Selective deficits in the circadian light response in mice lacking PACAP
Department of Psychiatry and Biobehavioural Sciences, University of California, Los Angeles, Los Ángeles, California, United States AJP Regulatory Integrative and Comparative Physiology
(Impact Factor: 3.11).
12/2004; 287(5):R1194-201. DOI: 10.1152/ajpregu.00268.2004
Previous studies indicate that light information reaches the suprachiasmatic nucleus through a subpopulation of retinal ganglion cells that contain both glutamate and pituitary adenylyl cyclase-activating peptide (PACAP). Although the role of glutamate in this pathway has been well studied, the involvement of PACAP and its receptors is only beginning to be understood. To investigate the functions of PACAP in vivo, we developed a mouse model in which the gene coding for PACAP was disrupted by targeted homologous recombination. RIA was used to confirm a lack of detectable PACAP protein in these mice. PACAP-deficient mice exhibited significant impairment in the magnitude of the response to brief light exposures with both light-induced phase delays and advances of the circadian system impacted. This mutation equally impacted phase shifts induced by bright and dim light exposure. Despite these effects on phase shifting, the loss of PACAP had only limited effects on the generation of circadian oscillations, as measured by rhythms in wheel-running activity. Unlike melanopsin-deficient mice, the mice lacking PACAP exhibited no loss of function in the direct light-induced inhibition of locomotor activity, i.e., masking. Finally, the PACAP-deficient mice exhibited normal phase shifts in response to exposure to discrete dark treatments. The results reported here show that the loss of PACAP produced selective deficits in the light response of the circadian system.
Available from: Christopher S Colwell
- "Mice were entrained to a 12∶12 hr light:dark (LD) cycle for a minimum of 2 weeks prior to collection of 10–14 days of data under LD conditions, followed by 10–14 days in constant darkness (DD) to obtain free-running activity. The behavioral response to a phase delaying 10 min pulse of light (100 lux at cage level) at circadian time (CT) 16 was measured as previously described , . Following these assays, the mice were entrained to 12∶12 LD for a minimum of 14 days. "
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ABSTRACT: Sleep and circadian disruptions are commonly reported by patients with neurodegenerative diseases, suggesting these may be an endophenotype of the disorders. Several mouse models of Huntington's disease (HD) that recapitulate the disease progression and motor dysfunction of HD also exhibit sleep and circadian rhythm disruption. Of these, the strongest effects are observed in the transgenic models with multiple copies of mutant huntingtin gene. For developing treatments of the human disease, knock-in (KI) models offer advantages of genetic precision of the insertion and control of mutation copy number. Therefore, we assayed locomotor activity and immobility-defined sleep in a new model of HD with an expansion of the KI repeats (Q175). We found evidence for gene dose- and age-dependent circadian disruption in the behavior of the Q175 line. We did not see evidence for loss of cells or disruption of the molecular oscillator in the master pacemaker, the suprachiasmatic nucleus (SCN). The combination of the precise genetic targeting in the Q175 model and the observed sleep and circadian disruptions make it tractable to study the interaction of the underlying pathology of HD and the mechanisms by which the disruptions occur.
Available from: jneurosci.org
- "BrdU LIs were calculated as the BrdU-positive cells over total cells as described previously (Suh et al., 2001). Tissue from each embryo was used to determine genotype using touchdown PACAP PCR and primers described previously (Colwell et al., 2004). Cell cultures. "
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ABSTRACT: During corticogenesis, pituitary adenylate cyclase-activating polypeptide (PACAP; ADCYAP1) may contribute to proliferation control by activating PAC1 receptors of neural precursors in the embryonic ventricular zone. PAC1 receptors, specifically the hop and short isoforms, couple differentially to and activate distinct pathways that produce pro- or anti-mitogenic actions. Previously, we found that PACAP was an anti-mitogenic signal from embryonic day 13.5 (E13.5) onward both in culture and in vivo and activated cAMP signaling through the short isoform. However, we now find that mice deficient in PACAP exhibited a decrease in the BrdU labeling index (LI) in E9.5 cortex, suggesting that PACAP normally promotes proliferation at this stage. To further define mechanisms, we established a novel culture model in which the viability of very early cortical precursors (E9.5 mouse and E10.5 rat) could be maintained. At this stage, we found that PACAP evoked intracellular calcium fluxes and increased phospho-PKC levels, as well as stimulated G1 cyclin mRNAs and proteins, S-phase entry, and proliferation without affecting cell survival. Significantly, expression of hop receptor isoform was 24-fold greater than the short isoform at E10.5, a ratio that was reversed at E14.5 when short expression was 15-fold greater and PACAP inhibited mitogenesis. Enhanced hop isoform expression, elicited by in vitro treatment of E10.5 precursors with retinoic acid, correlated with sustained pro-mitogenic action of PACAP beyond the developmental switch. Conversely, depletion of hop receptor using short-hairpin RNA abolished PACAP mitogenic stimulation at E10.5. These observations suggest that PACAP elicits temporally specific effects on cortical proliferation via developmentally regulated expression of specific receptor isoforms.
Available from: Francis J P Ebling
- "The NMDA receptor can also contribute to non-glutamatergic pathways involved in the modulation of photic entrainment, such as those utilizing pituitary adenylyl cyclase activating peptide (PACAP), neuropeptide Y (NPY) and 5-hydroxytryptophan (5-HT) . In the case of PACAP, activation of PACAP receptors results in increased cyclic adenosine monophosphate (cAMP) and this then can activate NMDARs through phosphorylation on NR1 Ser897 . "
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ABSTRACT: Glutamate neurotransmission and the N-methyl-D-aspartate receptor (NMDAR) are central to photic signaling to the master circadian pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN). NMDARs also play important roles in brain development including visual input circuits. The functional NMDAR is comprised of multiple subunits, but each requiring the NR1 subunit for normal activity. The NR1 can be alternatively spliced to produce isoforms that confer different functional properties on the NMDAR. The SCN undergoes extensive developmental changes during postnatal life, including synaptogenesis and acquisition of photic signaling. These changes are especially important in the highly photoperiodic Siberian hamster, in which development of sensitivity to photic cues within the SCN could impact early physiological programming. In this study we examined the expression of NR1 isoforms in the hamster at different developmental ages. Gene expression in the forebrain was quantified by in situ hybridization using oligonucleotide probes specific to alternatively spliced regions of the NR1 heteronuclear mRNA, including examination of anterior hypothalamus, piriform cortex, caudate-putamen, thalamus and hippocampus. Gene expression analysis within the SCN revealed the absence of the N1 cassette, the presence of the C2 cassette alone and the combined absence of C1 and C2 cassettes, indicating that the dominant splice variants are NR1-2a and NR1-4a. Whilst we observe changes at different developmental ages in levels of NR1 isoform probe hybridization in various forebrain structures, we find no significant changes within the SCN. This suggests that a switch in NR1 isoform does not underlie or is not produced by developmental changes within the hamster SCN. Consistency of the NR1 isoforms would ensure that the response of the SCN cells to photic signals remains stable throughout life, an important aspect of the function of the SCN as a responder to environmental changes in quality/quantity of light over the circadian day and annual cycle.
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