Decrease in tyrosine hydroxylase, but not aromatic L-amino acid decarboxylase, messenger RNA in rat olfactory bulb following neonatal, unilateral odor deprivation

Effects of orochemical stimulation on postnatal development of gustatory recipient zones within the nucleus of the solitary tract

Previous receptor damage studies and artificial rearing (AR) studies in rat have demonstrated that orochemical stimulation between the postnatal ages of P2 and P14 is necessary for development of primary gustatory axons and terminal endings in the rostral nucleus of the solitary tract (NST). Objectives of the present experiment were to evaluate the qualitative nature of orochemical stimulation and amount of orochemical stimulation that is necessary to produce normal axonal and terminal development in gustatory recipient zones of the rostral and intermediate NST. To this end, ultra-pure water, 30, 150, and 500 mM NaCl, 80 and 340 mM lactose, whole rat milk, and rat milk that had been subject to extensive dialysis (12-14 kD MWCO) was delivered to independent groups of rat pups during AR procedures. Unstimulated AR animals and matched mother-reared (MR) animals were used as controls. AR animals received experimental orochemical stimulation between the ages of P4 and P10, and were thereafter returned to lactating dams until the time of weaning; MR animals received experimental orochemical stimulation during the course of normal nursing. Following maturation, anterograde fluorescent dual-labeling experiments were conducted to map the course and distribution of primary gustatory axons within the NST. Results show that experimental stimualtion with water during AR procedures is not sufficient to produce normal development of primary gustatory axons and terminal endings in the gustatory NST. Stimulation with 30, 150, and 500 mM NaCl produced normal axonal development in the NST, as did 80 and 340 mM lactose, whole rat milk, and dialyzed rat milk.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of tyrosine hydroxylase in olfactory bulb cultures: selective inhibition of depolarization-induced increase by endogenous opioids

Regulation of tyrosine hydroxylase (TH) by second messenger pathway activators was examined in rat olfactory bulb cell cultures. The number of TH-immunoreactive neurons was increased 2-3-fold by 36 h treatments with forskolin (Fsk, 10(-6) M) or phorbol myristate acetate (PMA, 10(-7) M), but was not significantly increased by a depolarizing concentration of KCl (45 mM). In contrast, KCl increased media [Met5]enkephalin (ME) immunoreactivity 2-fold in these cultures, equivalent to stimulation with Fsk or PMA. The possibility was examined that ME or another opioid produced by the cultures selectively inhibited the TH response to KCl. Pretreatment with the opioid receptor antagonist naloxone (10(-6) M) greatly increased the number of TH-immunoreactive neurons observed in response to KCl treatment, but had no effect on basal or Fsk-stimulated TH immunostaining, nor on basal or stimulated ME release. The increase in TH-immunoreactivity observed with combined KCl plus naloxone treatment was prevented by pretreating the cultures with the calcium channel blocker nimodipine (10(-6) M), which had no effect on Fsk stimulation or basal TH immunostaining. These data suggest that endogenous opioids selectively inhibit KCl-stimulated Ca2+ entry and thus TH induction in olfactory bulb cell cultures. These cultures offer a simple model system for further study of TH regulation in dopaminergic neurons.

Early induction of rat brain tryptophan hydroxylase (TPH) mRNA following parachlorophenylalanine (PCPA) treatment

Tryptophan hydroxylase (TPH) is the first and presumably rate-limiting enzyme in serotonin (5-HT) biosynthesis. End-product inhibition of rate-limiting enzymes is common and 5-HT is known to inhibit TPH activity in vivo. However, it is not known whether levels of 5-HT could also be involved in the regulation of the TPH gene. In order to determine whether TPH gene regulation is dependent on the 5-HT concentration, 5-HT levels were reduced by the administration of parachlorophenylalanine (PCPA). PCPA is a potent, specific and irreversible inhibitor of TPH activity which drastically reduces 5-HT concentration in the 5-HT neurons and terminals. When PCPA was administered, TPH activity in both cell bodies and nerve terminal areas, was reduced to 10% of control values and recovered to the control levels by day 7 in raphe nucleus, and within 14 days in the hypothalamus. In serotonergic terminal areas, 5-HT could not be detected immunohistochemically at day 1, but slowly recovered within 2 weeks. At all time points examined, aromatic L-amino acid decarboxylase (AADC) levels were not changed either in the cell body or terminal areas. The steady state levels of TPH mRNA estimated by in situ hybridization increased at day 1 and returned to control levels by day 4. AADC message levels were not altered throughout the periods. These data suggest that a decrease in 5-HT concentration may lead to an up-regulation of TPH gene transcription, by an, as yet, unknown mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral naris closure and olfactory system development

In most animals there is bilateral access of odorants to the olfactory sensory epithelium. Air enters the nose through two external nares and passes back through the nasal cavity, which is divided down the midline by a cartilaginous nasal septum. The olfactory mucosa, a sheet of ciliated bipolar receptor cells, is found in the caudal two thirds of the nasal cavity. Axons from the sensory cells project to an ipsilateral extension of the telencephalon known as the olfactory bulb. If a single external naris of a rat pup is surgically closed (usually via brief cauterization) on the day after the day of birth (P1) and the subject is examined on P30, the size of the ipsilateral olfactory bulb is reduced by approximately 25%. The large reduction in size, coupled with the clear lamination and other features of the olfactory system, indicates that the manipulation is an ideal preparation for examining the regulation of early growth. We know that both olfactory bulbs are of equal size at the time of occlusion, but that 30 days later there is a large discrepancy. What series of events produces the changes? The present paper outlines what is known about the anatomical, biochemical and physiological changes introduced by naris occlusion in order to lay a framework for further work.

Adult naris closure profoundly reduces tyrosine hydroxylase expression in mouse olfactory bulb

Peripheral afferent innervation appears to be required for the expression of the dopamine phenotype in the rodent main olfactory bulb. Experiments utilizing neonatal naris closure as a means of sensory deprivation also suggest that odor-induced afferent activity is required for the expression of the phenotype. These experiments are confounded, however, by the significant postnatal maturation of the dopamine system. The current experiments utilized adult unilateral naris closure to address this issue. As with neonatal closure, adult deprivation produces a profound reduction in the expression of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway. By 4 days a small decrease is observed in TH activity and immunoreactivity. Activity reaches a nadir of 12% of control levels at about 1 month. TH mRNA is reduced similarly when analyzed at about 2 months post-closure. Glutamic acid decarboxylase protein and mRNA expression, which are co-localized with TH, remain at close to control levels indicating the continued presence of the dopamine neurons. The time-course of the loss of TH is identical to that for zinc sulphate-induced denervation of the olfactory bulb. These data support the hypothesis that odor modulated afferent activity is required for expression of the dopamine phenotype and that, if a trophic factor is involved, its release is also activity dependent.

Discrete expression of Ca2+/calmodulin-sensitive and Ca(2+)-insensitive adenylyl cyclases in the rat brain

Physiological studies and inferences from invertebrate models implicate Ca2+/calmodulin-sensitive adenylyl cyclase with memory processes. However, Ca2+/calmodulin-insensitive adenylyl cyclase also occurs in brain, and its neuronal functions are less clear. Two oligonucleotide probes, based on rat cDNAs for Types I and II adenylyl cyclase, which appear to correspond to these functional forms, were used to conduct in situ hybridization analysis of the relative abundance and localization of these two species in the rat brain as a first step in evaluating their neuronal role. Quite discrete patterns of expression were encountered; in some areas, both species were co-expressed, but in others, little overlap was observed. The differential expression of the two mRNAs suggests that discrete roles may be fulfilled by the two adenylyl cyclases in neural tissues.

Regulation of protein kinase C activity by sensory deprivation in the olfactory and visual systems

Environmental regulation of sensory function has provided an important model of plastic mechanisms mediating neural information processing. To define potential commonalities in information processing in different systems, we investigated molecular changes elicited by sensory deprivation in the developing rat olfactory and visual systems. Protein kinase C (PKC), an intracellular messenger implicated in synaptic plasticity and memory, was analyzed. Initial, developmental studies indicated that PKC activity in the soluble and particulate fractions of the olfactory bulb increased three- to fourfold from birth to 3 months of age. Unilateral olfactory deprivation prevented the developmental increase in both soluble and particulate PKC activities in the ipsilateral olfactory bulb and piriform cortex, the second-order relay. Phorbol ester binding localized PKC to intrinsic neuronal populations and their dendrites in the control and deprived bulbs. Moreover, PKC was similarly lower in the visual cortex of dark-reared rats than in light-reared controls. The changes in PKC were region specific, as activity was unchanged by either treatment in the parietal cortex, a control area that does not process primary olfactory or visual information. Our results suggest that the important intracellular messenger, PKC, is similarly regulated in entirely different sensory systems by different environmental stimuli. Consequently, different sensory systems may use common molecular mechanisms to process information.

Changes in activity and mRNA for rat tryptophan hydroxylase and aromatic L-amino acid decarboxylase of brain serotonergic cell bodies and terminals following neonatal 5,7-dihydroxytryptamine

In the present study, we examined time-dependent changes in activity, mRNA and immunoreactivity of the serotonin biosynthetic enzymes, tryptophan hydroxylase (TPH) and aromatic L-amino acid decarboxylase (AADC) in dorsal raphe nucleus (DRN), caudal brainstem and hypothalamus, following intracisternal injection of 5,7-dihydroxytryptamine (5,7-DHT) in neonatal rats. TPH activity in central serotonergic cell bodies and terminals was reduced to 20-30% of control levels at 1-8 weeks after neonatal, low-dose 5,7-DHT injection (24 micrograms free base). In contrast, AADC activity was either not changed or decreased to 40% of control levels, depending on the region. In situ hybridization and immunocytochemical staining indicated that 5,7-DHT caused a marked reduction in TPH and AADC message levels as well as the number of 5-HT and AADC-immunoreactive cells within the DRN as early as 1 week after 5,7-DHT. Even 15 weeks after drug administration recovery did not occur. This apparent neuronal loss was region-specific suggesting that some serotonergic neurons are more resistant to neonatal 5,7-DHT treatment than others. Taken together, these studies indicate that neonatal treatment with 5,7-DHT produces a marked and permanent (up to 15 weeks) reduction in the number of central serotonergic neurons.

Tyrosine hydroxylase protein and messenger RNA in the dopaminergic nigral neurons of patients with Parkinson's disease

To analyze the roles of transcriptional and post-transcriptional regulatory mechanisms of tyrosine hydroxylase (TH) gene expression during dopaminergic denervation in Parkinson's disease (PD), the cellular content of TH messenger RNA (mRNA) and TH protein in the substantia nigra were compared in control subjects and patients with PD. The average amounts of TH mRNA as well as those of TH protein per neuron were variable among controls but correlated to each other. In PD patients, both TH mRNA and TH protein content in nigral neurons were reduced relative to controls, however, the ratio between TH protein and TH mRNA levels was unaffected. The data suggest that, in PD: (1) TH protein content is decreased in the surviving nigral dopaminergic neurons, most likely as a result of a lowered TH mRNA cellular content. Thus the surviving neurons at end stages of the disease may be in a premorbid state. (2) The TH mRNA translation rate is not modified to compensate for dopamine deficiency.

Parallel up-regulation of catecholamine biosynthetic enzymes by dexamethasone in PC12 cells

We sought to investigate whether dexamethasone produces a coordinated, time-dependent effect on all enzymes in the catecholamine biosynthetic pathway in PC12 cells. The levels of mRNAs of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), and dopamine beta-hydroxylase (DBH) were examined at 0, 6, 12, 24, and 48 h after dexamethasone (5 microM) treatment to PC12 cells. The levels of all enzyme mRNAs steadily increased for 24 h, although the increase of AADC mRNA content was slow. The increased mRNA levels of TH and AADC were maintained at 48 h, whereas the level of DBH mRNA was sharply decreased at 48 h. The maximally induced mRNA levels were approximately 5.0-, 2.4-, and 7.0-fold higher than the control levels of TH, AADC, and DBH, respectively. The elevation of enzyme activities was detected later than the increase in levels of mRNAs. The maximal activities of TH, AADC, and DBH were reached between 48 and 72 h with 3.6-, 1.8-, and 8.0-fold increases, respectively. Low, but detectable, phenylethanolamine N-methyltransferase (PNMT) activity was observed in PC12 cells, and dexamethasone increased its activity 5.6-fold at 72 h. The PNMT mRNA was easily detected by northern blot analysis after exposure for 24 h to dexamethasone. The data suggest that, in PC12 cells, dexamethasone up-regulates all catecholamine biosynthetic enzyme genes in a parallel fashion.

Olfactory afferent regulation of the dopamine phenotype in the fetal rat olfactory system

Recent studies strongly suggest that functional olfactory receptor cell innervation is necessary for the maintenance of the dopamine phenotype in the adult rat olfactory bulb. To determine whether afferent innervation is required for the initial expression of the dopaminergic phenotype during development, the current studies investigated the association between afferent innervation and phenotypic expression using both in vivo and in vitro systems. Ontogeny of the dopamine phenotype in the rat main olfactory bulb was assessed by the appearance of immunoreactivity for tyrosine hydroxylase, the first enzyme in the dopamine biosynthetic pathway. Development of receptor afferent innervation of the bulb was demonstrated with olfactory marker protein immunoreactivity. Tyrosine hydroxylase-immunoreactive cells occurred only in regions of the olfactory bulb receiving afferent innervation. However, the appearance of afferent fibers in the olfactory bulb preceded tyrosine hydroxylase expression by three to four days (gestational days 14-15 versus 18, respectively). In explant cultures, significant numbers of tyrosine hydroxylase-containing cells were observed only in en bloc co-cultures of presumptive olfactory bulb and epithelium. Explant cultures of presumptive olfactory bulb alone contained few, if any, tyrosine hydroxylase-immunoreactive cells. Similarly, explants produced by recombining previously separated presumptive olfactory bulb and epithelium exhibited very few tyrosine hydroxylase-immunostained cells. These data suggest that expression of the dopamine phenotype, as indicated by the presence of tyrosine hydroxylase, depends on a critical level of afferent innervation. The results also support previous studies which indicated that neuronal activity or an activity-dependent process may be required for induction of tyrosine hydroxylase expression.

Region-specific expression of a K+ channel gene in brain

Northern blot analysis and in situ hybridization studies reveal the highly localized expression in rat brain of transcripts from a gene (KShIIIA) encoding components for voltage-gated K+ channels. KShIIIA expression is particularly prominent throughout the dorsal thalamus. The expression of KShIIIA is compared to that of a closely related gene, here called NGK2-KV4. These two genes encode transcripts that induce currents in Xenopus oocytes that are as of yet indistinguishable, but they show very different patterns of expression in rat brain. NGK2-KV4 transcripts are particularly abundant in the cerebellar cortex, where KShIIIA expression is very weak. These results demonstrate the existence of cell-type-specific K+ channel components and suggest that one reason for the unusually large diversity of K+ channel proteins is the presence of subtypes that participate in specific brain functions.

Human urinary trypsin inhibitor (urinastatin)-like substance in mouse liver

Mouse liver contains a human urinary trypsin inhibitor (urinastatin, UT)-like immunoreactive substance with trypsin inhibitory activity. Northern blot analysis demonstrates the presence of the appropriate 1.3 kb mRNA band in liver tissue but not in kidney or other tissues examined. Administration of hydrocortisone, which is known to increase the urinary excretion of the UT-like substance, increased the levels of UT-like substance in serum and in the liver tissue. In contrast, deoxycorticosterone acetate did not have such an effect. These results suggest that the gene encoding UT-like substance is primarily expressed in the liver of the mouse, and that glucocorticoids play an important role in regulating the hepatic synthesis of UT-like substance. Furthermore, these findings indicate that the mouse is a suitable species for research on the biological function of UT or UT-like substances.

Differential effect of functional olfactory bulb deafferentation on tyrosine hydroxylase and glutamic acid decarboxylase messenger RNA levels in rodent juxtaglomerular neurons

Expression of the dopaminergic phenotype in olfactory bulb (OB) juxtaglomerular neurons (constituting a population of periglomerular and external tufted cells) is dependent upon functional innervation by peripheral olfactory receptors. Loss of functional input in rodents, by either peripheral deafferentation or deprivation of odorant access, results in a profound decrease in the expression of juxtaglomerular tyrosine hydroxylase (TH). We have examined the effects of such treatments on the expression of the neurotransmitter biosynthetic enzyme glutamic acid decarboxylase (GAD), which is colocalized with TH in the majority of TH-containing juxtaglomerular neurons. Following either chemically induced OB deafferentation in adult mice or unilateral odor deprivation in neonatal rats, steady-state OB GAD messenger RNA levels remained essentially unchanged as assessed by Northern blot analysis 20-40 days after treatment. These results were confirmed by in situ hybridization analysis, which demonstrated a profound loss of juxtaglomerular TH messenger RNA but no accompanying decrease in regionally colocalized GAD message. Since GAD is found in nearly all dopaminergic OB cells, the preservation of juxtaglomerular GAD message implies that olfactory receptor neurons exert a differential transneuronal regulation of TH and GAD gene transcription.

Species-specific distribution of aromatic L-amino acid decarboxylase in the rodent adrenal gland, cerebellum, and olfactory bulb

Aromatic L-amino acid decarboxylase (AADC), the enzyme that converts L-dopa to dopamine, displayed species-specific differences in both activity and immunoreactivity in the cerebellum, olfactory bulb, and adrenal glands of three rodent species, the hamster, rat, and mouse. Specifically, in the hamster but not the rat or mouse, AADC immunoreactive cells were observed in the cerebellum and adrenal cortex. The unusual distribution of the enzyme was confirmed biochemically. AADC activity was greater in the adrenal gland and the cerebellum in the hamster than in the mouse or rat. In addition, by Western blot analysis, one band of appropriate molecular weight was observed both in the hamster adrenal gland and cerebellum. The rat adrenal gland displayed a similar immunoreactive protein on the Western blot; however, the protein could not be detected in the rat cerebellum by the technique utilized. Tyrosine hydroxylase (TH) immunoreactivity in these same tissues did not differ among the species. In the main olfactory bulb of the mouse, juxtaglomerular cells exhibited very limited immunoreactivity for AADC, but TH-immunoreactivity in these cells was robust. In contrast, juxtaglomerular cells in the rat displayed a similar intensity of immunostaining for both AADC and TH. AADC activity in the mouse, consistent with the reduced immunostaining for the enzyme, was 50% of that in the rat and the hamster. These data demonstrate that AADC protein, which is contained in cells of diverse function, also displays qualitative and quantitative species specific variations in both distribution and amount.