Classical aversive conditioning induces increased expression of mature-BDNF in the hippocampus and amygdala of pigeons.

The expression of brain-derived neurotrophic factor (BDNF), which is found in the pro-BDNF, truncated-BDNF and mature-BDNF isoforms, changes with learning. Mature-BDNF shows a peak of late expression in the hippocampus that is involved in the persistence of aversive memory in rodents. However, the role of BDNF in the hippocampal synaptic mechanisms involved in the classical conditioning aversive memory in birds still needs clarification. This study investigated the late expression of BDNF in the hippocampus and amygdala of pigeons trained with tone-shock conditioning and the effects of intra-hippocampal infusion of anisomycin (Ani) in these changes. Seven days after implantation of intra-hippocampal microcannulae, adult pigeons trained with three tone-shock pairings were assigned to one of three groups: Conditioning and Ani (CondANI), Conditioning and saline vehicle (CondSAL) and Conditioning only (Cond). NAIVE group had no treatment or conditioning. Homogenates of tissues from the hippocampus and amygdala, obtained 12h after training, were used to determine the content of mature-BDNF, truncated-BDNF and pro-BDNF using Western blotting. Higher values for mature-BDNF than for truncated- and pro-BDNF content were seen in the hippocampus of Cond and CondSAL birds, but not in the hippocampus of CondANI or NAIVE birds (p<0.05). The values of mature-BDNF in the amygdala of all the three conditioned groups were higher than those observed for truncated- and pro-BDNF (p<0.05), which indicates that the activation of this protein in the amygdala was not affected by the infusion of Ani in the hippocampus. The data indicate that the tone-shock conditioning induced the activation of molecular pathways of BDNF in the hippocampus and amygdala of the pigeons. The decreases in the content of truncated- and pro-BDNF isoforms found in conditioned pigeons may suggest cleavage mechanisms induced by the training. Our data confirm previous observations of rodent studies and extend these observations to pigeons, revealing that, in spite of the anatomical differences between the hippocampus of rodents and pigeons, there are functional and molecular mechanisms that are conservative between the species.

Induction of Zenk protein expression within the nucleus taeniae of the amygdala of pigeons following tone and shock stimulation

In this study, we evaluated the expression of the Zenk protein within the nucleus taeniae of the pigeon’s amygdala (TnA) after training in a classical aversive conditioning, in order to improve our understanding of its functional role in birds. Thirty-two 18-month-old adult male pigeons (Columba livia), weighing on average 350 g, were trained under different conditions: with tone-shock associations (experimental group; EG); with shock-alone presentations (shock group; SG); with tone-alone presentations (tone group; TG); with exposure to the training chamber without stimulation (context group; CG), and with daily handling (naive group; NG). The number of immunoreactive nuclei was counted in the whole TnA region and is reported as density of Zenk-positive nuclei. This density of Zenk-positive cells in the TnA was significantly greater for the EG, SG and TG than for the CG and NG (P < 0.05). The data indicate an expression of Zenk in the TnA that was driven by experience, supporting the role of this brain area as a critical element for neural processing of aversive stimuli as well as meaningful novel stimuli.

Induction of Zenk protein expression within the nucleus taeniae of the amygdala of pigeons following tone and shock stimulation.

In this study, we evaluated the expression of the Zenk protein within the nucleus taeniae of the pigeon's amygdala (TnA) after training in a classical aversive conditioning, in order to improve our understanding of its functional role in birds. Thirty-two 18-month-old adult male pigeons (Columba livia), weighing on average 350 g, were trained under different conditions: with tone-shock associations (experimental group; EG); with shock-alone presentations (shock group; SG); with tone-alone presentations (tone group; TG); with exposure to the training chamber without stimulation (context group; CG), and with daily handling (naive group; NG). The number of immunoreactive nuclei was counted in the whole TnA region and is reported as density of Zenk-positive nuclei. This density of Zenk-positive cells in the TnA was significantly greater for the EG, SG and TG than for the CG and NG (P < 0.05). The data indicate an expression of Zenk in the TnA that was driven by experience, supporting the role of this brain area as a critical element for neural processing of aversive stimuli as well as meaningful novel stimuli.

Glutamatergic neurotransmission mediated by NMDA receptors in the inferior colliculus can modulate haloperidol-induced catalepsy.

The inferior colliculus (IC) is primarily involved in the processing of auditory information, but it is distinguished from other auditory nuclei in the brainstem by its connections with structures of the motor system. Functional evidence relating the IC to motor behavior derives from experiments showing that activation of the IC by electrical stimulation or excitatory amino acid microinjection causes freezing, escape-like behavior, and immobility. However, the nature of this immobility is still unclear. The present study examined the influence of excitatory amino acid-mediated mechanisms in the IC on the catalepsy induced by the dopamine receptor blocker haloperidol administered systemically (1 or 0.5 mg/kg) in rats. Haloperidol-induced catalepsy was challenged with prior intracollicular microinjections of glutamate NMDA receptor antagonists, MK-801 (15 or 30 mmol/0.5 microl) and AP7 (10 or 20 nmol/0.5 microl), or of the NMDA receptor agonist N-methyl-d-aspartate (NMDA, 20 or 30 nmol/0.5 microl). The results showed that intracollicular microinjection of MK-801 and AP7 previous to systemic injections of haloperidol significantly attenuated the catalepsy, as indicated by a reduced latency to step down from a horizontal bar. Accordingly, intracollicular microinjection of NMDA increased the latency to step down the bar. These findings suggest that glutamate-mediated mechanisms in the neural circuits at the IC level influence haloperidol-induced catalepsy and participate in the regulation of motor activity.

Immunohistochemical distribution of AMPA-type label in the pigeon (C. livia) hippocampus.

The avian hippocampal formation (HF) is reported to have a role equivalent to that of the mammalian hippocampus, which may involve the glutamatergic system as well. In the present paper we offer evidence of the occurrence and distribution of the subunits composing AMPA-type glutamate receptors on neurons in the hippocampus region of the pigeon brain. The experiment analyzed the immunolabeling of glutamate receptor (GluR)(1)(,) GluR(4,) and GluR(2/3) receptor subunits in adult pigeons and found consistent evidence that neurons located in the five main areas of the avian HF have these AMPA-type subunits, but their incidence varies according to position and neuro-type. About 20%-35% of the irregular and 35%-70% of the triangular neurons on the lateral and medial "V" arms contain GluR(1) and GluR(2/3), while GluR(4) was found only at rounded neurons. The majority of the triangular neurons (over 90%) and about half of the irregular neurons in the medial area contain GluR(1) and GluR(2/3,) whereas the rounded neurons contain primarily GluR(4) (95%). Labeling revealed GluR(1) (40%-60%) and GluR(2/3) (30%) in the dorsomedial and lateral areas but only in irregular neurons, while 60%-80% of the rounded neurons synthesize GluR(4). While triangular and irregular neurons appear to match the description of projecting neurons, rounded ones seem to participate in local circuits. A discussion of the functional significance of the avian HF concentrates on a postulation of the "V" arms as equivalent to the dentate gyrus and the dorsomedial area being similar to the Ammon's horn.

Classical tone-shock conditioning induces Zenk expression in the pigeon (Columba livia) hippocampus.

The hippocampus is involved in fear conditioning, although the molecular events underlying this function are still under investigation. The authors analyzed the expression of the Zenk proto-oncogene product within the pigeon (Columba livia) hippocampus after training with a classical aversive conditioning protocol using tone-shock associations. Control groups were trained with shock or tone alone or were only exposed to the experimental chamber and manipulated. Experimental pigeons showed significant increases of Zenk expression in the ventromedial region of the hippocampus, whereas both the experimental and shock groups had increased Zenk expression in the dorsal region. The expression of Zenk in specific neuronal populations within the pigeon hippocampus may be indicative of plasticity-associated aversive classical conditioning.

Operant discriminative learning and evidence of subtelencephalic plastic changes after long-term detelencephalation in pigeons.

We analyzed operant discrimination in detelencephalated pigeons and neuroanatomical substrates after long-term detelencephalation. In Experiment I, experimental pigeons with massive telencephalic ablation and control pigeons were conditioned to key peck for food. Successive discrimination was made under alternating red (variable-ratio reinforcement) and yellow (extinction) lights in one key of the chamber. These relations were interchanged during reversal discrimination. The sessions were run until steady-state rates were achieved. Experiment II analyzed the morphology of the nucleus rotundus and optic tectum in long-term detelencephalated and control birds, using a Klüver-Barrera staining and image analyzer system. Detelencephalated birds had more training sessions for response shaping and steady-state behavior (p < 0.001), higher red key peck rates during discrimination (p < 0.01), and reversal discrimination indexes around 0.50. Morphometric analysis revealed a decreased number of neurons and increased vascularity, associated with increases in the perimeter (p < 0.001) in the nucleus rotundus. In the optic tectum, increases in the perimeter (p < 0.05) associated with disorganization in the layers arrangement were seen. The data indicate that telencephalic systems might have an essential function in reversal operant discrimination learning. The structural characteristics of subtelencephalic systems after long-term detelencephalation evidence plastic changes that might be related to functional mechanisms of learning and neural plasticity in pigeons.

Role of the hippocampus in contextual memory after classical aversive conditioning in pigeons (C. livia)

We investigated the effects of hippocampal lesions with ibotenic acid (IBO) on the memory of the sound-context-shock association during reexposure to the conditioning context. Twenty-nine adult pigeons were assigned to a non-lesioned control group (CG, N = 7), a sham-lesioned group (SG, N = 7), a hippocampus-lesioned experimental group (EG, N = 7), and to an unpaired nonlesioned group (tone-alone exposure) (NG, N = 8). All pigeons were submitted to a 20-min session in the conditioning chamber with three associations of sound (1000 Hz, 85 dB, 1 s) and shock (10 mA, 1 s). Experimental and sham lesions were performed 24 h later (EG and SG) when EG birds received three bilateral injections (anteroposterior (A), 4.5, 5.25 and 7.0) of IBO (1 µl and 1 µg/µl) and SG received one bilateral injection (A, 5.25) of PBS. The animals were reexposed to the training context 5 days after the lesion. Behavior was videotaped for 20 min and analyzed at 30-s intervals. A significantly higher percent rating of immobility was observed for CG (median, 95.1; range, 79.2 to 100.0) and SG (median, 90.0; range, 69.6 to 95.0) compared to EG (median, 11.62; range, 3.83 to 50.1) and NG (median, 7.33; range, 6.2 to 28.1) (P<0.001) in the training context. These results suggest impairment of contextual fear in birds who received lesions one day after conditioning and a role for the hippocampus in the modulation of emotional aversive memories in pigeons

Operant discrimination learning in detelencephalated pigeons (Columba livia)

Operant discrimination learning was analyzed in pigeons after massive telencephalic lesions. Twenty-one pigeons were divided into the three groups: non-lesioned (N=6), sham-lesioned (N=5) and telencephalon lesioned (N=10). Lesion surgeries were carried out before any experimental training. Learning procedures were run in the same sequence for all groups and under a food deprivation of 80 percent of the ad libitum weight. Successive discrimination was programmed by the alternation of red and yellow lights in the right key of a standard operant chamber: the red key was correlated with extinction. Sessions were run until steady-state key peck rates were obtained. The following results demonstrate discrimination learning required a larger number of sessions for lesioned pigeons (P<0.05). They showed increased response rates in red (26.43 +/- 2.59) and yellow (11.17 +/- 2.86) components...

Habituation to sound stimulation in detelencephalated pigeons (Columbia livia)

Habituation to sound stimulation was analyzed in terms of the functional role of the telencephalon in learning. Sixteen pigeons were exposed to 1000-Hz, 83-dB, 1-s sound (stimulus A) at 30-s intervals until there was habituation of the exploratory and pre-exploratory responses. The learning criterion was 10 trials without the occurrence of these responses. Twenty-four hours after habituation to stimulus A the birds were tested with a 500-Hz, 85-dB, 1-s sound (stimulus B). On the day following habituation to stimulus B, the birds of the experimental group (N=8) suffered ablation of the telencephalon and the birds of the control group (N=8) had sham surgery. Retesting with the same sequence of procedures was carried out 10 days after surgery. in the POST-lesion situation there was a decrease of the number of habituation trials to stimulus A (P<0.01) and to stimulus B (P<0.05) by experimental pigeons compared to the PRE-lesion situation. The data suggest an interaction of a facilitatory effect of the lesion and long-term learning effects

Effects of massive telencephalic lesions on the organization of behavior in pigeons (Columba livia)

The effect of massive lesions of the telencephalon on the repertoire of captive pigeons were investigated. The behavior of four birds with an intact telencephalon was compared to that of four birds submitted to ablation of telencephalic structures. Behavioral audio recording was done according to previously defined categories in three daily sessions for fifteen days. Experimental birds were followed up for month. Immediately after the lesion, operated birds showed decreases in the occurrence of different behaviors such as coording movements, feeding, interaction, preening, maintenance, exploration and vocalization and increases in locomotion and discrete movements of the body when compared to the control birds (P<0.05). Recovery of exploration (P<0.05), feeding and localization was during the follow-up period. These data are interpreted as suggestive of a functional role of the telencephalon in the organization of behavior and a long-term recovery of behavior after detelencephalation