SS or VIPexpressing neurons, by combining immunofluorescence labeling of
presynaptic and postsynaptic sites with antibodies to presynaptic markers and
gephyrin, respectively. PV or SSpositive axon terminals made close contacts
to the dendrite, whereas axon terminals of VIPexpressing neurons preferred the
soma.
In the present study, we visualize axon terminals of CCKexpressing neurons by
immunofluorescence staining in the transgenic mice, observe the close appositions
to PVexpressing neurons under confocal laserscanning microscope, and analyze
the inputs quantitatively.
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Elimination of somatic climbing fiber synapses proceeds with the
differentiation of cerebellar interneurons
In the developing cerebellum, the soma of individual Purkinje cells PCs is
innervated by multiple climbing fibers CFs. Through their competition, only
a single winner CF translocates to dendrites and the remaining somatic CF
synapses are eliminated, leading to the establishment of CF monoinnervation.
Concomitantly, basket cell fibers BFs begin to form inhibitory synapses on
PC somata. Here, we examined anatomical relationship between declining CFs
and developing inhibitory neurons at PC soma by light and electron microscopic
analysis. In the first postnatal week of murine life, CFs innervated the entire
somatic surface. Thereafter, BFs expanded their innervation from the apical
side of PC somata downwards in synchrony with the reduction of somatic CF
synapses. Furthermore, CF terminals frequently detached from the basal side of
PC somata and often formed synapses on the somatodendritic domain of Lugaro
cells LCs, a cerebellar interneuron lying just below the PC layer. These findings
suggest that elimination of somatic CFs proceeds with the differentiation of
cerebellar interneurons, such as BFs expelling somatic CF synapses and LCs
accommodating perisomatic CF terminals.
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Tectothalamic inhibitory neurons in the inferior colliculus receive
converged axosomatic excitatory inputs from multiple sources
Tectothalamic inhibitory TTI cells in the inferior colliculus IC are encircled
by dense excitatory terminals positive for vesicular glutamate transporter 2
VGLUT2. Four auditory brainstem nuclei including IC itself were identified
as possible sources by examining mRNA expression of VGLUT1 and VGLUT2
in ICprojecting cells. In this study, Sindbis/palGFP virus was injected in these
nuclei to elucidate whether neurons in the nuclei make axosomatic contacts on
TTI cells or not. Labeled neurons in all four nuclei made axosomatic contacts
on large GABAergic neurons with dense axosomatic terminals, presumable TTI
PTTI cells. Furthermore, a single axon made one to six contacts on a PTTI cell.
In 3 cases, single IC excitatory cell was successfully labeled, and analyzed for
spatial relationship between the labeled axon and PTTI cells. Single IC excitatory
cell made axosomatic contacts on 1030 PTTI cells in the ipsilateral IC. Finally,
double injection of Sindbis/palGFP and Sindbis/palmRFP viruses in 2 nuclei
revealed convergence of inputs from 2 nuclei on a single PTTI cell. The results
imply both divergence and convergence of auditory information on the cell bodies
of TTI cells.
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Axon terminals of the corticocollicular projection in the rat auditory
system
The corticocollicular projection was visualized by Sidbis virus and studied
morphologically. The axons visualized with Golgi method in the inferior colliculus
IC have been classified into three types and studied electronmicroscopically, A.
J. Rocket and E. G. Jones, 1972,1973 with their origins mentioned prooflessly.
We successfully visualized corticocollicular projection exclusively by infection
of a recombinant Sindbis virus into cortical projection neurons in the auditory
area. The Sindbis virus which expresses palmitoilationsiteadded GFP as the
reporter gene is a kind gift from Dr. Kaneko in Kyotouniversity. The cortico
collicular axon terminal images in the inferior colliculus was morphologically
studied and compared with intrinsic axons from IC neuron which are stained in the
same way. We further observed cortical projections into the nucleus of brachium
of IC, external nucleus of IC, central nucleus of IC and deep layer of the superior
colliculus. It should be noted that different types of termination exist in the above
mentioned auditory brainstem.
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Afferent projection to amygdaloid subnuclei and intrinsic connection
of each subnuclei
The amygdala is structurally diverse and comprised of several subnuclei. Extra
and intraamygdala inputs into these subnuclei were extensively investigated by
injection of CTb into various amygdaloid subnucleri, respectively. Ce received
moderate to heavy inputs from almost all amygdaloid subnuclei, and from limbic
cortex and hippocampus APir and AI, thalamus PV and MGM, hypothalamus
VMH and midbrain PB. Me received moderate to heavy inputs from BM, Co,
and from limbic cortex and hippocampus Pir, AHi and CA1, thalamus PV and
hypothalamus VMH. BM received moderate inputs from Me, Co and BL, and
from limbic cortex AI and thalamus PV. BL received moderate inputs from
Me, La, BM, Co, and from limbic cortex and hippocampus LEnt, APir and CA1,
thalamus PV and midbrain PB. La received moderate to heavy inputs from
Me, Co, BM and BL, and from limbic cortex Ect and PRh, thalamus MGM
and hypothalamus VMH. Co received light to heavy inputs from La, Me, and
from limbic cortex and hippocampus AI, Pir and DEn and thalamus PV, PT and
MGM. These subnucleispecific afferent projections are involved in emotional
process in a different manner.
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