Advances in Bioscience and Biotechnology, 2010, 1, 391-397 ABB
doi:10.4236/abb.2010.15052 Published Online December 2010 (
Published Online December 2010 in SciRes.
Significance of the astrocyte domain organization for
qualitative information structuring in the brain
Bernhard J. Mitterauer
Volitronics-Institute for Basic Research, Psychopathology and Brain Philosophy, Gotthard Guenther Archives, Salzburg, Austria.
Received 3 August 2010; revised 25 August 2010; accepted 27 August 2010.
Astrocytes, the dominant glial cell type, modulate
synaptic information transmission. Each astrocyte is
organized in non-overlapping domains. Here, a for-
mally based model of the possible significance of as-
trocyte domain organization is proposed. It is hy-
pothesized that each astrocyte contacting n neurons
with m synapses via its processes generates dynamic
domains of synaptic interactio ns based on qualita tive
criteria so that it exerts a structuring of neuronal
information processing. The formalism (morpho-
grammatics) describes the combinatorics of the
various astrocytic receptor types for occupancy with
cognate neurotransmitters. Astrocytic processes are
able both to contact synapses and retract from them.
Rhythmic oscillations of the astrocyte may program
the domain organization, where clock genes may play
a role in rhythm generation. For the interpretation of
a domain organization a player of a string instrument
is used as a paradigm. Since astrocytes form net-
works (syncytia), the interactions between astrocyte
domains may be comparable to the improvisations in
a jazz ensemble. Given the fact of a high combina-
tional complexity of an astrocyte domain organiza-
tion, which is formally demonstrable, and an un-
computable complexity of a network of astrocyte
domains, the model proposed may not be testable in
biological brains, but robotics could be a real alter-
Keywords: Astrocyte Domain Organization; Qualitative
Formalism; Synaptic Information Structuring; Musical
Paradigms; Robotics
Astrocytes, the dominant glial cell type, have become
the focus of much attention in the past two decades. In
addition to their roles in many of the supportive func-
tions of the brain, new functions are beginning to emerge.
Abundant evidence now supports the notion that astro-
cytes are actively involved in synaptic transmission in
most brain regions. Although astrocytes are not them-
selves electrically excitable, they release transmitters,
triggered by increases in cytosolic Ca2+ concentrations
that modulate the activity of neighboring cells, including
both neurons and other glia. Astrocytes express a large
number of primarily metabotropic receptors that mobi-
lize intracellular Ca2+ stores in a phospholipase C- and
inosital (1, 4, 5) triphosphate-dependent fashion [1].
Importantly, astrocytes are thereby able to respond to
neuronal activity in a receptor-dependent fashion, and in
return they can modulate synaptic transmission by
transmitter release, thereby permitting feedback control
of neuronal activity levels [2,3]. Astrocytes release glu-
tamate, serine and adenosine-triphosphate, and possible
other transmitters that might regulate the activity of sur-
rounding neurons [4-6]. Moreover, it is experimentally
well established that astrocytes form non-overlapping
territories that define functional domains [7-9]. Ober-
heim et al. [10] pose the question of what the functional
significance of astrocyte domain organization could be,
since it is as yet not fully understood. Here, I hypothe-
size that each astrocyte contacting n neurons with m
synapses via its processes generates dynamic domains of
synaptic interactions based on qualitative criteria, so that
it exerts a structuring of neuronal information process-
In all mammals, protoplasmic astrocytes are organized
into spatially non-overlapping domains that encompass
both neurons and vasculature. An astrocyte domain de-
fines a contiguous cohort of synapses that interacts ex-
clusively with a single astrocyte. Synapses within a par-
B. J. Mitterauer / Advances in Bioscience and Biotechnology 1 (2010) 391-397
Copyright © 2010 SciRes. ABB
ticular territory are thereby linked via a shared astrocyte
partner, independent of a neuronal networking [10].
Figure 1 shows an outline of an astrocyte domain or-
ganization. An astrocyte (Acx) contacts the synapses (Sy)
of four neurons (N1…N4) via its processes (P1…P4).
Each process is equipped with one to four receptor
qualities (Rq). For example, P1 contacts the synapses of
N2 exclusively via its receptors of quality a. P2 has al-
ready two receptor qualities available (a, b), P3 three
receptor qualities (a, b, c) and P4 is able to contact the
synapses of N1 via four receptor qualities (a, b, c, d).
Astrocyte (Acx) is interconnected with another astrocyte
(Acy) via gap junctions (g.j.) forming an astrocytic net-
work (syncy- tium). The neurons per se are also inter-
connected (neuronal network).
It is experimentally verified that astrocytes can ex-
press almost all receptors for important transmitter sys-
tems [11]. In certain cases, individual astroglial cells
express as many as five different receptor systems linked
to Ca2+ mobilization [12]. Each astrocyte territory repre-
sents an island made up of many thousands of synapses
(about 140.000 in the hippocampal region of the brain,
for instance), whose activity is controlled by that astro-
cyte [9]. On the average, human astrocytes extend 40
large processes radially and symmetrically in all direc-
tions from the soma so that each astrocyte supports and
modulates the function of roughly two million synapses
in the cerebral cortex [10]. Astrocytic receptors are
mainly located on the endfeet of the processes. Here, we
apparently deal with a high combination al complexity of
astrocyte-synaptic interactions.
3.1. General Considerations
Guenther [13,14] described living systems as individual
units with a new universal theory of structure, called
morphogrammatics. Accordingly, a theory of structure
should be universal and composed of empty places. Such
places can either be of equal or different quality. They
can also stay empty or be occupied by anything. Based
on the principle of identity and difference, these places
or their structure can be analysed on three levels of
1) Protostructure: How many different places are there?
This corresponds to cardinality.
2) Deuterostructure: How are these places distributed?
This correspond s to distribution.
3) Tritostructure: Where are the individual places lo-
cated? This corresponds to position.
Since the tritostructure represents the highest com-
Rq abcdRq a
Rq abcRq ab
Figure 1. Outline of an astrocyte domain organization. An
astrocyte (Acx) is interconnected via four processes (P1…P4)
with the synapses (Sy) of four neurons (N1…N4). Each process
is on its endfoot equipped with receptors for the occupancy
with neurotransmitters according to a combinational rule
(shown in Table 1). As an example, the receptor P1 contacting
N2 embodies only one receptor quality (Rqa). P2 contacts N3
with two different receptor qualities (Rqab). P3 contacts N4
with Rqabc and P4 contacts N1 with Rqabcd. This simple dia-
gram represents an astrocyte domain. Astrocyte (Acx) is inter-
connected with Acy via gap junctions (g.j.) as shown in more
detail in Figure 3.
plexity, it may underly the astrocytic domain organiza-
tion. Here, the morphograms are termed tritograms.
3.2. Development of a Tritostructure
Formalizing an Astrocyte Domain
Figure 2 shows the development of tritograms with n
places. The structure for tritograms with length 1 to 5 (5
levels) is represented by a tree. This is the generation
rule: a tritogram x with length n+1 may be generated
from a tritogram y with length n if x is equal to y on the
first n places, e.g. 12133 may be generated from 1213
but not from 1212. The numerals are representations of
domains (properties, categories) that should be viewed
as ‘place-holders’ reserved for domains, e.g. 12133
should be read as five places for five entities, such that
the first and the third entity belong to domain one, the
second entity to domain two, and the fourth and fith en-
tity to domain three.
Now let us interpret the tritostructure (n = 4) as an as-
trocyte domain organization. Table 1 shows 15 tri-
tograms each consisting of the same or different places
symbolized as numerals 1 to 4. Since the position of the
places is relevant, one can also speak of a qualitative
counting of different domains [15]. This tritostructure is
interpreted as the formal basis of an astrocyte with 15
processes, each embodying a receptor sheet of identical
or different qualitative domains for synap tic information
processing. These various receptor domains are located
on the endfeet of the astrocytic processes contacting
cognate neuronal synapses and modulating neurotrans-
mission. Most importantly, it is experimentally verified
that astrocytes display elaborate process extension and
B. J. Mitterauer / Advances in Bioscience and Biotechnology 1 (2010) 391-397
Copyright © 2010 SciRes. ABB
n = 1
n = 2
1 1
1 2
1111 1
n = 3
1122 2
1212 3
1111 11111 1 1 1 1 1 1
n = 4
1111 12222 2 2 2 2 2 2
1122 21112 2 2 3
1212 31231 2 3 1 2 3 4
n = 5
Figure 2. Tritogrammatic tree. Generation of 52 tritograms (n = 5) corresponding to 52 astrocytic processes. Each tritogram repre-
sents a qualitative astrocytic receptor sheet. The structure for tritograms with length 1 to 5 is represented by a tree. Generation rule: a
tritogram x with length n + 1 may be generated from a tritogram y with length n if x is equal to y on the first n places, e.g. 12133 may
be generated from 1213 but not from 1212. The numerals are representations of places of the same or different qualities interpreted as
astrocytic receptors on the endfeet of the processes. Each tritogram corresponds to an astrocytic processor.
Table 1. Tritostructure. Generation of 15 tritograms corresponding to 15 astrocytic processes.
receptor qualities
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 2 2 2 2 2 2 2 2 2 2
1 1 2 2 2 1 1 1 2 2 2 3 3 3 3
1 2 1 2 3 1 2 3 1 2 3 1 2 3 4
tritograms [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
15 tritograms (n = 4) are generated according to the generation rule shown in Figure 2. Each tritogr am consists of t he same or different pl aces symbolized as
numerals (1…4). Since the position is relevant one can also speak of qualitative counting of different domains. This tritostructure is interpreted as the formal
basis of an astrocyte with 15 processes, each embodyin g a receptor sheet of identical or different qualitative domains for synaptic information processing.
retraction, and likely use the active cytoskeleton for mo-
tility [16,17]. To integrate these experimental results into
the model proposed here, astrocytes may be searching
for synapses that are equipped with neurotransmitter
types appropriate for the occupancy of specific astro-
cytic receptors in various compositions (Table 1). More-
over, this implies that in the whole astrocyte domain not
all processes or receptors are active, leading to ‘breaks’
in glial-neuronal synaptic interactions. Hence, we deal
with a dynamic exchange that occurs between astrocytes
and synapses in the sense of concerted structural plastic-
ity of glial-neuronal interaction. Ho wever, in this context
we are faced with the issue how and where such motile
behavior of astrocytes may be controlled?
For understanding the domain organization of an astro-
cyte, its rhythmic contraction waves may be decisive.
Astrocytes, when they get swollen and/or depolarized,
can potentially release accumulated K+, neurotransmit-
ters, neuromodulators (e.g. taurine), and water into inter-
stitial fluid in a pulsatile manner [18]. Such discharge
processes represent mechanisms by which astrocyte
networks (syncytia) could influence neuronal firing in a
B. J. Mitterauer / Advances in Bioscience and Biotechnology 1 (2010) 391-397
Copyright © 2010 SciRes. ABB
coordinated fashion [19]. Moreover, astrocytes may play
a direct role in generating pacemaker rhythms [20].
This originally speculative assumption has already
been verified. Parri et al. [21] showed that astrocytes in
situ could act as a primary source for generating neu-
ronal activity in the mammalian central nervous system.
Slow astrocyte calcium oscillations (every 5 to 6 minutes)
occur spontaneously (without prior neuronal activation)
and can cause excitations in nearby neurons. Consider-
ing experimental findings of the structural interplay be-
tween astrocytes and synapses in hippocampal slices,
dynamic structural changes in astrocytes help control the
degree of glial-neuronal communication [17]. Since the
time scales of both astrocyte calcium oscillations and
morphological changes in astrocytes occur within min-
utes, a pacemaker function may determine the motility
of astrocyte processes and the generation of a structural
pattern of astrocyte-synaptic interactions.
In comparison of the rapid synaptic information proc-
essing within milliseconds, the pulsations and morpho-
logical changes of astrocytes are relatively slow. Thus, it
is often argued that glia cannot exert an effect in synap-
tic information processing. This argument may be erro-
neous if cognitive processes are considered. Cognitive
processes, such as thinking and planning, etc., occur in a
timescale of minutes, hours, days or weeks, since they
need a relatively long timespan. I hypothesize that an
astrocyte domain is organized within this long time scale
generating a specific qualitative structure of glial-neu-
ronal information processing.
For a general unders tanding of a single astrocyte do main
organization, I will use a player of a string instrument as
a paradigm. Let us assume he/she has a melody in mind.
At the same time he/she would like to know what the
melody sounds like. He/she takes his/her instrument and
presses the fingers of the left hand on the strings over
precisely those places that will produce the desired mel-
ody. In parallel, the fingers of the right hand must acti-
vate the strings. Now, the formalism of tritograms (Ta-
ble 1) allows the following interpretation:
Supposing the instrument is equipped with four
strings, each embodies an empty place of a specific
quality comparable to four types of neuronal synapses.
According to the underlying combinatorics, the same
and different strings, if activated, can be chosen by
pressing them. This means in biological terms that the
astrocyte (player) contacts synapses (strings) via its
processes (fingers) generating a specific structure of
astrocyte-synaptic interactions according to a combina-
tion rule in the sense of an astrocyte domain organiza-
tion (melody). Most importantly, not all strings are al-
ways pressed in generating a melody, but often single
strings must be selected. Here, we may deal with the
same dynamic organization principle as in an astrocyte
domain where processes both contact synapses and re-
tract from them as well.
In attempting to interpret the organization of astrocyte
domains into networks (syncytia), the musical paradigm
can be elaborated further, as shown by the harmonization
in a jazz ensemble.
First, the main biological structure of an astrocytic net-
work, called syncytium, must be outlined.
6.1. Outline of an Astrocytic Syncytium
Figure 3 shows a diagrammatic schema depicting an
astrocytic syncytium composed of two astrocytes (Ac1,
Ac2) interconnected via gap junctions (g.j.). Each astro-
cyte contacts four synapses (Sy) with four different
qualities (a, b, c, d) building an astrocyte-neuronal do-
main. A quality (astrocytic receptor domain) is defined
as the specific neurotranmsitter type that operates in
synaptic neurotransmission, say glutamate (a), GABA
(b), noradrenaline (c), dopamine (d). The gap junctions
consist of four identified astrocytic connexins Cx 43, Cx
30, Cx 26, and Cx 45, forming homotypic (same con-
nexins) and heterotypic (different connexins) gap junc-
tion channels (for the sake of clarity not shown in the
figure). As already discussed, the interactions of astro-
cytes with synapses occur in a pulsatile manner in vari-
Figure 3. Diagrammatic schema of an astrocytic
sync y ti um. Two astrocytes (Ac1, Ac2) are intercon-
nected via gap junctions (g.j.). Each astrocyte con-
tacts four synapses (Sy) with four different quali-
ties (a, b, c, d) building two astrocytic-neuronal
domains. Since these two domains are intercon-
nected via gap junctions, a network is generated,
called syncytium.
B. J. Mitterauer / Advances in Bioscience and Biotechnology 1 (2010) 391-397
Copyright © 2010 SciRes. ABB
ous time scales. Although astrocyte-synaptic interactions
within milliseconds are also identified [22], the domi-
nating time scales are minutes to hours. Moreover, do
the organizational principles of a single astrocyte do-
main also hold in an astrocytic syncytiu m? Can they also
be compared to the creation of music? How do the indi-
vidual astrocyte domains (instruments) with different
time scales cooperate to produce an integrative behavior?
Let us take the improvisation in a jazz ensemble as an
6.2. Harmonization in a Jazz Ensemble
Members of a classical orchestra have a strictly defined
environment as they perform directly from notes of the
page. The jazz ensemble, however, plays within a de-
fined harmonic structure in which every musician can
improvis e, dev e l op, and vary themes. Certain themes can
be played best by one instrument while the other instru-
ments play accompaniment or rest until their turn to im-
provise. Every instrument can principally carry the mel-
ody. Each musician listens to what the others play in that
moment and participates in the harmonization or rests.
Each musician can in his way synchronize his musical or
harmonic intention with the ‘environment’ of the rest of
the ensemble by playing with them, by improvising a
solo, or by resti ng.
A comparable organization may be at work in the as-
trocytic syncytium and its synaptic interactions with the
neuronal system. My biological interpretation is this:
each astrocyte domain stands for a musician playing the
same or different intstruments. They are able to listen to
one another, since astrocytes are interconnected via gap
junctions. Astrocyte domains can rest by retracting their
processes from synapses or by not activating (playing) a
synapse, when it is silent. Silent synapses are experi-
mentally well established [23]. Importantly, here we do
not deal with synchronization, but with a special kind of
self-organization of intentional and environment-depen-
dent structuring of information, comparable to harmonic
structuring in music [24,25].
Molecular and cellular processes in the brain are deter-
mined by a plethora of various biological clocks. Not
only do circadian rhythms exist, but also ultradian rhy-
thms [26]. These ultradian rhythms include a time scale
from pico-seconds and milliseconds to minutes and
hours [27]. The investigation of circadian clocks is
making significant progress. The McKnight group re-
ported that the transcription factor neuronal PAS domain
protein 2 (NPAS 2) likely functions as part of a molecu-
lar clock operative in the mammalian forebrain [28]. The
discovery may provide a molecular link between cir-
cadian oscillations and energy homeostasis interlocked
through negative feedback loops [29]. The problem of
the synchronization of this rhythmic diversity, however,
remains unsolved. The following hypothesis may resolve
this issue: a domain or domains whose rhythm at a cer-
tain moment best corresponds to internal and external
environment conditions command, and therefore, deter-
mine the rhythm of the molecular processes of the entire
system. This is comparable to a melody which can be
best realized by certain instrument groups while other
instrument groups assume a secondary function, as ac-
companiment or rest altogether. However, since theo-
retically all instruments could be melodic carriers, a
“redundancy of potential command” [30] rules orches-
tration. Those instruments best suited through their tim-
bre, tone color or intensity of sound in any given “envi-
ronmental situation” will take a predominant role. Con-
cerning the interaction of biological clocks, Lloyd [27]
proposes a safety-net of redundancy and checkpoints, so
that if one timing circuit fails another deputizes. How-
ever, Lloyd does not penetrate the principle of the re-
dundancy of potential comman d. At least in the brains of
Drosophila melanogaster neuronal and glial cells con-
taining clock genes have been identified [31]. A recent
study focuses on glial cells that may be responsible for
setting the beat [32]. This experimental finding could
implicate that the rhythmic pulsations of an astrocyte
could be generated and controlled by clock genes. Pres-
ently, one can only guess that this may also be the case
in human brains, since pertinent data are not yet avail-
The model of a single astrocyte domain organization and
the generation of networks operate on qualitative criteria
what the interaction of the astrocytic receptors with the
neuronal compartments of a synapse concerns. This in-
teraction is highly dynamic and occurs in a pulsatile
manner. Since only a specific amount of astrocyte proc-
esses contact cognate synapses at a given moment, as-
trocytes may exert an information structuring function
comparable to playing a music instrument or improvis-
ing in a jazz ensemble. Moreover, this theoretical model
should be testable.
Given the estimation that the mean number of astro-
cytic processes is 40 with a potential of contacting of
about two million synapses, testing my model in bio-
logical brains may seem to be impossible. However, a
real alternative could be a computer simulation of the
dynamic organization of an astrocyte based on the pro-
B. J. Mitterauer / Advances in Bioscience and Biotechnology 1 (2010) 391-397
Copyright © 2010 SciRes. ABB
posed formalism. As a first technical step in the imple-
mentation of a glial-neuronal domain, I have simulated a
“clocked perception system” [33]. Since then, the model
has been further developed, especially what a possible
generation of intentional programs in the astrocytic
syncytium concerns [34]. If we could build a chip it
might function comparable to an astrocyte domain in-
teracting with n-neuronal synapses. Moreover, if a set of
chips interact like astrocytes in their syncytium, a robot
brain that operates according to qualitative criteria
structuring environmental info rmation could stepwise be
constructed. Remarkably, although neuronal computing
or neuronal network technologies are dominating, re-
cently computer modelling of glial-neuronal interactions
in synapses is emerging [35].
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