Frog Telencephalon Research Articles

Functional regeneration of the olfactory bulb requires reconnection to the olfactory nerve in Xenopus larvae

Larvae of the South African clawed frog (Xenopus laevis) can regenerate the telencephalon, which consists of the olfactory bulb and the cerebrum, after it has been partially removed. Some authors have argued that the telencephalon, once removed, must be reconnected to the olfactory nerve in order to regenerate. However, considerable regeneration has been observed before reconnection. Therefore, we have conducted several experiments to learn whether or not reconnection is a prerequisite for regeneration. We found that the olfactory bulb did not regenerate without reconnection, while the cerebrum regenerated by itself. On the other hand, when the brain was reconnected by the olfactory nerve, both the cerebrum and the olfactory bulb regenerated. Morphological and histological investigation showed that the regenerated telencephalon was identical to the intact one in morphology, types and distributions of cells, and connections between neurons. Froglets with a regenerated telencephalon also recovered olfaction, the primary function of the frog telencephalon. These results suggest that the Xenopus larva requires reconnection of the regenerating brain to the olfactory nerve in order to regenerate the olfactory bulb, and thus the regenerated brain functions, in order to process olfactory information.

The LIM-Homeodomain Gene Family in the DevelopingXenopusBrain: Conservation and Divergences with the Mouse Related to the Evolution of the Forebrain

A comparative analysis of LIM-homeodomain (LIM-hd) expression patterns in the developing stage 32 Xenopus brain is presented. x-Lhx2, x-Lhx7, and x-Lhx9 were isolated and their expression, together with that of x-Lhx1 and x-Lhx5, was analyzed in terms of prosomeric brain development and LIM-hd combinatorial code and compared with mouse expression data. The results show an almost complete conservation of expression patterns in the diencephalon. The Lhx1/5 and Lhx2/9 subgroups label the pretectum/ventral thalamus/zona limitans versus the dorsal thalamus, respectively, in alternating stripes of expression in both species. Conversely, strong divergences in expression patterns are observed between the telencephalon of the two species for Lhx1/5 and Lhx2/9. Lhx7 exhibits particularly conservative patterns and is proposed as a medial ganglionic eminence marker. The conservation of diencephalic segments is proposed to mirror the conservative nature of diencephalic structures across vertebrates. In contrast, the telencephalic divergences are proposed to reflect the emergence of significant novelty in the telencephalon (connectivity changes) at the anamniote/amniote transition. Moreover, the data allow the new delineation of pallial and subpallial domains in the developing frog telencephalon, which are compared with mouse subdivisions. In the pallium, the mouse combinatorial expression of LIM-hd is notably richer than in the frog, again possibly reflecting evolutionary changes in cortical connectivity.

In vivo evidence for the production of sulfated steroids in the frog brain

It is well established that sulfated neurosteroids are potent regulators of neuronal activity but the biosynthesis of sulfate esters of steroids in the central nervous system (CNS) has received little attention. In particular, the localization of hydroxysteroid sulfotransferase (HST), the enzyme which is responsible for the formation of sulfated steroids, has never been determined in the brain. We took advantage of the availability of an antiserum raised against rat liver HST to investigate the distribution of this enzyme in the CNS of the frog Rana ridibunda. Two populations of HST-positive neurons were localized in the anterior preoptic area and the magnocellular nucleus of the hypothalamus. Numerous HST-immunoreactive fibers were visualized throughout the telencephalon and the diencephalon. Reversed-phase high performance liquid chromatography (HPLC) analysis of frog telencephalon and hypothalamus extracts combined with radioimmunoasssay (RIA) detection showed the presence of substantial amounts of DHEAS-immunoreactive material which coeluted with synthetic DHEAS. The concentrations of DHEAS detected in the telencephalon and hypothalamus were respectively eight and five times higher than in the serum. The present study demonstrates the occurrence of HST-immunoreactive material in neurons of the frog telencephalon and diencephalon. This report also provides evidence for the presence of HST bioactivity, in vivo, in the frog brain.

The distribution of reduced nicotinamide adenine dinucleotide phosphate-diaphorase in the leopard frog telencephalon and related projections.

The distribution of reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D) was mapped histochemically in the forebrain of Rana pipiens, the leopard frog. Intense staining was observed which was strikingly restricted to certain nuclear groups and fiber tracts. The densest concentrations of NADPH-D stained cell bodies and fibers were observed in the granule layer of the accessory olfactory bulb and in the ventral aspect of the lateral pallium. Intense staining has also been reported in the presumed mammalian homologues of these regions. Less densely packed clusters of intensely stained neurons were found in the striatum, the anterior entopeduncular nucleus, the olfactory tubercle and the pars lateralis of the amygdala, whereas the preoptic region and the medial septum exhibited dense accumulations of lightly stained cells. Several fiber systems or terminal fields could be detected, including a ring of heavy staining which enclosed the striatum and an apparent terminal field in the lateral part of the medial pallium. A prominent compact tract, which may be homologous to a component of the stria terminalis of mammals, could be also followed from the ventral portion of the lateral pallium to the infundibular hypothalamus.

In Vivo and In Vitro Evidence for the Biosynthesis of Testosterone in the Telencephalon of the Female Frog

Neurons and glial cells are capable of synthesizing various steroid hormones, but biosynthesis of testosterone in the CNS has never been reported. The aim of the present study was to demonstrate the synthesis of testosterone in the frog brain. The presence of 17beta-hydroxysteroid dehydrogenase (17beta-HSD)-like immunoreactivity was detected in a population of glial cells located in the telencephalon. Reversed-phase HPLC analysis of brain tissue extracts combined with radioimmunoassay detection revealed the presence of substantial amounts of testosterone and 5alpha-dihydrotestosterone (5alpha-DHT) in the telencephalon where 17beta-HSD-positive cells were visualized. In male frogs, castration totally suppressed testosterone and 5alpha-DHT in the blood and in the rhombencephalon but did not affect the concentration of these two steroids in the telencephalon. Chemical characterization of testosterone in female frog telencephalon extracts was performed by coupling HPLC analysis with gas chromatography-mass spectrometry. Using the pulse-chase technique with [3H]pregnenolone as a precursor, the formation of a series of metabolites was observed, including dehydroepiandrosterone, androstenedione, testosterone, 5alpha-DHT, and estradiol. These data demonstrate the existence of an active form of 17beta-HSD in the frog telencephalon, which is likely involved in testosterone biosynthesis within the brain.

Localization of 17beta-hydroxysteroid dehydrogenase and characterization of testosterone in the brain of the male frog.

Several enzymes involved in the formation of steroids of the pregnene and pregnane series have been identified in the brain, but the biosynthesis of testosterone has never been reported in the central nervous system. In the present study, we have investigated the distribution and bioactivity of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) (EC 1.1.1.62; a key enzyme that is required for the formation of testosterone and estradiol) in the brain of the male frog Rana ridibunda. By using an antiserum against human type I placental 17beta-HSD, immunoreactivity was localized in a discrete group of ependymal glial cells bordering the telencephalic ventricles. HPLC analysis of telencephalon and hypothalamus extracts combined with testosterone radioimmunoassay revealed the existence of two peaks coeluting with testosterone and 5alpha-dihydrotestosterone. After HPLC purification, testosterone was identified by gas chromatography/mass spectrometry. Incubation of telencephalon slices with [3H]pregnenolone resulted in the formation of metabolites which coeluted with progesterone, 17alpha-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, and 5alpha-dihydrotestosterone. The newly synthesized steroid comigrating with testosterone was selectively immunodetected by using testosterone antibodies. These data indicate that 17beta-HSD is expressed in a subpopulation of gliocytes in the frog telencephalon and that telencephalic cells are capable of synthesizing various androgens, including dehydroepiandrosterone, androstenedione, testosterone, and 5alpha-dihydrotestosterone.

Evolution of neurotransmitter-related markers in the vertebrate telencephalon. comparative microchemical study in discrete brain regions of a frog and a turtle

1. Neurochemical markers related to cholinergic, GABAergic and glutamatergic/aspartatergic neurotransmission have been measured in telencephalic areas obtained by microdissection from frog ( Rana esculenta) and turtle ( Pseudemys scripta elegans) brain. 2. In both species, pallial areas showed remarkably higher levels of synaptosomal d-3H-aspartate high affinity uptake than basal regions. Conversely, striatal and septal areas possessed higher levels of the GABAergic marker glutamate decarboxylase (GAD) than the pallium. 3. A differential distribution of GAD was noticed in striatal regions, highest levels of the enzyme being present in the ventral striatum, followed by the nucleus accumbens and the dorsal striatum. 4. Cholinergic markers choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were rather uniformly distributed in the frog telencephalon, while, in the turtle, cholinergic markers were several-fold higher in the basal telencephalon, particularly in the striatum, than in the pallium. 5. The turtle dorsal ventricular ridge possessed ChAT levels more similar to the striatal than to the cortical ones. On the contrary, d-3H-aspartate uptake in the dorsal ventricular ridge was close to the highest levels found in cortical areas. 6. The quantitative neurochemical approach adopted for the present study appears to be a useful tool to investigate the problem of homologies and to gain new information on the evolution of neuron populations and neuronal connections in the vertebrate telencephalon.

Sodium pathway markers in normal and kindled frog brains

The present report evaluates Na,K-ATPase activity as well as Na channel levels in the frog telencephalon after kindling, i.e. the acquisition of an epileptic focus through localized low-voltage electrical stimulation of one hemisphere. K-dependent phosphatase activity and binding of tritiated ouabain were measured, revealing no change in Na,K-ATPase activity 14 h after the last seizure. Na channels were measured by binding assays using a tritiated ethylenediamine tetrodotoxin derivative. Na channels were reduced in kindled brain as compared to controls.

Immunoreactive melanocyte-stimulating hormone (α-MSH) in the brain of the frog ( Rana esculenta L.)

MSH and ACTH levels in the hypophysis, diencephalon, telencephalon, and posterior encephalon of Rana esculenta were measured by use of sensitive and specific radioimmunoassays. Significant amounts of α-MSH-like peptide were observed in the diencephalon, telencephalon, and rhombencephalon. This component seems to be of extrahypophysial origin, since it was found in animals 8 days after hypophysectomy. Sephadex G-50 gel chromatography of tissue extracts showed that frog brain MSH behaved similarly to rat MSH and to synthetic α-MSH. Frog brain MSH was degraded by rat plasma and by liver or brain homogenates at the same velocity as rat hypophysial MSH or synthetic α-MSH. Enzymatic systems able to degrade endogenous MSH were also found in the frog telencephalon. These results provide evidence that frog brain extracts contain an α-MSH-like peptide and that a number of tissues, including rat plasma, brain, and liver, as well as frog brain, contain enzymatic mechanisms capable of degrading the α-MSH.

An epileptogenic focus in the frog telencephalon. Pathways of propagation of focal activity

The routes by which focal epileptic activity spreads from one forebrain hemisphere into the contralateral one were studied in the frog, using artificial penicillin foci and transection of pathways which could be involved in this propagation. The preferential pathways here are the forebrain commissural connections, the latency of the secondary discharge being about 20 msec. After interruption of these connections, a considerably longer, multineuronal pathway through thalamic and lower brain structures can be used. The latency of the secondary discharge in this case is several times longer (more than 100 msec). Thalamus and lower (mesencephalic and rhombencephalic) centers, or sensory impulses transmitted through brain-stem structures, or both, have an important influence on the development of the secondary (mirror) focus and on the seizure susceptibility of the forebrain. In an isolated forebrain with preserved commissural pathways—modified cerveau isolé preparation—the secondary focus and the transition of the focal activity in an electrographic seizure, after metrazol application, are remarkably altered. In about one third of these cerveau isolé preparations, a high-voltage slow-wave activity was observed in the spontaneous EEG resembling the telencephalic sleep of higher vertebrates.

Effects of strychnine and gamma-aminobutyric acid on spike and wave activity in the frog telencephalon

In the paleopallium of the frog it is possible to evoke by electrical stimulation paroxysmal spike and wave activity which is in its shape and frequency characteristics very similar to the analogous electrographic seizure phenomena in the mammalian brain. In previous experiments it was demonstrated that the surface-negative slow wave of the spike and wave complex is accompanied by prolonged negativity in the dendritic layer of the pallium. The present paper presents further analysis of the electrogenesis of the spike and wave complex in the pallium of the frog. The changes of the surface electrogram and of unit activity in the granular layer were evaluated after application of strychnine and gamma-aminobutyric acid. Neither local nor general application of strychnine changed significantly the shape and frequency of the surface spike and wave electrogram, or the amount and time distribution of unit activity during the seizure. Gamma-amino butyric acid, applied locally, suppressed the negative wave in the surface electrogram, changing the spike and wave activity into an activity of slow surface-positive spikes. At the same time, unit activity in the granular layer was augmented. The results are interpreted in the sense that the wave of the spike and wave complex is the product of synchronized axodendritic EPSP in the dendritic layer, being at the same time an inhibitory correlate as regards unit activity in the granular layer of the pallium.

Propagation of after-discharge between temporal lobes.

ArticlesPROPAGATION OF AFTER-DISCHARGE BETWEEN TEMPORAL LOBESReinaldo Poblete, Robert J. Ruben, and A. Earl WalkerReinaldo Poblete, Robert J. Ruben, and A. Earl WalkerPublished Online:01 Sep 1959https://doi.org/10.1152/jn.1959.22.5.538MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByCortical kindled convulsions: Disruption of inhibitory avoidancePhysiology & Behavior, Vol. 25, No. 1Bilateral synchrony of epileptic discharge associated with chronic asymmetrical cortical fociElectroencephalography and Clinical Neurophysiology, Vol. 34, No. 1Some results of studies on split brainPhysiology & Behavior, Vol. 7, No. 5Electrically-induced afterdischarges in the inferotemporal cortex of monkeys: Effects on visual discrimination and discrimination-reversal performanceNeuropsychologia, Vol. 8, No. 4Retrograde amnestic effects of inferotemporal and amygdaloid seizures upon conditioned suppression of lever-pressing in monkeysNeuropsychologia, Vol. 8, No. 4Paradoxical interocular transfer of mirror-image discriminations in the optic chiasm sectioned monkeyBrain Research, Vol. 10, No. 2An epileptogenic focus in the frog telencephalon. Pathways of propagation of focal activityExperimental Neurology, Vol. 21, No. 4Regional differences in the hippocampus of the catElectroencephalography and Clinical Neurophysiology, Vol. 16, No. 5Regional differences in the hippocampus of the catElectroencephalography and Clinical Neurophysiology, Vol. 16, No. 5A statistical analysis on the location of EEG abnormalitiesElectroencephalography and Clinical Neurophysiology, Vol. 12, No. 4 More from this issue > Volume 22Issue 5September 1959Pages 538-553 https://doi.org/10.1152/jn.1959.22.5.538PubMed14433553History Published online 1 September 1959 Published in print 1 September 1959 Metrics