Central role for differential gene expression in mammalian hibernation

Mammalian hibernators experience dramatic reductions in body temperature, metabolic rate, respiratory rate, and heart rate during hibernation. These changes are precisely controlled and reversible with only internally driven mechanisms, suggesting specific biochemical regulation. We present a model that integrates our observations of differential liver gene expression during preparation for, and maintenance of, the hibernating state, with the known phylogenetic interspersion of hibernating species in several major mammalian lineages. This model predicts a major role for the differential expression of existing mammalian genes in the biochemical regulation of hibernation.

Specificity of a target cell-derived stop signal for afferent axonal growth

With a novel model culture system in which afferents are co-cultured with purified populations of target neurons, we have demonstrated that a target cell within the central nervous system (CNS), the cerebellar granule neuron, poses a "stop-growing signal" for its appropriate afferents, the mossy fibers. To ask whether this stop signal is afferent specific, we co-cultured granule neurons with another cerebellar afferent system, the climbing fibers from the inferior olivary nuclei, which normally contact Purkinje neurons, and with retinal ganglion cell afferents, which never enter the cerebellum. Granule neurons do not pose a stop signal to either of these afferents. In contrast to pontine mossy afferents that grow well on laminin and showed reduced outgrowth on granule neurons, both olivary and retinal fibers displayed similar growth on laminin alone or on granule neurons. In addition, each afferent showed different degrees of fasciculation and growth cone morphology on laminin. Thus, the growth arrest signal sent by granule neurons is specifically recognized by their appropriate afferents. Moreover, these three types of afferents exhibit varying growth patterns on the same noncellular and cellular substrates, implicating distinct molecular characteristics of growth regulation for different classes of neurons that would contribute to specificity of synapse formation.

Temperature dependence of electrophysiological properties of guinea pig and ground squirrel myocytes

The effects of changing temperature on the electrophysiology of isolated cardiac myocytes of the guinea pig and Richardson's ground squirrel were studied by patch-clamp techniques. In cells from both species, the resting membrane potential declined on cooling from 36 to 12 degrees C by approximately 6 mV. The duration of the plateau of the action potential in guinea pig cells increased monotonically on cooling. In contrast, the action potential of ground squirrel cells showed a biphasic response, increasing in duration from 36 to 24 degrees C and then decreasing on cooling from 24 to 12 degrees C. From voltage-clamp studies, the properties of L-type calcium currents (ICa) on cooling were compared in the two species and were found to be similar: In both cases, ICa decreased in amplitude from approximately 2 nA peak current at 36 degrees C to less than 400 pA at 12 degrees C. The Q10 of both the maximum amplitude and time to peak for ICa in both species was approximately 1.8. The time for half inactivation had a greater Q10 of 2.5-3. It is concluded that, surprisingly, factors affecting the resting membrane potential and properties of L-type calcium channels are not major contributors to cardiac dysfunction on cooling. Rather, it is sarcoplasmic reticulum calcium release and reuptake that are likely to be the most important cold-sensitive processes.

Prolonged stable hypothermia: effect on blood gases and pH in rats and ground squirrels

Richardson's ground squirrels [body temperature (Tb) 7 degrees C] survive prolonged stable hypothermia for three times as long as do rats (Tb 19 degrees C) (72 vs. 24 h). We have examined the changes in blood gases and acid-base state to assess whether these contribute to this difference in survival time. None of the variables (measured at ambient temperature of 25 degrees C) differed significantly between rats and ground squirrels before hypothermic induction. During cooling, neither hematocrit nor plasma lactate changed significantly, but arterial and venous PO2 and PCO2 increased and arterial and venous pH decreased in both groups. During prolonged hypothermia, hematocrit increased significantly in rats (58.8 +/- 1.7% at 24 h) but not in ground squirrels (39.1 +/- 1.0% at 72 h). Both species maintained stable arterial blood gases but showed decreased venous PO2; arterial and venous pH decreased significantly with time in both species in conjunction with increased plasma lactate. These patterns of decreased venous PO2 and increased plasma lactate suggest that reduced tissue oxygenation occurs during hypothermia. This happens earlier in rats at a Tb of 19 degrees C than in ground squirrels at a Tb of 7 degrees C, possibly as a result of increased hematocrit in hypothermic rats. Remedial measures directed at improving tissue O2 delivery may therefore prolong the hypothermic survival of rats.

Experimental infection routes of Angiostrongylus cantonensis in mice

Stomach intubation is the most common method used in the experimental infection of animals with Angiostrongylus cantonensis. In order to compare the effectiveness of other possible transmission methods, groups of BALB/c mice were given infective third-stage larvae of A. cantonensis by different routes including intraperitoneal or subcutaneous injections, and penetration of anal mucosa, vaginal mucosa, conjunctival mucosa, lacerated skin, unabraded skin, foot pad and tail skin, while stomach intubation was used as control. Recovery of fifth-stage larvae was higher in mice inoculated with third-stage larvae subcutaneously. Successful infections were established through all experimental transmission routes except tail skin penetration. This study suggests that oral infection may not be the only route for the transmission of human angiostrongyliasis, and subcutaneous infection may be a better method for experimental infection.

Seasonal variations in the rate and capacity of cardiac SR calcium accumulation in a hibernating species

The rate of calcium uptake and the level of calcium accumulation was measured in cardiac muscle SR from hibernating and nonhibernating Richardson's ground squirrels. In whole heart homogenates, the rate of calcium uptake was higher (P less than 0.05) in hibernating animals than it was in active animals. Further purification of homogenates into sacroplasmic reticulum (SR) preparations showed that the hibernating animals had the highest rate of calcium uptake and the greatest level of calcium accumulation. These results could not be explained by variations in non-SR membrane contaminants nor by changes in the maximal activity or total amount of a SR marker enzyme, the Ca(2+)-ATPase. The addition of ryanodine to the calcium uptake medium increased the level of calcium accumulation in all groups by a similar amount. It is concluded that the high rate of calcium uptake by isolated cardiac SR vesicles from hibernating ground squirrels reflects the activity of the organelle in vivo, and that the ability of the ryanodine-insensitive population of SR vesicles to accumulate calcium is affected by hibernation.

Optimal temperature in short-term hypothermic preservation of rat pancreas

Rat pancreases were hypothermically preserved for 24 hr in University of Wisconsin preservation solution at specific temperatures (4, 7, 10, and 15 degrees C) to evaluate the effect of preservation temperature on islet yield and islet function. Following hypothermic storage, the loss of recoverable islets was highest in the 15 degrees C-preservation group, followed by that of the 4 degrees C group and significantly less in the 7 and 10 degrees C groups (p less than 0.05). Islet function, as measured by insulin output following glucose challenge in perifusion, was reduced (p less than 0.0001) in all preservation groups. The mean insulin secretion rate was lowest in the 4 degrees C group, highest in the 7 degrees C group, and intermediate in the 10 degrees C group. The islet preservation index, a parameter taking into consideration both islet yield and islet function after preservation, was more than double in the 7 and 10 degrees C preservation groups as compared to the 4 degrees C group (p less than 0.0001). This study shows that significant improvement in islet yield and function occurs when the rat pancreas was preserved at 7-10 degrees C rather than at 4 degrees C.

Seasonal changes in methionine-enkephalin immunoreactivity in the brain of a hibernator, Spermophilus columbianus

To identify the actual location of central endogenous opioid systems which may be involved in regulating the hibernation cycle, differences in the pattern of central methionine-enkephalin (Met-EK) immunoreactivity were compared between hibernating (body temperature, Tb = 7 degrees C) and non-hibernating (Tb = 37 degrees C) Columbian ground squirrels using the peroxidase-antiperoxidase technique. In non-hibernating animals, Met-EK-immunoreactive perikarya were observed in telencephalic (putamen, caudate nucleus, medial septum-diagonal band complex, amygdala) and diencephalic (periventricular hypothalamic nucleus, lateral hypothalamic area) regions, whereas immunoreactive fibers were found in the lateral septum, stria terminalis nucleus, various hypothalamic areas, arcuate nucleus, median eminence, thalamic intralaminar, periventricular nucleus and lateral habenular nucleus. Compared to the non-hibernating animal, a marked increase in the number of Met-EK-immunoreactive fibers was found in the lateral septal nucleus, the periventricular nucleus, the intralaminar thalamus and the paraventricular hypothalamus of hibernating ground squirrels. Since these changes in immunoreactivity were not observed in the artificially induced hypothermic ground squirrels (Tb = 7 degrees C), it is unlikely that the dissimilarity in immunoreactivity between animals from different hibernating phases is due to differences in their Tb. In combination with our previous studies, these results tend to suggest that hibernation may be brought about by an increase in endogenous opioid activity, especially in the lateral septal region.

Altered properties of calsequestrin and the ryanodine receptor in the cardiac sarcoplasmic reticulum of hibernating mammals

A novel isoform of calsequestrin was identified in sarcoplasmic reticulum vesicles from myocardial tissue of two species of hibernating ground squirrel. The protein was identified as calsequestrin by its cross-reactivity with antibodies raised against bovine cardiac calsequestrin, its pH-sensitive mobility in sodium dodecylsulphate-polyacrylamide gels, staining blue with the cationic carbocyanine dye 'Stains-All', binding peroxidase-conjugated concanavalin A, its endoglycosidase F sensitivity. Its NH2-terminal amino acid sequence is similar, but not identical, to that already determined for cardiac calsequestrin. Some of the biochemical properties of this protein distinguish it from the other mammalian isoforms. It has a unique electrophoretic mobility in both alkaline and neutral sodium dodecylsulphate-polyacrylamide gel electrophoresis, it appears to have a molecular weight approximately 7% greater than that of cardiac calsequestrin from other mammalian species, and its glycosylation pattern differs. This novel form of calsequestrin is expressed in cardiac SR vesicles which possess an abnormally high number of Ca2(+)-release channel/ryanodine receptor molecules. This ryanodine receptor also shows an altered Ca2(+)-sensitivity of ryanodine binding. The divergent biophysical properties of this novel form of cardiac calsequestrin, together with the apparently atypical ryanodine receptors in the cardiac sarcoplasmic reticulum membranes may have some functional significance in the adaptive mechanisms which allow the heart to function despite the severely reduced body temperatures (to approx. 0 degree C) encountered during hibernation.

Plasma glucagon, glucose, and free fatty acid concentrations and secretion during prolonged hypothermia in rats

Impairment of metabolic substrate mobilization and utilization may be a factor limiting survival in hypothermia. Using a newly developed technique for maintaining stable low body temperature (Tb), substrate profiles and their regulation by glucagon were examined in hypothermic rats (Tb 19 +/- 0.3 degrees C) over 20 h. During cooling, plasma glucagon, glucose, and free fatty acid (FFA) concentrations increased significantly (536 +/- 55 pg/ml, 304 +/- 26 mg/100 ml, and 844 +/- 81 mueq/l, respectively). Plasma glucagon and glucose concentrations continued to increase up to 8 h (peaks 810 +/- 103 pg/ml and 451 +/- 33 mg/100 ml, respectively) and remained high throughout the rest of the hypothermic period. FFA concentrations decreased steadily during the hypothermic period. Exogenous glucagon (20 micrograms/kg) induced significant increases in plasma glucose (+129 +/- 31 mg/100 ml) and FFA concentrations (+351 mueq/l) at 2 h but had no effect at 15 h of hypothermia. In vitro evaluation of pancreatic alpha-cell function indicated that glucagon secretion is independent of temperature between 37 and 19 degrees C. Our data indicate that hypothermia is characterized by a disturbed substrate metabolism, which is likely due to an imbalance in pancreatic alpha- and beta-cell function and a time-dependent decrease in tissue sensitivity to glucagon. These deleterious changes may limit survival in hypothermia.

Cardiac mechanical restitution in active and hibernating Richardson's ground squirrel

The cardiac mechanical restitution was compared in papillary muscles between the active and the hibernating Richardson's ground squirrels at 0.1, 2.8, and 5 mM external Ca2+ concentration [( Ca2+]o). The amplitude of the restitution was significantly higher in hibernating animals between 37 and 7 degrees C at all [Ca2+]o. The first postrest contraction (F1) was highest at 20 degrees C and lower at 37 and 7 degrees C in both groups. The pause duration for maximum F1 was 30 s in active but 10 s in hibernating animals at 37 degrees C and increased to 100 s in both groups at 7 degrees C. The postrest potentiation was eliminated by 10(-6) M ryanodine at 20 degrees C in both groups, and this inhibitory effect was more pronounced in the hibernating group. Together, our results suggest that the activator Ca2+ for excitation-contraction coupling is mainly derived from the sarcoplasmic reticulum (SR) pool in both active and hibernating ground squirrel, and the dependence on SR Ca2+ release via ryanodine-sensitive Ca2+ channels is more marked in the hibernating state. Furthermore, there is no significant difference in sensitivity of the cardiac mechanical restitution to [Ca2+]o between the active and the hibernating condition.

State-dependent variation in the inhibitory effect of [D-Ala2, D-Leu5]-enkephalin on hippocampal serotonin release in ground squirrels

Accumulated evidence has suggested that increased endogenous opioid activities may facilitate the onset of hibernation either directly or possibly through modulation of other neurotransmitter systems. The seasonal change of [D-Ala2, D-Leu5]-enkephalin (DADLE), a delta receptor agonist, in modulating K+ (35 mM)-induced [3H]-5-hydroxytryptamine (5-HT) release from the hippocampal and hypothalamic slices of euthermic and hibernating Richardsons' ground squirrels was therefore investigated. DADLE (0.1-10 microM) had no effect on 5-HT release in the hypothalamic slices but elicited a dose-related inhibition on [3H]-5-HT release from the hippocampal slices of the euthermic ground squirrel. The inhibitory effect of DADLE was completely reversed by naloxone (10 microM), but not by tetrodotoxin (1 microM). In contrast, DADLE failed to alter the K(+)-induced 5-HT release from the hippocampal slices of the hibernating ground squirrel. This state-dependent reduction in responsiveness to an opioid is consistent with the hypothesis that enhanced endogenous opioid activity in the hibernating phase could lead to down regulation of the opioid receptors and minimize its inhibition on hippocampal serotonergic activity. A high 5-HT activity would inhibit midbrain reticular activating system indirectly through non-serotonergic fibers, which in turn facilitate the onset or maintenance of hibernation.

Effects of ginsenoside Rb1 on central cholinergic metabolism

Ginsenosides, the saponins of ginseng, are bioactive ingredients which exert many beneficial effects. One ginsenoside, Rb1, extracted from North American ginseng (Panax quinquefolium L.), partially prevents the memory deficits induced by a cholinergic agent (scopolamine) in rats. In vitro studies show that Rb1 has no effect on quinuclidinyl benzylate binding or on acetylcholinesterase activity, but facilitates the release of acetylcholine (ACh) from hippocampal slices. The increase in ACh release is associated with an increased uptake of choline into nerve endings; however, calcium influx is unaltered. The ability of Rb1 to prevent memory deficits may be related to facilitation of ACh metabolism in the central nervous system.

Effect of low temperature on the cytosolic free Ca2+ in rat ventricular myocytes

The effect of low temperature on the cytosolic free Ca2+ [( Ca2+]i) has been investigated in isolated ventricular myocytes from adult rats using the fluorescent probe Indo-1. The distribution of Indo-1 between the mitochondrial and cytoplasmic compartments was first determined in the isolated myocytes using the digitonin and Triton X-100 treatments. By subtracting the mitochondrial [Ca2+]i from the total [Ca2+]i measured with Indo-1, the average cytosolic [Ca2+]i was found to increase significantly (P less than 0.05) from 139 nM to 255 and 297 nM when the temperature was decreased from 37 degrees C to 15 degrees and 5 degrees C, respectively. A marked increase in cytosolic [Ca2+]i to a new steady state level was observed when the membrane of myocytes was depolarized by 60 mM KCI; the average magnitude of increase being 110, 243 and 186 nM, at 37 degrees, 15 degrees and 5 degrees C respectively. Our results support the hypothesis that the cardiac arrhythmia typically observed in the hypothermic rat is due to an increased cytosolic [Ca2+]i with decreasing body temperature.

Berberine-induced morphologic differentiation and down-regulation of c-Ki-ras2 protooncogene expression in human teratocarcinoma cells

A pluripotent human teratocarcinoma cell clone, NT2/D1, which was derived from the Tera-2 cell line, was induced to differentiate into cells with neuronal cell morphology by treatment with berberine. As early as 1 day after a 24-h treatment of cells with berberine at a non-toxic dose of 0.1 mg/ml in culture medium, the cells started to show morphologic changes, developing into terminally differentiated neuronal cells with long, inter-connecting network-like cellular structures. This process is much faster as compared with that induced by treatment with retinoic acid (RA), which took at least several days to develop. Unlike RA, berberine could not induce murine teratocarcinoma cell line, F9, to differentiate into endodermal cells. It was also found that, although the NT2/D1 cell clone exhibited amplification and enhanced mRNA expression of c-Ki-ras2 gene as did the parent cell line, a marked down-regulation of c-Ki-ras2 mRNA expression was observed. However, there was no change in actin mRNA expression even after differentiation had occurred. Thus, morphologic differentiation of teratocarcinoma cells into neuronal cells is found to be associated with down-regulation of a protooncogene which plays some definite role in oncogenesis. The mechanism by which berberine induces differentiation in these cells needs further investigation.

Effect of intracerebroventricular injection of neokyotorphin on the thermoregulatory responses in rats

Intracerebroventricular injection of neokyotorphin (NKT) (0.5-2.0 micrograms) caused a dose-related increase in body temperature (Tb) of rats maintained at 28 degrees C. The change in Tb of the rat induced by the optimal dose of NKT (1 microgram) was attenuated when the rat was exposed to 18 degrees C. At both ambient temperatures, heat production was not affected but heat loss was significantly reduced at 28 degrees C in rats receiving 1 microgram NKT. Pretreatment with naloxone (5 mg/kg, IP) significantly reduced the hyperthermic effect induced by NKT (1 microgram). These results suggest that NKT can affect the prevailing thermoregulatory heat loss activities and this effect may be mediated through stimulated release of endogenous opioids.

Improvement of cold tolerance by selective A1 adenosine receptor antagonists in rats

Previously we have shown that the improvement of cold tolerance by theophylline is due to antagonism at adenosine receptors rather than inhibition of phosphodiesterase. Since theophylline is a nonselective adenosine receptor antagonist for both A1 and A2 receptors, the present study investigated the adenosine receptor subtype involved in theophylline's action. Acute systemic injection of selective A1 receptor antagonists (1,3-dialkyl-8-aryl or 1,3-dialkyl-8-cyclopentyl xanthine derivatives) significantly increased both the total and maximal heat production as well as cold tolerance. In contrast, injection of a relatively selective A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine (compound No. 19), failed to significantly alter the thermogenic response of the rat under cold exposure. Further, the relative effectiveness of these compounds in increasing total thermogenesis was positively correlated with their potency in blocking the A1 adenosine receptor (r = .52, p less than 0.01), but not in A2 adenosine receptor (r = .20, p less than 0.2). It is likely that the thermally beneficial effects of adenosine A1 antagonists are due to their attenuation of the inhibitory effects of endogenously released adenosine on lipolysis and glucose utilization, resulting in increased substrate mobilization and utilization for enhanced thermogenesis.

Graft compliance and anastomotic flow patterns

The oscillatory flow patterns at the venous anastomosis of a hemodialysis angioaccess loop graft system were studied using two new compliant vascular prostheses: a longitudinally compliant polytetrafluoroethylene-composite (Baxter Ultraflex PTFE-Plus) graft (BA) and a radially compliant ultrafine polyester fiber (TORAY-UFPF) graft (TR). A non-compliant Gore-Tex polytetrafluoroethylene graft was used as the control. The experimental grafts were 8 mm inside diameter x 25 cm long. Flow experiments were done in a transparent, elastic bench-top flow model; fabrication was based on silicone rubber casts obtained from femoral-to-femoral arteriovenous loop grafts surgically implanted in dogs. The loop graft constructed in the dog model was made to mimic the branchial-to-cephalic angioaccess loop graft commonly used in hemodialysis patients. The flow model was connected to a pulse generator, an adjustable arterial afterload, and a venous afterload. Under identical input conditions, the pressure and flow waveforms were monitored simultaneously at the proximal and distal ends of both the arterial and venous anastomoses. For each graft studied, the anastomotic flow field was visualized using laser illuminated hydrogen bubbles as tracers. At pulse rates of 60 and 90 beats/min, graft flow rates were 2.2 and 2.5 L/min, respectively. Among the grafts studied, measurable differences in pressure and flow wave attenuation and their respective phase lags resulted in characteristically dissimilar flow patterns at the venous anastomosis. Growth of the separation zone at the toe of the anastomosis, and the pattern of retrograde flow in the distal vein are visibly different in all three grafts.

Do adenosine antagonists improve cold tolerance by reducing hypothalamic adenosine activity in rats?

Previously we have shown that systemic injection of adenosine antagonists can significantly improve cold tolerance in both rats and humans. However, it is not clear whether systemic administration of adenosine antagonist acts peripherally or centrally at the thermoregulatory site. To resolve this, theophylline (nonselective adenosine receptor blocker), cyclopentyltheophylline (selective A1 receptor blocker) or adenosine deaminase (an enzyme which inactivates adenosine by converting it into inosine) was injected directly into preoptic anterior hypothalamus (POAH) of rats and their thermogenic responses assessed. In contrast to that observed after systemic administration, intrahypothalamic injection of either adenosine antagonists or deaminase at various doses failed to elicit any enhancement in heat production beyond that of the controls. These results suggest that the beneficial effect of systemically injected adenosine antagonists in improving cold tolerance is not the result of altering the thermoregulatory functions mediated via the POAH.

Enhancement of maximal thermogenesis by reducing endogenous adenosine activity in the rat

Adenosine has been shown in vitro to be a potent antilipolytic agent and an inhibitor of insulin-stimulated glucose utilization in skeletal muscle. To test whether endogenously produced adenosine (e.g., from ATP hydrolysis) shares these deleterious effects on substrate mobilization and utilization and thus limits maximum thermogenesis in vivo, adenosine deaminase (converts adenosine to inosine) was given to rats 15 min before cold exposure. Significant (P less than 0.05) increases in thermogenesis were observed under both well-fed (100 units/kg ip) and food-rationed (200 units/kg ip) states. Significant (P less than 0.05) increases in thermogenesis and cold resistance were also observed after pretreatment with selective adenosine receptor antagonists [8-cyclopentyltheophylline (1 microgram/kg ip) greater than 1,3-dipropyl-8-p-sulfophenylxanthine (1.25 mg/kg ip) greater than aminophylline (18.7 mg/kg ip)], indicating an A1-receptor-mediated effect. These results indicate that endogenously released adenosine can indeed attenuate the thermogenic capacity in severe cold and that adenosine antagonists, especially those selective for A1-receptor, are useful in improving cold resistance under varying nutritional states.

Smooth muscle contractility and calcium channel density in hibernating and nonhibernating animals

Hibernating animals consistently survive prolonged periods of cold with body temperatures near the freezing point. Previous studies have suggested that regulation of calcium influx may be a fundamental cellular mechanism for cold tolerance in hibernating species. The present study was undertaken to compare (i) the calcium dependence of contractility and (ii) [3H]nitrendipine binding in homogenates of ileal longitudinal smooth muscle from the nonhibernating guinea pig (Cavia porcellus) and a hibernator, the ground squirrel (Spermophilus richardsonii). The contractility studies indicate that both the activation threshold for calcium and the concentration-response curve were shifted to the right in ground squirrel when compared with guinea pig. The binding site density in ground squirrel muscle was about an order of magnitude less than in guinea pig (Bmax = 10 +/- 2 (n = 12) and 86 +/- 6 fmol/mg protein (n = 5), respectively). These results indicate that ground squirrel tissues are less sensitive to external calcium and clearly have fewer calcium channels than the smooth muscle of the non-hibernator. The results continue to support the hypothesis that cold tolerance in hibernating species involves calcium homeostatic control mechanisms.

Acquired immunity in rats against Angiostrongylus cantonensis infection

Acquired immunity against Angiostrongylus cantonensis was induced by immunizing rats with somatic antigens from fifth-stage larvae and adult worms and live third-stage larvae. Rats immunized twice had significantly fewer worms than rats immunized three times. Fewer worms were recovered from rats immunized with 200 live third-stage larvae than from any other groups. Rats immunized with somatic antigens had higher enzyme-linked immunosorbent assay (ELISA) antibody levels than rats immunized with live larvae. Rats immunized with live third-stage larvae of Angiostrongylus cantonensis were more strongly protected against challenge infections (62-92%) than rats immunized with antigens extracted from fifth-stage larvae (0-30%) and adult worms (11-24%).

[Morphological study on the role of coated vesicle in the specialization of synaptic membrane in synaptogenesis]

Our object was to characterize the morphological changes of coated vesicles and synaptic membranes during synaptogenesis. Neurons from spinal cords of fetal mice were established as isolated cells in primary culture. After a few days in vitro, the neurons extended their neurites and started their interaction. At timed intervals thereafter, cultures were fixed for electron microscopic observation. Coated vesicles were prominent in the neuronal cytoplasm at the time of synaptogenesis (about 7-10 days in vitro). Similar vesicles were seen in continuity with some cisternae in the Golgi regions and there was an increase in number during the synaptogenic period. Indeed it is not established whether the coated vesicles were exocytotic or pinocytotic in nature, but the cisternae which were in continuity with coated vesicles could be labelled by glucose-6-phosphatase (G6Pase) but not by thiamine pyrophosphatase (TPPase). Such vesicles were also seen in continuity with the neuronal plasmalemma near the closest contact site and contributed their undercoating to pre- and postsynaptic densities. The formation of bilateral membrane specialization was described as being structurally similar to synaptic active zones and appeared to be the first definitive sign of synapseformation. It has been suggested that the synaptic dense material may derive wholly or in part from the exocytic coated vesicles which apparently budding off from endoplasmic reticulum cisternae. This incorporation could provide the mechanism for confining specific characteristics of neuronal membrane to the synaptic region.

[Development of endoplasmic reticulum and its enzymic marker in cultured mouse spinal neurons]

In an attempt to elucidate the relationship between synapse formation and cell development, the morphology and cytochemistry of the endoplasmic reticulum and its enzymic marker, glucose-6-phosphatase (G-6-Pase), in cultured mouse spinal neurons were investigated ultrastructurally. It was found that in the early period of the development, neurons were characterized by scarceness of organelles; only a few of granular or agranular endoplasmic reticulum and mitochondria were seen. The endoplasmic reticulum and nuclear envelope were packed specifically with G-6-Pase resection product but the product was weak. After a period of culture, most of the neurons had well-developed endoplasmic reticulum, Golgi apparatus, mitochondria and microtubules, etc. The Golgi apparatus was relatively large, having some cisternae associated with vesicles. Either concave of convex face of the saccules was labeled by thiamine pyrophosphatase (TPPase) specifically. GERL, labeled by cytidine monophosphatase (CMPase), was also seen close to the inner or outer face of some Golgi apparatus. The endoplasmic reticulum at this stage was distributed throughout the cytoplasm, including that in dendrites; its enzyme marker (G-6-Pase) localized consistently within the lumen of all endoplasmic reticulum, nuclear space and subsurface cisternae, and frequently in the concave saccules of the Golgi apparatus. After a long-term culture, some neurons became "aged". The endoplasmic reticulum cisternae enlarged and G-6-Pase reaction reduced. Along with the neuronal development, especially maturation of the endoplasmic reticulum and its enzymic marker, synapse formation was begun at the neuropile area. The axo-dendritic synapses always occurred between the axonal terminals and dendrites where the endoplasmic reticulum had showed positive G-6-Pase reactions. Considering the fact, it suggests that the appearance and change of these specific enzymes may be related to the maturation of the neurons in vitro, and also related to the synapse formation between neurons.