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P M Whitaker-Azmitia

Publications and source records attributed to P M Whitaker-Azmitia.

51 records · Page 3Linked to original sources
PubMed1989

Physiological effects of selective 5-HT1a and 5-HT1b ligands in rat hippocampus: comparison to 5-HT.

The responses of CA1 neurons to topical application of serotonin (5-HT) and selective 5-HT1a and 5-HT1b agonists were examined with intracellular recording in the hippocampal slice. 5-HT produced a uniform hyperpolarizing response associated with an increase in K conductance as previously reported. In addition a marked reduction was recorded in slow afterhyperpolarization (AHP) which follows a burst discharge. 8-OH-DPAT, ipsapirone and LY165,163 partially mimicked the hyperpolarizing response to 5-HT when first applied to the slice. However, these 5-HT1a ligands antagonized responses to subsequent applications of 5-HT. Topical application of the 5-HT1b ligand TFMPP on the slice did not produce the direct or antagonistic action seen with the 5-HT1a ligands. It is suggested that the physiological response to 5-HT in the rat hippocampus is mediated by a 5-HT1a receptor. The currently available 5-HT1a ligands show a low agonist potential and a high antagonist action towards the responses of hippocampal neurons to 5-HT. Definite classification of the hyperpolarizing response to 5-HT awaits development of more specific ligands having a pure agonistic activity.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1989

Stimulation of astroglial serotonin receptors produces culture media which regulates growth of serotonergic neurons.

Our work has been concerned with the role of high affinity serotonin receptors in regulating the development of the serotonergic system. In previous studies, we have found evidence that these receptors occur on astroglial cells and that their number is developmentally linked. The current work is aimed at investigating the mechanism by which these receptors may regulate serotonin neuronal growth. Primary cultures of astroglial cells were exposed to serotonin (5-HT) or the selective receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-D-PAT, for 5-HT1a receptors) or trifluoro-methyl-phenyl-piperazine (TFMPP) and m-chlorophenylpiperazine (mCPP) (for 5-HT1b receptors). Media was collected after 4 or 24 h, and added to primary cultures of serotonergic neurons. Growth was determined by specific uptake of radiolabeled serotonin into the cultures. Our results show the presence of a factor(s) in the glial-conditioned media which can be stimulatory or toxic to serotonin neurons, depending on the neuronal plating density. This factor is significantly present after 24 h, is found in both brainstem and cortical astroglial-conditioned media and appears to be linked to the 5-HT1a receptor. Thus, it appears possible that the serotonergic neuronal system can regulate its own development through an action on astroglial cells.

Animals↗
PubMed1989

SKF 38393: vacillatory behavior in immature rats.

SKF 38393 was administered to postnatal rat pups on day 15 and day 30. Behaviors measured on day 15 revealed that SKF 38393-treated groups displayed significant deficits, in comparison to controls, in spontaneous alternation and decision-making: less alternation and more vacillatory behavior at every dosage tested. On day 30, all SKF 38393-related behaviors disappeared.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1988

Effects of prenatal 5-methoxytryptamine and parachlorophenylalanine on serotonergic uptake and behavior in the neonatal rat.

Parachlorophenylalanine (pCPA) or 5-methoxytryptamine (5MT) was administered to pregnant Sprague Dawley rats from day 8 (D8) of gestation till D17 and from D12 until birth respectively. Birth weights of both drug groups of neonates were approximately 20% less than the saline-injected controls. 5MT neonates showed a significant reduction of high affinity 3H-5HT uptake in the brainstem at all three time points: D1, D15, D30, and a slight reduction in the forebrain reaching significance only on D30. The pCPA animals showed a significant reduction in the brainstem and forebrain on D1 and D30, but only a small nonsignificant reduction in both areas on D15. Behaviors measured on day 15 revealed that in general activity, spontaneous alternation, and passive avoidance both drug groups of neonates showed deficits: less activity, less alternation, and less avoidance.

5-Methoxytryptamine↗
PubMed1987

Selective beta-antagonists are equally and highly potent at 5-HT sites in the rat hippocampus.

Serotonin (5-hydroxytryptamine, 5-HT) and various tryptamine-related drugs were equi-potent to known beta-antagonists in competition experiments of 125Iodo-cyanopindolol binding in the rat hippocampus. IC50 values for all the tryptamine related drugs (5,7-DHT, 5-MT, 5-MEO, DMT) were very similar to those obtained for (-)-propranolol, (+/-)-cyanopindolol, zinterol and atenolol and were all in the nanomolar range. Saturation experiments demonstrated that in the rat hippocampus, a subpopulation of serotonin recognition sites comprised 50% of 125I-CYP binding. The KD was 140 +/- 30 pM and the Bmax was 71 +/- 7 fmole/mg protein. This suggests that 125I-CYP binding studies for the quantitation of beta-adrenergic receptors should be re-evaluated and caution should be exercised in the choice of the displacing agent for the definition of non-specific binding. (+/-)-[125Iodo]cyanopindolol (I-CYP) has been used as a radioligand which binds with high affinity and specificity to beta-adrenoceptors (Engel, Hoyer, Berthold and Wagner, 1981). The reported low dissociation constant (27-40 pM) of 125I-CYP for beta-adrenoceptors in various tissues, in combination with its high specific radioactivity (2175 Ci mmole-1) allowed binding studies to be carried out with low protein and ligand concentrations. These factors have established 125I-CYP as the choice ligand for the quantitation of beta-adrenoceptors in our laboratory (Edwards and Henn, 1985).(ABSTRACT TRUNCATED AT 250 WORDS)

5,7-Dihydroxytryptamine↗
PubMed1987

Postnatal changes in serotonin receptors following prenatal alterations in serotonin levels: further evidence for functional fetal serotonin receptors.

Recent work by ourselves and others has indicated that serotonin (5-HT) acts as a regulator of neuronal growth in fetal tissue, probably through an action on the high affinity 5-HT receptors known to be present. In order for our hypothesis to be correct, these receptors must be shown to be functional in fetal tissue. Furthermore, since 5-HT has a dual role in neuronal development, these receptors must be functional both in the region of the serotonergic cell body (brainstem) and in projection areas (forebrain). We have tested the functional status of fetal 5-HT receptors by testing their ability to adapt to changes in the level of 5-HT. Pregnant rats were treated with saline, p-chlorophenylalanine (a 5-HT depletor) or 5-methoxytryptamine (a 5-HT agonist) and the characteristics of the high affinity 5-HT receptors in the rat pups determined using a binding assay with [3H]5-HT. Our results show that both forebrain and brainstem receptors respond to alterations in transmitter level in a manner similar to adult brain. Thus, fetal 5-HT receptors are functional and capable of playing a role in neuronal development.

5-Methoxytryptamine↗
PubMed1987

Target cell stimulation of dissociated serotonergic neurons in culture.

Dissociated mesencephalic raphe cells from fetal rats (14-18 days) were grown in culture in 96 well Linbro plates. The maturation of serotonergic cells was qualitatively studied using immunocytochemistry with a serotonin antibody and quantitatively by measuring the retention of radioactivity following incubation in the presence of a low concentration of [3H]5-hydroxytryptamine (6 X 10(-8) M). The 5-hydroxytryptamine immunoreactive neurons showed specific staining in the perikaryon, nucleus, dendrites, axons and growth cones. These neurons formed varicose fibers and growth cones after 18 h in culture and survived for up to 21 days in culture. Each serotonergic neuron concentrated approximately 1 fmol of serotonin after 20 min of incubation. Maturation of mesencephalic serotonergic neurons was increased in co-cultures of both normal (hippocampus, cerebral cortex, olfactory bulb and striatum) and abnormal (spinal cord) target neurons. The best stimulation was produced by dissociated hippocampal neurons (14-18 days of gestation) on mesencephalic raphe cells (14 days of gestation) after 4 days in culture. This stimulation was seen in culture conditions which favored neuronal but not glial survival. Our results obtained using cultures of dissociated serotonergic cells are consistent with an expansive network pattern developed by this chemical transmitter system in the adult brain.

Animals↗
PubMed1986

Autoregulation of fetal serotonergic neuronal development: role of high affinity serotonin receptors.

A microculture technique was used to study the factors regulating the development of fetal rat serotonergic neurons. Mesencephalic raphe cells from E14 rats co-cultured with hippocampal cells from E18 were grown for up to 4 days in the presence of various agents known to alter serotonergic function in the mature brain. Pargyline (a non-specific monoamine oxidase inhibitor) alone and with serotonin (10(-8) to 10(-6) M) both inhibited growth of serotonergic neurons as assessed by uptake of [3H]serotonin. 5-methoxytryptamine (5-MT), a serotonin agonist with selectivity for serotonin autoreceptors, inhibited growth at low concentrations, but this inhibition was overcome at higher concentrations. Using immunocytochemistry with a primary anti-serotonin antibody, 5-MT was observed to produce stunted processes, increase autoinnervation and lead to neuronal death. A model is proposed whereby high affinity serotonin receptors in fetal brainstem tissue and in fetal forebrain tissue regulate direction and extent of growth. We have confirmed the presence of these receptors using a direct binding assay.

5-Methoxytryptamine↗
PubMed1986

[3H]5-hydroxytryptamine binding to brain astroglial cells: differences between intact and homogenized preparations and mature and immature cultures.

[3H]5-hydroxytryptamine ([3H]serotonin) binds with high affinity (KD 2-12 nM) to a finite number of sites on brain astroglial cells. The number of binding sites in the C6 glioma line is decreased significantly (Bmax = 315 versus 30 fmol/mg) by homogenization. In intact primary cultures, derived from newborn rat brain, the number of binding sites is far greater in cultures of immature astrocytes than in cultures treated with dibutyryl cyclic AMP (Bmax = 1,520 versus 580 fmol/mg). A role for these receptors in development is suggested.

Animals↗
PubMedDate not supplied

Antipeptide antibodies against the 5-HT1A receptor.

The availability of the primary amino acid sequence for a large number of molecules provides a fruitful opportunity for their cellular localization by utilizing the procedure of antipeptide antibody formation. This procedure permits a synthetic peptide sequence to be attached to a carrier molecule for the purpose of inoculating an animal to raise specific antibodies against the selected protein sequence. In this report we describe a number of steps that can be taken to increase the likelihood that the selected peptide sequence will be specific and antigenic. In addition, we describe how the peptides are synthesized, purified and coupled to keyhold limpet hemocyanin. The preparation of the antibody and its characterization are also presented in this method report. The immunocytochemical staining at both the light and ultrastructural level with serotonin (5-HT1A) receptor antipeptide antibodies is discussed. The advantages and disadvantages of this procedure are summarized.

Amino Acid Sequence↗
PubMedDate not supplied

Role of the 5-HT1A receptor in development of the neonatal rat brain: preliminary behavioral studies.

Serotonin exerts an influence on the prenatal development of rat brain. However, later developmental times may be more applicable to the understanding of the role of serotonin in human developmental disorders. Therefore, the current study was undertaken to gain preliminary information on the postnatal effects of serotonin on rat brain development. As the 5-HT1A receptor has been shown to be involved in much of the developmental functions of serotonin, an agonist for this receptor, 8-hydroxy-DPAT (8-OH-DPAT), was used. Neonatal rat pups at three ages (postnatal days, PNDs) 3-10, 10-17 or 17-24) were injected daily with 1 mg/kg 8-OH-DPAT and evaluated for behavioral consequences. The youngest group showed accelerated incisor eruption and eye-opening, a possible consequence of 5-HT1A receptor interactions with epidermal growth factor (EGF). Behaviorally, the animals were more anxious. Animals treated from PND 10-17, showed no change in craniofacial development but showed greater behavioral maturity in measures of spontaneous alternation and activity in the open field. The oldest animals (PND 17-24) showed no behavioral alterations, suggesting that this time length is beyond the critical period for serotonin's influence in brain development.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMedDate not supplied

Use of tissue culture models to study neuronal regulatory trophic and toxic factors in the aged brain.

Dementia is believed to result from the loss of selective neurons within the brain, but approaches for systematic study of that degenerative process are hampered by the complexity of the neuronal milieu. Tissue culture models provide a means to reduce dramatically the variables inherent in the study of neuronal plasticity. Three levels of complexity can be described: cellular and molecular diversity; primary and secondary interconnections; and finally, the dynamics influenced by age. The following review discusses the advantages and disadvantages of tissue culture models for the detailed study of neuronal trophic and toxic factors. Our selection of factors is broadened to include ions, intermediate metabolites, antioxidants, steroids, neuropeptides, gangliosides, metals, neurotransmitters, brain extracts, and protein molecules. Most of these factors have been shown to be altered in the aged brain, to have a significant effect on cultured neurons, or both. This multilevel analysis provides the reader with an overview of the events regulating neuronal survival, differentiation and death. An understanding of these basic questions is necessary to sequence the molecular events resulting in neuronal death.

Aging↗