[H]Dexamethasone binding in rat frontal cortex

The work described in this paper presents evidence for the existence of specific glucocorticoid receptors in the rat frontal cortex. Using [³H]dexamethasone we found a K_d ≈ 6nM and a B_max≈ 270fmol/mg protein, concentrations that were about 75% of those found in hippocampus. [³H]dexamethasone binding in the frontal cortex, like that in hippocampus, was regulated by the corticosterone: thus, one-week treatment with corticosterone results in a decrease and long-term adrenalectomy results in an increase in [³H]dexamethasone binding. Developmentally, as reported for other brain regions, [³H]dexamethasone binding in frontal cortex was low during the first week of life and then rose during the following 10 days to approximate adult levels. These results are discussed in terms of providing a possible mechanism for the influence of corticoids on catecholamine activity in the frontal cortex.     

Glucocorticoid binding to receptor-like proteins in rat brain and pituitary: ontogenetic and experimentally induced changes.

Cytosol binding of [3H]corticosterone and [3H]dexamethasone was measured in various brain areas and the pituitary of perfused rats 12 h and 72 h, respectively, after adrenalectomy (ADX). A considerable regional heterogeneity was found 12 h post ADX representing differences of the normal cytosol binding capacities between various areas. When the second phase of the adrenalectomy-induced increase in binding capacity was allowed to develop (72 h post ADX), the cytosol binding of all regions increased to various extents. The highest percentage increases were found in those areas with the highest glucocorticoid binding capacity, namely the hippocampus and the septum. The ontogeny of the cytosol glucocorticoid binding macromolecules was investigated in the hippocampus, hypothalamus and pituitary using [3H]corticosterone and [3H]dexamethasone. The concentration of corticosterone binding sites is lowest in all three areas around day one and then increases by a factor of 2-3 reaching adult levels around day 32. For [3H]dexamethasone a similar pattern was observed in the hippocampus and hypothalamus. In the pituitary, however, the concentration of binding sites was slightly higher at day 1 than at any later developmental stage. Interruption of the fimbria in 3-day-old rats did not affect the development of the binding sites in the hippocampus. In an attempt to interfere with the normal glucocorticoid binding of the hippocampus as well as with the postadrenalectomy increase of the cytosol binding sites, bilateral transection of the fimbria was performed either 3 days or 80 days before ADX.In neither case did fimbria transection prevent the increase of the binding sites. The intrinsic (12 h post ADX) cytosol binding capacity of the hippocampus was also not affected by this lesion.     

Corticosterone receptors decline in a site-specific manner in the aged rat brain

Putative glucocorticoid receptors were measured in the brain and pituitary glands of young and aged rats in vivo and in vitro. Adrenalectomized rats were injected with a set dose of radiolabeled corticosterone plus unlabeled corticosterone; 2 h later [3H]corticosterone levels were measured in purified nuclear pellets from pituitary and 5 brain regions. Substantial decreases were seen in aged subjects in the maximal number of corticosterone binding sites in hippocampus and amygdala; all other regions showed no age-related changes. In contrast, there were no declines in the nuclear uptake of [3H]dexamethasone (DEX) in the aged rat brains. Since DEX interacts selectively with non-neuronal receptors in vivo, the deficit in glucocorticoid binding is selective for neurons. Subsequent studies assessing glucocorticoid receptor levels in cytosol preparations in vitro revealed significant declines in hippocampus and amygdala quantitatively comparable to the decline observed in nuclear binding in these loci. This suggests that the primary deficit leading to nuclear depletion may be the reduction of cytosolic receptor number, rather than other possible factors such as the reduction in receptor affinity or translocation of steroid-receptor complex. This decline may play a role in a number of limbic functions which are influenced by glucocorticoids and show deficits with age.     

Sexual dimorphism of glucocorticoid binding in rat brain

Glucocorticoids bind with high affinity to intracellular receptors located in high density within discrete regions of the rodent and primate brain. The binding of [3H]corticosterone was compared in the brains of male vs female rats. The number and affinity of cytosol receptors in the hippocampus and hypothalamus were examined in vitro. The cytosolic binding capacity of the hippocampus is greater in the female than in the male. This difference in binding capacity is not dependent on the presence of gonadal steroids: the effect of gonadectomy was not significant for either sex. The difference is not due to transcortin since the binding capacity of [3H]dexamethasone is also greater in the female hippocampus. Receptor affinity in the female hippocampus is half that of the male value. In the hypothalamus, the dimorphism is in the opposite direction: the number of [3H]corticosterone cytosolic binding sites was found to be greater in the male. The male hypothalamus also showed a greater affinity for [3H]corticosterone than did the female. Ovariectomy increased the number of binding sites in the female hypothalamus. In vivo nuclear uptake of a tracer dose of [3H]corticosterone was determined in animals having intact gonads. The percent of tissue [3H]corticosterone present in cell nuclei from 4 brain regions, including the hippocampus and hypothalamus, was calculated per unit DNA. The concentrations of [3H]corticosterone in nuclei relative to tissue homogenates were higher in females than males for the 4 brain regions, but not for the pituitary or liver. The data are interpreted as suggesting that glucocorticoid secretion under basal conditions and during stress may differentially effect specific brain structures in male vs female rats.     

Interactions in vivo and in vitro of corticoids and progesterone with cell nuclei and soluble macromolecules from rat brain regions and pituitary.

Adrenalectomized-ovariectomized (ADX-OVX) rats were given tail vein infusions of [3H]corticosterone, dexamethasone, cortisol, deoxycorticosterone or progesterone in doses around 10 nmoles/kg body weight. After a 30-60 min uptake period, cell nuclei were isolated from 9 brain regions and pituitary. Patterns of cell nuclear retention of [3H]corticosterone and [3H]dexamethasone differed: the former steroid was highest in hippocampus and septum and low in pituitary; the latter steroid was highest in pituitary and more uniformly distributed in the brain. The other 3H steroids showed very little cell nuclear labeling in vivo. In contrast, in vitro cytosol binding in hippocampus for [3H]progesterone, cortisol, deoxycorticosterone, and dexamethasone was 40-60% of that observed for [3H]corticosterone. The specificity of cell nuclear binding in slices of hippocampus in vitro was similar to that observed for cytosol binding. Reasons for the selectivity of in vivo cell nuclear labeling remain to be discovered but the selectivity does not appear to be an intrinsic feature of the receptors themselves. The pattern of in vivo labeling by [3H]corticosterone and [3H]dexamethasone differs from the in vivo distribution of [3H]estradiol in ADX-OVX rats using the same dissection procedure and this demonstrates the regional differentiation within brain of steroid hormone uptake and 'receptor' processes.     

Corticosterone binding to hippocampus: nuclear and cytosol binding in vitro

Uptake and cell nuclear binding of [³H]corticosterone was studied in 300 μm slices of brain regions of adrenalectomized rats. (1) Slice uptake of radioactivity was linear as a function of hormone concentration, while nuclear binding was saturated at2 × 10^?8 M [³H]corticosterone. Once bound to nuclei, [³H]corticosterone could not be displaced by1 × 10^?5 M corticosterone during a 30 min incubation at 25 °C. (2) Nuclear binding was optimal at 25 °C. Decreased binding at 0 °C was not due to limitations of cellular energy production, as shown in experiments with metabolic inhibitors. (3) Nuclear binding was highest in hippocampus, followed by amygdala, cerebral cortex, hypothalamus-preoptic area, midbrain, and cerebellum. Thesein vitro results agree with the regional distribution of binding obtained in previousin vivo labeling experiments. (4) [³H]Corticosterone binds better to hippocampal nuclei than [³H]hydrocortisone, while [³H]progesterone does not bind to nuclei. Unlabeled corticosterone and, to a lesser extent, both hydrocortisone and progesterone all prevent nuclear binding of [³H]corticosterone. (5) The soluble brain corticosterone-binding protein (K_aat0 °C4.2 × 10⁸ M^?1) does bind [³H]progesterone as well as [³H]corticosterone and [³H]hydrocortisone, and unlabeled progesterone prevents binding of [³H]corticosterone to this protein. It is suggested that, in binding to the cytosol protein, progesterone prevents nuclear accumulation of [³H]corticosterone, and the likelihood of cytosol to nuclear transfer of hormone is discussed. (6) The soluble brain corticosterone-binding protein is shown to differ from serum corticosterone-binding protein by binding dexamethasone and having sulfhydryl groups essential for hormone binding.     

[H]corticosterone binding in rat superior cervical ganglion

Binding of [³H]corticosterone was examined in the soluble fraction (100,000 g) from superior cervical ganglia dissected from adrenalectomized and perfused rats. A large binding capacity (2100 fmol/mg protein) was found. However, no binding for [³H]-dexamethasone and [³H]triamcinolone was detected. The binding protein present in the ganglion preparation was characterized by DEAE-cellulose and DNA-cellulose chromatography and by isoelectric focusing. The corticosterone binding protein from the ganglia was found to be different from the cytoplasmic glucocorticoid receptor, but similar to plasma transcortin. A large portion (approximately 75%) of the transcortin-like [³H]corticosterone binding protein was located in the interstitial space between the sheath and the ganglionic cells. However, 25% of the binding protein was retained in the desheathed ganglion even after extensive washing with saline. Our findings indicate that cytoplasmic glucocorticoid receptors are not present in the superior cervical ganglion. It is possible that the transcortin-like protein associated with the desheathed ganglion may be intracellular, as other investigators have suggested similar intracellular presence of a transcortin-like protein in the liver, uterus, and pituitary.     

Multifaceted Interaction of Corticosteroids with the Intracellular Receptors and with Membrane GABAA Receptor Complex in the Rat Brain

In vitro assays using crude synaptosomal membrane preparations from the cortex and cytosolic fraction of hippocampus have shown that in the brain, steroids can bind to the intracellular corticosteroid receptors as well as to the membrane-bound GABA-receptor complex. Corticosteroid, deoxycorticosterone and spironolactone bound with higher affinity to the mineralocorticoid (relative binding affinity (IC₅₀ in nM) 1.2, 3.9 and 4.9, respectively) than to the glucocorticoid receptors (IC₅₀ 5.2, 14.0 and 88.0 nM, respectively) in hippocampal cytosol. They enhanced significantly the binding of [³⁵S]t-butylbicyclophosphorothionate to cortical membrane. Steroids such as 3α,5α-tetrahydroxydeoxycorticosterone and 3a-hydroxy-5α-dihydroprogesterone displaced the binding of [³⁵S]t-butylbicyclophosphorothionate with IC₅₀ (in nM) of 236.7 and 315.0, respectively. In the presence of 10 to 12.5μM added GABA, they bound with higher affinity (IC₅₀ 18.0 and 20.5 nM, respectively). Pentobarbital also bound to this site with IC₅₀ of 430,000 and 240,000 nM, respectively, in the absence and presence of GABA. These compounds also enhanced the binding of [³H]flunitrazepam which was not affected by the presence of added GABA. They showed no affinity for mineralocorticoid or glucocorticoid receptors. Data from this study showed that steroids which preferentially bound to the mineralocorticoid receptor sites (corticosterone, deoxycorticosterone and spironolactone) also enhanced the binding of [³⁵S]t-butylbicyclophosphorothionate to their recognition sites. Steroids which did not interact with the intracellular receptors (3α,5α-tetrahydroxydeoxycorticosterone and 3a-hydroxy-5α-dihydroprogesterone) displaced [³⁵S]t-butylbicyclophosphorothionate binding and enhanced [³H]flunitrazepam binding.     

Deafferentation reduces the hypothalamic cell nuclear binding of corticosterone

Hypothalamic or hippocampal slices and adenohypophyseal lobes taken from adrenalectomized male rats either intact or with complete hypothalamic deafferentation (CHD) were incubated in Krebs-Ringer bicarbonate buffer in the presence of either 10–50 nM [³H]corticosterone or [³H]dexamethasone with or without 500-fold excess of unlabeled steroid for 15–60 min. The cell nuclear binding in the hypothalamic slices from the CHD rats, was markedly reduced by approximately 50% but remained unchanged in the hippocampi and in the pituitaries. These results suggest that brain sites outside the mediobasal hypothalamus are important for the regulation of corticosterone binding in the hypothalamus.     

A comparison of the glucocorticoid receptor system in the spinal cord and hippocampus

Studied under in vivo conditions, uptake of [3H]corticosterone (CORT) by purified cell nuclei of the hippocampus was much higher than in the spinal cord, although the latter may contain in cytosol up to 50% of glucocorticoid receptors found in cytosol of hippocampus. Experiments were undertaken to explain these differences. First, the in vivo affinity of receptors for exogenous CORT was comparable in both tissues. Second, an inhibitor of translocation, although present, was not preferentially concentrated in the spinal cord as compared to the hippocampus. However, the sensitivity towards RNAase A, an enzyme that increased binding to DNA-cellulose (taken as a measure of increased affinity for nuclear components), was preserved in the hippocampus but absent in the cord. We discuss the possibility that refractoriness to RNAase A may play a role in the reduced nuclear uptake of [3H]CORT shown by the spinal cord in vivo, but also consider possible that heterogeneity of receptor types binding CORT in the spinal cord and hippocampus may account for the differences observed in both tissues.     

Autoradiographic study of NMDA-displaceable [H]glutamate and [H]MK-801 binding during butorphanol withdrawal in the rat brain

Influences of continuous administration of butorphanol on the autoradiography of [³H]glutamate binding and [³H]MK-801 binding were investigated to study the effects of butorphanol withdrawal on NMDA receptors. Rats were administered butorphanol (26 nmol μl⁻¹ h⁻¹) by continuous intracerebroventricular (i.c.v.) infusion through pre-implanted cannula connected to osmotic mini-pumps for 3 days. Rats were then sacrificed at 2, 7, and 24 h after discontinuation of butorphanol infusion. [³H]MK-801 binding was slightly increased in the cortical area, hippocampus, and cerebellum in 2, 7, and 24 h withdrawal groups and was shown most significant increase in the 7 h withdrawal group. NMDA-displaceable [³H]glutamate binding was markedly increased in the cortical area, striatum, septum, hippocampus, thalamus, and cerebellum in 7 h withdrawal group and was significantly increased in the striatum, hippocampus, and thalamus in 24 h withdrawal group. These results demonstrate that the development of butorphanol withdrawal is more prominent by 7 h after discontinuation of butorphanol infusion and suggest that NMDA binding sites at NMDA receptors may play more important role in the development of butorphanol withdrawal than that of channel blocking sites.     

Ontogeny of type I and type II corticosteroid receptors in the rat hippocampus

The ontogeny of the corticoid receptors in the rat hippocampus was examined by in vitro [3H]corticosterone (CORT) binding to soluble molecules in the cytosol, using the selective Type II glucocorticoid agonist, RU 28362, to discriminate between Type I and Type II receptor sites. Type I receptors were undetectable until 8 days after birth. From this age on, the receptor showed adult characteristics for both the binding capacity (Bmax) and affinity (Kd). The Type II receptor concentration increased gradually over the observed period; however, at 3 weeks of age concentrations were still only about 65% those found in adults. The binding affinity of Type II to CORT was high during the first week of life but decreased thereafter towards adult value. These data thus suggest clear distinctions in the developmental patterns of Type I and Type II receptors for corticosteroids in the rat.     

Alteration of nicotinic cholinergic agonist binding sites in hippocampus after fimbria transection

Nicotinic cholinergic agonist binding sites were studied in rat hippocampus by the binding of [³H]acetylcholine in the presence of 1.5 μM atropine sulfate. Following transection of the fimbria/fornix there was a 49% increase in the binding of [³H]acetylcholine reflecting an increase in the affinity of the receptor binding site from K_d = 18.82 ± 3.6 nM in control animals to K_d = 9.06 ± 1.2 nM in experimental tissue. Chronic administration of the agonist nicotine (4 mg/kg/day) by osmotic minipumps produced an increased in the binding of 10 nM [³H]acetylcholine after 14 days (49% increase over control) and after 28 days (141% increase over controls). These data are consistent with the suggestion that [³H]acetylcholine labels a nicotinic cholinergic receptor in rat brain. Further they support the notion that some of the termination sites of the septal-cholinergic projection to the hippocampus are nicotinic.     

Benzodiazepine receptors in rat brain are altered by adrenalectomy

The effects of adrenalectomy on benzodiazepine receptors in discrete regions of rat brain were examined using [³H]flunitrazepam as a binding ligand. The concentration of benzodiazepine receptors was significantly increased by 25, 50 and 71% in hippocampus, striatum and hypothalamus, respectively, after adrenalectomy. In contrast, adrenalectomy did not affect the concentration of benzodiazepine receptors in cerebral cortex, olfactory bulb and cerebellum. No significant differences in the apparent binding affinity (K_d) values were seen following adrenalectomy in any brain region examined. The adrenalectomy-induced increases [³H]flunitrazepam binding sites were completely reversed by glucocorticoid replacement with dexamethasone. These results demonstrate that adrenalectomy is capable of selectively modulating benzodiazepine receptors in brain regions presumably involved with glucocorticoid negative feedback. The data further suggest additional mechanisms by which endogenous hypothalamic-pituitary-adrenocortical hormones may affect ‘anxiety’ levels.     

Autoradiographic localization of α5 subunit-containing GABAA receptors in rat brain

Multiple subtypes of GABA_A receptors are expressed in the rat central nervous system (CNS). To determine the distribution and proportion of α5 subunit containing receptors, quantitative autoradiographic analyses were performed with both [³H]L-655,708 and [³H]Ro15-1788, an α5 selective and a non selective benzodiazepine binding site ligand, respectively. High densities of [³H]L-655,708 binding sites were observed in hippocampus and olfactory bulb, where α5 receptors accounted for 20–35% of total [³H]Ro15-1788 binding sites. Low levels of [³H]L-655,708 sites were associated with the cortex as well as amygdala, thalamic, hypothalamic and midbrain nuclei. These observations indicate that although [³H]L-655,708 binding sites have an overall low expression in rat CNS, they may contribute significantly to GABAergic inhibition in specific brain regions.     

Estrogen-sensitive progestin binding sites in the brain of the lizard,Anolis carolinensis

Cytosol binding sites for the synthetic progestin [³H]R5020 have been identified in the brain and oviduct from untreated and estrogen primed ovariectomized female lizards (Anolis carolinensis). Competition of various unlabeled steroids at either 10 nM (brain) or 10 and 100 nM (oviduct) revealed that progestins were effective competitors whereas two glucocorticoids as well as testosterone and estradiol were ineffective. The apparent dissociation constant (K_d) of the receptor for [³H]R5020 in the hypothalamus and telencephalon of the brain was determined to be 0.7–0.8 nM. The concentration of binding sites in the hypothalamus was approximately twice as great as in the telencephalon. The dissociation constant of the binding site for [³H]R5020 in the oviduct was determined to be 1.4–1.7 nM.Although sucrose density gradient centrifugation of brain cytosols labeled with [³H]R5020 failed to reveal a discretely sedimenting peak of radioactivity, oviduct cytosol gradients contained two broad peaks of [³H]R5020 binding at 3–6S and 8–9S. The concentration of [³H]R5020 binding sites in both the oviduct and hypothalamus was found to increase after estrogen treatment. Scatchard analysis of oviduct cytosol [³H]R5020 binding showed that estrogen priming increased binding levels 3-fold. Single point assays with 0.4 nM [³H]R5020 demonstrated that estrogen priming increased binding by 55% in hypothalamus but did not alter binding in cytosol from the telencephalon sample. These results suggest that the [³H]R5020 binding sites identified in the brain and oviduct of the lizardA. carolinensis may correspond to cytoplasmic progestin receptors. Furthermore, the finding of an estrogen-induced increase in the concentration of these receptors in the hypothalamus and oviduct indicate that the capability of estrogen to modulate the concentration of progestin receptor is present in a representative of a vertebrate class whose progenitors gave rise to birds and mammals.     

Characterization of Glucocorticoid Type II Receptors in Neuronal and Glial Cultures from Rat Brain

The purpose of this study was to characterize and compare the properties of glucocorticoid Type II receptors in neuronal and astrocyte glial cultures prepared from rat brain. Type II receptors in cytosol prepared from cultured cells were labeled with [³ H]dexamethasone (DEX) at 0°C. The binding was saturable and specific, with a complete displacement by unlabeled DEX or RU 28362 (a pure glucocorticoid). Scatchard analysis of [³ H]DEX binding suggested a single class of receptors with a slightly lower dissociation constant (K_d) in neuronal (1.13 nM) versus astrocyte glial (1.64 nM) cytosol. The number of binding sites (B_max) in astrocyte glial cultures was four times that in neuronal cultures on a per milligram protein basis (120.3 versus 29.3 fmol/mg protein). The presence of Type II receptors in cultured neurons and astrocyte glia was further confirmed by immunofluorescent staining with a monoclonal antibody against this receptor (BuGR-2). The steroid specificity of Type II receptors was studied by examining the displacement of [³ H]DEX binding to cytosol with unlabeled steroids. For both types of cultures, the potency series for competition was RU 28362> DEX> corticosterone> > aldosterone. Switching cultured cells from serum-supplemented to serum-free medium reduced [³ H]DEX binding at low concentrations (0.5 to 5 nM) of the ligand in both types of culture, thus resulting in a decrease in the apparent affinity. This treatment did not, however, have any significant effect on the total number of binding sites. In summary, these results demonstrate that both neuronal and astrocyte glial cells in culture contain specific glucocorticoid Type II receptors, which resemble those seen in the brain and peripheral tissues.     

Up-regulation of brain [H]diazepam binding sites in chronic caffeine-treated rats

Brain [³H]diazepam and l-[³H]phenylisopropyladenosine binding sites in caffeine-treated (75 mg/kg/day, i.p. 12 days) and caffeine-withdrawn (30 days) rats were examined. Treatment with caffeine (75 mg/kg/day) for 12 days increases the B_max (maximum binding capacity) for [³H]diazepam binding by 30.9% whereas the same treatment increased the B_max for l-[³H]PIA binding by 120%. The B_max for [³H]diazepam binding sites returns to slightly below control levels but l-[³H]PIA binding sites still remain elevated after 30 days of caffeine withdrawal. The up-regulation of [³H]diazepam binding sites seen in caffeine-treated rats may indicate an interaction between caffeine and benzodiazepines at the receptor level and it may account for the supersensitivity to benzodiazepines seen in behavioral testing.     

An autoradiographic study of [H]AMPA receptor binding and in situ hybridization of AMPA sensitive glutamate receptor A (GluR-A) subunits following morphine withdrawal in the rat brain

Chronic treatment with opioids is well known to result in the development of physical dependence. More recently, glutamatergic mechanisms have been implicated in expression of the withdrawal syndrome from opioids. To better examine glutamatergic involvement, an autoradiographic study of [³H]AMPA receptor binding and an assessment of in situ hybridization of AMPA sensitive glutamate receptor A (GluR-A) subunits in the rat brain were each performed 7 h after withdrawal from morphine infusion. Animals were rendered dependent by intracerebroventricular (i.c.v.) infusion of morphine (26 nmol/μl/h) via osmotic minipumps for 3 days. Brain sections of 14-μm thickness were incubated with 15 nM [³H]AMPA for quantitation of binding to the AMPA receptor. The probe for in situ hybridization was labeled at its 3′ end using terminal deoxynucleotidyl transferase and [³⁵S]dATP. The highest degree of [³H]AMPA binding was shown in the hippocampus. The extent of [³H]AMPA binding was increased significantly in the cortex areas (18–21%), caudate-putamen (20%), and hippocampus (7–9%) of rats following withdrawal from morphine. The highest levels of mRNA for GluR-A, flop and flip subunits, were found in the dentate gyrus and in the CA3 region of the hippocampus, respectively. The levels of mRNA for the flop form of GluR-A were decreased in the CA3 of hippocampus (8%) of the rat brain. The levels of mRNA for the flip form of GluR-A were increased in the parietal cortex (7%) and the entorhinal cortex (8%). Increases in the binding of [³H]AMPA to its receptor may play an important role during withdrawal from morphine dependence.     

Retrograde axonal transport of β-adrenoreceptors in rat brain: Effect of reserpine

Retrograde axonal transport of β-adrenoreceptors was assessed by measuring the accumulation of binding sites for the β-receptor ligand [¹²⁵I]iodocyanopindolol ([¹²⁵I]ICP) distal to a unilateral 6-hydroxydopamine (6-OHDA) lesion placed in the ascending noradrenergic axons of the locus coeruleus. Accumulation of binding sites was linear over a 3 day period and was blocked by intracerebroventricular 6-OHDA given 1 day prior to sacrifice. A single dose of reserpine (5 mg/kg, i.p.) caused a long lasting (6–8 week) biphasic depletion of frontal cortex norepinephrine (NE) associated with increased frontal cortex binding of another β-receptor ligand. [³H]dihydroalprenolol ([³H]DHA), at 7–14 days, and again at 28 days post-reserpine. Unlike the changes in cortical β-receptors, retrograde transport of [¹²⁵I]ICP in presynaptic noradrenergic neurons was decreased or blocked completely at 7–14 days and at 6 weeks, and was increased to 470% and 240% of control at 21 days and 8 weeks after reserpine. Anterograde transport of [³H]DHA binding sites was measured by accumulation proximal to a 6-OHDA lesion in this pathway. This transport varied in a pattern similar to that seen for retrograde transport of [¹²⁵I]ICP binding sites. These data and others suggest that presynaptic β-receptors are regulated independently of frontal cortex β-receptors, which appear to be located primarily on postsynaptic cells. On the other hand, the regulation of both anterograde and retrograde transport appears to be interrelated since both types of transport were altered in a similar way in the face of long-term NE depletion by reserpine.