Evidence for a role of GABA and Mas-allatotropin in photic entrainment of the circadian clock of the cockroach Leucophaea maderae

SUMMARY Accumulating evidence suggests that the accessory medulla is the location of the circadian pacemaker in the fruit fly Drosophila melanogasterand the cockroach Leucophaea maderae. γ-Aminobutyric acid(GABA) and Mas-allatotropin are two putative neurotransmitters, in the accessory medulla in the cockroach Leucophaea maderae. Neurons immunoreactive to the neuropeptide Mas-allatotropin are local neurons with arborizations in the noduli of the accessory medulla, while GABA-immunoreactive neurons connect the noduli of the accessory medulla to the medulla and to the lamina via processes in the distal tract. Injections of GABA and Mas-allatotropin into the vicinity of the accessory medulla resulted in stable phase-dependent resetting of the circadian locomotor activity of the cockroach. The resulting phase response curves closely matched light-dependent phase response curves, suggesting that both substances play a role in circuits relaying photic information from circadian photoreceptors to the central pacemaker.

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Gap Junctions Between Accessory Medulla Neurons Appear to Synchronize Circadian Clock Cells of the Cockroach Leucophaea maderae

Journal of Neurophysiology ◽

10.1152/jn.00835.2005 ◽

2006 ◽

Vol 95 (3) ◽

pp. 1996-2002 ◽

Cited By ~ 20

Author(s):

Nils-Lasse Schneider ◽

Monika Stengl

Keyword(s):

Gap Junctions ◽

Circadian Clock ◽

Phase Difference ◽

Temporal Organization ◽

Stable Phase ◽

Circadian Pacemaker ◽

Potential Oscillations ◽

Synaptic Release ◽

Accessory Medulla ◽

Leucophaea Maderae

The temporal organization of physiological and behavioral states is controlled by circadian clocks in apparently all eukaryotic organisms. In the cockroach Leucophaea maderae lesion and transplantation studies located the circadian pacemaker in the accessory medulla (AMe). The AMe is densely innervated by γ-aminobutyric acid (GABA)–immunoreactive and peptidergic neurons, among them the pigment-dispersing factor immunoreactive circadian pacemaker candidates. The large majority of cells of the cockroach AMe spike regularly and synchronously in the gamma frequency range of 25–70 Hz as a result of synaptic and nonsynaptic coupling. Although GABAergic coupling forms assemblies of phase-locked cells, in the absence of synaptic release the cells remain synchronized but fire now at a stable phase difference. To determine whether these coupling mechanisms of AMe neurons, which are independent of synaptic release, are based on electrical synapses between the circadian pacemaker cells the gap-junction blockers halothane, octanol, and carbenoxolone were used in the presence and absence of synaptic transmission. Here, we show that different populations of AMe neurons appear to be coupled by gap junctions to maintain synchrony at a stable phase difference. This synchronization by gap junctions is a prerequisite to phase-locked assembly formation by synaptic interactions and to synchronous gamma-type action potential oscillations within the circadian clock.

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Two families of phase-response curves characterize the resetting of the hamster circadian clock

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1992.262.6.r1149 ◽

1992 ◽

Vol 262 (6) ◽

pp. R1149-R1153 ◽

Cited By ~ 6

Author(s):

R. D. Smith ◽

F. W. Turek ◽

J. S. Takahashi

Keyword(s):

Golden Hamster ◽

Phase Response ◽

Phase Shifting ◽

Circadian Pacemaker ◽

Test Statistics ◽

Response Curves ◽

Phase Response Curves ◽

Light Pulses ◽

Circular Test ◽

The Common

Phase-response curves (PRCs) have been reported for a wide variety of agents that induce phase shifts in the circadian rhythm of locomotor activity in the golden hamster. Many of these PRCs appear to be quite similar to one another. Because of the important role that the interpretation of PRCs has played in understanding the dynamics of the mammalian circadian pacemaker, a review of PRCs for the golden hamster reported from 1964 to 1991 was conducted to systematically summarize the common characteristics among these PRCs. Plots of phases associated with the peak of the advance portions, or of phases associated with the transitions between the delay and advance portion of the PRCs, revealed bimodal distributions of PRCs 11-13 h apart. Mardia-Watson-Wheeler circular test statistics indicated that the PRCs were distributed as two distinct populations. PRCs were either characteristic of those for light pulses (L-PRCs), or of those for dark pulses (D-PRCs). Taken with anatomical and physiological evidence, these data suggest that either one or two final common pathways may exist to mediate the phase-shifting effects of different stimuli.

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