20 research outputs found
Stereological estimations and neurochemical characterization of neurons expressing GABAA and GABAB receptors in the rat pedunculopontine and laterodorsal tegmental nuclei
To better understand GABAergic transmission at two targets of basal ganglia downstream projections, the pedunculopontine (PPN) and laterodorsal (LDT) tegmental nuclei, the anatomical localization of GABAA and GABAB receptors was investigated in both nuclei. Specifically, the total number of neurons expressing the GABAA receptor γ2 subunit (GABAAR γ2) and the GABAB receptor R2 subunit (GABAB R2) in PPN and LDT was estimated using stereological methods, and the neurochemical phenotype of cells expressing each subunit was also determined. The mean number of non-cholinergic cells expressing GABAAR γ2 was 9850 ± 1856 in the PPN and 8285 ± 962 in the LDT, whereas those expressing GABAB R2 were 7310 ± 1970 and 9170 ± 1900 in the PPN and LDT, respectively. In addition, all cholinergic neurons in both nuclei co-expressed GABAAR γ2 and 95–98% of them co-expressed GABAB R2. Triple labeling using in situ hybridization revealed that 77% of GAD67 mRNA-positive cells in the PPT and 49% in the LDT expressed GABAAR γ2, while 90% (PPN) and 65% (LDT) of Vglut2 mRNA-positive cells also expressed GABAAR γ2. In contrast, a similar proportion (~2/3) of glutamatergic and GABAergic cells co-expressed GABAB R2 in both nuclei. The heterogeneous distribution of GABAAR and GABABR among non-cholinergic cells in PPN and LDT may give rise to physiological differences within each neurochemical subpopulation. In addition, the dissimilar proportion of GABAAR γ2-expressing glutamatergic and GABAergic neurons in the PPN and LDT may contribute to some of the functional differences found between the two nuclei
Thalamic interaction between the input and the output systems of the basal ganglia
The striatal return through the thalamus is largely neglected in current studies dealing with basal ganglia function, and its role within this circuitry remains obscure. In this contribution the thalamus is regarded as an important place of interaction between the input and the output organization of the basal ganglia. In support of this idea, a brief overview is provided of some of the most recent findings concerning the thalamus in relation to the basal ganglia circuitry. In particular, we have focused on the thalamostriatal projections themselves, on the output of the basal ganglia to the thalamus and also on the overlapping territories between the thalamic projection of the output nuclei and the thalamostriatal neurons. These data support the existence of several thalamic feedback circuits within the basal ganglia neural system. Finally, some considerations are provided upon the functional significance of these thalamic feedback circuits in the overall organization of the basal ganglia
Barrel pattern formation requires serotonin uptake by thalamocortical afferents, and not vesicular monoamine release
Thalamocortical neurons innervating the barrel cortex in neonatal rodents transiently store serotonin (5-HT) in synaptic vesicles by expressing the plasma membrane serotonin transporter (5-HTT) and the vesicular monoamine transporter (VMAT2). 5-HTT knock-out (ko) mice reveal a nearly complete absence of 5-HT in the cerebral cortex by immunohistochemistry, and of barrels, both at P7 and adulthood. Quantitative electron microscopy reveals that 5-HTT ko affects neither the density of synapses nor the length of synaptic contacts in layer IV. VMAT2 ko mice, completely lacking activity-dependent vesicular release of monoamines including 5-HT, also show a complete lack of 5-HT in the cortex but display largely normal barrel fields, despite sometimes markedly reduced postnatal growth. Transient 5-HTT expression is thus required for barrel pattern formation, whereas activity-dependent vesicular 5-HT release is not
Stereological estimates of glutamatergic, GABAergic, and cholinergic neurons in the pedunculopontine and laterodorsa tegmental nuclei in the rat
The pedunculopontine tegmental nucleus (PPN) and laterodorsal tegmental nucleus (LDT) are functionally associated brainstem structures implicated in behavioral state control and sensorimotor integration. The PPN is also involved in gait and posture, while the LDT plays a role in reward. Both nuclei comprise characteristic cholinergic neurons intermingled with glutamatergic and GABAergic cells whose absolute numbers in the rat have been only partly established. Here we sought to determine the complete phenotypical profile of each nucleus to investigate potential differences between them. Counts were obtained using stereological methods after the simultaneous visualization of cholinergic and either glutamatergic or GABAergic cells. The two isoforms of glutamic acid decarboxylase (GAD), GAD65 and GAD67, were separately analyzed. Dual in situ hybridization revealed coexpression of GAD65 and GAD67 mRNAs in ∼90% of GAD-positive cells in both nuclei; thus, the estimated mean numbers of (1) cholinergic, (2) glutamatergic, and (3) GABAergic cells in PPN and LDT, respectively, were (1) 3,360 and 3,650; (2) 5,910 and 5,190; and (3) 4,439 and 7,599. These data reveal significant differences between PPN and LDT in their relative phenotypical composition, which may underlie some of the functional differences observed between them. The estimation of glutamatergic cells was significantly higher in the caudal PPN, supporting the reported functional rostrocaudal segregation in this nucleus. Finally, a small subset of cholinergic neurons (8% in PPN and 5% in LDT) also expressed the glutamatergic marker Vglut2, providing anatomical evidence for a potential corelease of transmitters at specific target areas
Axonal branching patterns of nucleus accumbens neurons in the rat
ABSTRACT
The patterns of axonal collateralization of nucleus
accumbens (Acb) projection neurons were investigated
in the rat by means of single-axon tracing techniques
using the anterograde tracer biotinylated dextran
amine. Seventy-three axons were fully traced, originating
from either the core (AcbC) or shell (AcbSh) compartment,
as assessed by differential calbindin D28kimmunoreactivity.
Axons from AcbC and AcbSh showed
a substantial segregation in their targets; target areas
were either exclusively or preferentially innervated from
AcbC or AcbSh. Axon collaterals in the subthalamic nucleus
were found at higher than expected frequencies;
moreover, these originated exclusively in the dorsal
AcbC. Intercompartmental collaterals were observed
from ventral AcbC axons into AcbSh, and likewise,
interconnections at pallidal and mesencephalic levels
were also observed, although mostly from AcbC axons
toward AcbSh targets, possibly supporting crosstalk
between the two subcircuits at several levels. Cell
somata giving rise to short-range accumbal axons, projecting
to the ventral pallidum (VP), were spatially intermingled
with others, giving rise to long-range axons
that innervated VP and more caudal targets. This anatomical
organization parallels that of the dorsal striatum
and provides the basis for possible dual direct and indirect
actions from a single axon on either individual or
small sets of neurons. J. Comp. Neurol. 518:4649–
4673, 2010
Two-color fluorescence labeling in acrolein-fixed brain tissue
SUMMARY Acrolein is a potent fixative that provides both excellent preservation of ultrastructural
morphology and retention of antigenicity, thus it is frequently used for immunocytochemical
detection of antigens at the electron microscopic level. However, acrolein is not
commonly used for fluorescence microscopy because of concerns about possible autofluorescence
and destruction of the luminosity of fluorescent dyes. Here we describe a simple protocol
that allows fine visualization of two fluorescent markers in 40-mm sections from acroleinperfused
rat brain. Autofluorescence was removed by pretreatment with 1% sodium borohydride
for 30 min, and subsequent incubation in a 50% ethanol solution containing 0.3%
hydrogen peroxide enhanced fluorescence labeling. Thus, fluorescence labeling can be used
for high-quality detection of markers in tissue perfused with acrolein. Furthermore, adjacent
acrolein-fixed sections from a single experiment can be processed to produce high-quality
results for electron microscopy or fluorescence labeling
Two-color fluorescence labeling in acrolein-fixed brain tissue
SUMMARY Acrolein is a potent fixative that provides both excellent preservation of ultrastructural
morphology and retention of antigenicity, thus it is frequently used for immunocytochemical
detection of antigens at the electron microscopic level. However, acrolein is not
commonly used for fluorescence microscopy because of concerns about possible autofluorescence
and destruction of the luminosity of fluorescent dyes. Here we describe a simple protocol
that allows fine visualization of two fluorescent markers in 40-mm sections from acroleinperfused
rat brain. Autofluorescence was removed by pretreatment with 1% sodium borohydride
for 30 min, and subsequent incubation in a 50% ethanol solution containing 0.3%
hydrogen peroxide enhanced fluorescence labeling. Thus, fluorescence labeling can be used
for high-quality detection of markers in tissue perfused with acrolein. Furthermore, adjacent
acrolein-fixed sections from a single experiment can be processed to produce high-quality
results for electron microscopy or fluorescence labeling
Stereological estimations and neurochemical characterization of neurons expressing GABAA and GABAB receptors in the rat pedunculopontine and laterodorsal tegmental nuclei
To better understand GABAergic transmission at two targets of basal ganglia downstream projections, the pedunculopontine (PPN) and laterodorsal (LDT) tegmental nuclei, the anatomical localization of GABAA and GABAB receptors was investigated in both nuclei. Specifically, the total number of neurons expressing the GABAA receptor γ2 subunit (GABAAR γ2) and the GABAB receptor R2 subunit (GABAB R2) in PPN and LDT was estimated using stereological methods, and the neurochemical phenotype of cells expressing each subunit was also determined. The mean number of non-cholinergic cells expressing GABAAR γ2 was 9850 ± 1856 in the PPN and 8285 ± 962 in the LDT, whereas those expressing GABAB R2 were 7310 ± 1970 and 9170 ± 1900 in the PPN and LDT, respectively. In addition, all cholinergic neurons in both nuclei co-expressed GABAAR γ2 and 95–98% of them co-expressed GABAB R2. Triple labeling using in situ hybridization revealed that 77% of GAD67 mRNA-positive cells in the PPT and 49% in the LDT expressed GABAAR γ2, while 90% (PPN) and 65% (LDT) of Vglut2 mRNA-positive cells also expressed GABAAR γ2. In contrast, a similar proportion (~2/3) of glutamatergic and GABAergic cells co-expressed GABAB R2 in both nuclei. The heterogeneous distribution of GABAAR and GABABR among non-cholinergic cells in PPN and LDT may give rise to physiological differences within each neurochemical subpopulation. In addition, the dissimilar proportion of GABAAR γ2-expressing glutamatergic and GABAergic neurons in the PPN and LDT may contribute to some of the functional differences found between the two nuclei
Continuous performance of a novel motor sequence leads to highly correlated striatal and hippocampal perfusion increases
The time course of changes in regional cerebral perfusion during a continuous motor learning task performed
with the right hand was monitored using the arterial spin labeling (ASL) technique at high field (3 T). ASL
allowed measuring explicit learning related effects in neural activity elicited throughout a 6 minute task
period. During this time learning took place as demonstrated by performance improvement. Comparing the
initial and final learning phases, perfusion decreases were detected in most of the cortical regions recruited
during early learning. More interestingly however perfusion increases were observed in a few cortical and
subcortical regions of the contralateral hemisphere: the supplementary motor area, the primary somatosensory
area, the posterior insula and posterior putamen, the hippocampus and bilaterally the retrosplenial
cortex. Moreover, perfusion increases in the posterior putamen and hippocampus were highly correlated
during the learning period. These results support the hypothesis that the striatum and hippocampus form
interactive memory systems with parallel processin
Effects on resting cerebral blood flow and functional connectivity induced by metoclopramide: a perfusion MRI study in healthy volunteers
Background and purpose: The substituted benzamide, metoclopramide, is a dopamine receptor anatagonist and is widely prescribed in the symptomatic treatment of nausea and vomiting, although it can cause adverse motor and non-motor side effects. The effects of metoclopramide on brain metabolism have not been investigated to date. Experimental approach: To determine effects of metaclopramide on brain function, cerebral perfusion changes after a single oral dose were assessed in healthy volunteers using magnetic resonance imaging (MRI) techniques. Arterial spin labeling (ASL) perfusion MRI was used to measure cerebral blood flow before and after metoclopramide. Blood haemodynamics in the vertebral and internal carotid arteries were evaluated using phase-contrast MRI. Key results: Metoclopramide altered haemodynamics in the carotid arteries and the cerebral perfusion. Perfusion increased bilaterally in the putamen, consistent with antagonism of dopamine D(2) receptors by metoclopramide and possibly related to its motor side-effects. In contrast, reduced perfusion was observed in the insular cortices and anterior temporal lobes. In addition, functional connectivity between the insular cortex and the dorsolateral prefrontal cortex was decreased. Conclusions and implications: These cortical changes affecting neural circuits between high-order association areas may underlie certain neuropsychiatric conditions occasionally reported after metoclopramide administration. The present results show the sensitivity of ASL to detect small changes in regional blood flow, closely related to brain function, after a single pharmacological challenge, highlighting the potential of this technique for human pharmacological studies