Tyrosine hydroxylase and serotonin containing cells in embryonic rat rhombencephalon: A whole‐mount immunocytochemical study

Abstract

Rhombencephala from rat embryos were processed as whole-mounts for immunocytochemical detection of monoaminergic cell populations, using antibodies to tyrosine hydroxylase (TH) and serotonin (5-HT). Specific advantages of the whole-mount technique over the classical serial-section method were that even isolated immunoreactive (IR) cells could be detected easily, and three-dimensional relationships could be ascertained without the need for serial reconstruction. Embryos between embryonic days (E) 12 and 16 (the day following nocturnal mating being considered as E1) were used in this study. Both TH and 5-HT immunoreactivities were already detectable at E12, even in the smallest embryos (crown-rump length: 6 mm), but there was a striking difference in the number and regional distribution of these two types of IR cells. TH was expressed in several cell groups located in the rostral rhombencephalon (the presumed anlage of the A4-7 complex) as well as in the caudal rhombencephalon (the presumed anlagen of groups A1-2 and C1-3), whereas 5-HT was expressed in very few cells located near the rostral border of the rhombencephalon (presumed anlage of the B4-9 complex). Although the three-dimensional distribution of the TH-IR cell groups underwent some modifications during the period studied, its general pattern remained relatively stable after E12. This contrasted with the sequential appearance of the 5-HT-IR cell groups and their spatial transformations during this period. Using the rhombencephalic isthmus as a landmark, we found that conspicuous 5-HT-IR fibre bundles penetrated into the mesencephalon from E13 onwards, but that the 5-HT IR cell bodies were exclusively located caudal to the borderline between the mesencephalon and the rhombencephalon (the rhombencephalic isthmus). We therefore suggest the term "rostral rhombencephalic raphe nuclei" for the rostral 5-HT cell groups instead of "mesencephalic raphe nuclei," which is a misnomer. Close spatial association between TH and 5-HT-IR elements was observed mainly in the caudal rhombencephalon, where 5-HT-IR fibres coursed through an area containing numerous TH-IR cell bodies (the presumed anlagen of groups A1-2 and C1-3).

Early neuromeric distribution of tyrosine-hydroxylase-immunoreactive neurons in human embryos

“…König et al (1988) mapped TH-IR cells along the whole hindbrain length, but without referring to rhombomeres. They found such cells exclusively in the ''lateral hindbrain'' (their terminology).…”

“…Cell groups A1/C1-C3 in the rat were reconstructed by König et al (1988) as a continuous domain across the caudal hindbrain (our r7/r8), reaching possibly the r6/r7 boundary, as in our material. We concluded that only cells related to the solitary nucleus, area postrema, and dorsal column nuclei should be regarded as alar (A2/C2-alar part).…”

“…These cells formed an irregular longitudinal band with distinct portions that may correspond to specific segments (their Figure 2). The pontine-flexure plane used by König et al (1988) to separate rostral and caudal parts of the hindbrain corresponds to the center of r3, judged from the trigeminal (r2) and facial (r4) nerve roots depicted in their Figure 1. The rat A4-A7 cell groups accordingly seem to extend from isthmus into r3, which roughly correlates with our analysis in Homo (Fig.…”

Gabrb3 gene deficient mice exhibit increased risk assessment behavior, hypotonia and expansion of the plexus of locus coeruleus dendrites

“…During this period, a dense plexus of GABA-immunoreactive fibers can be visualized in the rat brainstem as early as embryonic day 13 (Lauder et al, 1986), coinciding temporally and spatially with the appearance and differentiation of tyrosine hydroxylase (TH) containing neurons in the same region (Konig et al, 1988). GABA A receptors are heterooligomeric GABA-gated chloride channels constructed from eight classes of subunits exhibiting varying amino acid sequence homologies (α 1-6 , β 1-4 , γ 1-3 , δ, ρ 1,2 , π, ε and θ ) and when combined produce multiple isoforms of GABA A receptors with varying GABA sensitivities and pharmacologies (Bonnert et al, 1999;Olsen and DeLorey 1999).…”

Neurotransmitters and Neuropeptides in the Developing Human Central Nervous System

“…However, these neurotransmitters and neuropeptides may have other effects on development. For example, catecholamines have been suggested to play an organizing and induction role in the development of the nervous system [35,36]. In an experiment with noradrenaline, Commissiong [35] implanted the locus ceruleus into a transected spinal cord of a rat and reported on an extensive sprouting from the injured fibers, thus implying an induction or trophic effect of the catecholamine secreted by the neurons of the locus ceruleus.…”