284
Xenopus
FIGURE 19.2 (Continued)
consumption in specifc brain regions in relation to sensory or motor computations (H). Anterior, horizontal, posterior semicircular
canal; Cup, cupula; EAC, EHC, EPC, electrode stimulating the AC, HC, PC sensory epithelium; Hb, hindbrain; IR, infrared; IVth, IVth
ventricle; LE, RE, left eye, right eye; La, lagena; LR, lateral rectus; OT, optic tectum; Sa, saccule; SC, spinal cord; Te, telencephalon;
Ut, utricle; VR, spinal ventral root.
Source: Panels B, D, H, G, I are adapted from Gensberger et al., 2016; Soupiadou et al., 2020; Özugur et al., 2020; Lambert et al., 2012, respectively.
compartments with any type of recording electrode, as well
as imaging of intracellular calcium gradients in identif able
neuronal populations at cellular resolution (e.g. Gensberger
et al., 2016; Lambert et al., 2018; Özugur et al., 2020).
Moreover, the vitality and functionality of isolated amphibian whole-head preparations represents an unprecedented
experimental condition, comparable to the circumstances
of the isolated brain of the fctional character William living in Ringer solution (Dahl, 1960). The integrity of practically all sense organs such as eyes or inner ear endorgans
in these preparations (Lambert et al., 2008; Gravot et al.,
2017) allows application of natural stimuli in an experimentally reconstructed sensory environment, such as provided
by virtual reality setups (Figure 19.2A). In addition, simple
motor behaviors like swim-related tail-oscillations or eye
movements (Lambert et al., 2020) can be recorded at high
resolution with spatio-temporal characteristics that match
those expected from intact animals (Hänzi and Straka,
2017). The virtually unlimited access to the CNS, the use
of multi-methodological approaches, and the possibility to
study animals at all developmental stages make Xenopus a
unique in vitro animal model (Straka and Simmers, 2012).
The introduction of isolated frog in vitro preparations
began during the early period of electrophysiological studies. Electrode recordings in the frog cerebellum were among
the frst to beneft from isolated brains (Hackett, 1972). Such
preparations, however, were only used by relatively few
scientists over the subsequent decades, mostly for pharmacological studies of synaptic connections (e.g. Cochran et
al., 1987) or to demonstrate the spatio-temporal specif city
of defned neuronal circuits (Straka and Dieringer, 1993).
Beyond functional aspects, neuroanatomical studies benef ted from the use of in vitro preparations, particularly due
to visually guided application of retro- and anterogradely
transported neuronal tracers to brain areas that are inaccessible in intact animals (Birinyi et al., 2000; Straka et al.,
2001). Isolated anuran whole-brain or head preparations
were traditionally used for combined anatomical and physiological exploration of small ensembles of neurons with relatively defned synaptic connections (Straka and Dieringer,
1993). Subsequent use of this approach has since expanded
into more distributed circuits and entire systems predominantly using Xenopus laevis (Lambert et al., 2008 , 2020).
This extension was possible due to several characteristic
features, which are favorable toward systemic studies under
sustained in vitro conditions. This includes retention of those
parts of the tissue that are relevant for a particular question,
such as the brain and the eyes (Gravot et al., 2017), when
profling central circuits that control visuo-motor responses
(Figure 19.2A,D). Furthermore, targeted surgical manipulations can be performed with ease at any level of the circuit or
system, without drawbacks typical for in vivo studies, such
as bleeding, pulsations induced by respiration, and blood
circulation or consequences of the anesthesia, which are all
absent in vitro (Soupiadou et al., 2020). Several neuroscientif c felds have thus benefted considerably from the use of
in vitro Xenopus preparations, particularly over the past 15
years, due to the applicability of modern analytical tools.
Collectively, these applications have yielded in-depth protocols for generating preparations and applying experimental
regimes to answer specifc questions on, for example, the
retinotectal circuitry (Pratt, 2021), arguably one of the most
heavily studied felds in Xenopus neuroscience. Olfactory
research has also taken advantage of in vitro preparations,
using the spatial proximity of the olfactory epithelium and
olfactory bulb to generate slices and explants that effectively
consist only of the sensory epithelia and the f rst central
neuronal processing center. Due to the aquatic lifestyle of
Xenopus, naturalistic yet highly controlled stimulation of
the mucosa is achieved by simply fushing odorants into
the Ringer solution, with the olfactory bulb available for
any manner of functional imaging or electrophysiological
recording (Manzini et al., 2002; Offner et al., 2020).
Another feld which utilizes in vitro Xenopus preparations aims at deciphering general principles of self-motion
processing and has succeeded in discovering a wide spectrum of developmental and computational mechanisms
involved in implementing the respective CNS circuitry.
Self-motion perception derives from a combination of
visual, vestibular, and predictive motor signals, which
converge centrally from independent afferent pathways.
Dissociation of the relative infuences of each modality was
accomplished with such preparations by natural stimulation paradigms coupled with measurements of neuronal
activity (Lambert et al., 2012; von Uckermann et al., 2016).
Motion-sensitive visual input can be activated either in isolation (Figure 19.2A) or in tandem with galvanically evoked
activation of vestibular endorgans in the inner ear (Figure
19.2B). Activation of the vestibular system can in addition
be achieved by motion of a multi-axis turntable (Figure
19.2C ) with or without corresponding visual scene motion
(Lambert et al., 2012; Soupiadou et al., 2020). The tractability of sensory stimuli in these paradigms recapitulates in
vivo-like conditions while simultaneously granting a high
degree of fexibility to selectively activate desired sensory
pathways. As in in vivo studies, traditional methods of profling neuronal activity range from behavior (Soupiadou et
al., 2020), to electrophysiological recordings of selected
Xenopus
FIGURE 19.2 (Continued)
consumption in specifc brain regions in relation to sensory or motor computations (H). Anterior, horizontal, posterior semicircular
canal; Cup, cupula; EAC, EHC, EPC, electrode stimulating the AC, HC, PC sensory epithelium; Hb, hindbrain; IR, infrared; IVth, IVth
ventricle; LE, RE, left eye, right eye; La, lagena; LR, lateral rectus; OT, optic tectum; Sa, saccule; SC, spinal cord; Te, telencephalon;
Ut, utricle; VR, spinal ventral root.
Source: Panels B, D, H, G, I are adapted from Gensberger et al., 2016; Soupiadou et al., 2020; Özugur et al., 2020; Lambert et al., 2012, respectively.
compartments with any type of recording electrode, as well
as imaging of intracellular calcium gradients in identif able
neuronal populations at cellular resolution (e.g. Gensberger
et al., 2016; Lambert et al., 2018; Özugur et al., 2020).
Moreover, the vitality and functionality of isolated amphibian whole-head preparations represents an unprecedented
experimental condition, comparable to the circumstances
of the isolated brain of the fctional character William living in Ringer solution (Dahl, 1960). The integrity of practically all sense organs such as eyes or inner ear endorgans
in these preparations (Lambert et al., 2008; Gravot et al.,
2017) allows application of natural stimuli in an experimentally reconstructed sensory environment, such as provided
by virtual reality setups (Figure 19.2A). In addition, simple
motor behaviors like swim-related tail-oscillations or eye
movements (Lambert et al., 2020) can be recorded at high
resolution with spatio-temporal characteristics that match
those expected from intact animals (Hänzi and Straka,
2017). The virtually unlimited access to the CNS, the use
of multi-methodological approaches, and the possibility to
study animals at all developmental stages make Xenopus a
unique in vitro animal model (Straka and Simmers, 2012).
The introduction of isolated frog in vitro preparations
began during the early period of electrophysiological studies. Electrode recordings in the frog cerebellum were among
the frst to beneft from isolated brains (Hackett, 1972). Such
preparations, however, were only used by relatively few
scientists over the subsequent decades, mostly for pharmacological studies of synaptic connections (e.g. Cochran et
al., 1987) or to demonstrate the spatio-temporal specif city
of defned neuronal circuits (Straka and Dieringer, 1993).
Beyond functional aspects, neuroanatomical studies benef ted from the use of in vitro preparations, particularly due
to visually guided application of retro- and anterogradely
transported neuronal tracers to brain areas that are inaccessible in intact animals (Birinyi et al., 2000; Straka et al.,
2001). Isolated anuran whole-brain or head preparations
were traditionally used for combined anatomical and physiological exploration of small ensembles of neurons with relatively defned synaptic connections (Straka and Dieringer,
1993). Subsequent use of this approach has since expanded
into more distributed circuits and entire systems predominantly using Xenopus laevis (Lambert et al., 2008 , 2020).
This extension was possible due to several characteristic
features, which are favorable toward systemic studies under
sustained in vitro conditions. This includes retention of those
parts of the tissue that are relevant for a particular question,
such as the brain and the eyes (Gravot et al., 2017), when
profling central circuits that control visuo-motor responses
(Figure 19.2A,D). Furthermore, targeted surgical manipulations can be performed with ease at any level of the circuit or
system, without drawbacks typical for in vivo studies, such
as bleeding, pulsations induced by respiration, and blood
circulation or consequences of the anesthesia, which are all
absent in vitro (Soupiadou et al., 2020). Several neuroscientif c felds have thus benefted considerably from the use of
in vitro Xenopus preparations, particularly over the past 15
years, due to the applicability of modern analytical tools.
Collectively, these applications have yielded in-depth protocols for generating preparations and applying experimental
regimes to answer specifc questions on, for example, the
retinotectal circuitry (Pratt, 2021), arguably one of the most
heavily studied felds in Xenopus neuroscience. Olfactory
research has also taken advantage of in vitro preparations,
using the spatial proximity of the olfactory epithelium and
olfactory bulb to generate slices and explants that effectively
consist only of the sensory epithelia and the f rst central
neuronal processing center. Due to the aquatic lifestyle of
Xenopus, naturalistic yet highly controlled stimulation of
the mucosa is achieved by simply fushing odorants into
the Ringer solution, with the olfactory bulb available for
any manner of functional imaging or electrophysiological
recording (Manzini et al., 2002; Offner et al., 2020).
Another feld which utilizes in vitro Xenopus preparations aims at deciphering general principles of self-motion
processing and has succeeded in discovering a wide spectrum of developmental and computational mechanisms
involved in implementing the respective CNS circuitry.
Self-motion perception derives from a combination of
visual, vestibular, and predictive motor signals, which
converge centrally from independent afferent pathways.
Dissociation of the relative infuences of each modality was
accomplished with such preparations by natural stimulation paradigms coupled with measurements of neuronal
activity (Lambert et al., 2012; von Uckermann et al., 2016).
Motion-sensitive visual input can be activated either in isolation (Figure 19.2A) or in tandem with galvanically evoked
activation of vestibular endorgans in the inner ear (Figure
19.2B). Activation of the vestibular system can in addition
be achieved by motion of a multi-axis turntable (Figure
19.2C ) with or without corresponding visual scene motion
(Lambert et al., 2012; Soupiadou et al., 2020). The tractability of sensory stimuli in these paradigms recapitulates in
vivo-like conditions while simultaneously granting a high
degree of fexibility to selectively activate desired sensory
pathways. As in in vivo studies, traditional methods of profling neuronal activity range from behavior (Soupiadou et
al., 2020), to electrophysiological recordings of selected