Mamillothalamic tract transection blocks anterior thalamic training- induced neuronal plasticity and impairs discriminative offidance behavior in rabbits

Abstract

Rabbits with bilateral transecting lesions of the mamillothalamic tract, control (tract-sparing and sham) lesions, or no lesions, and chronic, fixed-position anterior ventral (AV) and medial dorsal (MD) thalamic and posterodorsal subicular complex unit recording electrodes were trained to step in an activity wheel in response to a 0.5 sec tone (CS+) in order to avoid a brief foot shock. The rabbits also learned to ignore a different tone (CS-) not predictive of shock. Behavioral acquisition was significantly retarded in rabbits with mamillothalamic tract transection compared to controls. When trained, transected rabbits failed to avoid the shock more often than controls. Mamillothalamic tract transection abolished and control lesions attenuated AV thalamic discriminative training-induced activity (i.e., development with training of greater discharges in response to the CS+ than to the CS-). Transection and control lesions attenuated AV thalamic excitatory training-induced activity (greater elicited activity during training than during unpaired tone-shock presentations before training) as well as AV thalamic “spontaneous” baseline unit activity. CS-elicited discharge magnitude was reduced by control lesions and it was further reduced by tract transecting lesions. Significant lesion-related changes were not found in the subicular or MD thalamic neuronal receptor. Mamillothalamic tract afferent information flow is thus essential for AV thalamic discriminative training-induced activity, excitatory training-induced activity, tone- elicited discharges and maintenance of conditioned avoidance responses. The effects of the control lesions suggested that afferents which course in parallel with and near the mamillothalamic tract may contribute to AV thalamic spontaneous activity and excitatory training- induced activity.

The role of the anterior, mediodorsal, and parafascicular thalamus in instrumental conditioning

“…These and other studies (e.g., Sparenborg and Gabriel, 1992; Gabriel et al, 1995) represent, therefore, a significant body of work implicating the ANT-AC pathway and to a lesser extent the MD, in discrimination learning. It should be emphasized that the authors did not claim a role for this pathway in the regulation of instrumental behavior per se , but rather referred to their discrimination task as requiring an instrumental response.…”

Amygdalar Efferents Initiate Auditory Thalamic Discriminative Training-Induced Neuronal Activity

“…A stainless steel machine screw threaded into the frontal sinus served as the electrical reference for the recordings. Details regarding the procedures of electrode manufacture and recording are provided elsewhere (Gabriel et al, 1995).…”

“…In the first session, each tone was presented 60 times without the foot shock US. In the second session, the tones and the US were presented in an explicitly unpaired manner (Gabriel et al, 1995). The preliminary training sessions provided baseline data for CRs and neuronal responses induced by pairing of the C S and the US during conditioning.…”

REM sleep deprivation: The wrong paradigm leading to wrong conclusions

“…Given that arche inhibits stress and alarm, and arche is well known to mediate explicit learning (Aggleton & Brown 1999;Krieckhaus 1988;Squire et al 1990) then it would be expected that arche lesions would uniquely interfere with learning to initiate bold action in threatening or risky scenes just the deficit seen following arche (MBs) lesions (Gabriel et al 1995;Krieckhaus 1988;. Finally, if revonsuo is correct that dreaming is risky VTED, then arche should be critically involved in risky dreams just as it is in risky actions.…”