Development of Bombesin-Like and Histamine-Like Innervation in the Bullfrog <i>(Rana catesbeiana) </i>Central Nervous System

Abstract

Amphibians rely exclusively on behavioral thermoregulation to maintain body temperature within species- and developmental stage-specific critical limits. Several members of the bombesin family of peptides and histamine are included in a class of neurochemicals that have potent thermoregulatory effects in ectothermic and endothermic vertebrate species and may be involved in behavioral thermoregulation in amphibians. Because amphibians respond to environmental temperature cues differently in larval versus adult animals, we used immuno-cytochemistry to study developmental changes in bombesin-like (BN) and histamine-like (HA) innervation in the bullfrog brain and spinal cord. Neurons and fibers that were BN-immunoreactive and HA-immunoreactive were present in the earliest stage tadpoles examined (Gossner stage 29); BN-immunoreactive perikarya were found only in the preoptic area, posterior thalamic nucleus and in the rostroventral tegmentum of the mesencephalon. In the preoptic area, dramatic changes were observed in the number and staining intensity of BN-ir so-mata; neuronal labelling was greatest in tadpoles undergoing tail resorption (i.e. metamorphic climax) and was nearly absent in adults. Neurons immunoreactive to BN in the ventral mesencephalon also were developmental stage-dependent; limb-bud growth stage tadpoles had the largest numbers of labelled neurons, whereas in the adults, labelled cells were rarely visible in this area. The highest density of fibers was in the medial septum, lateral amygdala, and the optic tectum. Fewer fibers were observed within the dorsal and ventral hypothalamus, the pineal gland, and all the thalamic nuclei. Perikarya immunoreactive to HA were localized in the dorsal infundibular nucleus of the hypothalamus. Immunoreactivity was present in all developmental stages examined, and the numbers of labelled cells increased throughout metamorphosis to a maximum in adult brains. Fibers were found in the medial septum, medial amygdala, preoptic area, thalamus, pineal gland, hypothalamus and optic tectum. These results show that BN- and HA-immunoreactivities are established early in larval development, but their phenotypes are differentially expressed during larval and adult growth stages. This pattern suggests that reorganization of BN-like and HA-like neural circuitry may occur during metamorphosis and may be involved in the reported developmental changes in amphibian thermoregulation. In addition, BN-like peptides and HA may modulate other related mechanisms of amphibian thermoregulation and behaviour, such as thermal acclimation, circadian shifts in temperature selection and feeding. To what extent they are involved in amphibian thermoregulation remains to be investigated.

Development and Differentiation of the Anuran Auditory Brainstem during Metamorphosis: An Acetylcholinesterase Histochemical Study

“…Transient changes in staining patterns for bombesin have been observed over metamorphosis [Leger and Mathieson, 1997]. This may reflect differences in thermoregulatory behaviors between tadpoles and adult frogs rather than a specific role in neuronal reorganization or plasticity.…”

“…Histochemical staining for other putative neurotransmitters shows the presence of immunoreactivity at early embryonic or late prometamorphic stages [Carr et al, 1990;Gonzalez et al, 1994;Leger and Mathieson, 1997].…”

Afferent and Efferent Connections of the Pineal Organ in the European Sea Bass <i>Dicentrarchus labrax:</i> A Carbocyanine Dye Tract-Tracing Study

“…Neuropeptidergic innervation has also been reported in the pineal gland of mammals and amphibians [Ekström et al, 1990;Artero et al, 1991;Leger and Mathieson, 1997;Moller et al, 1998], suggesting that this innervation is a shared characteristic of vertebrates. Previous studies performed in the sea bass described the presence of NPY cells medioventrally to the nucleus of the thalamic eminentia, in the ventral thalamus (ventromedial nucleus), the dorsal thalamus (anterior nucleus; central posterior nucleus) and the periventricular pretectum [Cerdá-Reverter et al, 2000].…”

Histamine Influences Body Temperature by Acting at H1and H3 Receptors on Distinct Populations of Preoptic Neurons

“…A role of CNS histamine signaling in thermoregulation has been found in various organisms from invertebrates (Hong et al, 2006) to lower vertebrates (Leger and Mathieson, 1997) and mammals (Green et al, 1976). The neurons of the tuberomammillary nucleus represent the main source of histamine in the brain.…”