naloxone and saclofen

The mossy fiber (MF) pathway is critical to hippocampal function and influenced by gonadal hormones. Physiological data are limited, so we asked whether basal transmission and long-term potentiation (LTP) differed in slices of adult male and female rats. The results showed small sex differences in basal transmission but striking sex differences in opioid receptor sensitivity and LTP. When slices were made from females on proestrous morning, when serum levels of 17β-estradiol peak, the nonspecific opioid receptor antagonist naloxone (1 μm) enhanced MF transmission but there was no effect in males, suggesting preferential opioid receptor-dependent inhibition in females when 17β-estradiol levels are elevated. The μ-opioid receptor (MOR) antagonist Cys2,Tyr3,Orn5,Pen7-amide (CTOP; 300 nm) had a similar effect but the δ-opioid receptor (DOR) antagonist naltrindole (NTI; 1 μm) did not, implicating MORs in female MF transmission. The GABAB receptor antagonist saclofen (200 μm) occluded effects of CTOP but the GABAA receptor antagonist bicuculline (10 μm) did not. For LTP, a low-frequency (LF) protocol was used because higher frequencies elicited hyperexcitability in females. Proestrous females exhibited LF-LTP but males did not, suggesting a lower threshold for synaptic plasticity when 17β-estradiol is elevated. NTI blocked LF-LTP in proestrous females, but CTOP did not. Electron microscopy revealed more DOR-labeled spines of pyramidal cells in proestrous females than males. Therefore, we suggest that increased postsynaptic DORs mediate LF-LTP in proestrous females. The results show strong MOR regulation of MF transmission only in females and identify a novel DOR-dependent form of MF LTP specific to proestrus.

Topics: Animals; Baclofen; Bicuculline; Dendritic Spines; Estrous Cycle; Female; GABA-A Receptor Antagonists; Hippocampus; Long-Term Potentiation; Male; Mossy Fibers, Hippocampal; Naloxone; Narcotic Antagonists; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Opioid; Sex Characteristics; Somatostatin; Synapses

Using an in vitro neonatal rat gastric-brainstem preparation, the activity of majority neurons recorded in the nucleus tractus solitarius (NTS) of the brainstem were significantly inhibited by GABA A receptor agonist, muscimol (30 microM), and this inhibition was reversed by selective GABA A receptor antagonist, bicuculline (10 microM). Application of kavalactones (300 microg/ml) and dihydrokavain (300 microM) into the brainstem compartment of the preparation also significantly reduced the discharge rate of these NTS neurons (39 % and 32 %, respectively, compared to the control level), and this reduction was partially reversed by bicuculline (10 microM). Kavalactones or dihydrokavain induced inhibitory effects were not reduced after co-application of saclofen (10 microM; a selective GABA B receptor antagonist) or naloxone (100 nM; an opioid receptor antagonist). Pretreatment with kavalactones (300 microg/ml) or dihydrokavain (300 microM) significantly decreased the NTS inhibitory effects induced by muscimol (30 microM), approximately from 51 % to 36 %. Our results demonstrated modulation of brainstem GABAergic mechanism by kavalactones and dihydrokavain, and suggested that these compounds may play an important role in regulation of GABAergic neurotransmission.

Topics: Animals; Baclofen; Drug Interactions; GABA Agents; GABA Agonists; GABA Antagonists; Kava; Lactones; Muscimol; Naloxone; Narcotic Antagonists; Plant Extracts; Pyrones; Rats; Rats, Sprague-Dawley; Solitary Nucleus; Stomach

Cholinergic neurons were identified in rat striatal slices by their size, membrane properties, sensitivity to the NK(1) receptor agonist (Sar(9), Met(O(2))(11)) Substance P, and expression of choline acetyltransferase mRNA. A(1) receptor mRNA was detected in 60% of the neurons analysed, and A(2A) receptor mRNA in 67% (n=15). The A(1) receptor agonist R-N(6)-(2-phenylisopropyl)adenosine (R-PIA) hyperpolarized cholinergic neurons in a concentration dependent manner sensitive to the A(1) antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 100 nM). In dual stimulus experiments, the A(2A) receptor antagonist 8-(3-chlorostyryl)caffeine (CSC, 500 nM) decreased release of [(3)H]-acetylcholine from striatal slices (S2/S1 0.78+/-0.07 versus 0.95+/-0.05 in control), as did adenosine deaminase (S2/S1 ratio 0.69+/-0.05), whereas the A(1) receptor antagonist DPCPX (100 nM) had no effect (S2/S1 1.05+/-0.14). In the presence of adenosine deaminase the adenosine A(2A) receptor agonist 2-p-((carboxyethyl)phenylethylamino)-5'-N-ethylcarboxamidoadeno sin e (CGS21680, 10 nM) increased release (S2/S1 ratio 1.03+/-0.05 versus 0.88+/-0.05 in control), an effect blocked by the antagonist CSC (500 nM, S2/S1 0.68+/-0.05, versus 0.73+/-0.08 with CSC alone). The combined superfusion of bicuculline (10 microM), saclofen (1 microM) and naloxone (10 microM) had no effect on the stimulation by CGS21680 (S2/S1 ratio 0.99+/-0.04). The A(1) receptor agonist R-PIA (100 nM) inhibited the release of [(3)H]-acetylcholine (S2/S1 ratio 0.70+/-0.03), an effect blocked by DPCPX (S2/S1 ratio 1.06+/-0.07). It is concluded that both A(1) and A(2A) receptors are expressed on striatal cholinergic neurons where they are functionally active.

Topics: Acetylcholine; Adenosine; Adenosine Deaminase; Animals; Baclofen; Bicuculline; Caffeine; Cholinergic Fibers; Corpus Striatum; Dose-Response Relationship, Drug; GABA Antagonists; Gene Expression; Male; Membrane Potentials; Naloxone; Narcotic Antagonists; Neurons; Phenethylamines; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P1; RNA, Messenger; Tritium; Xanthines

Whole-cell patch-clamp recordings were obtained from nodose ganglion neurons acutely dissociated from 10-30-day-old rats to characterize the Ca2+ channel types that are modulated by GABA(B) and mu-opioid receptors. Five components of high-threshold current were distinguished on the basis of their sensitivity to blockade by omega-conotoxin GVIA, nifedipine, omega-agatoxin IVA and omega-conotoxin MVIIC. Administration of the mu-opioid agonist H-Tyr-D-Ala-Gly-Phe(N-Me)-Gly-ol (0.3-1 mM) or the GABA(B) agonist baclofen in saturating concentrations suppressed high-threshold Ca2+ currents by 49.9+/-2.4% (n=69) and 18.7+/-2.1% (n=35), respectively. The inhibition by H-Tyr-D-Ala-Gly-Phe(N-Me)-Gly-ol exceeded that by baclofen in virtually all neurons that responded to both agonists (67%), and occlusion experiments revealed that responses to mu-opioid and GABA(B) receptor activation were not linearly additive. In addition, administration of staurosporine, a non-selective inhibitor of protein kinase A and C, did not affect the inhibitory responses to either agonist or prevent the occlusion of baclofen-induced current inhibition by H-Tyr-D-Ala-Gly-Phe(N-Me)-Gly-ol. Blockade of N-type channels by omega-conotoxin GVIA eliminated current suppression by baclofen in all cells tested (n=11). Mu-opioid-induced inhibition in current was abolished by omega-conotoxin GVIA in 12 of 30 neurons tested, but was only partially reduced in the remaining 18 neurons. In the latter cells administration of omega-agatoxin IVA reduced, but did not eliminate the mu-opioid sensitive current component that persisted after blockade of N-type channels. This residual component of mu-opioid-sensitive current was blocked completely by omega-conotoxin MVIIC in nine neurons, whereas responses to H-Tyr-D-Ala-Gly-Phe(N-Me)-Gly-ol were still recorded in the remaining cells after administration of these Ca2+ channel toxins and nifedipine. Dihydropyridine-sensitive (L-type) current was not affected by activation of mu-opioid or GABA(B) receptors in any of the neurons. These data indicate that in nodose ganglion neurons mu-opioid receptors are negatively coupled to N-, P- and Q-type channels as well as to a fourth, unidentified toxin-resistant Ca2+ channel. In contrast, GABA(B) receptors are coupled only to N-type channels. Furthermore, the results do not support a role for either protein kinase C or A in the modulatory pathway(s) coupling mu-opioid and GABA(B) receptors to Ca2+ channels, but rather lend

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Analgesics, Opioid; Animals; Baclofen; Cadmium; Calcium; Calcium Channel Agonists; Calcium Channel Blockers; Calcium Channels; Calcium Channels, L-Type; Calcium Channels, N-Type; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; GABA Agonists; GABA Antagonists; Naloxone; Narcotic Antagonists; Nerve Tissue Proteins; Neurons; Nifedipine; Nodose Ganglion; omega-Agatoxin IVA; omega-Conotoxin GVIA; omega-Conotoxins; Patch-Clamp Techniques; Peptides; Rats; Rats, Sprague-Dawley; Receptors, GABA-B; Receptors, Opioid, mu; Spider Venoms