Jourrial of Nrurochrmistry, 1976. Val. 26, pp. 191-192. Pergamon Press. Printed in Great Britain.
SHORT COMMUNICATION
Acetylcholinesterase activity not associated with innervation in the pedicled electroplaque of Mormyrid fishes (Received 8 May 1975. Accepted 28 May 1975).
INEARLIER histological investigations on the pedicled elec- external part, the nerve fibre region can be observed. On troplaques of some Mormyrid fishes, SZABO(1956, 1958) the left of Fig. I b two positive branched pedicles (b) are seen observed that in these species the innervation is limited to the terminal swelling of the pedicle which derives from the posterior face of the electroplaque and emerges through its perforations. That contrasts with the usual type of electroplaques where the active face is uniformly innervated. COUTEAUX & TAXI(1952) and COUCEIRO et a / . (1953) showed that cholinesterase was specifically localized at the innervated face of such electroplaques. But for the Mormyrid, Marcusenius senegalensis elongatus,‘ COUTEAUX & SZABO(1959) have localized cholinesterase activity solely in the innervated part of the pedicles on isolated electroplaques. These authors also observed some enzymatic reaction at the site of the perforations of this electroplaque. We have reinvestigated the acetylcholinesterase (AchE; EC 3.1.1.7.) distribution on isolated and on transversely sectioned electroplaques of some Mormyrid fishes. We confirmed the previous histochemical observation of COUTEAUX & S Z A (1959) ~ and observed further an intense AchE activity on all branched pedicles and on the anterior face of the electroplaques. These results shed more light on AchE distribution of this type of electroplaque and its meaning will be discussed herein.
without nerve fibres. On Fig. 1b the posterior face of the electroplaques with its papillae reveals no AchE activity. The branched pedicles are continuous with the anterior face of the electroplaque. On the top right of Fig. l b such a finely branched pedicle is seen invaginating (i) into the electroplaque. Figure 2a shows a part of an isolated electroplaque of Brienomyrus hrachyistius. As in Gnathonemus petersii, the terminal swellings of the pedicles (s) are positive. The branched pedicles (b) are also positive. The AchE positive rings which are seen on Fig. 2a correspond to the perforation of the electroplaque where the branched pedicles are running through. The background of the electroplaque seems to be negative. But here too, as for Gnathonemus petersii, on a transversal section (Fig. 2b), it is visible that the anterior face of the electroplaque is highly positive. Some pedicles seem to traverse the electroplaque (t-n bottom right of Fig. 2b two such pedicles are visible-and are AchE positive on both the anterior and the posterior side of the electroplaque. These pedicles are seen as positive rings at their site of penetration into the electroplaque observed in toto (see Fig. 2a). We observed on some sections that the fine pedicles lose their AchE activity as they are fusing with a pappila of the posterior face.
MATERIALS AND METHODS The electric organ of two Mormyrid fishes, Gnathonemus petersii and Brienomyrus brachyistius have been used. In order to reveal AchE activity, the modified thiocholine method of Koelle (TSUJI,1974) was employed either on whole electroplaques isolated from the fixed electric organ (5% glutaraldehyde in 0.1 M-phosphate buffer at pH 7.2) or on cryostat sections prepared from fresh or fixed electric organ. The control of specificity with butyrylthiocholine was negative and that with iso-OMPA(10-5) was positive.
DISCUSSION The present histochemical study has confirmed that in Mormyrid electroplaques the AchE activity is localized on the terminal swelling of the pedicles. But furthermore we observed, especially in transverse section, that the anterior face of the electroplaque was enzymatically active just as the surface of the pedicles along their whole length. In Brienomyrus brachyistius the AchE positive rings, already observed by COUTEAUX & SZABO(1959) on the isolated electroplaque of Marcusenius senegalensis dongatus, may now be understood as the AchE activity of RESULTS Figure la shows a part of an isolated electroplaque of the pedicles at the penetrating site into the electroplaque. We wonder about the meaning of the AchE activity Gnathonemus petersii. The terminal swelling of the pedicles (s) is intensely AchE-positive and covered by the bundle observed on the anterior face of the Mormyrids’ electroplaof myelinated nerve fibres (N). The branched pedicles (b) ques where no innervation has ever been described. are also positive. The background seems to be faintly posi- Although the innervation is concentrated on the pedicles tive on an electroplaque in toto. But on a transverse section in these species, the AchE activity still found on the anterit becomes evident that the anterior face of the electropla- ior face of the electroplaque could be the remnant of an ques reveals an intense AchE reaction. (Fig. lb). On Fig. earlier (phylogenic or ontogenic) functional innervated site. l b (middle and right) positive transversal section of the We tried to identify a trace of innervation at the anterior terminal swelling of 2 pedicles (s) are visible. On their face of this electroplaque. Like SCHWARTZet al. (1975), we observed deep numerous invaginations of the plasma membranes of the anterior face of this electroplaque. We I The recent classification of Mormyrids by TAVERNE could observe above these invagination some atypical (1971) is used in the present paper. knobs difficult to interpret as remnants of nerve terminals. 191
192
Short communication
Acknowledgement-I am greatly indebted to Prof. R. ConTEAUX for criticism of this paper and to Dr. J. DAGET for identification of the specimens.
COUTEAC~X R. & SZAROT. (195Y) C.r. hibd. &;uric. Acpd. Sci., Paris 248. 457460. C O U ~ A URX . & TAXIJ. (1952) Arch. Anat. micro. 41. 352-
S. Tsuii
SCHWARTZ I. R., PAPPASG. D. & BENNETTM. V. L. (1975) J . Neurocytol. 4. 87-1 14. SZABOT. (1956) C.r. hibd. Sianc. Acad. Sci., Paris 242,
REFERENCES Couci I K O A,. DI ALMHDAD. F. & FKHRE J. R. C. (1953) An. Acad. nac. Farm. B r a d Ci. 25. 205-214.
SZABOT. (1958) Z. Zeflforsch. mikrosk. Anal. 49. 3345. TAVEKNE L. (1971) Rev. Zool. Bot. ufi. 84. 99-110. Tsun S. (1974) Histochemistry 42. 99-1 10.
392.
Lahoratoire de Biologie Animale, Uniuersiti Paris V I , 12 rue Cuvier, 75005-Paris, France
2045-2048.
FIG. 1. Electroplaque of Gnathonernus petersii. Modified thiocholine method of Koelle. ( x 200). (a) a portion of an isolated fixed electroplaque. (b) transversal frozen fixed section. s-terminal swelling of the pedicle. b-branched pedicle. N-nerve. i-a pedicle invaginating into the electroplaque. AP-anterior-posterior direction. hc--192
FIG.2. Electroplaque of Brieaomyrus brachyistius. Modified thiocholine method of Koelle. ( x 200). (a) a portion of an isolated fixed eleclroplaque. (b) transversal cryostat section of fresh electric organ. s-terminal swelling of the pediclc. b-branched pedicle. N-nerve. t-pedicle lraversing the electroplaque. AP-anterior-posterior direction.
SHORT COMMUNICATION
Acetylcholinesterase activity not associated with innervation in the pedicled electroplaque of Mormyrid fishes (Received 8 May 1975. Accepted 28 May 1975).
INEARLIER histological investigations on the pedicled elec- external part, the nerve fibre region can be observed. On troplaques of some Mormyrid fishes, SZABO(1956, 1958) the left of Fig. I b two positive branched pedicles (b) are seen observed that in these species the innervation is limited to the terminal swelling of the pedicle which derives from the posterior face of the electroplaque and emerges through its perforations. That contrasts with the usual type of electroplaques where the active face is uniformly innervated. COUTEAUX & TAXI(1952) and COUCEIRO et a / . (1953) showed that cholinesterase was specifically localized at the innervated face of such electroplaques. But for the Mormyrid, Marcusenius senegalensis elongatus,‘ COUTEAUX & SZABO(1959) have localized cholinesterase activity solely in the innervated part of the pedicles on isolated electroplaques. These authors also observed some enzymatic reaction at the site of the perforations of this electroplaque. We have reinvestigated the acetylcholinesterase (AchE; EC 3.1.1.7.) distribution on isolated and on transversely sectioned electroplaques of some Mormyrid fishes. We confirmed the previous histochemical observation of COUTEAUX & S Z A (1959) ~ and observed further an intense AchE activity on all branched pedicles and on the anterior face of the electroplaques. These results shed more light on AchE distribution of this type of electroplaque and its meaning will be discussed herein.
without nerve fibres. On Fig. 1b the posterior face of the electroplaques with its papillae reveals no AchE activity. The branched pedicles are continuous with the anterior face of the electroplaque. On the top right of Fig. l b such a finely branched pedicle is seen invaginating (i) into the electroplaque. Figure 2a shows a part of an isolated electroplaque of Brienomyrus hrachyistius. As in Gnathonemus petersii, the terminal swellings of the pedicles (s) are positive. The branched pedicles (b) are also positive. The AchE positive rings which are seen on Fig. 2a correspond to the perforation of the electroplaque where the branched pedicles are running through. The background of the electroplaque seems to be negative. But here too, as for Gnathonemus petersii, on a transversal section (Fig. 2b), it is visible that the anterior face of the electroplaque is highly positive. Some pedicles seem to traverse the electroplaque (t-n bottom right of Fig. 2b two such pedicles are visible-and are AchE positive on both the anterior and the posterior side of the electroplaque. These pedicles are seen as positive rings at their site of penetration into the electroplaque observed in toto (see Fig. 2a). We observed on some sections that the fine pedicles lose their AchE activity as they are fusing with a pappila of the posterior face.
MATERIALS AND METHODS The electric organ of two Mormyrid fishes, Gnathonemus petersii and Brienomyrus brachyistius have been used. In order to reveal AchE activity, the modified thiocholine method of Koelle (TSUJI,1974) was employed either on whole electroplaques isolated from the fixed electric organ (5% glutaraldehyde in 0.1 M-phosphate buffer at pH 7.2) or on cryostat sections prepared from fresh or fixed electric organ. The control of specificity with butyrylthiocholine was negative and that with iso-OMPA(10-5) was positive.
DISCUSSION The present histochemical study has confirmed that in Mormyrid electroplaques the AchE activity is localized on the terminal swelling of the pedicles. But furthermore we observed, especially in transverse section, that the anterior face of the electroplaque was enzymatically active just as the surface of the pedicles along their whole length. In Brienomyrus brachyistius the AchE positive rings, already observed by COUTEAUX & SZABO(1959) on the isolated electroplaque of Marcusenius senegalensis dongatus, may now be understood as the AchE activity of RESULTS Figure la shows a part of an isolated electroplaque of the pedicles at the penetrating site into the electroplaque. We wonder about the meaning of the AchE activity Gnathonemus petersii. The terminal swelling of the pedicles (s) is intensely AchE-positive and covered by the bundle observed on the anterior face of the Mormyrids’ electroplaof myelinated nerve fibres (N). The branched pedicles (b) ques where no innervation has ever been described. are also positive. The background seems to be faintly posi- Although the innervation is concentrated on the pedicles tive on an electroplaque in toto. But on a transverse section in these species, the AchE activity still found on the anterit becomes evident that the anterior face of the electropla- ior face of the electroplaque could be the remnant of an ques reveals an intense AchE reaction. (Fig. lb). On Fig. earlier (phylogenic or ontogenic) functional innervated site. l b (middle and right) positive transversal section of the We tried to identify a trace of innervation at the anterior terminal swelling of 2 pedicles (s) are visible. On their face of this electroplaque. Like SCHWARTZet al. (1975), we observed deep numerous invaginations of the plasma membranes of the anterior face of this electroplaque. We I The recent classification of Mormyrids by TAVERNE could observe above these invagination some atypical (1971) is used in the present paper. knobs difficult to interpret as remnants of nerve terminals. 191
192
Short communication
Acknowledgement-I am greatly indebted to Prof. R. ConTEAUX for criticism of this paper and to Dr. J. DAGET for identification of the specimens.
COUTEAC~X R. & SZAROT. (195Y) C.r. hibd. &;uric. Acpd. Sci., Paris 248. 457460. C O U ~ A URX . & TAXIJ. (1952) Arch. Anat. micro. 41. 352-
S. Tsuii
SCHWARTZ I. R., PAPPASG. D. & BENNETTM. V. L. (1975) J . Neurocytol. 4. 87-1 14. SZABOT. (1956) C.r. hibd. Sianc. Acad. Sci., Paris 242,
REFERENCES Couci I K O A,. DI ALMHDAD. F. & FKHRE J. R. C. (1953) An. Acad. nac. Farm. B r a d Ci. 25. 205-214.
SZABOT. (1958) Z. Zeflforsch. mikrosk. Anal. 49. 3345. TAVEKNE L. (1971) Rev. Zool. Bot. ufi. 84. 99-110. Tsun S. (1974) Histochemistry 42. 99-1 10.
392.
Lahoratoire de Biologie Animale, Uniuersiti Paris V I , 12 rue Cuvier, 75005-Paris, France
2045-2048.
FIG. 1. Electroplaque of Gnathonernus petersii. Modified thiocholine method of Koelle. ( x 200). (a) a portion of an isolated fixed electroplaque. (b) transversal frozen fixed section. s-terminal swelling of the pedicle. b-branched pedicle. N-nerve. i-a pedicle invaginating into the electroplaque. AP-anterior-posterior direction. hc--192
FIG.2. Electroplaque of Brieaomyrus brachyistius. Modified thiocholine method of Koelle. ( x 200). (a) a portion of an isolated fixed eleclroplaque. (b) transversal cryostat section of fresh electric organ. s-terminal swelling of the pediclc. b-branched pedicle. N-nerve. t-pedicle lraversing the electroplaque. AP-anterior-posterior direction.
