The expression of Fos within the suprachiasmatic nucleus of the diurnal rodent Arvicanthis niloticus

Brain Research 791 Ž1998. 27–34

Research report

The expression of Fos within the suprachiasmatic nucleus of the diurnal rodent ArÕicanthis niloticus Catherine Katona, Sandra Rose, Laura Smale

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Department of Psychology and Neuroscience Program, Michigan State UniÕersity, East Lansing, MI 48824-1117, USA Accepted 26 August 1997

Abstract Rhythms in the expression of the nuclear phosphoprotein Fos, have been demonstrated in the suprachiasmatic nucleus ŽSCN. of nocturnal rodents. When rats are housed in a 12:12-h lightrdark ŽLD. cycle the number of Fos-immunoreactive Ž-IR. cells within the SCN is higher during the day than at night w9,23x. In the two experiments reported here, Fos-IR was examined in the SCN of a diurnal murid rodent, ArÕicanthis niloticus. First, thirty-six adult male A. niloticus housed in a 12:12-h LD cycle were perfused at six equally spaced time points beginning 1 h after lights on Ž n s 6 per time point.. Brains were sectioned and treated with immunohistochemical procedures for the identification of Fos. The number of Fos-IR cells in the SCN varied significantly as a function of time, and was highest 1 h after lights on and decreased thereafter. The distribution of Fos-IR within the SCN overlapped with that of arginine-vasopressin-IR ŽAVP-IR. and vasoactive intestinal peptide-IR ŽVIP-IR., but not with that of gastrin-releasing peptide-IR ŽGRP-IR.. In the second study, double-labeling techniques revealed extensive Fos expression within SCN neurons containing AVP-IR, but not neurons containing GRP-IR. In conclusion, although the overall rhythm of Fos-IR in the SCN is similar in diurnal and nocturnal rodents, differences may exist with respect to the relative distribution of Fos-immunoreacte cells within different SCN cell populations. q 1998 Elsevier Science B.V. Keywords: Immediate–early gene; ArÕicanthis niloticus; Diurnal; Suprachiasmatic nucleus; Fos; Rhythm

1. Introduction There is extensive evidence that the hypothalamic suprachiasmatic nucleus ŽSCN. is the anatomical substrate for the primary circadian pacemaker in mammals. Lesions of the SCN abolish a variety of circadian rhythms w39x, and transplants of fetal SCN tissue into animals with SCN lesions can restore a number of these rhythms w26x. In addition, a variety of rhythms intrinsic to the SCN have been documented in several species. For example, both in vitro and in vivo rates of glucose metabolism are higher in the SCN during the day than at night w40,41x, as are rates of single and multiple unit activity w14,19,20,44x. Thus, the SCN generates its own rhythms and is responsible for many circadian rhythms found in mammals. Within the SCN of rats and hamsters the ventrolateral and dorsomedial regions are anatomically and functionally ) Corresponding author. [email protected]

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distinct. The ventrolateral region receives projections from the geniculohypothalamic tract ŽGHT. and the retinohypothalamic tract ŽRHT., both of which transmit visual input to the SCN w5,15,30x. At least some of the fibers of the GHT contain neuropeptide-Y ŽNPY; w5,16x.. The ventrolateral SCN is populated by cells containing VIP w27,48x, whereas cells in the dorsomedial SCN contain AVP w47x. These different areas are also characterized by different patterns of rhythmicity with respect to the expression and release of these various peptides. In the ventrolateral SCN the concentration of NPY is high around the transitions between light and dark phases of a 24-h lightrdark ŽLD. cycle w21x, and the peptide VIP as well as its messenger RNA peak during the dark phase of a 24-h LD cycle w2,33,45,49x. In contrast, the in vivo expression of AVP messenger RNA is higher during the day than at night w49,50x as is the release of AVP from the dorsomedial SCN in vitro w8,13x. Rhythms in the expression of the nuclear phosphoprotein Fos have also been documented within the SCN of

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nocturnal rodents kept in various lighting conditions w3,7,10,18,24,38,43x. The proto-oncogene c-fos encodes for the nuclear phospho-protein Fos, which binds to the DNA as a heterodimer with Jun and is involved in the regulation of gene transcription. The SCN of rats housed in a 12:12-h LD cycle exhibits a 24-h rhythm of Fos-IR which peaks during the light phase w9,23x. When different sub-regions of the rat SCN are examined separately, it becomes apparent that Fos-IR in the ventrolateral SCN is much higher during the light phase than the dark phase, whereas Fos-IR in the dorsomedial SCN is somewhat higher during the dark compared to the light phase w9x. In mice kept on a 12:12-h LD cycle, Fos-IR in the SCN is high immediately after lights on, drops by the middle of the day, and remains low until the lights are turned on again w7x. In rats kept in constant light ŽLL., Fos-IR is higher in the ventrolateral SCN during the subjective night than during the subjective day, but it remains unclear whether there is a rhythm in Fos-IR in the dorsomedial SCN w9,10x. In the SCN of mice and rats housed in constant dark ŽDD., no rhythm of Fos-IR is seen w7,9x, whereas hamsters kept in DD exhibit a slight rhythm in Fos-IR in the rostral SCN, with a peak in the middle of the subjective day w6x. In nocturnal rodents housed in DD, light pulses during the subjective night induce a dramatic increase in Fos-IR, whereas light pulses during the subjective day do not w38,43x. Thus, Fos-IR in the SCN of nocturnal rodents is expressed rhythmically in animals kept in LD cycles and LL, and responds to light pulses during DD in a time-dependent manner. Research on neural mechanisms underlying mammalian circadian rhythms has focused primarily on nocturnal rodents, and nothing is currently known about how these mechanisms differ in diurnal and nocturnal species. Theoretically the differences could be due to differences within some subpopulation of SCN neurons, to differences in responsiveness to SCN signals, or to some combination of these two factors. With respect to three variables, rhythms within the SCN are similar in diurnal and nocturnal species. Rates of glucose utilization and electrical activity are higher during the day than at night in the SCN of both nocturnal and diurnal mammals w13,19,25,37,42x, and immunoreactive AVP within the SCN is elevated during the day compared to the night in both humans and nocturnal rodents w17x. In spite of these findings, it remains possible that some aspect of SCN function differs in nocturnal and diurnal species, and is responsible for their differing patterns of rhythmicity. Here we present two additional tests of the hypothesis that some aspect of SCN function differs in nocturnal and diurnal species. The diurnal animal model we have used is ArÕicanthis niloticus, a small murid rodent found in subSaharan Africa. This species is diurnal with respect to its patterns of wheel-running, general activity, body temperature and copulatory behavior w22,28x. In the first study, we documented the rhythm in Fos-IR within the SCN of members of this species sacrificed at different phases of a

12:12-h LD cycle. In the second study we examined patterns of double-labeling of Fos and two different peptides found within SCN neurons, AVP and GRP.

2. Materials and methods Animals used in this study were adult A. niloticus bred in the laboratory from a wild group captured in 1993 in Kenya. All animals were housed in plexiglass cages Ž38 = 34 = 16 cm. with same-sex siblings until 24–72 h before sacrifice, at which time they were individually housed. Animals were provided rodent chow ŽHarlan 8640 Teklad 22r5 Rodent diet. and water ad libitum, and were kept on a 12:12-h LD schedule; a red light Ž- 5 lux. was kept on constantly. 2.1. Immunohistochemical procedures Animals were anesthetized with Equithesin Ž1 ccranimal. and perfused transcardially with 250 ml phosphate-buffered saline Ž0.01 M, pH 7.2. followed by 250 ml of fixative Ž4% paraformaldehyde with 0.1% glutaraldehyde. in 0.1 M phosphate buffer. During the dark part of the cycle animals were anesthetized under the red light and perfused while wearing a light tight hood that covered their eyes. Brains were post-fixed for 4 h ŽExpt. 1. or 8 h ŽExpt. 2., transferred into 20% sucrose for 24 h at 48C, frozen on a sliding microtome and sectioned coronally at 40 mm. Tissue was stored in cryoprotectant w51x until sections Žone out of every four for Expt. 1, and one out of every 2 for Expt. 2. were processed. Tissue was processed for immunocytochemical ŽICC. detection of Fos-IR using the Santa Cruz c-fos w4x antibody Žcat. no. sc-52.. Sections were preincubated in 4% normal goat serum with 3% Triton-X, and then incubated in the primary antibody Ž1:1000, Expt. 1 and 1:4000, Expt. 2. in 3% Triton-X with 2% normal goat serum, for 24 h at 48C. The tissue was put into the secondary antibody Žbiotinylated goat anti-rabbit, 1:200; Vector Labs. in 3% Triton-X with 2% normal goat serum. After incubation in the secondary antibody, we followed the procedures described in the protocol of the ABC Vectastain kit, using diaminobenzidine in Trizma buffer ŽpH 7.2. reacted with hydrogen peroxide. Two control series were treated as described above except that the primary and secondary antibodies were deleted, respectively; no reaction product was observed in these sections. For the second, double-labeling experiment, tissue was first processed as described above, rinsed thoroughly in PBS, and then labeled for either GRP or VP, using the procedure described in w29x. Specifically, sections were incubated for 1 h in 5% normal goat serum, rinsed in PBS and then incubated overnight at room temperature in rabbit antisera directed against either GRP or AVP ŽPenninsula.

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at a concentration of 1:4000. Sections were then rinsed in PBS with 1% bovine serum albumin ŽBSA. and 0.3% Triton-X, then incubated for 1.5 h in 0.5% biotinylated goat anti-rabbit secondary, and then rinsed in PBS for 0.5 h. Sections were then incubated in 1.8% avidin–biotin complex ŽVectastain Elite Kit, Vector., rinsed in PBS followed by 1 M acetate buffer, and then reacted. The reaction involved combining Ž1. 90 ml dH 2 O containing 0.040 g benzidine dihydrochloride, Ž2. 10 ml 0.5 M acetate buffer containing 0.08 g sodium nitroprusside, and Ž3. 1.33 ml 3% hydrogen peroxide. The reaction was stopped with two quick rinses in 0.05 M acetate buffer. All tissue was rinsed, mounted, dried, dehydrated and cover slipped. 2.2. Experiment 1: single labeling Six male A. niloticus were perfused at each of six time points evenly spaced across the day. Specifically, with lights on at ZT 0 and off at ZT 12, animals were sacrificed at ZT 1, 5, 9, 13, 17 and 21. Brains were processed for single labeling of Fos, and Fos-IR cells were counted bilaterally from 2.7 " 0.2 sections through the central SCN of each animal. Camera lucida drawings were made from each section by two individuals blind to the times at which animals were perfused. The number of Fos-IR cells in the SCN in each pair of drawings was averaged, and for each animal, the average number of Fos positive cells per section was calculated. These scores were then analyzed using a one-way analysis of variance followed by Fisher’s post-hoc tests. Differences were considered significant when P - 0.05.

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Fig. 1. Mean Ž"S.E.M.. number of Fos-IR cells in the suprachiasmatic nucleus ŽSCN. of A. niloticus housed in a 12:12-h lightrdark cycle and sacrificed at 4-h intervals. x-Axis represents time of sacrifice with lights on at ZT 0 and off at ZT 12. ns6 subjects for ZT 1, 5, 13, 17, and 21, and 5 for ZT 9.

were significantly higher than at ZT 13 Ž P s 0.05., 17 and 21. There were no statistical differences in the number of Fos-IR cells among animals sacrificed at ZT 13, 17 and 21.

2.3. Experiment 2: double labeling For double labeling of Fos plus AVP, four animals Žthree males and one female. were perfused at ZT 5–7. For double labeling of Fos and GRP, four adult males were perfused at ZT 5, and four at ZT 17. From the SCN of each animal, the number of Fos-positive nuclei, the number of VP or GRP-positive cell bodies, and the number of double-labeled cells was counted.

3. Results 3.1. Experiment 1: single labeling Fos-IR was clearly observable within the nuclei of cells in the SCN, and the number of Fos-IR cells in the SCN changed significantly as a function of time of day ŽFig. 1 and Fig. 2; F s 18.792, P - 0.001.. The number of Fos-IR cells was highest 1 h after lights-on ŽZT 1. and decreased progressively over the next 23 h ŽFig. 1.. Cell numbers at ZT 1 were significantly higher than at any other time point ŽFisher’s t-test, P - 0.002., and those at ZT 5 and ZT 9

Fig. 2. Camera lucida drawings Fos-IR within the SCN of animals sacrificed at ZT 1, 5, 9, 13, 17 and 21.

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Fig. 3. Double labelling of Fos and AVP ŽA and B. and GRP ŽC. in the SNC of A. niloticus.

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At each time point, Fos-IR cells were present in all areas of the SCN ŽFig. 2., but regional differences in the density of labeled cells were apparent during the light phase when the overall concentration of Fos-IR was highest ŽFig. 2, left.. At these times, labeled cells were evenly distributed within the most rostral portion of the SCN, but in middle and caudal sections Fos-IR cells were most concentrated in the ventral, medial and dorsal SCN, and were relatively sparse in the central-lateral region ŽFig. 2, left.. During the dark phase, when the number of Fos-IR cells was low, Fos-IR cells were generally scattered evenly through the SCN and were not obviously concentrated in any one area ŽFig. 2, right.. 3.2. Experiment 2: double labeling The distribution of Fos-IR cells within the SCN that was observed in Expt. 1 suggested extensive overlap with the dorsal region which contains VP-IR cells, and relatively little overlap with the mid-lateral region which contains GRP-IR neurons ŽSmale and Boverhof, unpublished observations.. In this experiment we therefore examined double labeling of Fos and these two SCN peptides. Interestingly, there was clear and extensive Fos expression within VP-IR neurons ŽFig. 3 A,B.. For the three males the average Ž"S.E.M.. percent of VP-IR cells containing FosIR was 29.8 " 3.8%; for the female this value was 31.8%. For the three males, 7.0 " 3.2% of Fos neurons contained AVP-IR; for the female this value was 4.9%. Unlike VP-IR neurons, GRP-IR neurons contained almost no Fos ŽFig. 3 C.. Of a total of 403 GRP-IR neurons counted in the eight animals from the two time points, only two Ž0.5%. contained Fos; this represents a negligible proportion of the 3825 Fos-IR neurons counted in these animals. Both of the double-labeled cells came from animals sacrificed at ZT 17.

4. Discussion In the first experiment the concentration of Fos-IR cells in the SCN of A. niloticus was higher during the light hours than during the dark hours, and the transition from ZT 21 to ZT 1 was marked by a dramatic increase in Fos-IR. The number of Fos-IR cells in the SCN was highest at ZT 1, lower at ZT 5 and ZT 9, and still lower during the dark phase of a 12:12 LD cycle ŽZT 13, 17, 21.. A slight decrease in the levels of Fos-IR occurred over the course of the dark period, but this was not significant. The overall pattern of change in Fos-IR in the SCN of A. niloticus was thus quite similar to that found in the SCN of nocturnal rodents kept in a 12:12-h LD cycle w3,7,9,23,24x. As in rats, Fos-IR was higher during the light period than during the dark. One difference between these two species was that in A. niloticus Fos-IR was highest at ZT 1 and decreased progressively thereafter, whereas in

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rats, Fos-IR did not begin to decrease until after ZT 5, and did not drop as dramatically during the dark hours relative to the light hours as in A. niloticus w23x. It seems unlikely that this difference is related to fundamental differences between nocturnal and diurnal animals because mice, nocturnal mammals, are more similar to A. niloticus than to rats in this respect. Specifically, In the mouse, 6 h after the lights come on, Fos-IR levels are already as low as they are during the dark hours of a 12:12-h LD cycle w7x. Thus, Fos expression in the SCN increases after lights on in A. niloticus and nocturnal rodents, but the pattern of Fos expression after this initial increase varies somewhat from species to species, irrespective of whether the animal is nocturnal or diurnal. These minor differences may be due to a difference in the rate of decline of Fos after the lights come on or to differences in the production of new Fos during the light period. The functional consequence of these species differences are unclear, and they do not correlate with differences along a nocturnal–diurnal dimension in any obvious way. It seems likely that photic stimulation at the beginning of the light period is the cause of the peak in Fos expression observed at this time in A. niloticus. In both nocturnal and diurnal species, pulses of light in the early subjective day produce phase advances in circadian rhythms w31,36x. This is also the case in A. niloticus ŽBult and Smale, unpublished observations.. In both nocturnal and diurnal rodents, pulses of light at this time also induce Fos expression within the SCN. To clearly establish if this is the case in A. niloticus, Fos expression will have to be examined in animals housed in DD and exposed to light pulses Žor not. at different circadian times. The SCN of nocturnal and diurnal mammals exhibits similar rhythms in glucose utilization and firing rates, with peaks occurring during the light phase, or subjective day w13,19,25,37,42x. If this is the case in A. niloticus, which seems likely, then the heightened Fos expression throughout the light phase reported here could be functionally coupled to elevated daytime activity of SCN cells. That is, heightened metabolism andror electrical activity could result in Fos induction during the day, which could, in turn, up regulate the transcription of proteins or peptides whose stores are depleted during this time w32x. Although the temporal pattern of Fos-IR in the SCN is similar in diurnal and nocturnal rodents, its spatial pattern is quite different. In A. niloticus, retinal inputs are distributed throughout the SCN, although they are most densely concentrated in the most ventral aspect of its rostral half, and in the central and lateral aspects of its caudal half ŽSmale and Boverhof, unpublished data.. Thus, the relative density of Fos-IR cells does not correlate with the relative density of retinal fibers, as it does in rats w35x. In A. niloticus, VIP cells are most concentrated in the ventral portion of the SCN; AVP cells are found throughout the dorsal half of the SCN, but also extend into its medial and lateral regions. Cells containing GRP and

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corticotrophin releasing factor ŽCRF. are found in the ventral SCN but are also concentrated in the mid-region of the caudal SCN ŽSmale and Boverhof, unpublished data.. Thus, during the light period, when the number of Fos-IR cells is highest, Fos is relatively scarce in the region containing the highest concentration of GRP and CRF, and Fos is relatively concentrated in regions containing both VP and VIP. In rats, by contrast, Fos is most densely concentrated in the region of the SCN containing VIP and GRP, and is relatively sparse in the region containing VP w11,34x. The spatial distribution of Fos-IR cells within the SCN of A. niloticus suggests that different populations of cells express Fos in this species than in nocturnal rodents. This hypothesis was supported by data from Expt. 2. Whereas Fos has been reported in 40% of GRP-IR neurons in the SCN of rats w11x, we found Fos in only two of 403 GRP-IR neurons Ž- 1%. in the SCN of A. niloticus. This result does not reflect a problem in staining for Fos, as a total of 3825 Fos-IR neurons was counted in the SCN of these animals. By contrast, Fos has rarely been seen in AVP-IR neurons in the SCN of rats w11,29x, but was found in approximately 30% of AVP-IR neurons in the SCN of A. niloticus. Thus, the pattern of co-expression of Fos within AVP-IR and GRP-IR neurons in the SCN appears to be reversed in the diurnal species, A. niloticus, compared to the nocturnal species, R. norÕegicus. These results suggest, for the first time, a difference in SCN function in nocturnal and diurnal species. It is important to note, however, that the results reported here for A. niloticus are not strictly comparable to results reported from double-labeling studies on the SCN of laboratory rats, because in the current study animals were housed in a 12:12-h LD cycle. This procedure was employed because our central aim is to identify the neural mechanisms responsible for diurnality, a pattern most apparent in the context of a 24-hour lightrdark cycle. In contrast, all of the double-labeling studies that have been done in nocturnal rats have examined animals held in constant darkness and pulsed with light during the photosensitive phase. It is possible that Fos is expressed in different subpopulations of neurons, and serves different functions, in these two different contexts. Therefore, to determine if the nocturnal and diurnal animals are really fundamentally different with respect to which SCN neurons express Fos, it will be important to examine doublelabeling of Fos and SCN peptides in rats kept on a 12:12-h LD cycle, and in A. niloticus kept in DD and pulsed with light. These studies are currently under way. These results also point to the need to examine co-expression of Fos and SCN peptides other than GRP and VP in diurnal species. In rats, some of the Fos-containing neurons also express peptide histamine isoleucine w29x, approximately 1% contain VIP w11x, and 5–10% contain glial fibrillary acidic protein and are astrocytes w4x. In the hamster SCN approximately 40% of Fos is found in

neurons that contain calbindin w46x. The variety of cells in which Fos is expressed suggests that it may play multiple roles in the control of circadian rhythms. It is important to determine whether these roles are similar or different in nocturnal and diurnal species. Additional evidence that the function of Fos expression within the SCN may be different in nocturnal and diurnal species comes from a report of Fos in the SCN of diurnal chipmunks w1x. Specifically, whereas Fos appears to play a role in photic entrainment in nocturnal rodents, there is some evidence that this may not be the case in the chipmunk. Fos expression is induced in the SCN of nocturnal rodents only by light pulses during times that light can phase shift the circadian system w3,34,38x, and antisense oligos that block Fos synthesis in the SCN also block light-induced phase shifts w52x. Although light-induced Fos can be dissociated from light-induced phase shifts by pharmacological treatments w12,34x, these events have always been tightly coupled in unmanipulated nocturnal rodents Žrat: w34x; mouse: w7x; hamster: w6,35x.. This was not the case in the diurnal chipmunk Ž Eutamias asiaticus . w1x. In this species the induction of Fos by light pulses was higher during the subjective night than day, as in nocturnal rodents, but none of these light pulses induced phase shifts in locomotor activity rhythms w1x. Thus, although light induces Fos expression in a time dependent manner in both diurnal and nocturnal rodents, it remains possible that Fos ordinarily mediates photic entrainment in nocturnal species but not diurnal species. In summary, Fos expression in the SCN responds similarly to the environmental light cycle in the diurnal rodent A. niloticus and nocturnal rodents. Fos-IR is high in the SCN during the light hours compared to the dark hours in the rat, hamster, mouse and A. niloticus. There are some minor differences between species with respect to precise details of the pattern of the rhythm in Fos-IR cell number. Most importantly, however, A. niloticus appears to differ from the nocturnal species with respect to the distribution of Fos relative to other peptides within the SCN. Specifically, whereas no VP-IR containing neurons in the SCN of nocturnal rodents express Fos, a substantial proportion of these neurons express Fos in A. niloticus. By contrast, a sizeable number of GRP neurons contain Fos in rats, whereas none of these neurons express Fos in A. niloticus. This is the first indication that the SCN may function differently in nocturnal and diurnal species.

Acknowledgements We are grateful to Antonio Nunez, Cheryl Sisk and Kay Holekamp for comments on an earlier draft of the manuscript. This work was supported by NIMH Grant RO1 MH534rNS534433-01, and by the Neuroscience Training Program at Michigan State University.

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References w22x w1x H. Abe, S. Honma, K. Shinohara, K.I. Honma, Circadian modulation in photic induction of Fos-like immunoreactivity in the suprachiasmatic nucleus cells of diurnal chipmunk Eutamias asiaticus, J. Comp. Physiol. A 176 Ž1995. 159–167. w2x H.E. Albers, E.G. Stopa, R.T. Zoeller, J.S. Kauer, J.C. King, F.S. Fink, H. Mobtaker, H. Wolfe, Day–night variation in prepro vasoactive intestinal peptiderpeptide histidine isoleucine mRNA within the rat suprachiasmatic nucleus, Mol. Brain Res. 7 Ž1990. 85–89. w3x N. Aronin, S.M. Sagar, F.R. Sharp, W.J. Schwartz, Light regulates expression of a Fos-related protein in rat suprachiasmatic nuclei, Proc. Natl. Acad. Sci. USA 87 Ž1990. 5959–5962. w4x M.R. Bennett, W.J. Schwartz, Are glia among the cells that express immunoreactive c-Fos in the suprachiasmatic nucleus?, Neuroreport 5 Ž1994. 1737–1740. w5x J.P. Card, R.Y. Moore, Organization of lateral geniculate-hypothalamic connection in the rat, J. Comp. Neurol. 284 Ž1989. 402–406. w6x I. Chambille, S. Doyle, J. Serviere, Photic induction and circadian expression of Fos-like protein. Immunohistochemical study in the retina and suprachiasmatic nuclei of hamster, Brain Res. 612 Ž1993. 138–150. w7x C.S. Colwell, R.G. Foster, Photic regulation of Fos-like immunoreactivity in the suprachiasmatic nucleus of the mouse, J. Comp. Neurol. 324 Ž1992. 135–142. w8x D.J. Earnest, C.D. Sladek, Circadian vasopressin release from perfused rat suprachiasmatic explants in vitro: Effects of acute stimulation, Brain Res. 422 Ž1987. 398–402. w9x D.J. Earnest, M. Iadarola, H.H. Yeh, J.A. Olschowka, Photic regulation of c-fos expression in neuronal components governing the entrainment of circadian rhythms, Exp. Neurol. 109 Ž1990. 353–361. w10x D.J. Earnest, S. Ouyang, J.A. Olschowka, Rhythmic expression of Fos-related proteins within the rat suprachiasmatic nucleus during constant retinal illumination, Neurosci. Lett. 140 Ž1992. 19–24. w11x D.J. Earnest, S. DiGiorgio, J.A. Olschowka, Light induces expression of fos-related proteins within gastrin-releasing peptide neurons in the rat suprachiasmatic nucleus, Brain Res. 627 Ž1993. 205–209. w12x D.J. Earnest, J.A. Olschowka, Circadian regulation of c-fos expression in the suprachiasmatic pacemaker by light, J. Biol. Rhythms 8 Ž1993. S65–S71. w13x M.U. Gillette, S.M. Reppert, The hypothalamic suprachiasmatic nuclei: Circadian patterns of vasopressin secretion and neuronal activity in vitro, Brain Res. Bull. 19 Ž1987. 135–139. w14x D.J. Green, R. Gillette, Circadian rhythm of firing rate recorded from single cells in the rat suprachiasmatic brain slice, Brain Res. 245 Ž1982. 198–200. w15x G.A. Groos, J.H. Meijer, Effects of illumination on suprachiasmatic nucleus electrical discharge, Ann. NY Acad. Sci. 453 Ž1985. 134– 146. w16x M.E. Harrington, D.M. Nance, B. Rusak, Double-labeling of neuropeptide Y-immunoreactive neurons which project from the geniculate to the suprachiasmatic nuclei, Brain Res. 410 Ž1987. 275–282. w17x M.A. Hofman, D.F. Swaab, Diurnal and seasonal rhythms of neuronal activity in the suprachiasmatic nucleus of humans, J. Biol. Rhythms 8 Ž1993. 283–295. w18x O.C. Ikonomov, A.G. Stoynev, Gene expression in suprachiasmatic nucleus and circadian rhythms, Neurosci. Biobehav. Rev. 18 Ž1994. 305–312. w19x S.I.T. Inouye, H. Kawamura, Persistence of circadian rhythmicity in a mammalian hypothalamic ‘island’ containing the suprachiasmatic nucleus, Proc. Natl. Acad. Sci. USA 76 Ž1979. 5962–5966. w20x S.J.T. Inouye, H. Kawamura, Characteristics of a circadian pacemaker in the suprachiasmatic nucleus, J. Comp. Physiol. 146 Ž1982. 153–160. w21x M. Jhanwar-Uniyal, B. Beck, C. Burlet, S.F. Leibowitz, Diurnal rhythm of neuropeptide-Y-like immunoreactivity in the suprachias-

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w43x

33

matic, arcuate, paraventricular nuclei and other hypothalamic sites, Brain Res. 536 Ž1990. 331–334. C. Katona, L. Smale, Running-wheel rhythms in the diurnal rodent ArÕicanthis niltocius, in: Meetings for the Society for Research on Biological Rhythms, 1994. J. Kononen, J. Koistinaho, H. Alho, Circadian rhythm in c-fos like immunoreactivity in the rat brain, Neurosci. Lett. 120 Ž1990. 105– 108. J.M. Kornhauser, D.W. Nelson, K.E. Mayo, J.S. Takahashi, Photic and circadian regulation of c-fos gene expression in the hamster suprachiasmatic nucleus, Neuron 5 Ž1990. 127–134. S. Kurumiya, H. Kawamura, Circadian oscillation of multiple unit activity in the guinea pig suprachiasmatic nucleus, J. Comp. Physiol. 162 Ž1988. 301–308. M.N. Lehman, R. Silber, E.L. Bittman, Anatomy of SCN grafts, in: D. Klein, R.Y. Moore ŽEds.., The Suprachiasmatic Nucleus: The Mind’s Clock, Oxford University Press, New York, 1991, pp. 349–374. I. Loren, P.C. Emson, J. Fahrenkrug, A. Bjorklund, J. Alumets, R. Hakanson, F. Sundler, Distribution of vasoactive intestinal polypeptide in the rat and mouse brain, Neuroscience 4 Ž1979. 1953–1976. T.M. McElhinny, L. Smale, K.E. Holekamp, Patterns in body temperature, activity and reproductive behavior in a tropical murid rodent, ArÕicanthis Niloticus, Physiol. Behav. 62 Ž1997. 91–96. J.D. Mikkelsen, P.J. Larsen, G.G. Sorensen, D. Woldbye, T.G. Bolwig, M.H. Hastings, F.J.P. Ebling, A dual-immunocytochemical method to localize c-fos protein in specific neurons based on their content of neuropeptides and connectivity, Histochemistry 101 Ž1994. 245–251. R.Y. Moore, N.J. Lenn, A retinohypothalamic projection in the rat, J. Comp. Neurol. 146 Ž1972. 1–14. M.C. Moore-Ede, F.M. Sulzman, C.A. Fuller, The Clocks That Time Us, Harvard University Press, 1983. J.I. Morgan, T. Curran, Immediate-early genes: ten years on, Trends Neurosci. 18 Ž1995. 66–67. A. Morin, Denroy, M. Jouvet, Daily variations in concentration of vasoactive intestinal polypeptide immunoreactivity in discrete brain areas of the rat, Brain Res. 538 Ž1991. 136–140. M.A. Rea, Light increases fos-related protein immunoreactivity in the rat suprachiasmatic nuclei, Brain Res. Bull. 23 Ž1989. 577–581. M.A. Rea, Different populations of cells in the suprachiasmatic nuclei express c-fos in association with light-induced phase delays and advances of the free-running activity rhythm in hamsters, Brain Res. 579 Ž1992. 107–112. M.A. Rea, A.M. Michel, L.M. Lutton, Is Fos expression necessary and sufficient to mediate light-induced phase advances of the suprachiasmatic circadian oscillator?, J. Biol. Rhythms 8 Ž1993. S59–S64. N.F. Ruby, H.C. Heller, Temperature sensitivity of the suprachiasmatic nucleus of ground squirrels and rats in vitro, J. Biol. Rhythms 11 Ž1996. 126–136. B. Rusak, H.A. Robertson, W. Wisden, S.P. Hunt, Light pulses that shift rhythms induce gene expression in the suprachiasmatic nucleus, Science 248 Ž1990. 1237–1240. B. Rusak, I. Zucker, Biological rhythms and animal behavior, Annu. Rev. Psych. 26 Ž1979. 137–171. W.J. Schwartz, Suprachiasmatic nucleus: Use of 14 C-labeled deoxyglucose uptake as a functional marker, Science 197 Ž1977. 1089–1091. W.J. Schwartz, L.C. Davidsen, C.B. Smith, In vivo metabolic activity of a putative circadian oscillator, J. Comp. Neurol. 189 Ž1980. 157–167. W.J. Schwartz, S.M. Reppert, S.M. Eagan, M.C. Moore-Ede, In vivo metabolic activity of the suprachiasmatic nuclei: A comparative study, Brain Res. 274 Ž1983. 184–187. W.J. Schwartz, J. Takeuchi, W. Shannon, E.M. Davis, N. Aronin, Temporal regulation of light-induced Fos and Fos-like protein ex-

34

w44x

w45x

w46x

w47x

w48x

C. Katona et al.r Brain Research 791 (1998) 27–34 pression in the ventrolateral subdivision of the rat suprachiasmatic nucleus, Neuroscience 58 Ž1994. 573–583. S. Shibata, Y. Oomura, H. Kita, K. Hattori, Circadian rhythmic changes of neuronal activity in the suprachiasmatic nucleus of the rat hypothalamic slice, Brain Res. 247 Ž1982. 154–158. K. Shinohara, K. Tomihaga, Y. Isobe, S.I.T. Inouye, Photic regulation of peptides located in the ventrolateral subdivision of the suprachiasmatic nucleus of the rat: Daily variations of vasoactive intestinal peptide, gastrin-releasing peptide and neuropeptide-Y, J. Neurosci. 13 Ž1993. 793–800. R. Silver, J. LeSauter, P.A. Tresco, M.N. Lehman, A diffusible coupling signal from the transplanted suprachiasmatic nucleus controlling circadian locomotor rhythms, Nature 382 Ž1996. 810–813. M.W. Sofroniew, A. Weindl, Identification of parvocellular vasopressin and neurophysin neurons in the suprachiasmatic nucleus of a variety of mammals including primates, J. Comp. Neurol. 193 Ž1988. 659–675. E.G. Stopa, K.N. Minamitani, J.A. Jonassen, J.C. King, H. Wolfe, H. Mobtaker, H.E. Albers, Localization of vasoactive intestinal

w49x

w50x

w51x

w52x

peptide and peptide histidine isoleucine immunoreactivity and mRNA within the rat suprachiasmatic nucleus, Mol. Brain Res. 4 Ž1988. 319–325. Y. Takahashi, H. Okamura, N. Yanaihara, S. Hamada, S. Fujita, Y. Ibata, Vasoactive intestinal peptide immunoreactive neurons in the rat suprachiasmatic nucleus demonstrate diurnal variation, Brain Res. 497 Ž1989. 374–377. G.R. Uhl, S.M. Reppert, Suprachiasmatic nucleus vasopressin messenger RNA: Circadian variation in normal and Brattleboro rats, Science 232 Ž1986. 390–393. R.E. Watson, S.J. Wiegand, R.W. Clough, Use of cryoprotectant to maintain long-term peptide immunoreactivity and tissue morphology, Peptides 7 Ž1986. 155–159. F. Wollnik, W. Brysch, E. Uhlmann, F. Gillardon, R. Bravo, M. Zimmermann, K.H. Schlingensiepen, T. Herdegen, Block of c-Fos and JunB expression by antisense oligonucleotides inhibits light-induced phase shifts of the mammalian circadian clock, Eur. J. Neurosci. 7 Ž1995. 388–393.