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The development of descending projections from the brainstem to the spinal cord in the fetal sheep.

Stockx EM, Anderson CR, Murphy SM, Cooke IR, Berger PJ - BMC Neurosci (2007)

Bottom Line: At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract.The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ritchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia. elaine.stockx@med.monash.edu.au

ABSTRACT

Background: Although the fetal sheep is a favoured model for studying the ontogeny of physiological control systems, there are no descriptions of the timing of arrival of the projections of supraspinal origin that regulate somatic and visceral function. In the early development of birds and mammals, spontaneous motor activity is generated within spinal circuits, but as development proceeds, a distinct change occurs in spontaneous motor patterns that is dependent on the presence of intact, descending inputs to the spinal cord. In the fetal sheep, this change occurs at approximately 65 days gestation (G65), so we therefore hypothesised that spinally-projecting axons from the neurons responsible for transforming fetal behaviour must arrive at the spinal cord level shortly before G65. Accordingly we aimed to identify the brainstem neurons that send projections to the spinal cord in the mature sheep fetus at G140 (term = G147) with retrograde tracing, and thus to establish whether any projections from the brainstem were absent from the spinal cord at G55, an age prior to the marked change in fetal motor activity has occurred.

Results: At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract. This pattern of labelling is similar to that previously reported in other species. The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.

Conclusion: The brainstem nuclei that contain neurons which project axons to the spinal cord in the fetal sheep are the same as in other mammalian species. All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation. The demonstration that the neurons responsible for transforming fetal behaviour in early ontogeny have already reached the spinal cord by G55, an age well before the change in motor behaviour occurs, suggests that the projections do not become fully functional until well after their arrival at the spinal cord.

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Level before obex (G140). At G140, CTB labelled cells were found in the raphe pallidus (RPa), raphe obscurus (ROb), medullary reticular nucleus ventral and dorsal (MdV and MdD), nucleus of the solitary tract (Nsol), the lateral reticular nucleus (LRt), in and around the ambiguus nucleus (Amb), paramedian reticular nucleus (PMn) and in the 'ventral edge nucleus'. Both sides of the figure are ipsilateral labelling (see methods).
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Figure 3: Level before obex (G140). At G140, CTB labelled cells were found in the raphe pallidus (RPa), raphe obscurus (ROb), medullary reticular nucleus ventral and dorsal (MdV and MdD), nucleus of the solitary tract (Nsol), the lateral reticular nucleus (LRt), in and around the ambiguus nucleus (Amb), paramedian reticular nucleus (PMn) and in the 'ventral edge nucleus'. Both sides of the figure are ipsilateral labelling (see methods).

Mentions: At a level just caudal to the obex (Fig. 3) there was labelling of cells around and within the ambiguus nucleus and the lateral reticular nucleus. These cells had irregular triangular shapes and were large in size with a number of strongly-labelled dendrites (see arrows in Fig. 1a). The medullary reticular nuclei (dorsal and ventral) contained many labelled cells, with a denser aggregation of cells ventrally, compared to the dorsal region. Labelled cells were found in the paramedian reticular nucleus and in the raphe complex, both in the raphe pallidus and raphe obscurus nuclei. The majority of cells within the raphe pallidus nucleus, which spanned the ventral midline, had a rounded shape (Fig. 1b). There was labelling of cells located immediately within and around the solitary tract. A number of cells were labelled ventral to the inferior olive and lateral reticular nucleus.


The development of descending projections from the brainstem to the spinal cord in the fetal sheep.

Stockx EM, Anderson CR, Murphy SM, Cooke IR, Berger PJ - BMC Neurosci (2007)

Level before obex (G140). At G140, CTB labelled cells were found in the raphe pallidus (RPa), raphe obscurus (ROb), medullary reticular nucleus ventral and dorsal (MdV and MdD), nucleus of the solitary tract (Nsol), the lateral reticular nucleus (LRt), in and around the ambiguus nucleus (Amb), paramedian reticular nucleus (PMn) and in the 'ventral edge nucleus'. Both sides of the figure are ipsilateral labelling (see methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1919385&req=5

Figure 3: Level before obex (G140). At G140, CTB labelled cells were found in the raphe pallidus (RPa), raphe obscurus (ROb), medullary reticular nucleus ventral and dorsal (MdV and MdD), nucleus of the solitary tract (Nsol), the lateral reticular nucleus (LRt), in and around the ambiguus nucleus (Amb), paramedian reticular nucleus (PMn) and in the 'ventral edge nucleus'. Both sides of the figure are ipsilateral labelling (see methods).
Mentions: At a level just caudal to the obex (Fig. 3) there was labelling of cells around and within the ambiguus nucleus and the lateral reticular nucleus. These cells had irregular triangular shapes and were large in size with a number of strongly-labelled dendrites (see arrows in Fig. 1a). The medullary reticular nuclei (dorsal and ventral) contained many labelled cells, with a denser aggregation of cells ventrally, compared to the dorsal region. Labelled cells were found in the paramedian reticular nucleus and in the raphe complex, both in the raphe pallidus and raphe obscurus nuclei. The majority of cells within the raphe pallidus nucleus, which spanned the ventral midline, had a rounded shape (Fig. 1b). There was labelling of cells located immediately within and around the solitary tract. A number of cells were labelled ventral to the inferior olive and lateral reticular nucleus.

Bottom Line: At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract.The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Ritchie Centre for Baby Health Research, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia. elaine.stockx@med.monash.edu.au

ABSTRACT

Background: Although the fetal sheep is a favoured model for studying the ontogeny of physiological control systems, there are no descriptions of the timing of arrival of the projections of supraspinal origin that regulate somatic and visceral function. In the early development of birds and mammals, spontaneous motor activity is generated within spinal circuits, but as development proceeds, a distinct change occurs in spontaneous motor patterns that is dependent on the presence of intact, descending inputs to the spinal cord. In the fetal sheep, this change occurs at approximately 65 days gestation (G65), so we therefore hypothesised that spinally-projecting axons from the neurons responsible for transforming fetal behaviour must arrive at the spinal cord level shortly before G65. Accordingly we aimed to identify the brainstem neurons that send projections to the spinal cord in the mature sheep fetus at G140 (term = G147) with retrograde tracing, and thus to establish whether any projections from the brainstem were absent from the spinal cord at G55, an age prior to the marked change in fetal motor activity has occurred.

Results: At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract. This pattern of labelling is similar to that previously reported in other species. The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.

Conclusion: The brainstem nuclei that contain neurons which project axons to the spinal cord in the fetal sheep are the same as in other mammalian species. All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation. The demonstration that the neurons responsible for transforming fetal behaviour in early ontogeny have already reached the spinal cord by G55, an age well before the change in motor behaviour occurs, suggests that the projections do not become fully functional until well after their arrival at the spinal cord.

Show MeSH
Related in: MedlinePlus