Stereological quantification of olfactory receptor neurons in mice

The total number of olfactory receptor neurons (ORNs) in the mouse main olfactory epithelium (MOE) was estimated using stereological sampling. Noses and skulls of male and female 8-week-old C57BL/6J mice were de-calcified, embedded in paraffin, cut into 10-μm-thick sections serially at 100-μm intervals, and processed for immunohistochemistry for the olfactory marker protein (OMP), a specific marker for ORNs. The number of OMP (+) receptor neurons was measured using an optical fractionator with the Stereo-Investigator software. The mean values of the total number of OMP (+) receptor neurons in the unilateral MOE were 5,140,000±380,000 in males and 5,210,000±380,000 in females, with no significant differences between the sexes. We concluded that the total number of ORNs in the unilateral MOE is approximately 5×10(6) in mice.

A transverse ligament located anterosuperiorly in the lower orbital fat space restricts lower eyelid retraction in the Mongoloid eye

We previously reported that a lower positioned transverse ligament, which was identified just above the fusional line between the orbital septum and the levator aponeurosis or anteroinferiorly in the upper orbital fat space, determines the lower position of the preaponeurotic fat, and restricts the upper eyelid retraction causing the external features that define the appearance of the Mongoloid eye. Because the narrow palpebral fissure of the Mongoloid eye is composed of the restricted upper eyelid and the restricted lower eyelid, we surmised that the ligamentous tissue, which is analogous to the lower positioned transverse ligament in the upper eyelid, might also exist in the lower eyelid.

Differential effects of hypoglossal and facial nerve injuries on survival and growth of rats at different developmental stages

The hypoglossal (XII) nerve is made up of functionally different nerve branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. The present study was performed to determine the effects of facial (VII) and XII nerve injuries on the survival and growth of rats in which the unilateral or bilateral VII and XII nerve components (main trunk, XII-trunk; medial branch, XII-med; lateral branch, XII-lat) had been resected at different developmental stages. In the suckling period, unilateral as well as bilateral injuries in the XII-trunk or XII-med nerve produced disturbed milk intake, lower survival rates and growth retardation in the nerve-injured rats. In the transition and mastication periods, only bilateral injury in the XII-trunk or XII-med nerve produced disturbed food intake followed by lower survival rates and growth retardation in those animals. The unilateral XII-lat nerve injury did not have significant effects on milk and food intake, whereas the bilateral injury caused disturbance in milk intake especially at the early neonatal stage. The unilateral VII nerve injury at the early neonatal stage caused deteriorating effects on food intake resulting in lower survival rate and severe growth retardation in the nerve-injured rats. The results indicate that the survival and growth of XII and VII nerve-resected rats differ considerably depending on the nerves injured and the developmental ages of the animals at the time of nerve insult.

Effects of hypoglossal and facial nerve injuries on milk-suckling

Functional roles of the perioral anatomical structures involved in breastfeeding were examined in newborn rat pups in which the hypoglossal (XII) and facial (VII) nerves had been resected at the neonatal stage. The XII nerve controls tongue movement and is comprised of two functionally distinct branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. Newborn rat pups with bilateral resection of either of the XII nerve components (main trunk: XII-trunk; medial branch: XII-med; lateral branch: XII-lat) failed to suckle milk and did not survive. Unilateral XII nerve-resected neonates showed different milk-suckling capabilities, which thus resulted in differences in survival rate (XII-trunk: 38%; XII-med: 24%; XII-lat: 92%) and postnatal growth during the postnatal 3 weeks until P21. Unilateral and bilateral resections of the VII nerve innervating the buccolabial musculature produced lowered suckling capabilities and retarded postnatal growth, although all pups showed 100% survival. The results indicate a crucial role of the tongue, especially of protruding muscular elements innervated by the XII-med nerve, in breastfeeding. The results also indicate differential effects of the VII and XII nerve components on suckling capability, survival, and postnatal growth of newborn rat pups.

Effects of bilateral resection of facial nerves on suckling in developing rats

The purpose of the present study is to investigate functional role of the facial nerve on suckling in developing rats. The bilateral resection of facial nerves on postnatal day 1 (P1) resulted in cell loss of facial motoneurons and complete facial paralysis without any whisker movement or nictitating reflex at the end of the postnatal 3 weeks. Although the body weight of the nerve-resected rats increased gradually for the postnatal 3 weeks, they weighed less than the control rats without nerve resection. The nerve-resected rats contained less milk (0.25 +/- 0.02 g) than the control rats (0.35 +/- 0.02 g) in the stomach on P17. On P21, the body weight of the nerve-resected rats (25.33 +/- 0.32 g) was decreased by 28% compared to that of the control rats (35.08 +/- 0.57 g). Although their growth was substantially more retarded than that of the control animals, most (92%) of the nerve-resected pups could survive without facial nerve innervation. The orofacial musculature innervated by the facial nerve plays an important role in breastfeeding, but the present study shows that these muscles are not essential for the survival of neonatal rats.

Neurotrophic effect of hepatocyte growth factor on neonatal facial motor neurons

The neurotrophic effect of hepatocyte growth factor (HGF) on axotomized facial motor neurons was examined after local application of HGF to the proximal facial nerve stump of the neonatal rat on post-natal day one (P1). Motor neuron survival was expressed as the neuronal cell count on the injured side as a percentage of that on the noninjured side. Motor neuron survival of the control group was 76% on P3, 54% on P5 and 23% on P8, that of the HGF-treated group 78% on P3, 69% on P5 and 31% on P8, and that of the brain-derived neurotrophic factor (BDNF)-treated group 91% on P5 and 45% on P8. The motor neuron survival rates were then adjusted by deducting the facial motor neurons corresponding to the uninjured retroauricular branch (20%) of the facial nerve. The adjusted values were 70% (P3), 42% (P5) and 4% (P8) for the control group, 72% (P3), 61% (P5) and 14% (P8) for the HGF-treated group, and 88% (P5) and 32% (P8) for the BDNF-treated group. These findings demonstrate that HGF has a neuroprotective effect on injured facial motor neurons and suggest that HGF has neurotrophic properties distinct from those of BDNF.

Regenerative process of the facial nerve: rate of regeneration of fibers and their bifurcations

After the main trunk of the mouse facial nerve was injured by crushing, a fiber tracing method was used to quantify the facial motor neurons that extended regenerating nerve fibers to the specific site of the facial nerve branch. The total number of motor neurons retrogradely labeled with a fluorescent tracer, Fluoro-Gold (FG), were 0 on postsurgical days (PSDs) 1 and 2, 75+/-25 on PSD3, 264+/-21 on PSD4, 378+/-19 on PSD6, 428+/-19 on PSD8, 491+/-13 on PSD12 and 532+/-15 on PSD16. Assuming that the FG-positive neurons (535+/-11) of the control mice represent 100%, the FG-labeled neurons accounted for 0, 14, 49, 71, 80, 92 and 99% on the corresponding days. Two different fluorescent tracers were applied to the different facial nerve branches 16 days after facial nerve injuries. Double-labeled neurons were consistently found in the nerve-crushed facial nucleus (3.2%), and their number increased in the nerve-transected facial nucleus (12.2%). The present study indicates that the regenerating facial nerve consists of heterogeneous nerve fibers with varying growth rates and that excessive axonal branching occurs more frequently in the nerve-transected than in the nerve-crushed injuries.

Proliferating cell populations in experimentally-induced hydrocephalus in developing rats

To examine the fate of proliferating brain cells in hydrocephalus (Hydro), experimental Hydro was induced in neonatal rats by intracisternal injection of kaolin and, 3 weeks later, the rats were injected with bromodeoxyuridine (BrdU). The BrdU (+) cells were immunohistochemically analyzed by using antibodies against neural (nestin), neuronal (NeuN) and glial (GFAP and MBP) markers in the posterior cerebrum. The percentage of nestin expression for the BrdU (+) cells was 8% in control and increased from 17% in the Hydro to 33% in the Hydro at an earlier stage after the shunt procedure, but was restored to 6% in the Hydro at a later stage after the shunt procedure. The percentages of GFAP expression showed a similar tendency to those of nestin expression. The BrdU (+) cells did not express either NeuN or MBP throughout the experiments.

Great potentiality of neonatal facial motor neurons for neural plasticity as determined by functionally essential neuronal population

The present study was undertaken to determine the neuronal population essential for normal and minimal facial function of young adult rats that had received various degrees of crush injuries to the facial nerve in the neonatal period. Using a neuronal tracer, it was found in young adult rats receiving neonatal injuries that the minimum number of tracer-labeled facial motor neurons necessary for normal facial function corresponded to 13-14% of the neurons (2540+/-64) of the age-matched control animals, whereas the minimum number of neurons necessary for minimal facial function corresponded to 5%. On the other hand, the minimum numbers of tracer-labeled facial motor neurons necessary for normal and minimal facial function of young adult rats that received various degrees of crush injuries corresponded to 61 and 27-30%, respectively, of the neurons (2540+/-64) of the uninjured control animals. These results indicate that the facial function of animals with nerves crushed at the neonatal stage can be adequately maintained by a very small population of neurons, implying a great potential of neonatal neurons for neural plasticity.

Functionally essential neuronal population of the facial motor nucleus

Cranial nerve impairment is one of the more serious complications in neurosurgery. Nevertheless, the important question of how many neurons are required for cranial nerve functions remains unanswered. The VIIth cranial nerve (facial nerve) in mice was subjected to graded crush injuries. After assessment of the facial function, the number of uninjured, healthy facial motor neurons was quantified with a retrograde neuronal tracer. We report that normal facial function is preserved if intact neurons account for more than 56% of the control value, while complete facial paralysis occurs if intact neurons are reduced to less than 32% of the control value.

Differential neurogenesis and gliogenesis by local and migrating neural stem cells in the olfactory bulb

The rostral migratory stream (RMS) is a unique forebrain structure that provides a long-distance migratory route for the neural stem cells of the periventricular region towards the olfactory bulb (OB). The purpose of the study presented here is to examine the extent of neurogenesis and gliogenesis by the neural stem cells of different origins (periventricular vs. intrabulbar) in the OB. After the RMS had been subjected to injury, the rats received intraperitoneal injections of 5-bromodeoxyuridine (BrdU) and were further reared for 2 weeks. Neuronal and glial differentiations of the BrdU(+) cells in the olfactory bulbar granule cell (OB-GCL) and the olfactory glomerular (OB-GL) layers were examined immunohistochemically using antibodies against neuronal (NeuN, neuronal nuclei) and glial (GFAP, glial fibrillary acidic protein) markers in the OBs with injured and uninjured (control) RMS. In the completely RMS-lesioned OB, where migration of the periventricular neural stem cells was inhibited, a small number of BrdU(+) NeuN(+) cells were found in both the OB-GCL and OB-GL. The BrdU(+) NeuN(+) cells accounted for a much higher percentage of the BrdU(+) cells on the control side (OB-GCL, 36.7%; OB-GL, 8.8%) than on the completely RMS-lesioned side (OB-GCL, 3.7%; OB-GL, 0.6%). The percentage of the BrdU(+) GFAP(+) cells relative to the BrdU(+) cells did not show any major difference between the control and completely RMS-lesioned sides. This study revealed differences in neurogenesis and gliogenesis between the local and migrating neural stem cells in the OB of the adult rodent.

Stimulation of the regrowth of MPP+-damaged dopaminergic fibers by the treatment of mesencephalic cultures with basigin

Basigin (Bsg) is a transmembrane glycoprotein belonging to the immunoglobulin superfamily and widely expressed in the central nervous system. To elucidate functional role of Bsg in the central nervous system, the effects of its glutathione-S-transferase (GST) fusion protein on the number and neurite outgrowth of cultured rat mesencephalic dopaminergic neurons were measured. The fusion protein was not able to promote the survival and neurite outgrowth of tyrosine hydroxylase (TH)-positive neurons under serum-free condition. However, the treatment of 1-methyl-4-phenylpyridinium (MPP+)-exposed cultures with the fusion protein resulted in stimulation of the regrowth of damaged TH-positive fibers. Basic fibroblast growth factor (bFGF) also stimulated the regrowth of neurites in damaged neurons. These results indicate that Bsg may play an important role in the regrowth of damaged dopaminergic fibers.

Cell dynamics of calretinin-immunoreactive neurons in the rostral migratory stream after ibotenate-induced lesions in the forebrain

It is now apparent that adult neurogenesis is taking place during life in the olfactory bulb (OB) of the rodent brain. In the olfactory nervous system, the precursor cells of the subventricular zone are known to continually proliferate, migrate through the rostral migratory stream (RMS) and differentiate into the bulbar neurons. The RMS, consisting of heterogeneous cell populations of the neural and neuronal precursor cells, is the unique forebrain structure that provides a long-distance migratory route for the precursor cells. The present study was undertaken to examine whether neuronal regeneration, focusing on calretinin-immunoreactive (+) cells, may proceed in the RMS following lesions induced by an excitotoxin. Two days after ibotenate injections, massive degeneration of calretinin (+) cells occurred in the RMS and its adjacent forebrains. Thereafter, calretinin (+) cells gradually increased in the RMS and reached above their control value 2 weeks after ibotenate injections. Removal of the OB also produced a marked increase in calretinin (+) cells in the RMS. Autoradiographic experiments using (3)H-thymidine showed that calretinin (+) cells were continually generated in the RMS and underwent neuronal turnover within 8 weeks in a normal condition. The results indicate that, in terms of calretinin (+) cells, neuronal differentiation and replacement is continually taking place within the RMS, and that the RMS is capable of repopulating those cells which were injured by ibotenate.

The minimum number of neurons in the central olfactory pathway in relation to its function: a retrograde fiber tracing study

The present study was aimed at determining the functionally essential size of the neuronal population in the central olfactory nervous system. Using conditioned rats who had learnt to avoid repellent (cycloheximide) solution by olfaction, varying degrees of injuries were made to the lateral olfactory tract, a major central olfactory pathway connecting the olfactory bulb to the olfactory cortex. After examining their olfactory ability to discriminate cycloheximide solution from water, intact bulbar projection neurons (mitral cells) with fiber connections to the olfactory cortex were quantified using a retrograde fiber tracing technique. The numbers of retrogradely labeled mitral cells from the rats with normal olfaction ranged between 20 and 92% of the control value, while those numbers from the anosmic rats ranged between 0 and 22%. We conclude that the functionally essential neuronal population is approximately one-fifth of the total in the central olfactory pathway, a presumed threshold value in terms of the ability to avoid cycloheximide solution by olfactory discrimination.

Onset of calbindin-D 28K and parvalbumin expression in the lateral geniculate complex and olivary pretectal nucleus during postnatal development of the rat

The onset and distribution of calbindin (CB) and parvalbumin (PV) immunoreactivity were investigated in the lateral geniculate nuclear complex and the olivary pretectal nucleus (OPT) in developing rats. CB expression occurred early (before eye-opening) in the relay neurons of the intergeniculate leaflet, parvocellular portion of the ventral lateral geniculate nucleus and OPT relating to ambient vision mediated by W-like retinal ganglion cells. On the contrary, PV expression occurred late (after eye-opening) in the relay neurons of the magnocellular portion of the ventral lateral geniculate nucleus (VLGMC) and OPT relating to focal vision mediated by Y-like retinal ganglion cells. A unilateral eye enucleating experiment indicated that the VLGMC and OPT received dense input from PV-positive Y-like retinal ganglion cells. The results show the different onsets of CB and PV expressions in the retino-recipient thalamic and pretectal nuclei receiving inputs from different kinds of retinal ganglion cells.

Continual replacement of newly-generated olfactory neurons in adult rats

It has been known that stem cells do exist in the central nervous system, and adult neurogenesis is continually taking place in the olfactory bulb during life. We report here, with the combined method of autoradiography using (3)H-thymidine and immunohistochemistry for a neuronal marker, that 65.3-76.9% of calretinin-immunoreactive bulbar neurons are replaced during the short period of 6 weeks in the adult rodent. The results indicate that neuronal replacement is a common phenomenon in the olfactory bulb during life.

Plume-tracking robots: a new application of chemical sensors

Many animals have the ability to search for odor sources by tracking their plumes. Some of the key features of this search behavior have been successfully transferred to robot platforms, although the capabilities of animals are still beyond the current level of sensor technologies. The examples described in this paper are (1) incorporating into a wheeled robot the upwind surges and casting used by moths in tracking pheromone plumes, (2) extracting useful information from the response patterns of a chemical sensor array patterned after the spatially distributed chemoreceptors of some animals, and (3) mimicking the fanning behavior of silkworm moths to enhance the reception of chemical signals by drawing molecules from one direction. The achievements so far and current efforts are reviewed to illustrate the steps to be taken toward future development of this technology.

Fate of newly formed periglomerular cells in the olfactory bulb

It is well established that olfactory receptor cells are replaced during life. Periglomerular (PG) cells of the olfactory bulb have recently been demonstrated to be produced following proliferation and migration of periventricular neuronal precursor cells even in adulthood. The purpose of the present study was to examine the fate of newly formed PG cells in adult rodents. Using 5-bromodeoxyuridine (BrdU), we carried out a quantitative immunohistochemical analysis of BrdU-positive cells in the bulbar glomerular layer at different survival periods. Each number of BrdU-positive PG cells per 100 olfactory glomeruli was 34.1 +/- 3.3 (1 week), 57.2 +/- 2.7 (2 weeks), 28.0 +/- 4.7 (4 weeks) and 25.9 +/- 1.6 (8 weeks). These results indicate that bulbar PG cells, similar to olfactory receptor cells, are mostly replaced during life, and that the olfactory system is composed of disposable neuronal networks centrally as well as peripherally.

An anatomic examination of the suprascapular flap

To investigate the potential utility of a suprascapular flap, the authors examined dissected cadavers to identify the ramification of the suprascapular artery, and directly injected 2.5% patent blue dye to observe the distribution of its cutaneous perforators. Results indicate that a suprascapular flap is not practicable. The branching pattern of the suprascapular artery from the subclavian artery varies widely, making dissection of the vessels highly problematic. Moreover, no constant presence of cutaneous perforators from the artery could be identified in either the suprascapular fossa or the shoulder.

A new video/computer method to measure the amount of overall movement in experimental animals (two-dimensional object-difference method)

Evaluation of the amount of overall animal movement is important for investigations of motor control mechanisms in the central nervous system. We describe a new method to quantify overall free movements of an animal without any markers using a video camera and a personal computer equipped with a video-capture board. The operating principle is that the amount of overall movement of an object can be expressed by the difference in total area occupied by the object in two consecutive picture frames. The software for this application operates in real-time. Using this method and with proper setting for the cage and recording view, we can estimate three-dimensional movements of animals. The major advantages are low cost, easy operation and high sensitivity. The experimental results indicate that this method can be applied to various fields of motion analysis.

Calretinin-immunoreactive neurons in rostral migratory stream: neuronal differentiation

The purpose of the present study was to examine immunohistochemically the expression of nestin and polysialylated neural cell adhesion molecule in calretinin-immunoreactive neurons of the rostral migratory stream, the restricted pathway through which neuronal precursor cells migrate towards the olfactory bulb. Using mirror sectioning, calretinin-immunoreactive neurons of the rostral migratory stream were shown to co-express nestin (20.8%) and polysialylated neural cell adhesion molecule (61.8%). The results show that calretinin-immunoreactive neurons in the rostral migratory stream still express immature neural and neuronal phenotypes.

TrkA expression in olfactory epithelium and bulb during development

The purpose of the present study was to examine immunohistochemically the expression of high-affinity nerve growth factor receptor (trkA) in the olfactory nervous system of developing mice and of colchicine-treated adult mice. Olfactory epithelia of embryos and neonates showed trkA immunoreactivity not only in basal cells but in receptor cells, with trkA-immunoreactive olfactory nerve fibers in the subepithelium and the bulb. In adults, trkA immunoreactivity was found only in basal cells of olfactory epithelia. Olfactory epithelia of colchicine-treated adult mice, however, exhibited appearance of trkA-immunoreactive receptor cells and increased trkA immunoreactivity in olfactory nerve fibers. These findings indicate that expression of trkA continually occurs in the olfactory nervous system during life and that trkA can be highly expressed during development.

TrkA expression in mouse olfactory tract following axotomy of olfactory nerves

The olfactory bulb is one of the brain regions that synthesizes the nerve growth factor (NGF). Functional roles of the bulbar NGF remain to be determined. The aim of the present study was, using an antibody specific to the high-affinity NGF receptor (trkA), to examine immunohistochemically the distribution of the NGF receptor in the mouse olfactory tract, under normal conditions and during regenerative processes. In normal mouse olfactory epithelia, trkA immunoreactive cell bodies were only seen in basal cells. Cell bodies of olfactory receptor cells did not express trkA immunoreactivity, but their neuronal processes (olfactory nerve fibres and bundles in the olfactory mucosa and the olfactory bulb) displayed trkA immunoreactivity. After axotomy of olfactory nerves, regenerating olfactory cells (basal cells and olfactory receptor cells) expressed trkA immunoreactivity in intramucosal and intrabulbar neuronal processes of olfactory receptor cells. These results suggest involvement of the bulbar NGF in the process of synaptogenesis and/or regeneration of the olfactory nervous system.

Electron microscopic study of synaptogenesis and myelination of the olfactory centers in developing rats

Development of the central olfactory system was studied in the rat with an electron microscope at three main structures: the olfactory bulb, the lateral olfactory tract, and the primary olfactory cortex (the piriform cortex). As a parameter of development, the synaptic density was examined quantitatively in the bulbar glomerulus and layer Ia (termination of bulbofugal fibers) of the piriform cortex. which are the key stations of the olfactory pathway. The synaptic densities in the glomerulus and those in layer Ia were 5.7% and 4.6% on embryonic day 19, 15.8% and 12.5% on postnatal day (P) 0, and 57.3% and 37.2% on P10, as compared with the adult (100%). As another parameter of development, the density of myelinated axons in the lateral olfactory tract was examined quantitatively. The densities of myelinated axons in the tract were 0% on P5, 15.1% on P10, and 73.5% on P21 of the adult density. Maturation in the tract was still progressing, even at P21, in terms of bundle formation and the thickness of myelin sheaths. The results show that synaptogenesis in the bulbar glomerulus is followed by synaptogenesis in layer Ia of the piriform cortex, and that myelination in the lateral olfactory tract occurs over a prolonged period, even in the stages after P21.

Anatomical plasticity in the medial superior olive following ablation of the inferior colliculus in neonatal and adult rats

We evaluated the consequences of unilateral ablation of the inferior colliculus (IC) upon the ascending projection from the medial superior olive (MSO) to the IC. Ablation of the IC was performed in rats aged between postnatal day 1 (P1) and maturity. All the rats were given injections of Fluoro-Gold (FG) into the ipsilateral IC at birth (P0) (before the ipsilateral IC was ablated in any case) so that growth of early-developing axons to the ipsilateral IC could be examined for any labeled neurons in the ipsilateral MSO. Upon reaching adulthood, the rats received injections of Fluoro-Ruby (FR) into the contralateral (intact) IC so that aberrant crossed projections to the intact IC could be examined for any labeled neurons in the ipsilateral MSO. These rats were killed 2 days after FR injections. The number of surviving cells in the ipsilateral MSO were counted in Nissl-stained sections for quantitative analysis of retrograde degeneration. The results show that: (1) the total number of neurons was reduced to 64-34% in the ipsilateral MSO as a result of IC ablation; (2) cell reduction by retrograde degeneration followed a U-shaped curve with a maximal effect in rats operated at P7 (reduced to 34%); (3) adult ablation of the IC led to retrograde degeneration that was less severe than that in late neonatal (P7) ablation; (4) an aberrant projection from the MSO to the contralateral IC occurred in rats operated at P1 and P3 but not in rats operated at P7 or maturity. Thus, our findings suggest that growth of late-developing axons is a major factor in the plasticity of this system of projection.

Postnatal development of the projection from the medial superior olive to the inferior colliculus in the rat

Normal projection development from the medial superior olive (MSO) to the inferior colliculus (IC) was examined by injecting Fluoro-Gold (FG), a retrograde tracer, into the IC unilaterally at postnatal days 0 (P0), P3, P7 and maturity. The rats were killed 1 day after FG injection. At all ages, labeled neurons in the MSO appeared on the ipsilateral side only, as in adult controls. The total number of MSO neurons counted in Nissl-stained sections was constant throughout the postnatal periods. The labeled frequency index of MSO neurons was increased stepwise (from 35% to 90%) with increasing postnatal stages (from P0 to adulthood), suggesting differential growth of early- and late-developing axons.

Bulbar morphology and expression of bulbar dopamine and parvalbumin in experimentally-induced anosmic rats

Morphological study was carried out in rats with olfactory dysfunction induced by deafferentation of serotonergic fibers in the olfactory bulb. With a computer capable of area measurements, olfactory bulbs of the anosmic rats were found to be decreased in size to 61% of control bulbs, and all bulbar layers were involved in the bulbar shrinkage. Given areas of each bulbar layer in control bulbs to be 100%, percentages of each bulbar layer in the anosmic rats were 23% in the olfactory nerve layer, 54% in the glomerular layer, 63% in the external plexiform layer, 83% in the internal plexiform layer and 81% in the granule cell layer. Dopamine-and parvalbumin-containing neurons were examined immunohistochemically in the experimentally-induced anosmic rats. As a result, immunoreactive neurons for these two chemical substances were significantly decreased in number (dopamine, 33% of control value; parvalbumin, 46% of control value). The present study, using an animal model of anosmia, provided quantitative data on the bulbar atrophy and showed effects of anosmia on expression of dopamine and parvalbumin in the bulb.

Differentiation of the olfactory epithelium during development

Maturation of the olfactory epithelium was studied in the rat. As a developmental index of the olfactory epithelium, quantitation was based on the thickness and the number of cell layers of the epithelium. Mean epithelial thicknesses were 84 microns on embryonic day (E) 19, 94 microns on postnatal day (P) 0, 98 microns on P10 and 57 microns in adult. Average numbers of cell layers were 7 (E19), 8 (P0), 10 (P10) and 7 (adult). Thus the olfactory epithelium progressively increased in thickness between P0-P10, and later decreased in thickness as well as in number of cell layers toward adult. To clarify the number of mature receptor cells sending their axons to the olfactory bulb, the percentages of receptor cell labeling (number of labeled cells/total number of receptor cells) were estimated with an aid of retrograde fluorescent tracer injected into the olfactory bulb. As a result, their percentages were 34% (P1-P3), 50% (P8-P10) and 78% (adult). The ablation experiment of the bulb on P1 pups and adult rats revealed that the percentages of receptor cell degeneration were 31% in neonates (P1) and 76% in adults, confirming the results obtained from the retrograde tracing. Thus the present study shows the substantial increase of mature receptor cells during development and may provide a morphological basis in understanding of the functional maturity of olfaction.

Olfactory disturbance induced by deafferentation of serotonergic fibers in the olfactory bulb

The serotonergic neurons of the brain stem project widely throughout the central nervous system, and the olfactory bulb is one of the major forebrain targets of the ascending serotonin pathway. According to physiological studies, neurons of the olfactory bulb were found to reduce their spontaneous discharge rates by electrophoretically applied serotonin. However, roles of the bulbar serotonin in the sense of smell remain unanswered. In the present study, using 5,7-dihydroxytryptamine, a specific neurotoxin for serotonin, we found that the conditioned rats who learned to avoid a repellent by olfaction lost ability of discrimination by deafferentation of the bulbar serotonergic fibers. Such olfactory dysfunction did not occur in the early stage (three days after injection of the toxin) when the serotonergic fibers disappeared in the bulb, but developed a few weeks later. Interestingly, histological examination revealed marked shrinkage of the bulbar glomerulus which is a major termination site of the bulbopetal serotonergic fibers, and also a synaptic site of olfactory receptor cells and bulbar output neurons. The results indicate that depletion of the serotonergic fibers in the olfactory bulb causes glomerular atrophy and olfactory disturbance in the rat.

Non-selective reinnervation by regenerating facial motoneurons after peripheral nerve crush in the developing rat

To study the regeneration process after the facial nerve crush in the neonatal period, the location of cranial motoneurons supplying the posterior belly of the digastric muscle (PDG) and the vibrissae follicular muscles was examined using retrograde tracing methods in the rat with facial nerves that had been surgically injured 1-2 day(s) after birth. In different stages after the induced facial palsy was functionally recovered, i.e. 4-20 weeks after the surgical operation, Fluoro-Gold (FG) was injected into the PDG, while wheat germ-agglutinated horseradish peroxidase (WGA-HRP) was injected into the vibrissae follicular muscles. Distribution of neurons retrogradely labeled with FG and/or WGA-HRP was then examined in the brainstem. On the intact side, used as a control, FG-positive neurons were restrictedly seen within the accessory facial nucleus (Acs7), while HRP-positive neurons were found in the main facial nucleus (FMN) proper. On the injured sides with any survival periods: 1) FG-positive neurons were diffusely seen not only in the Acs7 but also in the FMN, where the normal myotopical representation seemed to be no longer maintained. 2) HRP-positive neurons were also seen scattered not only in the FMN but in the Acs7. 3) The volume and cell number in both the Acs7 and the FMN were notably reduced. Thus, the present results indicate: 1) that the misdirectional regeneration of nerve fibers occurs widely across the facial motoneuron pools, and 2) that the non-selective distribution can never be restored to the selective one when severely damaged even in the neonatal periods.

Neurogenetical segregation of the vestibulospinal neurons in the rat

The time of origin of the vestibulospinal projection neurons was determined by a double-labeling method using 5-bromodeoxyuridine (BrdU), the thymidine analogue, and Fluoro-Gold (FG), a retrograde fluorescent tracer. Rat fetuses were exposed to BrdU in utero to label the vestibular neurons on one of the embryonic (E) days between E12 and E15. Upon reaching adulthood, the rats were given unilateral injections of FG into the cervical cord to identify the spinal projection neurons. Brainstem sections were immunohistochemically processed for BrdU and then examined for neurons that were both BrdU-positive and FG-positive in the vestibular nuclei. In the lateral vestibular nucleus (LVe), most of the vestibulospinal neurons were generated on E12. In the inferior vestibular nucleus (IVe), the vestibulospinal neurons were produced almost equally on both E12 and E13. In the medial vestibular nucleus (MVe), the vestibulospinal neurons were generated consistently on days between E12 and E14 with a mild peak on E13. The present results thus demonstrate that genesis of the vestibulospinal neurons occurs sequentially in the following order: firstly in the LVe, secondly in the IVe, and finally in the MVe. The different sequential generation of vestibulospinal neurons among the LVe, MVe and IVe may reflect the fact that the vestibulospinal projections are differentially organized depending on the nature of each subnucleus.

Transection of the olfactory nerves induces expression of nerve growth factor receptor in mouse olfactory epithelium

Expression of nerve growth factor receptor (NGFR) was found in the mouse olfactory epithelium after olfactory nerve transection, although no immunoreactivity to NGFR was detectable in the olfactory epithelium in the control animals. After axotomy, however, NGFR-immunoreactive cells transiently appeared in the supporting cells, receptor neurons and basal cells between postoperative day 7 and 35, and thereafter disappeared by postoperative day 49. The results indicate that nerve growth factor may contribute to the regeneration of olfactory receptor neurons after olfactory nerve transection.

Ultrastructural morphology of projections from the medial geniculate nucleus and its adjacent region to the basal ganglia

The efferent projections of the medial geniculate nucleus (MG) and its adjacent nuclei to the basal ganglia were studied in the rat by the antero- and retrograde tracing methods. Injections of wheat germ agglutinin conjugated to horseradish peroxidase into the caudal parts of the striatum and globus pallidus produced retrograde neuronal labeling in the medial division of the MG (MGm) and its adjacent structures including the suprageniculate, posterior intralaminar and peripeduncular nuclei, and substantia nigra pars lateralis. Injections of [3H]leucine into the MG and its surroundings resulted in anterograde labeling not only in the striatum but also in the globus pallidus. The resulting labeling was distributed exclusively in the caudal parts of these two nuclei. The electron microscopic autoradiography showed preferential radiolabeling of terminals and myelinated axons in both the globus pallidus and striatum. Labeled terminals in the pallidum mostly made symmetrical synapses on somata and major dendrites, while labeled terminals in the striatum established asymmetrical synapses on dendritic spines. These morphological differences in the synapses of the efferent systems originating from the MGm and its surrounding region suggest functional/chemical differentiations at their target sites in the basal ganglia.

Separate neuronal populations of the rat substantia nigra pars lateralis with distinct projection sites and transmitter phenotypes

The topographic organization of the nigral cells sending axons to the striatum, amygdala and inferior colliculus was studied in the rat substantia nigra pars lateralis by using retrograde fluorescent tracers. Nigral perikarya projecting to the inferior colliculus were located dorsolaterally within the substantia nigra pars lateralis, whereas nigral perikarya projecting to the striatum or to the amygdala were mostly situated ventromedially within the substantia nigra pars lateralis. The transmitter substances of the nigrotectal cells were examined by combining a retrograde tracing method with immunohistochemistry for tyrosine hydroxylase or glutamate decarboxylase. Nigral neurons projecting to the inferior colliculus lacked tyrosine hydroxylase immunoreactivity, but exhibited immunoreactivity for glutamate decarboxylase. The substantia nigra pars lateralis is made up of different neuronal populations: one projecting to the inferior colliculus and another directed to the striatum and amygdala. The pars lateralis pathway to the inferior colliculus utilized GABA as a neurotransmitter, whereas the previously characterized nigral cells projecting to the striatum and superior colliculus use GABA and dopamine as neurotransmitters.

Choline acetyltransferase-immunoreactive neurons in the rat entopeduncular nucleus

Using a monoclonal antibody against choline acetyltransferase, neurons of the rat entopenduncular nucleus were found to express choline acetyltransferase immunoreactivity. These cholinergic cells were located mostly in the rostral portion of the entopeduncular nucleus with a marked decrease towards its caudal portion. To identify their target sites, a retrograde fiber tracing technique was combined with immunohistochemistry for choline acetyltransferase. After injection of wheatgerm agglutinin conjugated with horseradish peroxidase into the habenula, some of the entopedunculo-habenular cells were found to be immunoreactive for choline acetyltransferase. The cells in the peripallidal region (the substantia innominata, nucleus basalis magnocellularis and ansa lenticularis) with choline acetyltransferase immunoreactivity did not contain horseradish peroxidase. Following injection of fluorescent tracer into the frontal cerebral cortex, retrogradely labeled cells were observed in the rostral part of the entopedunucular nucleus. A majority of these entopedunculo-cortical cells exhibited choline acetyltransferase immunoreactivity, similar to the cells of the peripallidal region projecting to the neocortex. Employing two different fluorescent tracers, entopedunculo-cortical cells were shown to constitute a distinct cell population from the numerous entopedunculo-habenular cells. The present study demonstrated, in the rat entopeduncular nucleus, the presence of cholinergic neurons that projected to the neocortex and habenula.

Is there a dopaminergic projection from the A11 catecholamine cell group to the amygdala?

The dopaminergic nature of the pathway from the subparafascicular thalamic nucleus and its adjacent region to the amygdala was reexamined by means of retrograde fluorescent tracers coupled with tyrosine hydroxylase (TH) immunofluorescence. After injecting a small amount of tracer into the amygdala, retrogradely labeled cells were found in the subparafascicular thalamic nucleus and its adjacent periventricular region. TH immunofluorescence showed that these labeled cells completely lacked TH immunoreactivity. Similar results were obtained when a larger amount of tracer was applied to the amygdala. The present study, in contrast to the previous report describing the dopaminergic innervation of the amygdala by the cells in and around the subparafascicular area (A11 catecholamine cell group), indicates that the A11 cell group does not contribute to a dopaminergic input to the amygdala.

Establishment of the ethanol-induced place preference in rats

Ethanol failed to induce a place preference in both 15 and 50 min conditioning schedules in free-feeding and in food deprived rats. Acetaldehyde, the primary metabolic product of ethanol, induced a weak place aversion, dose-dependently. Ethanol combined with pyrazole (an alcohol dehydrogenase inhibitor) significantly induced a place preference in rats (ethanol; 300 mg/kg, i.p., pyrazole; 100 mg/kg, i.p.) in a 50 min conditioning schedule. The ethanol (300 mg/kg) combined with pyrazole (100 mg/kg)-induced place preference was antagonized or reduced by 5-HT3 antagonists (MDL72222, ICS205-930). These results suggest that a blockade of ethanol metabolism is very important for development of the ethanol-induced place preference in rats, and that the ethanol-induced place preference may be mediated by the mesolimbic dopamine system through 5-HT3 receptors.

Separate neuronal populations of the rat globus pallidus projecting to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental area

The topographic arrangement of globus pallidus neurons sending axons to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental nucleus was studied in the rat using retrograde fluorescent tracers. Neurons projecting to the subthalamic nucleus were localized in the rostral part of the globus pallidus, while neurons projecting to the auditory cortex and to the pedunculopontine tegmental nucleus were located in the caudal part. The two populations of pallidocortical and pallidotegmental neurons were also distributed in a separate manner within the caudal globus pallidus. The former neurons were large and located more ventromedially, whereas the latter were medium-sized and located more dorsolaterally. Using a retrograde fluorescent tracing technique combined with choline acetyltransferase immunofluorescence histochemistry, it was found that a vast majority of pallidocortical neurons expressed choline acetyltransferase immunoreactivity, and that pallidotegmental neurons rarely exhibited choline acetyltransferase immunoreactivity. A method of retrograde tracing with wheatgerm agglutinin conjugated with horseradish peroxidase associated to immunohistochemistry for glutamate decarboxylase confirmed the GABAergic nature of the pallidotegmental pathway. The present study revealed the independent nature of the globus pallidus neurons projecting to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental nucleus. Within this cellular arrangement, the presence of functionally distinct neuronal populations at the caudal pallidal level was also identified, with large cholinergic cells innervating the neocortex and medium-sized GABAergic cells "feeding" the mesencephalic tegmentum.

Development of a new geometrical form of micropipette: electrical characteristics and an application as a potassium ion selective electrode

Using a mix of thermal and anodic bonding together with microlithographic techniques, the safe transference of a Si3N4 film with a pore (diameter down to 1 micron) to a glass tube tip (external diameter 800 microns) was accomplished, yielding a new geometrical form of micropipette. Compared with conventional glass micropipettes the device has shown lower resistance, more stable capacitance (independent of the tip immersion depth), tip potential closer to that of a salt bridge, and a simplified filling process. Using this device as a potassium ion selective electrode (ISE), a faster response time ISE was achieved. These features indicate that the new device can advantageously substitute the conventional glass micropipettes when cell impalement is not required.

Anatomical and functional compartmentalization of the subparafascicular thalamic nucleus in the rat

The localization and the transmitter phenotype of subparafascicular thalamic nucleus (Spf) neurons projecting to the inferior colliculus (IC) and to the spinal cord (Sp) were studied by using a retrograde fluorescent double labeling technique, and a combined technique of retrograde tracing and immunohistochemistry for tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD). The cell population of Spf-IC neurons was totally differentiated from that of Spf-Sp neurons which have been reported to be dopaminergic. The former were densely distributed, small to medium sized cells and localized in the central portion of the Spf, while the latter were sparsely distributed, large cells and localized in the marginal portion of the Spf. Spf-IC neurons were completely devoid of TH immunoreactivity and, instead, approximately half of them showed GAD immunoreactivity. From these findings, it is concluded that the Spf is distinctly compartmentalized by the presence at least two separate neuronal subpopulations, which are distinguishable in terms of their cell size, distribution patterns, transmitter phenotypes and trajectories.

Passage time measurement of individual red blood cells through arrayed micropores on Si3N4 membrane

A new system has been developed for determining the deformability of individual red blood cells (RBCs), simulating the passage of RBCs in capillaries. The kernel of this system was the micropore array filter with an accurately defined pattern made by semiconductor microprocessing techniques. Individual microscopic RBC images were processed in parallel through a microcomputer and its interfacing circuit. An experiment with a normal RBC from a human donor demonstrated that it could pass the circular pore filter with a diameter as small as 1.0 micron at 2 cm H2O pressure difference. Deformability of RBCs treated with diamide or acetylphenylhidralazine was also measured, showing that the system was sufficiently sensitive to detect the deformability loss due to membrane damage or to polymerization of the cytoplasma.

Cholinergic nigrotectal projections in the rat

In order to verify a possible target site of cholinergic neurons in the substantia nigra of the rat, a retrograde fiber tracing method was combined with choline acetyltransferase immunohistochemistry. After injection of WGA-HRP into the superior colliculus, approximately 12% of retrogradely labeled cells in the substantia nigra were found to express choline acetyltransferase immunoreactivity. These double labeled cells were located in the dorsal and lateral portions of the substantia nigra pars reticulata at its middle and caudal levels.

Pallidotectal projection to the inferior colliculus of the rat

After injection of fluorescent tracer into the inferior colliculus (IC), retrogradely labeled cells were observed not only in the temporoauditory cortex (ACx) and the substantia nigra pars lateralis, but also in the globus pallidus (GP). These labeled GP cells were localized exclusively in the caudal portion of the GP, which has been known to project to the ACx. Employing a retrograde fluorescent double labeling technique, the GP-IC neurons were found to be distributed in a separate manner from the GP-ACx neurons within the caudal GP. The present study provides further anatomical evidence that the caudal GP has a functional role in auditory processing.

Non-dopaminergic projection from the subparafascicular area to the temporal cortex in the rat

Following injection of fluorescent tracer into the rat temporal cortex, retrogradely labeled cells were found in the subparafascicular area. In the thalamus, numerous cell labeling was seen in the medial geniculate complex. Labeled cells in the subparafascicular area were small (10-20 microns), and did not display tyrosine hydroxylase immunoreactivity. From these findings, the subparafascicular area has, at least, two distinct projection systems towards the cerebral cortex; the previously described large dopaminergic cells innervating the frontal cortex and small non-dopaminergic cells innervating the temporal cortex.

Measurement of human red blood cell deformability using a single micropore on a thin Si3N4 film

The filtration method for the evaluation of the RBC deformability has been further refined to simulate the deformations encountered in the recticuloendothelial system (in particular the spleen), a recognized site of aged and sickled cells removal. The core of the developed measuring system is a very thin (0.4 micron thick) filter that consists of single micropore (diameters down to 1 micron) on a Si3N4 film which has been constructed using silicon microfabrication techniques. Individual RBC's deformability is quantified measuring the cell pore passage time. From one blood sample 200 passage times are analyzed by a computer, displaying mean and median values as deformability indexes, and class and cumulative histograms for studying the passage times distribution. In this paper the effectiveness of the developed system as a routine clinical evaluation tool is demonstrated by studying several factors that are known to affect the RBC deformability, such as temperature, addition of diamide and glutaraldehyde, and blood storage conditions. In addition, it is experimentally demonstrated that the human RBC can traverse a pore with a diameter as small as 1 micron when the pore length is very short, thus broadening the experimental conditions under which the RBC deformability (fluidity) can be studied.