Neither peripheral nerve input nor cortical NMDA receptor activity are necessary for recovery of a disrupted barrel pattern in rat somatosensory cortex.

Elevating cortical serotonin (5-HT) in rats from postnatal day (P-) 0 to P-6 by administering the monoamine oxidase (MAO(A)) inhibitor, clorgyline, produces a dose-dependent spectrum of effects on rat somatosensory organization, ranging from enlarged with indistinct septa to a complete lack of vibrissae-related patterns. However, if clorgyline treatment is stopped on P-6, a qualitatively and quantitatively normal vibrissae-related pattern of thalamocortical afferents appears in somatosensory cortex (S-I) on P-10. We employed high performance liquid chromatography (HPLC), infraorbital nerve (ION) transection, N-methyl-D-aspartate (NMDA) receptor blockade, 1,1'-dioctadecyl-3,3,3"3'-tetramethylindocarbocyanine perchlorate (DiI) labeling of thalamic afferents, and CO histochemistry to determine whether peripheral nerve input and/or cortical NMDA receptor activity were required for the recovery of vibrissae-related patterns in clorgyline-treated animals.

Clorgyline treatment elevates cortical serotonin and temporarily disrupts the vibrissae-related pattern in rat somatosensory cortex.

Manipulation of cortical serotonin (5-HT) levels in perinatal rodents produces significant alterations in the development of the layer IV cortical representation of the mystacial vibrissae. Monoamine oxidase A (MAO(A)) knockout mice have highly elevated cortical 5-HT and completely lack barrels in somatosensory cortex (S-I). The present study was undertaken to determine whether the effects on thalamocortical development seen in MAO(A) knockout mice can be replicated in perinatal rats treated with an MAO(A) inhibitor and, second, to determine whether these effects persist with continued treatment or after discontinuation of the drug.

Selective facilitation of the serotonin(1B) receptor causes disorganization of thalamic afferents and barrels in somatosensory cortex of rat.

Alteration of serotonin (5-HT) levels influences developing thalamocortical afferents (TCAs) in primary somatosensory cortex (SI) of rats and mice. The 5-HT(1B) receptor, present on TCAs during the first postnatal week, may be involved in these effects. The present study asked whether administration of 5-nonyloxytriptamine (NNT), a selective 5-HT(1B) receptor agonist, affects TCA organization in rat SI.

Time course of expression and function of the serotonin transporter in the neonatal rat's primary somatosensory cortex.

Immunocytochemical and autoradiographic techniques were employed to determine the time course of expression of the serotonin (5-HT) transporter (SERT) on thalamocortical afferents in the rat's primary somatosensory cortex (S-I), and to correlate this expression to the transient vibrissae-related patterning of 5-HT immunostaining previously described. In additional in vivo and in vitro experiments, 5-HT and 3H-5-HT were applied directly to the cortices of untreated and 5,7-dihydroxytryptamine-treated (5,7-DHT) rats in order to determine the period during which SERT functions on thalamocortical axons to take up 5-HT. In postnatal rats, SERT immunohistochemistry revealed a somatotopic patterning in S-I that persisted until P-15, which is 6 days after the disappearance of the vibrissae-related 5-HT immunostaining.

Differential expression of acetylcholinesterase in the brainstem, ventrobasal thalamus and primary somatosensory cortex of perinatal rats, mice, and hamsters.

Acetylcholinesterase (AChE) is transiently expressed by thalamocortical axons in the rat, and staining for this enzyme has been used extensively to study the development of thalamocortical projections. In the present study, patterns of AChE staining were compared in the trigeminal brainstem, thalami and primary somatosensory cortices of perinatal rats, mice, and hamsters. As previously reported, the ventral posteromedial nucleus (VPM) of rats showed dense AChE staining from P-0 at least through P-8.

Effects of serotonin on neurite outgrowth from thalamic neurons in vitro.

Altering levels of serotonin in the primary somatosensory cortex during early postnatal life influences thalamocortical development. Recent in vivo experiments suggest that serotonin may have direct effects on the growth of thalamocortical axons, and the present study was undertaken to determine whether this amine influences process outgrowth from thalamic cells maintained in culture. Ventrobasal thalamic neurons were harvested from newborn rats and maintained in culture for eight days.

Effect of activity blockade on changes in vibrissae-related patterns in the rat's primary somatosensory cortex induced by serotonin depletion.

Depletion of cortical serotonin (5-HT) during development results in a decrease in the size of the patches of thalamocortical afferents representing the mystacial vibrissae in lamina IV of the primary somatosensory cortex (SI). We previously suggested that this change may be due to a reduction in 5-HT-induced suppression of thalamocortical activity in these animals. The present experiments directly tested the role that modulation of activity may play in the morphologic changes observed after reducing cortical 5-HT concentrations.

Augmentation of serotonin in the developing superior colliculus alters the normal development of the uncrossed retinotectal projection.

A previous study from this laboratory showed that sprouting of serotoninergic axons in the hamster's superior colliculus (SC) induced by a single subcutaneous injection of 5,7-dihydroxytryptamine (5,7-DHT) at birth (postnatal day 0; P-0) resulted in an abnormal terminal distribution of the uncrossed retinotectal projection. The present study provided further evidence to support the role of increased 5-HT levels within the SC in this phenomenon. Slow-release polymer (ELVAX) chips impregnated with serotonin (5-HT) were placed over the SC on either P-1 or P-3, and retinotectal projections were assessed via anterograde transport of horseradish peroxidase when animals reached P > 18.

Sensitive period for lesion-induced reorganization of intracortical projections within the vibrissae representation of rat's primary somatosensory cortex.

Previous experiments from this laboratory demonstrated that intracortical connections in lamina IV of the rat primary somatosensory cortex (SI) are most dense outside the patches of cytochrome oxidase (CO) staining that correspond to the mystacial vibrissae. This pattern of intracortical connections becomes apparent on postnatal day 4 (P-4), at least 2 days after the appearance of the vibrissae-related pattern of thalamocortical afferents. Transection of the infraorbital nerve (ION) on the day of birth (P-0) disrupts both the CO and intracortical projection patterns.

Long-term effects of neonatal axoplasmic transport attenuation on the organization of the rat's trigeminal system.

The current study examined the long-term effects of infraorbital nerve (ION) axoplasmic transport attenuation with vinblastine on the organization of trigeminal (V) primary afferents and central vibrissae-related patterns. Retrograde tracing and single unit recording were used to evaluate the innervation of vibrissae follicles in adult (P > 60) rats that sustained application of vinblastine to the ION at birth. Single units recorded from vinblastine-treated animals yielded responses to deflection of a single vibrissa, and a significantly (P < 0.

Projection status of calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus.

Immunocytochemistry and retrograde labeling were used to define the thalamic projections of calbindin- and parvalbumin-containing cells in superficial layers of the rat's superior colliculus (SC). Quantitative analysis revealed that 90.8 +/- 2.

Organization, development, and effects of infraorbital nerve transection on galanin binding sites in the trigeminal brainstem complex.

Previous experiments from this laboratory have indicated that transection of the infraorbital nerve (ION, the trigeminal [V] branch that supplies the mystacial vibrissae follicles) at birth and in adulthood has markedly different effects on galanin immunoreactivity in the V brainstem complex. Adult nerve transection increases galanin immunoreactivity in the superficial layers of V subnucleus caudalis (SpC) only, while neonatal nerve transection results in increased galanin expression in vibrissae-related primary afferents throughout the V brainstem complex. The present study describes the distribution of binding sites for this peptide in the mature and developing V ganglion and brainstem complex and determines the effects of neonatal and adult ION damage and the associated changes in galanin levels upon their distribution and density.

Contributions of raphe-cortical and thalamocortical axons to the transient somatotopic pattern of serotonin immunoreactivity in rat cortex.

Two experiments were carried out to evaluate the relative contributions of thalamocortical and raphe-cortical fibers to the transient somatotopically organized pattern of serotonin (5-HT) immunoreactivity that appears in the primary somatosensory cortex (SI) of rats during the first 2 weeks of life. In the first experiment, the specific 5-HT uptake inhibitors, fluoxetine and paroxetine, were administered systemically, animals were killed 3, 6, or 12 h later, and cortices evaluated for 5-HT immunoreactivity. Fluoxetine treatment had no appreciable effect on the density of 5-HT immunoreactivity in the cortex.

Neonatal damage to the rat's infraorbital nerve upregulates both galanin and neuropeptide Y in individual vibrissae-related primary afferent axons.

Previous studies in adult animals have suggested that the peptides galanin and neuropeptide Y (NPY) may be upregulated in the same primary afferent neurons after peripheral axotomy. The present study was undertaken to determine whether such upregulation occurred in vibrissae-related primary afferent neurons and their axons after damage to the infraorbital nerve [ION; the trigeminal (V) branch that innervates the vibrissae follicles]. Double-labelling experiments demonstrated that approximately 75% of axotomized V ganglion cells and the central arbors of vibrissae-related primary afferents expressed both galanin and NPY after perinatal, but not adult, nerve damage.

Differential age-dependent effects of retinal deafferentation upon calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus.

Several recent studies have reported varied effects of different forms of visual deprivation on the expression of calcium-binding proteins in the CNS. Most of these studies have surveyed only a single protein from this family and have not systematically evaluated the influence of the age of the animal upon the effects observed. The present study combined immunocytochemistry and quantitative morphometry to determine the effects of eye removal in fetal life, at birth, or in adulthood upon the expression of calbindin and parvalbumin by neurons in the retinorecipient laminae (the stratum griseum superficiale (SGS) and stratum opticum (SO)) of the rat's superior colliculus (SC).

Thalamocortical afferents in rat transiently express high-affinity serotonin uptake sites.

Autoradiographic techniques using [3H]citalopram were employed in 8-day-old (P-8) and adult rats to delineate the distribution of high-affinity serotonin (5-HT) uptake sites in the cerebral cortex. In the postnatal rats, [3H]citalopram binding sites were densely distributed in the lower portion of layer III, lamina IV, and upper layer V in the primary visual, somatosensory, and auditory cortices. In the primary somatosensory cortex, these binding sites were arrayed in a manner exactly matching the representation of the body surface as demonstrated by other methods such as staining for cytochrome oxidase (CO) or acetylcholinesterase (AChE).

Effect of neonatal axoplasmic transport attenuation in the infraorbital nerve on vibrissae-related patterns in the rat's brainstem, thalamus and cortex.

This study evaluated the effects of neonatal attenuation of axoplasmic transport in the infraorbital nerve (ION) on the organization of vibrissae-related patterns in the rat's CNS. Application of colchicine- or vinblastine- impregnated implants to the ION from birth until postnatal day (P)6 to P10 resulted in a 92.4% reduction in the number of trigeminal (V) ganglion cells labelled by application of horseradish peroxidase to the vibrissa pad and a 44.

Development and plasticity of local intracortical projections within the vibrissae representation of the rat primary somatosensory cortex.

Labelling with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-A) was used to assess the development of projections within the primary somatosensory cortex (SI) of rats aged between postnatal day 2 and 8 (P-2 and P-8). 1,1'-Dioctadecyl-3,3,3,"3'-tetramethylindocarbocyanine perchlorate (Di-I) was used in these same animals to label thalamocortical afferents. Particular attention was paid to the emergence of lamina IV intracortical projections that form a pattern complementary to vibrissae-related thalamocortical afferents.

Axon and ganglion cell injury in rabbits after percutaneous trigeminal balloon compression.

New Zealand white rabbits were used to determine whether the changes in the Vth cranial nerve sensory root after compression were associated with the loss of a specific subclass of Vth cranial nerve ganglion cells, the disappearance of a distinct subset of primary afferent terminals in Vth cranial nerve nucleus caudalis, and/or injury to a specific axonal fiber type. There was no significant difference in the size of surviving ganglion cells after Vth cranial nerve compression, as measured 2 to 3 months after injury (P > 0.5, n = 4).

Effects of neurotensin on visual neurons in the superficial laminae of the hamster's superior colliculus.

Autoradiography with 125I-neurotensin in normal and enucleated hamsters was used to define the distribution of receptors for this peptide in the superficial layers of the superior colliculus (SC). Neurotensin binding sites were densely distributed in the stratum griseum superficiale (SGS), and results from the enucleated animals indicated that they were not located on retinal axons. The effects of neurotensin on individual superficial layer cells were tested in single-unit recording experiments.

Serotonin modulates retinotectal and corticotectal convergence in the superior colliculus.

A dense serotonin (5-HT)-containing projection to the superficial layers of the superior colliculus (SC) has been demonstrated in diverse mammalian species, but how 5-HT may affect visual signals within these laminae is largely unknown. This study undertook to investigate the distribution of 2 types of 5-HT receptors in the SC and to ascertain their physiological effects on transmission of visual signals to the SC from the retinotectal and corticotectual pathways. Autoradiography of tissue sections exposed to [3H]-8-OH-DPAT (8-hydroxy-dipropylaminotetraline) or to [125I]cyanopindolol plus isoproterenol showed that 5-HT1A and 5-HT1B receptors, respectively, were present in the superficial SC layers.

Differential effects of peripheral manipulations on vibrissae-related patterns in the trigeminal brainstem.

The expression of galanin and neuropeptide Y (NPY) by primary afferent neurons, including those in the trigeminal (V) system, is markedly up-regulated after peripheral nerve damage and might be expected to influence the response of central somatosensory cells to such damage. In the present study, we assessed the effects of four manipulations that have been used to study development and maintenance of vibrissae-related patterns in the V system-nerve transection, whisker clipping, activity blockade with tetrodotoxin (TTX), and axoplasmic transport attenuation with vinblastine-upon the expression of galanin and NPY by V ganglion cells and their central axons in the V brainstem complex. Both neonatal transection of the infraorbital nerve (ION) and application of vinblastine to it resulted in a marked up-regulation of galanin and NPY in V ganglion cells and their central axon arbors in animals killed on postnatal day 6.

Fenfluramine depletes serotonin from the developing cortex and alters thalamocortical organization.

A previous experiment from our laboratory showed that neonatal destruction of cortical serotoninergic (5-HT) axons with 5,7-dihydroxytryptamine (5,7-DHT) reduced the size of the clusters of vibrissae-related thalamocortical axons. This result suggested an important role for 5-HT in thalamocortical development, but could be questioned because of potentially direct toxic effects of 5,7-DHT on thalamocortical axons. In the present study, 5-HT was depleted from the cortex using a different method, neonatal administration of +fenfluramine, and vibrissae-related patches of thalamocortical afferents were measured when animals reached 6 days of age.

The formation of a cortical somatotopic map.

The primary somatosensory cortex of small rodents is an isomorphic representation of the body surface. Similar representations are characteristic of the subcortical pathways, leading from the periphery to the cortex, and these representations develop in a sequence that begins at the periphery, and that ends in the cortex. Furthermore, central representations at all levels of the neural axis are altered by perinatal perturbations of the peripheral surface.