Decreased synaptic and mitochondrial density in the postmortem anterior cingulate cortex in schizophrenia

Schizophrenia (SZ) is a mental illness characterized by psychosis, negative symptoms, and cognitive deficits. The anterior cingulate cortex (ACC), a structurally and functionally diverse region, is one of several brain regions that is abnormal in SZ. The present study compared synaptic organization and mitochondrial number and morphology in postmortem ACC in SZ versus normal control (NC). Total synaptic density in the combined ACC was decreased in SZ, to 72% of normal controls (NCs), due to selective decreases in axospinous synapses, both asymmetric (excitatory) and symmetric (inhibitory). These changes were present in layers 3 and 5/6. The density of mitochondria in all axon terminals combined in SZ was decreased to 64% of NC. In layer 3, mitochondrial density was decreased only in terminals forming asymmetric synapses with spines, while in layers 5/6 mitochondrial density was decreased in terminals forming symmetric synapses with spines and dendrites. The proportion of terminals making symmetric synapses that contained mitochondria was significantly lower in SZ than in NCs, especially for symmetric axospinous synapses. The number of mitochondria per neuronal somata was decreased in the ACC in SZ compared to NCs; this finding was present in layers 5-6. The size of mitochondria in neuronal somata and throughout the neuropil was similar in SZ and NCs. Our results, though preliminary, are well supported by the literature, and support an anatomical substrate for some of the altered executive functions found in SZ.

A direct anterior cingulate pathway to the primate primary olfactory cortex may control attention to olfaction

Behavioral and functional studies in humans suggest that attention plays a key role in activating the primary olfactory cortex through an unknown circuit mechanism. We report that a novel pathway from the anterior cingulate cortex, an area which has a key role in attention, projects directly to the primary olfactory cortex in rhesus monkeys, innervating mostly the anterior olfactory nucleus. Axons from the anterior cingulate cortex formed synapses mostly with spines of putative excitatory pyramidal neurons and with a small proportion of a neurochemical class of inhibitory neurons that are thought to have disinhibitory effect on excitatory neurons. This novel pathway from the anterior cingulate is poised to exert a powerful excitatory effect on the anterior olfactory nucleus, which is a critical hub for odorant processing via extensive bilateral connections with primary olfactory cortices and the olfactory bulb. Acting on the anterior olfactory nucleus, the anterior cingulate may activate the entire primary olfactory cortex to mediate the process of rapid attention to olfactory stimuli.

Positive symptoms and white matter microstructure in never-medicated first episode schizophrenia

BACKGROUND

We investigated cerebral structural connectivity and its relationship to symptoms in never-medicated individuals with first-onset schizophrenia using diffusion tensor imaging (DTI).

METHOD

We recruited subjects with first episode DSM-IV schizophrenia who had never been exposed to antipsychotic medication (n=34) and age-matched healthy volunteers (n=32). All subjects received DTI and structural magnetic resonance imaging scans. Patients' symptoms were assessed on the Positive and Negative Syndrome Scale. Voxel-based analysis was performed to investigate brain regions where fractional anisotropy (FA) values significantly correlated with symptom scores.

RESULTS

In patients with first-episode schizophrenia, positive symptoms correlated positively with FA scores in white matter associated with the right frontal lobe, left anterior cingulate gyrus, left superior temporal gyrus, right middle temporal gyrus, right middle cingulate gyrus, and left cuneus. Importantly, FA in each of these regions was lower in patients than controls, but patients with more positive symptoms had FA values closer to controls. We found no significant correlations between FA and negative symptoms.

CONCLUSIONS

The newly-diagnosed, neuroleptic-naive patients had lower FA scores in the brain compared with controls. There was positive correlation between FA scores and positive symptoms scores in frontotemporal tracts, including left fronto-occipital fasciculus and left inferior longitudinal fasciculus. This implies that white matter dysintegrity is already present in the pre-treatment phase and that FA is likely to decrease after clinical treatment or symptom remission.

Cytology and receptor architecture of human anterior cingulate cortex

Anterior cingulate cortex (ACC) is involved in emotion, mood, and autonomic regulation. Although a subgenual part of ACC (sACC) may be vulnerable in depression and area 25 is cytologically unique, there are no assessments that contrast this region with pregenual ACC (pACC). Thus, we undertook independent multimodal verifications of architectural differences among subregions and areas. Areas 24a and 24b have pregenual and subgenual components. The latter have a thin layer III. Area 24c has dorsal (pd24c) and ventral (pv24c) parts. Area pd24c has larger neurofilament-expressing neurons in layer Va, and neurons in Vb form aggregates in area pv24c. Area pd24c occupies both banks of the cingulate sulcus, with pv24c on the ventral bank. Layer III of pd24cd has many larger neurofilament-expressing neurons and a richer dendritic plexus. Area 32 has pregenual (p32) and subgenual (s32) components. Layer II in s32 is of particular note because it has a neuron-dense IIa and sparse IIb. Area 25 has anterior (25a) and posterior (25p) parts; 25p has the thinnest layer III in the cingulate gyrus. Area 25a contains significantly higher AMPA, kainate, NMDA, GABA(A), GABA(B), and alpha(1) densities than 25p. Area 33 continues around the genu and ventrally to encompass the full caudal extent of area 25. Subgenual ACC has significantly higher GABA(A), GABA(B), benzodiazepine (BZ), alpha(1), and 5-HT(1A) densities than pACC. GABA(B), BZ, and alpha(1) binding confirms the subdivision of area pd24c. In conclusion, ACC comprises two parts that are unique in terms of their cytoarchitecture and neurotransmitter receptor organization.

Age-related and laminar-specific dendritic changes in the medial frontal cortex of the rat

Early hypotheses that normal brain aging involves widespread loss of neurons have been revised in light of accumulating evidence that, in most regions of the brain, the number of neurons is stable throughout adulthood and senescence. It is not clear, however, that all aspects of neuronal structure are similarly maintained, and anatomical changes are likely to contribute to age-related declines in cognitive function. The extent and pattern of dendritic branches is one likely target for age-dependent regulation since dendrites remain plastic into adulthood and since dendrites, as the site of most synapses, critically regulate neuronal function. This study quantified the dendritic extent and geometry of superficial and deep pyramidal neurons in the medial frontal cortex of Brown Norway rats from young adulthood through senescence. This region of cortex is of specific interest given its involvement in a variety of cognitive functions that change with age. In the present study, age-related changes in dendritic extent were found to occur with remarkable specificity. Superficial, but not deep, pyramidal neurons exhibited ongoing dendritic growth after 2 months-of-age and then dendritic regression after 18 months-of-age. Apical and basal dendrites were similarly regulated; in each arbor adult growth and regression were limited to terminal dendritic segments. The focal specificity of age-related changes suggests several possible regulatory mechanisms, including regional changes in trophic support and in neuronal activity. Although restricted to specific neuronal populations, dendritic regression in aged animals is likely to contribute to cognitive changes associated with senescence.

Distribution of 1,25-dihydroxyvitamin D3 receptor immunoreactivity in the limbic system of the rat

We used immunocytochemistry to obtain a complete cellular and subcellular mapping of the 1,25-dihydroxyvitamin D3 receptor protein (VDR) in the rat limbic system. We observed specific VDR immunostaining in the nucleus as well as in the perinuclear cytoplasm of neuronal cells. The limbic system consists of a variety of neuronal structures, and is known to have influence on memory, behavior, emotions and reproduction. In the hippocampal formation, we found strong nuclear staining as well as less distinguished cytoplasmic VDR staining in CA1, CA3 and CA4. The CA2 area showed a unique cytoplasmic predominance of VDR. The amygdala was found to exhibit specific patterns of VDR distribution in the various regions of the nucleus. We observed distinct differences of VDR localization within the limbic preoptic areas of the hypothalamus. Further parts of the brain we analyzed included the mammillary bodies, the indusium griseum and the cingulate cortex. The subcellular distribution of VDR in regions of the limbic system suggests a specific functional role of the receptor protein and indicates a role for calcitriol as a neuroactive steroid.

Presence of NMDA-type glutamate receptors in cingulate corticostriatal terminals and their postsynaptic targets

The glutamatergic projection from the anterior cingulate cortex to the medial caudate-putamen nucleus (CPN) has been implicated in motor and cognitive functions, many of which are potently modulated by activation of N-methyl-D-aspartate subtype of glutamate receptors (NMDARs). To determine the functional sites for NMDAR activation within this circuitry, we combined anterograde transport of biotinylated dextran amine (BDA) from deep layers of the rat anterior cingulate cortex with immunogold labeling of NMDAR subunit, NMDAR1, in the dorsomedial CPN. BDA-containing axons were seen in patch-like clusters in a neuropil that showed more uniform immunogold-silver labeling for NMDAR1. Electron microscopy of these regions showed that BDA-labeling was present exclusively in axons and terminals, 23% (98 of 421) of which also contained NMDAR1-immunoreactivity (IR). BDA-labeled terminals often apposed NMDAR1-immunoreactive neuronal and glial profiles. These terminals also formed asymmetric excitatory-type synapses with dendritic spines. Of 155 anterogradely labeled axon terminals forming asymmetric synapses, 34% were with NMDAR1-labeled, and 66% with unlabeled dendritic spines. These results provide ultrastructural evidence for the involvement of NMDARs in presynaptic regulation of glutamate transmission, and in postsynaptic modulation of the excitability of spiny neurons in patch-like compartments of the dorsomedial CPN. These dual NMDAR-mediated actions are likely to play a major role in the acquisition of new behaviors and reward-related processes that have been associated with cortical input to the striatal patch compartments.

N-Methyl-D-aspartate antagonists and apoptotic cell death triggered by head trauma in developing rat brain

Morbidity and mortality from head trauma is highest among children. No animal model mimicking traumatic brain injury in children has yet been established, and the mechanisms of neuronal degeneration after traumatic injury to the developing brain are not understood. In infant rats subjected to percussion head trauma, two types of brain damage could be characterized. The first type or primary damage evolved within 4 hr and occurred by an excitotoxic mechanism. The second type or secondary damage evolved within 6-24 hr and occurred by an apoptotic mechanism. Primary damage remained localized to the parietal cortex at the site of impact. Secondary damage affected distant sites such as the cingulate/retrosplenial cortex, subiculum, frontal cortex, thalamus and striatum. Secondary apoptotic damage was more severe than primary excitotoxic damage. Morphometric analysis demonstrated that the N-methyl-D-aspartate receptor antagonists 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonate and dizocilpine protected against primary excitotoxic damage but increased severity of secondary apoptotic damage. 2-Sulfo-alpha-phenyl-N-tert-butyl-nitrone, a free radical scavenger, did not affect primary excitotoxic damage but mitigated apoptotic damage. These observations demonstrate that apoptosis and not excitotoxicity determine neuropathologic outcome after traumatic injury to the developing brain. Whereas free radical scavengers may prove useful in therapy of head trauma in children, N-methyl-D-aspartate antagonists should be avoided because of their propensity to increase severity of apoptotic damage.

Neuronal degeneration and microglial reaction in the fetal and postnatal rat brain after transient maternal hypoxia

This study examined the neuropathological changes in different areas of the brain of fetal and postnatal rats after transient maternal hypoxia. At different time intervals following hypoxia, reactive microglia as determined immunohistochemically with the antibody OX-42 that recognizes complement type three (CR3) receptors, responded vigorously to the hypoxic stress. Microglial activation was particularly evident in the cingulate cortex and the corpus callosum between 3 h and 14 days after hypoxia. Massive cell degeneration as determined ultrastructurally and significant neuronal loss as evaluated by cell counts were observed in the cingulate cortex at 1 and 3 days after hypoxic insults; thereafter, however, the neuronal density was restored to normal levels. Present results suggest that the cingulate cortex is most vulnerable to the hypoxic injury probably due to a redistribution of cerebral blood flow and/or metabolic changes. Besides being involved in the phagocytosis of cellular debris, it is suggested that the reactive microglial cells may have both neurotoxic and neurotrophic functions.

Ultrastructure and distribution of corticothalamic fiber terminals from the posterior cingulate cortex and the presubiculum to the anteroventral thalamic nucleus of the rat

The ultrastructure of axon terminals in the anteroventral thalamic nucleus arising in the cingulate cortex and in the presubiculum was examined using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase in rats. Anterogradely labeled axonal arborizations arising from the posterior cingulate cortex were concentrated bilaterally in the ventral part of the anteroventral nucleus. In electron micrographs these thalamic terminals arising from the posterior cingulate cortex were consistently small, contained round vesicles, and established asymmetric contacts on distal dendritic processes. In contrast, the axonal arborizations arising from the presubiculum were concentrated ipsilaterally in the dorsal part of the anteroventral nucleus and comprised two identifiable populations of terminals. The smaller terminals, which contained densely packed round vesicles, established asymmetric synaptic contacts on distal dendritic processes and resembled the posterior cingulate cortex terminals described above. The other population of the presubiculum terminals consisted of medium-sized terminals. These contained loosely packed round vesicles and established asymmetric synaptic contacts on proximal dendritic processes. These results indicate that the posterior cingulate cortex and the presubiculum project differentially upon the anteroventral thalamic nucleus. They also indicate that although the posterior cingulate cortex gives rise to only one type of corticothalamic terminal, the presubiculum gives rise to two types of corticothalamic terminals. When taken together, these data suggest that these different limbic cortical areas might subserve distinct roles in the anteroventral thalamic nucleus function.

Glutamate receptor dysfunction and schizophrenia

In this article, we advance a unified hypothesis pertaining to combined dysfunction of dopamine and N-methyl-D-aspartate glutamate receptors that highlights N-methyl-D-aspartate receptor hypofunction as a key mechanism that can help explain major clinical and pathophysiological aspects of schizophrenia. The following fundamental features of schizophrenia are accommodated by this hypothesis: (1) the occurrence of structural brain changes during early development that have the potential for producing subsequent clinical manifestations of schizophrenia, (2) a quiescent period in infancy and adolescence before clinical manifestations are expressed, (3) onset in early adulthood of psychotic symptoms, (4) involvement of dopamine (D2) receptors in some cases but not others that would explain why some but not all patients are responsive to typical neuroleptic therapy, and (5) ongoing neurodegenerative changes and cognitive deterioration in some patients. We propose that since N-methyl-D-aspartate receptor hypofunction can cause psychosis in humans and corticolimbic neurodegenerative changes in the rat brain, and since these changes are prevented by certain antipsychotic drugs, including atypical neuroleptic agents (clozapine, olanzapine, fluperlapine), a better understanding of the N-methyl-D-aspartate receptor hypofunction mechanism and ways of preventing its neurodegenerative consequences in the rat brain may lead to improved pharmacotherapy in schizophrenia.

Tempo of neurogenesis and synaptogenesis in the primate cingulate mesocortex: comparison with the neocortex

In the neocortex, the onset of the rapid phase (phase 3) of synaptogenesis occurs after the end of neurogenesis. However, we still do not know whether or not these two developmental events are causally related. The present study compares the time-course and tempo of neurogenesis and synaptogenesis in the anterior cingulate cortex (area 24 of Brodmann) and in the primary visual cortex (area 17) in a series of pre- and postnatal rhesus monkeys. Autoradiographic analysis of animals fetally injected with 3H-thymidine showed that all neurons destined for area 24 are generated by embryonic day 70, which is 30 days earlier than in area 17. The rapid phase of synaptogenesis in area 24 starts during the third embryonic month and continues at the same rate through the remainder of gestation and the first 2 months after birth, as has been seen in neocortical areas examined previously. Statistical analysis of the linear portions of the rapid phase indicates that, although neurogenesis in area 24 is completed 1 month earlier than in area 17, the rapid phase of synaptogenesis occurs 41 days later. Moreover, the tempo of synaptic accretion was remarkably similar to that in motor, somatosensory, visual, or associational areas. All were grouped within the same time window of about 40 days, centered at birth. After the second postnatal month, synaptic density in area 24 remains at a high level until sexual maturity. This work shows that the rapid phase of synaptogenesis in the cingulate mesocortex is not linked temporally to the end of neurogenesis. We suggest that it is regulated by the same genetic or humoral factors that control synaptogenesis in the phylogenetically newer neocortical areas.

YM90K, an AMPA antagonist, has no neurotoxic effects on cerebrocortical neurons in rats

The neuroprotective properties of glutamate receptor antagonists arise from their ability to antagonize the excitotoxic actions of endogenous excitatory amino acids. However, J. W. Olney et al. (1989, Science 224: 1360-1362) have reported that MK-801, an N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, induced morphological damage in neurons in the cerebral cortex of rats. YM90K is a potent alpha-amino-3-hydroxy-5-methylisoxazole propionic acid receptor antagonist which has high neuroprotective efficacy against delayed neuronal injury. The purpose of this study was to investigate whether YM90K induces a vacuolar reaction in the cytoplasm of neurons similar to that seen after the administration of MK-801. All experiments were performed on female F344 rats. YM90K was administered by iv infusion for 3 h at the dose of 40 mg/kg/h. MK-801 was given by single sc injection at the dose of 1 mg/kg. All rats receiving MK-801 showed neuronal vacuolation. The affected neurons were recognized as medium-sized pyramidal-shaped neurons which were distributed between layers II and IV in the posterior cingulate and retrosplenial neocortices. Most of these vacuoles contained multiple small and round structures that appeared to be remnants of mitochondria. Other vacuoles were recognized as enlarged sER or those present within the bilaminar nuclear membrane. MK-801 also induced heat shock protein immunoreactivity in the same neurons. In contrast, no such pathomorphological changes could be detected in the YM90K-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of interaural time differences on middle-latency and late auditory evoked magnetic fields

To determine if interaural time differences (ITDs) in binaural stimuli affect the middle-latency auditory evoked fields (AEFs) in the same manner as they affect the N100m deflection, neuromagnetic responses were recorded over the whole head using a 122-channel SQUID magnetometer. Binaural stimuli were lateralized to three positions, left, midline, and right, on the basis of ITDs. The N100m was significantly larger to stimuli with contralaterally-leading ITDs than to stimuli with no, or with ipsilaterally-leading ITDs. Neither the P30m nor the P50m deflections of the middle-latency response were significantly affected by ITD, although the P30m showed a tendency, similar to but smaller than that of N100m, to be larger to stimuli with contralaterally-leading ITDs. In some subjects, the source location of the P50m was anterior and inferior to the sources of the P30m and N100m, which are generated in the superior surface of the temporal lobe. Sound-related muscular artifacts were seen in the posterior recording channels of one subject, and the contribution of this activity to the signals over the temporal area was determined.

The nature and time course of neuronal vacuolation induced by the N-methyl-D-aspartate antagonist MK-801

N-Methyl-D-aspartate (NMDA) antagonists cause neuronal vacuolation in the posterior cingulate and retrosplenial cortex of the rat. Because the nature of neuronal pathologic changes due to NMDA antagonists may affect the potential clinical use of this class of drugs, we undertook experiments to define the nature and time course of the vacuolation caused by high-dose (5 mg/kg) MK-801 (dizocilpine, 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine). Ultrastructural examination revealed the vacuoles to be not a form of hydropic cellular degeneration, but rather a dilatation of several intracellular compartments, chiefly endoplasmic reticulum and mitochondria. Study of the time course of the alterations revealed no light or ultrastructural features of neuronal necrosis in over 1 thousand neurons examined in layers 3 and 4 of the cingulate and retrosplenial cortex, 153 of which were vacuolated. The vacuoles resolved over time by decreasing in magnitude. Oxalate-pyroantimonate methodology revealed no redistribution of cell calcium in either vacuolated or non-vacuolated neurons. At 6 h, when vacuoles were consistently prominent in glutaraldehyde-fixed plastic-embedded tissue, a separate series of experiments was undertaken to vary methods of tissue preparation, and determine conditions under which vacuolation occurs. Frozen sections revealed no vacuoles. Subsequent paraffin embedding of the previously frozen tissue revealed no vacuoles, but vacuoles were seen in paraffin after perfusion fixation. Immersion fixation with brain refrigeration for 12 h prior to fixation revealed no vacuoles. Alcohol fixation also led to no visible vacuoles.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential regulation of substance P and somatostatin in Martinotti cells of the developing cat visual cortex

In order to determine their morphological development and ontogenetic fate, Martinotti neurons immunoreactive for substance P and somatostatin have been analysed in the cat visual cortex. Martinotti neurons are located in layers V and VI. They are multipolar to bitufted, and most dendrites remain in layers V and VI. Their typical features is the ascending axon, which emerges from an apical dendrite or from the upper pole of the soma. A number of collaterals branch off in layer V, forming a local terminal plexus. The axon then branches into 2-8 collaterals, which ascend as a bundle to layers III and II, where a second terminal plexus is formed. Some collaterals ascend to layer I where they adopt a horizontal course. Horizontal collaterals in the terminal layers V, III, II, and in layer I may reach up to 400 microns in length. Martinotti neurons begin to differentiate perinatally. The quantitative analysis reveals that the initial time course of differentiation of Martinotti cells is very similar in material stained for substance P and for somatostatin. Double immunofluorescence then confirms that the two peptides are colocalized in Martinotti cells of layers V and VI during the early postnatal period. Further, substance P is colocalized with GABA. Substance P expression in Martinotti cells can be observed only in the immature visual cortex. After postnatal day 15, the Martinotti neuron system becomes less and less detectable by substance P immunoreactivity. It declines to virtually undetectable levels after the third postnatal month. The adult visual cortex is almost devoid of substance P-immunoreactive cell bodies, processes and axon terminals. In situ hybridization confirms this finding, revealing beta-preprotachykinin mRNA-expressing cell bodies in layers V and IV at postnatal day (P)6 and P12, but not in the adult cortex. This suggests a downregulation of the substance P expression at the transcriptional level. In contrast, somatostatin-immunoreactive Martinotti cells, most of which have coexpressed substance P during early postnatal life, can still be observed in the adult cortex. Thus, the Martinotti neurons constitute a persisting cell type, although many individual neurons of this type disappear during the second postnatal month by degeneration and cell death. In summary, while somatostatin is permanently expressed in Martinotti neurons in the cat visual cortex, substance P peptide and mRNA are transiently expressed during an early postnatal period, and apparently are downregulated later in development.

Histochemical localization of synaptic zinc in the developing cat visual cortex

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Collateral sprouting of serotonergic fibers in the cingulate cortex and the septum following cortical-hippocampal lesions

The parietal cortex and dorsal hippocampus of adult rats were unilaterally ablated. One and 3 months after this operation, changes in serotonergic fiber distribution in the forebrain were studied immunohistochemically. At 1 month, increased numbers of serotonergic fibers were seen in the cingulate cortex and the medial and lateral septal nuclei of the lesioned side. This increase continued to 3 months in the ipsilateral cingulate cortex. In the present study, two different processes of serotonergic fiber collateral sprouting were noted. Plastic changes in serotonergic fibers in the ipsilateral septal nuclei and cingulate cortex may be attributable to the collateral sprouting underlying reactive synaptogenesis and the pruning effect, respectively.

Changes in filipin-sterol binding in the rat cingulate cortex after the administration of antidepressant drugs. A freeze-fracture study

The amount of cholesterol in cell membranes of cingulate cortex nerve cells from rats treated with Imipramine (tricyclic antidepressant drug) or mianserin (non-tricyclic antidepressant) was investigated using filipin-sterol binding and freeze-fracture. The number of filipin-sterol complexes decreased within membranes of neurons from cingulate cortex chronically treated with imipramine or mianserin. These results suggest that the decreased content of cholesterol causes the cell membrane to become more fluid. This increased fluidity of the cell membrane may play an important role in regulating the interaction of transmitters and drugs with their membrane receptors.

Organization and development of the cingulum: laminar arrangement of acetylcholinesterase-rich components in rat

The cingulum of the rat is seen to be composed of several distinct fiber and neuronal somal components. In histochemical preparations, three acetylcholinesterase (AChE)-rich fiber zones are noted. The most dorsal originates in the cholinergic cell groups of the basal forebrain, (BF). There is a second, poorly reactive region subjacent to the BF afferent zone. The third, and most ventral zone, has not been described previously. It is operationally dubbed the entocingular fasciculus, ECF. It consists of a moderately dense plexus of AChE-reactive axons and dendrites. In contrast to the regularity and coherence of BF afferents, ECF fibers run in all directions in relation to adjacent cortical (cingulate, sensory-motor), subcortical and transcallosal sites. Knife cut lesions indicate the presence of a substantial proportion of fibers that travel either rostrally or caudally within the ECF itself. The small number of neuronal somata within the cingulum are mostly localized to the ECF. Ultrastructurally, these cells appear to synthesize AChE and form a single type of axo-somatic synapse; synapses are not common in the ECF. Altogether, these observations suggest that the ECF is a conduit for AChE-rich fibers directed towards targets outside of this structure. The AChE reactivity within the ECF first becomes apparent in the second postnatal week, lagging somewhat behind the enzymological maturation of BF afferents. It is concluded that in addition to BF afferents, other AChE-rich fibers travel in the cingulum. A distinctive population of fibers appears to bridge between various cerebral sites via the ECF. These latter observations raise the speculative possibility of a role for the ECF in limbic and sensorimotor cortical interactions.

The effects of various antidepressant drugs on the fine-structure of neurons of the cingulate cortex in culture

We have examined the effects of antidepressant drugs on the morphology and fine-structure of cingulate cortex neurons and synapses in vitro. Dissociated cell cultures from 16-day-old rat fetuses were maintained for up to three weeks in the presence of amitriptyline and desipramine (tricyclic antidepressants) mianserin and citalopram (non-tricyclic antidepressants) or without drugs as controls. Synapses in cultures exposed to amitriptyline and desipramine displayed increased numbers of presynaptic vesicles and more extensive membrane specializations than in control cultures, and increased numbers of coated vesicles both pre- and postsynaptically. In mianserin- and citalopram-treated cultures, synaptic specializations were increased in length, and aggregates of mitochondria at the base of neurites were observed. Our results indicate that long-term exposure to antidepressant drugs results in significant changes in intracellular structure, including changes in synaptic ultrastructure.

[Effect of hypokinesia on the ultrastructure of emotion-controlling structures in the rat brain]

Hypokinesia lasting 40 and 90 days causes a number of ultramicroscopic reorganizations in neurons, synapses and glial elements of the singular cortex and the central amygdaloid nucleus. The longer the time of hypokinesia, the more numerous and variable the reorganizations become. For the amygdaloid body presence of neurons with various degree of chromatolysis, reactive and destructive changes of organells, agglutination and reduction in number of the synaptic vesicles, increasing number of synapses, possessing certain features of low functional activity are most specific. For the singular cortes are peculiar convolution of nuclear and cellular membranes, synaptic contact, increasing intercellular spaces, as well as changes in the structure of some axo-spine synapses, the spine apparatus including.

Ultrastructural characteristics of GD3 ganglioside-positive immature glia in rat forebrain white matter

Immunocytochemistry and electron microscopy were used to examine the ultrastructural features of immature neuroectodermal cells of the rat forebrain in their early stages of differentiation. We used a monoclonal antibody (AbR24) to GD3 ganglioside, which binds to cells of the subventricular zone (SVZ). R24 also labels immature cells in developing white and gray matter (LeVine and Goldman: J. Neurosci. in press, '88, and accompanying paper). Sections of developing cingulum and white matter adjacent to the cingulum were examined at E18, P4, and P10 by using a preembedding immunocytochemical technique with PAP reagents. Labeled cells seen earliest were large, with high nuclear to cytoplasmic ratios and few cytoplasmic organelles. With time, smaller forms appeared, with prominent Golgi apparatus and processes containing microtubules. Labeled cells with similar characteristics but which contained cytoplasmic vacuoles were also observed. The results indicate a series of ultrastructural transformations that are consistent with oligodendrocyte differentiation.

Increased vertical axon numbers in cingulate cortex of schizophrenics

Data generated from an earlier study have suggested a model in which greater numbers of long, vertical, associative axons may occur in the anterior cingulate cortex of schizophrenic patients relative to control subjects. This hypothesis has now been tested using neuron-specific antibodies raised against the 200-kilodalton neurofilament subunit, a component of neuronal cytoskeleton, to immunostain axons of human postmortem cingulate cortex. A manual method for counting axons in the region of layer II and sublamina IIIA has been designed and applied blindly to parallel control and schizophrenic immunoprocessed specimens. The results show that there are 25% more vertical axons in the schizophrenic than in the control specimens. Preferentially higher numbers of both long vertical axons (62%) and axons associated with blood vessels (52%) have also been noted in the schizophrenic specimens. By contrast, the number of large-caliber horizontal axons was the same in the two groups; therefore, the greater number of vertical axons in schizophrenic specimens does not appear to represent a nonspecific effect. When these data are corrected for the effects of several confounding variables using analysis of covariance, the overall pattern of the results persists. These findings suggest the possibility that there might be an increase of associative inputs into the anterior cingulate cortex of schizophrenic patients, although it is not clear at present whether the differences noted, if replicative, may be primarily or perhaps only secondarily related to the disorder.

The influence of some antidepressant drugs on the nuclear volume of rat cingular cortex cells in culture

The changes in the volume of cell nuclei of the rat cingular cortex were investigated in culture after incubation with some antidepressant drugs. Two-week incubation of the cingular cortex culture with both tricyclic (desipramine, imipramine, amitryptyline) and non-tricyclic (mianserin) antidepressants in concentration of 3 X 10(-6) M resulted in a decrease of the volume of the cell nuclei. Because the size of the nucleus is regarded as a criterion of the cell metabolic activity, our results may point to a diminished activity of metabolic processes of the cells.

Dissociated cingulate cortical neurons: morphology and muscarinic acetylcholine receptor binding properties

Identifiable cortical neurons were obtained from area 29c of rat cingulate cortex using enzymatic and mechanical dissociation techniques. Dissociated neurons were either analyzed morphologically with the electron microscope or processed autoradiographically to evaluate the distribution of specific 3H-propylbenzilylcholine mustard (PrBCM) binding. Ultrastructurally, neurons appeared healthy and contained a full complement of cytoplasmic organelles. Membranes were intact and no presynaptic endings adhered to cell bodies or dendrites. Dendritic spines were not observed in these dissociations and serial sections of identified neurons indicated that all dendritic processes were smooth. Receptor binding studies were conducted on small and medium-to-large pyramidal neurons and multipolar cells. Specific binding of PrBCM was determined by calculating the mean number of grains/10 micron somal perimeter or dendritic length and subtracting mean values from a matched series of neurons that were coincubated in atropine. Specific binding was to somata and dendrites of all neurons. Nonspecific binding was an average of 33% of total binding. A 2 X 2 factorial analysis of variance comparing total and nonspecific binding for pairs of processes indicated that there were no regional differences in dendritic binding, either by cell type or by order of dendritic branching. Both somatic and dendritic PrBCM binding was antagonized by pirenzepine (PZ); however, PZ appeared to be more effective at secondary dendritic, rather than at somatic and primary apical dendritic sites. Thus, the IC50 values for somata and primary apical dendrites of small pyramids were 6 X 10(-7) and 9 X 10(-7) M PZ, respectively, while that for secondary basal dendrites of the same neurons was 5.8 X 10(-8) M. Morphological and pharmacological results together suggest that (1) muscarinic receptors are present on the smooth surfaces of all pyramidal and multipolar neurons; (2) many of the binding sites are high affinity, PZ-sensitive, M1 receptors; and (3) this binding is associated with the postsynaptic specialization of symmetric, cholinergic synapses.

Afferent specific localization of muscarinic acetylcholine receptors in cingulate cortex

The laminar distribution of acetylcholine receptors in rat cingulate cortex and their localization to axons of neurons in the anterior thalamic nuclei (ATN) were evaluated with the muscarinic antagonist [3H]propylbenzilylcholine mustard (PrBCM) in vitro. Specific binding of PrBCM in granular area 29 was heterogeneous, with a 57% variation from the highest binding in layer Ia to the lowest in layer II-III. In contrast, binding in area 24 was homogeneous, with only a 14% variation. The heterogeneity of PrBCM binding almost exactly duplicated the distribution of termination of ATN afferents in layers I to IV of area 29c. Four experiments indicated that 50% of the excess binding in layers Ia and IV was due to axonal receptor sites. First, ATN lesions abolished 41% and 27% of total specific binding in layers Ia and IV, respectively. Second, an undercut procedure that totally deafferented layers I to Va showed changes similar to those following ATN lesions, suggesting that other afferents to these layers may not have muscarinic receptors associated with them. Third, the sequence of losses in receptor binding and acetylcholinesterase (AChE) activity was evaluated 2, 3, 5, 9, and 14 days following ATN lesions. Since AChE was present in ATN axons, as evidenced by early postlesion losses, the correlation of both losses as well as previous analyses of axon degeneration in this cortex confirmed that these receptors were in axons. Fourth, binding peaks in layers Ia and IV remained in area 29c following destruction of virtually all neurons with the neurotoxin ibotenic acid. This is the first evidence that the activity of a major neocortical thalamic afferent may be regulated by axonal acetylcholine receptors.

[Ultrastructural characteristics of the 1st cortical layer of the cingulate area of the brain in rats]

The limiting membrane, participating in formation of the liquor- and hematoencephalic barrier on the brain surface, and specialized intercellular contacts are considered as factors regulating entrance of substances from liquor and blood into the intercellular medium. Heteromorphism of the cingulate cortex first layer takes place: in the 1-b sublayer a large amount of myelinated fibres is revealed, in the 1-c sublayer numerous longitudinal sections of dendrites are seen, they arrange perpendicularly or tangentially to the brain surface. In the 1-a sublayer, more often than in others, multifocal axodendritic synapses are observed they are of convergent or divergent types, several synapses occur. In the first layer of the cingulate cortex, axonal profiles are revealed, they resemble axons of the neurosecretory cells described in the literature. This cannot exclude any hormonal mechanisms affecting the neurons of the cingulate cortex. Numerous synaptic contacts, formed by afferent fibers that come from different brain structures, with processes of the first layer cells and ascending dendrites of deeper layers are considered as a morphological substrate of integrative and modulating activity of the first layer.

Responses of cortical neurons to stimulation of corpus callosum in vitro

1. An in vitro slice preparation of rat cingulate cortex was used to analyze the responses of layer V neurons to electrical stimulation of the corpus callosum (CC). In addition, synaptic termination of callosal afferents with layer V neurons was evaluated electron microscopically to provide a structural basis for interpreting some of the observed response sequences. 2. Layer V neurons had a resting membrane potential (RMP) of 60 +/- 0.68 (SE) mV, an input resistance of 47 +/- 4.74 M omega, a membrane time constant of 4.37 +/- 0.51 ms, an electrotonic length constant of 1.38 +/- 0.25, and produced spontaneous action potentials that were 50 +/- 0.3 mV in amplitude. Intracellular depolarizing current pulses evoked spikes that were sometimes associated with low-amplitude (2-5 mV) depolarizing (5-10 ms in duration) and hyperpolarizing (10-20 ms in duration) afterpotentials. 3. A single stimulus of increasing intensities to the CC produced one of the following response sequences: a) antidromic spike and an excitatory postsynaptic potential (EPSP), which initiated one or more spikes; b) antidromic spike, EPSP-evoked action potentials, and a hyperpolarization, which may have represented an intrinsic cell property or inhibitory synaptic activity; c) EPSP and evoked spikes only; d) high-amplitude EPSP with an all-or-none burst of action potentials. 4. Antidromically activated (AA) neurons always produced EPSPs in response to CC stimulation. When compared with nonantidromically activated neurons, AA cells had a more negative RMP, greater electrotonic length constant (LN), higher ratio of dendritic to somatic conductance (rho), and formed shorter duration, callosal-evoked EPSPs. 5. Neurons in anterior cingulate cortex produced EPSPs of longer duration than did those in posterior cortex (50 +/- 3.57 versus 26 +/- 1.56 ms, respectively). EPSPs in anterior neurons also had a higher maximum amplitude (20.5 +/- 1.0 versus 11.5 +/- 0.79 mV) and longer time to peak (11.6 +/- 2.2 versus 8.2 +/- 0.8 ms). 6. Electron microscopy of Golgi-impregnated neurons following contralateral lesions demonstrated that both pyramidal and nonpyramidal neurons received direct callosal afferents. Synaptic termination of callosal axons with the apical dendritic trees of anterior pyramidal cells was 6 times greater than it was with posterior pyramidal neurons. 7. EPSP shape differences in anterior and posterior neurons may be partially accounted for by the density and distribution of callosal afferents to these two cortices.

Monosodium glutamate-induced lesions in the rat cingulate cortex

The brains of neonate albino rats were examined with the light and electron microscope following subcutaneous administration of monosodium glutamate (MSG). In addition to lesions in areas known to be vulnerable to glutamate, such as the arcuate nucleus of the hypothalamus, distinct areas of necrotic tissue were detected in the granular portion of the retrosplenial cingulate cortex. The affected cells display the cytological features characteristic of MSG-lesioned brain tissue, including vacuolization of the endoplasmic reticulum and clumping of chromatin. Numerous pyknotic nuclei can be detected as early as 3 h following treatment. The possible causes of the lesion, particularly the role that may be played by astrocytes, are discussed.

Ultrastructure of the axon reaction in the immature rat thalamus

The axon reaction was studied using immature rats aged 4 or 14 days at the time of unilateral removal of the cingulate cortex. After survival times of one to 5 days they were sacrificed and the anterior thalamic nucleus was examined using ultrastructural methods. The degree of degenerative change was much more intense in the 4-day group where the center of the reactive area was characterized by pronounced lysis of the neuropil and the loss of most neurons. Dark neurons were observed in both groups but mitochondrial proliferation was restricted to the 14-day group. Evidence for microglial formation from pericytes was observed in the 4-day group while reactive astrocytes were observed in both groups. It was concluded that a rapid maturation of the thalamic injury response occurs between the 4th and the 14th day in the rat so that by the 14th day the response is similar in many respects to that of mature animals.