J Comp Neurol
March 27, 2000;
Patterns of calretinin, calbindin, and tyrosine-hydroxylase expression are consistent with the prosomeric map of the frog diencephalon.
This paper re-examines a previously published segmental map of the frog diencephalon
(Puelles et al.  Brain
Behav.Evol. 47:279-310) by means of immunocytochemical mapping of calretinin
, and tyrosine hydroxylase. The distribution of neuronal populations, axon
tracts, and neuropils immunoreactive for these markers was studied in adult specimens of Rana perezi and Xenopus laevis sectioned sagittally or horizontally. Emphasis was placed on study of the relationship of observed chemoarchitectural boundaries with the postulated overall prosomeric organization and the schema of nuclear subdivisions we reported previously, based on acetylcholinesterase
histochemistry and Nissl pattern in Rana. The data reveal a large-scale correspondence with the segmental map in both species, although some differences were noted between Rana and Xenopus. Notably, retinorecipient neuropils were generally immunoreactive for calretinin
only in Rana. Importantly, calretinin
immunostaining underlines particularly well the transverse prosomeric boundaries of the dorsal thalamus
. A number of nuclear subdivisions noted before with AChE
were corroborated, and some novel subdivisions became apparent, particularly in the anterior nucleus
of the dorsal thalamus
and in the habenular complex. The mapping of tyrosine hydroxylase clarified the segmental distribution of the catecholaminergic cell groups in the frog forebrain
, which is comparable to that observed in other vertebrates.
J Comp Neurol
[+] show captions
Fig. 1. Lateral sagittal sections of a Xenopus brain immunoreacted
for calretinin, shown in lateromedial order (A–C). Dorsal is oriented
upward and rostral to the left, as in all other sagittal sections shown
in this paper. The diencephalic prosomeres p1–p3 and the isthmus are
delimited by dash lines. The alar-basal boundary in p2 and p3 passes
just under the horizontal course of the thalamotelencephalic tract
(tht) as it extends from the dorsal thalamus to the root of the lateral
forebrain bundle in the secondary prosencephalon (best seen in A and
B). Scale bar 5 1 mm in C (also applies to A,B).
Fig. 2. Adjacent lateral sagittal sections of the same brain as in Figure1, but immunoreacted for
calbindin. Each lateromedial level (A–C) corresponds to one of the CR-stained ones in Figure 1. Scale
bar 5 1 mm in C (also applies to A,B).
Fig. 3. A,B: Continuation of the CR-immunoreacted sagittal section
series begun in Figure 1, to be compared with Figure 4A,B. A is
lateral to B. Transverse diencephalic interprosomeric boundaries and
the isthmus are indicated by dashed lines as in Figure 1. C: Detail at
higher magnification of CB in the habenular region in a section
slightly medial to that in B. Note the CB-IR neurons in the dorsocaudal
thalamic area (DC), which separate the habenular complex from
the pretectum (p1). Scale bar 5 250 mm in C (1 mm for A,B).
Fig. 4. A,B: Sagittal sections adjacent to those in Figure 3A,B,
immunoreacted for calbindin. C: Higher magnification detail of CB in
the mammillary and retromammillary regions in a sagittal section
slightly medial to B. D: Higher magnification detail of CB in the
hypothalamus in a section medial to C: note CB-IR fibers possibly originating
in the preoptic magnocellular nucleus (PMg) passing through
the retrochiasmatic periventricular area into the tuberal hypothalamus;
the median floor area of the mammillary, retromammillary, and
tuberculum posterior regions shows intense cellular and neuropil
staining. Scale bar 5 250 mm in D (also applies to C; 1 mm for A,B).
Fig. 7. Horizontal sections of Xenopus or Rana brains immunoreacted
for calretinin. Rostral is oriented to the bottom of the page. A:
Xenopus. Dorsal section passing through the habenular region and
the caudal poles of the telencephalon. B: Rana/Xenopus (corresponding
halves are shown for comparison; identified at the top). Sections at
dorsal levels of the neuropil of Bellonci (compare with schema in Fig.
5B). Note staining differences in the retinorecipient neuropils. Curiously,
the lateral thalamic neuropil (LN) is more CR-IR in Xenopus
than in Rana. Scale bar 5 250 m in B (also applies to A).
Fig. 8. A: Rana/Xenopus (corresponding halves are shown for
comparison; identified at the top; orientation as in Fig. 7). Horizontal
CR-immunoreacted sections at level schematized in Figure 5C, passing
through the lower part of the neuropil of Bellonci. Note differences
in retinorecipient neuropils. B: Xenopus. Horizontal CRimmunoreacted
section ventral to the neuropil of Bellonci. Scale bar 5
250 mm in B (also applies to A).
Fig. 9. A: Xenopus. Detail of horizontal CR-immunoreacted section
through the dorsal thalamus and pretectum (PT), showing the bisbenzimide
fluorescent counterstain used here to identify roughly the
proportion of CR-IR cells in the dorsal thalamus. The ventricle lies at
the right and the optic tract at the left. Note CR-negative cells building
up mainly in the periventricular stratum (in contrast to the
largely CR-negative PT). B, C: Xenopus/Rana (roughly corresponding
halves shown for comparison; identified at the top). Horizontal CRimmunoreacted
sections approximately at the ventralmost part of the
diencephalic alar plate [note the fiber bundles of the thalamotelencephalic
tract (tht) and the lateral forebrain bundle (lfb)]. Note again
differences in retinorecipient neuropils, as well as in the suprachiasmatic
and preoptic regions. Scale bar 5 250 mm in C (also applies to
Fig. 10. A–D: Continuation of the dorsoventral series of horizontal
CR-immunoreacted sections through the Xenopus brain illustrated in
Figures 7–9. A: Section at the level of the optic chiasma (oc), showing
the transition from the diencephalic alar plate into the corresponding
basal plate, which has a quite different expression pattern (note
horizontal course of the tht tract). B–D: Successively more ventral
section levels through the hypothalamus, ending at the mammillary
nucleus. E: Sagittal CR-immunoreacted section through a Rana
brain; rostral to the left. The plane passes just through the thin
thalamoeminential tract (compare Figs. 7B and 8A), illustrating the
slight dorsoventral dispersion of its component fiber bundles. Note as
well the CR-IR uncinate neuropil and basal optic nucleus (U; BON).
Scale bar 5 250 mm in A–D; 1 mm in E.
Fig. 11. A: Higher magnification detail of a sagittal section lying
in between Figure 1A,B, showing the CR-IR thin fibers of the
thalamohypothalamic tract (thh) as they course out of the p2 alar
plate (dorsal thalamus) and enter the underlying basal plate. Note the
contrasting change of course of the thalamotelencephalic fibers (tht),
which are more immunoreactive. B: Higher magnification detail of
CR-IR cells and fibers of the magnocellular nucleus of the posterior
commissure, as observed in a sagittal section, also containing the
adjoining superficial griseum tectale formation of the midbrain (GTs).
C: Higher magnification detail of the CR-IR core of the neuropil of
Bellonci in a sagittal section in Xenopus. Rostral is oriented to the left.
Scale bar 5 300 mm in C (also applies to A,B).