The anti-amnesic effects of sigma1 (sigma1) receptor agonists confirmed by in vivo antisense strategy in the mouse

The sigma1 (sigma1) receptor cDNA was recently cloned in several animal species, including the mouse. In order to firmly establish the implication of sigma1 receptors in memory, a phosphorothioate-modified antisense oligodeoxynucleotide (aODN) targeting the sigma1 receptor mRNA and a mismatched analog (mODN) were administered intracerebroventricularly for 3 days in mice. Scatchard analyses of in vitro (+)-[3H]SKF-10,047 binding to sigma1 sites showed that Bmax values were significantly decreased in the hippocampus (-58.5%) and cortex (-38.1%), but not in the cerebellum, of aODN treated mice, as compared to saline- or mODN-treated animals. In vivo binding levels were also significantly decreased after aODN treatment in the hippocampus and cortex but not in the cerebellum. The anti-amnesic effects of the selective sigma1 agonists PRE-084 or SA4503 were evaluated against the learning impairments induced by dizocilpine or scopolamine, respectively, using spontaneous alternation behavior and passive avoidance task. The anti-amnesic effects of PRE-084 or SA4503, observed after saline- or mODN-treatment, were blocked after aODN administration. These observations bring a molecular basis to the modulatory role of sigma1 receptors in memory processes.     

Chronic ethanol administration alters the modulatory effect of 5α-pregnan-3α-ol-20-one on the binding characteristics of various radioligands of GABAA receptors

In this study, we investigated the modulatory effect of 5α-pregnan-3α-ol-20-one, a neurosteroid, on the binding characteristics of [ ]flunitrazepam (2 nM), [ ]muscimol (5 nM), and 4 nM [ ]t-butylbicyclophosphorothionate (TBPS) in cerebral cortex, cerebellum, and hippocampus of control, ethanol-dependent, and ethanol-withdrawn rats. 5α-Pregnan-3α-ol-20-one potentiated the binding of [ ]flunitrazepam and [ ]muscimol in all the rat brain regions investigated in this study. There was a significant increase in the maximal potentiation of [ ]flunitrazepam as well as [ ]muscimol binding (E_max) in the ethanol-dependent rat cerebellum as compared to control group (p<0.025). Furthermore, 5α-pregnan-3α-ol-20-one elicited a biphasic response, i.e., it potentiated the binding of [ ]TBPS at lower concentrations (100 nM) and inhibited the binding at higher concentrations (>100 nM). There was a significant higher inhibition of [ ]TBPS binding (−E_max) by 5α-pregnan-3α-ol-20-one in the hippocampus of ethanol-dependent as well as ethanol-withdrawn rats (p<0.025). These observations suggest that the neurosteroid binding site associated with the γ-aminobutyric acid_A (GABA_A) receptors in cerebellum and hippocampus plays an important role during ethanol-dependence and ethanol-withdrawal, and some of the changes following ethanol dependence and its withdrawal may be mediated through the neurosteroid binding site.     

The resolution of dopamine and β1- and β2-adrenergic-sensitive adenylate cyclase activities in homogenates of cat cerebellum, hippocampus and cerebral cortex

The stimulation of adenylate cyclase by dopamine and various β-adrenergic agonists has been investigated in homogenates from 3 areas of cat brain: the cerebral cortex, cerebellum and hippocampus. The purpose of the study was to determine whether the β-adrenergic receptors coupled to adenylate cyclase could be classified as either β₁ and β₂ subtypes in the different regions studied.The stimulation of adenylate cyclase by the β-adrenergic agonist, (−)isoproterenol (5 × 10⁻⁶M), was completely blocked by the specific β-adrenergic antagonist, (−)alprenolol (10⁻⁵ M), but not by the dopaminergic antagonist, fluphenazine (10⁻⁵ M), whereas the stimulation of adenylate cyclase by (−)epinephrine (10⁻⁴ M) was blocked to varying extents by these two drugs in each of the 3 regions studied. The (−)epinephrine effect was always blocked in the combined presence of (−)alprenolol and fluphenazine. The adenylate cyclase stimulation by (−)epinephrine which is not blocked by (−)alprenolol was due to interaction of (−)epinephrine with a dopaminergic-sensitive adenylate cyclase which has been characterized in cerebral cortex, hippocampus and cerebellum.Regional differences in the affinity of β-adrenergic-sensitive adenylate cyclase for various agonists were investigated in the presence of fluphenazine (10⁻⁵ M). In the cerebellum the potency order was (±)protokylol> (±)hydroxybenzylisoproterenol> (±)isoproterenol> (−)epinephrine> (±)salbutamol> (−)norepinephrine, indicating the presence of a β₂-adrenergic receptor. In the cerebral cortex the potency order was (−)isoproterenol> (±)protokylol> (±)hydroxybenzylisoproterenol> (−)epinephrine= (−)norepinephrine((±)salbutamol being inactive). A similar pattern was found in the hippocampus indicating the presence of a β₁-adrenergic receptor in these two regions. (±)Salbutamol was a partial agonist in the cerebellum and a competitive antagonist in the cerebral cortex.The ratio of the antagonist potencies of (±)practolol and (±)butoxamine preferential β₁- and β₂-adrenergic antagonists respectively, to block the stimulation of adenylate cyclase was 25 in the cerebellum, compared to 0.5 in the cerebral cortex and 1.6 in the hippocampus. These results confirm the presence of a β₂ subtype of receptor coupled to adenylate cyclase in the former and β₁ subtypes in the latter two regions. The comparison between the affinities of a series of β-adrenergic agonists and antagonists for the β-adrenergic receptors coupled with an adenylate cyclase in cerebral cortex and cerebellum with their affinities for well characterized β₂-adrenergic receptors in lung and β₁-adrenergic receptor in heart substantiated this conclusion.     

Specific bindings of prostaglandin D2, E2 and F2α in postmortem human brain

Binding activities specific for each of [³H]prostaglandin (PG) D₂, E₂ and F_2α were detected in the P₂ fraction of the human brain homogenates. The bindings were time-dependent, saturable and of high affinity;K_dvalues were 30 nM for all the PG bindings. Regional distribution of these binding activities was determined by measuring specific bindings with 10 nM [³H]PG-D₂, [³H]PG-E₂ and [³H]PG-F_2α in the P₂ fractions from 17 brain regions. The PG-D₂ binding activity was high in the hypothalamus, amygdala and hippocampus followed by cerebellar nuclei, thalamus, nucleus accumbens and cerebral cortex. The PG-E₂ binding sites were similarly concentrated in the hypothalamus and the limbic system, but, unlike the PG-D₂ binding, no significant binding of [³H]PG-3₂ was observed in cerebellar nuclei, cerebellar cortex and putamen. Compared with these two PG bindings, PG-F_2α binding activity was low in many areas, but significant binding was detected in the amygdala, cingulate cortex, cerebellar medulla, hippocampus, nucleus accumbens, midbrain and hypothalamus. These results suggest the presence and specific distribution of three distinct types of PG binding activities, i.e. specific binding of PG-D₂, PG-E₂ and PG-F_2α, in the human brain.     

Regulation of central α-adrenoceptors by serotoninergic denervation

α₁- and α₂-adrenoceptors were assessed by binding studies using [³H]prazosin and [³H]p-aminoclonidine as ligands in membrane preparations from the cortex, hippocampus and hypothalamus of rats, 3 weeks after intracerebroventricular injection of the neurotoxin 5,7-dihydroxytryptamine. Cortical α₁ and hippocampal α₂ adrenoceptors were significantly increased. Treatment also affected the affinity of cortical α₂ adrenoceptors. These results suggest a heterologous, region-specific regulation of both subtypes of central α-adrenergic receptors by serotonin.     

The formation and regional distribution of prostaglandins D2 and F2α in the brain of spontaneously convulsing gerbils

The distribution of the two major cycloxygenase products prostaglandin D₂ (PGD₂) and prostaglandin F_2α (PGF_2α) in 7 different regions of the brain (medulla, cerebellum, hypothalamus, striatum, midbrain, hippocampus and cerebral cortex) was studied. Basal levels were highest in hypothalamus and cortex. Following convulsions elicited by environmental stress prostaglandin concentrations increased in all areas, with largest increases (10–20-fold) in hippocampus and cortex, reaching 70 ng/g PGD₂ in hippocampus and 115 ng/g PGD₂ in cortex. These results demonstrate that, during spontaneous seizures, there is a greater increase in prostanoid production in those areas involved in the convulsive process.     

α2, α2A, α2B/2C-Adrenoceptor subtype antagonists prevent lipopolysaccharide-induced fever response in rabbits

Exogenous pyrogens, e.g., bacterial lipopolysaccharides (LPS), are thought to stimulate macrophages to release endogenous pyrogens, e.g., TNFα, IL-1 β, and IL-6, which act in the hypothalamus to produce fever. We studied the effect of different α₁⁻ and α₂-adrenoceptor subtype antagonists, applied intraperitoneally, on the febrile response induced by LPS in rabbits. Evidence was obtained that prazosin, an α₁⁻ and α_2B/2C-adrenoceptor antagonist; WB-4101, an α₁⁻ and α_2A-adrenoceptor antagonist; CH-38083, a highly selective α₂-adrenoceptor antagonist (α₂: α₁ > 2000); BRL-44408, an α_2A-adrenoceptor antagonist; and ARC-239, an α_2B/2C⁻ and also α₁-adrenoceptor antagonist, blocked the increase of colonic temperature of the rabbit produced by 2 μg/kg LPS administered intravenously without being able in themselves to affect colonic temperature. In addition, prazosin, WB-4101 and CH-38083 antagonized the fall in skin temperature that occurred at the time when the colonic temperature was rising in control animals injected with LPS. All these results suggest that norepinephrine, through stimulation of both α₁⁻andα₂⁻ (α_2A⁻andα_2B/2C⁻) adrenoceptor subtypes, is involved in producing fever in response to bacterial LPS.     

α2-Adrenergic receptor activation inhibits calcitonin gene-related peptide expression in cultured dorsal root ganglia neurons

Calcitonin gene-related peptide (CGRP), a potent vasodilator, is produced in dorsal root ganglia (DRG) neurons which extend nerves peripherally to blood vessels and centrally to the spinal cord. We previously reported that neuronal CGRP expression is significantly reduced in the spontaneously hypertensive rat (SHR) which could contribute to the elevated BP. Other studies suggest that the enhanced activity of the sympathetic nervous system in the SHR may mediate, at least in part, this reduction in neuronal CGRP expression via activation of α₂-adrenoreceptors (α₂-AR) on DRG neurons. To test this hypothesis in vitro we employed primary cultures of adult rat DRG neurons. Neuronal cultures were initially exposed (24 h) to either the α₂-AR agonist UK 14,304 (10⁻⁶ M) or vehicle; however, no changes in CGRP mRNA content or immunoreactive CGRP (iCGRP) release were observed. Using the rationale that in vivo DRG neurons receive a continuous supply of target tissue derived nerve growth factor (NGF), which stimulates CGRP synthesis, the cultured neurons were treated (24 h) with either vehicle, NGF (25 ng/ml) alone, or NGF plus UK. NGF treatment increased CGRP mRNA accumulation 5.5±0.9-fold (p<0.001) and iCGRP release 2.9±0.4-fold (p<0.001) over control levels. The stimulatory effects of NGF were markedly attenuated, but not abolished, by UK (NGF+UK vs. control, CGRP mRNA, 2.9±0.4-fold, p<0.05; iCGRP, 1.7±0.2-fold, p<0.05). These values were also significant (p<0.05) when compared to NGF treatment alone. Experiments performed using the α₂-antagonist yohimbine confirmed that the effects of UK were mediated by the α₂-AR. These results, therefore, demonstrate that α₂-AR activation attenuates the stimulatory effects of NGF on CGRP expression in DRG neurons.     

Pharmacological properties of the norepinephrine-induced depolarization of astrocytes in primary culture: evidence for the involvement of an α1-adrenergic receptor

The membrane potentials of astrocytes in primary cultures prepared from neonatal rat cerebral cortices were depolarized by (−)-norepinephrine. The average first response to 10⁻⁵ M (−)-norepinephrine was 24 mV from an average resting potential of −68 mV, and the average for the second response was 14 mV. Thus this process showed marked desensitization. The response was attributed to an activation of an α₁-receptor since it was about 1000 times more sensitive to inhibition by prazosin than to yohimbine or idazoxan. In addition, depolarization was seen to the application of 10⁻⁵ M phenylephrine.     

Regional differences in the enhancement by GABA of [H]zolpidem binding to ω1 sites in rat brain membranes and sections

The potential heterogeneity in the allosteric coupling between GABA and ω₁ binding sites within the native GABA_A receptor complex has been evaluated in the rat by measuring the enhancement by GABA of [³H]zolpidem binding to ω₁ site in membranes from three rat brain structures (neocortex, cerebellum and hippocampus) and brain sections. The maximal stimulatory effect of GABA was significantly higher (265 ± 47%) in cortical membranes than in cerebellar (165 ± 48%) or in hippocampal (118 ± 17%) membranes. These differences are not due either to the presence of different amounts of residual GABA in the membrane preparations or to the labeling, in presence of GABA, of binding sites other than ω₁ since: (1) the pharmacological properties of the [³H]zolpidem binding sites were similar in the three regions; (2) the degree of allosteric enhancement was unrelated to the relative proportion of ω₁ sites in each structure; and (3) GABA did not increase the B_max for [³H]zolpidem. Regional differences in the effect of 100 μM GABA on [³H]zolpidem binding were also observed by quantitative autoradiography. Regions where the strongest (3–4-fold) effects of GABA in [³H]zolpidem binding were observed included the substantia nigra, lateral geniculate body, olfactory tubercule and red nucleus. A large increase in [³H]zolpidem binding was also demonstrated in the cingulate and frontoparietal cortices with higher effects in deep (4.2-fold) rather than in superficial layers (3.3-fold). Heterogeneous subregional increases in [³H]zolpidem binding in the presence of GABA were quantified within the cerebellum, hippocampus and superior colliculus. In the cerebellum the effect of this neurotransmitter was larger in the molecular (3.8-fold) than in the granular (2.2-fold) layer. In the hippocampus the effect of GABA was also heterogeneous with larger increases in CA1 and CA2 fields (3.5-fold) than in CA3 field (2.2-fold) and dentate gyrus (2.5-fold). Finally in the deep layers of the superior colliculus GABA stimulation of [³H]zolpidem binding was greater than the superficial layer. In the other structures examined the GABA-induced increase in [³H]zolpidem binding was less than 3-fold. The smallest stimulations were quantified in the entorhinal cortex (2.1-fold), amygdala (2.4-fold) and nucleus accumbens (1.7-fold). These results suggest that [³H]zolpidem sites are associated to, at least, two GABA_A receptor subtypes that can be differentiated by their allosteric interaction between GABA and [³H]zolpidem sites.     

Interferon gamma up-regulates α2 macroglobulin expression in human astrocytoma cells

An established human astrocytoma cell line (T67) was shown to constitutively produce the proteinase inhibitor α₂macroglobulin (α₂M). Interferon gamma (IFNγ), a potent immunoregulatory lymphokine, was able to increase the synthesis of α₂M by these cells, as measured by ELISA on cell supernatants. The α₂M induction was also observed in other human glioma cell lines (T70 and ADF) and in human fetal astrocyte cultures following IFNγ treatment. In T67 cells this effect was dose-dependent and the maximum (2.7-fold increase) was obtained with 2000 U/ml of IFNγ. A corresponding enhanced α₂M mRNA accumulation was demonstrated by PCR and Northern blot techniques. Our results suggest an important role of α₂M during inflammatory and immune processes in the CNS. An increased release of α₂M following IFNγ stimulation may allow the removal of the bulk of proteases released at the site of inflammation, strengthening at the same time the antigen presentation processes.     

Relationship of interleukin-1β and β2-microglobulin with neuropeptides in cerebrospinal fluid of patients with dementia of the Alzheimer type

We studied interleukin-1β (IL-1β), β₂-microglobulin (β₂-m, β-endorphin, substance P, neuropeptide Y and somatostatin concentrations in the cerebrospinal fluid of 13 patients with dementia of the Alzheimer type (DAT), 13 patients with multi-infarct dementia (MID) and 15 age-matched control subjects. Substance P was significantly lower in DAT than in controls (P < 0.05), as well as somatostatin in DAT as compared to both controls (P < 0.01) and MID (P < 0.05), whereas β₂-m was higher in DAT than in controls (P < 0.01). Neuropeptide Y, β-endorphin and IL-1β showed similar concentrations in the three groups studied. A significantly positive correlation was observed between IL-1β and substance P (r = 0.79, P < 0.01) and somtostatin (r = 0.75, P < 0.05) in DAT, which was not observed in MID. In addition, β₂-m showed a negative correlation with IL-1β (r = −0.73, P < 0.05) in DAT, and age correlated negatively with IL-1β in controls and MID, but positively in DAT. Therefore, these results support the idea that an altered relationship may exist in Alzheimer's disease between the nervous and immune system.     

Antibodies to macrophage inflammatory protein-1β in preoptic area of rats fail to suppress PGE2 hyperthermia

This study determined whether macrophage inflammatory protein-1β (MIP-1β) plays a role in the hyperthermia caused by prostaglandin E₂ (PGE₂) given intracerebroventricularly (i.c.v.) in the rat. In these experiments, anti-murine MIP-1β antibody (anti-MIP-1β) was micro-injected in the anterior hypothalamic, preoptic area (AH/POA) just before i.c.v. PGE₂. The results showed that anti-MIP-1β failed to alter the PGE₂ hyperthermia. However, immunocytochemical studies revealed MIP-1β immunoreactivity detectable in both the organum vasculosum laminae terminalis (OVLT) and AH/POA in the febrile rat. These data thus demonstrate that MIP-1β is sequestered in diencephalic structures underlying thermoregulation even though it is not involved in PGE₂ hyperthermia. This dissociation supports the viewpoint that at least two distinct systems exist in the brain which underlie a febrile response: MIP-1β underlies one component whereas PGE₂ comprises the other.     

The role of dopamine in the maintenance and breakdown of D1/D2 synergism

The neurochemical factors involved in the maintenance and breakdown of dopamine D₁/D₂ receptor synergism were investigated by giving rats various pharmacological treatments that diminish the ability of dopamine to interact with its D₁ and/or D₂ receptors. Following these treatments, rats were observed for the expression of stereotyped motor behavior in response to independent stimulation of D₁ or D₂ receptors. Independent D₂-mediated responses were observed: (a) 2 h after the last of three daily reserpine (1 mg/kg) injections, (b) 48 h after bilateral 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal pathways, (c) 24 h after a concentrated 48-h regimen (one injection/6 h) of eticlopride (0.5 mg/kg) or eticlopride + SCH 23390 (0.5 mg each), and (d) 2 h after a concentrated 48-h regimen (one injection/6 h) of α-methyl-p-tyrosine (αMPT; 100 mg/kg), but not after control treatments or a concentrated regimen of SCH 23390 alone. By contrast, independent D₁-mediated responses were observed only after three daily reserpine injections or 48 h after bilateral 6-OHDA lesions. Independent D₁-mediated stereotypy was not observed under control conditions or following a concentrated 48-h regimen of (a) SCH 23390 or eticlopride (0.5 mg/kg each) alone or in combination, (b) a high dose of SCH 23390 (1.0 mg/kg), (c) αMPT (100 mg/kg), or (d) αMPT (100 mg/kg)+SCH 23390 (1.0 mg/kg). Reserpine, bilateral 6-OHDA, and αMPT treatments produced striatal dopamine depletions of 96%, 92%, and 71%, respectively. These data indicate that the breakdown in D₁/D₂ synergism consists of two components: (a) D₁ independence from the controlling influence of D₂ receptors, and (b) D₂ independence from the controlling influence of D₁ receptors. The interaction of synaptic DA with its D₂ receptors plays a major role in determining whether these receptors can function independently of D₁ receptors, whereas reduced DA-D₁ activity alone appears insufficient to elicit D₁ independence.     

Cortisol stimulation by recombinant interferon-α2

Serum cortisol concentrations were determined by radioimmunoassay in cancer patients undergoing experimental therapy with recombinant interferon-α₂. Cortisol concentration rose steadily after interferon administration and was significantly different from that on control day at 8 h following intramuscular injection of interferon-α₂. Cortisol elevation was increased as weekly doses of interferon were increased (0–120 × 10⁶ units). Recent clinical trials of interferons for treatment of neurological and malignant diseases provide a compelling need to understand the actions and side effects of exogenously administered interferons.     

Reduced antiheparin effect of desialyzed α1-acid glycoprotein

α₁-Acid glycoprotein (α₁-acid GP) of human plasma counteracts the heparin-accelerated, antithrombin III-mediated inactivation of thrombin and factor Xa. In some preparations of α₁-acid GP which had a reduced antiheparin effect, less than normal amounts of sialic acid were found. No antiheparin activity remained after almost complete desialization of the purified glycoprotein with insolubilized neuraminidase. The significance of the sialyl residues for the antiheparin effect of α₁-acid GP is discussed.     

Prostaglandin E2 mediates the stimulatory effect of methoxamine on in vivo luteinizing hormone-releasing hormone (LH-RH) release in the ovariectomized female rhesus monkey

Previously, we found that noradrenergic input throughα₁-receptors modulates pulsatile release of luteinizing hormone-releasing hormone (LH-RH) in ovariectomized rhesus monkeys in the absence of estrogen. In the present study, the role of prostaglandin E₂ (PGE₂) in mediating α-adrenergic stimulation of LH-RH release is investigated. In the first experiment the effects of theα₁-adrenergic agonists methoxamine (MTX) on LH-RH and PGE₂ release were examined. Push-pull perfusion of the stalk-median eminence (S-ME) was performed in conscious, ovariectomized monkeys, and perfusate samples were collected on ice. MTX (10⁻⁵ M) was infused into the S-ME through the push cannula for 10 min at 90-min intervals, and LH-RH and PGE₂ in aliquots of the same perfusate samples were measured by radioimmunoassay. Infusion of MTX significantly stimulated LH-RH release (n = 12; P < 0.01) and PGE₂ release (P < 0.05). In the second experiment, the effect of PGE₂ infusion on LH-RH release was tested. PGE₂ (10⁻⁷ M) was infused using the same protocol as above, and LH-RH was measured in the perfusates. Infusion of PGE₂ through the push cannula significantly stimulated LH-RH release (n = 23; P < 0.05). These results suggest that the stimulatory effect of MTX on LH-RH release is at least partly mediated by PGE₂, since MTX stimulated not only LH-RH but also PGE₂ release, and since PGE₂ itself stimulated LH-RH release. Therefore, PGE₂ may be an important endogenous mediator ofα₁-adrenergic input stimulating pulsatile PH-RH release. Moreover, the stimulatory effects of MTX and PGE₂ can be observed in the absence of estrogen in the rhesus monkey, unlike in rhodents. Our results also demonstrate the usefulness of the push-pull perfusion technique for studies of cellular mechanisms in neuroendocrine research.     

α1-Adrenergic receptors and stimulation of [H]inositol metabolism in rat brain: Regional distribution and parallel inactivation

The relationship between norepinephrine-stimulated phosphatidyl-inositol metabolism andα₁-adrenergic receptor density was examined in rat brain. Increases in phosphatidyl-inositol metabolism were determined by accumulation of [³H]inositol phosphates in the presence of lithium in brain slices, while receptor density was determined by specific binding of¹²⁵I-BE 2254 (¹²⁵IBE) in membrane fractions. Treatment of slices of cerebral cortex with increasing concentrations of the irreversibleα₁-adrenergic receptor antagonist phenoxybenzamine caused a parallel inactivation of specific¹²⁵IBE binding sites and norepinephrine-induced [³H]inositol phosphate accumulation, although approximately 20% of the binding sites remained after abolition of the inositol response. Comparison of the density of¹²⁵IBE binding sites and the magnitude of norepinephrine-stimulated [³H]inositol phosphate accumulation in 8 different brain regions did not show a particularly good correlation. The thalamus had the highest density of binding sites and an intermediate inositol response, while the hippocampus had the highest inositol response but an intermediate density of binding sites. However, the cerebellum had the lowest density of binding sites and no measurable inositol response. Treatment of slices of each region with 300 nM phenoxybenzamine abolished the inositol response and caused a 59–73% decrease in the density of¹²⁵IBE binding sites. The lack of correlation between receptor density and inositol response between brain regions could not be explained on the basis of receptor affinity, spare receptors, protein content, nor differences in slice size. These results suggest thatα₁-adrenergic receptors labeled by¹²⁵IBE are coupled to [³H]inositol metabolism in rat brain, but the receptor density is not the sole determinant of the magnitude of norepinephrine-induced increases in [^3H]inositol metabolism.     

Behavior and binding: Correlations between α1-adrenergic stimulation of acoustic startle and α1-adrenoceptor occupancy and number in rat lumbar spinal cord

The relationship between alterations in α₁-adrenoceptors and behavioral effects of α₁-adrenergic agonists were investigated in a localized region of the rat central nervous system. Direct infusion of the α₁-adrenergic agonists,d-amphetamine or phenylephrine. into the subarachnoid space of the lumbar cord (intrathecal administration) increased the amplitude of the acoustic startle reflex, The magnitude of this behavioral facilitation correlated highly with the degree of α₁-adrenoceptor occupation measured by [³H]prazosin binding in lumbar spinal tissue. Using an in vitro estimate of receptor occupation, maximal potentiation of startle occurred following approximately 30% occupation of the receptors, using eitherd-amphetamine or phenylephrine. Intrathecal administration of 6-OHDA produced a 95% decrease in spinal norepinephrine and markedly enhanced the behavioral response to intrathecal phenylephrine as well as the number of α₁-adrenoceptors. The correlation between the time course of the behavioral and binding changes was 0.99. No change in receptor affinity (K_D) or receptor occupation by phenylephrine was found after 6-OHDA. The data indicate that receptor binding parameters do have predictive value for behavior, especially if localized regions of the nervous system, critical to the behavior, are analyzed.