Taste/tactile cue discriminations in taste-aversion learning foIIowing depletion of noradrenaIine

Four experiments were performed to investigate the effect of noradrenaline (NA) depletion, following systemic DSP4 treatment, upon a tastehactile discrimination in taste-aversion learning. In Experiments 1 and 2 , noisy bottle (A) + lithium chloride pairings were alternated with saccharin (B) + saline pairings, and vice versa, during Phase I conditioning. The particular order of reinforcement presentation in each case was then reversed, so that a noisy bottle (A) + saline pairing was now altered with a saccharin (B) + lithium chloride pairing, etc., during Phase II (reversal) conditioning. In Experiments 3 and 4 , saccharin in noisy bottle (AB) + lithium chloride pairings alternated with either noisy bottle (A) + saline or saccharin (B) + saline pairings, and vice versa, during Phase I conditioning; the order of reinforcement presentation was then reversed, as above. None of the four experiments performed offered any evidence of impairments of the discrimination task as a result of NA depletion. These results are discussed in the context of associative preparedness and of discrimination learning in operant tasks and recent findings on compound conditioning, following the loss of NA.     

Marble burying and spontaneous motor activity in mice: interactions over days and the effect of diazepam

Spontaneous motor activity of mice was studied in the presence or absence of 24 coloured glass marbles with and without treatment with different doses of the anxiolytic compound, diazepam. The three parameters of motor activity, locomotion, rearing and total activity, were measured in automated test cages. All the groups exposed to the marbles exhibited considerable and comparable marble burying, but there was an important interaction between marble burying and locomotor activity over test days. The "marbles" group performed fewer locomotion counts than the "no marbles" group on Day 1 but more counts on Day 3. The "marbles" group performed more rearing and less total activity than the "no marbles" group generally and this relationship was not altered over test days. Diazepam caused a dose-dependent decrease of both marble burying and the three parameters of motor activity but did not cause further increases in motor activity in the groups exposed to the marbles. These results are discussed with regard to the effects of "coping" behaviours on measures of motor activity. In conclusion, the present motor activity-marble burying test appears to be a suitable animal model for testing potential anxiolytic compounds.     

Serotonin neurons and aversive conditioning in the rat

The acute and long-term effects of p -chloroamphetamine (PCA) on one-way and two-way active avoidance (AA), passive avoidance (PA) learning, fear retention (FR) and on central monoamine concentrations were examined in the male rat. Acute PCA administration (0.63–5 mg/kg i.p.), which releases presynaptic 5-HT, produced a dose-related impairment of both one-and two-way AA acquisition, AA retention, PA and fear retention. The selective serotonin (5-HT) uptake inhibitor zimelidine, but not the noradrenaline (NA) uptake inhibitor desipramine, blocked the avoidance deficit induced by acute PCA. Degeneration of brain 5-HT neurons by a high neurotoxic dose of PCA (2 × 10 mg/kg i.p.) failed to change AA and PA learning but blocked the avoidance deficit induced by acute PCA. Degeneration of locus coeruleus NA neurones with DSP4 (1 × 50 mg/kg), a selective NA neurotoxin, failed to block the acute PCA action. Thus, the acute avoidance learning impairment appears to be specifically related to the acute release of endogenous 5-HT. Both acute and long-term PCA treatment affected 5-HT neurones preferentially in the forebrain while marginal effects were observed in the midbrain and spinal cord. A marked impairment in the retention and retrieval of fear conditioning in the rat was also observed following acute PCA administration. The serotoninergic mechanisms underlying the retrieval deficit were found to be similar but not identical to those involved in AA acquisition. These results suggest an important role for central 5-HT neurones in aversive learning processes. The possible involvement of 5-HT neurones in learning, memorial and/or retrieval processes is discussed.     

Serotonin neurons and aversive conditioning in the rat

The acute and long-term effects of p-chloroamphetamine (PCA) on one-way and two-way active avoidance (AA), passive avoidance (PA) learning, fear retention (FR) and on central monoamine concentrations were examined in the male rat. Acute PCA administration (0.63–5 mg/kg i.p.), which releases presynaptic 5-HT, produced a dose-related impairment of both one-and two-way AA acquisition, AA retention, PA and fear retention. The selective serotonin (5-HT) uptake inhibitor zimelidine, but not the noradrenaline (NA) uptake inhibitor desipramine, blocked the avoidance deficit induced by acute PCA. Degeneration of brain 5-HT neurons by a high neurotoxic dose of PCA (2 × 10 mg/kg i.p.) failed to change AA and PA learning but blocked the avoidance deficit induced by acute PCA. Degeneration of locus coeruleus NA neurones with DSP4 (1 × 50 mg/kg), a selective NA neurotoxin, failed to block the acute PCA action. Thus, the acute avoidance learning impairment appears to be specifically related to the acute release of endogenous 5-HT. Both acute and long-term PCA treatment affected 5-HT neurones preferentially in the forebrain while marginal effects were observed in the midbrain and spinal cord. A marked impairment in the retention and retrieval of fear conditioning in the rat was also observed following acute PCA administration. The serotoninergic mechanisms underlying the retrieval deficit were found to be similar but not identical to those involved in AA acquisition. These results suggest an important role for central 5-HT neurones in aversive learning processes. The possible involvement of 5-HT neurones in learning, memorial and/or retrieval processes is discussed.     

Signalled and unsignalled avoidance impairments following noradrenaline depletion with DSP4: An hypothesis incorporating and associative and a non-associative factor

Four experiments were performed to investigate the effect of a single prior administration of the selective noradrenaline neurotoxin, DSP4 (50 md/kg, i.p.), upon signalled and unisgnalled variations of the two-way active avoidance procedure. Noradrenaline depletio following DSP4 caused a significant impairment in the acquisition but not in the retention of signalled avoidance. Two unsignalled discrete trial avoidance procedures were used, one of which the 50/10 procedure, was designed to be considerably more difficult than the other, the 50/40 procedure. DSP4- treated rats were found to be impaired on the difficult 50/10 task but not on the 50/40 task. It was also shown that the DSP4 group in the 50/10 experiment made fewer crossings that did not result in shock postponement ('nonreinforced' or intertrial crossings) while in the 50/40 experiment the DSP4 group in the 50/10 experiment made fewer crossings that did not result in shock postponement ('nonreinforced' or 'intertrial' crossings) while in the 50/40 experiment the DSPS group made more 'intertrial' crossings. Response latencies were not significantly altered as a result of the treatment in both instances. The results of the present experiments in conjunction with much accumulate evidence from several other investigations were assimilated in order to develop an hypothesis to account for the consistent signalled two-way avoidance deficits resulting from DSP4 administration. This hypothesis incorporates two main components: (1) It may be that DSP4-treated rats are unable to develop the correct coping behaviour required in the stressful task confronting it, i.e. they fail to make the appropriate crossing (running) respose whether an escape or an avoidance response; (2) It is possible that DSP4-treated rats may fail to associate adequately a successful avoidance response with either the tone that signals shock or the postponement of shock.