Excitatory connection from lateral hypothalamic self-stimulation sites to escape sites in medullary reticular formation

Abstract

Behavioral tests show that noncontingent stimulation of self-stimulation sites in the lateral hypothalamus increases escape and avoidance from central or peripheral stimuli. The present study investigated the possibility that this phenomenon was mediated by an excitatory connection from the lateral hypothalamus to neurons in aversive regions of the brainstem. Most of the 24 rats participated in two phases of the experiment: unit recording under anesthesia ; and behavioral tests with intracranial stimulation in the waking state. Recordings of 120 units were obtained from the n. gigantocellularis reticularis (NGC) since stimulation of this region in the awake rat consistently elicited escape behavior. Unit responses could be divided into t\vo catagories: 61% responded to deep pinch or fout #shock (or both) but not to light brushing of the hair; and 39% responded to light brushing of the hair or were not responsive. Stimulation of behaviorally confirmed self-stimulation sites in lateral hypothalamus evoked short-latency (2 and 4 msec) excitation of 88% of the NGC units in the first category and only 15% in the second. Nearly all hypothalamic site.s not eliciting self-stimulation also failed to excite NGC units. The excitatory hypothalamic-bulboreticular connection may serve to increase the excitability of a nociceptive system during self-stimulation.

Prolonged unit responses in thalamic reticular, ventral, and posterior nuclei following lateral hypothalamic and midbrain reticular stimulation

“…In 14 male rats (Holtzman, 400 gm) which were found to have correct electrode placements, 272 well-isolated single units were recorded extracellularly with etched tungsten microelectrodes (50-150 kS2 at 2 kHz). Unit responses over 10-sec periods, quantified by a digital counter, were tested following stimuli (0.2 sec, 100 Hz, 0.5 msec, 100-600 pA cathodal pulses), similar to those that have been used in behavioral tests of self-stimulation and escape (Keene and Casey, 1970). The stimuli were delivered to MFB, RET, and medial thalamus, via twisted pairs of 250 pm nichrome wire exposed at the cross section of the tips, and from constant-current devices isolated from ground.…”

Medial forebrain stimulation enhances intracranial nociception and attenuates morphine analgesia suggesting the existence of an endogenous opioid antagonist

“…Olds and Olds (1962) found that responding for escape from aversive dorsal tegmental stimulation was enhanced by continuous stimulation of areas that support self-stimulation. In an experiment with greater similarly to the one described here, stimulation delivered to the nucleus gigantocellulariis (NGC) at subthreshold levels became aversive by the non-contingent stimulation of hypothalamic sites that support self-stimulation (Keene and Casey, 1970). Since the NGC is part of the medullary reticular formation this finding along with those of the present study suggest that the stimulation of hypothalamic reward areas could enhance the effects of aversive stimuli delivered throughout the extent of the recticular formation.…”

“…Although the above mentioned experiments suggest that stimulation a reward pathway would attenuate nociception in the rat some experiments found that lateral hypothalamic stimulation appeared to enhance the aversive effects of stimulation of either the tegmentum (Olds and Olds, 1962) or the nucleus gigantocellularis reticularis (NGC) (Keen and Casey, 1970). Other investigators have reported the opposite result for paired LH-NGC stimulation (Carr and Coons, 1982).…”

Opposite medical thalamic unit responses to rewarding and aversive brain stimulation

“…First, A-delta and C fibers in peripheral nerve have been found to be selectively responsive to noxious stimuli (3, 23). Second, neurons recorded in nucleus gigantocellularis (NGC) in medullary reticular formation respond selectively to A-delta inputs in cat (6) and to noxious peripheral stimuli in both cat (7) and rat (13). Finally, low-current (100 pa) stimulation at the sites from which these neurons were recorded has elicited, in cat (7) and rat (13), escape behavior as well as natural painrelated behavior such as vocalization, crouching or rapid movement, defecation, and urination.…”