In birds, the thalamic nucleus rotundus relays visual information from the midbrain optic tectum to the forebrain ectostriatum. Using brain slices, the present study investigates the firing patterns and morphological features of 41 neurons in various divisions of the pigeon nucleus rotundus. The results indicate that these rotundal cells could be physiologically categorized into two types according to their firing patterns in response to depolarizing current pulses. Type I cells (76%) are characterized by a multi-phase firing pattern producing a single spike, late-spiking and fast-spiking as current intensity increases. Cells of type II (24%) are characterized by a rapid spiking-inactivation, discharging only one or two small spikes at the onset of current injections. However, intracellular staining shows no significant morphological differences between the two physiological types of cells in terms of somatic and dendritic field sizes, or an average density of dendritic varicosities, although each cell type includes both small- and large-sized dendritic fields. It is likely that the firing patterns and morphological features of rotundal neurons might not be correlated with each other or with rotundal divisions.

1.
Benowitz, L.I., and H.J. Karten (1976) Organization of the tectofugal visual pathway in the pigeon: a retrograde transport study. J. Comp. Neurol., 167: 503–520.
2.
Deng, C., and L.J. Rogers (1998) Organization of the tectorotundal and SP/IPS-rotundal projection in the chick. J. Comp. Neurol., 394: 171–185.
3.
Domenici, L., H.J. Waldvogel, C. Mature, and P. Streit (1988) Distribution of GABA-like immunoreactivity in the pigeon brain. J. Neurosci., 25: 931–950.
4.
Engelage, J., and H.J. Bischof (1993) The organization of the tectofugal pathway in birds: a comparative review. In Vision, Brain, and Behavior in Birds (ed. by H.P. Zeigler and H.J. Bischof), MIT Press, MA, pp. 137–158.
5.
Gao, H.F., G.Y. Wu, B.J. Frost, and S.R. Wang (1995) Excitatory and inhibitory neurotransmitters in the nucleus rotundus of pigeons. Vis. Neurosci., 12: 819–825.
6.
Grace, A.A., and R. Llinàs (1985) Dehydration-induced morphological artifacts in intracellularly stained neurons: circumvention using rapid DMSO clearing. Neuroscience, 16: 461– 475.
7.
Granda, A.M., and S. Yazulla (1971) The spectral sensitivity of single units in the nucleus rotundus of pigeon, Columba livia. J. Gen. Physiol., 57: 363–384.
8.
Hardy, O., E. Audinat, and D. Jassik-Gerschenfeld (1987) Electrophysiological properties of neurons recorded intracellularly in slices of the pigeon optic tectum. Neuroscience, 23: 305– 318.
9.
Hellmann, B., and O. Güntürkün (1999) Visual-field-specific heterogeneity within the tecto-rotundal projection of the pigeon. Eur. J. Neurosci., 11: 2635–2650.
10.
Hellmann, B., and O. Güntürkün (2001) Structural organization of parallel information processing within the tectofugal visual system of the pigeon. J. Comp. Neurol., 429: 94–112.
11.
Huang, L.H., J.L. Li, and S.R. Wang (1998) Glutamatergic neurotransmission from the optic tectum to the contralateral nucleus rotundus in pigeons. Brain Behav. Evol., 52: 55–60.
12.
Karten, H.J., K. Cox, and J. Mpodozis (1997) Two distinct populations of tectal neurons have unique connections within the retinotectorotundal pathway of the pigeon (Columba livia). J. Comp. Neurol., 387: 449–465.
13.
Karten, H.J., and W. Hodos (1967) A Stereotaxic Atlas of the Brain of the Pigeon (Columba livia). Johns Hopkins Press, Baltimore, MD.
14.
Karten, H.J., and A.M. Revzin (1966) The afferent connections of the nucleus rotundus in the pigeon. Brain Res., 2: 368–377.
15.
Laverghetta, A.V., and T. Shimizu (1999) Visual discrimination in the pigeon (Columba livia): effects of selective lesions of the nucleus rotundus. NeuroReport, 10: 981–985.
16.
Luksch, H., K. Cox, and H.J. Karten (1998) Bottlebrush dendritic endings and large dendritic fields: motion-detecting neurons in the tectofugal pathway. J. Comp. Neurol., 396: 399– 414.
17.
Martinez-de-la-Torre, M., S. Martinez, and L. Puelles (1990) Acetylcholinesterase histochemical differential staining of subdivisions within the nucleus rotundus in the chick. Anat. Embryol., 181: 129–135.
18.
Mpodozis, J., K. Cox, T. Shimizu, H.J. Bischof, W. Woodson, and H.J. Karten (1996) GABAergic inputs to the nucleus rotundus (pulvinar inferior) of the pigeon (Columba livia). J. Comp. Neurol., 374: 204–222.
19.
Onn, S.P., and A.A. Grace (1994) Dye-coupling between rat striatal neurons recorded in vivo: Compartmental organization and modulation by dopamine. J. Neurophysiol., 71: 1917– 1934.
20.
Saito, Y., and T. Isa (1999) Electrophysiological and morphological properties of neurons in the rat superior colliculus. I. Neurons in the intermediate layer. J. Neurophysiol., 82: 754–767.
21.
Thin, N.D., G. Egedi, and T. Tömböl (1992) Golgi study on neurons and fibers in nucl. rotundus of the thalamus in chicks. J. Hirnforsch., 33: 203–214.
22.
Wang, Y.C., and B.J. Frost (1992) ‘Time to collision’ is signalled by neurons in the nucleus rotundus of pigeon. Nature, 356: 236–238.
23.
Wang, Y., Y. Gu, and S.R. Wang (2000) Modulatory effects of the nucleus of the basal optic root on rotundal neurons in pigeons. Brain Behav. Evol., 56: 287–292.
24.
Wang, Y.C., S.Y. Jiang, and B.J. Frost (1993) Visual processing in pigeon nucleus rotundus: luminance, color, motion, and looming subdivisions. Vis. Neurosci., 10: 21–30.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.