Microinjection of carbachol into the rostral pontine tegmentum of the cat induces a state that is comparable to naturally occurring active (REM, rapid eye movement) sleep. We sought to determine, during this pharmacologically induced behavioral state, which we refer to as active sleep-carbachol, the distribution of activated neuron within the pons and medulla using c-fos immunocytochemistry as a functional marker. Compared with control cats, which were injected with saline, active sleep-carbachol cats exhibited higher numbers of c-fos-expressing neurons in (1) the medial and portions of the lateral reticular formation of the pons and medulla, (2) nuclei in the dorsolateral rostral pons, (3) various raphe nuclei, including the dorsal, central superior, magnus, pallidus, and obscurus, (4) the medial and lateral vestibular, prepositus hypoglossi, and intercalatus nuclei, and (5) the abducens nuclei. On the other hand, the mean number of c-fos-expressing neurons found in the masseter, facial, and hypoglossal nuclei was lower in carbachol-injected than in control cats. The data indicate that c-fos expression can be employed as a marker of state-dependent neuronal activity. The specific sites in which there were greater numbers of c-fos-expressing neurons during active sleep-carbachol are discussed in relation to the state of active sleep, as well as the functional role that these sites play in generating the various physiological patterns of activity that occur during this state.
The lateral eye of Limulus is innervated by an efferent system of fibers containing a substance P-like peptide. They were detected and their distribution was studied using indirect immunocytochemical techniques and monoclonal and serum antibodies. These thin, efferent fibers travel up the optic nerve, cross the lateral plexus, and branch out profusely when reaching the ommatidial layer. Innervation is extended to more than one component of the ommatidia, including the pigment, retinular, and eccentric cells. Immunoreactive staining could be abolished by absorbing the antisera with as little as 1 microM synthetic substance P. The efferent character of the fibers was established by means of ligation experiments, a technique also used to determine their origin in the circumesophageal connectives. Radioimmunoassay with two different C-terminal serum antibodies confirmed the presence of substance P-like material in the eye in the amounts of 61.44 pg/micrograms of protein, or up to 18 ng/eye. Gel filtration chromatography of crude extracts of the lateral eye, followed by radioimmunoassay, revealed an elution pattern extremely similar but not identical to that of synthetic substance P. These results show that a system of efferent fibers containing a substance P-like peptide originates in cells in the circumesophageal ring and innervates the ommatidia of the lateral eye. Their distribution and origin suggest an involvement in the modulation of photosensitivity, as part of a larger, generalized, level-setting regulator that is driven by a circadian clock but can also be activated by other systems.
A system of efferent substance P-like immunoreactive fibers innervates the ommatidia of the Limulus lateral eye. Thus, we tested the physiological effects of substance P on the lateral eye by measuring the electroretinogram, a population potential reflecting the photoreceptors' response to light, under different experimental conditions. Substance P had no direct effect on the photoreceptors, but it induced an increase in their responsiveness to test flashes of light. The latency, magnitude, and duration of this reversible modulatory effect was dose-dependent. The lateral eye displays an endogenous circadian rhythm in its responsiveness to light. Application of exogenous substance P in the daytime causes an immediate rise as well as an increase in the nocturnal peak, while injection of one of its antagonists (D-Pro2, D-Phe7, D-Trp9 substance P) in the afternoon retards the normal rise in sensitivity and reduces the nighttime levels. Passive incubation with substance P antibodies at midnight caused a drop to diurnal levels of photosensitivity. Short-term changes in photosensitivity, similar in their nature to the substance P-induced ones, were caused by arousing the subjects. Arousal had an effect on the ongoing circadian rhythm similar to that of substance P application. Thus, the substance P efferent system may regulate neural responsiveness in both a short-term, environmentally induced manner, as well as for level setting in a circadian fashion. The mechanism for substance P-induced increases in photosensitivity involves changes in ommatidial structure: contraction of distal pigment cells, resulting in an increased aperture, and contraction of the retinular cells and rhabdom, resulting in a wider diameter of the latter. These structural modifications result in a greater angle of acceptance and increased light quantum catch.
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