Unilateral Naris Occlusion Research Articles

β‐secretase expression in normal and functionally deprived rat olfactory bulbs: Inverse correlation with oxidative metabolic activity

Cerebral hypometabolism, mitochondrial dysfunction, and beta-amyloid peptide (Abeta) accumulation are well-characterized manifestations of Alzheimer's disease (AD). beta-Secretase (BACE) is a prerequisite for amyloidogenesis, and it is up-regulated in sporadic AD. To explore a potential in vivo mechanism by which Abeta production is modulated by neuronal activity and/or oxidative metabolism, we compared BACE expression with cytochrome c oxidase (CO) or succinic dehydrogenase (SDH) activity in normal and functionally deprived adult rat olfactory bulb. In normal bulb, BACE was expressed predominantly in the glomerular layer, but labeling intensity within individual glomeruli varied substantially. A strong negative correlation existed between BACE labeling intensity and CO or SDH activity among individual glomeruli. Unilateral naris occlusion resulted in elevated glomerular BACE labeling in the deprived bulbs relative to the nondeprived counterparts, which was correlated with decreased CO activity in the same anatomic location. Enhanced BACE labeling was confirmed by measurements of elevated protein levels, enzymatic activity, and beta-site cleavage products of amyloid precursor protein in bulb extracts. Our findings reveal a negative regulation of BACE expression by physiological neuronal activity and an intrinsic inverse correlation between BACE expression and oxidative metabolism at the first synapse on the olfactory pathway. The results point to a biological role of BACE in synapse function and plasticity as well as a potential mechanism whereby reduced neuronal activity or metabolism could lead to amyloid overproduction in synaptic terminals.

Changes in the serotonergic system in the main olfactory bulb of rats unilaterally deprived from birth to adulthood

The serotonergic system plays a key role in the modulation of olfactory processing. The present study examined the plastic response of this centrifugal system after unilateral naris occlusion, analysing both serotonergic afferents and receptors in the main olfactory bulb. After 60 days of sensory deprivation, the serotonergic system exhibited adaptive changes. Olfactory deprivation caused a general increase in the number of fibres immunopositive for serotonin but not of those immunopositive for the serotonin transporter. HPLC data revealed an increase in serotonin levels but not in those of its major metabolite, 5-hydroxyindole acetic acid, resulting in a decrease in the 5-hydroxyindole acetic acid/serotonin ratio. These changes were observed not only in the deprived but also in the contralateral olfactory bulb. Double serotonin-tyrosine hydroxylase immunolabelling revealed that the glomerular regions of the deprived olfactory bulb with a high serotonergic fibre density showed a strong reduction in tyrosine hydroxylase. Finally, the serotonin(2A) receptor distribution density and the number of juxtaglomerular cells immunopositive for serotonin(2A) receptor remained unaltered after olfactory deprivation. Environmental stimulation modulated the serotonergic afferents to the olfactory bulb. Our results indicate the presence of a bilateral accumulation of serotonin in the serotonergic axon network, with no changes in serotonin(2A) receptor density after unilateral olfactory deprivation.

Effects of unilateral naris occlusion on the olfactory epithelium of adult mice

Sensory stimulation is an essential component of neuronal functions, including information processing, dendritic and axonal refinement, synaptic plasticity, and neuronal survival. We examined the roles of sensory stimulation in the maintenance of olfactory sensory neurons in the olfactory epithelium using the adult mouse olfactory system as the model system. Obstruction of sensory stimulation through unilateral naris occlusion caused downregulation of proliferation and upregulation of apoptosis of neurons in the olfactory epithelium. Sensory stimulation is therefore important in maintaining homeostasis in the adult olfactory epithelium. Our study contributes to further understanding the roles and mechanisms of sensory stimulation in the postnatal neuronal development as well as to the damage and potential treatments of patients who suffer recurrent nasal obstruction.

Naris occlusion alters transductory protein immunoreactivity in olfactory epithelium.

We have recently shown that unilateral naris occlusion (UNO) causes an increase in olfactory marker protein (OMP) immunoreactivity (IR) in mouse olfactory sensory neurons (OSN) from the occluded side of the nasal cavity and a decrease in OMP-IR on the non-occluded side, relative to controls. Given OMP's demonstrated role in olfactory modulation, these OMP-IR changes have been interpreted as a compensatory response by OSNs to odor deprivation on the occluded side and to supernormal exposure to odor on the non-occluded side of the nasal cavity. In the current study, we examined the developmental timing and the regional distribution of this process throughout the nasal cavity using immunocytochemistry. Results demonstrate that OMP-IR diverges in OSNs from the occluded side relative to the non-occluded side of the nasal cavity within eleven days after UNO, with statistically significant differences measurable after 17 days (n=16). We also measured relative levels of the Type 4 phosphodiesterase (PDE4A), another potential olfactory modulator, in nasal cavity tissue from UNO (n=8) and untreated mice (n=9) using western blots and immunocytochemistry. Like OMP, PDE4A-IR increased on the occluded side of the nasal cavity after UNO. Finally, we used immunocytochemistry to assess relative levels of olfactory-specific adenylyl cyclase (ACIII, n=4) and G-protein (Golf, n=2) in OSNs from the occluded and non-occluded sides of the nasal cavity of UNO mice. Following UNO, ACIII but not Golf -IR levels diverged comparing the occluded to the non-occluded sides of the nasal cavity. Taken together, our findings provide support for the previously unknown phenomenon of compensatory responses by OSNs to odor environment.

Comparison of odor and mating-induced glomerular activation in the main olfactory bulb of estrous female ferrets

Previously [S.K. Woodley, M.J. Baum, Differential activation of glomeruli in the ferret's main olfactory bulb by anal scent gland odors from males and females: an early step in mate identification, Eur. J. Neurosci. 20 (2004) 1025–1032], the receipt of intromission from a male activated glomeruli (indexed by Fos immunoreactivity in juxtaglomerular cells) in the main olfactory bulb (MOB) of estrous female ferrets which exceeded the activation seen after exposure to male anal scent gland odorants alone. We asked whether centrifugal inputs (e.g., from the locus coeruleus to the MOB) generated by the receipt of vaginal-cervical stimulation influence odor-induced MOB glomerular activation. We compared the activation of MOB glomeruli in estrous female ferrets which received a unilateral naris occlusion prior to exposure to: unscented air, volatile odorants from an anesthetized male, volatile + non-volatile odorants from direct physical contact with an anesthetized male, or mating stimulation. Little glomerular activation was observed in the MOB ipsilateral to an occluded naris, including females which received intromission. An equivalent distribution of activated glomeruli was observed in the ventral MOB of estrous females which either received mating stimulation or had direct physical contact with an anesthetized male. Considerably less glomerular activation occurred in females exposed only to volatile male odors. The MOB of female ferrets responded to body odorants from the opposite sex; however, there was no evidence that mating-induced centrifugal inputs directly activated MOB glomeruli or modified odor-induced glomerular activation.

Naris occlusion alters olfactory marker protein immunoreactivity in olfactory epithelium

Though its function remains obscure, olfactory marker protein (OMP) has been implicated in olfactory transduction and the enhancement of neurogenesis within olfactory epithelium. Here we show, using Western blot analysis and immunocytochemistry, that unilateral naris occlusion (UNO) on postnatal day 1 alters OMP immunoreactivity (IR) differentially on the occluded and non-occluded sides of the nasal cavity in 18, 24 and 70-day-old mice. Compared to untreated animals, UNO-treated animals had a decrease in OMP-IR in olfactory receptor neurons on the non-occluded side and an increase in OMP-IR in olfactory receptor neurons on the occluded side of the nasal cavity. These results suggest that OMP concentration is up- or down-regulated depending on the amount of odor stimulation olfactory receptor neurons receive. It is proposed that this apparent change in protein concentration may be part of a more general compensatory response by olfactory neurons to levels of odor in the environment.

Trans-neuronal regulation of cortical apoptosis in the adult rat olfactory system

Previous work has identified a population of neurons within the anterior piriform cortex that undergo rapid apoptosis following de-afferentation by olfactory bulbectomy in adult rats. The specific initiation signal for apoptosis in this paradigm is unknown, but may include an activity-dependent trans-neuronal cascade. The present report examined the effect of adult-onset unilateral naris occlusion, which reduces olfactory bulb afferent excitation of piriform cortex, on apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling [TUNEL]) in the rat anterior piriform cortex. Adult Long-Evans hooded rats received unilateral naris occlusion or a control manipulation and were sacrificed after 1, 5, 7, 10 or 20 days later. For comparison, a second group of rats received a unilateral bulbectomy and were sacrificed 24 h later. Counts of TUNEL-stained cell profiles were performed for layers I/II and layer III of the anterior piriform cortex ipsilateral and contralateral to the manipulation. The results confirmed that unilateral bulbectomy produced a dramatic increase in TUNEL labeling in layers I/II of the ipsilateral piriform cortex 24 h after bulbectomy. Unilateral naris closure also produced enhanced TUNEL labeling, although the magnitude of the effect was less than that produced by bulbectomy, and enhanced TUNEL labeling was apparent both ipsilateral and contralateral to the sealed naris compared to controls. Deprivation-induced TUNEL labeling was detectable by 24 h post-closure, peaked at 5 days and was no different from controls by 20 days post-closure. Neither bulbectomy nor naris closure affected TUNEL labeling in layer III. Together, these results suggest that there is a population of superficial cells in piriform cortex whose survival is tightly regulated by sensory input.

A postnatal sensitive period for plasticity of cortical afferents but not cortical association fibers in rat piriform cortex

Male and female rats underwent unilateral naris occlusion or sham surgery on either post-natal day (PN) 1 or after PN30. Following at least 30 days of unilateral olfactory deprivation, rats were urethane anesthetized and recordings were made from anterior piriform cortex (aPCX). Shock stimulation of afferent fibers (lateral olfactory tract) and association/commissural fibers evoked field potentials in aPCX that were analyzed across groups and between ages. The results demonstrate that early-onset unilateral olfactory deprivation depresses field potentials evoked by stimulation of the deprived cortical afferent, while late-onset deprivation did not. In contrast, intracortical association fiber mediated field potentials in the deprived cortex were enhanced after both early-onset and late-onset deprivation. These results suggest differential developmental plasticity of afferent and association fiber pathways in paleocortex that mirrors that previously described in neocortical sensory systems.

Neurotrophin modulation of voltage-gated potassium channels in rat through TrkB receptors is time and sensory experience dependent.

The whole-cell configuration of the patch-clamp technique, immunoprecipitation experiments and unilateral naris occlusions were used to investigate whether the voltage-gated potassium channel Kv1.3 was a substrate for neurotrophin-induced tyrosine phosphorylation and subsequent functional modulation of current properties in cultured rat olfactory bulb (OB) neurons. Membrane proteins of the OB included all three Trk receptor kinases, but the truncated form of the receptor, lacking an intact kinase domain, was the predominant form of the protein for TrkA and TrkC, while TrkB was predominantly found as the full-length receptor. Acute (15 min) stimulation of OB neurons with bath application of 50 ng ml(-1) brain-derived neurotrophic factor (BDNF), which is a selective ligand for TrkB, caused suppression of the whole-cell outward current and no changes in the kinetics of inactivation or deactivation. Acute stimulation with either nerve growth factor or neurotrophin-3 failed to evoke any changes in Kv1.3 function in the OB neurons. Chronic exposure to BDNF (days) caused an increase in the magnitude of Kv1.3 current and speeding of the inactivation and deactivation of the channel. Acute BDNF-induced activation of TrkB receptors significantly increased tyrosine phosphorylation of Kv1.3 in the OB, as shown using a combined immunoprecipitation and Western blot analysis. With unilateral naris occlusion, the acute BDNF-induced tyrosine phosphorylation of Kv1.3 was increased in neurons lacking odour sensory experience. In summary, the duration of neurotrophin exposure and the sensory-dependent state of a neuron can influence the degree of phosphorylation of a voltage-gated ion channel and its concomitant functional modulation by neurotrophins.

Neonatal olfactory sensory deprivation decreases BDNF in the olfactory bulb of the rat

We hypothesized that brain-derived neurotrophic factor (BDNF) may be down-regulated in the olfactory bulb ipsilateral to experimental naris occlusion. Unilateral naris occlusion was performed on rats at postnatal day three (P3). On P10, P30, and P60 olfactory bulbs were weighed and assayed for tyrosine hydroxylase (TH), BDNF, and TrkB by Western blotting to determine the response of BDNF and its cognate receptor, TrkB, both during the acute phase of sensory loss (P10) and longer term. TH levels, which are highly dependent on intact input from the olfactory epithelium, were assayed as a means of determining the success of occlusion in each animal. At P10, BDNF protein expression was variable but most often increased ipsilateral to deprivation. In contrast, by P30 and P60 TH levels were found to be significantly decreased in the ipsilateral bulbs as were the levels of BDNF. TrkB protein levels changed little relative to the control side. Immunohistochemical localization of BDNF within the control-side olfactory bulb revealed small cells located mainly in the mitral cell layer and internal plexiform layer. Very few of the BDNF immunoreactive cells were visible in the bulb ipsilateral to the occlusion by P30. Given the roles of BDNF in survival of cells and plasticity during development, the decrease in BDNF expression subsequent to olfactory sensory deprivation may contribute to cellular and synaptic deficits observed by others following olfactory sensory deprivation.

Brain insulin receptor causes activity-dependent current suppression in the olfactory bulb through multiple phosphorylation of Kv1.3.

Insulin and insulin receptor (IR) kinase are found in abundance in discrete brain regions yet insulin signaling in the CNS is not understood. Because it is known that the highest brain insulin-binding affinities, insulin-receptor density, and IR kinase activity are localized to the olfactory bulb, we sought to explore the downstream substrates for IR kinase in this region of the brain to better elucidate the function of insulin signaling in the CNS. First, we demonstrate that IR is postnatally and developmentally expressed in specific lamina of the highly plastic olfactory bulb (OB). ELISA testing confirms that insulin is present in the developing and adult OB. Plasma insulin levels are elevated above that found in the OB, which perhaps suggests a differential insulin pool. Olfactory bulb insulin levels appear not to be static, however, but are elevated as much as 15-fold after a 72-h fasting period. Bath application of insulin to cultured OB neurons acutely induces outward current suppression as studied by the use of traditional whole-cell and single-channel patch-clamp recording techniques. Modulation of OB neurons is restricted to current magnitude; IR kinase activation does not modulate current kinetics of inactivation or deactivation. Transient transfection of human embryonic kidney cells with cloned Kv1.3 ion channel, which carries a large proportion of the outward current in these neurons, revealed that current suppression was the result of multiple tyrosine phosphorylation of Kv1.3 channel. Y to F single-point mutations in the channel or deletion of the kinase domain in IR blocks insulin-induced modulation and phosphorylation of Kv1.3. Neuromodulation of Kv1.3 current in OB neurons is activity dependent and is eliminated after 20 days of odor/sensory deprivation induced by unilateral naris occlusion at postnatal day 1. IR kinase but not Kv1.3 expression is downregulated in the OB ipsilateral to the occlusion, as demonstrated in cryosections of right (control) and left (sensory-deprived) OB immunolabeled with antibodies directed against these proteins, respectively. Collectively, these data support the hypothesis that the hormone insulin acts as a multiply functioning molecule in the brain: IR signaling in the CNS could act as a traditional growth factor during development, be altered during energy metabolism, and simultaneously function to modulate electrical activity via phosphorylation of voltage-gated ion channels.

Differentiation of mitral cell dendrites in the developing main olfactory bulbs of normal and naris-occluded rats

The morphological differentiation of mitral cell dendrites during embryonic and early postnatal development was examined in the main olfactory bulb of rats to determine a possible role of afferent activity in the development of the dendrites. Mitral cells and olfactory nerve fibers were labeled with 1,1`-dioctadecyl-3,3,3`,3`-tetramethylindocarbocyanine perchlorate (DiI) and fluorescein-conjugated lectin (Ulex europeus agglutinin-I), respectively. Morphogenesis of mitral cell dendrites proceeded as previously described (Malun and Brunjes [1996] J. Comp. Neurol. 368:1–16); that is, undifferentiated dendrites with radial orientation were transformed into a single primary dendrite having a glomerular tuft and secondary dendrites extending tangentially into the external plexiform layer. Quantitative examinations in both pre- and postnatal rats revealed that the differentiation of primary dendrites, including tuft formation, increases in diameter and decreases in branching, started before birth, whereas differentiated secondary dendrites were only observed in postnatal animals. Mitral cells with more than two primary dendrites were found after embryonic day 21. The proportion of the mitral cells with differentiated dendrites increased postnatally. At postnatal day 10, almost all mitral cells had fully differentiated dendrites, and mitral cells with multiple primary dendrites were no longer seen. No significant change was found during development in the number of stem dendrites that arose directly from the cell body. Unilateral naris occlusion started on postnatal day 1 retarded differentiation of primary and secondary dendrites, and increased the proportion of mitral cells with multiple primary dendrites. These finding revealed that differentiation of mitral cell primary dendrites precedes that of secondary dendrites, and suggested that the differentiation of secondary dendrites proceeds in an activity-dependent manner. J. Comp. Neurol. 418:402–410, 2000. © 2000 Wiley-Liss, Inc.

Differentiation of mitral cell dendrites in the developing main olfactory bulbs of normal and naris-occluded rats

The morphological differentiation of mitral cell dendrites during embryonic and early postnatal development was examined in the main olfactory bulb of rats to determine a possible role of afferent activity in the development of the dendrites. Mitral cells and olfactory nerve fibers were labeled with 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (DiI) and fluorescein-conjugated lectin (Ulex europeus agglutinin-I), respectively. Morphogenesis of mitral cell dendrites proceeded as previously described (Malun and Brunjes [1996] J. Comp. Neurol. 368:1-16); that is, undifferentiated dendrites with radial orientation were transformed into a single primary dendrite having a glomerular tuft and secondary dendrites extending tangentially into the external plexiform layer. Quantitative examinations in both pre- and postnatal rats revealed that the differentiation of primary dendrites, including tuft formation, increases in diameter and decreases in branching, started before birth, whereas differentiated secondary dendrites were only observed in postnatal animals. Mitral cells with more than two primary dendrites were found after embryonic day 21. The proportion of the mitral cells with differentiated dendrites increased postnatally. At postnatal day 10, almost all mitral cells had fully differentiated dendrites, and mitral cells with multiple primary dendrites were no longer seen. No significant change was found during development in the number of stem dendrites that arose directly from the cell body. Unilateral naris occlusion started on postnatal day 1 retarded differentiation of primary and secondary dendrites, and increased the proportion of mitral cells with multiple primary dendrites. These finding revealed that differentiation of mitral cell primary dendrites precedes that of secondary dendrites, and suggested that the differentiation of secondary dendrites proceeds in an activity-dependent manner.

Unilateral naris occlusion and the rat accessory olfactory bulb.

Blocking airflow through half of the nasal cavity during early life results in a 25% reduction in the size of the ipsilateral main olfactory bulb. The present study indicates that the size of the accessory bulb is relatively unaffected by the procedure.

Compensatory responses to early olfactory restriction.

The emphasis on the effects of early olfactory restriction has been on the deleterious nature of the consequences of this abnormal early experience. While these effects are certainly present and dramatic, it is also the case that the olfactory system is left fairly intact by this experimental manipulation. If one asks what mechanisms may account for the preservation of the developing olfactory system in the face of diminished activity, there are a number of neural responses that could help the system compensate for the damage inflicted upon the system by the loss of early sensory stimulation. I describe what may be compensatory responses to the decrease in dopamine, the increase in norepinephrine, the structural changes induced in the glomeruli and the increase in cell death within the olfactory bulb that follow neonatal unilateral naris occlusion.

Early olfactory enrichment and deprivation both decrease beta-adrenergic receptor density in the main olfactory bulb of the rat.

The density of noradrenergic locus coeruleus projections and beta-adrenergic receptors in the main olfactory bulb of the rat increases with age. Both beta 1- and beta 2-adrenergic receptor subtypes exhibit laminar distributions, with focal regions of high receptor density present within the neuropil of individual glomeruli. Since the first synaptic contacts between olfactory receptor neurons and bulbar neurons occur within the glomeruli, early olfactory experiences possibly could influence the density or distribution of beta-adrenergic receptors in the bulb. We therefore investigated the effects of olfactory deprivation and early olfactory enrichment on the density and distribution of beta-adrenergic receptors in the main olfactory bulb. Animals were subjected to either unilateral naris closure on postnatal day 1 or odor training from postnatal days 1-18. Bulbs were removed on postnatal day 19 and subjected to quantitative autoradiography using the beta-adrenergic receptor antagonist [125I]iodopindolol and specific receptor subtype antagonists ICI 118,551 (beta 2-antagonist) and ICI 89,406 (beta 1-antagonist). Unilateral naris occlusion decreased both the number of beta 2 glomerular foci and the density of beta 1 and beta 2 receptors in the deprived bulb compared to the nondeprived bulb. Early odor training resulted in a significant decrease in the number, area, and receptor density of beta 2 glomerular foci in the midlateral region of the bulb. The distribution of beta 2 glomerular foci also differs with these two sensory manipulations. Changes in beta-adrenergic receptor density in response to both early learning and olfactory deprivation may be induced by a transient increase in olfactory bulb norepinephrine.

Olfactory experience modulates apoptosis in the developing olfactory bulb

Early sensory stimulation plays a key role in shaping the structure and function of the developing olfactory system. Here, we provide the first direct evidence for apoptotic cell death in the olfactory bulbs of rat pups during normal development and we also demonstrate that olfactory deprivation by unilateral naris occlusion causes a dramatic increase in apoptotic cell death in the glomerular and granule cell layers of the deprived bulb. The accessory olfactory bulbs displayed a remarkably high basal level of apoptosis but the occluded accessory bulb did not differ in that regard from the control accessory bulb. These results suggest that apoptosis may be an important mechanism by which the olfactory system can adjust its cell numbers in response to sensory stimuli experienced in early life, thereby underlying one form of plasticity in the developing olfactory system.

Retronasal or internasal olfaction can mediate odor-guided behaviors in newborn mice

Studies of olfactory deprivation have most frequently used unilateral naris occlusion to effect deprivation. Recent psychophysical evidence suggests that adult rodents with either acute or chronic naris occlusion show little decrement in olfactory ability. In this study the effect of naris occlusion coupled with ipsilateral or contralateral olfactory bulb deafferentation on odor-guided behaviors was tested in neonatal mice. Animals that received bilateral bulbectomy or control manipulation were also included. In Experiment 1, olfactory lesions were produced by bulb aspiration on the second day after birth (P2). Daily weight gain, a reliable measure of suckling success, was recorded until P21. In Experiment 2, olfactory lesions consisted of bulb transection on P2. Daily weights were recorded until subjects were P10. Animals with bilateral bulbectomy had the highest mortality rate and slowest growth rate. Both naris occlusion groups grew more slowly than controls but were not significantly different at P5 or P10. They diverged, thereafter, such that at P20 the group with naris occlusion ipsilateral to bulbectomy was similar to controls, while the contralateral group was similar to the bilateral bulbectomy group. In Experiment 2, the weights of the naris occlusion groups diverged by the day after surgery, with the contralateral group suffering the most arrested growth. Behavioral tests were combined from the two experiments for analysis. Subjects were tested at P5 for their ability to find the nipple, at P8 for their ability to find the nest, and at P10 for unwashed vs. washed nipple preferences. Only the contralateral group had a significantly depressed ability to find the nipple, while all lesion groups had a significant but similar decline in nest-finding ability. Controls and both naris occlusion groups showed significant preferences for unwashed nipples. These results suggest that while naris occlusion produces some deficits in olfactory ability it does not produce complete odor deprivation. It is concluded that the olfactory epithelium in the occluded nasal fossa may gain access to stimuli by a retronasal or internasal route.

Changes in Cell Proliferation in the Developing Olfactory Epithelium Following Neonatal Unilateral Naris Occlusion

Surgical closure of an external naris reduces airflow through one side of the nasal cavity. Previous studies using [ 3H]thymidine autoradiography have demonstrated that rats subjected to the procedure on Postnatal Day 1 (P1) exhibit reduced cellular proliferation in the olfactory mucosa by P30. We investigated cell production at earlier ages to determine (a) when the effect first emerges, and (b) whether septal, dorsal, and lateral regions of the nasal cavity responded similarly. Both short (2-h) and long (30-day) survival groups were tested. Results from the first group indicate that changes in proliferation emerge between P10 and P20, and that the septum is more affected than other regions of the nasal cavity. No differences were observed in the long survival groups, perhaps due to changes in patterns of cell production or death.

Unilateral naris closure and vascular development in the rat olfactory bulb

The blood supply to the brain has been linked closely to nervous system function and metabolism, thereby possibly playing a direct role in brain maturation. Previously, we demonstrated that closure of an external naris early in life results in large changes within the olfactory bulb, including reductions in laminar volume and cell number and a rapid decline in metabolism and protein synthesis. To understand the role of the blood supply in the dramatic changes following naris closure, the present study examines the development of olfactory bulb vasculature in unilaterally odor-deprived and control rats. On post-partum day 1 (P1; the day after birth), littermate rat pups underwent either unilateral naris occlusion or sham surgery. On P5, P10, P15, P20, P30 and P60, animals were perfused with an india ink-gelatin mixture to assess blood vessel amount and complexity. Densitometric analyses were performed to obtain values of blood vessel area ratios (vessel area/tissue area), branch point number and branch point density. Considerable vessel development in all bulbs occurred over the first two to three weeks post-partum. By P20, large reductions in vessel area ratios were observed in all constituent laminae of deprived bulbs. While similar reductions in number of vessel branch points/tissue area were seen, few changes were noted in the number of branch points/vessel area. The effects were primarily confined to early developmental periods: bulb vasculature in animals deprived at older ages (P40) appeared normal. The results indicate that the vasculature responds to alterations in sensory stimulation early in life, therefore potentially playing an important regulative role in neural development.