Buccal Muscles Research Articles

Serotonin and the Small Cardioactive Peptides Differentially Modulate Two Motor Neurons That Innervate the Same Muscle Fibers inAplysia

The anterior portion of intrinsic buccal muscle 3 (I3a) is innervated by two motor neurons, B3 and B38, which appear to use glutamate as their fast excitatory transmitter. B3 and B38 express the neuropeptides FMRFamide and the small cardioactive peptides (SCPs), respectively. We have shown previously that stimulation of B38 causes release of the SCPs from terminals in the muscle. The I3a muscle also receives input from neurons that use 5HT as a modulatory transmitter. The SCPs and 5HT potently facilitated B38-evoked excitatory junction potentials (EJPs) but had only a small effect on B3-evoked EJPs; however, both the SCPs and 5HT strongly potentiated contractions evoked by both B3 and B38, indicating that the two substances must also act on excitation-contraction coupling. The selective facilitation of B38-evoked EJPs, however, did manifest itself in other parameters. Decreases in the firing frequencies and burst durations that were threshold to evoke contractions and decreases in the latency between the onset of a burst and the onset of the evoked contraction were all much larger for B38 than for B3. Indeed, B38 bursts recorded during feeding-like behavior would be subthreshold for evoking contractions in the absence of this modulation. All of the effects of the SCPs reversed during washout, whereas those of 5HT were persistent, lasting many hours after washout. Thus, the SCPs and 5HT dramatically change the behavioral output of these motor neurons, increasing the amplitude of contractions evoked by both B3 and B38, and shifting the temporal relationship between bursts in B38 and its evoked contractions.

Maximal Expiratory Pressures in Spinal Cord Injury Using Two Mouthpieces

A technique for assessing expiratory muscle strength is the measurement of maximal expiratory pressure (PEmax). Previous studies have shown that a tube-style mouthpiece yields greater PEmax values than a flange-style mouthpiece because the latter technique is limited by the strength of the buccal muscles. In individuals with weak muscles of exhalation, this limitation may not apply because the strength of their buccal muscles may exceed that of the respiratory muscles. A tube-style mouthpiece and flange-style mouthpiece were used to measure PEmax. The order of the mouthpiece used in testing was alternated between subjects and the greatest values obtained after three efforts were compared. Department of Veterans Affairs Medical Center. Fifty subjects with chronic spinal cord injury without acute medical illnesses recruited from veterans and the community. The mean difference between PEmax(tube) and PEmax(flange) was 20.7+/-26.4 cm H2O (p = 0.0001). Differences were negligible in those with the weakest muscles of exhalation but were substantial even in some quadriplegic subjects. Even in individuals with neuromuscular disorders, errors in assessment of expiratory strength occur when a flange-style mouthpiece is used, and we recommend that this technique be abandoned in the measurement of PEmax.

NADPH-diaphorase localization in the CNS and peripheral tissues of the predatory sea-slugPleurobranchaea californica

The distribution of putative nitric oxide synthase (NOS)-containing cells in the opisthobranch mollusc Pleurobranchaea californica was studied histochemically via NADPH-diaphorase (NADPH-d) reduction of Nitro Blue Tetrazolium (NTB). Whole mounts and cryostat sections were prepared from the central nervous system and peripheral organs, including the buccal muscles, esophagus, salivary glands, foot, mantle, and gills. NADPH-d-positive neurons were localized predominantly to the buccal and pedal ganglia as well as to distinct areas of the cerebropleural and visceral ganglia. A variety of identified neurons were positive for NADPH-diaphorase in various central ganglia, including the metacerebral cells of the cerebropleural ganglion, putative locomotor neurons of the pedal ganglia, and buccal motoneurons. Specific staining was observed only in somata of central neurons, whereas neuropil areas remained unstained. However, NADPH-d-reactive axons were dense in buccal ganglion nerves, whereas peripheral nerves and connectives of other ganglia had few or no NADPH-d positive terminals. In the periphery, NADPH-d activity was detected only in a few neurons of the rhinophore and tentacle ganglia. NADPH-d staining was marked in the salivary glands and gills, but there was no or very little staining in the esophagus, buccal mass, and foot. Histochemical stain production required the presence of both beta-NADPH and NBT; alpha-NADPH could not substitute for beta-NADPH. The inhibitor of NOS, 2,6-dichlorophenol-indophenol, at 10(-3) M, totally abolished NADPH-d-positive staining. The apparent high activity of central NADPH-d contrasts with much lower activity in the ganglia of the related gastropod Tritonia. These data suggest a role for nitric oxide as a signal molecule in the central nervous system of Pleurobranchaea.

Activity patterns of the B31/B32 pattern initiators innervating the I2 muscle of the buccal mass during normal feeding movements in Aplysia californica

1. B31 and B32 are pattern-initiator neurons in the buccal ganglia of Aplysia. Along with the B61/B62 neurons, B31/B32 are also motor neurons that innervate the 12 buccal muscle via the I2 nerve. This research was aimed at determining the physiological functions of the B31/B32 and B61/B62 neurons, and of the I2 muscle. 2. Stimulating the I2 muscle in the radula rest position produces radula protraction. In addition, in behaving animals lesioning either the muscle or the I2 nerve greatly reduces radula protraction. 3. During buccal motor programs in reduced preparations, B31/B32 and B61/62 fire preceding activity in neuron B4, whose firing indicates the onset of radula retraction. In addition, during both ingestion-like and rejection-like patterns the activity in the I2 nerve is correlated with protraction. 4. B31/B32 fire at frequencies of 15-25 Hz. Neither B31/B32 nor B61/B62 elicit facilitating end-junction potentials (EJPs) and electromyograms (EMGs) in the I2 muscle. EMGs from B31/B32 are smaller than those from B61/B62. B31/B32 and B61/B62 innervate all areas of the muscle approximately uniformly. 5. In behaving animals, EMGs consistent with B31/B32 activity are seen in the I2 muscle during the protraction phase of biting, swallowing, and rejection movements. In addition, the I2 muscle receives inputs that cannot be attributed to either the B31/B32 or B61/B62 neurons, either because the potentials are too large, firing frequencies are too low, or a prominent facilitation is seen. Such potentials are associated with lip movements, and also with radula retraction. 6. EMGs were recorded from the I2 muscle during feeding behavior after a lesion of the I2 nerve. Animals that had severe deficits in protraction showed no activity consistent with B31/B32 or B61/B62, but did show activity during retraction. 7. Our data indicate that the I2 muscle and the B31/B32 motor neurons are essential constituents contributing to protraction movements. Activity in these neurons is associated with radula protraction, which occurs as a component of a number of different feeding movements. The I2 muscle may also contribute to retraction, via activation by other motor neurons.

Aplysia limacina myoglobin cDNA cloning: an alternative mechanism of oxygen stabilization as studied by active-site mutagenesis.

The isolation and cloning of the cDNA coding for myoglobin (Mb) from the mollusc Aplysia limacina is reported here. Five amino acid differences from the previously published protein sequence have been found in positions 22, 26, 27, 77 and 80 by back transplanting the cDNA; some of these may be relevant for overall structure stabilization in this Mb. High-level expression of the holoprotein in Escherichia coli has been achieved in the presence of the haem precursor delta-aminolevulinic acid, underlying the importance of tuning haem and apoprotein biosynthesis to achieve high-level expression of haemproteins in bacteria. The recombinant protein is identical to the protein purified from the mollusc buccal muscle. Native A. limacina Mb has an oxygen dissociation rate constant of 70 s(-1) [as compared with the value of 15 s(-1) for sperm whale Mb, which displays His(E7) and Thr(E10)] (amino acid positions are referred to within the eight helices A-H of the globin fold). In order to understand the mechanism of oxygen stabilization in A. limacina Mb, we have prepared and investigated three active-site mutants: two single mutants in which Val(E7) and Arg(E10) have been replaced by His and Thr, respectively, and a double mutant carrying both mutations. When Arg(E10) is substituted with Thr, the oxygen dissociation rate constant is increased from 70 s(-1) to more than 700 s(-1), in complete agreement with the previously proposed role of the former residue in ligand stabilization. In the His(E7)-containing single and double mutants, both displaying high oxygen dissociation rates, the stabilization of bound oxygen by the distal His is insufficient to slow down the ligand dissociation rate constant to the value of sperm whale Mb. These results essentially prove the hypothesis that in A. limacina Mb a mechanism of oxygen stabilization involving Arg(E10), and thus different from that mediated by His(E7), has evolved.

Mechanism of lung ventilation in the caecilian Dermophis mexicanus.

The pattern of lung ventilation in the terrestrial caecilian Dermophis mexicanus was investigated by recording pressure changes of buccal and pleuroperitoneal cavities and activity of the buccal musculature. This species uses a fairly typical sarcopterygian buccal pumping system to inflate its single lung. What distinguishes it from other amphibians is the large number of buccal pumping cycles that occur in each ventilatory cycle. Up to 29 buccal cycles were observed to occur in a single respiratory cycle, with a mean of 16.1 ± 3.0 buccal cycles. This long series of buccal cycles avoids the sarcopterygian pattern of rebreathing expired air because only the first buccal cycle pumps expired air back into the lung. The series of buccal cycles also generates pleuroperitoneal pressures that are three to ten times greater than those observed in other amphibians. We suggest that these high pleuroperitoneal pressures are necessary for the maintenance of body form and locomotor function in terrestrial caecilians. © 1995 Wiley-Liss, Inc.

Modulation of the buccal muscle contraction by identified serotonergic and peptidergic neurons in the snail Achatina fulica

Serotonergic and peptidergic modulation of buccal muscle contraction at an identified neuromuscular synapse in the African giant snail Achatina fulica was examined. A pair of excitatory motoneurons of the radula protractor was identified in the buccal ganglia and these were named B10 neurons. Pharmacological experiments revealed the B10s to be cholinergic. The serotonergic cerebral neuron v-CDN enhanced B10-evoked contraction of the radula protractor, and it is suggested that this effect is mediated postsynaptically by serotonin released from the v-CDN terminals. Immunohistochemical analyses revealed that the B10 motoneurons contained an Achatina cardioexcitatory peptide-1 (ACEP-1)-like substance in their cell body, axon and terminals in the radula protractor. From electron microscopic observation, the ACEP-1-like immunoreactive substance was found to be localized in dense-cored vesicles but not in clear vesicles in the nerve terminals. ACEP-1 applied to the radula protractor markedly enhanced B10-evoked contraction of the muscle by increasing the amplitude of excitatory junction potentials (EJPs). The increase of EJP amplitude in the presence of the peptide was probably due to the increased release of acetylcholine from the terminals of B10. It is suggested that the cholinergic motoneuron B10 uses ACEP-1 as an excitatory cotransmitter.

Neuromuscular regeneration by buccal motoneuron B15 after peripheral nerve crush in Aplysia californica.

1. We studied regeneration of neuromuscular connections by identified buccal motoneuron B15 after axotomy produced by crushing nerve 4; the intact contralateral nerve 4 served as control. Electrophysiological recordings, intracellular dye injections, and light and electron microscopy were used to characterize the nature and time course of neuromuscular reinnervation as well as the fate of the isolated distal stump of the motor axon. 2. Axonal outgrowth or sprouting in the form of numerous "regenerites" occurred from the proximal stump of the transected B15 axon, and these regenerites projected through the crush site along the length of the nerve to innervate target muscles at the periphery. 3. Reinnervation of one of the target muscles, the accessory radula closer (I5), was first detected 3 wk after nerve crush. Neuromuscular excitatory postsynaptic potentials measured in individual I5 muscle fibers were initially small and approached control amplitudes by 8 wk postlesion. Newly regenerated neuromuscular synapses displayed facilitation and depression to repeated B15 stimulation with properties similar to those of control synapses, even at early times postlesion. 4. Reinnervation of other buccal muscles by B15, such as I4, appeared slightly delayed relative to that observed for I5. No evidence of abnormal or enlarged fields of innervation were observed, and as in control preparations, regenerated neuromuscular connections were strictly limited to muscles ipsilateral to the B15 cell body. 5. Physiological evidence suggested that the distal axon stumps of B15, although isolated from their cell bodies, survive for several weeks after axotomy. In addition, several large axon profiles indicative of motor axons were seen in cross-sections of nerve 4 taken close to the muscle and distal to the crush site, indicating survival of distal axon stumps. 6. When B15 was selectively stimulated, the newly formed regenerites failed to fire the distal axon stump of B15, demonstrating that the regenerites do not reinnervate the distal stump. 7. Degeneration of axons in nerve 4 distal to the crush site was observed in cross-sections of the nerve at 8 wk postlesion; using ultrathin sections we found cellular debris in individual axon profiles as well as large acellular masses within nerve 4, the latter likely representing the concretion of many axons. Additional evidence for such degenerative changes appeared in the form of autofluorescing spherical bodies or "spheroids" both in individual axons and the nerve distal to the crush site.(ABSTRACT TRUNCATED AT 400 WORDS)

Ionic mechanisms mediating the acetylcholine-elicited contraction in Aplysia buccal muscle

Ion channel mechanisms mediating acetylcholine (ACh)-elicited contractions in Aplysia buccal muscles were investigated using conventional force and membrane potential recording techniques and whole-cell voltage clamping of dissociated buccal muscle fibers. Previous work on buccal muscles of Aplysia showed that acetylcholine (ACh) depolarizes muscle fibers to, at most, −30 mV and that contraction is dependent upon extracellular calcium. In intact muscle, removal of either calcium or sodium from the extracellular medium reduced ACh-elicited depolarization. Absence of each ion reduced the depolarization approximately 50% at low [ACh], but at high [ACh], absence of sodium had a greater effect, while absence of calcium had a proportionally smaller effect on depolarization. Nifedipine (3 μM) reduced contraction by 50% with little accompanying change in depolarization. In whole cell voltage-clamping of isolated muscle fibers, ACh elicited an inward current at resting potential. The reversal potential for ACh-elicited current was −24±6mV. The current- voltage curve was rectified, with a bend in the inward direction near −35 mV. In zero calcium medium, ACh-elicited current averaged 54% of control, and in zero sodium medium, 42% of control. Nifedipine reduced ACh-elicited current by less than 20%. Amiloride, an inhibitor of Aplysia buccal muscle contraction, reduced ACh-elicited current by 30–70%. A model based on the above results is that ACh depolarizes muscle fibers by opening channels with a reversal potential of about —30 mV that are permeable to calcium, sodium, and at least one other ion. Depolarization activates voltage-dependent calcium channels, enabling activator calcium to enter the fibers through both ACh-operated and voltage-dependent channels.

Distribution and anatomy of GABA-like immunoreactive neurons in the central and peripheral nervous system of the snail Helix pomatia.

Gamma-aminobutyric acid (GABA)-like immunoreactive neurons were studied in the central and peripheral nervous system of Helix pomatia by applying immunocytochemistry on whole-mount preparations and serial paraffin sections. GABA-immunoreactive cell bodies were found in the buccal, cerebral and pedal ganglia, but only GABA-immunoreactive fibers were found in the viscero-parietal-pleural ganglion complex. The majority of GABA-immunoreactive cell bodies were located in the pedal ganglia but a few could be found in the buccal ganglia. Varicose GABA-ir fibers could be seen in the neuropil areas and in distinct areas of the cell body layer of the ganglia. The majority of GABA-ir axonal processes run into the connectives and commissures of the ganglia, indicating an important central integrative role of GABA-immunoreactive neurons. GABA may also have a peripheral role, since GABA-immunoreactive fibers could be demonstrated in peripheral nerves and the lips. Glutamate injection did not change the number or distribution of GABA-immunoreactive neurons, but induced GABA immunoreactivity in elements of the connective tissue ensheathing the muscle cells and fibers of the buccal musculature. This shows that GABA may be present in different non-neural tissues as a product of general metabolic pathways.

Nitric oxide synthase-immunoreactive cells in the CNS and periphery of Lymnaea.

The presence and distribution of nitric oxide synthase (NOS) in the CNS and peripheral organs (buccal muscles, oesophagus, salivary glands, foot, mantle and pneumostome) of the pulmonate mollusc, Lymnaea stagnalis were studied using an antiserum developed against rat cerebellar NOS. NOS-immunopositive neurones in Lymnaea were localized predominantly in the buccal ganglia as well as in distinct areas of the cerebral and suboesophageal ganglia. NOS-immunoreactive terminals were also found on the somata of some central neurones. In the periphery, NOS-immunostaining was detected only in a few neurones in the pneumostome area and in the osphradial ganglion. In addition, approximately 100 NOS-immunopositive cells have been found in the salivary glands. Our data supports other recent reports indicating that NO may be a signal molecule in the CNS of molluscs.

Some aspects of temporal dynamics of feeding behaviour inAplysia fasciata

Gastropods, particularly the opisthobranch Aplysia, represent an optimal biological model for system analysis in feeding behaviour. In the present study, behaviour was monitored in seminatural conditions and for a time of sufficient length to investigate the organization of feeding activity in the medium and long term. The experiments used Aplysia fasciata collected from the Tyrrhenian coasts. Electromyographic recordings were obtained by an electrode chronically implanted in a buccal muscle involved in feeding behaviour. The electromyograms, transformed by a circuit calculating the root mean square, were logged by a personal computer. Data analysis, based on the study of the distributions of the intervals between elementary behavioural acts, showed that elementary feeding cycles are not continuous and randomly distributed during the day, but clustered in ‘sequences’. These frequently can be gathered in other defined temporal partitions or ‘groups’ that are finally lumped in ‘meals’. Each interval distrib...

Antagonists of cholinergic and serotonergic responses of Aplysia buccal muscle

Cholinergic and serotonergic receptors of Aplysia californica buccal muscles were characterized pharmacologically by determining compounds that effectively inhibited contractile responses to acetylcholine (ACh) and modulatory effects of serotonin (5-HT), respectively. pA50 for ACh to elicit contraction averaged 4.7 ± 0.1 (mean ± SE, equivalent to 2 × 10 −5 M). Both hexamethonium bromide and atropine inhibited ACh-elicited contractions, but neither inhibited the response completely, nor were the two together able to antagonize the response completely. Curare caused inhibition only at low ACh doses, and muscarinic antagonists pirenzapine and 4-diphenylacetoxy- N-methylpiperidine methiodide caused partial inhibition. The most effective blocker of ACh-elicited contractions was the nicotinic antagonist mecamylamine. 10 −4M mecamylamine completely blocked the cholinergic response. ACh contractions were inhibited 90% within 10 min and took >40 min to recover from mecamylamine. Specificity was indicated by the lack of effect of mecamylamine on potassium-elicited contraction. NAN-190 blocked the potentiating effect of 5-HT without having inhibitory or potentiating effects by itself on ACh-elicited contractions. NAN-190 blocked the potentiating effect of 8-OH-DPAT. Cholinergic receptors on Aplysia buccal muscles are most effectively inhibited by mecamylamine and may have mixed nicotinic/muscarinic character. Serotonergic receptors have pharmacological similarities to vertebrate 5-HT 1A receptors and may be closely related to the gastropod 5-HTlym receptor.

Acetylcholine-activated chloride channels produce an inhibitory junction potential in buccal muscle cells of Aplysia

Action potentials in Aplysia MA1 neurons are known to produce inhibitory junction potentials (IJPS) in muscle cells in a specific portion (mm block) of the buccal musculature. These IJPS are reversibly blocked by curare (d-TC), suggesting that the transmitter is acetylcholine (ACh) and the receptor is a cholinergic ACh receptor. In the present study, we identified the ACh receptor channel in dissociated buccal muscle fibres from the mm portion of the I$^{3}$ muscle by using the patch-clamp technique. Under the whole-cell current clamp, iontophoretically applied ACh induced a transient hyperpolarization when the cells were dialysed with isotonic 150 mM K D-aspartate (KAsp) or 150 mM Cs D-aspartate (CsAsp) solution. In contrast, when cells were dialysed with 150 mM KCl solution, ACh induced a transient depolarization instead of hyperpolarization. ACh-induced membrane currents were recorded under the whole-cell voltage clamp, and the reversal potential was estimated from the current-voltage relations. The reversal potential was estimated to be -52.0$\pm $2.0 mV (mean$\pm $s.d.; n = 3) when dialysed with KAsp solution, and -39.5 $\pm $ 1.5 mV (mean$\pm $s.d.; n = 3) when dialysed with 150 mM CsAsp solution. When 150 mM CsCl was used as the internal solution, the reversal potential was -0.4$\pm $s.d; n = 3), which is close to the equilibrium potential for Cl$^{-}$ (-4 mV). All those responses to ACh were reversibly blocked by 10$^{-4}$ M d-TC. These results suggest that the ACh receptor of the muscle fibres of the I$^{3}$ muscle in the mm block is associated with a Cl$^{-}$ channel, which generates IJPS in the Aplysia buccal muscle fibres in response to action potentials in the MA1 neurons.

Modulation of neuromuscular transmission by conventional and peptide transmitters released from excitatory and inhibitory motor neurons in Aplysia

The anterior portion of intrinsic buccal muscle (I3a) is innervated by two excitatory motor neurons, B3 and B38, and the newly identified inhibitory motor neuron, B47. We show that B47 is cholinergic while B3 and B38 are not. B3 and B38 have previously been shown to express the neuropeptides FMRFamide and the small cardioactive peptides (SCPs) A and B, respectively. We present evidence here that B47 synthesizes the neuropeptide myomodulin A (Mma). When placed in culture, B3, B38, and B47 continued to synthesize their respective peptides. These peptides were released in a stimulation- and Ca(2+)-dependent manner, suggesting that they are transmitters in these neurons. By using B3-evoked excitatory junction potentials (EJPs) and muscle contractions as assays, we next examined the modulatory effects of superfusion of peptides and stimulation of motor neurons B38 and B47. Superfusing the muscle with low concentrations of the SCPs, FMRFamide, or Mma enhanced B3-evoked EJPs and contractions. Stimulation of B47 simultaneously with B3 reduced the amplitude of B3-evoked contractions. However, when either B47 or B38 was stimulated in extended bursts designed to release their peptide transmitters, subsequent B3-evoked EJPs and contractions were enhanced. We believe that this modulation is due at least in part to the release of peptides from the terminals of B38 and B47. The SCPs potently increase cAMP levels in I3a muscle fibers. Likewise, stimulation of B38 in extended bursts increased cAMP levels in the muscle. This provides independent evidence that the SCPs are released from B38 terminals in the muscle. Therefore, we have described a neuromuscular preparation amenable to the study of both excitatory and inhibitory motor neurons that utilize a variety of conventional and peptide transmitters. Our results suggest that these motor neurons can function in two states. When stimulated in single brief bursts, they primarily release conventional transmitters. When stimulated in a series of prolonged bursts, they release both conventional transmitters and peptide cotransmitters. These dual states are most pronounced in the case of B47, which, depending on the stimulation paradigm, can act selectively to inhibit or enhance the effects of a second motor neuron innervating the same muscle.

Control of intrinsic buccal muscles by motoneurons B11, B15, and B16 in Aplysia californica

To further define the control of intrinsic buccal muscles by identified motoneurons B11, B15, and B16 in Aplysia californica, we made physiological recordings from semi-intact and isolated preparations of the buccal ganglia and buccal mass. B15 and B16 were previously known to innervate muscle 15 (also called the accessory radula closer muscle). We show here that these motoneurons also innervate other buccal muscles ipsilateral to their cell bodies; for example, B15 reliably innervates and can cause contraction in intrinsic muscle I4. Likewise, B11 appears to innervate all of the intrinsic buccal muscles, but elicits contractions only in I4. The form and time course of synaptic plasticity displayed by these motoneurons is common to all the muscles they innervate. No evidence for electrical coupling between fibers of adjacent muscles could be obtained, suggesting that all recorded innervation is direct. Like B15 and B16 (Cohen et al., '78), B11 neuromuscular synapses appear to be cholinergic, since they are reversibly antagonized by hexamethonium and d-tubocurarine (acetylcholine [ACh] receptor antagonists). In addition, direct application of ACh elicits depolarizing responses and contractions in I4 which are also blocked by hexamethonium. Application of glutamate and GABA do not elicit depolarizations or contractions in I4 or I5. We conclude that these motoneurons control radula position through complex synaptic actions on multiple intrinsic buccal muscles, using ACh as their conventional transmitter.

Studies on the Metabolic Fate of Miconazole. (3). The Absorption, Distribution and Metabolism after Application of Miconazole to Oral Mucosa of Rats.

[14C]MCZゲルを雄ラットの口腔内に塗布したときの血漿中濃度，分布および代謝について検討した． 1．血漿中放射能濃度は，塗布後2時間でCmax1.82μg eq./m1を示し，以後，同用量の[14C]MCZを経口投与した後の血漿中濃度推移と同様の推移で低下した． 2．塗布後1時間における拡大オートラジオグラフィーにおいて，上下口唇，口蓋，舌および頬粘膜の各上皮に強い放射能が認められ，また，組織内放射能濃度は舌および頬粘膜上皮が高く，頬筋肉のそれは低値であった． 3．塗布後1および/もしくは6時間において，未変化体が頬筋肉および頬粘膜上皮中の放射能の大部分であり，また，両組織でイミダゾール環の酸化的開環体(M8)，頬筋肉でさらに未同定の代謝物として，Uk3およびUk10がわずかに認められた．

Neuromuscular organization of the buccal system in Aplysia californica

The intrinsic muscles and peripheral nerves in the buccal system of the sea hare Aplysia californica were studied to build a foundation on which to base future investigations of feeding in intact animals. A detailed description of the bilaterally paired intrinsic muscles is given identifying previously unreported muscles. Each of the six buccal nerves (n1-n6) and the cerebrobuccal connective (CBC) have been characterized in several respects. Cell bodies in the buccal ganglion with projections into each of the buccal nerves have been identified via the cobalt backfilling technique. All nerves contain axons of cell bodies in the ipsilateral as well as the contralateral ganglia. For each nerve, there is a consistent pattern in the distribution of cell bodies in the paired ganglia with the number of cell bodies in the contralateral ganglion being less than or equal to the number in the ipsilateral ganglion. Although the total number of backfilled cell bodies varies among the nerves, their size ranges are similar with the majority being small. Nerves 1, 2, 4, 5, and 6 provide motor innervation to the intrinsic buccal muscles in varying degrees with nerve 4 supplying all the intrinsic muscles; nerve 2 supplies only one. The axon composition of each nerve was scrutinized and revealed large numbers of axon profiles, the majority of which were less than 2 microns in diameter. The present study provides a framework for analysis of feeding behavior in Aplysia californica.

Contraction, Serotonin-Elicited Modulation, and Membrane Currents of Dissociated Fibers of Aplysia Buccal Muscle.

Feeding muscles of the buccal mass of Aplysia are innervated by cholinergic and serotonergic neurons. Buccal muscle 15 contracts in response to acetylcholine (ACh). During feeding arousal, ACh-elicited contraction of muscle 15 is potentiated by serotonin (5-HT). This paper demonstrates a dissociated cell preparation of muscle 15 in which cellular mechanisms regulating contraction can be investigated. Dissociated muscle fibers contracted in response to both KCl and ACh. Serotonin (10-6 M) significantly potentiated the shortening caused by both KCl and ACh. Potentiation lasted at least 4 min, similar to potentiation in intact muscles. Four types of currents recorded by patch clamp methods are illustrated. With 540 mM KCl in the patch electrode, stretch-activated channels having a chord conductance of 150 pS are observed in on-cell patches. In whole cell configuration, ACh elicits inward current at a holding potential of -60 mV. With high potassium in the electrode, depolarization elicits an outward current. The voltage-dependent outward current is blocked with cesium in the electrode and 4-aminopyridine and tetraethylammonium outside the cells. The remaining voltage-dependent inward current is calcium dependent. The voltage-dependent inward and outward currents are activated within the range of depolarization produced by ACh and may therefore play roles in regulating contractile responses elicited by ACh.

Peptidergic motoneurons in the buccal ganglia of Aplysia californica Immunocytochemical, morphological, and physiological characterizations

We used physiological recordings, intracellular dye injections and immunocytochemistry to further identify and characterize neurons in the buccal ganglia of Aplysia californica expressing Small Cardioactive Peptide-like immunoreactivity (SCP-LI). Neurons were identified based upon soma size and position, input from premotor cells B4 and B5, axonal projections, muscle innervation patterns, and neuromuscular synaptic properties. SCP-LI was observed in several large ventral neurons including B6, B7, B9, B10, and B11, groups of s1 and s2 cluster cells, at least one cell located at a branch point of buccal nerve n2, and the previously characterized neurons B1, B2 and B15. B6, B7, B9, B10 and B11 are motoneurons to intrinsic muscles of the buccal mass, each displaying a unique innervation pattern and neuromuscular plasticity. Combined, these motoneurons innervate all major intrinsic buccal muscles (I1/I3, I2, I4, I5, I6). Correspondingly, SCP-LI processes were observed on all of these muscles. Innervation of multiple nonhomologous buccal muscles by individual motoneurons having extremely plastic neuromuscular synapses, represents a unique form of neuromuscular organization which is prevalent in this system. Our results show numerous SCPergic buccal motoneurons with widespread ganglionic processes and buccal muscle innervation, and support extensive use of SCPs in the control of feeding musculature.