Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0029713 (immaturity)
 4,335 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the development of retinal projections in a diminutive polyprotodont marsupial, the fat-tailed dunnart, Sminthopsis crassicaudata. Here, we document the most immature mammalian visual system at birth described to date. At postnatal day (P) 0, the retinal ganglion cell layer has yet to form, and axons have not entered the optic stalk. By P4, the retinal ganglion cell layer could be distinguished at the posterior pole, and the front of growing axons extended one-third the length of the optic stalk, a distance of approximately 150 microm; a few pioneer growth cones had grown beyond the main axon group but had still to reach the midline. Axons had decussated at the optic chiasm by P10 to penetrate the base of the contralateral optic tract and, by P15, had reached the dorsal lateral geniculate nucleus (dLGN), superior colliculus (SC), and accessory optic system (AOS); ipsilaterally projecting axons matured slightly later. From P20, axons had reached the caudal SC both contralaterally and ipsilaterally and terminated throughout the depth of the retinorecipient layers. After P30, the projections gradually refined. Within the rostral dLGN, segregation into four contralateral and four ipsilateral bands occurred by P50, approximately 5 days after eye opening. The projection to the ipsilateral SC underwent refinement by P50, becoming restricted to its rostral pole, and presented as discrete patches within the stratum opticum. At birth, the dunnart visual system is comparable to early to midembryonic stages [embryonic day (E) 12, E14, E19, E24, and E30, respectively] in the mouse, rat, ferret, cat, and monkey. The extreme immaturity of the neonatal dunnart together with the observation that the entire development of the primary optic pathway occurs postnatally over a protracted period make this marsupial especially valuable for investigating factors that control pathway formation in the early developing mammalian primary visual system.
 ...
PMID:Development of primary visual projections occurs entirely postnatally in the fat-tailed dunnart, a marsupial mouse, Sminthopsis crassicaudata. 921 38

We investigated hyposensitivity after amphetamine in early (postnatal Day 30; P30) and late (P45) adolescent rats compared to adults (P70) in experiment 1. Locomotor activity was measured for 1 hr after the first (acute) and second (24 hr later) injection of amphetamine (0.5 or 1.5 mg/kg). P30 and P45 rats were transiently hypoactive compared to adults, as indicated by reduced locomotor activity after acute amphetamine and enhanced activity after the second injection in adolescents only. In experiment 2, ovariectomy did not alter locomotor activity during habituation at any age compared to intact rats, and, as for intact adolescents, ovariectomized adolescents continued to be less active after amphetamine than adults, suggesting gonadal immaturity alone cannot account for age differences in experiment 1. However, ovariectomy attenuated the increase in activity after the second treatment. In experiment 3 involving untreated rats, tyrosine hydroxylase immunoreactivity was reduced in P30, P40, and P50 compared to P90 rats in the nucleus accumbens core and the medial prefrontal cortex. Thus, adolescents may have an increased threshold of behavioral activation that can be overcome with either a higher dose or with repeated amphetamine treatment, and may be related to changes in the dopamine system over development.
 ...
PMID:Changes in hyporesponsiveness to acute amphetamine and age differences in tyrosine hydroxylase immunoreactivity in the brain over adolescence in male and female rats. 1949 63