Increased Acetylcholine Content Induced by Antidromic Stimulation of a Sympathetic Ganglion: A Possible Retrograde Action of Adenosine

Abstract: Prolonged high-frequency orthodromic stimulation of superior cervical ganglia is known to result in increased acetylcholine (ACh) synthesis and ACh content after the period of stimulation. In a previous study, we provided evidence to suggest that adenosine acts as an extracellular signal to activate this increased ACh synthesis and we proposed that the source of that adenosine might be postsynaptic. Thus, the purpose of the present study was to test whether direct stimulation of the postganglionic nerves could affect ganglionic ACh content. Antidromic conditioning of ganglia (15 Hz, 45 min) did not affect significantly their ACh content. However, if ganglia were allowed a 15-min rest period after this antidromic conditioning, their ACh stores were increased by 20%; a similar increase was induced by 4-Hz stimulation before the rest period. During the 15-Hz antidromic stimulation, ACh release was not clearly increased above the basal level, suggesting that preganglionic nerve endings were not stimulated to an extent that could explain the increased ACh content. Orthodromic stimulation (5 Hz) of ganglia 15 min after they had been subjected to antidromic conditioning (15 Hz, 45 min) showed increased ACh release in comparison with that from control unconditioned ganglia. Moreover, the extra ACh released by the conditioned ganglia was quantitatively similar to the increase in the ACh stores, as if most, or all, of the additional ACh was released by preganglionic stimulation. If the antidromic conditioning and the rest period were done during perfusion with Ca²⁺-free medium, the ganglia did not accumulate extra ACh. The ACh content was also not changed if ganglia were conditioned in the absence of Ca²⁺ but rested with normal Ca²⁺. However, ACh content was increased by 23% when the antidromic stimulation was done with normal Ca²⁺ but the rest period was without Ca²⁺. To test the role of adenosine in this retrograde effect, the effect of nucleoside transport inhibitors was tested. Dipyridamole blocked the antidromic stimulation-induced increase, but nitrobenzylthioinosine did not. Overall, these results are consistent with the idea that a diffusible retrograde messenger activates ACh synthesis. The sensitivity to blockade by dipyridamole suggests that adenosine might be that signal.     

Mobilization of a Vesamicol-Insensitive Pool of Acetylcholine from a Sympathetic Ganglion by Ouabain

Abstract: These experiments investigate the release of transmitter from the perfused superior cervical ganglia of cats induced by ouabain in the absence or presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol), a blocker of acetylcholine (ACh) uptake. Ouabain, perfused through the ganglia, released ACh in a Ca²⁺-dependent way. Vesamicol caused some inhibition of the release of ACh by ouabain; however, under this condition, the Na⁺, K⁺-ATPase inhibitor released five times more transmitter than did preganglionic stimulation at 5 Hz. Also, when ganglia exposed to vesamicol were depleted of the impulse-releasable pool of ACh, subsequent perfusion with ouabain released ACh, and this included ACh newly synthesized in the presence of vesamicol; this phenomenon could be inhibited by the lack of Ca²⁺ and presence of EGTA, and was completely abolished by perfusion with a medium containing 18 mM Mg²⁺. To test whether the release of this vesamicol-insensitive Ca²⁺-dependent pool by ouabain is associated with a decrease in the number of synaptic vesicles, ganglia treated with the ATPase inhibitor after the depletion of the impulse-releasable pool of ACh were fixed for electron microscopy. In the presence of Ca²⁺, coincident with the release of the vesamicol-insensitive pool of ACh, nerve terminals were almost depleted of synaptic vesicles; ganglia treated similarly, but with medium containing 18 mM Mg²⁺ instead of Ca²⁺, were not depleted of synaptic vesicles. These results suggest that ouabain releases a vesamicol-insensitive pool of ACh from the sympathetic ganglion and also support the notion that this compartment is vesicular and its exocytosis depends on extracellular Ca²⁺. It is suggested that empty-vesicle recycling in the presence of vesamicol restricts mobilization of full vesicles to release sites.     

The Action of Serotonin on Calcium-45 Efflux from the Anterior Byssal Retractor Muscle of Mytilus edulis

⁴⁵Ca efflux was studied in resting anterior byssal retractor muscle. The data are described by a three-compartment system. The most rapidly exchanging compartment, with an average time constant of 7 min, contains about 0.9 mM Ca/liter muscle, and probably represents extracellular space. A second compartment, with a time constant of 83 ± 5 min, contains 1.2 mM Ca/liter, and may represent a membrane calcium store. The presence of a third, or more, compartments, probably representing sarcoplasmic reticulum and contractile proteins, is indicated by the fact that the final time constant is 10 times the 83 min time constant of the second compartment. Serotonin (5HT), on initial application, increases ⁴⁵Ca efflux from this third compartment(s). This effect has a typical dose-response relationship with a maximum response appearing at 10^-7 M5HT. In addition, removal of 5HT causes a secondary increase in ⁴⁵Ca efflux which has a maximum at a 5HT concentration of 10^-7 M and declines at both higher and lower doses.     

Calcium Buffering and Free Ca2+ in Rat Brain Synaptosomes

Abstract: The effects of K⁺ depolarization and of stimulation by veratridine on apparent cytosolic free Ca²⁺ ([Ca²⁺]_cyt) and net Ca²⁺ accumulation were measured in isolated rat brain presynaptic nerve terminals (synaptosomes). [Ca²⁺]_cyt was determined with fura-2, and Ca²⁺ accumulation was measured with tracer ⁴⁵Ca. [Ca²⁺]_cyt was ～ 325 nM in synaptosomes incubated in the normal physiological salt solution under resting conditions. When [K⁺]₀, was increased from the normal 5 mM to 30 or 50 mM, ⁴⁵Ca uptake and [Ca²⁺]_cyt both increased within 1 s. Both increases were directly related to [Ca²⁺]₀ for [Ca²⁺]₀= 0.02–1.2 mM; however, the increase in ⁴⁵Ca uptake greatly exceeded the increase in [Ca²⁺]_cyt. With small Ca²⁺ loads ≤100 μmol/L of cell water, equivalent to the Ca²⁺ entry during a train of ≤60 impulses), the ⁴⁵Ca uptake exceeded the increase in [Ca²⁺]_cyt by a factor of nearly 1,000. This indicates that ～99.9% of the entering Ca²⁺ was buffered and/or sequestered within ～ 1 s. With larger Ca²⁺ loads, a larger fraction of the entering Ca²⁺ was buffered; ～99.97% of the load was buffered with loads of 250–425 μmol/L of cell water. The ratio between the total Ca²⁺ entry and the increase in [Ca²⁺]_cyt, the “calcium buffer ratio”β, was therefore ～ 3,500:1. This ratio was somewhat lower than the ratio of total intraterminal calcium: [Ca²⁺]_cyt, which ranged between ～7,300:1 and 12,800:1. When the synaptosomes were activated with 10 μM veratridine ([Ca²⁺]₀= 0.2–0.6 mM), ⁴⁵Ca influx and [Ca²⁺]_cyt increased progressively for ～10 s (β= 2,700:13,050:1) and then leveled off. Application of 10 μM tetrodotoxin before the introduction of veratridine prevented the increases in ⁴⁵Ca influx and [Ca²⁺]_cyt. Application of 10 μM tetrodotoxin after 5–10 s of exposure to veratridine caused both the [Ca²⁺]_cyt and the veratridine-stimulated ⁴⁵Ca within the terminals to decline, thereby demonstrating that the Ca²⁺ loading is reversible in the presence of extracellular Ca²⁺. These data show that synaptosomes are capable of buffering and metabolizing Ca²⁺ in a manner expected for intact neurons.     

Calcium efflux from frog twich muscle fibers

An apparatus is described which collects the effluent from the center 0.7 cm of a single muscle fiber or bundle of muscle fibers. It was used to study the efflux of ⁴⁵Ca from twitch muscle fibers. The efflux can be described by three time constants 18 ± 2 min, 300 ± 40 min, and 882 ± 172 min. These kinetics have been interpreted as those of a three-compartment system. The fastest is thought to be on the surface membrane of the muscle and of the T system. It contains 0.07 ± 0.03 mM Ca/liter of fiber and the Ca efflux is 0.11 ± 0.04 pM Ca/cm². sec. The intermediate rate compartment is thought to represent the Ca in the longitudinal reticulum. It contains approximately 0.77 mM Ca/liter. Only the efflux from this compartment increases during stimulation. The most slowly exchanging compartment is poorly defined. Neither Ca-free nor Ni-Ringer solutions alter the rate of loss from the fastest exchanging compartment. Ni apparently alters the rate of loss from the slowest compartment.     

CHOLINE UPTAKE BY CHOLINERGIC NEURON CELL SOMAS

The cellular compartments of ciliary ganglia take up choline by a single, saturable process with K_m=7.1 × 10^?5 M and V_max= 4.66 pmol/min per ganglion: Denervation of the ganglia and the resultant degeneration of nerve terminals caused no significant decrease of the rate of accumulation of choline by the ganglia. This indicates that the measured uptake is by the postganglionic ncurons and nonneural elements (NNE: glial and connective tissue cells) in the ganglia. This uptakc is not dependent on metabolic energy and is not affectcd by lowcring Na⁺ or raising K⁺ concentrations in the incubating mcdia but is depressed in the presence of ouabain and hemicholinium-3. The presence or Na⁺-dependent. rapidly saturable uptake in the preganglionic nerve terminals which is not detectablc kinetically is, however, inferred from a decrease in ACh synthesis in dcncrvatcd prcparations and a similar decrcasc in intact ganglia incubated in low Na+ solution.     

Electrical activity of the sympathetic ganglia during the depressor reflex

Tonic activity of neurons of the superior cervical sympathetic ganglion was recorded by the "sucrose gap" method and in the 4th and 5th lumbar sympathetic ganglia with the aid of focal nonpolarizing electrodes in acute experiments on anesthetized cats and rabbits. The preganglionic fibers of the ganglia were left intact. Stimulation of the depressor nerve not only sharply inhibited the tonic activity of the ganglia but also led to the appearance of electropositive potentials of 0.7 ± 0.2 mV in the superior cervical ganglion and 20–250 µV in the lumbar ganglia. The amplitude of this potential was unchanged by atropine (1 · 10^–6M). A similar effect occured without stimulation of the depressor nerve, after division of the preganglionic fibers or blocking of their conduction; it is attributed to the cessation of preganglionic tonic impulses which induce not only spikes, but also many EPSPs in neurons of the ganglion. Their frequency in the lumbar ganglia was 4/sec. Summation of these EPSPs leads to constant electronegativity of the ganglion surface relative to the postganglionic fibers, and its disappearance is recorded as a positive potential. Stimulation of the depressor nerve thus does not induce IPSPs in the ganglion; consequently, the inhibition of synaptic activity observed under these circumstances is located in the CNS and not in the ganglion.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 6, No. 5, pp. 519–524, September–October, 1974.     

Role of N‐ and L‐type calcium channels in depolarization‐induced activation of tyrosine hydroxylase and release of norepinephrine by sympathetic cell bodies and nerve terminals

Multiple types of voltage‐activated calcium (Ca²⁺) channels are present in all nerve cells examined so far; however, the underlying functional consequences of their presence is often unclear. We have examined the contribution of Ca²⁺ influx through N‐ and L‐ type voltage‐activated Ca²⁺ channels in sympathetic neurons to the depolarization‐induced activation of tyrosine hydroxylase (TH), the rate‐limiting enzyme in norepinephrine (NE) synthesis, and the depolarization‐induced release of NE. Superior cervical ganglia (SCG) were decentralized 4 days prior to their use to eliminate the possibility of indirect effects of depolarization via preganglionic nerve terminals. The presence of both ω‐conotoxin GVIA (1 μM), a specific blocker of N‐type channels, and nimodipine (1 μM), a specific blocker of L‐type Ca²⁺ channels, was necessary to inhibit completely the stimulation of TH activity by 55 mM K⁺, indicating that Ca²⁺ influx through both types of channels contributes to enzyme activation. In contrast, K⁺ stimulation of TH activity in nerve fibers and terminals in the iris could be inhibited completely by ω‐conotoxin GVIA alone and was unaffected by nimodipine as previously shown. K⁺ stimulation of NE release from both ganglia and irises was also blocked completely when ω‐conotoxin GVIA was included in the medium, while nimodipine had no significant effect in either tissue. These results indicate that particular cellular processes in specific areas of a neuron are differentially dependent on Ca²⁺ influx through N‐ and L‐type Ca²⁺ channels. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 137–148, 1999     

Alpha-adrenergic receptor modulation of the intrathoracic efferent sympathetic nervous system regulating the canine heart

The augmentation of ventricular inotropism induced by electrical stimulation of acutely decentralized efferent sympathetic preganglionic axons was reduced, but still present, following administration of hexamethonium (10 mg/kg i.v.). While hexamethonium continued to be administered, the cardiac augmentations so induced were enhanced significantly following administration of the alpha-adrenergic receptor blocking agent, phentolamine myselate (1 mg/kg i.v.). Stimulation of the sympathetic efferent postganglionic axons in cardiopulmonary nerves induced cardiac augmentations that were unchanged following administration of these agents singly or together. The cardiac augmentations induced by stimulation of efferent preganglionic sympathetic axons were unchanged when phentolamine was administered alone. The augmentations of cardiac inotropism induced by efferent postganglionic sympathetic axonal stimulation were decreased following local administration of the beta-adrenergic antagonist timolol into the ipsilateral stellate and middle cervical ganglia. Thereafter, these augmentations were unchanged following the subsequent intravenous administration of phentolamine. It is concluded that the activation of cardiac neurons in the stellate and middle cervical ganglia by stimulation of efferent preganglionic sympathetic axons can be modified by alpha-adrenergic receptors and that these effects are dependent upon beta-adrenergic receptors, not nicotinic ones, in intrathoracic ganglia.     

A study of pre- and postganglionic fibres in the intestinal nerve (Remak's nerve) of the chicken

Summary The mean peak CV's of two electrophysiologically defined groups of fibres in the intestinal nerve of the chicken have been determined.One group of fibres is constituted by the processes of enteric cholinergic neurones which project along the side branches of the intestinal nerve and synapse within the nerve trunk. These preganglionic fibres have a mean peak CV (at 40 °C) of 0.31 m·s^–1.The other group is made up of fibres of postganglionic neurones which project orally along the nerve trunk. The results suggest that some postganglionic neurones project only as far as the next ganglion whilst others project beyond the next two ganglia for distances greater than 5 mm. The postganglionic fibres have a mean peak CV (at 40 °C) of 0.71 m·s^–1.These figures demonstrate that both pre- and postganglionic fibres are unmyelinated. The temperature coefficient (Q₁₀) for the CV of unmyelinated fibres in the intestinal nerve was 1.57.Abbreviations CAP compound action potential - CV conduction velocity - Q ₁₀ temperature coefficient     

Membrane ATPase Activity of Barley Roots and Potassium Uptake by Isolated Stele and Cortex

Uptake of potassium ions by isolated stelar tissues of barley from 0.5 and 10 mM K⁺ was respectively 13 and 3.6% of that of the cortical tissues. 0.1 mM H₂PO₄, LO mM ATP and 10 mM Ca(NO₃)₂ did not increase the potassium uptake of either stele or cortex during 5 h of uptake period. A time-course incubation for histological demonstration of the ATPase activity of the plasmalemma and tonoplast of the matured sections of the roots demonstrated a greater activity for the cortical than the stelar tissue. In the stelar parenchyma cells, the plasma lemma showed a higher activity than the tonoplast. These results, which support the “leakiness hypothesis” of the stele, are discussed in relation to the proposed mechanisms of radial ion transport in roots.     

Presynaptic augmentation induced by NaF in sympathetic ganglion of bullfrog

Effects of NaF on the synaptic transmission of bullfrog sympathetic ganglia were studied by extra- and intracellular recordings. The results obtained were as follows: 1) The amplitude of the orthodromic compound action potential (CAP) evoked by preganglionic nerve stimulation was remarkably augmented with 10 microM NaF, whereas that of the antidromic CAPs remained unchanged with the same dose of NaF. The low amplitude of the orthodromic CAP which was diminished by a low-Ca2(+)-ringer's solution reversed with an additional administration of NaF. The amplitudes of the orthodromic CAPs were enhanced by phosphodiesterase inhibitors such as isobutylmethylxanthine, theophylline, and physostigmine. In addition, augmentation of the orthodromic CAPs was induced by an adenylate cyclase activator (forskolin) and d.b-cAMP; however, its augmented responses were not affected by an additional administration of NaF. 2) In the intracellular recording, NaF showed no effect on the resting membrane potential and depolarizing response induced by acetylcholine. However, the EPSP appearing in the phase of afterhyperpolarization of the orthodromic action potential was significantly increased by NaF, whereas no effect was found on the antidromic action potential. In order to evaluate these findings, effects of NaF on the decreased low-Ca2(+)-action potential were observed. After application of NaF, the low-Ca2(+)-orthodromic EPSPs were reversed, and when the height of the EPSP was raised to the critical firing level, a spike potential was driven in the cell. These facts suggest that the site of NaF action seems to exist in the presynaptic rather than postsynaptic process. Furthermore, it suggests that NaF probably acts on Gs-protein which activates adenylate cyclase at the presynaptic membrane. This resulted in a great increase in intracellular cAMP at the synaptic terminal and it triggered the Ca2(+)-increase. As an inevitable consequence, release of transmitter from the nerve terminals of the frog sympathetic ganglion was finally facilitated. These factors supposedly resulted in augmentation of the amplitude of the orthodromic CAP.     

ACETYLTRIETHYLCHOLINE: A CHOLINERGIC FALSE TRANSMITTER IN CAT SUPERIOR CERVICAL GANGLION AND RAT CEREBRAL CORTEX

The accumulation and metabolism of [¹⁴C]triethylcholine by cat superior cervical ganglia [rested or stimulated (20 Hz)] and by rat cerebral cortex minces was measured. In ganglia, preganglionic nerve stimulation increased the accumulation (2.4 fold) and the acetylation (5.7 fold) of triethylcholine; however the depletion of the ganglion's acetylcholine content was 9.5 times greater than the amount of acetyltriethylcholine synthesized. In the presence of eserine, neither stimulated nor rested ganglia synthesized any extra (surplus) acetyltriethylcholine. It is concluded that the rate-limiting step in acetyltriethylcholine synthesis is the acetylation of triethylcholine by choline acetyltransferase. Subsequent preganglionic nerve stimulation of ganglia, which had been stimulated during the exposure to [¹⁴C]-triethylcholine, caused the increased release of only acetyltriethylcholine; the release was frequency-dependent, required the presence of Ca²⁺, and was blocked by increasing the ratio of Mg²⁺/Ca²⁺ in the perfusion fluid. All of the acetyltriethylcholine which had been accumulated was available for release. Rat cerebral cortex also accumulated triethylcholine and acetylated about 3% of the accumulated choline analogue. Subsequent stimulation by high K⁺ (46 mM)-atropine (3 μM) caused the increased release of acetyltriethylcholine from the cortex and this release required the presence of Ca²⁺. Triethylcholine can therefore form a cholinergic false transmitter in the cat superior cervical ganglion and the rat cerebral cortex.     

Calcium-dependent increase in spike duration during repetitive firing of Aplysia axon in the presence of TEA

Repetitive stimulation was studied in the axon of the giant neuron, R2, of Aplysia in the presence of TEA. In 25 or 50 mM extracellular TEA, a plateau develops on the axon spike during repetitive stimulation at frequencies greater than 3/sec. The plateau in extracellular TEA is inhibited by 30 mM CoCl₂ or 1 mM CdCl₂, and is enhanced by raising the Ca concentration. Intracellular TEA induces a plateau on the axon spike at frequencies less than 1/30sec. This plateau increases in duration with repetitive stimulation at higher frequencies and is inhibited by 30 mM CoCl₂ or 1 mM CdCl₂. The increase in spike duration during repetitive firing in the presence of TEA is indicative of an increased entry of Ca during the spike train.     

Intracellular Concentrations of Major Ions in Rat Myelinated Axons and Glia: Calculations Based on Electron Probe X-Ray Microanalyses

Abstract: Electron probe x-ray microanalysis (EPMA) was used to measure water content (percent water) and dry weight elemental concentrations (in millimoles per kilogram) of Na, K, Cl, and Ca in axoplasm and mitochondria of rat optic and tibial nerve myelinated axons. Myelin and cytoplasm of glial cells were also analyzed. Each anatomical compartment exhibited characteristic water contents and distributions of dry weight elements, which were used to calculate respective ionized concentrations. Free axoplasmic [K⁺] ranged from ≈155 mM in large PNS and CNS axons to ≈120–130 mM in smaller fibers. Free [Na⁺] was ≈15–17 mM in larger fibers compared with 20–25 mM in smaller axons, whereas free [Cl^?] was found to be 30–55 mM in all axons. Because intracellular Ca is largely bound, ionized concentrations were not estimated. However, calculations of total (free plus bound) aqueous concentrations of this element showed that axoplasm of large CNS and PNS axons contained ≈0.7 mM Ca, whereas small fibers contained 0.1–0.2 mM. Calculated ionic equilibrium potentials were as follows (in mV): in large CNS and PNS axons, E_K = ?105, E_Na = 60, and E_Cl = ?28; in Schwann cells, E_K = ?107, E_Na = 33, and E_Cl = ?33; and in CNS glia, E_K = ?99, E_Na = 36, and E_Cl = ?44. Calculated resting membrane potentials were as follows (in mV, including the contribution of the Na⁺,K⁺-ATPase): large axons, about ?80; small axons, about ?72 to ?78; and CNS glia, ?91. E_Cl is more positive than resting membrane potential in PNS and CNS axons and glia, indicating active accumulation. Direct EPMA measurement of elemental concentrations and subsequent calculation of ionized fractions in axons and glia offer fundamental neurophysiological information that has been previously unattainable.     

Recurrent inhibition of sympathetic preganglionic neurons of the lateral horns of the spinal cord

Experiments on anesthetized and immobilized cats showed that repeated antidromic discharges can be evoked in 32.5% of sympathetic preganglionic neurons of the lateral horns in segments T3, T8–9, and L2 of the spinal cord, with intervals of 16 msec or more between them, which is much greater than the refractory period of these neurons. This feature was shown not to be connected with the properties of axons of that group of neurons and, in particular, with their after-subnormality. After orthodromic discharges in neurons of this group, for a much longer period of time than could be accounted for by possible collision, no antidromic discharges likewise were evoked. As a result of antidromic activation of some of these neurons in one segment, definite inhibition of the orthodromic response of other neurons of the same segment appeared, etiher by a reflex mechanism or through stimulation of descending pathways. The results point definitely to the existence of a mechanism of recurrent inhibition in some sympathetic preganglionic neurons of the lateral horns.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 382–389, July–August, 1977.     

Quinine and caffeine effects on 45Ca movements in frog sartorius muscle

1 mM caffeine, which produces only twitch potentiation and not contracture in frog sartorius muscle, increases both the uptake and release of ⁴⁵Ca in this muscle by about 50 %, thus acting like higher, contracture-producing concentrations but less intensely. Quinine increases the rate of release of ⁴⁵Ca from frog sartorius but not from the Achilles tendon. The thresholds for the quinine effect on ⁴⁵Ca release and contracture tension are about 0.1 and 0.5 mM, respectively, at pH 7.1. Quinine (2 mM) also doubles the uptake of ⁴⁵Ca by normally polarized muscle. However, there are variable effects of quinine upon ⁴⁵Ca uptake in potassium-depolarized muscle. Quinine (2 mM), increases the Ca, Na, and water content of muscle while decreasing the K content. Both caffeine (1 mM) and quinine (2 mM) act to release ⁴⁵Ca from muscles that have been washed in Ringer''s solution from which Ca was omitted and to which EDTA (5 mM) was added. These results, correlated with those of others, indicate that a basic effect of caffeine and quinine on muscle is to directly release activator Ca²⁺ from the sarcoplasmic reticulum in proportion to the drug concentration. The drugs may also enhance the depolarization-induced Ca release caused by extra K⁺ or an action potential. In respect to the myoplasmic Ca²⁺ released by direct action of the drugs, a relatively high concentration is required to activate even only threshold contracture, but a much lower concentration, added to that released during excitation-contraction coupling, is associated with the condition causing considerable twitch potentiation.     

Depletions in the cervical and thoracolumbar sympathetic system following removal of neural crest from the embryo of Chelydra serpentina

Neural crest and dorsal neural tube of cervical and thoracolumbar levels were removed from embryos of Chelydra serpentina at stages ranging from 8 to 18 somites. Extirpation extended from the levels of the last four somites posteriorly around the neurenteric canal. Deficiencies in sensory and sympathetic ganglia occurred. Motor roots of the associated spinal nerves differentiated. In the absence of postganglionic neurons, the preganglionic fibers form a neuron-free plexus in the thoracolumbar region. Some observations in the cervical region indicate that the postganglionic neurons depend on preganglionic fibers for their differentiation. The cortex of the adrenal gland formed without related medulla in appropriate experiments. The normal morphology of the sympathetic trunks is illustrated. Superficial and deep cervical sympathetic trunks are described. The latter ascends the neck in a paravertebral position. Along its course are segmental ganglia and rami communicantes; it terminates by joining the medial branch of the superficial sympathetic trunk rostral to the ninth cranial nerve.     

THE UPTAKE, METABOLISM AND RELEASE OF HOMOCHOLINE: STUDIES WITH RAT BRAIN SYNAPTOSOMES AND CAT SUPERIOR CERVICAL GANGLION

The accumulation of [³H]homocholine (3-trimethylamino-propan-1-01) by isolated synaptosomes prepared from rat brain was resolved kinetically into a high (K_T= 3.0 μM) and a low (K_T= 14.5 μM) affinity system. Although homocholine was not acetylated by solubilized choline acetyltransferase, 64% of the homocholine accumulated by intact synaptosomes via the high affinity uptake process was acetylated. Homocholine was also acetylated in the superior cervical ganglion of the cat, and the amount of acetylhomocholine formed was increased (12-fold) by preganglionic nerve stimulation. In ganglia, acetylhomocholine was available for release by preganglionic nerve impulses, and its release was Ca²⁺-dependent, It is concluded that homocholine can form a cholinergic false transmitter, and that the substrate specificity of choline acetyltransferase in vitro might be different from that in situ.     

A Histochemical Study of the Gas Gland Innervation in the Atlantic God,Gadus morhua

A histochemical study was made of the distribution of catecholamines and cholinesterases in two autonomic ganglia closely associated with the swimbladder of the Atlantic cod, Gadus morhua. The “swimbladder nerve ganglion” comprised large (40 μm) neurones, the majority of which are positive for both catecholamines and acetylcholinesterase. It is argued that these neurones are mainly adrenergic postganglionic elements of sympathetic pathways which pass through the vago-sympathetic trunk. The “gas gland ganglion” comprised small (20 μm) neurones, positive for acetylcholinesterase but showing no catecholamine reaction. It is argued that these neurones are cholinergic postganglionic elements of the parasympathetic vagal innervation of gas gland cells.