Caudal diencephalon of the urethane-anesthetized rat. BLAND, BRIAN H., JAN KONOPACKI, IAN J. KIRK, SCOTT D. ODDIE, AND CLAYTON T. DICKSON. Department of Psychology, Behavioral Neuroscience Research Group, University of Calgary, 2500 University Drive, Calgary, Alberta, Canada, T2N 1N4.
APStracts 2:0068N, 1995.
SUMMARY AND CONCLUSIONS
1. Single-unit discharge patterns of cells in specific nuclei of the caudal diencephalon were characterized in relation to simultaneously recorded field activity from the stratum moleculare of the dentate gyrus according to the criteria that have been used previously to classify cells in the hippocampal formation (including entorhinal cortex), medial septum and cingulate cortex. Theta (I)-related cells were classified as: i) tonic I-ON, if they discharged non-rhythmically and increased their discharge rates during hippocampal I relative to large, irregular hippocampal field activity (LIA); ii) tonic I- OFF, if they discharged non-rhythmically and decreased their discharge rates during I relative to LIA; iii) phasic I-ON if they discharged rhythmically, and in phase, with ongoing I, but non-rhythmically during LIA. Cells not meeting any of the above criteria were classified as non-related. 2. A total of 127 cells were recorded from the caudal diencephalon. Fifty-four cells were recorded from the posterior hypothalamic nucleus (PH), 16 from the supramammillary nucleus (SuM), 20 from the PH/SuM border, and 23 from the medial mammillary nucleus (MM). Nine cells were also recorded from the central median nucleus of the thalamus (CM), and 5 from the dorsomedial hypothalamic nucleus (DMH). 3. Of the 54 PH cells, 43 (80%) were classified as tonic I-ON, and 11 (20%) as non-related. Tonic I-On cells in the PH discharged at significantly higher rates during I, either occurring spontaneously (9.6+/-1.7Hz) or elicited with a tail-pinch (TPI; 10.6+/-1.9Hz), than during LIA (3.6+/-1.4Hz). Of the 9 CM cells, 7 (78%) were tonic I-ON and 2 (22%) were non- related. Tonic I-ON cells discharged at significantly higher rates during I (17.5+/-7.8Hz) or theta induced by a tail pinch (TPI; 18.0+/-7.1Hz) than during LIA (7.3+/-4.8Hz). All DMH cells were non-related. 4. Of the 20 PH/SuM border cells 15 (75%) were classified as tonic I-OFF and discharged at significantly higher rates during LIA (5.3+/-1.5Hz) than during I (0.8+/- 0.4Hz), or TPI (0.4+/-0.3Hz). Five (25%) cells in the PH/SuM border were non- related. 5. All ofthe 16 cells (100%) recorded from the body of the SuM were phasic I-ON. The discharge rates of these cells did not change significantly across hippocampal field states (LIA=8.3+/-1.6; I=7.3+/-1.6; TPI=8.6+/-1.7Hz). However, all of these cells changed from a non-rhythmic discharge pattern during LIA to a rhythmic (or phasic) discharge pattern during I. Most of the SuM cells (12/16; 75%) discharged on the negative-going phase of the hippocampal I recorded from the fissure/stratum moleculare of the dentate gyrus (151+/-14§; 0§=+ve peak of I). 6. Of the 23 cells recorded from the MM, 19 (83%) were also phasic I-ON. The remaining 4 cells (17%) were non-related. The discharge rates of MM phasic I-ON cells did not change significantly across hippocampal field states (LIA= 9.1+/-2.0; I=9.9+/-1.5; TPI=9.4+/- 1.4Hz). However, all of these cells changed from a non-rhythmic discharge pattern during LIA to a rhythmic (or phasic) discharge pattern during I. In contrast to SuM phasic I-ON cells, most of the MM cells (15/19; 75%) discharged on the positive-going phase of I (300+/-12§). 7. On the basis of these, and previously published data, it is suggested that tonic I-ONcells in the PH (and possibly CM) act in synergy with phasic I-ON cells in the SuM during hippocampal I to relay ascending reticular input to the septum. MM cells may, as has previously been suggested, act to relay I-rhythmic signals from the septum or hippocampus to other parts of the limbic system. It is suggested that tonic I-OFF cells in the PH/SuM border inhibit discharge of I- ON cells in the PH and SuM during non-I hippocampal states. 

Received 26 September 1994; accepted in final form 3 March 1995.
APS Manuscript Number J603-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  3 April 1995.