Development of an mHealth App to Support the Prevention of Sexually Transmitted Infections Among Black Men Who Have Sex With Men Engaged in Pre-exposure Prophylaxis Care in New Orleans, Louisiana: Qualitative User-Centered Design Study

BACKGROUND

Sexual health disparities exist for Black men who have sex with men (BMSM) in New Orleans, Louisiana. Rates of sexually transmitted infections (STIs) are high for both BMSM and those taking HIV pre-exposure prophylaxis (PrEP).

OBJECTIVE

In this study, we introduced an existing PrEP adherence app to new potential users-BMSM engaged in PrEP care in New Orleans-to guide app adaptation with STI prevention features and tailoring for the local context.

METHODS

Using a user-centered design, we conducted 4 focus group discussions (FGDs), with interim app adaptations from December 2020 to March 2021. During the FGDs, a video of the app, app website, and mock-ups were shown to participants. We asked about facilitators of and barriers to STI prevention in general, current app use, impressions of the existing app, new app features to potentially facilitate STI prevention, and how the app should be tailored for BMSM. We used applied qualitative thematic analysis to identify themes and needs of the population.

RESULTS

Overall, 4 FGDs were conducted with 24 BMSM taking PrEP. We grouped themes into 4 categories: STI prevention, current app use and preferences, preexisting features and impressions of the prep'd app, and new features and modifications for BMSM. Participants noted concern about STIs and shared that anxiety about some STIs was higher than that for others; some participants shared that since the emergence of PrEP, little thought is given to STIs. However, participants desired STI prevention strategies and suggested prevention methods to implement through the app, including access to resources, educational content, and sex diaries to follow their sexual activity. When discussing app preferences, they emphasized the need for an app to offer relevant features and be easy to use and expressed that some notifications were important to keep users engaged but that they should be limited to avoid notification fatigue. Participants thought that the current app was useful and generally liked the existing features, including the ability to communicate with providers, staff, and each other through the community forum. They had suggestions for modifications for STI prevention, such as the ability to comment on sexual encounters, and for tailoring to the local context, such as depictions of iconic sights from the area. Mental health emerged as an important need to be addressed through the app during discussion of almost all features. Participants also stressed the importance of ensuring privacy and reducing stigma through the app.

CONCLUSIONS

A PrEP adherence app was iteratively adapted with feedback from BMSM, resulting in a new app modified for the New Orleans context and with STI prevention features. Participants gave the app a new name, PCheck, to be more discreet. Next steps will assess PCheck use and STI prevention outcomes.

Evaluation of an HIV Pre-Exposure Prophylaxis Referral System: From Sexual Health Center to Federally Qualified Health Center Pre-Exposure Prophylaxis Clinic

Innovative delivery strategies are needed to facilitate access to HIV pre-exposure prophylaxis (PrEP). The objective of this study was to evaluate a navigator-facilitated PrEP referral process from a sexual health center (SHC) to a co-located PrEP clinic as an alternative delivery model. Electronic health record (EHR) data were used to calculate the number of clients seen at the SHC in 2019. Charts were manually reviewed to determine whether a PrEP clinic referral was made and document type of referral method: face-to-face appointment scheduling with the navigator (warm handoff), EHR messaging to navigator to schedule the appointment at a later time (EHR message), or provision of navigator's contact information to the client (card only). In 2019, 2481 unique potentially PrEP-eligible clients were seen at the SHC; 220 (9%) received a PrEP referral. Of referred clients, median age was 30 years (interquartile range, 24-34), 182 (83%) were male, 89 (40%) were non-Hispanic Black, and 24 (11%) were Latinx. In total, 94/220 (43%) referred clients attended an initial PrEP visit with a provider, and the proportion attending by referral method was 81%, 36%, and 27% for warm handoff, EHR message, and card only, respectively (p < 0.0001). Despite co-location of these two clinics, there were significant drop-offs along the PrEP care continuum for this referral system. Warm handoff was the most effective referral method, but further efforts are needed to understand barriers to referral. Implementation of same-day PrEP services at SHCs is one potential solution to engaging additional clients.

Brain death determination: the imperative for policy and legal initiatives in Sub-Saharan Africa

The concept of brain death (BD), defined as irreversible loss of function of the brain including the brainstem, is accepted in the medical literature and in legislative policy worldwide. However, in most of Sub-Saharan Africa (SSA) there are no legal guidelines regarding BD. Hypothetical scenarios based on our collective experience are presented which underscore the consequences of the absence of BD policies in resource-limited countries (RLCs). Barriers to the development of BD laws exist in an RLC such as Kenya. Cultural, ethnic, and religious diversity creates a complex perspective about death challenging the development of uniform guidelines for BD. The history of the medical legal process in the USA provides a potential way forward. Uniform guidelines for legislation at the state level included special consideration for ethnic or religious preferences in specific states. In SSA, medical and social consensus on the definition of BD is a prerequisite for the development BD legislation. Legislative policy will (1) limit prolonged and futile interventions; (2) mitigate the suffering of families; (3) standardise clinical practice; and (4) facilitate better allocation of scarce critical care resources in RLCs. There is a clear-cut need for these policies, and previous successful policies can serve to guide these efforts.

Role of serotonergic neurons in the maintenance of the 10-Hz rhythm in sympathetic nerve discharge

We studied the effects of serotonin (5-HT)-receptor agonists and antagonists on the naturally occurring 10-Hz rhythm in sympathetic nerve discharge (SND) of urethan-anesthetized, baroreceptor-denervated cats. Intravenous doses of the 5-HT1A-receptor agonists 8-hydroxy-2(di-n-propylamino)-tetralin (8-OH-DPAT) and U-93385E, which inhibit the firing of serotonergic medullary raphe neurons, decreased the power in the 10-Hz band of SND without affecting the power at frequencies < or = 6 Hz. The inhibitory effects of 8-OH-DPAT and U-93385E were reversed by the 5-HT1A-receptor antagonists spiperone and WAY-100135. Microinjection of 8-OH-DPAT into medullary raphe nuclei also selectively eliminated the 10-Hz rhythm in SND. Intravenous administration of the 5-HT2-receptor antagonist methysergide blocked the 10-Hz rhythm in SND, whereas the 5-HT2-receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane increased peak frequency and power in the 10-Hz band of SND. Microinjection of N-methyl-D-aspartic acid into the medullary raphe also enhanced the 10-Hz rhythm in SND. These data support the view that the naturally occurring discharges of serotonergic medullary raphe neurons preferentially enhance the 10-Hz rhythm in SND.

Rapid and long duration tolerance to the vagal bradycardic effects of 5-HT1A receptor agonists

Administration of a single dose of the 5-HT1A receptor high intrinsic agonist U-93385E (either 0.3, 1.0 or 3.0 mg/kg, i.v.) results in a 20-30% decrease in heart rate. In contrast, cumulative dosing of U-93385E (0.01-3.0 mg/kg, i.v.) failed to lower heart rate in the spinal cat. Similarly, infusion of 1 mg/kg of U-93385E over a 2 h period failed to lower heart rate and prevented a bradycardic effect of a single bolus dose of U-93385E or flesinoxan. In contrast, the alpha 2-receptor agonist clonidine decreased heart rate in animals receiving the U-93385E infusion. Single bolus doses of flesinoxan or U-93385E failed to decrease heart rate in cats treated for 7 days with U-93385E (3 mg/kg, b.i.d.) and then saline for 3 days. Similarly, U-93385E failed to lower heart rate 12 days following a 14 day infusion of U-93385E (1 mg/kg per day). These data indicate that a rapid and long duration tolerance develops to the vagal bradycardia produced by 5-HT1A receptor agonists.

Effects of inhibitory amino acids on the frequency components in sympathetic nerve discharge

The effects of the GABA antagonist picrotoxin and the glycine antagonist strychnine on the frequency components in sympathetic inferior cardiac nerve activity were observed. Picrotoxin (0.03-1.0 mg/kg) increased power in the 10-Hz component of sympathetic activity and produced a dramatic shift in the rhythm to higher frequencies. Only small changes were noted in the 2- to 6-Hz component. Strychnine produced a small generalized increase in power in both frequency bands in sympathetic activity. These data suggest that GABA may play an important role in the generation and maintenance of the 10-Hz rhythm in sympathetic activity while glycine likely inhibits activity at a site of convergence of the two rhythms in sympathetic activity.

Tolerance development to the vagal-mediated bradycardia produced by 5-HT1A receptor agonists

The purpose of this study was to characterize the bradycardic effects of 5-hydroxytryptamine (5-HT)1A receptor agonists in the chloralose-anesthetized spinal cat and to determine if tolerance develops to the bradycardia produced by these drugs. 5-HT1A receptor agonists studied included 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), buspirone, gepirone, flesinoxan and U-93385E (cis-(3aR)-(-)-2,3,3a,4,5,9b-hexahydro-3-propyl-1H-benz[e]indole-9 - carboxamide). These compounds reduced heart rate by 20 to 30% in the spinal cat and lowered arterial blood pressure. The hypotension resulted from a decrease in cardiac output. Atropine reversed and vagotomy prevented the bradycardia produced by a single dose of U-93385E. The decrease in heart rate produced by i.v. bolus doses of flesinoxan or U-93385 was reversed by administration of the 5-HT1A receptor antagonists spiperone or WAY 100135. Administration of a single dose of U-93385E (either 0.3, 1.0 or 3.0 mg/kg i.v.) resulted in a 20 to 30% decrease in heart rate. In contrast, cumulative dosing of U-93385E (0.01-3.0 mg/kg i.v.) failed to lower heart rate in the spinal cat. Similarly, infusion of 1 mg/kg of U-93385E over a 2-hr period failed to lower heart rate and prevented a bradycardic effect of a single bolus dose of U-93385E or flesinoxan. In contrast, the alpha-2 receptor agonist clonidine decreased heart rate in animals receiving the U-93385E infusion. Finally, single bolus doses of flesinoxan or U-93385E failed to decrease heart rate in cats treated for 7 days with U-93385E and then saline for 3 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of baroreceptor reflexes following kainic acid lesions of the lateral tegmental field

We examined the effects of kainic acid lesions of the lateral tegmental field on baroreceptor function in the anesthetized cat. Kainic acid lesions prevented the reflex inhibition of inferior cardiac sympathetic nerve activity observed during an increase in blood pressure. The temporal locking of sympathetic slow waves to the cardiac cycle was also abolished following tegmental field lesions. Finally, the periodicity of sympathetic nerve discharge shifted to a higher frequency range following kainic acid lesions. These observations are consistent with the conclusion that lesions of the lateral tegmental field impair baroreceptor reflexes.

Lateral tegmental field involvement in the central sympathoinhibitory action of 8-OH-DPAT

This study examined the effects of kainic acid and NMDA microinjections into the lateral tegmental field on the sympatholytic effect of the 5-HT1A agonist 8-OH-DPAT. Kainic acid has been reported to destroy cell bodies while leaving fibers of passage intact while NMDA excites the cell bodies but not the axons of neurons. Microinjection of kainic acid was found to block the usual sympatholytic effect of 8-OH-DPAT but not the sympathoinhibition produced by the alpha 2 agonist clonidine. Microinjection of NMDA elicited profound pressor responses related to an increase in sympathetic activity. Sympatholytic effects of 8-OH-DPAT and clonidine were transiently overridden by microinjections of NMDA, but not glutamate. A role for the lateral tegmental field in the generation of sympathetic tone and in the sympatholytic mechanism of 8-OH-DPAT is supported by the chemical lesion and stimulation studies.

8-OH-DPAT-induced inhibition of renal sympathetic nerve activity and serotonin neuronal firing

The effects of the 5-HT1A receptor 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) administered i.v. on medullary 5-HT neuronal firing and renal sympathetic nerve activity were determined in spontaneously breathing anaesthetized cats. Low doses of 8-OH-DPAT (1-3 micrograms/kg) caused a similar reduction in 5-HT neuronal firing and renal nerve activity while high doses (10-30 micrograms/kg) completely inhibited neuronal firing but caused only 80% inhibition of renal nerve activity. These data are discussed in relationship to the mechanism of sympatholytic action of 8-OH-DPAT and the serotonergic regulation of sympathetic nerve activity.

Evidence that the lateral tegmental field plays an important role in the central sympathoinhibitory action of 8-OH-DPAT

We examined the effects of 8-OH-DPAT and 5-HT on three types of sympathetic-related neurons identified in the lateral tegmental field of anesthetized cats using spike-triggered averaging techniques. Based on their response to baroreceptor activation, these neurons could be classified as sympathoexcitatory, sympathoinhibitory, or baroreceptor activation unresponsive. 8-OH-DPAT administered intravenously was found to inhibit sympathoexcitatory neurons with a high degree of correlation to inhibition of sympathetic activity, and to excite sympathoinhibitory neurons in a dose-dependent manner. Iontophoretic application of 8-OH-DPAT and 5-HT to the majority of sympathoexcitatory neurons caused inhibition of spontaneous activity while iontophoretic application of 8-OH-DPAT to sympathoinhibitory neurons had variable effects although 5-HT consistently caused excitation. Baroreceptor unresponsive neurons were insensitive to iontophoretic 8-OH-DPAT and showed only limited response to 5-HT. It is concluded that the lateral tegmental field plays an important role in the sympathoinhibitory action of 8-OH-DPAT.

Effects of muscular contraction on discharge patterns of neurons in the medullary raphe nuclei

Cells of the medullary raphe nuclei were characterized as sympathoinhibitory (SI), sympathoexcitatory (SE) or serotonergic (5-HT). When muscular contraction (MC) was evoked by stimulation of the L7 and S1 ventral roots, putative SI cells were inhibited while putative SE cells were excited. 5-HT cells were unaffected by MC. These data are discussed in relation to integration of somatosensory and cardiovascular reflexes.

Effects of clonidine on sympathoexcitatory neurons in the rostral ventrolateral medulla

The effects of intravenous and iontophoretic clonidine were determined on the firing rates of sympathoexcitatory neurons in the rostral ventrolateral medulla of the cat. As previously reported in the rat, we found that sympathoexcitatory neurons could be differentiated based on their sensitivity in clonidine. Approximately 50% of the neurons were inhibited by clonidine. There was only a weak correlation between the inhibition of unit activity and whole sympathetic nerve activity. The discharge rates of the remaining neurons were either not altered or were increased by clonidine. Unlike the rat, these two groups of neurons could not be further differentiated on the basis of axonal conduction velocity or discharge frequency. These data are discussed and the effects of clonidine and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on sympathoexcitatory neurons are compared.

Pharmacological characterization of medullary serotonin neurons

In the present study we investigated the characteristics of medullary raphe serotonergic neurons. Specifically, we sought to examine further the similarities between medullospinal 5-HT neurons and the more extensively studied neurons of the dorsal raphe. Intravenous administration of 5-methoxy-dimethyltryptamine (5-MeODMT) produced a dose-related inhibition of the firing of midline medullary 5-HT neurons. Microiontophoretically applied 5-MeODMT also inhibited medullary 5-HT neurons. The inhibitory potency of 5-MeODMT was nearly identical to that observed for dorsal raphe 5-HT neurons. Microiontophoretic or intravenous administration of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) did not alter the firing rate of medullary 5-HT neurons. Intravenous administration of the alpha 1-receptor antagonist prazosin resulted in an inhibition of the medullary 5-HT neuronal firing. The discharge of medullary 5-HT neurons increased during iontophoresis of norepinephrine. These data are discussed in relation to the identification and characterization of medullary 5-HT neurons. In addition, the data suggest that the firing rate of medullary 5-HT neurons is regulated in part by a tonic excitatory noradrenergic input.

Studies on the site and mechanism of the sympatholytic action of 8-OH DPAT

Studies in our laboratory indicate that the 5-HT1A agonist 8-OH DPAT acts in the central nervous system at postsynaptic receptor sites to inhibit sympathetic nerve activity and lower arterial blood pressure. The present study was designed to investigate possible postsynaptic sites on central sympathetic neurons where 8-OH DPAT might produce its sympatholytic action in anesthetized cats. The sympatholytic effect of 8-OH DPAT was compared in midcollicular transected and sham operated control animals. Administration of 8-OH DPAT (0.01-1.0 mg/kg, i.v.) inhibited sympathetic activity and decreased blood pressure in both the transected and sham animals to a similar degree. The effects of microiontophoretically applied 8-OH DPAT and 5-HT on antidromically identified sympathetic preganglionic neurons were determined. Microiontophoretically applied 5-HT consistently increased the firing rate of sympathetic preganglionic neurons. Iontophoretic 8-OH DPAT failed to affect the firing of sympathetic preganglionic neurons but blocked the excitatory effects of 5-HT. The effects of 8-OH DPAT and 5-HT on the firing of sympathoexcitatory neurons located in the rostral ventrolateral medulla were also determined. Sympathoexcitatory neurons were identified using spike triggered averaging techniques and by their response to baroreceptor activation. Intravenous administration of 8-OH DPAT inhibited the firing of sympathoexcitatory neurons in the rostral ventrolateral medulla. The inhibition of unit firing produced by 8-OH DPAT was exactly paralleled by the shutoff of inferior cardiac nerve activity. Microiontophoretic application of 8-OH DPAT and 5-HT onto sympathoexcitatory neurons in the rostral ventrolateral medulla failed to affect the firing rate of these neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the site and mechanism of the sympathoexcitatory action of 5-HT2 agonists

Intravenous administration of the selective 5-HT2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), produced an increase in sympathetic activity recorded from the inferior cardiac nerve in chloralose-anesthetized cats. Microiontophoretically applied 5-HT increased the firing rate of antidromically identified sympathetic preganglionic neurons. Microiontophoretic DOI failed to affect the firing of sympathetic preganglionic neurons. The effect of DOI was also studied on medullospinal sympathoexcitatory neurons located in the rostral ventrolateral medulla. Intravenous DOI increased the firing of sympathoexcitatory neurons and sympathetic nerve discharge to a similar extent. Microiontophoretic application of DOI failed to affect the firing of sympathoexcitatory neurons. The data are discussed in relation to the site and mechanism of the sympathoexcitatory action of 5-HT2 agonists.

Studies on the mechanism of the sympatholytic effect of 8-OH DPAT: lack of correlation between inhibition of serotonin neuronal firing and sympathetic activity

Previous studies indicate that the selective 5-HT1A agonist, 8-OH DPAT, acts in the central nervous system to inhibit sympathetic nerve activity. Based on the observations that: (1) 8-OH DPAT acts at serotonin (5-HT) autoreceptors to inhibit 5-HT neuronal firing; and (2) medullary 5-HT neurons provide a tonic excitatory input to sympathetic preganglionic neurons, we have hypothesized that 8-OH DPAT produces its sympatholytic effects by inhibiting medullary 5-HT neuronal firing and thereby removing an excitatory input to sympathetic preganglionic neurons. The present study was designed to critically test this hypothesis. The sympatholytic effects of 8-OH DPAT were compared in intact animals and in animals which received large electrolytic lesions in the midline area of the lower brainstem. These lesions extended from the obex rostral through the level of the facial motor nucleus and encompassed the brain stem from the dorsal to the ventral surface. The sympatholytic effect of 8-OH DPAT was identical in intact animals and in animals receiving the lesion. The inhibitory effects of 8-OH DPAT on activity recorded simultaneously from the inferior cardiac sympathetic nerve and from medullospinal 5-HT neurons were determined. Medullary 5-HT neurons were identified using criteria modeled after the electrophysiological and pharmacological characteristics previously described for dorsal raphe 5-HT neurons. Medullary 5-HT neuronal activity was more sensitive to the inhibitory effects of 8-OH DPAT than was sympathetic activity. Indeed, low doses of 8-OH DPAT completely suppressed the firing of medullary 5-HT neurons but had little effect on sympathetic nerve activity. These data fail to support the hypothesis that inhibition of 5-HT neuronal firing is responsible for the central sympatholytic effects of 8-OH DPAT. Rather, the data suggest that 8-OH DPAT acts postsynaptically on 5-HT1A receptors located on central sympathetic neurons to inhibit sympathetic nerve activity.

Characterization of midline medulla role in the trigeminal depressor response

The purpose of the present investigation was to determine the role of the midline medulla in mediating the trigeminal depressor response. Previously we found that lesions of the midline medulla abolished the decrease in blood pressure resulting from electrical stimulation of the spinal trigeminal complex. Electrical stimulation (5 Hz) of the spinal trigeminal tract elicited a decrease in arterial blood pressure that was associated with an inhibition of sympathetic nerve activity recorded from the inferior cardiac nerve of anesthetized cats. The effect of single shocks applied to the trigeminal complex on sympathetic activity was determined using computer-averaging techniques. Single shock stimulation consistently elicited an excitation of sympathetic activity that was followed by an inhibition of sympathetic nerve discharge. The gamma-aminobutyric acid antagonist picrotoxin blocked the depressor response elicited by electrical stimulation of the midline medulla but not by stimulation of the spinal trigeminal complex. Extracellular recordings of the discharges of midline medullary neurons were made to determine the effects of trigeminal stimulation on sympathoinhibitory, sympathoexcitatory, and serotonin neurons. Sympathoinhibitory and sympathoexcitatory neurons were identified by the relationship between unitary discharges and sympathetic nerve activity and by their response to baroreceptor reflex activation. Serotonin (5-HT) neurons were identified using criteria previously developed in our laboratory. These included 1) a slow regular discharge rate, 2) sensitivity to the inhibitory action of the 5-HT1A agonist 8-OH 8-hydroxy-2-(di-n-propylamino)tetralin, 3) failure to respond to baroreceptor reflex activation, and 4) the discharges of the 5-HT neurons were not related to sympathetic activity. Stimulation of the spinal trigeminal complex typically inhibited the discharges of sympathoinhibitory neurons. In contrast, stimulation of the trigeminal complex consistently excited both sympathoexcitatory and 5-HT neurons. These results are discussed in relationship to the role of the midline medulla in mediating the trigeminal depressor response.

Identification of serotonergic and sympathetic neurons in medullary raphe nuclei

The purpose of the present study was to identify midline medullary serotonin (5-HT) neurons and to determine if these neurons were distinct from previously identified sympathoinhibitory and sympathoexcitatory neurons. Identification of medullary 5-HT neurons was based on electrophysiological and pharmacological similarities to dorsal raphe 5-HT neurons. Sympathoinhibitory and sympathoexcitatory neurons were characterized by an irregular discharge pattern which was temporally related to inferior cardiac sympathetic nerve discharge (SND) and to the cardiac cycle. Sympathoinhibitory neurons increased their discharge rate and the discharge of sympathoexcitatory neurons decreased during baroreceptor reflex activation. A third type of neuron fired in an extremely regular fashion (as judged by interspike interval analysis), fired at a rate of 1.1 spikes/s and had spike durations of approximately 2 ms. The discharges of regularly firing neurons were not temporally related to SND and were not affected during baroreceptor reflex activation. Regularly firing neurons and sympathoinhibitory neurons could be antidromically activated by electrical stimulation of the intermediolateral cell column of the spinal cord. Axonal conduction velocity of sympathoinhibitory neurons (2.4 m/s) was significantly greater than that for regularly firing neurons (1.3 m/s). Regularly firing neurons were completely inhibited by low doses of the 5-HT1A agonist 8-hydroxy-dipropylamino-tetralin (8-OH-DPAT) (i.e. 2 micrograms/kg, i.v.) while much higher doses of the drug failed to affect the discharges of sympathoinhibitory and sympathoexcitatory neurons. Microiontophoretic application of 5-HT and 8-OH-DPAT profoundly depressed the firing of regularly discharging neurons. Based on the striking similarities between regularly firing medullary neurons and dorsal raphe 5-HT neurons it is concluded that the regularly firing neurons were 5-HT-containing neurons. Furthermore, these medullary 5-HT neurons are distinct from sympathoinhibitory and sympathoexcitatory neurons.

Interactions between the lateral hypothalamus and the periaqueductal gray

Anatomical and physiological experiments were conducted to characterize the interactions between the lateral hypothalamus (LH) and the periaqueductal gray (PAG) and to determine the role of neurotensin in their interaction. Anatomical studies using injection of Phaseolus vulgaris leucoagglutinin into the LH showed an extensive projection to the ventromedial and the ventrolateral PAG and a less dense projection to the medial and dorsal parts of this region. Physiological experiments were performed on both deeply and lightly anesthetized animals. Electrical stimulation of the LH caused excitation of PAG cells with an onset latency of approximately 14 msec. There was a strong correlation between the response of PAG cells to electrical stimulation and injection of glutamic acid into the LH. Electrical or chemical stimulation of the LH produced an increase in tail flick latency in the lightly anesthetized animals that outlasted the stimulation period. There was a strong correlation between the response of PAG cells to electrical and chemical stimulation of the LH and their response to pressure-injected neurotensin. It is concluded that an excitatory projection from the LH to PAG exists which may involve neurotensin. This pathway may be involved in the analgesia produced by LH stimulation.