Effect of chronic cold exposure on tyrosine hydroxylase mRNA in rat adrenal gland

The effect of chronic stress on the levels of tyrosine hydroxylase (TH) RNA in rat adrenal gland was investigated by RNA-DNA hybridization using a cloned TH cDNA probe. Results of dot-blot hybridization experiments and northern analysis demonstrate that exposure of animals to cold for 1 week results in a 4-5-fold increase in the relative abundance of TH mRNA. This increase in TH mRNA level may underlie the increase in adrenal TH activity that is known to occur when rats are exposed to such cold stress.     

Neurokinin receptor mRNA localization in human midbrain dopamine neurons

The structurally related neurokinin peptides, substance P and neurokinin A, are found in abundance within the substantia nigra of a variety of mammalian species. Although it has been established recently that the neurokinin-3 (NK3) receptor is the predominant neurokinin receptor found in rat substantia nigra and adjacent midbrain nuclei, the nature of the neurokinin receptor expressed in human midbrain has not been elucidated. In the present study, neurokinin receptor messenger RNA (mRNA) content within rat and human midbrain were directly compared by using quantitative in situ hybridization histochemistry. In contrast to the high abundance of NK3 receptor mRNA within dopamine (DA) cells of the rat midbrain, neurokinin-1 (NK1), but not NK3, receptor mRNA was localized to human midbrain DA cells. Within the human midbrain, the abundance of NK1 receptor mRNA differed significantly among the distinct DA cell-containing nuclei, with the highest level of expression seen in several subdivisions of the substantia nigra. Thus different neurokinin receptor subtypes apparently mediate the effects of substance P and neurokinin A on human versus rat DA neurons. J. Comp. Neurol. 382:394-400, 1997. © 1997 Wiley-Liss, Inc.     

Nicotinic stimulation of catecholamine synthesis and tyrosine hydroxylase phosphorylation in cervine adrenal medullary chromaffin cells

The synthesis and secretion of catecholamines by the adrenal medulla is of major importance in the stress response. Tyrosine hydroxylase, the rate-limiting enzyme for catecholamine biosynthesis, has been extensively studied in adrenal medullary chromaffin cells from a number of species. Cervine chromaffin cells are of interest because the deer is known to be a relatively stress-prone reactive species. We report the first characterisation of tyrosine hydroxylase regulation in cervine chromaffin cells. Nicotinic receptor activation resulted in a time- and concentration-dependent increase in catecholamine synthesis, which was significantly reduced by the extracellular signal-regulated kinase (ERK)1/2 signalling pathway inhibitor PD98059 and the calcium/calmodulin protein kinase II inhibitor KN-93, but not by H89 or bisindolylmaleimide I, inhibitors of protein kinase A and C, respectively. Nicotinic stimulation also increased the phosphorylation of ERK1/2 and tyrosine hydroxylase. This latter response occurred on serine residues 19, 31 and 40 of the enzyme. The nicotinic-induced phosphorylation of ERK1/2 and serine 31 of tyrosine hydroxylase was suppressed by PD98059 but not bisindolylmaleimide I. These data indicate that nicotinic stimulation of tyrosine hydroxylase involves the phosphorylation of serine 31 via an ERK1/2-dependent, protein kinase C-independent pathway. Protein kinase C activation by phorbol 12-myristate 13-acetate also caused an ERK1/2-dependent increase in the serine 31 phosphorylation of tyrosine hydroxylase but, in contrast to the nicotinic response, was not accompanied by an increase in enzyme activity. Thus, ERK1/2-mediated serine 31 phosphorylation of tyrosine hydroxylase appears necessary but not sufficient for nicotinic activation of catecholamine synthesis in cervine chromaffin cells. These data present potentially important similarities and differences between the regulation of catecholamine synthesis in cervine and the more widely studied bovine adrenal medulla.     

Brainstem activation of the adrenal medulla in the cat

Stimulation of the locus coeruleus in 40 cats leads to generalized activation of the sympathetic nervous system characterized by an immediate pressor response which was followed in the post-stimulus period by an increase of 49 ± 10and44 ± 6% in common carotid arterial resistance ipsilateral and contralateral to stimulation, respectively. This later response was not affected by vagotomy or bilateral cervical sympathectomy but was blocked by high spinal cord section. The post-stimulus carotid vasoconstriction response could be entirely eliminated by acute bilateral physiological adrenalectomy in the form of adrenal hilar clamping, an effect which was reversible if the clamps were removed. The carotid vasoconstrictor response was associated with a rise in the circulating level of noradrenaline (260%) and adrenaline (196%), which was prevented by clamping the adrenal hilum. This response was not mediated via the hypothalamus because it persisted in the decerebrate animal, nor was it merely excitation of fibers of passage since it was reproduced by microinjection of glutamate into the locus coeruleus. The response was blocked by phentolamine suggesting it is mediated by α-adrenoceptors. These data represent the first conclusive demonstration that cell bodies in the brainstem are capable of activating the adrenal medulla. This fact is central to our present concept of the organization of the sympatho-adrenal axis.     

Repeated amphetamine evokes biphasic alterations in the tyrosine hydroxylase mRNA level in the rat adrenal medulla: an in situ hybridization study

Summary In the present study we estimated the effects of single and repeated administration of d-amphetamine (5mg/kg, i.p., twice a day for 14 days) on tyrosine hydroxylase (TH) mRNA levels in the rat adrenal medulla. In situ hybridization experiments, conducted using a [³⁵S]d-ATP-labelled deoxyoligonucleotide probe and a densitometric analysis of autoradiograms, showed that repeated d-amphetamine moderately increased the TH mRNA level (by ca. 24%) in the adrenal medulla at 2 h after the last injection. In contrast, after 48 h the TH mRNA level was decreased (by ca. 21%). No significant changes in the TH mRNA level in the adrenal medulla were found following single administration of d-amphetamine. These results suggest that repeated d-amphetamine administration leads to biphasic changes in the adrenal TH biosynthesis, which may reflect an adaptive response to chronic drug treatment.     

Combination of alkaline phosphatase in situ hybridization with immunohistochemistry: colocalization of calretinin-mRNA with calbindin and tyrosine hydroxylase immunoreactivity in rat substantia nigra neurons

We describe a method to combine non-radioactive in situ hybridization using alkaline phosphatase (AP) labelled oligonucleotide-probes with immunohistochemistry on the same thin paraffin section. The simultaneous detection of calretinin-mRNA and calbindin- or tyrosine hydroxylase-like immunoreactivity in neurons of rat substantia nigra, pars compacta, was used as a test system to develop the method. Brains were fixed by perfusion with 4% paraformaldehyde and embedded in paraffin. Five-μm-thick sections were processed for non-radioactive in situ hybridization with a 33-base alkaline phosphatase conjugated synthetic oligonucleotide complementary to calretinin mRNA. After hybridization and colour reaction to visualize calretinin mRNA, sections were incubated with antibodies against calbindin D_28K or tyrosine hydroxylase. Immunoreaction was visualized using the avidin-biotin-complex-technique and diaminobenzidine. As the colour of both reaction products differ markedly, the distribution of calretinin mRNA-containing neurons (purple-blue, alkaline phosphatase product) and calbindin/tyrosine hydroxylase immunopositive cells (brown peroxidase product) could be differentiated easily on the same section. Calbindin- and tyrosine hydroxylase-like immunoreactivity was found in the majority of calretinin mRNA-containing cells within the substantia nigra, pars compacta, indicating that in this nucleus a proportion of the dopaminergic neurons contain both calcium binding proteins calbindin and calretinin. In conclusion, non-radioactive in situ hybridization using alkaline phosphatase labelled oligonucleotide probes can be readily combined with immunohistochemistry.     

Effects of stress and adrenalectomy on tyrosine hydroxylase mRNA levels in the locus ceruleus by in situ hybridization

The locus ceruleus-norepinephrine system is one of the principal effectors of the stress response. Acute stress induces norepinephrine synthesis and release, and noradrenergic cells compensate by increasing the activity of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. Here we use in situ hybridization histochemistry to show the effects of acute and chronic intermittent stress on the expression of tyrosine hydroxylase mRNA in the rat locus ceruleus. Restraint stress increased tyrosine hydroxylase mRNA in the locus ceruleus but not in dopaminergic nuclei such as the substantia nigra or ventral tegmental area. One hour of footshock or restraint caused a rapid increase in locus ceruleus tyrosine hydroxylase mRNA which returned to basal levels within 24 h. Chronic intermittent stress (1 hour of restraint or footshock per day for 14 days) produced no change in tyrosine hydroxylase mRNA. Neither adrenalectomy nor dexamethasone replacement significantly affected mRNA expression. These findings indicate that acute stress can increase the expression of tyrosine hydroxylase mRNA in the locus ceruleus but that adaptation occurs to repeated stress, and that the expression of tyrosine hydroxylase mRNA in the locus ceruleus is independent of direct glucocorticoid modulation.     

Different effects of insulin and 2-deoxy- -glucose administration on tyrosine hydroxylase gene expression in the locus coeruleus and the adrenal medulla in rats

The major brain norepinephrinergic nucleus, locus coeruleus, is an important integrating element of extero- and interoceptive stimuli in organisms facing different physiological challenges. We investigated the effects of single and repeated (seven times) exposure to immobilization stress (120 min daily), insulin (5 IU/kg, i.p. daily) or 2-deoxy- -glucose (500 mg/kg, i.p. daily) administration on tyrosine hydroxylase (TH) mRNA levels, the rate-limiting enzyme in catecholamine biosynthesis, by in situ hybridization in locus coeruleus and by Northern blot analysis in the adrenal medulla of rats. Both the single and repeated immobilization caused a significant increase in TH mRNA levels in the locus coeruleus (1.5–2-fold; p < 0.05) and in the adrenal medulla (about 4-fold; p < 0.05) when compared with unstressed controls. Hypoglycemia induced by a single or repeated insulin administration led to about fourfold (p < 0.01) elevation in adrenal medullary TH mRNA levels, whereas TH mRNA in locus coeruleus remained unchanged when compared with saline-treated controls. In contrast to the effect of insulin-induced hypoglycemia, cellular glucoprivation caused by a single or repeated 2-deoxy- -glucose administration significantly elevated TH mRNA levels in both the adrenal medulla (fourfold; p < 0.01) and the locus coeruleus (twofold; p < 0.01). Our data suggest that in contrast to immobilization or cellular glucoprivation caused by 2-deoxy- -glucose administration, insulin-induced hypoglycemia is not a specific or quantitatively sufficient stimulus for induction of TH gene expression in the locus coeruleus, although all these stressors strongly activate the process in the adrenal medulla.     

Immunocytochemical localization of tyrosine hydroxylase in rat adrenal medulla by the peroxidase labeled antibody method: effects of enzyme activation on ultrastructural distribution of the enzyme

A monospecific antibody against tyrosine hydroxylase (TH), purified from a transplantable rat pheochromocytoma, was produced in rabbits. Immunohistochemical techniques were employed in order to determine if a relationship exists between the subcellular distribution of TH and the level of activation of the enzyme in the rat adrenal medulla. Tyrosine hydroxylase activity in adrenals removed from non-stressed rats following pentobarbital anesthesia was found to be 12.9 +/- 1.0 nmol DOPA formed x mg protein-1. The use of ether anesthesia (17.9 +/- 2.0 nmol DOPA formed x mg protein-1), and the administration of electroconvulsive shock (ECS) followed by decapitation (35.9 +/- 2.0 nmol DOPA formed x mg protein-1) was associated with an acute activation of adrenal TH. The subcellular distribution of TH within the cytosol of chromaffin cells from animals subjected to anesthesia or ECS, as determined by immunocytochemical techniques, was similar. In all treatment groups chromaffin cells were found which had TH associated with some chromaffin granules. The percentage of chromaffin granules which appeared to contain TH was lower in animals subjected to ECS plus decapitation as compared with anesthetized animals. These observations suggest that the activation of adrenal medullary TH is not associated with a shift in the subcellular distribution of the enzyme from the cytosol to membranous structures.     

Anatomical localization of calmodulin mRNA in the rat brain with cloned cDNA and synthetic oligonucleotide probes

Calmodulin is a small, acidic calcium-binding protein that regulates a number of calcium-dependent enzyme activities and is thought to be involved in neurotransmission. To begin to explore further the regulation of this important protein in the brain, we have cloned a rat calmodulin cDNA and designed an oligonucleotide probe based on this sequence. Both the cDNA and oligonucleotide probes revealed a markedly heterogeneous distribution of hybridization signal for calmodulin mRNA in the rat brain. The greatest apparent abundance of mRNA for calmodulin was seen in the hippocampus and cerebral cortex, whereas many brain regions showed relatively low hybridization signal, including the striatum and portions of the hypothalamus and brainstem.     

Developmental expression of neuronal calmodulin mRNA species in the rat brain analyzed by in situ hybridization.

The temporal and spatial distribution of calmodulin mRNAs which are preferentially expressed in neurons was determined during postnatal development of rat central nervous system. Expression of these mRNAs was strongly detected in the developing neocortex, hippocampus, and cerebellum. Differences in the pattern of expression of a 1.8 and 4.0 kb neuronal calmodulin mRNA species were identified in the developing cerebellum. Expression of the smaller mRNA appeared to correlate with proliferating and developing cerebellar granule neurons while the larger mRNA was present in the mature granule neuron population. A transient elevation in the neuronal calmodulin mRNA species was observed in the superior and inferior colliculus and in the thalamus at postnatal days 5 and 10.     

Localization of insulin-like growth factor binding protein-4 expression in the developing and adult rat brain: Analysis by in situ hybridization

We have previously isolated insulin-like growth factor binding protein-4 (IGFBP-4) from media conditioned by a neuronal cell line and have detected IGFBP-4 mRNA in selected regions of the developing and adult rat brain by Northern blot analysis. In this study, the ontogeny and regional distribution of IGFBP-4 expression were determined by in situ hybridization histochemistry. While IGFBP-4 mRNA expression at embryonic day 15 was restricted to choroid plexus primordium and meninges, by embryonic day 20 IGFBP-4 mRNA was also localized in the basal ganglia. In the postnatal rat, at days 1 and 5, IGFBP-4 was also present in the meningeal cell layer surrounding the developing cerebellum and in the hippocampal formation. The distribution of IGFBP-4 mRNA in the adult brain was considerably more widespread. The principal areas where IGFBP-4 mRNA was detected were the cerebral cortex (layers II and IV), olfactory peduncle (anterior olfactory nuclei), limbic system (hippocampus and amygdala), thalamus and basal ganglia, as well as choroid plexus and meninges. The widespread and persistent expression of IGFBP-4 is in marked contrast with IGFBP-2, the other IGFBP in the brain, whose localization by in situ hybridization is reported to be restricted to choroid plexus and meninges. The spatial pattern of IGFBP-4 expression in areas known to either overlap, be adjacent to, or project to regions that express the IGFs or their receptors may reflect a role for IGFBP-4 as a modulator of IGF action in the brain. © 1993 Wiley-Liss, Inc.     

Dopaminergic neurons in rat ventral midbrain express brain-derived neurotrophic factor and neurotrophin-3 mRNAs

Studies of the trophic activities of brain-derived neurotrophic factor and neurotrophin-3 indicate that both molecules support the survival of a number of different embryonic cell types in culture. We have shown that mRNAs for brain-derived neurotrophic factor and neurotrophin-3 are localized to specific ventral mesencephalic regions containing dopaminergic cell bodies, including the substantia nigra and ventral tegmental area. In the present study, in situ hybridization with ³⁵S-labeled cRNA probes for the neurotrophin mRNAs was combined with neurotoxin lesions or with immunocytochemistry for the catecholamine-synthesizing enzyme tyrosine hydroxylase to determine whether the dopaminergic neurons, themselves, synthesize the neurotrophins in adult rat midbrain. Following unilateral destruction of the midbrain dopamine cells with 6-hydroxydopamine, a substantial, but incomplete, depletion of brain-derived neurotrophic factor and neurotrophin-3 mRNA-containing cells was observed in the ipsilateral substantia nigra pars compacta and ventral tegmental area. In other rats, combined in situ hybridization and tyrosine hydroxylase immunocytochemistry demonstrated that the vast majority of the neurotrophin mRNA-containing neurons in the substantia nigra and ventral tegmental area were tyrosine hydroxylase immunoreactive. Of the total population of tyrosine hydroxylase-positive cells, double-labeled neurons constituted 25–50% in the ventral tegmental area and 10–30% in the substantia nigra pars compacta, with the proportion being greater in medial pars compacta. In addition, tyrosine hydroxylase/neurotrophin mRNA coexistence was observed in neurons in other mesencephalic regions including the retrorubral field, interfascicular nucleus, rostral and central linear nuclei, dorsal raphe nucleus, and supramammillary region. The present results demonstrate brain-derived neurotrophic factor and neurotrophin-3 expression by adult midbrain dopamine neurons and support the suggestion that these neurotrophins influence dopamine neurons via autocrine or paracrine mechanisms. These data raise the additional possibility that inappropriate expression of the neurotrophins by dopaminergic neurons could contribute to the neuropathology of disease states such as Parkinson's disease and schizophrenia. © 1994 Wiley-Liss, Inc.     

Alterations in tyrosine hydroxylase activity elicited by raphe nuclei lesions in the rat locus coeruleus: evidence for the involvement of serotonin afferents

The time course of the variations in tyrosine hydroxylase (TH) activity was measured in the rat locus coeruleus (LC) after lesions of the nucleus raphe dorsalis (NRD), nucleus raphe centralis superior (NRCS) and nucleus raphe pontis (NRP). A certain number of lesions were performed in the raphe magnus (RM), the caudal and rostral NRP and the caudal and rostral NRCS, lateral to raphe nuclei and in adrenalectomized animals. The serotonin (5-HT) content in the LC was also determined after these lesions. Only raphe nuclei producing significant decreases in the 5-HT content in the LC are successful in provoking increases in the TH activity in the LC, thus these results suggest that the noradrenaline (NA) synthesis in the LC may be regulated by 5-HT afferents. Moreover, intraventricular injections of 5,6-dihydroxytryptamine (5,6-DHT) and administration of parachlorophenylalanine (PCPA) also produce significant increases in TH in the LC. After immunotitrations of TH in the LC it was shown that, with exception of a high dose of 5,6-DHT (75 micrograms), all these treatments provoke an increase in the concentration of the enzyme. It therefore seems that one of the functional roles of 5-HT in the LC could be the regulation of the concentration of TH.     

Dopaminergic mRNA expression in the intact sebstantia nigra of unilaterally 6-OHDA-lesioned and grafted rats: an in situ hybridization study

Summary. The present study was performed to investigate the influence of intrastriatal fetal mesencephalic grafts on dopaminergic mRNA expression in the non-lesioned substantia nigra pars compacta of unilaterally 6- hydroxydopamine-lesioned rats. The expression of dopamine transporter mRNA, synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA was assessed in adjacent cryostat sections using in situ hybridization. Rotational behavior induced by apomorphine and amphetamine as well as hybridization of striatal sections cut at the grafting coordinates were used to prove the functional recovery and the presence of grafted cells, respectively. After grafting, the number of rotations was decreased and hybridization signals overlying cells in the grafted striatum were detected. Mean grain densities overlying labeled neurons in the substantia nigra pars compacta of grafted rats were compared to those of shamgrafted rats and revealed differential expression of dopamine transporter mRNA, whereas synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA expression showed no difference. The results will be discussed in relation to previous in vitro and in vivo studies suggesting a reduction of functional dopamine transporter molecules in the contralateral striatum. Received April 25, 2000; accepted August 17, 2000     

Fine structure of the nigrostriatal anlage in fetal rat brain by immunocytochemical localization of tyrosine hydroxylase

The developmental morphology and synaptic associations of neurons in the nigrostriatal anlage are examined by the electron microscopic immunocytochemical localization of tyrosine hydroxylase at embryonic (E) day 13.5 and 14.5 in rat brain. At E 13.5, immunoreactivity for the enzyme is localized throughout the cytoplasm of neuronal perikarya and processes including somatic, dendritic, and axonal growth cones. The cytoplasmic organelles in perikarya include primarily ribonucleic-protein particles, mitochondria and an immature Golgi apparatus. At E 14.5, the tyrosine hydroxylase labeled processes are detected in the lateral hypothalamus and ventrolateral caudate-putamen. The axonal processes showing immunoreactivity in the ventral mesencephalon and more rostral portions of the nigrostriatal bundle are frequently attached to unlabeled neurites by puncta adherentia. In the hypothalamus and caudate-putamen presumably transient synaptic junctions are also detected between the labeled axons and unlabeled neurons. The immature morphological features of neurons showing immunoreactivity for tyrosine hydroxylase thus indicate, that the biochemical differentiation of the nigrostriatal neurons precedes complete cytological differentiation.     

Contrasting effects of repeated treatment vs. withdrawal of methamphetamine on tyrosine hydroxylase messenger RNA levels in the ventral tegmental area and substantia nigra zona compacta of the rat brain

We have assessed the effect of repeated treatment with methamphetamine (METH) on the abundance of the messenger ribonucleic acid molecules encoding the enzyme tyrosine hydroxylase (TH) and preprocholecystokinin (PPCCK) in the substantia nigra zona compacta (SNc) and the ventral tegmental area (VTA) by in situ hybridization histochemistry. Rats were injected twice daily with METH (4 mg/kg of body weight) for 6 consecutive days and sacrificed either 5 h or 15 days after the last injection. TH mRNA in the VTA was unaffected by repeated METH treatment but was decreased 25% relative to controls in the SNc. Concurrent administration of METH and MK-801 decreased TH mRNA levels in the SNc to 47% relative to controls. In contrast, TH mRNA levels were found increased in the VTA (42%) but not SNc 15 days post-METH treatment. Coadministration of MK-801 with METH prevented the increase in TH mRNA in the VTA. PPCCK mRNA levels were not significantly affected by METH treatment in VTA or SNc either 5 h or 15 days posttreatment. The results demonstrate that exposure to repeated methamphetamine elicits changes of TH mRNA levels in the VTA that become manifest 2 weeks after withdrawal from this psychostimulant drug. © 1996 Wiley-Liss, Inc.     

Localization of monoamine oxidase A and B mRNA in the rat brain by in situ hybridization

Monoamine oxidases A and B (MAOA and MAOB) are the major catabolic isoenzymes of catecholamines and serotonin in the mammalian brain. Although the distribution of the monoamine oxidase protein has been mapped by ligand binding and immunohistochemistry, the sites of MAOA and MAOB synthesis have not been precisely determined. In this study, we used in situ hybridization to visualize MAOA and MAOB mRNAs in the rat brain by using specific cDNA and oligonucleotide probes. MAOA mRNA was localized in major monoaminergic cell groups, such as the dorsal vagal complex, the C1/A1 groups, the locus ceruleus, the raphe nuclei, the substantia nigra, and the ventral tegmental area. MAOA mRNA was also found in forebrain structures, such as the cortex, the hippocampus, the thalamus, and the hypothalamus. In contrast to the distribution of MAOA mRNA, high levels of MAOB mRNA were present in only three brain regions: the area postrema, the subfornical organ, and the dorsal raphe. The in situ visualization of MAO mRNA demonstrates that MAOA mRNA synthesis is wide spread in many catecholaminergic and serotonergic cell groups, whereas MAOB mRNA synthesis is far more discrete and limited. The different expression patterns of MAOA and MAOB suggests that may also have different physiological functions. Synapse 25:30–36, 1997. © 1997 Wiley-Liss, Inc.     

Modulation of tyrosine hydroxylase gene expression in rat brain and adrenals by exposure to cold

The long-term changes in tyrosine hydroxylase (TH) activity induced by chronic exposure to cold in brain noradrenergic neurons of the locus coeruleus (LC) were analyzed and compared to those measured in a peripheral tissue such as adrenals. This analysis was made possible at the level of one single tissue corresponding to one animal by the use of sensitive methods that allow assay of TH activity, protein, and mRNA levels in parallel from the same homogenate. The three parameters were measured in brain structures and adrenals of rats maintained at 4 degrees C during 4 days and were compared to those of control animals kept at normal housing temperature (22 degrees C). LC of rats exposed to cold contained 200% more TH mRNA than controls. The amount of TH protein in this area rose to as much as 164% that of controls. Similarly, the activity of the enzyme increased to 140% of the normal value. Thus, these observations show that 1) the increase in TH mRNA was much higher than the increase in protein levels, and that 2) the newly synthesized molecules have about the same activity as that present under normal conditions. In contrast to the LC, no variation of these parameters was observed in the substantia nigra. In the adrenals, the variations in the different parameters were qualitatively similar to that observed in the LC, although they were quantitatively higher: TH mRNA, TH protein, and TH activity levels were respectively 330%, 182%, and 167% that of control adrenals. Altogether, these results demonstrate that exposure to cold induces an alteration in TH synthesis in brain noradrenergic neurons as well as in adrenals.