Recent evidence suggests that a novel serotonin receptor 5-HT 7 localized in the hypothalamus downregulates in response to treatment with the antidepressant fluoxetine (Sleight et al. 1995). This receptor has also been implicated in the regulation of circadian rhythms (Lovenberg et al. 1993). Here Depression may involve many possible abnormalities corresponding to multiple biological correlates of dysfunction or dysregulation in either one or several brain neurotransmitter systems (Cooper et al. 1996;Nair and Sharma 1989), a property that may contribute to the apparent disparity in symptomology and response to antidepressant therapy. The strict classical notions of neurotransmitter dysregulation hypotheses that associate depression with a deficiency of a vailable neurotransmitter or subresponsivity of mainly noradrenergic and/ or serotonergic receptor systems are recently being expanded to include disturbances in biological rhythm regulation. Impairment of the efficiency of rhythm maintenance or rhythm desynchronization has been suggested by many to lead to mental fatigue and depression (Goodwin et al. 1982;Hallonquist et al. 1986;Healy 1987;Partonen 1994;Schwartz 1993;Wirz-Justice and Campbell 1982;Wirz-Justice et al. 1995). Clinically, it has been extensively documented that the timing and structure of rhythms in physiological, behavioral, and endocrinological functions seem to be abnormal in depression (Coiro et al. 1993;Duncan 1996;File 1990;Kupfer 1995;Nair and Sharma 1989;Wehr et al. 1979). Furthermore, studies investigating the patterns of circadian rhythms of patients diagnosed with depression have been undertaken with the premise of disturbed rhythmicity as a central theme underlying the etiology of some affective disorders (Duncan 1996;Goodwin et al. 1982;Healy 1987;Siever and Davis, 1985;Souetre et al. 1988).Although melatonin is generally thought to be a primary modulator of circadian function through the suprachiasmatic nucleus (SCN) of the hypothalamus (Armstrong and Redman 1993;Binkley 1993;Cassone et al. 1993;Dubocovich 1991;Ibata et al. 1997;Reiter 1993; From the Bristol-Myers Squibb Company (ULM, ASE), Neuroscience Drug Discovery, Wallingford, Connecticut; and University of Connecticut, Department of Pharmaceutical Sciences (GG), Storrs, Connecticut, USA.Address correspondence to: U. Lena Mullins, Ph.D., BristolMyers Squibb Company, Neuroscience Drug Discovery, Department 408, 5 Research Parkway, Wallingford, Connecticut 06492, USA.Received January 1, 1999; revised March 23, 1999; accepted March 26, 1999. N EUROPSYCHOPHARMACOLOGY 1999 -VOL . 21 , NO . 3 Effects of Antidepressants 353 Stankov et al. 1993), the serotonergic system also plays a critical role in circadian modulation. The SCN receives dense projections from the raphe serotonergic neurons originating in the brainstem (Jacobs and Azmitia 1992;Meyer-Bornstein and Morin 1996;Van De Kar and Lorens 1979). Lesions of the median raphe serotonergic system using the neurotoxic agent 5,7-dihydroxytryptamine (5,7-DHT) produce a sever...

To investigate the role of sensory C-fiber stimulation and tachykinin release in the immediate nasal responses to the sensory irritant acrolein, the upper respiratory tract of the urethan-anesthetized male Fischer 344 rat was isolated via insertion of an endotracheal tube, and acrolein-laden air [2, 5, 10, or 20 parts/million (ppm)] was drawn continuously through that site at a flow rate of 100 ml/min for 50 min. Uptake of the inert vapor acetone was measured throughout the exposure to assess nasal vascular function. Plasma protein extravasation into nasal tissue and nasal lavage fluid was also assessed via injection of Evans blue dye. At 20 ppm, acrolein induced 1) a twofold increase in acetone uptake, indicative of vasodilation, followed by a progressive decline toward basal levels and 2) increased plasma protein extravasation, as indicated by dye leakage into nasal tissue and nasal lavage. These responses were inhibited by capsaicin pretreatment and the neurokinin type 1 antagonist N-acetyltrifluoromethyl tryptophan benzyl ester and were potentiated by the peptidase inhibitors phosphoramidon and captopril, suggesting that these responses were mediated by tachykinin. At lower exposure concentrations, acrolein was without effect on dye leakage but produced vasodilation, as indicated by increased acetone uptake. The responses at the lower concentrations were inhibited by capsaicin pretreatment, implicating nasal sensory C-fiber involvement, but were not influenced by N-acetyltrifluoromethyl tryptophan benzyl ester, phosphoramidon, or captopril, suggesting the involvement of a mediator other than the tachykinins substance P and neurokinin A.

No abstract

This study was designed to characterize the acute nasal vasodilatory responses to the sensory irritants acetaldehyde and acetic acid. For this purpose, the upper respiratory tract of the urethane-anesthetized male F344 rat was isolated by insertion of an endotracheal cannula, and irritant-laden air was drawn continuously through that site at a flow rate of 100 ml/min for 50 min. Vascular function was monitored by measuring inert vapor (acetone) uptake throughout the exposure. Both acetaldehyde and acetic acid induced an immediate concentration-dependent vasodilation as indicated by increased steady-state acetone uptake rates. This response was observed at exposure concentrations of 25 ppm or 130 ppm or higher for acetaldehyde or acetic acid, respectively. The response to either vapor was significantly diminished in rats pretreated with the sensory nerve toxin capsaicin (50 mg/kg, 7 days prior to exposure), providing evidence that sensory nerves play a role in the response. Acetaldehyde is metabolized by aldehyde dehydrogenase to acetic acid. Pretreatment with the aldehyde dehydrogenase inhibitor cyanamide (10 mg/kg, 1 h prior to exposure) reduced the vasodilatory response to 200 ppm but not to 50 ppm acetaldehyde. These results suggest that formation of acetic acid is important in the sensory nerve-mediated vasodilatory response to high, but perhaps not to low, concentrations of acetaldehyde.

These data suggest that the antiparkinsonian actions of SKF 82958 may be due to stimulation of D1 receptors in the ventrolateral striatum and substantia nigra pars reticulata. In addition, these results indicate that GABA mechanisms in the substantia nigra pars reticulata may be important for the antiparkinsonian effects of D1 agonists.