Effects of prenatal exposure to gamma rays on circling and activity behavior in prepubertal and postpubertal rats.

The study departs from the finding that postural asymmetries in low-weight female neonates are greatly increased following prenatal lesions inflicted by gamma irradiation at day 15. Given that amphetamine-induced rotation in adult rats could be predicted by their infantile axial asymmetry we expected a greater tendency for circling in rats exposed at day 15. To examine this prediction, Sprague-Dawley rats were exposed to a single dose of gamma radiation at 1.5 Gy with a dose-rate of 0.15 Gy/min. The dose was delivered on one of the embryonic days (E15, 17 or 19) throughout the whole body of pregnant dams. Sham prenatal exposure of controls consisted of placing pregnant rats in the same environment for 10 min. All rats were tested during the active part of the circadian cycle. At postnatal day 27 (P27) exposed pups did not differ in rates of either spontaneous or d-amphetamine-induced circling from the shams. At P57, in keeping with our prediction, E15 rats manifested enhanced rotation and higher net asymmetry. However, E17 also showed higher gyration tendency compared to their shams while exposed E19 rats did not differ from their shams. The role of intrinsic DAergic imbalance presumably sharpened by irradiation at E15 and of neocortical deficit inflicted at E15 and E17 are discussed.

Dark-induced supersensitivity of dopamine D-1 and D-2 receptors in rat retina.

Light deprivation of rat retina leads to a rapid (within 6 h) development of a state of supersensitivity (upregulation) of dopamine D-1 receptors (positively coupled to adenylate cyclase), which are essentially involved in the modulation by light of the electrical activity and communication between horizontal cells. In contrast, the supersensitivity of D-2 receptors (negatively coupled to cAMP generating system) appears to develop only after 2 days (better after 4 days) of dark adaptation, although these receptors are linked to multiple light-dependent retinal functions. These results suggest the existence of different mechanisms of sensory adaptation for these two subtypes of dopamine receptors.

Retinal dopamine D1 and D2 receptors: characterization by binding or pharmacological studies and physiological functions.

1. In the retinal inner nuclear layer of the majority of species, a dopaminergic neuronal network has been visualized in either amacrine cells or the so-called interplexiform cells. 2. Binding studies of retinal dopamine receptors have revealed the existence of both D1- as well D2-subtypes. The D1-subtype was characterized by labeled SCH 23390 (Kd ranging from 0.175 to 1.6 nM and Bmax from 16 to 482 fmol/mg protein) and the D2-subtype by labelled spiroperidol (Kd ranging from 0.087 to 1.35 nM and Bmax from 12 to 1500 fmol/mg protein) and more selectively by iodosulpiride (Kd 0.6 nM and Bmax 82 fmol/mg protein) or methylspiperone (Kd 0.14 nM and Bmax 223 fmol/mg protein). 3. Retinal dopamine receptors have been also shown to be positively coupled with adenylate cyclase activity in most species, arguing for the existence of D1-subtype, whereas in some others (lower vertebrates and rats), a negative coupling (D2-subtype) has been also detected in peculiar pharmacological conditions implying various combinations of dopamine or a D2-agonist with a D1-antagonist or a D2-antagonist in the absence or presence of forskolin. 4. A subpopulation of autoreceptors of D2-subtype (probably not coupled to adenylate cyclase) also seems to be involved in the modulation of retinal dopamine synthesis and/or release. 5. Light/darkness conditions can affect the sensitivity of retinal dopamine D1 and/or D2-receptors, as studied in binding or pharmacological experiments (cAMP levels, dopamine synthesis, metabolism and release). 6. Visual function(s) of retinal dopamine receptors were connected with the regulation of electrical activity and communication (through gap junctions) between horizontal cells mediated by D1 and D2 receptor stimulation. Movements of photoreceptor cells and migration of melanin granules in retinal pigment epithelial cells as well as synthesis of melatonin in photoreceptors were on the other hand mediated by the stimulation of D2-receptors. 7. Other physiological functions of dopamine D1-receptors respectively in rabbit and in embryonic avian retina would imply the modulation of acetylcholine release and the inhibition of neuronal growth cones.

Behavioral and neurochemical abnormalities after exposure to low doses of high-energy iron particles.

Exposure of rats to high-energy iron particles (600 MeV/amu) has been found to alter behavior after doses as low as 10 rads. The performance of a task that measures upper body strength was significantly degraded after irradiation. In addition, an impairment in the regulation of dopamine release in the caudate nucleus (a motor center in the brain), lasting at least 6 months, was also found and correlated with the performance deficits. A general indication of behavioral toxicity and an index of nausea and emesis, the conditioned taste aversion, was also evident. The sensitivity to iron particles was 10-600 times greater than to gamma photons. These results suggest that behavioral and neurobiological damage may be a consequence of exposure to low doses of heavy particles and that this possibility should be extensively studied.

Irradiation inactivation studies of the dopamine D1 receptor and dopamine-stimulated adenylate cyclase in rat striatum.

In frozen rat striatal tissue, exposed to 10 MeV electrons from a linear accelerator, the sizes of the dopamine (DA) D1 receptor and the DA-sensitive adenylate cyclase complex were determined using target size analysis. The number of D1 receptors (labelled by [3H]SCH 23390) declined monoexponentially with increasing radiation intensity, yielding a molecular weight (mol.wt.) of 80 kDa. Also the activity of the catalytic unit (C) of the adenylate cyclase (as measured by forskolin stimulation), decreased monoexponentially, however with a mol.wt. of 145 kDa. Both basal, DA- and fluoride (F-)-stimulated activity declined in a concave-downward fashion with a limiting mol.wt. of 134, 138 and 228 kDa, respectively. It was estimated that the basal and DA-stimulated activity originated from an enzyme complex with a mol.wt. of 325 kDa, a value close to the combined size of RGs and C. These data suggest that F- stimulation of the adenylate cyclase, which occurs by a Gs activation, does not cause dissociation of Gs into the alpha s and beta gamma subunits. Further, the DA-regulated adenylate cyclase apparently exists as a complex consisting of RGs and C; the mechanism of hormonal activation is a dissociation of C from this complex.

Binding of [3H]SKF 38393 to dopamine D-1 receptors in rat striatum in vitro; estimation of receptor molecular size by radiation inactivation.

[3H]SKF 38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine) binds with high affinity to 3,4-dihydroxyphenylethylamine (dopamine) D-1 receptors in rat striatum in vitro (KD = 7 and 14 nM in nonfrozen and frozen striatum, respectively). The number of binding sites (Bmax) was approximately 80.0 pmol/g of original tissue, a value similar to the Bmax for the dopamine D-1 antagonist SCH 23390. Nondisplaceable [3H]SKF 38393 binding was approximately 45% of total binding. Irradiation (0-4 Mrad) of frozen whole striata decreased the number of [3H]SKF 38393 binding sites monoexponentially without changing the binding affinity. The functional molecular mass for the agonist dopamine D-1 binding site was 132,800 daltons, which is higher than the functional molecular mass of the antagonist dopamine D-1 binding site (approximately 80,000 daltons).

Serotonin-S2 and dopamine-D2 receptors are the same size in membranes.

Target size analysis was used to compare the sizes of serotonin-S2 and dopamine-D2 receptors in rat brain membranes. The sizes of these receptors were standardized by comparison with the muscarinic receptor, a receptor of known size. The number of serotonin-S2 receptors labeled with (3H)ketanserin or (3H)spiperone in frontal cortex decreased as an exponential function of radiation dose, and receptor affinity was not affected. The number of dopamine-D2 receptors labeled with (3H)spiperone in striatum also decreased as an exponential function of radiation dose, and D2 and S2 receptors were equally sensitive to radiation. In both striatum and frontal cortex, the number of muscarinic receptors labeled with (3H)QNB decreased as an exponential function of radiation dose, and were much less sensitive to radiation than S2 and D2 receptors. These data indicate that in rat brain membranes, S2 and D2 receptors are of similar size, and both molecules are much larger than the muscarinic receptor.

Distinct target size of dopamine D-1 and D-2 receptors in rat striatum.

Frozen rat striatal tissue was exposed to 10 MeV electrons from a linear accelerator. Based on the theory of target size analysis, the molecular weights of dopamine D-1 receptors (labelled by 3H-piflutixol) and dopamine D-2 receptors (labelled by 3H-spiroperidol) were 79,500 daltons and 136,700 daltons, respectively. The size of the dopamine-stimulated adenylate cyclase was 202,000 daltons. The estimated molecular sizes were deduced by reference to proteins with known molecular weights which were irradiated in parallel. The results showed that the molecular entities for 3H-piflutixol binding and 3H-spiroperidol binding were not identical. The present results do not allow conclusions as to whether D-1 and D-2 receptors are two distinct proteins in the membrane, or whether the receptors are located on the same protein. In the latter case the binding of 3H-spiroperidol needs the presence of a second molecule.

Amphetamine anorexia: the effect of radio-frequency lesions and 6-OHDA injections into dopaminergic nigro-striatal bundle in cats.

The effect of radio-frequency (RF) and 6-OHDA lesions of two levels of dopaminergic nigro-striatal bundle on amphetamine anorexia was investigated in 4 groups of cats. RF and 6-OHDA lesions of far-lateral hypothalamus produced significant facilitation of feeding after injection of amphetamine. RF and 6-OHDA destructions of substantia nigra were with slight or without (respectively) effect on amphetamine anorexia. The results suggest that nigrostriatal bundle is not essential for mechanisms mediating amphetamine anorexia.

Correspondency between different affinity states and target size of the bovine striatal D2 dopamine receptor.

Target size analysis of the D2 dopamine receptor in the bovine striatum revealed the presence of two populations of this receptor, in terms of apparent molecular size. The size of large target was approximately 150 X 10(4) daltons, while that of small target was 11 X 10(4) daltons. The antagonist [3H]spiperone labeled both large and small sized D2 receptors, while agonist [3H]n-propylapomorphine (NPA) labeled only the former. In addition, the apparent molecular size of a functional unit for the GTP effect was calculated to be 150 X 10(4) daltons, such appearing to be identical to that of large target sized D2 dopamine receptors. Therefore, the large sized D2 receptor, probably an oligomeric complex consisting of D2 receptor recognition protein and guanine nucleotide regulatory protein, has a high affinity for both agonist and antagonist, while the small sized receptor, probably a monomeric or dimeric receptor recognition protein, has a high affinity for only the antagonist.

Molecular size of the canine and human brain D2 dopamine receptor as determined by radiation inactivation.

Target-size analysis (radiation inactivation) has been utilized for determination of the molecular size of the striatal D2 dopamine receptor of both canine and human membranes. The dog and human receptors were found to have a molecular size of 123,000 daltons. The identity of molecular size values is consistent with available pharmacological and biochemical evidence supporting D2 dopamine receptor identity in canine and human tissues. These data suggest that the canine receptor may be a valid model for molecular and structural investigation of the human D2 dopamine receptor.