Hypothalamic circuits and circadian rhythms: Effects of knife cuts vary with their placement within the suprachiasmatic area

doi:10.1016/0361-9230(86)90142-5

Brain Research Bulletin

Volume 16, Issue 5, May 1986, Pages 705-711

https://doi.org/10.1016/0361-9230(86)90142-5 Get rights and content

Abstract

The suprachiasmatic nucleus (SCN) of the hypothalamus and its efferent projections are necessary for the generation of circadian rhythms. To further investigate the role of SCN connections in the generation of behavioral rhythms, intact and blinded-castrated male rats housed in constant conditions were given horizontal knife cuts aimed dorsal to the SCN, or sham surgery. Rhythms of locomotor activity and drinking behavior were monitored using a microcomputer. Cuts that spared the SCN failed to abolish rhythms. Effects of cuts that damaged the SCN ranged from changes in period length of the rhythms to abolition of drinking rhythms. These and previous results indicate that connections between the SCN and the paraventricular nucleus of the hypothalamus are not necessary for the expression of behavioral rhythms.

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Cited by (16)

Biological timekeeping
2012, Sleep Medicine Clinics
Citation Excerpt :
When the SCN is surgically isolated from the rest of the hypothalamus in rats, serum corticosterone oscillations continue, whereas locomotor rhythms are lost.154 In addition, surgical cuts to rodent brains between the SCN and PVN abolish reproductive rhythms in hamsters, but rhythmic locomotor activity is maintained in hamsters155,156 and rats.157 These findings provide early evidence for both synaptic coupling of SCN to output tissues, as well as the possibility that humoral signals entrain peripheral tissues.
Lesions of suprachiasmatic nucleus efferents selectively affect rest-activity rhythm
2006, Molecular and Cellular Endocrinology
The suprachiasmatic nucleus (SCN) of the hypothalamus controls circadian rhythms in behavioral, neuroendocrine and physiological functions. In this study, we test the hypothesis that caudal SCN efferents to the subparaventricular zone (SPVZ) control the rhythm in rest-activity (R-A) through projections on posterior hypothalamic area arousal systems (PHA). Small electrolytic lesions of the ventral SPVZ cause a selective loss of the circadian R-A rhythm, sparing the core body temperature rhythm. In contrast, large excitotoxic lesions of the posterior hypothalamic area (PHA) that effectively ablate populations of hypocretin and melanin concentrating hormone neurons projecting to cortex and subcortical arousal areas decrease R-A rhythm amplitude but do not disrupt circadian regulation. Since dorsomedial hypothalamic nucleus lesions have effects similar to PHA lesions (Chou, T.C., Scammell, T.E., Gooley, J.J., Gaus, S.E., Saper, C.B., Lu, J., 2003. Critical role of dorsomedial hypothalamic nucleus in a wide range of behavioral circadian rhythms. J. Neurosci. 23:10691–10702), these data support the view that the SPVZ is the principal relay nucleus for SCN signals to the multiple posterior hypothalamic arousal systems involved in generation of the R-A rhythm.
Temporal and spatial distribution of immunoreactive PER1 and PER2 proteins in the suprachiasmatic nucleus and peri-suprachiasmatic region of the diurnal grass rat (Arvicanthis niloticus)
2006, Brain Research
Citation Excerpt :
In laboratory rats, chemical lesions that destroy cells in the region but spare SCN cells and their axonal projections do not interfere significantly with body temperature rhythms but do interfere with activity rhythms (Lu et al., 2001); this effect could reflect either circadian mechanisms or masking. On the other hand, knife cuts that sever connections between the SCN and LSPV in laboratory rats do not appear to interfere with rhythms (Brown and Nunez, 1986). One potential explanation of this paradox is that a diffusible factor from the SCN may communicate circadian signals to the LSPV.
The suprachiasmatic nucleus (SCN) of the hypothalamus contains the primary circadian pacemaker in both diurnal and nocturnal mammals. The lower subparaventricular zone (LSPV) immediately dorsal to the SCN may also play an important role in the regulation of circadian rhythms. The SCN contains a multitude of oscillator cells that generate circadian rhythms through transcriptional/translational feedback loops involving a set of clock genes including per1 and per2. Little is known about the temporal and spatial features of the proteins encoded by these genes in day-active mammals. The first objective of this study was to characterize the expression of PER1 and PER2 in the SCN of a diurnal rodent, the unstriped Nile grass rat (Arvicanthis niloticus). The second objective was to evaluate the hypothesis that a molecular clock could exist in the LSPV, where endogenous rhythms in Fos expression are seen in grass rats but not in laboratory rats. Animals were kept on a 12:12 light/dark cycle and perfused at 4-h intervals, and their brains were processed for immunohistochemical detection of PER1 and PER2. Both proteins were seen in the SCN where they peaked early in the dark phase, providing further evidence that the differences between diurnal and nocturnal patterns of behavior emerge from mechanisms lying downstream from the pacemaker within the SCN. Rhythmic expression of PER1 and PER2 was also seen in the LSPV providing support for the hypothesis that this region might participate in circadian time keeping in the diurnal grass rat. In addition, rhythms were seen lateral to the LSPV and the SCN. Results of this study are discussed in light of similarities and differences in the circadian time-keeping systems of day- and night-active animals.
Differences in the suprachiasmatic nucleus and lower subparaventricular zone of diurnal and nocturnal rodents
2004, Neuroscience
Diurnal and nocturnal species are profoundly different in terms of the temporal organization of daily rhythms in physiology and behavior. The neural bases for these divergent patterns are at present unknown. Here we examine functional differences in the suprachiasmatic nucleus (SCN) and one of its primary targets in a diurnal rodent, the unstriped Nile grass rat (Arvicanthis niloticus) and in a nocturnal one, the laboratory rat (Rattus norvegicus). Grass rats and laboratory rats were housed in a 12:12 light:dark cycle, and killed at six time points. cFos-immunoreactive rhythms in the SCN of grass rats and laboratory rats were similar to those reported previously, with peaks early in the light phase and troughs in the dark phase. However, cFos-immunoreactivity in the lower subparaventricular zone (LSPV) of grass rats rose sharply 5 h into the dark phase, and remained high through the first hour after light onset, whereas in laboratory rats it peaked 1 h after light onset and was low at all other sampling times. Daily cFos rhythms in both the SCN and the LSPV persisted in grass rats, but not in laboratory rats, after extended periods in constant darkness. In grass rats, the endogenous cFos rhythm in the LSPV, but not the SCN, was present both in calbindin-positive and in calbindin-negative cells. Cells that expressed cFos at night in the region of the LSPV in grass rats were clearly outside of the boundaries of the SCN as delineated by Nissl stain and immunoreactivity for vasopressin and vasoactive intestinal peptide.
The LSPV of the grass rat, a region that receives substantial input from the SCN, displays a daily rhythm in cFos expression that differs from that of laboratory rats with respect to its rising phase, the duration of the peak and its dependence on a light/dark cycle. These characteristics may reflect the existence of mechanisms in the LSPV that enable it to modulate efferent SCN signals differently in diurnal and nocturnal species.
Effects of damage to SCN neurons and efferent pathways on circadian activity rhythms of hamsters
1993, Brain Research Bulletin
This experiment was designed to determine if entrainment to a light:dark (LD) schedule and the free-running rhythm in constant light are altered by partial lesions of suprachiasmatic nuclei (SCN) cells or SCN output pathways. Twenty-four male golden hamsters were housed under 12L:12D. Hamsters received either lesions (n = 16), sham surgery (n = 4), or no surgery (n = 4), and were placed into individual cages with running wheels under 14L: 10D. Each time after 4 weeks, the LD schedule was phase advanced by 6 h, phase delayed by 6 h, and then the animals were exposed to constant dim light. At the end of the experiment, brain sections were processed for peptide histidine isoleucine (PHI) and gastrin releasing peptide (GRP) immunohistochemistry. Alternate sections were stained for cells and fibers. Behavioral results indicate that (a) very few SCN cells and SCN efferent fibers, as labeled by PHI and GRP immunohistochemistry, are necessary for the expression of circadian rhythmicity in wheel running, and (b) damage to pathways rostral to the SCN may be more critical for entrainment and rhythmicity than damage to caudal pathways. Targets of PHI- and GRP-immunoreactive SCN efferent fibers were also identified.
Effects of aging on the diurnal pattern of water intake in rats
1992, Behavioral and Neural Biology
This study was undertaken to confirm previous findings that Long—Evans rats exhibit age-related changes in the diurnal/nocturnal distribution of water intake and to examine the circadian pattern of these age-related changes. Twenty-one aged and 10 young pathogen-free rats were continuously monitored for water consumption over 12:12 h light/dark cycles. ANOVA, profile analysis, and cosinor analysis each demonstrated that aged rats differed from young rats. The age-related changes in circadian pattern can be described as a blunted rhythm (decreased amplitude) and an altered timing of peak activity (advanced acrophase). These differences, however, were only apparent in a subset of aged rats with the remaining aged rats exhibiting a circadian pattern indistinguishable from that of the young group.

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^☆: Portions of these results were presented at the 13th Annual Meeting of the Society for Neuroscience, November 1983, Boston, MA, Abstract 312.15.

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Hypothalamic circuits and circadian rhythms: Effects of knife cuts vary with their placement within the suprachiasmatic area☆

Abstract

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