Quantitative analysis of axon collaterals of single pyramidal cells of the anterior piriform cortex of the guinea pig.

BACKGROUND: The role of the piriform cortex (PC) in olfactory information processing remains largely unknown. The anterior part of the piriform cortex (APC) has been the focus of cortical-level studies of olfactory coding, and associative processes have attracted considerable attention as an important part in odor discrimination and olfactory information processing. Associational connections of pyramidal cells in the guinea pig APC were studied by direct visualization of axons stained and quantitatively analyzed by intracellular biocytin injection in vivo. RESULTS: The observations illustrated that axon collaterals of the individual cells were widely and spatially distributed within the PC, and sometimes also showed a long associational projection to the olfactory bulb (OB). The data showed that long associational axons were both rostrally and caudally directed throughout the PC, and the intrinsic associational fibers of pyramidal cells in the APC are omnidirectional connections in the PC. Within the PC, associational axons typically followed rather linear trajectories and irregular bouton distributions. Quantitative data of the axon collaterals of two pyramidal cells in the APC showed that the average length of axonal collaterals was 101 mm, out of which 79 mm (78% of total length) were distributed in the PC. The average number of boutons was 8926 and 7101, respectively, with 79% of the total number of boutons being distributed in the PC. The percentage of the total area of the APC and the posterior piriform cortex occupied by the average distribution region of the axon collaterals of two superficial pyramidal (SP) cells was about 18 and 5%, respectively. CONCLUSION: Our results demonstrate that omnidirectional connection of pyramidal cells in the APC provides a substrate for recurrent processes. These findings indicate that the axon collaterals of SP cells in the PC could make synaptic contacts with all granule cells in the OB. This study provides the morphological evidence for understanding the mechanisms of information processing and associative memory in the APC.

Advanced cancer with situs inversus totalis associated with KIF3 complex deficiency: report of two cases.

Situs inversus totalis (SIT) is a relatively rare congenital anomaly, occurring at an incidence of 1 in 10 000-50 000 live births. Although there are some case reports of SIT with the presence of cancer, there are few reports on the relationship between SIT and cancer. However, the recent phylogenetic investigations of this condition suggest that this may be linked to the development and progression of cancer on the molecular level. The key elements are one of the intracellular motor proteins, the KIF3 complex, and the cell-adhesion factors N-cadherin and beta-catenin. We herein present the cases of advanced gastric cancer and lung cancer with SIT, and review the relationship between SIT and the development and progression of cancer.

Preferential neuron loss in the rat piriform cortex following pilocarpine-induced status epilepticus.

Structures within the piriform cortex (PC) including the endopiriform nucleus (DEN) and pre-endopiriform nucleus (pEn) have been implicated to be involved in seizure genesis in models of temporal lobe epilepsy. We used stereological methods to examine the specificity and extent of neuron loss in the PC of pilocarpine-treated rats. Both 7 days and 2 months post-status epilepticus rats showed significant neuron loss in the pEn and DEN, layer III of the intermediate PC, and layers II and III of the caudal PC. Total losses in the PC were 40 and 46% in 7 days and 2 months post-status epilepticus rats, respectively (p<0.01). The numbers of parvalbumin (PV)- and cholecystokinin (CCK)-immunopositive neuron profiles significantly decreased, and somatostatin (SS)-immunopositive neuron profiles tended to decrease. A large decrease in the number of PV-immunopositive neuron profiles occurred in the pEn, adjoining parts of the DEN and deep layer III of the PC, portions of the DEN bordering the claustrum and agranular insular cortex, and layer III of the caudal PC. The regions with decreased numbers of PV-, CCK-, and SS-immunopositive neuron profiles overlapped with those where many Nissl-stained neurons were lost and many degenerating cell bodies were detected. These results suggest that the decreases in the numbers of PV/SS/CCK-immunopositive neurons are related to neuron loss rather than to a low rate of synthesis of their peptides or proteins.

Quantitative analysis of development and aging of genital corpuscles in glans penis of the rat.

The aim of the present postnatal developmental study was to determine densities of unique genital corpuscles (GCs) in glans penis of developing and aged rats. GCs were identified as corpuscular endings consisting of highly branched and coiled axons with many varicosities, which were immunoreactive for protein gene product 9.5. In addition, GCs were immunoreactive for calcitonin gene-related peptide and substance P, but not for vasoactive intestinal polypeptide and neuropeptide Y. GCs were not found in the glans penis of 1 week old rats. Densities of GCs were low at 3 weeks, significantly increased at 5 and 10 weeks, reached the peak of density at 40 weeks, and tended to decrease at 70 and 100 weeks. Sizes of GCs were small in 3 weeks old rats, increased at 5 and 10 weeks, reached the peak-size at 40 weeks and reduced in size at 70 and 100 weeks. Considering sexual maturation of the rat, the results reveal that GCs of the rat begins to develop postnatal and reaches to the peak of their development after puberty and continues to exist until old age, in contrast to prenatal and early postnatal development of other sensory receptors of glabrous skin.

Quantitative analysis of axon collaterals of single cells in layer III of the piriform cortex of the guinea pig.

Recent physiological and morphological studies suggest that the piriform cortex (PC) functions like the association areas of the neocortex rather than the typical primary sensory area as was previously assumed. The axon connection patterns of single cells are important for understanding the functional organization of the PC. The axon collaterals of three single pyramidal cells and one spiny multipolar cell in layer III of the PC were labeled and quantitatively analyzed by intracellular injections of biocytin in guinea pigs. The individual pyramidal and spiny multipolar cells have highly distributed axon collaterals, which display little tendency for patchy concentrations, within the PC and multiple higher order behavior/reward/contextual-related areas, such as the prefrontal cortex, amygdaloid nuclei, and entorhinal cortex. For the pyramidal cells, the average length of axonal collaterals is 143 mm; the average number of boutons is 12,930. For the spiny multipolar cell, the length of the axonal collaterals is 88 mm; the number of boutons is 7,052. The pyramidal cells in the anterior subdivision of the PC (APC) have both rostrally and caudally directed intrinsic association fibers, whereas the pyramidal and spiny multipolar cells in the posterior subdivision (PPC) have predominantly caudally directed intrinsic association fibers in the PC. Our results reveal that the connection patterns of single cells in layer III resemble those of pyramidal cells in layer II, suggesting that the PC performs correlative functions analogous to those in the association area of other sensory systems. The rostrally-to-caudally directed connections in the APC provide a substrate for the recurrent process, whereas largely caudally directed connections in the PPC suggest the dominance of the feed-forward process.

Quantitative analysis of axon collaterals of single neurons in layer IIa of the piriform cortex of the guinea pig.

To study the various types of neurons in layer IIa in the piriform cortex (PC) and the spatial distribution of their axons, axon collaterals of three neurons in layer IIa were labeled and quantitatively analyzed by intracellular injection of biocytin in the guinea pig. Individual neurons have highly distributed axon collaterals, which display a little tendency toward patchy concentrations inside as well as outside the PC. One semilunar cell in the posterior PC had 54-mm-long axon collaterals and 4,200 boutons, out of which 2,100 (49% of the total number of boutons) were distributed in the PC. One semilunar-pyramidal transitional cell in the posterior PC had 256-mm-long axon collaterals and 23,000 boutons, out of which 16,100 (70% of the total number of boutons) and 4,000 (18% of the total number of boutons) were respectively distributed in all layers and in layer Ia of the PC. One multipolar cell in the posterior PC had 188-mm-long axon collaterals and 18,000 boutons, out of which 13,700 (78% of the total number of boutons) were distributed in the PC. Our results revealed that the connection patterns of individual cells in layer IIa have most of the features required for an associative neural network, which may function as a content-addressable memory for the association of odor stimuli.

Quantitative analysis of axon collaterals of single superficial pyramidal cells in layer IIb of the piriform cortex of the guinea pig.

To understand the functional organization of the piriform cortex (PC), the axon collaterals of three pyramidal cells in layer IIb of the anterior PC and one pyramidal cell in layer IIb of the posterior PC were labeled and quantitatively analyzed by intracellular biocytin injection in the guinea pig. Single pyramidal cells in the anterior and posterior PCs have widely distributed axon collaterals, which exhibit little tendency for patchy concentrations inside as well as outside the PC. The total lengths of the axon collaterals of the three fully analyzed pyramidal cells ranged from 68 to 156 mm, more than 50% of which were distributed in the PC. The total number of boutons of the three cells ranged from 6000 to 14,000, 5000-7000 of which were distributed in the PC. It was estimated that individual pyramidal cells in layer IIb form synaptic contacts with 2200 to 3000 other pyramidal cells in the PC, indicating that single pyramidal cells in layer IIb receive input from a large number of other pyramidal cells. This high connectivity of the network of pyramidal cells in the PC can be regarded as the neural network operating parallel distributed processing, which may play an important role in experience-induced enhancement in odorant discrimination in the PC.

Thalamocortical projection from the ventral posteromedial nucleus sends its collaterals to layer I of the primary somatosensory cortex in rat.

Here we examined quantitatively axonal projections originating from the ventral posteromedial thalamic nucleus (VPM) to layer I of the primary somatosensory cortex (SI) by extracellular and intracellular injections of biocytin as an anterograde tracer. Following the extracellular injections, two types of VPM afferents with different arborization patterns in SI were observed. The type I extended vertically, forming dense plexus in layers IV and VI, and projected collaterals to layer I. The type II rarely branched in SI, converged in the plexus formed by the type I, and projected no collaterals to the supragranular layers. The labeled fibers in layer I derived from the first type ran parallel to the brain surface, and their mean length was 339.7 +/- 87.5 microm. Intracellular injection into VPM neurons bearing both types of afferent demonstrated the full axonal arborization in both the reticular thalamic nucleus (Rt) and SI. The total length of the axon of a neuron bearing the type I was 86,968.8 microm, and the length of axonal collaterals in layer I of SI was 433.1 microm. The total axonal length of a neuron bearing the type II was very small. The present study is the first to demonstrate substantial projections from VPM to layer I of SI, and provide quantitative data on the entire extent of the axonal arborization of thalamocortical projections from single VPM neurons.

Ultrastructure of ascending cholinergic terminals in the anteroventral thalamic nucleus of the rat: a comparison with the mammillothalamic terminals.

In this study, to identify the ultrastructure and distribution of ascending cholinergic afferent terminals in the anteroventral thalamic nucleus, we used an anti-vesicular acetylcholine transporter antibody as marker of cholinergic afferents, and characterized the immunoreactive terminals at the ultrastructural level. We then compared the distribution pattern of the cholinergic terminals and that of the mammillothalamic terminals identified by anterograde transport of a tracer injected into the mammillary body. The cholinergic terminals were small, and formed both symmetrical and asymmetrical synaptic contacts throughout the dendritic arborizations, particularly in the distal region. This distribution pattern differed from that of mammillothalamic terminals, that were of LR (large terminal containing round synaptic vesicles) type and were preferentially distributed in the proximal region of dendrites. We also found relatively numerous cholinergic terminals making contact directly with immunonegative excitatory terminals, both LR and SR (small terminal containing round vesicles) terminals, without clear postsynaptic specialization. A few cholinergic terminals even seemed to form a synaptic complex with the LR or SR terminals. These findings suggest that the ascending cholinergic afferents in the anteroventral thalamic nucleus can effectively modulate excitatory inputs from both the mammillothalamic and corticothalamic terminals, in close vicinity to a synaptic site.