Factors Influencing the Formation of Nitrous Acid from Photolysis of Particulate Nitrate.

Enhanced photolysis of particulate nitrate (pNO3) to form photolabile species, such as gas-phase nitrous acid (HONO), has been proposed as a potential mechanism to recycle nitrogen oxides (NOx) in the remote boundary layer ("renoxification"). This article presents a series of laboratory experiments aimed at investigating the parameters that control the photolysis of pNO3 and the efficiency of HONO production. Filters on which artificial or ambient particles had been sampled were exposed to the light of a solar simulator, and the formation of HONO was monitored under controlled laboratory conditions. The results indicate that the photolysis of pNO3 is enhanced, compared to the photolysis of gas-phase HNO3, at low pNO3 levels, with the enhancement factor reducing at higher pNO3 levels. The presence of cations (Na+) and halides (Cl-) and photosensitive organic compounds (imidazole) also enhance pNO3 photolysis, but other organic compounds such as oxalate and succinic acid have the opposite effect. The precise role of humidity in pNO3 photolysis remains unclear. While the efficiency of photolysis is enhanced in deliquescent particles compared to dry particles, some of the experimental results suggest that this may not be the case for supersaturated particles. These experiments suggest that both the composition and the humidity of particles control the enhancement of particulate nitrate photolysis, potentially explaining the variability in results among previous laboratory and field studies. HONO observations in the remote marine boundary layer can be explained by a simple box-model that includes the photolysis of pNO3, in line with the results presented here, although more experimental work is needed in order to derive a comprehensive parametrization of this process.

Reciprocal connections between the 'nucleus rotundus' and the dorsal lateral telencephalon in the weakly electric fish Gnathonemus petersii.

Injections of horseradish peroxidase into the dorsal lateral telencephalon of the weakly electric mormyrid fish Gnathonemus petersii resulted in retrogradely filled cells and anterogradely labelled terminals in the 'nucleus rotundus' of the ipsilateral rostral diencephalon. This connection courses via the lateral part of the lateral forebrain bundle. The present results suggest a particularly close relationship between the Dla cell group of the lateral telencephalon and the 'nucleus rotundus'.

A direct cerebello-telencephalic projection in an electrosensory mormyrid fish.

After injections of the posterior part of the lateral zone of the area dorsalis telencephalic (Dlp) with either horseradish peroxidase or the newly available carbocyanine dye DiI, efferent cells were labeled in the valvula cerebelli of the mormyrid fish, Gnathonemus petersii. This may be a unique connection for this group of electrosensory teleosts, since no other vertebrate has ever been reported before to have a direct cerebello-telencephalic projection.

Effects of telencephalic ablation on habituation of arousal responses, within and between daily training sessions in goldfish.

Goldfish Carassius auratus were presented with a moving shadow stimulus at 2-min intervals and their cardiac and ventilatory responses were monitored. Normal fish, fish with their telencephalon ablated, and those with sham operations were compared for responsiveness and habituation to repeatedly presented stimuli over the 3-day test period. While all groups showed increased habituation on successive days testing, fish with their telencephalon ablated showed significantly slower response habituation within the daily test sessions when compared with the control groups. Subjects with their telencephalon ablated also showed a tendency for increased responsiveness on initial stimulus presentation and poorer retention between days of information relating to the eliciting test stimulus.

Epileptogenesis is associated with heightened arousal responses in fish.

Intramuscular injection of sodium penicillin in roach (Rutilus rutilus) caused delayed habituation of arousal responses to repeated presentation of the onset of illumination or of a 'tap' stimulus. Topical application of aluminum hydroxide to the telencephalon of roach had a similar effect but was shown, also, to induce electroencephalographic seizures, in which the EEG amplitude was elevated from 4-20 times its normal level. Both treatments caused intermittent, abnormal 'weaving' behaviour and sporadic, violent, uncoordinated motor activity. In goldfish, Carassius auratus, topical application of aluminum hydroxide also caused delayed habituation of quantitatively measured, cardiac arousal responses to a moving shadow stimulus, compared to controls. This delayed habituation was, however, largely a result of the elevated magnitude of these arousal responses. The results are discussed in relation to brain mechanisms normally operative during arousal which may be hyperactive in epilepsy.

Localization of telencephalic regions concerned with habituation of cardiac and ventilatory responses associated with arousal in the goldfish (Carassius auratus).

Goldfish (Carassius auratus) were presented with a "light-on" stimulus at 2-min intervals, and their cardiac and ventilatory responses were monitored. Normal fish, fish with sham operations for telencephalic lesions, and fish with bilateral electrolytic lesions of the telencephalon (anterior commissural and posterior telencephalic groups) were compared for responsiveness and habituation to regularly presented stimuli. There was no evident difference in responsiveness between the four groups, though 3 fish with lesions in the regions ventralis pars dorsalis and ventralis pars ventralis gave fright responses to novel stimuli. Lesions in posterior telencephalic regions dorsalis pars centralis and ventralis pars intermedialis and at the telencephalic/diencephalic border close to the habenula caused significant impairment of habituation.

Cardiac and ventilatory arousal responses and their habituation in goldfish: effects of the intensity of the eliciting stimulus.

Recordings were made of cardiac and ventilatory responses of goldfish to the onset of 10 sec illumination presented at 2 min intervals. These responses were measured by increases in cardiac interbeat interval, ventilatory interbreath interval and by reductions in ventilatory amplitude. Four groups of fish were subjected to intensities of 52, 78, 90 and 160 lux. Habituation of responses was considered to have occurred when its magnitude fell within the limits of normal variation of the physiological variable. It was found that the more intense the stimulus the greater was the magnitude of the initial physiological response and correlated with this the number of stimulus presentations required for habituation. The relationship between stimulus intensity, initial response magnitude and resistance to habituation was consistent for cardiac responses. The results are discussed with respect to current knowledge of arousal and its habituation.

Effects of olfactory bulb ablation on cardiac and ventilatory arousal responses and their habituation in the goldfish Carassius auratus.

The effects of olfactory bulb ablation on the cardiac and ventilatory arousal responses to the onset of illumination and habituation of these responses were investigated in goldfish. Bulbectomy did not effect the magnitude of response on novel stimulus presentation. Normal, sham operated, and olfactory bulb-ablated animals showed similar rates of habituation. These results suggest that deficits in feeding and sexual behavior in goldfish are due to the loss of specific olfactory influences on lower brain centers and not due to a decrease in general responsiveness.