Measuring vision using innate behaviours in mice with intact and impaired retina function.

Measuring vision in rodents is a critical step for understanding vision, improving models of human disease, and developing therapies. Established behavioural tests for perceptual vision, such as the visual water task, rely on learning. The learning process, while effective for sighted animals, can be laborious and stressful in animals with impaired vision, requiring long periods of training. Current tests that that do not require training are based on sub-conscious, reflex responses (e.g. optokinetic nystagmus) that don't require involvement of visual cortex and higher order thalamic nuclei. A potential alternative for measuring vision relies on using visually guided innate defensive responses, such as escape or freeze, that involve cortical and thalamic circuits. In this study we address this possibility in mice with intact and degenerate retinas. We first develop automatic methods to detect behavioural responses based on high dimensional tracking and changepoint detection of behavioural time series. Using those methods, we show that visually guided innate responses can be elicited using parametisable stimuli, and applied to describing the limits of visual acuity in healthy animals and discriminating degrees of visual dysfunction in mouse models of retinal degeneration.

Neuronal responses to iontophoretically applied angiotensin II, losartan and aldosterone, as well as gustatory stimuli, in non-anesthetized control and desoxycorticosterone acetate-pretreated rats.

The neuronal mechanism of the sodium appetite initiated in rats by priming with a mineralocorticoid (desoxycorticosterone acetate (DOCA)) treatment and subsequent central angiotensin II (Ang II) was investigated using electrophysiological-iontophoretic techniques and sapid salt stimulation of the tongue in non-anesthetized restrained, DOCA-pretreated (0.5 mg/day s.c. for 3 days) or non-pretreated male Wistar rats. The rats were trained to drink water and a 1.6% NaCl solution while their heads were painlessly held in a stereotaxic apparatus with an attachment fixed to the skull. A total of 634 neurons (375 in non-pretreated and 259 in DOCA-pretreated rats) were recorded in the medial septum and median preoptic area during iontophoretic application of Ang II, aldosterone or losartan, or tongue application of the salty solution or water. Of the 151 neurons recorded in control rats during the application of the solutions on the tongue, one (0.7%) was found specifically excited and 16 (10.6%) inhibited by the sapid sodium. Similarly, of the 110 neurons tested in the DOCA-pretreated rats, 5 (4.5%) were found specifically excited and 8 (7.3%) inhibited by the sapid sodium. The number of neurons responding to the iontophoretically applied agents was not significantly changed by the DOCA pretreatment. Thus, the DOCA pretreatment significantly increased the number of preoptic neurons that were specifically excited by a salty solution applied on the tongue. These results suggest that hormonally induced changes in the gustatory responsiveness of ventral forebrain neurons may be part of the sequence that alters the hedonic valence of NaCl during sodium appetite.

Angiotensin II receptor subtype antagonists can both stimulate and inhibit salt appetite in rats.

In urethane-anaesthetised male Wistar rats iontophoretic application of the angiotensin II (Ang II) type 1 (AT-1) receptor specific nonpeptide antagonist losartan in the septo-preoptic continuum can produce neuronal excitation of short- and long-term duration which has been interpreted as removal of tonic Ang II-induced inhibition. Mineralocorticoid pretreatment, which increases neuronal sensitivity to Ang II to enhance salt appetite, also removes this losartan-induced long-term excitation. These results suggested steroid modulation of the AT-1 receptor and a complex involvement of Ang II in salt appetite. To investigate the role of the inhibitory action of central Ang II on salt appetite, we gave intracerebroventicular injections of a single, low dose (10 ng) of losartan in normal euhydrated rats and this produced, paradoxically, a progressive increase in salt intake (1.6 +/- 0.3 ml/day to 3.5 +/- 0.9 ml/day, n = 15, P < 0.05). Treatment of these salt enhanced rats with DOCA (0.5 mg/day, s.c., for 3 days) further increased the salt appetite, but then a second i.c.v. injection of the same dose of losartan significantly inhibited the enhanced salt appetite (4.7 +/- 0.7 to 1.3 +/- 0.4, n = 9, P < 0.05). These results provide evidence for a complex action of Ang II on the At-1 receptor mediating the generation of salt appetite that appears to involve either at least two functional subtypes of this AT-1 receptor, as already suggested by previous electrophysiological experiments, or one AT-1 receptor with several activation states.

Effects of DOCA pretreatment on neuronal sensitivity and cell responsiveness to angiotensin II, in the bed nucleus of the stria terminalis in the rat.

A previous study has shown that DOCA pretreatment altered the responsiveness of neurons to microiontophoretic administration of angiotensin II (AII) and aldosterone (Aldo). This result coincided with an increase in activity in the septo-preoptic region and a decrease in activity of the central nucleus of the amygdala. The latter region is anatomically linked to the bed nucleus of the stria terminalis (BNST). Single unit activity was recorded in the BNST in response to iontophoretic application of AII, non-peptide AII-receptor antagonists or Aldo in DOCA-pretreated and in non-pretreated rats. DOCA-pretreatment significantly decreased the responsiveness to AII (28 cells (18.5%) vs. 8 cells (14.0%) u = 0.018 for excitation and 3 cells (8.6%) vs. 0 cells 0%, u = 0.011 for inhibition, P < 0.05) and to Aldo (24 cells (21.4%) vs. 4 cells (10.2%), u = 0.026 for excitation, and 3 cells (2.6%) vs. 0 cells, u = 0.009 for inhibition, P < 0.05) of the neurons localised in the BNST. A significant decrease was found in the inhibitory responses to iontophoretic application of losartan, an AII type-1 receptor (AT-1) antagonist (u = 0.042, P < 0.05). No significant differences were recorded with iontophoretic application of PD 123319, a specific AII-type-2 (AT-2) receptor antagonist. Therefore AT-1 receptors are likely responsible for the decreased responsiveness of the BNST correlated with the decrease in the activity within the amygdala.

Tonic neuronal inhibition by AII revealed by iontophoretic application of Losartan, a specific antagonist of AII type-1 receptors.

Short-term low-dose mineralocorticoid pretreatment enhances subsequent neuronal activity in the medial septum/preoptic region and in the stria terminalis/posterior amygdala of urethane anaesthetised male Wistar rats and sensitises these neurons to angiotensin II (AII). We have investigated the effect of iontophoretic application of Losartan, a specific nonpeptidergic AII type-1 receptor antagonist, on the background activity of spontaneously active neurons in these regions using a seven-barrelled microiontophoretic electrode sealed to a recording electrode. The influence of Losartan on the effects of iontophoretically applied AII in deoxycorticosterone acetate (DOCA) pretreated and nonpretreated rats was also investigated. Iontophoretically applied Losartan was observed to block the excitatory effect of AII in some neurons. In other spontaneously active neurons Losartan was seen to stimulate (or inhibit) immediately, this effect being greater in nonpretreated than in DOCA pretreated rats. Losartan was also observed to provoke persistent excitation of some spontaneously active neurons only in the nonpretreated rats. These results suggest that there exists a tonic inhibition by AII on the neurons in this area of the forebrain and that there may exist at least two subtypes of the AII type-1 receptor.

Water versus salty taste and Iontophoretic ANGII responses of septopreoptic neurons in dehydrated and euhydrated awake rats.

Little is known of the influence of gustatory, particularly salt, input on neurons of the forebrain and if the same neurons are sensitive to hydromineral balance humoral stimuli. In awake, nonpremedicated rats we recorded the activity of spontaneously active neurons in the preoptic/anterior hypothalamic area of dehydrated and euhydrated rats while allowing them to ingest water or a hypertonic salt solution (1.6% NaCl) administered to the tongue. The hormones angiotensin and aldosterone, both implicated in hydromineral balance, were applied by iontophoresis to the same neurons. In the dehydrated rats, 27% (15/55) of the spontaneously active neurons responded to a liquid (either water or the NaCl) applied to the tongue; in the euhydrated rats 23% (18/78) responded to the same stimuli. In the dehydrated rats, however, 33% (5/15) of the responding neurons were inhibited when the NaCl solution was applied to the tongue compared with only 5% (1/18) in the euhydrated rats. Iontophoretic application of angiotensin increased the spontaneous activity in 21% of those neurons tested that responded to taste. These results suggest that the state of hydration of an animal is able to change the neuronal response to substances applied to the tongue. Furthermore, it appears that these gustatory-sensitive neurons may also be related to hydromineral balance regulation since they are able to respond to angiotensin.