Stereological assessment of the dorsal anterior cingulate cortex in schizophrenia: absence of changes in neuronal and glial densities.

AIMS: The prefrontal and anterior cingulate cortices are implicated in schizophrenia, and many studies have assessed volume, cortical thickness, and neuronal densities or numbers in these regions. Available data, however, are rather conflicting and no clear cortical alteration pattern has been established. Changes in oligodendrocytes and white matter have been observed in schizophrenia, introducing a hypothesis about a myelin deficit as a key event in disease development. METHODS: We investigated the dorsal anterior cingulate cortex (dACC) in 13 men with schizophrenia and 13 age- and gender-matched controls. We assessed stereologically the dACC volume, neuronal and glial densities, total neurone and glial numbers, and glia/neurone index (GNI) in both layers II-III and V-VI. RESULTS: We observed no differences in neuronal or glial densities. No changes were observed in dACC cortical volume, total neurone numbers, and total glial numbers in schizophrenia. This contrasts with previous findings and suggests that the dACC may not undergo as severe changes in schizophrenia as is generally believed. However, we observed higher glial densities in layers V-VI than in layers II-III in both controls and patients with schizophrenia, pointing to possible layer-specific effects on oligodendrocyte distribution during development. CONCLUSIONS: Using rigorous stereological methods, we demonstrate a seemingly normal cortical organization in an important neocortical area for schizophrenia, emphasizing the importance of such morphometric approaches in quantitative neuropathology. We discuss the significance of subregion- and layer-specific alterations in the development of schizophrenia, and the discrepancies between post mortem histopathological studies and in vivo brain imaging findings in patients.

The distribution of dopamine D1 receptor and mu-opioid receptor 1 receptor immunoreactivities in the amygdala and interstitial nucleus of the posterior limb of the anterior commissure: relationships to tyrosine hydroxylase and opioid peptide terminal systems.

Mismatches between dopamine innervation and dopamine D1 receptor (D1) distribution have previously been demonstrated in the intercalated cell masses of the rat amygdala. Here the distribution of enkephalin and beta-endorphin immunoreactive (IR) nerve terminals with respect to their mu-opioid receptors is examined in the intercalated cell masses, along with a further immunohistochemical analysis of the dopamine/D1 mismatches. A similar analysis is also made within the extended amygdala. A spatial mismatch in distribution patterns was found between the mu-opioid receptor-1 immunoreactivity and enkephalin IR in the main intercalated island of the amygdala. Discrete cell patches of dopamine D1 receptor and mu-opioid receptor-1 IR were also identified in a distinct region of the extended amygdala, the interstitial nucleus of the posterior limb of the anterior commissure, medial division (IPACM), which displayed sparse tyrosine hydroxylase or enkephalin/beta-endorphin IR nerve terminals. Furthermore, distinct regions of the main intercalated island that showed dopamine/D1 receptor matches (the rostral and rostrolateral parts) were associated with strong dopamine and cyclic AMP regulated phosphoprotein, 32 kDa-IR in several D1 IR neuronal cell bodies and dendrites, whereas this was not the case for the dopamine/D1 mismatch areas (the rostromedial and caudal parts) of the main intercalated island. The lack of correlation between the terminal/receptor distribution patterns suggests a role for volume transmission for mu-opioid receptor- and dopamine D1 receptor-mediated transmission in distinct regions of the amygdala and extended amygdala. This may have implications for amygdaloid function, where slow long lasting responses may develop as a result of volume transmission operating in opioid peptide and dopaminergic communication.

Dynamics of volume transmission in the brain. Focus on catecholamine and opioid peptide communication and the role of uncoupling protein 2.

This review focuses on transmitter-receptor mismatches in the brain, which is one of the hallmarks of the Volume Transmission (VT) concept, and how this phenomenon may be related to local temperature gradients created by brain uncoupling protein 2 (UCP2), which uncouples oxidative phosphorylation from ATP synthesis, hereby generating heat. Recent studies on transmitter-receptor mismatches have revealed dopamine and opioid peptide receptor mismatches in the intercalated islands of the amygdala, which are GABAergic cell clusters regulating amygdaloid output. Such mismatches have also been found in regions belonging to the extended amygdala and the nucleus accumbens shell. Now substantial UCP2 immunoreactivity has been found within the above transmitter-receptor mismatch regions, suggesting that UCP2 may enhance diffusion and convection of DA and opioid peptides in such regions by generation of local temperature gradients, thereby contributing to a dynamic regulation of VT.

The dopamine D1 receptor-rich main and paracapsular intercalated nerve cell groups of the rat amygdala: relationship to the dopamine innervation.

The intercalated cell masses are GABAergic neurons interposed between the major input and output structures of the amygdala. Dopaminergic projections to the main and paracapsular intercalated islands were examined by determining the relationship of the dopamine nerve-terminal networks to the D1-receptor immunoreactive staining of cells within the intercalated islands, using double-fluorescence immunolabelling procedures in combination with confocal laser microscopy. The relationship of terminals positive for both tyrosine hydroxylase and dopamine beta-hydroxylase (noradrenaline and/or adrenaline) to terminals positive for tyrosine hydroxylase but negative for dopamine beta-hydroxylase (dopamine terminals) was studied in relation to the D1-receptor immunoreactivity in adjacent sections at various rostrocaudal levels. The microscopy and image analysis revealed that there was only a minor dopaminergic innervation of the D1 receptor-immunoreactive cells in the rostromedial and caudal component of the main intercalated island, suggesting volume transmission as the main communication mode for dopamine in these regions. In contrast, the D1 receptor-immunoreactive areas in the rostrolateral part of the main island and also the paracapsular intercalated islands showed a high degree of dopaminergic innervation, indicating that synaptic and perisynaptic dopamine transmission plays a dominant role in these regions. It is known that amygdala neurons are involved in the elicitation and learning of fear-related behaviors. We suggest that slow dopaminergic volume transmission in the rostromedial and caudal parts of the main intercalated island may have a role in tonic excitatory modulation in these parts of the main island, allowing GABAergic activity to develop in the central amygdaloid nucleus and thereby contributing to inhibition of fear-related behavioral and autonomic responses. In contrast, a faster synaptic and perisynaptic dopaminergic transmission in the rostrolateral part of the main intercalated island and in the paracapsular intercalated islands may have a role in allowing a more rapid elicitation of fear-related behaviors.

Intracerebral infusion of H-dopamine and H-mannitol in the striatum of halothane-anaesthetized male rats. A dual-probe microdialysis study of long-distance diffusion.

This report characterizes an in vivo intracerebral long-distance diffusion model using dual-probe microdialysis. Two probes 1 mm apart were implanted into the striatum of control and 6-hydroxydopamine (6-OHDA)-lesioned halothane-anaesthetized male rats. Either tritiated dopamine (500 nM 3H-DA) or mannitol (1.5 microM 3H-mannitol) was infused continuously for 5 h, while samples were collected from the other probe. Samples (10 microl) were counted by liquid scintillation. For the DA-infused rats, another 10 microL was separated with high-pressure liquid chromatography (HPLC)-electrochemical detection into individual fractions containing 3,4-dihydroxy phenylacetic acid (DOPAC) and homovanillinic acid (HVA), and counted for beta-decay. The total transfer of 3H-labelled compounds described the overall effect of cellular uptake, metabolism and clearance into the microcirculation, and was compared with that of an extracellular marker, 3H-mannitol. The migration reached steady-state levels, generating an equilibrium between delivery and removal from the extracellular space. The half-time of the steady-state values, t50%, was in all cases lower in 6-OHDA-treated rats compared with control. In addition, the t50% values of 3H-mannitol were lower than those following the 3H-dopamine infusion in both control or 6-OHDA-lesioned rats. However, it was not possible to detect any unmetabolized 3H-dopamine at the 1 mm distance. In conclusion, the dual-probe microdialysis approach proved to be a valid method to study in vivo diffusion and migration in the brain, and the intracerebral spread of compounds highly depends on the nature of the compound infused.