Thucydides L. Salunga

Identifiable Achatina giant neurones: Their localizations in ganglia, axonal pathways and pharmacological features

1. An African giant snail (Achatina fulica Férussac), originally from East Africa, is now found abundantly in tropical and subtropical regions of Asia, including Okinawa in Japan. This is one of the largest land snail species in the world. The Achatina central nervous system is composed of the buccal, cerebral and suboesophageal ganglia. The 37 giant neurones were identified in these ganglia by the series of studies conducted over about 20 years. The identifications were made by the localization of these neurones in the ganglia, their axonal pathways and their pharmacological features. 2. In the left buccal ganglion, the four giant neurones, d-LBAN, d-LBMB, d-LBCN and d-LBPN, were identified. In the left and right cerebral ganglia, d-LCDN, d-RCDN, v-LCDN and v-RCDN were identified. The suboesophageal ganglia are further composed of the left and right parietal, the visceral, the left and right pleural, and the left and right pedal ganglia. In the right parietal ganglion, PON, TAN, TAN-2, TAN-3, RAPN, d-RPLN, BAPN, LPPN, LBPN, LAPN and v-RPLN were identified. In the visceral ganglion, VIN, FAN, INN, d-VLN, v-VLN, v-VAN, LVMN, RVMN and v-VNAN were identified. In the left parietal ganglion, v-LPSN was identified. In the left and right pedal ganglia, LPeNLN, RPeNLN, d-LPeLN, d-LPeCN, d-RPeAN, d-LPeDN, d-LPeMN and d-LPeEN were identified. 3. Of the small molecule compounds tested, dopamine, 5-hydroxytryptamine, GABA, L-glutamic acid, threo- or erythro-beta-hydroxy-L-glutamic acid were effective on the Achatina giant neurones. We suppose that these compounds act as the neurotransmitters for these neurones. 4. Of the neuroactive peptides, achatin-I(Gly-D-Phe-Ala-Asp). APGW-amide(Ala-Pro-Gly-Trp-NH2) and Achatina cardioexcitatory peptide (ACEP-1)(Ser-Gly-Gln-Ser-Trp-Arg-Pro-Gln-Gly-Arg-Phe-NH2) were proposed as neurotransmitters, because these were effective on the Achatina giant neurones and their presence was demonstrated in the Achatina ganglia. Further, myomodulin (Pro-Met-Ser-Met-Leu-Arg-Leu-NH2), buccalin (Gly-Met-Asp-Ser-Leu-Ala-Phe-Ser-Gly-Gly-Leu-NH2), FMRFamide (Phe-Met-Arg-Phe-NH2). [Ser2]-Mytilus inhibitory peptide ([Ser2]-MIP) (Gly-Ser-Pro-Met-Phe-Val-NH2), catch-relaxing peptide (CARP) (Ala-Met-Pro-Met-Leu-Arg-Leu-NH2), oxytocin (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2) and small cardioactive peptideB (SCPB) (Met-Asn-Tyr-Leu-Ala-Phe-Pro-Arg-Met-NH2) could also be neurotransmitters because these peptides were also effective on the Achatina giant neurones, though their presence in the ganglia of this animal has not yet been demonstrated. 5. Calcium current (ICa) was recorded from Achatina giant neurones in the Na(+)-free solution containing K(+)-channel blockers under voltage clamp. The Ca2+ antagonistic effects of brovincamine, verapamil, eperisone, diltiazem, monatepil, etc., were compared using the ICa of the Achatina neurones. 6. Almost all of the mammalian small molecule neurotransmitters were effective on the Achatina giant neurones, suggesting that these compounds are acting on the neurones of a wide variety of animal species. However, the pharmacological features of the Achatina neurone receptors to these compounds were not fully comparable to those of the mammalian receptors. For example, we proposed that beta-hydroxy-L-glutamic acid (either threo- or erythro-) could be an inhibitory neurotransmitter for an Achatina neurone. 7. In contrast, the Achatina giant neurones appear to have no receptor for the mammalian neuroactive peptides, except for oxytocin and Arg-vasotocin. On the other hand, many neuroactive peptides were isolated from invertebrate nervous tissues, including achatin-I, a neuroexcitatory tetrapeptide having a D-phenylalanine residue.

Dopaminergic inhibition of excitatory inputs onto pyramidal tract neurons in cat motor cortex

The role of dopamine (DA) on motor cortical pyramidal tract neurons (PTNs) was studied in anesthetized cats with in vivo extracellular recordings in response to transcallosal (TC) and ventrolateral (VL) thalamic stimulations. An antidromic PT potential was evoked to recognize PTNs. In most PTNs, iontophoretic application of DA significantly reduced the spike activity exerted by 20 single-pulse stimulations. Both D(1)-like and D(2)-like receptor antagonists blocked (disinhibited) the effect in a similar way regardless of TC and VL stimulations, suggesting colocalization of two receptors. Except for the presence of jittering, the mean latency was usually fixed and short. These findings indicate that ventral midbrain DA imposes an intense suppression in modulating PTNs response to both callosal and thalamocortical excitatory inputs in motor cortex. Such DAergic suppression could play pivotal role to improve motor and sensorimotor signal integration.

Modulation by APGW-amide, an Achatina endogenous inhibitory tetrapeptide, of currents induced by neuroactive compounds on Achatina neurons: peptides.

1. Modulatory effects of APGW-amide (Ala-Pro-Gly-Trp-NH2), proposed as an inhibitory neurotransmitter of Achatina neurons, perfused at 3 x 10(-6) M on the currents induced by neuroactive peptides, ejected by brief pressure, were examined by using Achatina giant neuron types, v-RCDN (ventral-right cerebral distinct neuron) and PON (periodically oscillating neuron), under voltage clamp. 2. Outward current (Iout) caused by FMRFamide (Phe-Met-Arg-Phe-NH2) on v-RCDN, which was probably K+ dependent, was inhibited with membrane conductance (g) increase by APGW-amide. From the dose (pressure duration)-response curves of FMRFamide and a Lineweaver-Burk plot of these data, the inhibition caused by APGW-amide was mainly in an uncompetitive manner. 3. Iout caused by APGW-amide on v-RCDN, which was probably K+ dependent, was inhibited with g increase by APGW-amide. The inhibition caused by APGW-amide was partly in a competitive manner and partly in a noncompetitive manner. 4. Iout caused by [Ser2]-Mytilus inhibitory peptide, [Ser2]-MIP (Gly-Ser-Pro-Met-Phe-Val-NH2) on v-RCDN, which was probably K+ dependent, was inhibited with g increase by APGW-amide. Because the modulation of this current was not so marked, a dose-response study of this compound was not carried out. Iin induced by oxytocin on PON was not affected by APGW-amide. 5. From the dose-response curves of APGW-amide, perfused consecutively, the inhibitory effects of APGW-amide on the Iout caused by APGW-amide were stronger than those on the Iout caused by FMRFamide. 6. The inhibition of the APGW-amide-induced Iout on v-RCDN by APGW-amide was partly due to the competition in the receptor sites and partly to the g increase. The inhibition by APGW-amide on the Iout induced by FMRFamide and [Ser2]-MIP would be partly due to the g increase. In addition, we consider that APGW-amide affects intracellular signal transduction systems or ionic channels, thus modulating these currents. 7. The currents modulated by APGW-amide were different from those modulated by achatin-1, another Achatina endogenous neuroexcitatory peptide. We consider that the mechanisms underlying the modulatory effects of APGW-amide are different from those of achatin-I.

Modulation by APGW-Amide, an Achatina Endogenous Inhibitory Tetrapeptide, of Currents Induced by Neuroactive Compounds on Achatina Neurons: Amines and Amino Acids

1. Modulatory effects of APGW-amide (Ala-Pro-Gly-Trp-NH2), proposed as an inhibitory neurotransmitter of Achatina neurons, perfused at 3 x 10(-6) M on the currents induced by small-molecule putative neurotransmitters were examined by using Achatina giant neuron types, v-RCDN (ventral-right cerebral distinct neuron), TAN (tonically autoactive neuron) and RAPN (right anterior pallial nerve neuron), under voltage clamp. These putative neurotransmitters were ejected locally to the neuron by brief pneumatic pressure. 2. Outward current (Iout) induced by erythro-beta-hydroxy-L-glutamic acid (erythro-L-BHGA) on v-RCDN, which was probably K+ dependent, was enhanced with membrane conductance (g) increase under APGW-amide. From dose (pressure duration)-response curves of erythro-L-BHGA measured in physiological solution (control curve) and with APGW-amide (drug curve), ED50 values of the two curves were nearly comparable, whereas Emax of the drug curve was significantly larger than that of the other. From a Lineweaver-Burk plot of these data, the cross point of the control line and the drug line was on the abscissa. 3. K(+)-dependent Iout caused by dopamine (DA) on v-RCDN was inhibited with a g increase by APGW-amide. The inhibition of this current caused by APGW-amide was mainly in a noncompetitive and partly uncompetitive manner. 4. 5-Hydroxytryptamine (5-HT) produced an inward current (Iin) with two (fast and slow) components on TAN, which was probably Na+ dependent. The fast component of the Iin was inhibited by APGW-amide. The inhibition was mainly in a noncompetitive manner. 5. The currents induced by acetylcholine, gamma-aminobutyric acid and L-glutamic acid on Achatina neuron types were not affected by APGW-amide. 6. The inhibitory effects of APGW-amide on the Iin (fast component) induced by 5-HT were nearly equipotent or a bit stronger than those on the Iout caused by DA. 7. The g increase produced by APGW-amide would be a cause for inhibiting the Iout induced by DA. In addition, we consider that APGW-amide affects intracellular signal transduction systems or ionic channels, thus modulating these currents.

Blocking effects of promethazine,triprolidine and their analogues on the excitation caused by the peptide,achatin-I

An Achatina endogenous tetrapeptide, achatin-I (Gly-d-Phe-Ala-Asp), applied by brief pressure, produced an inward current (Iin) on an Achatina giant neurone type, PON (periodically oscillating neurone). Promethazine, triprolidine and their analogues tested, applied by perfusion, showed a tendency to inhibit the Iin, suggesting that the effective structures vary to a wide extent. With respect to promethazine and its analogues, the presence of 2-bromo, 5-oxo, 3-dimethylsulfamido and 2-methoxy weakened the effects. 10-(2-methylamino-2-methylethyl) instead of 10-(2-dimethylamino-2-methylethyl) of promethazine and the azepine ring instead of phenothiazine ring potentiated the effects. From the dose (pressure duration)-response study of achatin-I, the two promethazine analogues, RP 6497 and RP 6549 (the structures are shown in Fig. 1), inhibited the Iin in partly competitive and partly noncompetitive manners. Regarding triprolidine and its analogues, the compounds in Z-configuration seemed to be more effective than those in E-configuration. The presence of 4-methyl in 1-phenyl, and 1-(4-pyridyl) instead of 1-(2-pyridyl) potentiated the effects. 3-Dimethylamino instead of 3-pyrrolidino weakened the effects. The two triprolidine analogues, Trip Der 3 and Trip Der 6 (the structures in Fig. 2), inhibited the Iin in an uncompetitive manner.

GABA B Receptor Antagonists Shortened the Transcallosal Response Latency in the Cat Cortical Neurons but Dopamine Receptor Antagonists Did Not

GABAergic and dopaminergic influences in the cortex have been found to be inhibitory and predominantly inhibitory, respectively. Activation of GABAB receptors produces slow IPSPs with long duration while postsynaptic activation of GABAA receptors evokes fast IPSPs with an increase in Cl- conductance. GABAB-mediated slow (late) IPSPs accompanied by an increase in K+ conductance build up very slowly and continue to develop for more than 500 ms in cat cerebral cortical neurons. Suppression of cortical IPSPs by GABAB antagonists is suggested to be involved in postsynaptic events. Our study, however, elucidated that GABAB receptor antagonists CGP35348 and phaclofen shortened the transcallosal response latency of cat motor cortical neurons predominantly presynaptically. Shortening of the latency by postsynaptic mechanism was also observed in some neurons. On the other hand, iontophoretic dopamine (DA) application reduced the action potentials. The complex DAergic modulation is known to be mediated by D1 and D2 receptors positively and negatively coupled to adenylate cyclase, respectively. The inhibitory effect of DA on EPSCs via both D1 and D2 receptors has already been reported. Recently, the presence of DA receptor in presynaptic terminals has been suggested. However, our experiments elucidated that D1 antagonists SCH23390 (SCH) and D2 antagonists sulpiride (SUL) and haloperidol (HAL) facilitated the transcallosal activity on cat motor neurons by blocking the suppressive effect of DA but did not change the response latency.

Inward Current Induced by Achatin-I Attenuated by Some H1-Receptor Antagonists and Their Analogues

Achatin-I, a neuropeptide isolated from the ganglia of Achatina fulica Ferussac, was proposed as an excitatory neurotransmitter and neuromodulator for A. fulica neurons (Kamatani et al. 1989; Kim et al. 1991; Liu and Takeuchi 1993). This peptide induced an inward current (Iin) on the giant neuron type, periodically oscillating neuron (PON). This Iin was found to be Na2+-dependent and is mediated by the cyclic AMP-PKA and calmodulin systems (Kim et al. 1991; Emaduddin et al. 1996). It was also found that some histamine H1 receptor antagonists inhibited this Iin (Santos et al. 1995). This paper, which is a part of studies on the characterization of Iin induced by achatin-I on PON, describes the suppressing effects of some H1 receptor antagonists and their analogues on this current. Their structure-activity relationship was also elucidated.

Ventrolateral thalamic influence upon cat motor cortical response to dopaminergic manipulation

The ventrolateral thalamic influence upon motor cortex was investigated in v~vo by iontophoretic application of dopamine (DA) and its D, and D, receptor antagonists On ipsilateral VL stimulation, cat motor cortical response for PTNs and non-F’TNs to DAergic manipulation was recorded with a multibarrel glass microelectrode. Total spike number obtained from single unit activity evoked on 20 trials of VI< stimulation was counted as response for each condition. In most cases, the spike discharge changed significantly whereas the latency remamed unchanged. DA chiefly decreased the firing rate while the antagomsts restored the effect almost to control level. Alternatively, opposite effect was also elicited in some neurons However, no significant difference was observed between the effects of D, and DZ antagonists, regardless of PTNs and non-PTNs. In brief, DAergic inhibition of the \‘L thalanuc activity on cat motor cortex w’as found to be predominant. It seems obvious from what has been reported by many researchers, in addition to this study,, that the VI, thalamic influence on DAergic distribution might have a critical relation with the modulation of cat motor signahng.

260 Blocking effects of promethazine triprolidine and their analogues on the excitation caused by the peptide, achatin-I

An Achatina endogenous tetrapeptide, achatin-I (Gly-D-Phe-Ala-Asp), applied by brief pressure, produced an inward current (Iin) on an Achatina giant neurone type, PON (periodically oscillating neurone). Promethazine, triprolidine and their analogues tested, applied by perfusion, showed a tendency to inhibit the Iin, suggesting that the effective structures vary to a wide extent. With respect to promethazine and its analogues, the presence of 2-bromo, 5-oxo, 3-dimethylsulfamido and 2-methoxy weakened the effects. 10-(2-methylamino-2-methylethyl) instead of 10-(2-dimethylamino-2-methylethyl) of promethazine and the azepine ring instead of phenothiazine ring potentiated the effects. From the dose (pressure duration)-response study of achatin-I, the two promethazine analogues, RP 6497 and RP 6549 (the structures are shown in Fig. 1), inhibited the Iin in partly competitive and partly noncompetitive manners. Regarding triprolidine and its analogues, the compounds in Z-configuration seemed to be more effective than those in E-configuration. The presence of 4-methyl in 1-phenyl, and 1-(4-pyridyl) instead of 1-(2-pyridyl) potentiated the effects. 3-Dimethylamino instead of 3-pyrrolidino weakened the effects. The two triprolidine analogues, Trip Der 3 and Trip Der 6 (the structures in Fig. 2), inhibited the Iin in an uncompetitive manner.

1547 Effects of dopamine and its antagonists on motor cortical neurons after transcallosal stimulation

1546 MORPHOLOGICAL STUDY OF EXTERNAL OBLIQUE MOTOR NERVE AND NUCLEUS IN THE CAT Dept. of Occupational Therapy, Ibaraki Prefectural Univ. Health Sci. 4669-2 Ami, Ami-machi, Inashikigun, Ibaraki 300-03, Japan’, Center for Medical Sci. Ibaraki Prefectural Univ. Health Sci. 4669-2 Ami, Ami-machi, Inashiki-gun, Ibaraki 300-03, Japan 2, Dept. of Anesthesiology, Tokyo Medical College, 6-l-l Shinjuku, Shinjuku-ku, Tokyo 160, Japan3